Preclinical safety assessment of topical drugs and associated pathologyFlandre TIATP and STP-I WebinarJanuary 2020

TM – PCS

Agenda

Topical/wound healing drug safety assessment Formulation Pathology associated with topical drug Pathology associated with wound healing drug

IATP and STP-I Webinar – preclinical safety of topical drugs2

Important Reminder: Please send any questions you may have to Satish Panchal: Satish.Panchal@gmail.com

Questions will be addressed at the end of the presentation

Why safety assessment of topical/wound healing drug ? Hazard identification: Characterize hazard Risk assessment Fulfilling regulatory expectations

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Hazard identification

Characterize hazard/safety findings– Qualitative and quantitative assessment effects (latency; reversibility)– Species specificity – translatability to humans?– Clinical monitorability (at EARLY stage)– Threshold value– Molecular mechanism – target-related?

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Hazards

Genetic toxicity– Proliferative changes are expected, but is it uncontrolled or mutagenic?

Local toxicity– Is it tolerated by skin and exposed tissue?– Is the vehicle tolerated?

Is the toxicity identified relevant for humans?– Is it species-specific?– Related to mechanism of action?– Monitorable? Reversible?

Phototoxicity is a special consideration given skin is the target organ

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Risk assessment

Risk assessment– Determine and describe exposure– Quantify possible exposure in man and estimate likelihood for hazard to occur

Assess risk – Human relevance of hazard Translatability to human– Safety factors (consider populations particularly sensitive to the toxicity)– Differs depending on the indication, dose, treatment route and duration

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Risk management

Is there a therapeutic window?– What should the therapeutic index (TI) be? 10, 30, or some other number?– What is being used to estimate the TI?– The longer you treat, the more toxicity you expect to see which reduces the TI

Is the hazard species-specific or translatable to humans? Is there extensive systemic exposure?

– Evaluate absorption from skin (intact or wounded), compare this to a systemically available dose (iv or po administration)

– If topical delivery yields high systemic exposure, your risk is much greater for target organ toxicity and DDIs

Is there phototoxicity?– Phototoxicity guidances give special consideration for dermal treatments; both UVA and UVB must

be considered in the safety testing– Threshold will be different (lower) with topical drug as skin is the target organ

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Regulatory requirements/expectations

No dedicated guidance for preclinical safety assessment for topical/wound healing products– Principles and procedures for evaluating toxicity of household substances, NAS, 1977

(acute dermal toxicity)– OECD 410, Repeat dose dermal toxicity study, 1981 (21 or 28-day repeat dose dermal

toxicity)– EPA health effects test guidelines OPPTS 870.3200, 1998, (21 or 28-day repeat dose

dermal toxicity)– Guidance for Industry Chronic Cutaneous Ulcer and Burn Wounds — Developing

Products for Treatment, 2006

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Regulatory requirements/expectations

General guidelines for small molecules/biologics apply – ICH M3R2: guidance on non-clinical safety studies for FIH and marketing– ICH S2: Genotoxocity testing– ICH S3: Toxicokinetic– ICH S4: Chronic toxicity testing – ICH S6: Biotechnology derived pharmaceuticals– ICH S5: Reprotox testing– ICH S7: Safety pharmacology– ICH S10: Phototoxicity testing

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Regulatory expectations – general considerations Route of administration

– Intended clinical route needs to be used– Topical application yields low systemic exposure, limiting systemic tox assessment – Systemic dosing will provide target organ toxicity

Species selection– Small molecules are evaluated in two (or more) species: rodent + non-rodent– If for oral programs, rat and dog are default species unless scientific reason for an alternative,

for topical programs, minipig is well accepted as pig and human skin are similar– For biologics, nonhuman primate is typically the appropriate species if antibody specificity is limited

Duration and frequency of treatment in general toxicology studies– Day-for-day coverage up to chronic (>6 months) treatment – Treatment frequency also needs to cover or exceed clinical plan (qod would be covered with qod,

but given the high chance for misdose, qd would be added)

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Regulatory expectations – considerations for topical drugs In general, the preclinical safety program is targeted for the type of compound, application route, and

duration of treatment FDA and ICH Guidances for preclinical studies supporting human pharmaceutical development

(general guidances)– Content and Format of INDs (11/95)– Exploratory INDs (1/06)– M3-Nonclinical safety studies to perform clinical trials (7/97, updated 1/10)– S6-Preclinical testing of biologics (7/97)

Topical administration (cutaneous ulcers and burn applications, FDA June 2006)– Guidance includes toxicology guidance proposing vehicle and sham control groups, treatment multiples over

intended clinical dose, and administration to reflect the clinical route– Immunogenicity evaluation to be included for biologic agents– Carcinogenicity studies for “chronic wound” indication for small molecules. For others, tumor promotion models and

scientific assessment of tumor risk (including scar carcinomas) given the compounds are typically growth factors

Aerosol products require pulmonary toxicity testing

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Preclinical safety program – Key considerations for topical drugs Preclinical assessment to be performed in two species: a rodent and a non-

rodent Topical as well as systemic exposure and toxicity are measured Studies typically run in minipig (topical and systemic) and rat (systemic) Systemic rat studies in support of wound healing projects are accepted by the

regulatory agencies Testing the clinical concentrations in the topical arm (intact skin) will be

sufficient

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Preclinical safety program – Key consideration for wound healing drugs Study designs can be inspired from topical programs, and modified as

appropriate for wound healing, as there is no dedicated guidance for preclinical safety assessment for wound healing products

Lack of translatable chronic animal model Preclinical assessment to be performed in two species:

– Rodent for systemic exposure and toxicity– Non-rodent (minipig) for:

– Systemic exposure and toxicity– Topical exposure and toxicity (Intact + wounded skin) at same concentration as

clinic

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Pig as preferred non-rodent species for topical/wound healing drug – why ?

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Human NHP Pig Dog Rodent

Epidermal pattern Epidermal Epidermal Epidermal Infundibular Infundibular

Epidermal thickness (µm)

86.2 ± 6.8 26.9 ± 3.1 51.9 ± 1.5 21.2 ± 2.5 Rat 13.3 ± 2.2Mouse 21.7 ± 1.2

Sweat gland Eccrine glandsover entire body; apocrine in genitals, underarms

Eccrine glands over entire body; apocrine in genitals, underarms

Eccrine glands in carpal glands;apocrine glandsassociated with allfollicles

Eccrine glands in footpad, nose; apocrine glands associated with all follicles (andperianal region

Eccrine glands in footpads; no apocrine glands

Sebaceousglands

Associated withall follicles

Associated withall follicles

Associated withall follicles

Associated withall follicles

Associated withall follicles

Superficial vascular plexus

Yes Yes Yes Yes Yes (no in mouse)

Also metabolism and physiology (i.e. skin permeability) of the skin minipig is closer to human compared to dog or NHP

Pig as preferred non-rodent species for topical/wound healing drug – why ?

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Mouse Cyno Minipig Human

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Minipig wound healing toxicity study

Wound

Topical

Wound from punch biopsy in rat

Typical preclinical toxicity package for IND/CTA (GLP studies) 2- (or 4-)week rodent and nonrodent studies with 4-week recovery by the intended clinical

route of administration Safety pharmacology studies (rat CNS/respiratory, in vitro hERG, and non-rodent telemetry) for

small molecules (LMW) Genotoxicity (Ames and in vitro chromosome aberration) (for LMW) Photosafety (in vitro 3T3 NRU or in vivo study, based on UV/VIS spectra) (for LMW) Tissue cross-reactivity for biologicsNotes: Additional studies could be needed (eg to identify target organ toxicity in the absence of

significant exposure by the intended route). Shorter duration general tox studies may be employed under special circumstances.

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Preclinical safety program

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4/13-wk topical minipig

4/13-wk oral/iv minipig

4/13-wk oral/iv rat

topi

cal

syst

emic

geno

tox

othe

rs

topical UV-LLNA

Ames Test

Chromosomal Aberr.Micronucleus in vivo

hERG in vitro ECG telem. minipig

CNS + Resp in rat

39-wk topical minipig

26-wk oral/iv rat

Reprotox battery rat

Carcinogenicity dermal rat

Carcinogenicity mouse

2-wk oral/iv minipig

2-wk oral/iv rat

LLNA

Ames screen

MNT in vitro

Sec. safety pharm

4-d screening rat

hERG screen

2-wk minipig*3T3 screen

3T3

Therapeutic window

Therapeutic Index (also called safety margin or exposure multiple) is calculated for AUC and Cmax:– Animal AUC0-24h/Predicted human AUC0-24h

and/or – Animal Cmax/predicted human Cmax

Calculated for each route of exposure and each species Calculating human predictions are made based on the proposed clinical

dosing concentration and projected average treated area to be covered Safety margin generally shrinks the longer the animals are dosed

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Therapeutic window - consideration for wound healing drugs Wound size would impact exposure, limited size for preclinical studies relying

on TI for extrapolation to clinical studies:– Ratio of systemic exposure in the most sensitive animal species and the projected

human systemic exposure– Calculated human predictions are made based on the proposed highest clinical dosing

concentration and projected average wound area to be covered

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Formulation – general consideration

Topical formulation (cream, ointment, solution, gel, ...)– drives pharmacokinetic properties– might be the reason for clinical failure – might be the cause of species-specific dermal reactions

Systemic formulation– Exposure and safety– Identify target organs and reversibility– Used for establishing safety margin

Safety of the clinical formulation (CSF) should be tested in the GLP studies. Programs typically require a bridging study between DRF and GLP studies if the

former are run with an experimental formulation

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Formulation – tolerability of topical CSF

Choice of CSF for topical formulation– Aims on human use (cream, ointment, solution, gel, ...):– Will drive pharmacokinetic properties of compound – Might have neutral effects on wound healing for clinical trial (PoC)

Translation of local tolerability to human vs tox species not easy as sometimes tox species is/are oversensitive to a certain vehicle requesting a contingency plan

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Formulation tolerability

Here is an example of assessment of formulation tolerability in wound healing model for which re-epithelialization, granulation tissue and inflammation are benchmarked again control hydrogel formulation.

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HPMC

HPMC+HPbCD

Carbopol

Anhydrous G

elLiposo

mes

Occlusiv

e Ointm

ent

Simple

Cream

Complex Crea

m

0

50

100

150

HPMC

HPMC+HPbCD

Carbopol

Anhydrous G

elLiposo

mes

Occlusiv

e Ointm

ent

Simple

Cream

Complex Crea

m

0

1

2

3

4

5

HPMC

HPMC+HPbCD

Carbopol

Anhydrous G

elLiposo

mes

Occlusiv

e Ointm

ent

Simple

Cream

Complex Crea

m

0

1

2

3

4

5

Pathology associated with formulation

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Hydrogel (control)

Granulation tissue

Re-epithelialization

Pathology associated with formulation

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CarbopolFormulation

visible

Poor granulation

tissue

Poor re-epithelialization

Pathology associated with formulation

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Liposome

Inflammatory cells

Poor re-epithelialization

Pathology associated with topical drug

Potential microscopic findings associated with topical drug should be compared with untreated and formulation treated control skin.

Different mechanisms involved in skin damage:– direct toxicity (e.g., chemical burns from strong acids or alkalis)– immune-mediated reactions (i.e., allergic reactions)– phototoxic or photoallergic reactions– genotoxicity

In the following slides, few pictures of most common findings associated with topical drug administration.

Further description of microscopic finding terminology could be found on– goReni: https://www.goreni.org/– NTP: https://ntp.niehs.nih.gov/nnl/

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Single cell necrosis, epidermal (and vacuolation, epidermal)

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Hyperplasia, epidermal

Hyperkeratosis (orthokeratotic)

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Infiltration, inflammatory cells, dermal to epidermal

Vagina (topical): erosion/ulceration with inflammation

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Vehicle controlFormulation 1 + drug Formulation 2 + drug

Mucosa

Erosion/Ulceration

Prepuce (topical): erosion/ulceration with inflammation

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Vehicle controlFormulation 1 + drug Formulation 2 + drug

Mucosa

Erosion/Ulceration

Pathology associated with wound healing drug

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Re-epithelialization

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Anti-Keratin 5 (purple staining)Epidermis expressing K5in basal layer

Wound bed with no K5 expression

Wound border expressing K5

Delay in wound healing (decreased re-epithelialization, granulation tissue progression and collagen deposition)

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Control

Treated

Granulation tissue

Re-epithelialization

Inflammation (and bacterial colony )

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Granulomatous inflammation

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Pathology associated with UV-LLNA phototoxicity model Few examples of ear skin findings associated with phototoxicity model.

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Hyperplasia, epidermal (and edema)

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Infiltration, mononuclear cell, dermal (with hyperplasia and hyperkeratosis (crust))

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Acknowledgement

Boisclair J.Saravan C.Sukhdeep S.

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Important Reminder

Please send any questions you may have to Satish Panchal Satish.Panchal@gmail.com

Questions will be addressed at the end of the presentation.