Gene therapies, cell therapies, oligonucleotides, and other complex biologics do not always fit neatly into the traditional small-molecule safety pharmacology framework.

For sponsors developing these products, the challenge is not simply running a cardiovascular, CNS, or respiratory safety study. The study needs to reflect the biology of the therapy.

Test System Selection Matters

A relevant test system should respond to the therapy in a meaningful way.

For gene therapies, vector tropism, target expression, transgene activity, and immune response can influence whether a particular test system is informative. This may limit the usefulness of simply applying a standard test system and study design used for small molecules.

Persistence Changes Study Design

Gene and cell therapies may produce effects that persist well beyond administration.

For AAV products, traditional PK concepts are not directly applicable because exposure can involve several different measurements, including vector DNA, transgene RNA, expressed protein, and biological activity.

Study duration and endpoint timing should therefore reflect the expected persistence and biological activity of the therapy.

Immunogenicity Can Affect Safety and Interpretation

Immune responses can influence efficacy, exposure, and toxicity of AAV-based therapies.

Published industry guidance identifies pre-existing immunity and treatment-emergent immune responses as important considerations in both nonclinical and clinical development. (PubMed)

This means a safety finding may need to be interpreted alongside immunogenicity, biodistribution, clinical pathology, and transgene expression data rather than evaluated in isolation.

Route of Administration Also Matters

Intrathecal, intravitreal, and other targeted routes can introduce different technical and biological considerations than routine oral or IV administration.

Route, dose, volume, concentration, and procedure can influence both study conduct and interpretation.

For AAV programs, published studies have identified findings including dorsal root ganglion and peripheral nerve pathology, hepatotoxicity, immunogenicity, and inflammatory effects. The nature of those findings can vary with factors such as dose and administration route. (PubMed)

In Vivo Studies Still Have an Important Role

In vitro systems, computational approaches, and NAMs continue to improve and can provide valuable mechanistic and screening information.

However, some questions involving biodistribution, persistence, immune response, and integrated organ-system effects still require evaluation in an intact biological system.

The goal should not be to choose between in vitro and in vivo approaches. It should be to use the method that best answers the specific safety question.

What Sponsors Should Ask Their CRO

For a gene or cell therapy program, important questions include:

* Is the proposed test system pharmacologically relevant?

* Does persistence require a longer observation period?

* Could immunogenicity affect interpretation?

* Does the administration route require specialized expertise?

* Should safety pharmacology findings be interpreted with biodistribution, toxicology, or immunogenicity data?

The Biology Should Drive the Study

At Attentive Science, we design in vivo safety pharmacology and toxicology studies around the biology, route, persistence, and expected risks of the therapy.

Selected References

Kavita U, et al. PK/PD and Bioanalytical Considerations of AAV-Based Gene Therapies: an IQ Consortium Industry Position Paper. AAPS J. 2023;25:78. (PubMed)

Baldrick P, McIntosh B, Prasad M. Adeno-associated virus (AAV)-based gene therapy products: What are toxicity studies in non-human primates showing us? Regul Toxicol Pharmacol. 2023;138:105332. (PubMed)

Hordeaux J, et al. Adeno-Associated Virus-Induced Dorsal Root Ganglion Pathology. Hum Gene Ther. 2020;31:808-818. (PubMed)

Immunogenicity assessment of AAV-based gene therapies: An IQ consortium industry white paper. 2022. (PubMed)