Developments in Bioassays

For over 30 years, I have been involved in the quality control of experimental biologics and have witnessed both incredible outcomes and tragic disappointments in addressing many different unmet clinical needs. I recently attended a conference in-person and attended all 16 great talks that catalyzed valuable conversations about developments in bioassays, specifically how to best measure product potency.

Potency is central to a pharmaceutical product’s efficacy and safety profile. Designing and developing bioassays to measure this critical quality attribute for complex biologics is a resource intensive activity.   Adopting a phase appropriate approach allows drug developers to strategically focus time and effort in a stepwise fashion to best satisfy the regulatory requirement for a validated potency assay at licensure.

Relevant biology and statistical analyses are integral to evaluating risks and making smart decisions. My continuing education in this area comes from conferences, courses and ongoing conversations with my clients and colleagues. With in-person conferences on the rebound, I wish to share the following information with you.

Findings from the CASSS Bioassay Conference in Gaithersburg, Maryland (July 19-21, 2022)

Keynote Summary – Dr. Marjorie Shapiro
(Office of Biotechnology Products/OPQ/CDER/FDA)

1. We’re never done learning about how our products work and the diseases they are used to treat
2. Accumulation of knowledge is gained by industry and health authorities working together
3. Continuous learning leads to new and improved bioassays and better products

Conference Take Homes Applicable to Cell and Gene Therapy Products
Regulatory

1. The distinction between critical raw materials, drug substance and drug product can become blurred in complex C/GT products.The regulatory agencies are asking for more detailed CMC information, at earlier stages in development and with the expectation of “potency testing” on upstream materials that influence the potency of the final product.
2. Generation and characterization of reference materials must begin early in development and provide enough to evaluate and link pre-clinical and clinical lots using a phase appropriate, matrix-based approach to product potency testing.

Cell lines and Readouts

1. Primary cells may be more biologically relevant but banked cell lines including highly engineered cell lines (e.g. AAVR over expression, reporter gene) may be required to achieve an assay that is robust enough to be used in QC.
2. High tech readouts have recently been incorporated into QC testing. Big pharma players have validated FACS and Single Quadrupole Mass Spectrometry as bioassay readouts for lot release testing of an approved COVID vaccine and a gene therapy product in clinical development, respectively.FACS analysis is going to be essential for some cell and gene therapy products.
3. For CAR-T products, it is unclear whether INF-γ production is a meaningful potency measurement.Off-the-shelf cell lines (e.g. Target Cell Killing (promega.com) are now being used to more directly assess cell killing functionality.For autologous and allogeneic products, a lack of parallelism between reference material and product lots is not uncommon and may reflect the inherent variability of donor starting material and complicate calculation of a RP value.

Design and Data Analysis

1. In silico tools are being developed and implemented to identify the optimal spacing of dilutions of reference and test samples to cover the expected/desired range for bioassays that yield dose response curves that fit a 4 PL model.  A minimum of 8 points is required with 2 in each asymptote.

This article was originally published as the Sajjadi Consulting Quality Quarterly, sent July 2022. You are invited to subscribe to the quality quarterly.