ORIGINAL RESEARCH

Pharmacokinetics of Total and Unbound PaclitaxelAfter Administration of Paclitaxel Micellar or Nab-Paclitaxel: An Open, Randomized, Cross-Over,Explorative Study in Breast Cancer Patients

Olof Borga . Elsa Lilienberg . Helena Bjermo . Fredrik Hansson .

Nina Heldring . Renata Dediu

Received: June 26, 2019 / Published online: August 20, 2019� The Author(s) 2019

ABSTRACT

Introduction: Paclitaxel micellar is a novel for-mulation of paclitaxel in which retinoic acidderivates solubilize paclitaxel. The aim of thepresent study was to compare the unbound andtotal plasma pharmacokinetics of the new for-mulation with those of nanoparticle albumin-bound (nab)-paclitaxel and to further assess itssafety.Methods: In this open, randomized, cross-overstudy, 28 female patients with breast cancerwere given paclitaxel micellar and nab-pacli-taxel as a 1-h intravenous infusion at a dose of260 mg/m2. Plasma samples were collectedduring 10 h, which were projected to cover atleast 80% of the area to infinite time, AUCinf.

Unbound paclitaxel was measured in ultrafil-trate of plasma. Total paclitaxel in plasma wasmeasured after protein precipitation with ace-tonitrile. Both assays used ultra-performanceliquid chromatography (UPLC) followed by MS/MS for drug quantification. The unbound frac-tion, fu, was calculated as the ratio between theunbound and the total concentration.Results: No difference in fu of paclitaxelbetween the two formulations was observed.Statistical comparison of AUC0–10h and Cmax ofunbound paclitaxel demonstrated that the twoformulations met the criteria for bioequiva-lence. Regarding total paclitaxel levels, Cmax butnot AUC0–10h met the criteria. This study sup-ports a safe administration of paclitaxelmicellar.Conclusion: The two formulations, paclitaxelmicellar and nab-paclitaxel, behaved similarlyfollowing infusion. Probably, both formulationsdissociate immediately in the blood, where-upon released paclitaxel rapidly distributes intotissue. Judged from the bioequivalence demon-strated for unbound paclitaxel, the two formu-lations are considered clinically equivalent.Trial Registration: EudraCT no.: 2010-019838-27.Funding: Oasmia Pharmaceutical AB.

Keywords: Apealea; Bioequivalence; Cancer;Cross-over; Nab-paclitaxel; Paclitaxel micellar;Pharmacokinetics

Enhanced Digital Features To view enhanced digitalfeatures for this article go to https://doi.org/10.6084/m9.figshare.9263270.

O. BorgaBorga PK Consulting, Stockholm, Sweden

E. Lilienberg � H. Bjermo � N. Heldring (&)Oasmia Pharmaceutical AB, Uppsala, Swedene-mail: nina.heldring@oasmia.com

F. HanssonCTC Clinical Trial Consultants AB, Uppsala, Sweden

R. DediuArensia Exploratory Medicine in Collaboration withInstitutul de Pneumoftiziologie ‘‘Marius Nasta’’,Bucharest, Romania

Adv Ther (2019) 36:2825–2837

https://doi.org/10.1007/s12325-019-01058-6

INTRODUCTION

Paclitaxel has a very low solubility in water,reported to be\ 0.1–0.32 lg/ml [1, 2], and sev-eral strategies have been adopted for its solu-bilisation in water. The first marketed paclitaxelformulation was based on the solubilizers Cre-mophor EL and ethanol to enable parenteraladministration of paclitaxel [3]. However, Cre-mophor EL-containing formulations have beenassociated with severe adverse events, in par-ticular with severe hypersensitivity reactions;therefore, premedication with corticosteroidsand antihistamines (H1- and H2-antagonists) isrecommended before treatment [4]. To avoidthese events as well as the need for premedica-tion, other innovative formulations such asAbraxane� (nanoparticle albumin-bound pacli-taxel, nab-paclitaxel) and Apealea/Paclical (pa-clitaxel micellar) have been developed.

Paclitaxel micellar is a formulation of pacli-taxel in which paclitaxel is formulated with thesurfactant XR17. At the time of this study thedrug:surfactant ratio was 1:1.5 (w/w) but hassince then been optimized to 1:1.33 (w/w).XR17 is a mixture of two iso-forms of N-reti-noyl-L-cysteic acid methyl ester sodium salt.Once reconstituted in an aqueous solution forinfusion, drug and surfactant are present asmicelles at sizes of 20–30 nm in a clear solution.When the formulation has been administeredintravenously, the micelles seem to disintegraterapidly in the blood, thereby releasing pacli-taxel [5]. Paclitaxel micellar is given withoutpremedication. In the phase I study withmicellar paclitaxel [5], given as a 1-h infusion indoses ranging from 90 to 275 mg/m2, the fol-lowing paclitaxel pharmacokinetic (PK) param-eter values (mean ± SD) were obtained in atotal of 25 patients with recurrent malignantsolid tumours: (t�)a 0.55 ± 0.32 h, (t�)b8.83 ± 4.10 h, CL 13.4 ± 4.8 l/h/m2, Vss

63.3 ± 26.9 l/m2 and Vb 155 ± 49 l/m2.Nab-paclitaxel is an albumin-stabilized

nanoparticle formulation that is toleratedwithout any premedication [6]. The freeze-driedpaclitaxel nanoparticles (approximate size130 nm) are covered with human albumin inorder to form a stable colloidal solution of the

drug when reconstituted with 0.9% saline. In anEuropean Medicines Agency (EMA) assessmentreport of the formulation, it was suggested thatthe association of paclitaxel particles and albu-min is weak, permitting the two substances tofreely dissociate from each other when the for-mulation reaches the bloodstream [6]. Studiesof plasma protein binding of paclitaxel as suchhave shown that paclitaxel is bound equally toa1-acid glycoprotein and albumin, and it wasalso indicated that it binds to lipoproteins [7].

The primary aim of the present study was toperform an exploratory comparison of thepharmacokinetic (PK) plasma profiles of bothtotal and unbound paclitaxel plasma concen-trations following administration of paclitaxelmicellar and nab-paclitaxel. The two formula-tions were compared using a cross-over designin patients with metastatic breast cancer withadministration of the same dose of paclitaxelduring equally long infusion times. Secondaryobjectives were to assess the safety of paclitaxelmicellar and specifically to assess infusion sitereactions during the infusion.

METHODS

Patients and Study Design

In the present open, randomized, cross-overstudy performed during March 2014–May 2015,33 female patients diagnosed with metastaticbreast cancer were enrolled at ARENSIAExploratory Medicine-Phase I unit, ‘‘MariusNasta’’ Institutul de Pneumoftiziologie inBucharest, Romania (see Fig. 1). The protocolwas approved by the Ministry of Health,National Agency of Medicines and MedicalDevices in Romania (EudraCT no. 2010-019838-27) and the National Ethics Committee for theClinical Study of Medicines, Romania (ref no.845; 1767). The study was conducted in accor-dance with the protocol, regulatory require-ments, Good Clinical Practice and ethicalprinciples of the Declaration of Helsinki.Informed consent was obtained from all indi-vidual participants included in the study.

2826 Adv Ther (2019) 36:2825–2837

PatientsFemale patients C 18 years with a histologicallyor cytologically confirmed metastatic breastcancer, for whom previous treatment withanthracyclines had failed or anthracyclinetreatment was contraindicated, were includedin the study. Other inclusion criteria were a lifeexpectancy of at least 4 months and a willing-ness and ability to comply with the protocol

during the study. Patients with impaired liver,renal and bone marrow functions, patients whohad any uncontrolled medical problems thatwould preclude safe administration of the studydrugs in the opinion of the investigator,patients who had had prior anticancer therapyor investigational agents within the last 30 days,and patients with a pre-existing peripheralneuropathy (C grade 2), pregnancy or body

Fig. 1 Patient disposition. N number of patients. The patients included in the PK analysis set were fewer than in the safetyanalysis set because bioanalysis data were not available for both cycles

Adv Ther (2019) 36:2825–2837 2827

surface area [2.0 m2 were excluded from thestudy.

Study Design and Drug PreparationSample size was calculated to 14 patients ineach sequence (total sample size 28) to allowconcluding the equivalence of the two formu-lations with 90% power assuming the meansquare error (ln scale) for AUC0-10h to be 0.241(the standard deviation differences: 0.341) andthe expected ratio of means to be 1.000 [5]. If itwas not possible to obtain complete PK sam-pling during both treatment cycles, the patientwas replaced, and an additional patient wasrandomized.

The patients were randomized to two 21-daytreatment cycles. A single dose of 260 mg/m2

paclitaxel was given at day 1 as a 1-h intra-venous infusion as either paclitaxel micellar ornab-paclitaxel in the first cycle and the otherformulation in the second cycle. Blood sam-pling for PK evaluation was performed duringboth treatment cycles. Toxicity criteria wereassessed according to National Cancer Insti-tute’s Common Terminology Criteria forAdverse Events (CTCAE), version 4.0. Infusionsite reactions were assessed by visual inspectionduring the infusion and any symptoms or signsof pain, tenderness, erythaema and swellingwere graded according to the Food and DrugAdministration’s (FDA) Toxicity Grading Scalefor Healthy Adult and Adolescent VolunteersEnrolled in Preventive Vaccine Clinical Trials.

Before administration, each vial of lyophi-lized powder of paclitaxel micellar (Apealea�/Paclical�, Oasmia Pharmaceutical AB, Sweden)containing 60 mg paclitaxel was dissolved in60 ml reconstitution solution (i.e., Ringer lac-tate or Ringer acetate for injection) resulting ina 1 mg/ml paclitaxel solution. The lyophilizedpowder of nab-paclitaxel (Abraxane�, CelgeneEurope Limited, UK) was reconstituted accord-ing to the product label [8] beforeadministration.

Paclitaxel Pharmacokinetics

Blood SamplingBlood samples of 15 ml were collected during10 h at each treatment cycle to enable compar-isons of total and unbound plasma concentra-tions as well as the unbound fraction ofpaclitaxel during and after administration. Thisrelatively short sampling interval was chosensince the majority of the total area under thecurve to infinite time, AUCinf, is generatedduring the first 10 h, as the mean residual area(AUC10h-inf) accounts for only 15.7 ± 8.6% ofAUCinf [5]. The EMA guideline on the investi-gation of bioequivalence requires that at least80% of the AUC is covered by the samplingscheme [9].

Blood sampling was performed at the fol-lowing time points: 0 min (pre-dose), 30 min(during infusion), 1 h (immediately prior totermination of infusion), 1.5 h, 3 h, 5 h and10 h after the start of the 1-h infusion. Thesampling was done in the arm on the oppositeside relative to the site of the infusion. Theblood samples were collected in K2EDTA tubesfollowed by centrifugation. Thereafter, theplasma was transferred to and stored in cry-ovials at - 70 �C and shipped on dry ice to thebioanalytical laboratory.

Drug AnalysisTotal and unbound paclitaxel analyses wereconducted using validated ultra-high-perfor-mance liquid chromatography with tandemmass spectrometry (UPLC-MS/MS) methods.The analyses and validations were performed atICON Bioanalytical Laboratory Services, Inc.(NY, USA). The Waters Acquity liquid chro-matography system used a Fortis C18 column(1.7 lm, 2.1 9 100 mm) with a gradient flowconsisting of 0.2% formic acid in 10 mMammonium formate and 0.3% formic acid inacetonitrile at a 0.4 ml/min flow rate.

2828 Adv Ther (2019) 36:2825–2837

Analysis of Total Paclitaxel Each 100-ll ali-quot of standard, QC, or study sample wasmixed with 25 ll of working internal standardsolution [2500 ng/ml in 50/50 (v/v) acetoni-trile/water]. A 500-ll aliquot of acetonitrile wasadded and the samples were thoroughly mixedand then centrifuged at 3750 rpm for approxi-mately 5 min. A 300-ll aliquot of the super-natant was diluted with 200 ll of mobile phase.Then, a 10-ll aliquot was injected onto an LC-MS/MS system for analysis. The method wasvalidated over a range from 40 ng/ml (lowerlimit of quantification, LLOQ) to 4000 ng/ml.The inter-run overall precision and accuracy forall QCs including LLOQ were B 2.83% and- 1.75 to 0.00%, respectively. The intra-runoverall precision and accuracy for all QCsincluding LLOQ were B 3.20% and - 3.40 to2.50%, respectively.

Analysis of Unbound Paclitaxel Each 500-llaliquot of standard, QC, or study sample wastransferred to a Centrifree centrifugal filter andfollowing a 30-min equilibration period thesamples were filtered by centrifugation for15 min. A 25-ll aliquot of each ultrafiltrate wastransferred to the appropriate well of a 96-wellplate. A 75-ll aliquot of internal standard(30 ng/ml paclitaxel-d5 in acetonitrile) and50 ll of mobile phase A were added to each welland the samples were mixed. A 20-ll aliquotwas injected onto an LC-MS/MS system foranalysis. The method was validated over a rangefrom 1.0 ng/ml (i.e., LLOQ) to 350 ng/ml. Inter-run overall precision and accuracy for all QCsincluding LLOQ were B 4.60% and - 6.25 to- 3.67%, respectively. The intra-run overallprecision and accuracy for all QCs includingLLOQ were B 3.77% and - 10.5 to - 0.3%,respectively.

Pharmacokinetic EvaluationNon-compartmental analysis was performedwith individual plasma concentration-time datafrom each patient using the WinNonlin phar-macokinetic software (Pharsight Corp., Moun-tain View, CA, USA). The following PKparameters were calculated from total andunbound plasma levels of paclitaxel: the maxi-mum plasma concentration (Cmax), time of

occurrence of Cmax (Tmax), area under theplasma concentration vs. time curve from 0 to10 h (AUC0–10h) and unbound fraction of drugin plasma (fu).

All AUC values for the unbound or total drugconcentration (Cu and Ctot, respectively) werecalculated using the linear trapezoidal method.The fu was calculated as Cu/Ctot. The exact timesrather than the nominal times for samplingwere used in all calculations. Samples withplasma concentration below the LLOQ weretreated as zero.

Statistical Comparisons of the TwoFormulations

The two formulations were statistically com-pared by analysing AUC0–10h and Cmax as well astheir unbound counterparts, AUC0–10h,u andCmaxu , using analysis of variance (ANOVA)according to classical principles to establishbioequivalence. Factors for sequence, patientwithin sequence, period and formulation wereincluded in the model. The AUC0–10h of fu, i.e.,the integral of the fu-time curve over the entire10-h study interval, was analysed in the sameway. Prior to analysis, data were transformedusing a logarithmic transformation. The statis-tical method for testing relative bioavailabilitywas based upon the 90% confidence interval forthe ratio of the population means (test/refer-ence) for the parameters under consideration.As in classical bioequivalence analysis, theacceptance range for the AUC0–10h,u ratio, Cmaxu

ratio and AUC0–10h of the fu ratio was 0.80–1.25[9, 10]. A possible sequence effect on theinvestigated parameters, i.e., whether parame-ters differed between the two study periods, wasinvestigated. All statistical analyses were per-formed using SAS version 9.2 (SAS Institute,Cary, NC).

The data sets generated during and/or anal-ysed during the current study are not publiclyavailable because of confidentiality of OasmiaPharmaceutical AB but are available from thecorresponding author upon reasonable request.

Adv Ther (2019) 36:2825–2837 2829

RESULTS

Patient Characteristics

Patient disposition is presented in Fig. 1. A totalof 33 patients were randomized, of which 31received paclitaxel micellar and 30 receivednab-paclitaxel. Five patients were treated withonly one of the drugs; reasons for withdrawalwere incomplete blood sampling (n = 2), with-drawal of consent (n = 2) and adverse eventspecified as disease progression (n = 1). Theremaining 28 patients received both treatmentcycles and were included in the PK analysis set.All randomized patients were included in thesafety analysis set. All included patients (n = 33)were Caucasian females whereof 28 (85%) werepost-menopausal. The mean ± SD of their agewas 60.2 ± 11.9 years, height was156.9 ± 6.8 cm, weight was 68.5 ± 13.6 kg andbody surface area was 1.7 ± 0.2 m2.

Paclitaxel Pharmacokinetics

Plasma concentration data of both total andunbound paclitaxel were obtained in allpatients included in the PK analysis set. Thestatistics of all studied PK parameters are sum-marized per formulation in Table 1.

Total Concentrations of PaclitaxelWith both formulations, the mean total plasmalevel of paclitaxel increased during the infusionto peak around 8000 ng/ml and then declinedrapidly to one-tenth of this value during thefollowing 2 h (Fig. 2). Thereafter, the declinebecame less and less steep. A distinct finalmonoexponential phase was not reached dur-ing the 10 h that plasma levels were monitored.The initial part of the plasma curves of totalpaclitaxel were similar for the two formulationsand the mean total Cmax after nab-paclitaxel,8073 ± 4124 ng/ml (n = 28), was similar to themean total Cmax after paclitaxel micellar,8006 ± 1703 ng/ml (n = 28).

The mean curves of paclitaxel micellar andnab-paclitaxel of all individuals were almostsuperimposable when plotted in linear-linearmode (Fig. 2a). In the log-linear plot (Fig. 2b),

however, the mean curves tended to separatefrom each other after 1.5 h, resulting in lowermean AUC0–10h of total paclitaxel after nab-pa-clitaxel (11,388 ± 3123 h 9 ng/ml) comparedwith after paclitaxel micellar(13,484 ± 3491 h 9 ng/ml).

Unbound Concentrations of PaclitaxelThe unbound plasma PK profile reflected thetotal PK profile, with concentrations ofapproximately 5% of the corresponding totalconcentrations. Thus, the unbound curvespeaked at around 400 ng/ml (Fig. 3). Concen-trations at the last collection time point, 10 h,were in the 3–15 ng/ml range and were wellmeasurable since LLOQ was 1.0 ng/ml. Themean unbound Cmax after nab-paclitaxel,416 ± 229 ng/ml, was similar to the meanunbound Cmax after paclitaxel micellar,391 ± 72 ng/ml. Similarly to what was seenwith the total paclitaxel curves, the meanunbound paclitaxel curves for the two formu-lations overlapped during the initial part of thecurves (Fig. 3). After 1.5 h the curves tended toseparate and resulted in a mean AUC0–10h,u of580 ± 172 h 9 ng/ml after nab-paclitaxel while

Table 1 Summary statistics of PK parameters, all pre-sented as mean ± SD

Parameter Formulation (n number of patients)

Paclitaxel micellar(n = 28)

Nab-paclitaxel(n = 28)

Total paclitaxel

AUC0–10h

(h ng/ml)

13,484 ± 3491 11,388 ± 3123

Cmax (ng/ml) 8006 ± 1703 8073 ± 4124

Tmax (min) 50 ± 17 46 ± 20

Unbound paclitaxel

AUC0–10h

(h ng/ml)

646 ± 154 580 ± 172

Cmax (ng/ml) 391 ± 72 416 ± 229

Tmax (min) 48 ± 18 50 ± 20

2830 Adv Ther (2019) 36:2825–2837

Fig. 2 Mean (± SD) in all patients of total paclitaxel concentrations in plasma following a 1-h intravenous infusion ofpaclitaxel micellar or nab-paclitaxel, 260 mg/m2, plotted in a linear-linear and b log-linear scales

Fig. 3 Mean (± SD) in all patients of unbound paclitaxel concentrations in plasma following a 1-h intravenous infusion ofpaclitaxel micellar or nab-paclitaxel, 260 mg/m2, plotted in a linear-linear and b log-linear scales

Table 2 Mean ± SD of fu in all subjects, presented as % unbound drug, at various times from start of the infusion for thetwo formulations

Formulation Time (h) (n number of patients)

0.5 1 1.5 3 5 10(n = 27) (n = 28) (n = 28) (n = 28) (n = 28) (n = 28)

Paclitaxel micellar 5.2 ± 0.9 5.0 ± 0.9 4.5 ± 0.6 4.8 ± 0.7 4.4 ± 0.6 4.4 ± 0.6

Nab-paclitaxel 5.2 ± 0.9 5.3 ± 0.7 4.9 ± 0.6 4.8 ± 0.6 4.6 ± 0.7 4.8 ± 1.5

Adv Ther (2019) 36:2825–2837 2831

it was 646 ± 154 h 9 ng/ml after paclitaxelmicellar.

Unbound FractionThe mean unbound fraction of paclitaxel inplasma, fu, was approximately 5.2% during theinfusion of the two drugs when plasma levelswere high (Table 2). At 3 h and after, a slightlylower fu was observed at about 4.4–4.8% withboth formulations.

Statistical Comparisons of the TwoFormulations

The two formulations were compared by testingof bioequivalence of AUC and Cmax for bothunbound and total paclitaxel and the analysisresults are summarized in Table 3. Bioequiva-lence was shown for unbound drug, since bothAUC0–10h,u and Cmaxu were within the accep-tance range. Also, bioequivalence was shown forpaclitaxel fu. Bioequivalence for total drug wasnot clearly demonstrated since the confidenceinterval for the nab-paclitaxel/paclitaxel micel-lar ratio for AUC0–10h (0.76–0.94) was slightlyoutside the confidence interval 0.80–1.25, while

the ratio for Cmax was within the confidenceinterval. No sequence effect on the investigatedparameters was found.

Tolerability and Side Effects

All patients experienced at least one adverseevent after the paclitaxel infusion, except forone patient after administration of paclitaxelmicellar. No serious adverse events and nodeaths or life-threatening events (CTCAE grade4–5) were reported during the study. All repor-ted adverse events are presented by treatmentarm in Table 4. The most frequent adverseevents ([10 events in total) were neutropenia(paclitaxel micellar: n = 19, nab-paclitaxel:n = 17), leukopenia (paclitaxel micellar: n = 15,nab-paclitaxel: n = 14), paraesthesia (paclitaxelmicellar: n = 14, nab-paclitaxel: n = 7), pain(paclitaxel micellar: n = 9, nab-paclitaxel: n = 9)and nausea (paclitaxel micellar: n = 9, nab-pa-clitaxel: n = 7). The majority was of grade 1 or 2but 21 grade-3 events were reported in 11patients: 11 events after paclitaxel micellarinfusion and 10 events after nab-paclitaxelinfusion. These events were mainly connected

Table 3 Bioequivalence (BE) analyses of comparison of various PK parameters of total and unbound plasma concentrationsof paclitaxel micellar with nab-paclitaxel

PK parameter Formulation log scale point estimate (90% CI) BE comparisonpoint estimate(90% CI)

Nab-paclitaxel Paclitaxelmicellar

Nab-paclitaxel/paclitaxel micellar

Total paclitaxel

AUC0–10h

(h ng/ml)

9.31 (9.23:9.39) 9.48 (9.39:9.56) - 0.17 (- 0.27:- 0.07) 0.85 (0.76:0.94)

Cmax (ng/ml) 8.91 (8.80:9.01) 8.97 (8.86:9.07) - 0.06 (- 0.20:0.08) 0.94 (0.82:1.09)BE

Unbound paclitaxel

AUC0-10h, u

(h*ng/ml)

6.33 (6.24:6.41) 6.44 (6.36:6.53) - 0.12 (- 0.22:- 0.01) 0.89 (0.80:0.99)BE

Cmaxu (ng/ml) 5.93 (5.83:6.04) 5.95 (5.85:6.06) - 0.02 (- 0.16:0.12) 0.98 (0.86:1.12)BE

Ratio

fua - 0.75 (- 0.80:- 0.71) - 0.82 (- 0.86:- 0.77) 0.06 (0.01:0.12) 1.07 (1.01:1.12)BE

CI confidence interval, BE indicates that bioequivalence is showna Test parameter AUC0-10h of the fu-time curve; unit hours

2832 Adv Ther (2019) 36:2825–2837

Table 4 All reported adverse events by treatment arm

System organ class Preferred term Paclitaxel micellar(n = 31)

Nab-paclitaxel(n = 30)

Blood and lymphatic system disorders Neutropenia 19 17

Leukopenia 15 14

Anaemia 1 2

Thrombocytopenia 1 1

Gastrointestinal disorders Nausea 9 7

Diarrhoea 5 3

Vomiting 4 1

Abdominal pain 2 1

Constipation 2 1

Mouth ulceration 2 0

Dyspepsia 0 1

Dysphagia 1 0

General disorders and administration site conditions Pain 9 9

Infusion site pain 5 0

Injection site

inflammation

4 0

Disease progression 0 2

Fatigue 1 1

Oedema peripheral 1 0

Nervous system disorders Paraesthesia 14 7

Dizziness 3 0

Headache 0 3

Paraesthesia oral 1 0

Syncope 0 1

Skin and subcutaneous tissue disorders Alopecia 4 4

Pruritus 4 1

Erythaema 1 0

Pruritus generalised 0 1

Rash 1 0

Rash erythaematous 1

Adv Ther (2019) 36:2825–2837 2833

to bone marrow depression (neutropenia andleukopenia) reported for six patients followingpaclitaxel micellar and three patients followingnab-paclitaxel.

Infusion site reactions were only reportedduring infusion with paclitaxel micellar, whereseven patients reported a total of ten infusionsite reactions and the most frequent reactionwas pain (n = 6).

DISCUSSION

The present study was undertaken to investigateand compare the PK plasma profiles of twointravenous formulations, paclitaxel micellarand nab-paclitaxel. The two formulations wereshown to be bioequivalent regarding total(Cmax) and unbound paclitaxel (AUC0–10h,u andCmax;u). Bioequivalence for the unbound drug is

of particular importance since a basic principle

Table 4 continued

System organ class Preferred term Paclitaxel micellar(n = 31)

Nab-paclitaxel(n = 30)

Musculoskeletal and connective tissue disorders Arthralgia 4 2

Pain in extremity 3 1

Bone pain 3 0

Investigations Alanine aminotransferase

increased

2 2

Aspartate

aminotransferase

increased

2 1

Gamma-

glutamyltransferase

increased

1 1

Vascular disorders Hypertension 3 1

Phlebitis 1 0

Ear and labyrinth disorders Vertigo 2 0

Infections and infestations Oral candidiasis 1 0

Tooth infection 0 1

Metabolism and nutrition disorders Decreased appetite 1 0

Hyperglycaemia 0 1

Renal and urinary disorders Dysuria 2 0

Respiratory, thoracic and mediastinal disorders Dysphonia 1 1

Injury, poisoning and procedural complications Skin injury 0 1

Neoplasms benign, malignant and unspecified

(including cysts and polyps)

Metastatic pain 0 1

2834 Adv Ther (2019) 36:2825–2837

of PK is that the unbound drug is the biologi-cally active form exerting the pharmacologicaleffect.

The tendency for mean curves of paclitaxelmicellar and nab-paclitaxel to separate fromeach other after 1.5 h may possibly be an effectof metabolic interaction between paclitaxel andthe surfactant XR17 occurring soon afteradministration of paclitaxel micellar, whenplasma levels of the two compounds were high.However, further studies are needed to evaluatethis possibility.

In general, the rate of bioavailability withintravenous formulations is controlled by theinfusion rate, while the extent of bioavailabilityis by definition assumed to be complete. How-ever, the formulation components in an intra-venous formulation may affect the clearance,protein binding and distribution of the drug,whereof it follows that two different intra-venous formulations might be non-equivalent.For example, in the case of intravenous formu-lations of paclitaxel, having Cremophor EL inthe formulations has been shown to affect allthree of the above-mentioned parameters[11, 12]. There is evidence that this is caused bythe paclitaxel released from the formulationbeing bound anew to the nanomedicine plat-form, i.e., Cremophor EL micelles, in a rever-sible manner. Increasing doses will lead toincreasing plasma concentrations of Cre-mophor EL micelles, thus causing increasedbinding of paclitaxel in plasma, i.e., decreasingfu. This is manifested as a more than propor-tional increase in total plasma levels of pacli-taxel with increasing doses [12, 13]. When itcomes to nanomedicines, bioequivalence stud-ies based on total plasma levels of the activedrug may therefore not be sufficient, and theyshould be supplemented with measurements ofunbound levels of the active drug [12].

When the nab-paclitaxel formulation is dis-persed in saline, human albumin-covered par-ticles of paclitaxel of approximately 130 nmdiameter are formed [6]. However, the affinityof paclitaxel to albumin is weak and whenreaching the blood stream the particles dissoci-ate rapidly into their component molecules[6, 12]. Based on this, the nab-paclitaxel for-mulation is basically just a vehicle for

immediate delivery of the active pharmaceuti-cal ingredient, paclitaxel, to the circulation.However, other authors have depicted a differ-ent scenario: that the nab-paclitaxel formula-tion dissociates in blood into smallerstable albumin-bound paclitaxel complexes[14–17]. These complexes are suggested to beable to utilize biologically important activetransport processes to deliver paclitaxel to thetumour thanks to their albumin moiety [14–17].Because of these conflicting views, the presentstudy was designed to measure the unbound aswell as total concentrations of paclitaxel andthe ratio between the two, the unbound frac-tion, when comparing the PK of the two for-mulations. A rapid release of paclitaxel afterdrug administration of paclitaxel micellar haspreviously been established as its most plausiblemode of drug delivery [5].

In the present data, fu was virtually identicalfor paclitaxel micellar and nab-paclitaxel duringthe entire sampling interval. As a matter of fact,by analysis of the area under the fu-time curve,fu was demonstrated to be bioequivalent for thetwo formulations. Furthermore, during theinfusion part of the curves, the PK profiles of thetwo formulations were practically superimpos-able with regard to total and unbound drugthereby further emphasizing their similar rate ofdrug delivery. The notion of the formation of astable albumin-paclitaxel complex specific fornab-paclitaxel is thus not supported by thepresent data. By another token, such a complexwould not be able to pass through the ultrafil-tration membrane. It would therefore manifestitself by an increased bound fraction of pacli-taxel in plasma. Taken together, the presentdata indicate that both formulations dissociateimmediately in the blood at similar rates,whereupon released paclitaxel rapidly dis-tributes into tissue.

An expected decrease in the number of whiteblood cells was seen in both treatment arms,and the adverse events reported were in agree-ment with previously reported events for pacli-taxel micellar [5]. Infusion site reactions ofvarious kinds, predominately infusion site pain,have been observed in other clinical studieswith paclitaxel micellar (unpublished results).This study also reports pain as the most

Adv Ther (2019) 36:2825–2837 2835

common infusion site reaction. The severitygrading indicates that either the pain did notinterfere with activity or that a non-narcoticpain reliever could be used to avoid interferencewith daily activities. No serious events or deathswere reported in the present study, supportingpaclitaxel micellar to be a safe therapy. How-ever, the cross-over study design, the smallnumber of patients and the fact that thepatients received only one treatment with eachcompound prevent any definite conclusionsregarding the safety profile of the twocompounds.

CONCLUSIONS

This cross-over study of paclitaxel micellar andnab-paclitaxel demonstrated that the two for-mulations behaved similarly following intra-venous administration. When reaching theblood, the formulations most likely releasepaclitaxel immediately. Judged from the bioe-quivalence demonstrated for unbound pacli-taxel, the two formulations should beconsidered clinically equivalent.

ACKNOWLEDGEMENTS

The authors thank all participating patients andtheir families. We also thank the investigatorsand co-investigators involved in the clinicaltrial. In addition, the authors thank the ICONlaboratory for the excellent bioanalysis.

Funding. This study was funded by OasmiaPharmaceutical AB. This journal’s Rapid ServiceFee as well as the Open Access fee of thismanuscript was funded by the study sponsorOasmia Pharmaceutical AB. All authors had fullaccess to all of the data in this study and takecomplete responsibility for the integrity of thedata and accuracy of the data analysis.

Authorship. All named authors meet theInternational Committee of Medical JournalEditors (ICMJE) criteria for authorship for thisarticle, take responsibility for the integrity of

the work as a whole, and have given theirapproval for this version to be published.

Disclosures. Olof Borga is a salaried consul-tant at Oasmia Pharmaceutical AB. Elsa Lilien-berg is a full-time employee of OasmiaPharmaceutical AB. Helena Bjermo is a full timeemployee of Oasmia Pharmaceutical AB. FredrikHansson was the statistician in the clinical trial.Nina Heldring is a full-time employee of OasmiaPharmaceutical AB. Renata Dediu was theprincipal investigator of the clinical trial.

Compliance with Ethics Guidelines. Allprocedures performed in the study were inaccordance with the ethical standards of theinstitutional and/or national research commit-tee (Ministry of Health, National Ethics Com-mittee for the Clinical Study of Medicines,Bucharest, Romania) and with the 1964 Hel-sinki Declaration and its later amendments orcomparable ethical standards. Informed con-sent was obtained from all individual partici-pants included in the study.

Data Availability. The data sets generatedduring and/or analysed during the currentstudy are not publicly available because of theconfidentiality of Oasmia Pharmaceutical ABbut are available from the corresponding authorupon reasonable request.

Open Access. This article is distributedunder the terms of the Creative CommonsAttribution-NonCommercial 4.0 InternationalLicense (http://creativecommons.org/licenses/by-nc/4.0/), which permits any noncommer-cial use, distribution, and reproduction in anymedium, provided you give appropriate creditto the original author(s) and the source, providea link to the Creative Commons license, andindicate if changes were made.

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