Development of peptide therapeutics: A nonclinical safety assessment perspective.

Novel peptide drugs continue to gain interest as effective modalities against previously undruggable targets. As with any other technology, development and safety assessment of peptides presents with various complex challenges. Additionally, there is a lack of specific regulatory guidance for peptide development, with the industry relying mainly on associating existing small molecule [ICH M3(R2)] and biologic [ICH S6(R1)] guidance. To gain insights into regulatory requirements for therapeutic peptides, we developed a dataset of peptides approved in the United States from 1998 through 2019 for which the summary basis of approval (SBA) packages are publicly available. The dataset comprises a total of 47 peptides (22 chemically synthesized, 6 semi-synthetic, 18 recombinant, and 1 natural). This article summarizes our learnings from the dataset in regards to the development paradigm, guidances followed, strategies for selection of toxicology species; requirements and/or value of genotoxicity and immunogenicity assessment; impurity, metabolite, and safety pharmacology assessment; and safety assessment of peptides containing non-proteogenic amino acids. In the context of the learnings from the dataset, the authors provide their recommendations for improvement of strategies to develop peptide drugs.

Lens Capsule Perforation Without Inflammation in 4 Rabbits From Intravitreal Injection Studies.

Historically, it was thought that lens protein was sequestered, and injury to the lens capsule causing release of lens material into the eye would always result in ocular inflammation. Currently, it is believed that lens antigens are recognized as self, subject to normal T-cell tolerance. Three different single-dose intravitreal injection/implantation studies of 4 different test materials, ranging from 4 to 6 weeks in length, were performed in New Zealand White rabbits. The test materials included polymer microspheres, polymer rods, a solvent, and a hydrogel. Intravitreal injection/implantation procedures were performed on day 1, and indirect ophthalmoscopy and slit-lamp biomicroscopy examinations were performed by board-certified veterinary ophthalmologists periodically throughout the course of each study. None of the affected animals received corticosteroids or other immunomodulatory agents during the course of the studies. Four rabbits had perforation of the posterior lens capsule during the injection/implantation procedure on day 1, visible on clinical ophthalmic examination as lens capsule alterations described as "lens hits" and/or incipient posterior cataracts. Findings on slit-lamp biomicroscopy examination were limited to vitreous cells in 2 of the animals, although not centered on the area of lens capsule disturbance. Histologically, there was no evidence of inflammation in association with extruded lens protein material in any of the affected eyes. These results indicate that iatrogenic damage to the lens capsule during aseptically performed intravitreal injections/implantations does not appear to induce inflammation in rabbits.

Inflammation and immunogenicity limit the utility of the rabbit as a nonclinical species for ocular biologic therapeutics.

The nonclinical safety evaluation of therapeutic drug candidates is commonly conducted in two species (rodent and non-rodent) in keeping with international health authority guidance. Biologic drugs typically have restricted species cross-reactivity, necessitating the evaluation of safety in non-human primates and thus limiting the utility of lower order species. Safety studies of cross-reactive ocular biologic drug candidates have been conducted in rabbits as a second toxicology species, despite the fact that rabbits are not a rodent species. Such studies are often confounded by the development of anti-drug antibodies and severe ocular inflammation, the latter requiring studies to be terminated prematurely for animal welfare reasons. Notably, these confounding factors preclude the interpretation of safety. Nonclinical toxicology programs should be designed with consideration of ethical animal use and 3Rs principles (Replacement, Reduction and Refinement). The experience of several pharmaceutical sponsors, demonstrating that toxicology studies of ocular (intravitreal and topical ocular) biologic drug candidates in the rabbit are of limited interpretive value, calls into question the utility of such studies in this species and indicates that such studies should not be conducted.

Intravitreal administration of known phototoxicants in the rabbit fails to produce phototoxicity: implications for phototoxicity testing of intravitreally administered small molecule therapeutics.

CONTEXT: Intravitreal (ITV) dosing has become a clinically important route of administration for the treatment of uveitis, endophthalmitis, retinal vein occlusion, diabetic macular edema and age-related macular degeneration. Despite this, there are no validated non-clinical models of phototoxicity for ITV products. OBJECTIVE: The objective of this study was to develop an ITV rabbit model of phototoxicity for use in assessing the photosafety of small molecules therapeutics. MATERIALS AND METHODS: Dutch Belted rabbits were intravitreally injected bilaterally with four known phototoxicants: 8-methoxypsoralen, lomefloxacin, doxycycline and stannsoporfrin. Triescence(®), a non-phototoxic triamcinolone acetonide steroid formulation designed for ITV administration, was used as a negative control. One eye was then irradiated with solar-simulated ultraviolet radiation for 30 min, 1 h after dosing, while the other eye was occluded, serving as a non-irradiated control. RESULTS: Despite the direct administration of known phototoxicants into the vitreous, no evidence of ocular phototoxicity was observed in any dose group. Direct (non-phototoxic) retinal toxicity was observed in the doxycycline dose group only. CONCLUSION: These data suggest that the posterior segment of the rabbit eye is protected against phototoxicity by anatomical and/or physiological mechanisms, and is not a useful model for the assessment of phototoxicity of intravitreally administered molecules.

Solvent-based formulations for intravenous mouse pharmacokinetic studies: tolerability and recommended solvent dose limits.

1. Modern high-throughput small molecule drug discovery requires rapid screening of the pharmacokinetic parameters of multiple candidate molecules in parallel. The mouse is often used for such screening, as are solvent-based intravenous formulations. Despite this, the intravenous toxicity of many commonly used solvents is unknown. The purpose of this investigation is to establish recommended no-observed-effect level (NOEL) and maximum tolerated dose (MTD) for several commonly used intravenous solvents in the CD-1 mouse. 2. The acute tolerability of polyethylene glycol 400, N-methylpyrrolidone, dimethyl sulfoxide, ethanol, dimethylacetamide and propylene glycol was established, along with combinations of polyethylene glycol 400 and/or ethanol and DMSO. Based on these data, an acute NOEL and recommended MTD is reported for each solvent or solvent combination. 3. These data can guide the use of these solvents to support single-dose intravenous pharmacokinetic studies in mice. By establishing a defined dose tolerability range for the most commonly used intravenous solvents, undue pain and distress in animals can be avoided while maximizing the generation of critical pharmacokinetic data for project teams.

Assessment of hydroxypropyl methylcellulose, propylene glycol, polysorbate 80, and hydroxypropyl-ß-cyclodextrin for use in developmental and reproductive toxicology studies.

BACKGROUND: A series of studies were conducted to assess Polysorbate 80 (PS80), Propylene Glycol (PG), and Hydroxypropyl-ß-Cyclodextrin (HPßCD), when compared with Hydroxypropyl Methylcellulose (MC) in developmental and reproductive toxicology (DART) studies. METHODS: In the rat fertility study, 20 mg/kg MC, 10 mg/kg PS80, 1,000 mg/kg PG, 500 mg/kg HPßCD or 1,000 mg/kg HPßCD were administered orally before/during mating, and on gestation Day (GD) 0-7, followed by an assessment of embryonic development on GD 14. In the rat and rabbit teratology studies, the doses of MC, PS80, PG, and HPßCD were the same as those in the fertility study. In these teratology studies, pregnant females were dosed during the period of organogenesis, followed by an assessment of fetal external, visceral, and skeletal development. RESULTS: In the rat fertility and rat teratology studies, PS80, PG, and HPßCD did not exhibit toxicity, when compared with MC. Similarly, in the rabbit teratology study, there was no PS80 or PG-related toxicity, when compared with MC. However, individual rabbits in the 500 and 1,000 mg/kg HPßCD groups exhibited maternal toxicity, which included stool findings, decreased food consumption, and body weight gain. Furthermore, one rabbit each in the 500 and 1,000 mg/kg HPßCD groups exhibited evidence of abortion, which was considered secondary to maternal toxicity. CONCLUSIONS: Although HPßCD was not well tolerated in rabbits at doses of 500 and 1,000 mg/kg, PS80 and PG were comparable to MC and should be considered for use in developmental and reproductive toxicology studies.

The safety evaluation of long-acting ocular delivery systems.

The safety evaluation of ocular long-acting delivery (LAD) technologies is a nascent field. Here, we detail the challenges in assessing the safety of novel LAD technologies, and well as the most common types of toxicity encountered during early toxicity testing. A detailed understanding of the route of administration, pharmacology, and functionality and/or pharmacokinetics (PK) of the LAD, along with all of its component parts, including the active pharmaceutical ingredient and excipients, is crucial for the successful development of next-generation long-acting ocular therapeutics.

Determination of a No Observable Effect Level for Endotoxin Following a Single Intravitreal Administration to Cynomolgus Monkeys.

Purpose: To characterize the inflammatory response and determine the no-observable-effect level (NOEL) in cynomolgus monkey eyes after intravitreal (ITV) injection of endotoxin. Methods: The inflammatory response to endotoxin was assessed in a single-dose study in monkeys at doses of 0.01 to 0.51 endotoxin units (EU)/eye. Tolerability was assessed by clinical ophthalmic examinations, intraocular pressure measurements, fundus color photography, optical coherence tomography, and anatomic pathology. Results: ITV injection of endotoxin at ≥0.04 EU/eye resulted in a dose-related anterior segment inflammatory response. No aqueous flare or cell was noted in the 0.01 EU/eye dose group. A more delayed posterior segment response characterized by vitreous cell was observed beginning on day 5, peaking on day 15, and decreasing in some groups. Microscopic findings of mononuclear cell infiltrates in the vitreous were observed in eyes given ≥0.21 EU/eye. Conclusion: The NOEL for ITV endotoxin in cynomolgus monkeys was 0.01 EU/eye, suggesting that this species is as sensitive as rabbits to the effects of endotoxin. The vitreous cavity also appears more sensitive to endotoxin than the anterior segment/aqueous chamber. Overall, the magnitude of the inflammatory response at ≥0.04 EU/eye suggests that dose-response curve in monkeys is steeper than in rabbits. These data highlight the importance of assessing endotoxin level in ITV formulations, as levels as low as 0.04 EU/eye may confound the safety evaluations of ITV therapeutics in cynomolgus monkeys.

Rapid Development of Glaucoma Via ITV Nonselective ANGPT 1/2 Antibody: A Potential Role for ANGPT/TIE2 Signaling in Primate Aqueous Humor Outflow.

Purpose: Investigate a significant, dose-related increase in IOP, leading to glaucomatous damage to the neuroretina and optic nerve following intravitreal (ITV) administration of a bispecific F(ab')2 [anti-VEGF/Angiopoietins [ANGPT]F(ab')2] molecule in adult monkeys. Methods: ITV ocular tolerability and investigation of anti-VEGF/ANGPT F(ab')2 (blocking both ANGPT1 and ANGPT2) was done in monkeys; mechanistic studies were done in neonatal mice. Results: Following the second ITV dose of anti-VEGF/ANGPT F(ab')2, all 1.5- and 4-mg/eye treated monkeys developed elevated IOP, which eventually was associated with optic disc cupping and thinning of the neuroretinal rim. Histopathologic examination showed nonreversible axonal degeneration in the optic nerves of animals administered 1.5 mg/eye and higher that was considered secondary to high IOP. Anti-ANGPT Fab also caused elevated IOP in monkeys, but anti-VEGF Fab did not contribute to the IOP increase. In addition, an anti-ANGPT2-selective antibody did not change IOP. In mice simultaneous blockade of ANGPT1 and ANGPT2 impaired the expansion and formation of Schlemm's canal (SC) vessels, similar to genetic ablation of Angpt1/Angpt2 and their receptor TIE2. As previously reported, blocking ANGPT2 alone did not affect SC formation in mice. Conclusions: Dual inhibition of ANGPT1/ANGPT2, but not ANGPT2 alone, leads to increased IOP and glaucomatous damage in monkeys. This confirms a role for TIE2/ANGPT signaling in the control of IOP in adults, a finding initially identified in transgenic mice. Dual pharmacologic inhibition of ANGPT1/ANGPT2 may affect aqueous drainage and homeostasis in adult monkeys and may be useful in developing novel models of glaucoma.

Nonclinical Safety Assessment of Anti-Factor D: Key Strategies and Challenges for the Nonclinical Development of Intravitreal Biologics.

PURPOSE: The nonclinical toxicology program described here was designed to characterize the safety profile of anti-factor D (AFD; FCFD4514S, lampalizumab) to support intravitreal (ITV) administration in patients with geographic atrophy (GA). METHODS: The toxicity of AFD was assessed in a single-dose and 6-month repeat-dose study in monkeys at doses up to 10 mg/eye. Toxicity was assessed by clinical ophthalmic examinations, intraocular pressure measurements, ocular photography, electroretinography, fluorescein angiography, optical coherence tomography, and anatomic pathology. RESULTS: Systemic exposure to AFD generally increased with the increase in dose level. The increases in mean maximal concentration and area under the curve values were roughly dose proportional. No accumulation of AFD was observed following 10 doses, and drug exposures were not affected by anti-drug antibodies. AFD was locally and systemically well tolerated in monkeys following ITV doses of up to 10 mg/eye. Ocular effects associated with AFD were limited to transient, reversible, dose-related, aqueous cell responses and injection-related, mild, vitreal cell responses. In the 6-month repeat-dose study, 2 monkeys had a nonspecific immune response to AFD that resulted in severe ocular inflammation, attributed to administration of a heterologous (humanized) protein. CONCLUSIONS: The comprehensive toxicology program in monkeys described here was designed to evaluate the safety profile of AFD and to support multiple ITV injections in the clinic. Administration of a heterologous (humanized) protein presents a challenge, and immunogenicity in nonclinical species is not predictive of immunogenicity in humans. Taken together, the results of the nonclinical program described here support the use of AFD in patients with GA.

Determination of a No-Observable Effect Level for Endotoxin Following a Single Intravitreal Administration to Dutch Belted Rabbits.

Purpose: The purpose of this study was to characterize the inflammatory response and determine a no-observable effect level (NOEL) in rabbit eyes after endotoxin intravitreal (ITV) injection. Methods: Fifty-three naïve male Dutch Belted rabbits were treated with a single 50-µL ITV injection ranging from 0.01 to 0.75 endotoxin units/eye (EU/eye) and monitored for up to 42 days post treatment. Ophthalmic examination included slit-lamp biomicroscopy and indirect ophthalmoscopy. Laser flare photometry was performed in a subset of animals. On days 2, 8, 16, and 43, a subset of animals was necropsied and eyes processed for histopathological evaluation. Results: Intravitreal injection of endotoxin at ≥0.05 EU/eye resulted in a dose-related anterior segment inflammation response. No aqueous flare or cell response was noted in the 0.01 EU/eye dose group. A more delayed posterior segment response characterized by vitreal cell response was observed beginning on day 5, peaking on day 9, and decreasing starting on day 16 that persisted at trace to a level of 1+ on day 43. Microscopy findings of infiltrates of minimal mixed inflammatory cells in the vitreous and subconjunctiva and proteinaceous fluid in the anterior chamber and/or vitreous were observed in eyes given ≥0.1 EU/eye. Conclusions: We defined the NOEL for ITV endotoxin to be 0.01 EU/eye, suggesting that the vitreal cavity is more sensitive to the effects of endotoxin than the anterior segment and aqueous chamber. These data highlight the importance of assessing endotoxin level in intravitreal formulations, as levels as low as 0.05 EU/eye may confound the safety evaluations of intravitreal therapeutics in rabbits.

Evaluation of the Toxicity of Intravitreally Injected PLGA Microspheres and Rods in Monkeys and Rabbits: Effects of Depot Size on Inflammatory Response.

Purpose: Poly(lactic-co-glycolic) acid (PLGA) inserts have been successfully developed for the treatment of posterior eye disease as a means of reducing injection frequency of intravitreally administered therapeutics. PLGA microspheres are also of interest for the delivery of intravitreal drugs, since they offer the advantage of being easily injected without surgical procedures or large injectors. Methods: In the current study, the toxicity of PLGA microspheres and rods was investigated in nonhuman primates (NHPs) and rabbits. An in vitro assessment of cytokine responses to PLGA in peripheral blood mononuclear cells (PBMCs) and macrophages was also performed. Results: Intravitreal administration of 3, 10, or 12.5 mg/eye of PLGA microspheres in NHPs resulted in a severe immune response characterized by a foreign body response. Follow-up studies in the rabbit confirmed this finding for PLGA microspheres ranging in size from 20 to 100 µm. In contrast, administration of PLGA rod implants with a similar PLGA mass did not elicit a significant immune response. In vitro assays in PBMCs and macrophages confirmed proinflammatory cytokine release upon treatment with PLGA microspheres but not PLGA rods. Conclusions: These data demonstrate a lack of tolerability of PLGA microspheres upon intravitreal injection, and suggest that the size, shape, and/or surface area of PLGA depots are critical attributes in determining ocular toxicity.

Vehicle selection for nonclinical oral safety studies.

INTRODUCTION: The development of poorly soluble or permeable new chemical entities within the pharmaceutical industry often requires the use of nonstandard enabling nonclinical oral formulations. Despite this, the toxicity profile of many commonly used nonclinical vehicles is poorly understood. This lack of data can lead to unexpected formulation-related effects being observed in critical oral safety studies. AREAS COVERED: This article summarizes the key considerations for formulation selection for oral nonclinical safety studies, and provides a strategy for appropriate development-phase formulation selection. The industry's use of oral nonclinical vehicles is reviewed, based on data from the FDA's Orange Book. Finally, a summary of the repeat dose oral toxicity of commonly used vehicles is presented. EXPERT OPINION: The rapid identification of a suitable nonclinical oral formulation is a critical step in small-molecule drug development. In order to maintain flexibility and address the needs of a diverse set of new chemical entities (NCEs) with widely varying physiochemical properties, a "tool belt" of multiple oral formulations is recommended. The appropriate formulation is identified based on the goals of the study, as well as exposure required, species, duration and therapeutic indication of the NCE.

Non-clinical toxicological considerations for pharmaceutical salt selection.

INTRODUCTION: Over half of all active pharmaceutical ingredients currently approved for use in the USA are pharmaceutical salts. The safety assessment of a pharmaceutical salt provides additional challenges in addition to those encountered when assessing the safety of the free acid or base form of a new chemical entity (NCE). The addition of a counter ion may have an impact on pharmacokinetics, toxicity, impurity profile and potential route of administration. AREAS COVERED: In this review, the toxicologic profiles of commonly used counter ions and strategies for supporting the development of novel or alternate pharmaceutical salt forms are summarized. Furthermore, the article highlights the major concerns that may be encountered by the non-clinical toxicologist when considering a novel pharmaceutical salt. EXPERT OPINION: Given the large numbers of pharmaceutical salts approved for use in the USA, relatively little non-clinical toxicologic data are available for commonly used counter ions. This information gap leaves the non-clinical toxicologist with limited resources to assess the impact of a counter ion on the toxicologic program for an NCE. The data summarized in this review provide a starting point toward a more detailed understanding of counter ion-related effects on the toxicity of pharmaceutical salts.

Comprehensive investigation of hydroxypropyl methylcellulose, propylene glycol, polysorbate 80, and hydroxypropyl-beta-cyclodextrin for use in general toxicology studies.

This study was conducted to assess the safety and tolerability of the alternative formulation vehicles polysorbate 80 (PS80), propylene glycol (PG), and hydroxypropyl-beta-cyclodextrin (HPßCD) in general toxicology studies in the mouse, rat, dog, and monkey. Twenty (20) mg/kg of hydroxypropyl methylcellulose (MC, control), 10 mg/kg PS80, 1000 mg/kg PG, 500 mg/kg HPßCD, or 1000 mg/kg HPßCD were administered by oral gavage to mice, rats, dogs, and cynomolgus monkeys for approximately 90 days. The effects of these formulations on clinical observations, body weight and food consumption parameters, clinical pathology, and histopathology were evaluated across all species. The suitability of formulations containing up to 20 mg/kg MC, 10 mg/kg PS80, and 1000 mg/kg PG for use in preclinical safety studies was confirmed by a lack of effects on all parameters examined. However, formulations containing HPßCD produced elevated transaminase (aspartate and alanine aminotransferase) levels in rats and mice and fecal changes (loose and soft stool) in large animals. Although the etiology and toxicological significance of the transaminase elevations in rats and mice is uncertain, this finding could represent a significant liability for a preclinical formulation because of the critical importance of these biomarkers in the risk assessment of novel therapeutic agents. Based on these data, PS80 and PG are considered to be practical alternatives to MC in preclinical toxicology studies. However, formulations containing HPßCD should be used with caution because of the elevations in rodent transaminase levels.