eLearning Seminar
Regulatory and Nonclinical Considerations for the Development of CNS/Neurology Therapeutics

Module 1: Regulatory Considerations for the Development of CNS/Neurology Therapeutics

Mondona McCann, PhD

According to 21 CFR Part 312.23 (a)(8) of the US regulations, sufficient information derived from nonclinical pharmacology and toxicology studies is needed in order to support the decision that a clinical trial in human subjects is reasonably safe and scientifically feasible to conduct. The data resulting from the nonclinical studies should support scientific proof-of-principle and safety for the administration of the investigational product in the specified clinical population. In addition, nonclinical studies help guide the design of certain elements of a clinical trial. The development of cell and gene therapies for neurological indications over recent decades has demonstrated the potential clinical benefits of these therapies for this heterogeneous group of disorders. However, there remain significant questions, including the risks associated with these products that are not understood. Thus, a comprehensive nonclinical characterization of novel cell and gene therapy products and their associated risks are critical for the safe conduct of future clinical trials. This presentation will provide a general overview of the Center for Biologics Evaluation and Research’s Office of Therapeutic Products (OTP), the existing regulatory framework, including avenues for interactive communications, and resources to guide stakeholders in the nonclinical assessment of the safety and activity of cell and gene therapy products for neurological indications.

Module 2: Nonclinical Development of AAV-Based Gene Therapy for Spinal Muscular Atrophy

Francis Tukov, PhD, DVM, DABT

Nonclinical Development of Onasemnogene Abeparvovec: Challenges and Translational Clinical Experience. The use of gene therapies as a modality to treat rare monogenic diseases continues to increase as they represent a novel approach to treat, and potentially cure, many of these conditions, including rare CNS diseases. Most of these therapies have employed viral vectors as vehicles for delivering therapeutic genes. Recombinant adeno-associated virus (rAAV)-based vectors are frequently used based on their characteristics of being nonpathogenic and replication deficient and have a transduction profile that results in stable and prolonged transgene expression in nondividing target cells. OAV101 (onasemnogene abeparvovec) is a rAAV-based gene therapy indicated for the treatment of patients with spinal muscular atrophy (SMA) with biallelic mutations in the survival motor neuron 1 (SMN1) gene. First approved by the FDA in May 2019, OAV101(currently marketed as Zolgensma®) has demonstrated substantial clinical efficacy and relative safety in SMA patients following a single IV dose. To ensure that the benefits of OAV101 can be accessible to a significant segment of the SMA patient pool, intrathecal (IT) OAV101 is currently being developed for late-onset SMA patients aged 2 to 18 years. This talk will focus on the nonclinical program developed to support the initiation of clinical trials following IV infusion or IT injection of OAV101. In addition to the proof-of-concept efficacy studies in SMNΔ7 mice and an induced porcine model of SMA, a toxicology program consisting of single-dose integrated toxicity and biodistribution, tolerability, and investigative studies in neonatal mice and juvenile cynomolgus monkeys supported the clinical administration of OAV101. Potential safety risks such as hepatotoxicity, cardiotoxicity, DRG toxicity, immunogenicity, insertional mutagenesis and tumorgenicity based on OAV101 nonclinical studies as well as literature on other AAV-based gene therapies will be discussed with an emphasis on DRG toxicity and efforts made to better understand the pathogenesis. Operational challenges for nonclinical studies as well as translation of nonclinical findings in the clinical setting will also be addressed, including measures for clinical trial monitoring.

Module 3: Nonclinical Development of Antisense Oligonucleotide for Spinal Muscular Atrophy

Scott Henry, PhD

Nusinersen has been evaluated in a nonclinical program to support treatment of spinal muscular atrophy (SMA) using lumbar intrathecal (IT) administration. SMA is an autosomal recessive neuromuscular disease that primarily affects infants and children and is characterized by degeneration of the motor neurons in the spinal cord. Deletions in the survival motor neuron gene (SMN1) result in loss of SMN protein and eventual death of motor neurons. A duplicate gene, SMN2, is not functional due to a splicing defect that skips exon 7 and results in truncated SMN protein. Nusinersen is a fully 2'-O-methoxyethyl modified phosphorothioate antisense oligonucleotide designed to bind to SMN2 pre-mRNA and facilitate inclusion of exon 7, resulting in full-length SMN protein.

PK studies established the minimum tissue concentration that increased exon 7 in mRNA in transgenic mice (2 to 10 µg/g), and the half-life in monkey CNS tissue (~150 days). Toxicology studies included a single-dose IT study in cynomolgus monkeys, 14-week and 53-week repeat-dose IT toxicity studies in juvenile monkeys, 13-week SC study in juvenile CD-1 mice, and SC reproductive toxicity studies in CD-1 mice and NZW rabbits. Genetic toxicology studies (Ames test, chromosomal aberration, mouse micronucleus) were negative. The monkey was chosen for repeat-dose IT toxicology studies and a 53-week study in monkeys established loading and maintenance dose regimen, used to maximize CSF and CNS tissue exposure. Animals received 5 weekly IT doses at 0.3, 1, and 4 mg/dose followed by dosing every 6 weeks (total of 13 IT doses), with a NOAEL at the high dose (4 mg/dose). In clinical studies, infants received 4 loading doses followed by maintenance doses once every 4 months. Safety margins were based on the approximate 10-fold difference in CSF volume between monkeys and humans and the total cumulative yearly dose. The NOAEL of 4 mg/dose (administered 13 times/year) converts to a total human equivalent dose of 520 mg/year, and provides a safety margin of 14-fold compared to the chronic yearly maintenance dose of 36 mg/year in patients.

Module 4: Development of Biologics for CNS/Neurodegenerative Diseases, Part 1

Lorrene Buckley, PhD, DABT, ATS

Nonclinical Safety Assessment of Galcanezumab, a CGRP Monoclonal Antibody for the Treatment of Migraine. Emgality® (galcanezumab) is included as a case study of the nonclinical development of biologics for CNS diseases. Galcanezumab is a humanized IgG4 monoclonal antibody that binds to calcitonin gene-related peptide (CGRP) ligand with high affinity and selectivity and blocks its binding to the receptor. Elevated blood concentrations of CGRP, a potent vasodilator, have been associated with migraine attacks. Galcanezumab was approved by the US FDA in 2018 and is marketed under the tradename “Emgality®”, for the preventive treatment of migraine and for treatment of episodic cluster headache in the US.

The nonclinical safety assessment for galcanezumab was designed and conducted according to regulatory guidance (e.g., ICH S5, S6) and GLP guidelines. Galcanezumab is pharmacologically active in rats and rabbits, and the CGRP sequence in monkeys is identical to that in humans. The high doses in the toxicology studies were selected according to ICH S6 criteria: saturation of PD and exposures ̴10X in excess of human recommended doses. The clinical route of administration (subcutaneous) was used, and the dose regimens (QW or more frequently) were chosen to maintain exposure over the treatment periods.

The presentation will focus on the nonclinical safety package consisting of: 1) repeated-dose toxicology studies in rats and monkeys (SC, QW) up to 6 months, with safety pharmacology parameters (CNS, Respiratory, and Cardiovascular, CV) incorporated in the monkey studies; 2) a full developmental and reproductive toxicology package in rats including male fertility, female fertility and early embryonic development, embryofetal development (also rabbits), and pre- postnatal development; and 3) a juvenile toxicology study in rats. Genetic toxicology studies were not required, and carcinogenicity was assessed using a weight-of-evidence evaluation. Dose selection for initial clinical trials was based on in vitro characterization (binding affinity, selectivity, and functionality of binding to CGRP) and an in vivo model of capsaicin-induced increases in dermal blood flow (a PD biomarker of CGRP pathway modulation). Of topical interest to regulators were: 1) high dose selection/justification; and 2) the impact of long-term antagonism of the CGRP in humans, particularly in patients with CV risk factors (a theoretical concern considered low based on comprehensive reviews of the literature and data).

Module 4: The Art of CNS Drug Development: Delivery Strategies, Neurotoxicology Endpoints and Regulatory Considerations, Part 2

Simon Authier, DVM, MSc, MBA, PhD, DSP

The session will present and discuss central nervous system (CNS) drug delivery in preclinical species along with toxicology, translational, and regulatory considerations relevant to these specialized modalities. Fundamental and advanced neurotoxicity endpoints will be reviewed and contrasted as early and late drug development phases are presented. The session will address neurotoxicology concepts that may serve to design or interpret toxicology studies with CNS delivery.