pde4 inhibitors 2001. patent and literature activity 2000 - september 2001

Patent Analysis

2002 © Ashley Publications Ltd ISSN 1354-3776 93

Ashley Publicationswww.ashley-pub.com

1. Introduction

2. Clinical advances

3. Corporate approaches

4. New uses

5. Scientific developments

6. Expert opinion

Monthly Focus: Pulmonary-Allergy, Dermatological, Gastrointestinal & Arthritis

PDE4 inhibitors 2001. Patent and literature activity 2000 - September 2001Peter Norman18 Pink Lane, Burnham, Bucks, SL1 8JW, UK

Patenting activity relating to PDE4 inhibitors remains at a sustained level,with a slight upward trend in the number of published applications. A totalof 59 applications were published in 2000 and current trends suggest approx-imately 63 will be published in 2001. The most active companies, eachaccounting for 13 applications within this period are the two companies,GlaxoSmithKline and Byk Gulden, with compounds in advanced Phase IIIstudies. Another 18 companies and institutions have published their firstclaims in this field during this period, most notably ICOS, with 8 applicationspublished in June 2001. With regulatory filings for both cilomilast and roflu-milast likely to be filed in 2002, interest in this area is likely to increase duringthe next few years.

Keywords: asthma, COPD, dermatitis, leukaemia, PDE 4 inhibitor, rheumatoid arthritis, TNF, ulcerative colitis

Expert Opin. Ther. Patents (2002) 12(1):93-111

1. Introduction

The successful development of selective PDE4 inhibitors, devoid of cardiovascularand emetic side effects, has been a major effort by the pharmaceutical industry dur-ing the past decade [1-7]. Until recently, much of this effort has been concentrated onthe development of such compounds for the treatment of asthma but it is nowwidely recognised that PDE4 inhibitors offer one of the most promising approachesto the treatment of chronic obstructuve pulmonary disorder (COPD) [8]. However,PDE4 inhibitors are now also in clinical development for the treatment of Crohn'sdisease, ulcerative colitis, dermatitis, multiple sclerosis and rheumatoid arthritis,whilst at least one clinical trial has been performed in allergic rhinitis patients.

This review follows the theme of the earlier reviews in this series by consideringthe clinical developments with PDE4 inhibitors and then focusing on the patentand chemical literature, since January 2000. It highlights the increasing chemicaldiversity of known PDE4 inhibitors, with many compounds displaying lownanomolar, or even sub-nanomolar potency and comments on how the improvingunderstanding of the structure and function of the PDE4 isoforms may lead toimproved PDE4 inhibitors in the near future.

2. Clinical advances

Comparison with the corresponding table presented in last year's review shows thatthere have been limited changes in status [2]. The lack of information on the pro-gression of either V-11294A or YM-976, the latter being omitted fromYamanouchi's latest listing of its development pipeline [201], suggests that develop-ment of both compounds has been discontinued. Celgene's CDC-998, Kyowa'sKW-4490 and ICOS-485 have recently been reported to have entered Phase I stud-ies, but little information about any of these compounds is currently available, nor

PDE4 inhibitors 2001. Patent and literature activity 2000-September 2001

94 Expert Opin. Ther. Patents (2002) 12(1)

Table 1. Currently reported clinical development status of PDE4 inhibitors. This table summarises the reported status of all those PDE4 inhibitors currently in clinical development. Those compounds with significantly more information has been reported since last year's review [2] are marked, and further information is presented below.

Drug Compound Company Indication Status

cilomilast§ 1 GlaxoSmithKline COPD Phase III

roflumilast§ 2 Byk Gulden COPD/Asthma Phase III

BAY 19-8004§ 3 Bayer COPD Phase IIa

pumafentrine§ 4 Byk Gulden Asthma Phase II

V-11294A 5 Napp Asthma Phase IIa

CDC-801 6 Celgene Crohn's disease Phase II

cipamfylline 7 Leob Dermatitis Phase II

mesopram§ 8 Schering AG Multiple Sclerosis Phase II

MK-? _ Merck d Asthma/COPD Phase II

SCH-351591§ 9 Schering-Plough d Asthma Phase I

CDC-998 _c Celgene Inflammatory diseases Phase I

YM-976§ 10 Yamanouchi Asthma Phase I a

CI-1044 11 Pfizer Asthma/COPD Phase I e

KW-4490 _c Kyowa Asthma Phase I

IC-485 _c ICOS Inflammatory diseases Phase I§ discussed in more detail; a: possibly discontinued (see text); b: licensed from GlaxoSmithKline (SmithKline Beecham); c: structure not yet disclosed, licensed from Celltech Group; d: licensed from Celltech Group; e: status unconfirmed.

has there been official confirmation from Pfizer that CI-1044(11) is in clinical trials. Although Celltech has confirmed thata compound emanating from their collaborative program withMerck has progressed to clinical evaluation, no details areavailable about this compound. Data on related compoundsare discussed below. The most notable development is pumaf-entrine, a dual PDE3/PDE4 inhibitor, of which Byk Guldendelayed disclosure until Phase II studies had commenced.

2.1 CilomilastCilomilast (Ariflo™, SmithKline Beecham 1) remains thePDE4 inhibitor most advanced in clinical development withthree Phase III studies having already been completed inCOPD patients. It has also completed Phase II studies inasthmatics, but following a review of the inconsistent anddisappointing results it appears that the company has aban-doned any intention of developing cilomilast for this indica-tion. GlaxoSmithKline now expects to file a new drugapplication (NDA), for the COPD indication in 2002, withthe European marketing approval application (MAA) notbeing filed until 2004 [202] and is hopeful that Ariflo™ maybe launched in 2003 [9].

At the May 2001 American Thoracic Society (ATS) meet-ing it was indicated that three Phase III studies, of six monthsduration, with cilomilast had been performed in a total of2048 patients [10]. However, the FDA's reservations had led tothe initiation of a fourth study, resulting in a delay in filing forregulatory approval.

Much of the clinical data on cilomilast has been published inabstract form, from presentations at the ATS and European Res-piratory Society (ERS) meetings in recent years. The first peer-reviewed papers presenting some of this data have recently beenpublished documenting the bioavailability of cilomilast [11], itsabsorption in the elderly [12] and, more pertinently, a six weekPhase II study in 424 COPD patients [13]. The available clinicaland pharmacological data on cilomilast have recently been com-prehensively reviewed obviating a detailed discussion here [14]. Amore recent study has described how six weeks treatment withcilomilast significantly reduces the neutrophil levels in the spu-tum of COPD patients by 15% [15].

Since cilomilast currently represents the gold standardagainst which all other PDE4 inhibitors tend to be compared,it is pertinent to restate the potency of the compound. Cilo-milast is a moderately potent PDE4 inhibitor, with an IC50value of 95 nM against recombinant enzyme and inhibits[3H]-rolipram binding to the high affinity rolipram bindingsite (HARBS); the conformation of PDE4 that is believed tobe related to the propensity of compounds to cause emesis [16],with an IC50 value of 110 nM, with the ratio of the two IC50values suggested to be predictive of propensity to cause emesis[17,18]. Cilomilast inhibits antigen-induced effects in a guinea-pig model of asthma with an oral ID50 value of 17 mg/kg [19]

and is less emetic than rolipram in the ferret, although it stillinduces emesis. The induction of emesis is also the dose limit-ing side effect in man that has constrained the maximum clin-ical dose of cilomilast to 15 mg/kg b.i.d.

Norman

Expert Opin. Ther. Patents (2002) 12(1) 95

2.2 RoflumilastWhile cilomilast has barely advanced in status sincelast year's review of this area, Byk Gulden has made consid-erable advances with roflumilast (2). Roflumilast is now inPhase III trials for the treatment of both asthma and COPDand Byk Gulden is currently predicting a launch date of2003 for the asthma indication [20]. Roflumilast was thefocus of many presentations at this year's ATS and ERSmeetings and was also heavily featured in Altana's August2001 presentation to analysts [203]. In addition to the desig-nated indications, roflumilast has also been shown to be effi-cacious in the treatment of allergic rhinitis, albeit in a 25patient study [21]. Administration of 500 µg once daily wasfound to produce a significant improvement in nasal airflow,itching and rhinorrhea.

Roflumilast is a substantially more potent PDE4 inhibitorthan cilomilast, displaying an IC50 value of 0.8 nM on humanneutrophil PDE4, and is a potent inhibitor of a wide range ofinflammatory cellular responses [22]. As with a number of otherpyridylbenzamide PDE4 inhibitors, roflumilast undergoesmetabolic oxidation, of the pyridyl nitrogen to the N-oxide,which retains the activity of the parent compound. Both com-pounds were found to be equipotent in in vivo animal modelsof asthma and as inhibitors of LPS-induced TNF-α release,displaying 30- to 100-fold greater potency than cilomilast inthe same assays [23]. Roflumilast displayed ED50 values of 0.3,1.5 and 2.7 µmol/kg as an inhibitor of TNF-α release in therat, antigen-induced bronchoconstriction in the guinea-pigand antigen-induced eosinophilia in the rat, respectively.

Roflumilast has been shown to be well absorbed in man,with excellent bioavailability (79%) and a plasma half-life(15.7 h) suitable for once daily dosing [24]. Even at a dose of500 µg, roflumilast achieved a Cmax of 8.3 µg/l and its absorp-tion was barely affected by food intake [25].

The first six month study in COPD patients examined theefficacy of roflumilast administered as either 250 µg b.i.d. or500 µg once daily in 516 patients [203]. Neither dosage regimeninduced significantly more emesis than placebo and both werewell-tolerated. There were negligible differences between eithertreatment regimen and improvements in FEV1 were discernible

in both treatment groups after 4 weeks, with ~ 100 mlimprovement over the six month period. Both doses produceda reduced need for rescue medication, but the once daily dos-age was markedly more effective in reducing the number ofexacerbations, by 50%, during the study.

Greater improvements in FEV1 were seen in a study ofasthmatic patients in which a 500 µg dose of roflumilast wasshown to produce a > 300 ml improvement in FEV1 [26]. Inthis study, roflumilast was shown to be more effective than anundisclosed oral bronchodilator agent (most probably theo-phylline). This report augments the limited, early Phase IIdata that were presented at the previous year's ATS meeting,indicating that once daily administration of 500 µg roflumi-last could protect against exercise-induced asthma and that asingle 1000 µg dose could substantially inhibit antigen-induced bronchoconstriction [27,28].

Although the published clinical data on roflumilast arestill scant, with little having yet been presented at majorinternational meetings, it appears that the superior potencyof roflumilast relative to ciclomast translates from animalstudies to man. It would also appear, based upon the pres-entation of data in COPD patients, that it may be possibleto achieve greater efficacy than can be achieved with cilomi-last. It should be interesting to see what can be achievedwith higher doses of roflumilast, for which there do notappear to be dose-limiting side effects. It is probable that anumber of major studies will be presented at the May 2002ATS meeting.

2.3 PumafentrinePumafentrine (BYK-33043, 4) represents the latest progres-sion in a series of non-selective PDE inhibitors, active againstboth PDE3 and PDE4, which have been developed by BykGulden. Although the company has successfully pursued thedevelopment of selective PDE4 inhibitors, notably roflumi-last, it has also continued to explore non-selective inhibitorsbased on the phenathridine ring system and related ring sys-tems such as naphthyridines. Pumafentrine is a close analogueof the older compound tolafentrine that was discontinuedafter Phase II studies in asthmatics.

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The first report that pumafentrine had entered clinicaldevelopment was in Altana's March 2000 report of its R&Dpipeline. It was then indicated to have entered Phase I stud-ies. By March 2001 it had progressed to Phase II studies inboth asthma and COPD and is currently forecast to reach themarket in 2006 [30]. Despite its progress to Phase II studiesfew data are currently available about pumafentrine. Pumaf-entrine is ~ 10-fold more potent than tolafentrine as aninhibitor of both PDE4 and PDE3 with respective IC50 val-ues of 7 and 28 nM, [101]. Pumafentrine is reported to beabout 10-fold less potent than roflumilast in a rat model ofasthma, with 3 µmol/kg reported to be an inactive dose [101].

2.4 BAY 19-8004BAY 19-8004 (3) represents a structurally novel class of selec-tive PDE4 inhibitors and had completed Phase II studies inboth asthmatic and COPD patients by June 2001. Its devel-opment is currently on hold pending the full analysis of theCOPD patient data, although Phase III studies were sched-uled to begin by the end of 2001 [31]. Its development forasthma has been terminated, indicating that, like a number ofother PDE4 inhibitors, it failed to demonstrate adequate effi-cacy in the treatment of asthma.

The available data on BAY 19-8004 are currently confined tomaterial presented at the two previous annual ATS and ERSmeetings. These data show that BAY 19-8004 is a more potentPDE4 inhibitor than cilomilast, with respective IC50 values of49 and 245 nM against human neutrophil PDE4 and BAY 19-8004 displays moderately high affinity for the HARBS (IC5014 nM) [27]. BAY 19-8004 is a potent, orally-active, inhibitor of

antigen-induced bronchoconstriction in both guinea-pigs andmonkeys at doses of 3 and 0.1 mg/kg, respectively [32,33]. Itfailed to induce emesis in the ferret at doses of 100 mg/kg [32].

2.5 MesopramMesopram (SH-636, 8) represents a long delayed follow-up torolipram, the prototypical PDE4 inhibitor. Schering AG hascontinued to pursue the development of agents of this type forthe treatment of multiple sclerosis. Multi-centre Phase II studieswith mesopram commenced by March 2001 and the company iscurrently predicting that regulatory filing will occur in 2008 [34].

At present, few data are available on the biological activityof mesopram. It has been reported that the R-enantiomeraccounts for most of the PDE4 inhibitory activity observed inthe racemic compound yet displays lower affinity for theHARBS, Ki values of R 7.3 nM, S 0.47 nM [102]. Efficacy hasbeen demonstrated with mesopram in an animal model ofmultiple sclerosis [35]. For this indication the company hasdeveloped a controlled release formulation that is also claimedto stabilise the drug [103].

2.6 SCH-351591SCH-351591 (D-4396, 9) is a selective PDE4 inhibitor thatwas licensed, by Chiroscience, to Schering-Plough for clinicaldevelopment. It has currently progressed to Phase I clinicalstudies and replaced the earlier development candidate D-4418, which was found to undergo extensive N-oxidationin vivo. Until recently, no data on SCH-351591 were availa-ble, but presentations in September 2001 revealed both thecompound's structure and its pharmacological profile [36].

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Characterisation of the pharmacological activity of the N-oxide metabolite of the 2-trifluoromethyl analogue of D-4418indicated SCH-351591 to be a more potent PDE4 inhibitorthan D-4418, with respective IC50 values of 60 and 170 nM,although it also displayed enhanced affinity for the HARBS,respective IC50 values of 150 and 530 nM. SCH-351591 dis-plays excellent pharmacokinetics, superior to those of D-4396, in several species, including the rat (F 36%, T½ 10.2 h,Cmax 3054 ng/ml at 3 mg/kg) [36,104]. SCH-351591 is apotent inhibitor of antigen-induced effects in guinea-pigs andprimates, showing activity at doses as low as 0.3 mg/kg p.o.and has a low emetic effect. No evidence of emesis beingnoted in the primate whilst threshold effects (retching) wereonly observed in ferrets at 8 mg/kg.

2.7 YM-976YM-976 (10) was first reported to have entered clinical eval-uation in 1998, but until recently its structure had not beendisclosed. This disclosure makes it clear that YM-976 wasclaimed in a patent application filed in 1995 [105]. Thepast year has seen the appearance of four papers describingthe pharmacological properties of this pyrido-[2,3-d]pyrimi-din-2(1H)-one derivative, but no information has yet beendisclosed on the clinical effects of YM-976. These indicateYM-976 to be a potent, non-emetic, PDE inhibitor, so ifclinical development has been discontinued this wouldappear to be attributable to either inadequate efficacy, or tountoward but presumably non-emetic, side effects.

YM-976 is a potent PDE4 inhibitor (human neutrophilPDE4 IC50 = 2.2 nM), that also displays a high affinity for theHARBS (IC50 = 2.6 nM) [37,38]. YM-976 is highly selective forPDE4 relative to other PDEs but displays no selectivitybetween PDE4 isoforms, nor does YM-976 penetrate rat brain

[38]. In models of antigen-induced eosinophil infiltration inrats, mice and ferrets YM-976 was found to be a potent inhib-itor in all three species, with respective ED50 values of 1.7, 5.8and 1.2 mg/kg, whilst it does not induce emesis in ferrets at10 mg/kg [39]. In the more commonly employed guinea-pigmodels of asthma YM976 inhibited antigen-induced bron-choconstriction, airway plasma leakage, airway eosinophilinfiltration and airway hyper-reactivity with respective ED50values of 7.3, 5.7, 1.0 and 0.52 mg/kg [40].

2.8 CI-1044Presentations on CI-1044 (11) at the 2001 ATS and ERS meet-ings have failed to confirm that the compound has yet enteredthe clinic, nor has Pfizer officially confirmed that this is thecase. CI-1044 has been reported to be an orally-active inhibitorof LPS-induced airway neutrophilia in the rat, ID50 = 6.25 mg/kg, with superior efficacy to cilomilast [41]. It was subsequentlyreported to be inhibit LPS-induced TNF-α production in theblood of COPD patients with an IC50 value of 1.3 µM [42].

2.9 NIK-616Another compound, about which little is known but is report-edly poised to enter Phase I studies, is Nikken's NIK-616[201]. The first disclosure of this compound was a poster pre-sented at the ERS meeting in September 2001 [43]. It wasreported to be a non-emetic PDE4 inhibitor, with moderatepotency (IC50 = 43 nM) but good oral activity in guinea-pigmodels of asthma (ED50 = 0.3 mg/kg).

2.10 Patenting activityAs shown in Figure 1 the number of patent applicationsclaiming PDE4 inhibitors appears to be slowly increasing.After a decline in 1997 there has been a small increase

1995 1996 1997 1998 1999 2000 2001 2002

PDE4 patenting activity by yearN

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Figure 1. PDE4 patent applications since 1995. (2001 figure extrapolated from patents published to 30 September 2001.)



each year, which appears likely to continue for thecurrent year. This appears to be due to steady emergence ofinterests from additional pharmaceutical companies or otherinstitutions. Since January 2000 an additional 18 applicantshave demonstrated interest in either the design or the use ofPDE4 inhibitors.

Despite the 316 applications originating from 60 appli-cants, five companies account for 53% of all these applica-tions, as shown in Table 2, although the impact of recentmergers influences the totals from both the Celltech Groupand Pfizer. The majority of the applications belonging to theformer emanated from the former Chiroscience, whose appli-cations are assigned to Darwin Discovery Ltd., with only afew older applications originating from Celltech, although thelatter programme provided the basis for the subsequent effortsby Merck, to whom the rights were licensed. Although Pfizerwas a substantial applicant in its own right its total also incor-porates eight applications from the former Warner-Lambertsubsidiary Jouveinal.

Examination of the more recent patent activity, shown inTable 3, indicates the same companies also accounted for 50%of the 115 applications since December 1999. The most nota-ble difference is the sudden emergence of ICOS, with eightapplications being published on 28th June or 5th July 2001.Although ICOS had earlier been active in this field through asubsequently terminated collaboration with Glaxo Wellcome,it had shown little evidence of continuing to work on PDE4inhibitors in addition to its development of the PDE5 inhibi-tor cialis in collaboration with Eli Lilly. The previous year alsosaw Zambon enter this area with the publication of fourapplications. In contrast, Celgene, Merck and Bayer have allbeen active in this field for some years.

3. Corporate approaches

The approach exemplified by the past 21 months of patentapplications is addressed here on a corporate basis.

3.1 GlaxoSmithKlineAll the applications from GlaxoSmithKline emanated fromSmithKline Beecham, with the vast majority pertaining tocilomilast (1). The underlying strategy appears to be defen-sive patenting to optimise protection of what is likely tobecome a marketed product. These applications claim novelprocesses for cilomilast's preparation, new salt forms of thefree acid, combinations with agents such as, the long-actingβ2 agonist, formoterol [106] or inhaled steroids [107] and addi-tional methods of use. Only a single application [108]

describes novel compounds, albeit close analogues of cilomi-last, such as 11.

No indication of the potency of compounds such as 12 ispresented, but a recent poster presentation described theclosely related acetylenic analogues, such as 13 [44]. This indi-cated that replacement of the nitrile in cilomilast by aryla-lkynes provided significantly more potent PDE4 inhibitors,which also display better selectivity with respect to the rol-ipram binding site. The pyrimidine 13 was 14-fold morepotent than cilomilast in vitro and slightly more potentin vivo, whilst the oxadiazole 14 was even more effective inboth models, displaying an IC50 of 0.3 nM and an ED50 of0.6 mg/kg p.o. in the guinea-pig. As these appear to be withinthe scope of a significantly older application [109] it is likelythat the compounds of the newer application are at least com-parably effective as PDE4 inhibitors.

3.2 Byk GuldenIn contrast, the majority of the applications from Byk Guldenclaim novel PDE4 inhibitors, although three applications aredirected towards augmenting coverage of its two key develop-ment compounds. Combinations of roflumilast with PDE3inhibitors [110] and roflumilast or pumafentrine with long-act-ing β2 agonists [111], as well as their use as a method of treatingmultiple sclerosis are claimed [112].

Table 2. Leading applicants (filing more than eight applications) in the period 1995 to 2001.

Applicant No. of applications

GlaxoSmithKline 46

Byk Gulden 44

Pfizer 30

Celltech Group 29

Merck 20

Celgene 10

Merck KgAa 9

Kyowa Hakko 9

others 119

Table 3. Leading applicants in the period 1st January 2000 to 1st October 200.

Company Total

GlaxoSmithKline 13

Byk Gulden 13

Pfizer 11

ICOS Corp 8

Merck Frosst 8

Celltech Group 5

Celgene Corp. 4

Merck KGaA 4

Zambon Group SpA 4

Bayer AG 4

Others 41

Norman


The ten remaining applications suggest that emphasis ofthe chemical programme has switched from exploring cate-chols, or heterocyclic mimics thereof, such as benzofuranderivatives [1] to phenanthradine and phthalazine-based struc-tures attached to a catcehol mimic. Six applications, all pub-lished in 2000, claim phenanthridine derivatives [113-117] orrelated benzonaphthyridines [118], mostly as selective PDE4inhibitors. Within this group of applications the most potentcompound disclosed is the phenanthradine 15 [116], with anIC50 value of 1.3 nM. Those published to date in 2001 haveclaimed phthalazinone derivatives with very potent PDE4inhibitory activity. The compounds claimed in [114] aredescribed as dual PDE3/PDE4 inhibitors, e.g., 16, withrespective IC50 values of 35 nM and 45 pM, whilst thoseclaimed in [119] and [120] are simply indicated to be active asPDE4 inhibitors, e.g., 17 and 18, with respective IC50 valuesof 200 pM and 460 pM.

The evolution of this latter series of compounds hasrecently been described and was performed in collaborationwith a group at the Leiden-Amsterdam Centre for Drug

Research [45,46]. These were originally based upon elementsof the dual PDE3/PDE4 inhibitor zardaverine and a pyri-dopyridazinone that selectively inhibited PDE4. The use ofa fused tetrahydropyridazinone and the introduction of thebenzofuran substituent both enhanced PDE4 inhibitorsactivity with the cycloheptyl substituted compound 19being one of the more potent inhibitors described, IC50value 1 nM.

3.3 PfizerPfizer's ten applications include three applications filed byWarner-Lambert claiming fused heterocyclic derivatives, inaddition to seven claiming azole-based catechol mimics thatoriginated at Pfizer. However, while Pfizer has not disclosed anyclinical candidates in this area, since the termination of thedevelopment of the Warner-Lambert compound CI-1018 20,the patent strategy is more suggestive of a company activelydeveloping one or more agents. Two of these applications [121]

and [122] pertain to novel processes for the preparation of inda-zoles such as 21 and other applications, intriguingly, claim the

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use PDE4 inhibitors for the treatment of gastric motility disor-ders [123] and congestive heart failure [124]. Only two applica-tions [124,125], claim novel PDE4 inhibitors respectivelyclaiming closely related pyrimidinecarboxamides and nicotina-mide derivatives, such as 22 and 23. In neither case is anypotency data provided, although it is intimated that claimedcompounds may have IC50 values as low as 1 nM.

The former Warner-Lambert group has expanded upon theSAR around the fused benzodiazepine CI-1018 [47,48] and hasalso explored related fused heterocycles, such as the fusedquinazoline 24 [127] and the iminoazepine 25 [128]. The dis-closed potency of the latter, IC50 = 1.2 nM, suggests that thisis a series of greater interest, with a significant potencyimprovement over the benzodiazepines

3.4 ICOSICOS's effort in this area has relied on the use of recom-binant PDE enzymes and has been performed independ-ently since the termination of its collaboration with GlaxoWellcome in 1997, with IC-485 having been described as acandidate in preclinical development [204]. The set of eightpatent applications that appeared in June 2001 indicate thedirection that this effort has subsequently followed. Thestructures claimed indicate that, like many other compa-nies, ICOS has sought to improve on the template exempli-fied by rolipram 26, with five applications claimingcompounds covered by the generic structure 27 [129-133],whilst a sixth claimed the isosteric indazole 28 [134]. Thelimited biological data presented indicates that while someof these compounds are potent inhibitors, e.g., 28 at6.2 nM and 29 at 2.2 nM, while others only display micro-molar potency.

The two remaining applications claim compounds basedon carboxyazole templates, incorporating features seen in thecatechol based compounds. Both pyrazoles, such as 30 [135]

and pyrroles, such as 31 [136] are claimed and this relativelynovel template appears to provide compounds of reasonablepotency, 30 being reported to inhibit PDE4 with an IC50value of 53 nM.

3.5 MerckMerck has continued to build upon the template firstexploited in Celltech's CDP-840 (32). This has been featuredin each of the eight applications published in the past21 months and in the various compounds that have beendescribed in publications and at selected meetings. Thesecompounds have included the heavily fluorinated derivativesL-791943 (33) and L-826141 (34) [49]. L-791943 wasreported to display too long a duration of action (> 24 h) in anumber of animal species, but introduction of a methylgroup, to give L-826141, provided a more suitable, potentPDE4A inhibitor (IC50 = 1 nM), albeit not the developmentcandidate. L-826141 displayed oral ED50 values in the range0.5 - 3 mg/kg in squirrel monkeys, while not inducing emesisin ferrets at 30 mg/kg.

Although the introduction of the hexafluoro-2-hydroxy-propyl substituent provides enhanced potency within thisseries of compounds, when combined with the bis- dif-luromethoxy substitution, it does not provide good activity inwhole blood assays. This is restored by reversion to the use ofcycloalkyl ethers, as in 35 [50]. The active enantiomer of 35inhibits LPS-induced TNF-α production with an IC50 valueof 10 nM in a whole blood assay, in contrast to 700 nM and300 nM for L-791943 and L-826141, respectively.

This class of compounds has formed the focus of most of therecent patenting from this group. Five of the eight applicationspublished within this period have claimed compounds relatedto L-826141, in which a second hetero ring has replaced thealkyl substituted phenyl ring. These applications have claimedeither N-oxides or unoxidised pyridine derivatives, with the

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Norman


bulk of the effort concentrated on 6-substituted-3-pyridylderiv-atives e.g. 36. The compounds claimed have covered hydroxy-alkyl derivatives [137], arylalkoxy derivatives [138], arylaminoderivatives [139] and phenylthio derivatives [140]. A more recentdevelopment is the use of a substituted thiazole ring, as in 37[141]. These applications present limited biological data but thedata presented makes it evident that the use of a second heteroring does not attenuate the potency of the compounds, 36 dis-playing an IC50 value of 0.75 nM as an inhibitor of PDE4.

Although the bulk of Merck's effort has been focused uponthese triarylethane derivatives, two recent applications indi-cate that it is continuing to explore the use of alternativeclasses of triaryl derivatives. This is illustrated by two recentpatents, respectively claiming the styrene derivatives 38 [142]

and the trisubstituted indole 39 [143]. In neither case is anyclear indication of the compounds' potency given.

3.6 CelltechAlthough the origins of the Merck PDE4 programme lie inwork performed at Celltech in the UK, with the UK-basedeffort having long ceased, another part of the CelltechGroup, the former Chiroscience group, continues to publishpatent applications in this field, under the name Darwin Dis-covery. The five applications published represent further

investigations of previously described series. The most signif-icant application claims inter alia D-4396 (9) [144]. Threeapplications described the development of a series of 7-meth-oxybenzofuran-4-carboxamide derivatives in which five-membered, rather than six-membered, rings form the amidesubstituent and benzothiazoles and benzoxazoles, e.g., 40 areclaimed in addition to the parent benzofurans [146-148].

Some of the SAR of the earlier series has also beendescribed highlighting the potency of 2-acetylbenzofuranderivatives e.g., 41 [51]. This indicated that, although highpotency as PDE4 inhibitors could be obtained with a range of2-substituted benzofurans, including alkyl, hydroxyalkyl andheteroaroyl substituents, the use of 2-acetyl substituents pro-vided the best ratio of potency to HARBS, the respective IC50values for 41 were 1.6 and 43.4 nM. Studies in the ferret con-firmed that 41 was non-emetic at 10 mg/kg p.o.

3.7 CelgeneCelgene's efforts appear to remain firmly focussed upon aseries of phthalimide derivatives incorporating a catechol moi-ety, such as 42. All three applications published in 2001 claimcompounds of this type [148-150], whilst the preceding year sawthe grant of a related US patent [151]. In none of these applica-tions was any biological data presented, nor has the company

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31 32 33 R = H34 R = CH3

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published any further descriptions of the biological activity ofthis series of compounds, although it has presented a limitedamount of SAR data at recent meetings on inflammatory dis-eases. (This effort was discussed in more detail in earlierreviews in this series [1,2]).

3.8 ZambonThe Zambon group is a recent entrant to the PDE4 inhibitorfield with four patent applications appearing in 2000 reinforc-ing the company's effort in this field, first evidenced by theappearance of two applications, in 1999, claiming phthalazinederivatives [152,153]. The more recent applications indicate acontinuation of this effort with potent phthalazines, such as43 (IC50 = 7.1 nM) and 44 (IC50 = 2.0 nM) claimed [154,155].In contrast, tricyclic phthalazines appear to be less potentPDE4 inhibitors, e.g., 45 [156]. Some divergence of thisapproach to encompass benzazines, e.g., 46 (IC50 = 35.9 nM)was evidenced by the fourth application [157].

The compounds claimed in these applications highlightsome interesting features, the use of the 3,5-dichloro-4-pyridyl moiety widely favoured by a number of companies,but attached via a methylene rather than amide linkage, theuse of rolipram like substituents in 44, indicating the fusedring simply provides an alternative scaffold and most inter-estingly the apparent acceptability of replacing the secondether linkage by either a methylene group, as in 46, or byan alkyne, as in 43. The rationale underlying these changeshas been described in more detail in three recent communi-cations. The use of unsaturated carbon linkers has beenreported to enhance PDE4 inhibitory potency withoutenhancing affinity at the rolipram high affinity binding site[52]. A similar effect can be achieved by 4-substitution ofthe phthalazine ring with phenylethyne, thiazol-2-yl or thi-azol-2-ylmethyl groups [53]. A patent application coveringcompounds with this substitution pattern has not yet beenpublished.

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The thiazole derivative 47a is reported to display IC50 val-ues of 4 nM as an inhibitor of human neutrophil PDE4,3 nM as an inhibitor of TNF-α production in monocytesand 17 nM at the HARBS [53]. Similar effects can beachieved by 3-substitution of the dihydrophthalazine with asulfonyl 48 or acyl group 49 [54]. The cyclopentyl ether 44 isa potent inhibitor of both PDE4 and HARBS (IC50 =5 nM), switching to the deoxy analogue 48 causing a 10-fold reduction in potency in both assays (21 and 60 nM) butthe use of an acyl substituent dramatically reduced affinityfor the HARBS. Thus, compound 49 inhibited PDE4 withan IC50 value of 12 nM but only inhibited rolipram bindingby 36% at 100 nM.

Although it is less potent PDE4 inhibitor than the thiazole47a, the 1,2,4,-triazole analogue Z-153750A 47b was identi-fied at the 2001 ATS meeting as a preclinical candidate [55,56].Z-153750A inhibits human neutrophil PDE4 and TNF-αrelease from human monocytes with IC50 values of 241 and 72nM and has a Ki value of 383 nM at the HARBS [55]. Z-153750A inhibited antigen-induced bronchoconstriction inguinea-pigs and Brown Norway rats at doses of 10 and100 µm/kg but, in contrast to rolipram and cilomilast, did notinduce emesis in dogs even at a dose of 30 µm/kg iv. [55,56].

3.9 Merck KgAaThe past two years suggest that the group at Merck hasincreased its effort in this area, doubling the number of pub-lished patent applications that claim PDE4 inhibitors. Allfour of these applications claim derivatives of 1-benzoyl-1,4,5,6-tetrahydropyridazin-3-yl catechols but fail to provideany indication of the potency of the claimed compounds. The

compounds claimed include carbamates 50 [158], amides 51[159,160] and urea derivatives 52 [161].

3.10 Bayer AGFollowing a period in which the company had filed few patentapplications, despite progressing at least one compound toclinical development, the year 2000 saw the concurrentappearance of a batch of four applications claiming com-pounds closely related to sulfonylbenzofuran derivative BAY19-8004 3. These claimed ether 53 [162,163] and sulfonate ester54 [164] derivatives of 2-benzoyl-6-hydroxybenzofurans andalso benzofurans bearing aliphatic 2-acyl substituents 55 [165].

Following the company's usual approach with patents in thisarea these applications provide very limited indication of thepotency of the claimed compounds. No indication was pro-vided of the potency of the aliphatic derivatives 55 but both thesulfonate esters, 54 and 53 were reported to be potent inhibitorsof human neutrophil PDE4 with respective IC50 values of 1 and6 nM [164,163]. In contrast, the replacement of the primaryhydroxyl group in the ether series appears to reduce activity, 53was reported to have an IC50 value of 170 nM [162]. Althoughthis effort is a long-standing programme at Bayer, originated in1990, no details of the medicinal chemistry of these benzo-furan-based PDE4 inhibitors have yet been presented.

3.11 Napp (Euroceltique)Napp is another company that appears to have been reducingits effort in this field. Although V-11294A progressed to theclinic some time ago there has been little recent patenting ofPDE4 inhibitors by Euroceltique, the name employed by theMundipharma Group. The sole application published in the

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47a X = CH, Y = S, Z = CH47b X = N, Y = CH, Z = N

48 R = SO2CH3

49 R = COCH2 Ph50 R = alkoxy51 R = hetroaryl52 R = NH2, alkylNH

53 X = substituted alkyl54 X = alkylsulfonyl, arylsulfonyl

55



past two years claims further hybrid structural types in whicha catechol moiety is coupled to a xanthine nucleus [166]. Usinga hypoxanthine residue, rather than the xanthine employed inV-11294A, appears to provide for substantial enhancementsin potency. The compound 56 is a very potent PDE4 inhibi-tor with an IC50 value of 0.34 nM and is only weakly active(> 10 µM) against PDE3 or PDE5.

3.12 Kyowa HakkoKyowa's efforts in this field have had a low profile, but thecompany has commenced the clinical evaluation of KW-4490. Recent efforts have been continued to use of bicyclicanalogues of the more common catechol motif and havebeen confined to the appearance of two patent applicationsclaiming compounds such as 57, a bicyclic analogue of cilo-milast [167]. This compound is indicated to be highly effec-tive as a PDE4 inhibitor at 1 µM but no potency data arepresented.

3.13 NovartisNovartis is a major company that has shown some interest in theidentification of PDE4 inhibitors, but despite the company'savowed interest in the development of novel respiratory thera-peutics, it has shown little evidence of a coherent effort in thePDE4 inhibitor field. This year was the first since 1998 in whichany filings have appeared from the company. Yet, despite thisapparently limited effort, the past two years have also seen fourmedicinal chemistry publications in this area, describing three

very distinct classes of compound, none of which display muchresemblance to the company's published patent applications.

The claimed arylbenzoxadiazole derivatives, such as 58,appear to provide yet another variation of the catechol basedPDE4 inhibitors [168]. The benzoxadiazole ring appears toprovide another alternative isostere for the more commonlyutilised cyclopentylether. However, a recent report by Kelleret al. [57] indicates that further investigations are being per-formed, employing rolipram derivatives such as 59. In thisseries of compounds the (S)-enantiomers were found to bethe eutomers and to display low nanomolar potencies in arange of cellular assays. The majority of these compoundswere less potent as PDE4C inhibitors than against the otherthree isoforms of PDE4. The IC50 values for 59 were:PDE4A = 2.5 nM, PDE4B = 5 nM, PDE4C = 16 nM, PDE= 2 nM [57].

In contrast, the same group has also explored the activity of aseries of 8-phenyl-1,7-naphthyridines, such as 60 [58,59]. Com-pound 60 was reported to inhibit PDE4D with an IC50 valueof 1 nM and to be 88-fold selective (for PDE4D) relative toPDE4A, 49-fold selective relative to PDE4B and 68-fold selec-tive relative to PDE4C. The naphthyridine 60 also inhibitedbinding to the HARBS with a Ki value of 0.6 nM and wasshown to be 10-fold more potent than cilomilast in a rat modelof asthma. The fourth paper from this group described a seriesof hybrid prodrugs in which isoquinoline PDE4 inhibitors werecoupled to corticosteroids and these compounds were shown tobe cleaved in vivo to the active drugs [60].

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Norman


3.14 Yamanouchi and Boehringer IngelheimAlthough Yamanouchi has progressed YM-976 (10) to clinicalstudies it continues to further explore the pyrido[2,3-d]pyri-midin-2(1H)-one template. Introduction of a 3-amidinoalkylsubstituent, as in 62, having been found to be compatiblewith good activity [169]. A more novel approach is exemplifiedin a recent disclosure, of compounds such as 63, by Boe-hringer Ingelheim [170]. Boehringer was one of the few leadingpharmaceutical companies that had not previously indicatedan interest in this area, which was somewhat surprising giventhe company's strong interests in the respiratory field. Despitethis late entry into a crowded field Boehringer appears to haveidentified a novel class of PDE4 inhibitors, with 63 indicatedto inhibit PDE4 with an IC50 value of 18 nM.

3.15 Sanofi-SynthélaboAnother major pharmaceutical company, which has onlyjust entered this field, is Sanofi-Synthélabo. Its entry israther more surprising as the company has little interest ineither the respiratory or inflammatory therapeutic areas. Theapproach exemplified by the two patent applications thathave appeared to date is to seek yet another fused ring sys-tem as an alternative to the catechol moiety [171,172]. Bothapplications claimed tetrahydroisoquinolines and, based onthe reported PDE4 IC50 values, the presence of a third fusedring does not reduce inhibitory activity. The claimed com-pounds 64 and 65 displaying respective IC50 values of 2.9nM and 6 nM accompanied by negligible activity againstother PDEs.

3.16 InflazymeNew entrants to the PDE4 inhibitor field are not confined tomajor companies and the Vancouver-based company Infla-zyme Pharmaceuticals is another entrant to this field. Thecompany claims to have identified a series of potent, non-

emetic, PDE4 inhibitors exemplified by IPL-4088, the struc-ture of which has not yet been publicly disclosed. IPL-4088 isreported to be an orally-active inhibitor of antigen-inducedbronchoconstriction in the guinea-pig and colitis in the rat atdoses of 10 and 20 mg/kg [207]. The available informationdoes not permit an attempt to identify IPL-4088, but thecompany's two published patent applications make it clearthat it has identified some novel PDE4 inhibitors.

The first of these applications claimed simple δ-substi-tuted lactones, such as 66 [173], whilst the more recent appli-cation claimed benzylated derivatives of known PDE4inhibitors, such as 67 [174]. The latter claims that benzyla-tion retains the potency as PDE4 inhibitors whilst reducingthe affinity for the HARBS. Thus, the benzylated rolipramderivative 67 displays respective IC50 values of 400 and 360nM, compared to 420 and 6.5 nM for rolipram. In the com-monly employed ferret model of emesis 67 was found to beat least 10-fold less emetic than rolipram. (Note that com-pounds similar to 67, e.g., 59, have also been described bythe group at Novartis 49. The earlier application providesno indication of the potency of the claimed lactones asPDE4 inhibitors but does indicate that one compound iseffective in murine model of collagen-induced arthritis at10 mg/kg ip.

3.17 Mitsubishi and VernalisTwo more recent entrants to the PDE4 inhibitor field areMitsubishi and Vernalis. Mitsubishi has claimed a series ofhybrid catechol-xanthine structures, such as 68, that bear aresemblance to the approach first described by the group atNapp Pharmaceuticals. This provides potent compoundswith 68 having an IC50 value of 3.41 nM [175]. The applica-tions from Vernalis are more surprising since the claimedcompounds are non-selective PDE3/PDE4 inhibitors andbecause the company has now changed its focus on the

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development of CNS therapeutics. With the exception ofpumafentrine there is now little interest in the developmentof mixed inhibitors and the claimed pyrimido[6,1-a]isoqui-nolin-4-ones are weakly active as PDE4 inhibitors, display-ing greater potency as PDE3 inhibitors. The compoundsclaimed are exemplified by 69, with IC50 values of 0.43(PDE3) and 1.48 µM (PDE4) and 70 with IC50 values0.107 and 1.20 µM [176,177].

4. New uses

Most companies are interested in the development of PDE4inhibitors for the treatment of inflammatory diseases, princi-pally the treatment of airway inflammation, but a few patentshave claimed interesting new approaches to the use of suchagents. Boston Medical Center claims the use of rolipram andother PDE4 inhibitors, as a method of treating chronic lym-phocytic leukaemia [178]. The claims are based upon the obser-vation that rolipram can potentiate the apoptosis ofmononuclear cells induced by cytotoxic agents.

The successful use of the PDE5 inhibitor sildenafil for thetreatment of erectile dysfunction has led to an explosion inpatents claiming the use of various agents for this indication.One such application is from Vivus, which claims the trans-mucosal administration of PDE4, as well as PDE3 or PDE5,inhibitors for the treatment of erectile dysfunction [179]. Thecompounds whose use is claimed include rolipram and milri-none. E-L Management claims the use of topical 2-deoxycyclic nucleotides, indicated to inhibit PDE4, for the treat-ment of atopic dermatitis [180]. Both 2-deoxy cAMP and 2-deoxy cGMP were shown to be equipotent with rolipramwhen applied topically as anti-irritants. Whilst this indicationis not a novel application of the use of PDE4 inhibitors, thisuse of cyclic nucleotides is.

5. Scientific developments

The past two years have seen little progress with regard to theidentification of isoform selective PDE4 inhibitors, primarilyactive at one or other of the four isoforms. The exception tothis is a series of naphthyridine derivatives, e.g., compounds60 and 61, described by scientists at Novartis [58,59]. However,significant progress has been made in delineating the structure

and function of the enzyme as well as in understanding themechanisms by which emesis occurs.

Although recombinant preparations of each of the isoformsof PDE4 and their various splice variants have been availablefor some time there has been little evidence of companies rou-tinely employing these cloned enzymes rather than membranepreparations of PDE4, commonly from the neutrophil.Recent publications from Novartis make it evident that thecompany routinely evaluates its PDE4 inhibitors against allfour isoforms of PDE4 [57-59]. The description of the nitroph-enyl derivative 60 was the first indication that the companyhad identified selective PDE4D inhibitors and this effort hasnow been expanded to explore alternatives to this potentiallymutagenic agent. This has led to the description of fused ben-zoxadiazoles, such as 61, as suitable replacements that retainthe isoform selectivity [59]. This modification enhanced theselectivity for PDE4D (IC50 values: PDE4A = 602 nM,PDE4B = 34 nM, PDE4C = 1230 nM, PDE4D = 1.5 nM),but interestingly did not impact upon the affinity for theHARBS (IC50 1 nM). The benzoxadiazole 61 was alsoreported to be a more potent inhibitor than 60, of TNF-αrelease from human mononuclear cells and to be an effectiveinhibitor in the rat adjuvant-induced arthritis model (50%inhibition at 5 mg/kg p.o.). With the indication that 61 willbe evaluated in model detail in animal models of respiratorydisease it will be interesting to see whether the use of such aselective inhibitor offers any apparent advantages over equallypotent but less selective, inhibitors.

One of the most substantive advances to facilitate thefuture design of PDE4 inhibitors is the determination of thethree dimensional structure of the catalytic subunit ofPDE4B2B to 1.7 Å resolution [61]. Somewhat surprisingly thiswork was performed at (the former) Glaxo Wellcome, a com-pany that appeared to have abandoned its interest in develop-ing PDE4 inhibitors, at least prior to the merger withSmithKline Beecham. By taking note of these data and theinformation obtained from studies, using site-directed muta-genesis, on the inhibitor binding site of PDE4A [62,63], itshould prove feasible to design more selective and possiblymore potent compounds.

Despite its long-standing collaboration with Celltech, thathas only recently led to the progression of a follow-up toCDP-840 into the clinic, Merck has clearly been engaged in

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Norman


extensive research into how PDE4 inhibitors can induce eme-sis and the physiological significance of the HARBS usingbiochemical and pharmacological approaches. Studies with afluorescently labelled derivative L-791,760 enabled them toshow that the HARBS site is to be found on the Mg2+ com-plexed conformation of the enzyme whilst inhibitory potencycorresponds to the affinity for the free enzyme [64]. Later stud-ies highlighted a role for a second metal ion in the conforma-tional change process [65].

Concurrently with that approach, the Merck group hasbeen trying to clarify the molecular targets by the use of pho-toaffinity labels. To this end a number of aziridine-and azide-based PDE4 inhibitors were prepared as potential photoaffin-ity labels [66]. This led to the identification of APIIMQ 71 asboth a potent PDE4A inhibitor (IC50 = 0.4 nM) and a verypotent emetic agent in the ferret (MED 0.1 mg/kg p.o.), thusproviding a suitable tool for confirming, or denying, whetherthe emetic effects are attributable to a molecular target dis-tinct from PDE4. As pharmacological studies in the ferrethave suggested, such effects are mediated by noradrenaline-induced activation of α2 receptors and it remains distinctlypossible that the effector proteins are distinct from the PDE4enzyme [67]. Earlier studies had dismissed a potential role forsubstance P release of activation of 5-HT3 receptors [68].

In addition to these therapeutically focussed studies therehave been a considerable number of intracellular mechanisticstudies described by Miles Houslay's group. These are outsidethe scope of this review but much of this work is summarised inProfessor Houslay's recent comprehensive review on PDE4 [69].

6. Expert opinion

The identification and development of PDE4 inhibitors con-tinues to attract greater attention. By 2001 nearly all of thetop 20 pharmaceutical companies had filed one or more pat-ent applications claiming novel PDE4 inhibitors. In addition,the field continues to attract the interest of smaller pharma-ceutical and biotechnology companies. Inhibition of PDE4 isone of the most popular drug targets currently being targetedby the drug industry.

The therapeutic inhibition of PDE4 has been an aim ofsome pharmaceutical companies since the late 1980s and itnow appears that 2002 will finally see the filing of one, ormore, regulatory submissions for the approval of PDE4 inhib-itors. It appears highly probable that GlaxoSmithKline willfile a NDA for the use of cilomilast to treat COPD whilethere appear to be significant prospects of Byk Gulden filingfor approval of the use of roflumilast to treat asthma. Giventhe current development status of compounds for other indi-cations it appears unlikely that any PDE4 inhibitors will befiled for alternative indications before 2005.

The primary indication for which PDE4 inhibitors appearto have good prospects of being used is for the treatment ofCOPD. This disease offers a large, poorly treated, market forwhich any effective therapy, especially an orally-active anti-

inflammatory agent will offer significant progress. It seemslikely the end of 2001 will see three PDE4 inhibitors eitherin, or having completed, Phase III studies in COPD patientsand the eagerly awaited results should clarify how beneficialsuch agents will prove. This offers a major commercial oppor-tunity, with the scope of potential blockbuster products and isdiscussed comprehensively elsewhere [70].

Asthma has traditionally been the primary indication forPDE4 inhibitors but it appears increasingly unlikely that anyagents of this class will prove to be a major improvement in thetreatment of asthma. A number of potent PDE4 inhibitorshave now failed to demonstrate convincing efficacy in Phase IIstudies in asthmatics and while some of the problems may bedue to the use of inadequate dosage to produce sufficienteffects, e.g., with cilomilast, where side effects limited the dos-age employed, animal studies with PDE4 knockout mice havesuggested that PDE4 inhibitors may have little effect on allergicinflammation [71]. The clearest evidence for a role of PDE4inhibitors in the treatment of asthma should be provided by theongoing studies with roflumilast, this drug is significantly morepotent than those which have failed to demonstrate efficacy andcould presumably be used at a higher daily dose than 0.5 mg toobtain a maximal therapeutic effect.

The comparison of the effects of oral roflumilast with those ofinhaled steroids will thus be highly critical in assessing the com-mercial viability of PDE4 inhibitors in the treatment of asthma.One approach that might enhance the efficacy of PDE4 inhibi-tors would be to co-administer them with agents that stimulateadenylyl cyclase, either β2 agonists or prostaglandins. Althoughsuch an approach has potential pitfalls with regard to formulat-ing potential product the use of such combinations has attractedthe attention of both GlaxoSmithKline and Byk Gulden, withboth companies filing patent applications claiming the use ofPDE4 inhibitor/β2 agonist combinations.

Of the other indications for which PDE4 inhibitors arecurrently in clinical development there are currently no clin-ical data to support their potential utility in the treatment ofmultiple sclerosis or Crohn's disease. Similarly the potentialutility in the treatment of skin diseases remains to be con-vincingly demonstrated. Limited data suggest a possible util-ity in the treatment of rheumatoid arthritis with beneficialeffects likely to be due to the ability of these agents toinhibit TNF-α production. However, other approaches,such as the inhibition of p38 MAPK, may prove more effec-tive in this respect. But, the increasing availability of PDE4inhibitors with low nanomolar potencies increases the pros-pects of such agents proving useful in the treatment of otherconditions.

Given the increasingly high profile of agents such as cilomi-last and roflumilast it is probable that the next few years willcontinue to see the publication of a substantial number ofpatent applications claiming PDE4 inhibitors or novel uses ofPDE4 inhibitors. Whether there will continue to be furthercompanies entering this field is more doubtful, other thanthose who seek alternative uses for PDE4 inhibitors.



BibliographyPapers of special note have been highlighted as either of interest (•) or of considerable interest (••) to readers.

1. NORMAN P: PDE4 Inhibitors 1999. Expert Opin. Ther. Patents. (1999) 9:1101-1118.

•• Previous review in this series.

2. NORMAN P: PDE4 Inhibitors. Expert Opin. Ther. Patents (2000) 10:1415-1427.

•• Previous review in this series.

3. MARTIN T: PDE4 inhibitors - a review of the recent patent literature. Curr. Opin. Investig. Drugs (2001) 4:312-338.

4. DYKE HJ, MONTANA JG: The Therapeutic Potential of PDE4 Inhibitors. Expert Opin. Investig. Drugs (1999) 8:1301-1325.

•• Useful review that considers various therapeutic opportunities and current developments.

5. DOHERTY AM: Phosphodiesterase 4 inhibitors as novel anti-inflammatory agents. Curr. Opin. Chem. Biol. (1999) 3:466-473

• Another medicinal chemistry orientated review from a different perspective

6. DYKE HJ, MONTANA JG: Update on the therapeuticl potential of PDE4 inhibitors. Expert Opin. Investig. Drugs (2002) 11(1):1-13.

7. HUANG Z, DUCHARME Y, MACDONALD D, ROBICHAUD A: The next generation of PDE4 inhibitors. Curr. Opin. Chem. Biol. (2001) 5:432-438.

8. HAY DWP: Chronic obstructive pulmonary disease: emerging therapies. Curr. Opin. Chem. Biol. (2000) 4:412-419.

9. COOMBES J: Merrill Lynch Global Pharmaceutical Investor Conference. London, UK September 25 (2001)

10. COMPTON C, EDELSON JD, CEDAR E et al.: Cilomilast (Ariflo) 15 mg bid safety in a six month clinical trial program. Am. J. Respir. Crit. Care Med. (2001) 163: A909.

• Abstract summarising the Phase III data.

11. ZUSSMAN BD, DAVIE CC, KELLY J et al.: Bioavailability of the oral selective phosphodiesterase 4 inhibitor cilomilast. Pharmacotherapy (2001) 21(6):653-660.

12. ZUSSMAN BD, BENINCOSA LJ, WEBBER DM et al.: An overview of the pharmacokinetics of cilomilast (Ariflo), a new, orally active phosphodiesterase 4 inhibitor, in healthy young and elderly volunteers. J. Clin. Pharmacol.. (2001)

41(9):950-958.

13. COMPTON CH, GUBB J, NIEMAN R et al.: Cilomilast, a selective phosphodiesterase-4 inhibitor for treatment of patients with chronic obstructive pulmonary disease: a randomised, dose-ranging study. Lancet (2001) 358(9278):265-270.

•• The most significant clinical data published yet on a PDE4 inhibitor.

14. GIEMBYCZ MA: Cilomilast: a second generation phosphodiesterase 4 inhibitor for asthma and chronic obstructive pulmonary disease. Expert Opin. Investig. Drugs (2001) 10 (7):1361-1379.

• Comprehensive, up to date review.

15. RENNARD SI, EDELSON JD, ROBINSON CB et al.: Cilomilast reduces the percentage of sputum neutrophils in patients with chronic obstructive pulmonary disease (COPD) Chest (2001) 120: Suppl. 45S

16. DUPLANTIER AJ, BIGGERS MS, CHAMBERS RJ et al.: Biarylcarboxylic acids and -amides: inhibition of phosphodiesterase Type IV versus [3H]rolipram binding activity and their relationship to emetic behavior in the ferret. J. Med. Chem. (1996) 39:120-125.

17. CHRISTENSEN SB, GUIDER A, FORSTER CJ et al.: 1,4-cyclohexane-carboxylates: potent and selective inhibitors of phosphodiesterase 4 for the treatment of asthma. J. Med. Chem. (1998) 41:821-835.

18. TORPHY TJ: Phosphodiesterase isozymes. Molecular targets for novel antiasthma agents. Am. J. Respir. Crit. Care Med. (1998) 157: 351-370.

•• Still the outstanding review on PDE4 inhibition.

19. UNDERWOOD DC, BOCHNOWICZ S, OSBORN RR. et al.: Antiasthmatic activity of the second-generation phosphodiesterase 4 (PDE4) inhibitor SB 207499 (Ariflo) in the guinea pig. J. Pharmacol. Exp. Ther. (1998) 287:988-995.

20. ALTANA AG: (2000) Annual Report March 2001

21. SCHMIDT BM, KUSMA M, FEURING M et al.: The phosphodiesterase 4 inhibitor roflumilast is effective in the treatment of allergic rhinitis. J. Allergy Clin. Immunol. (2001) 108(4):530-536.

22. HATZELMANN A, SCHUDT C: Anti-inflammatory and immunomodulatory potential of the novel pde4 inhibitor roflumilast in vitro. J. Pharmacol. Exp. Ther.

(2001) 297(1):267-279.• In vitro characterisation.

23. BUNDSCHUH DS, ELTZE M, BARSIG J et al.: In vivo efficacy in airway disease models of roflumilast, a novel orally active PDE4 inhibitor. J. Pharmacol. Exp. Ther. (2001) 297(1):280-290.

•• Comprehensive in vivo characterisation and comparison with standard PDE4 inhibitors.

24. ZECH K, DAVID M, SEIBERLING M et al.: High oral absolute bioavailability of roflumilast, a new, orally active, once daily PDE4 inhibitor ERS 2001:A256.

25. DAVID M, BETHKE T, HARTMANN A et al.: Influence of food intake on the pharmacokinetics of roflumilast, a new, orally active, selective PDE4 inhibitor ERS 2001:A377.

26. RADTKE HW: Development of master allergic mediators SMI Conference - Asthma: New Drug Targets & Innnovative Therapeutics (2001).

27. W TIMMER, V LECLERC, G BIRRAUX et al.: Safety and efficacy of the new PDE4 inhibitor roflumilast administered to patients with exercise-induced asthma over 4 weeks. Am. J. Respir. Crit. Care Med. (2000) 161:A505.

28. H NELL, S LEICHTL, F RATHGEB et al. Acute anti-inflammatory effect of the novel phosphodiesterase 4 inhibitor roflumilast on allergen challenge in asthmatics after a single dose. Am. J. Respir. Crit. Care Med. (2000) 161:A200.

29. ALTANA AG: Company presentation, March 2001.

30. BAYER AG: Bayer's pharmaceutical research strategy pays off: more than 40 substances in the pipeline - development of asthma drug halted at Phase II - submission of registration dossier for vardenafil scheduled for fall 2001. News Release (2001) June 12.

31. STURTON RG, BUTT NM, PALFAI SP et al.: Molecular and cellular profile of the structurally novel phosphodiesterase (PDE) 4 inhibitor, BAY 19-8004. Am. J. Respir. Crit. Care Med. (2000) 161:A200.

32. FITZGERALD MF, BRIGGS BA, THOMPSON AM et al.: The evaluation of a selective phosphodiesterase (PDE) 4 inhibitor, Bay 19-8004, in guinea-pig antigen challenge and ferret emesis models Am. J. Respir. Crit. Care Med. (2000) 161:A201.

33. FITCH N, FREEMAN MS, STURTON

Norman


RG et al.: The effect of an oral phosphodiesterase (PDE) 4 inhibitor Bay 19-8004 in primate asthma models. Am. J. Respir. Crit. Care Med. (2000) 161:A201.

• Indicative of the high oral potency of this novel PDE4 inhibitor.

34. Schering AG: pipeline, 22 June 2001.

35. DINTER H, TSE J, HALKS-MILLER M et al.: The Type IV phosphodiesterase specific inhibitor mesopram inhibits experimental autoimmune encephalomyelitis in rodents. J. Neuroimmunol. 2000 Aug 1;108(1-2):136-146.

36. HUNT HJ, MONTANA JG, COOPER N et al.: The profile of SCH351591, a novel phosphodiesterase 4 inhibitor. 11th RSC-SCI Medicinal Chemistry Symposium. Cambridge, UK September 2001.

37. AOKI M, KOBAYASHI M, ISHIKAWA J et al.: A novel phosphodiesterase Type 4 inhibitor, YM976 (4-(3-chlorophenyl)-1,7-diethylpyrido[2,3-d]pyrimidin-2(1H)-one), with little emetogenic activity. J. Pharmacol. Exp. Ther. 2000 Oct 295(1):255-260.

38. AOKI M, FUKUNAGA M, SUGIMOTO T et al.: Studies on mechanisms of low emetogenicity of YM976, a novel phosphodiesterase Type 4 inhibitor. J. Pharmacol. Exp. Ther. (2001) 298(3):1142-1149.

39. AOKI M, FUKUNAGA M, KITAGAWA M et al.: Effect of a novel anti-inflammatory compound, YM976, on antigen-induced eosinophil infiltration into the lungs in rats, mice, and ferrets. J. Pharmacol. Exp. Ther. (2000) 295(3):1149-1455.

40. AOKI M, YAMAMOTO S, KOBAYASHI M et al.: Antiasthmatic effect of YM976, a novel PDE4 inhibitor, in guinea pigs. J. Pharmacol. Exp. Ther. (2001) 297(1):165-173.

41. PRUNIAUX MP, MOTTIN G, PLANQUOIS JM, BERTRAND C: The selective phosphodiesterase 4 inhibitor CI-1044 (PD-189659) inhibits LPS-induced neutrophil recruitment and TNF-alpha release in rat airways. Am. J. Respir. Crit. Care Med. (2001) 163:A991.

42. OUAGUED M, MARTIN-CHOULY C, LEPORTIER C et al.; The novel phosphodiesterase 4 inhibitor CI-1044 inhibits in vitro LPS-induced TNFα production in whole blood of COPD patients ERS September 2001, Berlin P333, Germany (2001).

43. YAMANA K, SUZUKI N, OTAN T: NIK-

616, a new type of selective phosphodiesteraseIV (PDE IV) inhibitor with reduced emetic activity, ERS September 2001, Berlin P335, Germany (2001).

44. KARPINSKI JM, BARNETTE MJ, BOCHNOWICZ S et al.: Comparison of the PDE4 activities of Ariflo (SB 207499) with related 4-acetylenic substituted cyclohexyl alcohols and amines 221st ACS. San Diego, USA (2001). MEDI 251.

45. VAN DER MEY M, HATZELMANN A, VAN DER LAAN IJ et al.: Novel selective PDE4 inhibitors. 1. synthesis, structure-activity relationships, and molecular modeling of 4-(3,4-Dimethoxyphenyl)-2H-phthalazin-1-ones and analogues. J. Med. Chem. 2001 44 (17) 2511-2522.

46. VAN DER MEY M, HATZELMANN A, VAN KLINK GPM et al.: Novel selective PDE4 inhibitors. 2. synthesis and structure-activity relationships of 4-aryl-substituted cis-tetra- and cis-hexahydrophthalazinones. J. Med. Chem. 2001 44 (17) 2523-2535.

47. BURNOUF C, AUCLAIR E, AVENEL N et al.: Synthesis, structure-activity relationships, and pharmacological profile of 9-amino-4-oxo-1-phenyl-3,4,6,7-tetrahydro[1,4]diazepino[6, 7,1-hi]indoles: discovery of potent, selective phosphodiesterase Type 4 inhibitors. J. Med. Chem. (2000) 43(26):4850-4867.

48. PASCAL Y, ANDRIANJARA CR, AUCLAIR E et al: Synthesis and structure-activity relationships of 4-oxo-1-phenyl-3,4,6,7-tetrahydro-[1,4]diazepino[6,7,1-hi]indoles: novel PDE4 inhibitors. Bioorg. Med. Chem. Lett. (2000) 10(1):35-38

49. FRENETTE R., BLOUIN M, BRIDEAU C et al.: Substituted 4-(2,2-diphenylethyl)-pyridine-N-oxides as phosphodiesterase-4 inhibitors: SAR study directed toward the improvement of pharmacokinetic parameters 221st ACS. San Diego, USA (2001). MEDI 247

50. GIRARD Y, BLOUIN M, BRIDEAU et al.; Phenyl substituted analogs of CDP-840 as phosphodiesterase-4 inhibitors with improved potency, oral activity, and metabolic stability. 84th Canadian Society for Chemistry Conference. Montreal, Canada (2001).

51. BUCKLEY G, COOPER N, DYKE HJ et al.: 7-Methoxybenzofuran-4-carboxamides as PDE 4 inhibitors: a potential treatment for asthma Bioorg. Med. Chem. Lett. (2000) 10(18):2137-2140.

52. NAPOLETANO M, NORCINI G, PELLACINI F et al.: The synthesis and

biological evaluation of a novel series of phthalazine PDE4 inhibitors I. Bioorg. Med. Chem. Lett. (2000)10:2235-2239

53. NAPOLETANO M, NORCINI G, PELLACINI F et al.: Phthalazine PDE4 inhibitors. II: The synthesis and biological evaluation of 6-methoxy-1,4-disubstituted derivatives. Bioorg. Med. Chem. Lett. (2001) 11:33-37.

54. NAPOLETANO M, NORCINI G, PELLACINI F et al.: Phthalazine PDE4 inhibitors. Part 3: the synthesis and in vitro evaluation of derivatives with a hydrogen bond acceptor. Bioorg. Med. Chem. Lett. (2001) 11. In press.

55. MORAZZONI G, FERLENGA P, ALLIEVI L et al.: Pharmacological characterization of Z15370A, a novel selective phosphodiesterase 4 inhibitor. Am. J. Respir. Crit. Care Med. (2001) 163:A431.

56. NAPOLETANO M, NORCINI G, PELLACINI F et al: Phthalazine PDE4 inhibitors.Part 3: the synthesis and in vitro evaluation of derivatives with a hydrogen bond acceptor. Bioorg.Med.Chem.Lett. (2002) 12:5-8

57. KELLER TH, BRAY-FRENCH K, DEMNITZ FW et al.: Synthesis and structure-activity relationship of N-arylrolipram derivatives as inhibitors of PDE4 isozymes. Chem. Pharm. Bull (Tokyo). (2001) 49(8):1009-1017.

58. HERSPERGER R, BRAY-FRENCH K, MAZZONI L et al.: Palladium-catalyzed cross-coupling reactions for the synthesis of 6, 8-disubstituted 1,7-naphthyridines: a novel class of potent and selective phosphodiesterase Type 4D inhibitors. J Med. Chem. (2000) 43(4):675-682.

• Interesting paper describing highly selective PDE4D inhibitors.

59. HERSPERGER R, DAWSON J, MUELLER T: Synthesis of 4-(8-benzo-[1,2,5]oxadiazol-5-yl-[1,7]naphthyridin-6-yl)-benzoic acid: a potent and selective phosphodiesterase Type 4D inhibitor. Bioorg. Med. Chem. Lett. (2001)11. In press.

60. CHARPIOT B, BITSCH F, BUCHHEIT K-H et al.: Disease activated drugs: a new concept for the treatment of asthma. Bioorg. Med. Chem. (2001) 9:7:1793-1805.

61. XU RX, HASSELL AM, VANDERWALL D et al.: Atomic structure of PDE4: insights into phosphodiesterase mechanism and specificity. Science. (2000) 288(5472):1822-1825.

62. RICHTER W, UNCIULEAC L,



HERMSDORF T et al.: Identification of substrate specificity determinants in human cAMP-specific phosphodiesterase 4A by single-point mutagenesis. Cell Signal. (2001) 13(3):159-167.

63. RICHTER W, UNCIULEAC L, HERMSDORF T et al.: Identification of inhibitor binding sites of the cAMP-specific phosphodiesterase 4. Cell Signal. (2001) 13(4):287-297.

64. LALIBERTÉ F, HAN Y, GOVINDARAJAN A et al.: Conformational difference between PDE4 apoenzyme and holoenzyme. Biochemistry (2000) 39(22):6449-6458.

65. LIU S, LALIBERTÉ F, BOBECHKO B et al.: Dissecting the cofactor-dependent and independent bindings of PDE4 inhibitors. Biochemistry (2001) 40(35):10179-10186.

66. MACDONALD D, PERRIER H, LIU S et al.: Hunting the emesis and efficacy targets of PDE4 inhibitors: identification of the photoaffinity probe 8-(3-azidophenyl)-6- [(4-iodo-1H-1-imidazolyl)methyl]quinoline (APIIMQ). J. Med. Chem. (2000) 43(22)3820-3823.

67. ROBICHAUD A, SAVOIE C, STAMATIOU PB et al.: PDE4 inhibitors induce emesis in ferrets via a noradrenergic pathway. Neuropharmacology (2001) 40(2):262-269.

68. ROBICHAUD A, TATTERSALL FD, CHOUDHURY I, RODGER IW: Emesis induced by inhibitors of Type IV cyclic nucleotide phosphodiesterase (PDE IV) in the ferret. Neuropharmacology (1999) 38(2):289-297.

69. HOUSLAY MD: PDE4 cAMP-specific phosphodiesterases. Prog. Nucleic Acid Res. Mol. Biol. (2001) 69:249-315.

•• Comprehensive review of the PDE4 filed from a biochemical perspective.

70. NORMAN P: Next generation respiratory disease therapeutics, an analysis of key competitor therapeutic pipelines. Decision Resources DR Report (2001). In press.

• Providing a detailed assessment of the commercial prospects of the PDE4 inhibitors in late stage development.

71. HANSEN G, JIN SC, UMETSU DT et al.: Absence of muscarinic cholinergic airway responses in mice deficient in the cyclic nucleotide phosphodiesterase PDE4D. Proc. Natl. Acad. Sci. USA (2000) 97:6751-6757.

Patents

101. BYK GULDEN LOMBERG CHEM FABRIK GMBH: WO0113953 (2001).

102. SCHERING AG: WO9715561 (1997).

103. SCHERING AG: WO0076484 (2000).

104. DARWIN DISCOVERY LTD.: WO0262081 (2000).

105. YAMANOUCHI PHARM. CO. LTD.: WO9606843 (1996).

106. SMITHKLINE BEECHAM CORP.: WO0012078 (2001).




110. BYK GULDEN LOMBERG CHEM. FABRIK GMBH: WO0066123 (2000).








118. BYK GULDEN LOMBERG CHEMISCHE FABRIK GMBH: WO0012501 (2000).



121. PFIZER PRODUCTS, INC.: EP-1046635 (2000).


123. PFIZER, INC.: EP-1040829 (2000).


125. PFIZER PRODUCTS, INC.: WO0157025 (2001).

126. PFIZER PRODUCTS INC.: WO0157036 (2001).

127. WARNER-LAMBERT CO.: WO0066584

(2000).

128. WARNER-LAMBERT CO.: WO0102403 (2000).

129. ICOS CORP.: WO0146136 (2001).

130. ICOS CORP.: WO0146184 (2001).

131. ICOS CORP.: WO0147879 (2001).

132. ICOS CORP.: WO0147914 (2001).

133. ICOS CORP.: WO0147915 (2001).

134. ICOS CORP.: WO0147915 (2001).

135. ICOS CORP.: WO0146172 (2001).

136. ICOS CORP.: WO0147880 (2001).

137. MERCK FROSST CANADA & CO.: WO0050402 (2000).









146. DARWIN DISCOVERY LTD: WO0158896 (2001).


148. CELGENE CORP.: WO0146183 (2001).

149. CELGENE CORP.: WO0134606 (2001).

150. CELGENE CORP.: WO0145702 (2001).

151. CELGENE CORP.: US6020358 (2000).

152. ZAMBON GROUP SPA: WO9932449 (1999).






158. MERCK PATENT GMBH: WO0026201 (2000).

Norman





162. BAYER AG: WO0069841 (2000).

163. BAYER AG: WO0069844 (2000).

164. BAYER AG: WO0069842 (2000).

165. BAYER AG: WO0069843 (2000).

166. EUROCELTIQUE SAC: WO0111967 (2001).

167. KYOWA HAKKO KOGYO CO. LTD.: WO0014085 (2000).

168. NOVARTIS AG: US06288092 (2001).

169. YAMANOUCHI PHARM. CO. LTD.: WO0130779 (2001).

170. BOEHRINGER INGELHEIM PHARMA KG: WO0035428 (2000).

171. SANOFI-SYNTHELABO: WO0164647 (2001).

172. SANOFI-SYNTHELABO: WO0164648 (2001).

173. INFLAZYME CORP.: WO0014083 (2000).

174. INFLAZYME CORP.: WO0168600 (2001).

175. MITSUBISHI CHEM. CORP.: WO0068231 (2000).

176. VANGUARD MEDICA LTD.: WO0058308 (2000).

177. VANGUARD MEDICA LTD.: WO0058309 (2000).

178. BOSTON MEDICAL CENTER: WO0016621 (2000).

179. VIVUS, INC.: WO0141807 (2001).

180. E-L MANAGEMENT CORP.: WO0066131 (2000).

Websites

201. Yamanouchi Pharmaceuticals: www.yamanouchi.com/eg/fi/fi0105/E_3.pdf September 2001.

202. GlaxoSmithKline plc: corp.gsk.com/financial/quarterlyreports.htm October 2001.

203. Altana AG: www.altana.de/download/ap_conference220801.ppt 22 August 2001.

204. JapanCorpNet www.japancorp.net/Article.Asp?Art_ID=982.

205. Icos Pharmaceuticals: www.icos.com/research/researchPipeline.html.

206. Inflazyme Pharmaceuticals: www.inflazyme.com/PDE4_body.htma

AffilliationPeter Norman18 Pink Lane, Burnham Bucks SL1 8JW, UKE-mail: [email protected]

pde4 inhibitors 2001. patent and literature activity 2000 - september 2001

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