Development and Validation of a Method to Determine CYP4V2 Enzyme Activity in rAAV-hCYP4V2 Gene Therapy Products Using a Bioluminescent Substrate Assay

Bietti crystalline dystrophy like retinal degeneration (BCD) is an inherited retinal degenerative disease caused by defects in the CYP4V2 gene. Recombinant AAV-based gene replacement therapy holds promise for this disease, yet reliable enzymatic activity assays for product potency evaluation remain urgently needed. This study established and validated a method for determining the enzymatic activity of CYP4V2 based on the bioluminescent substrate Luciferin-MultiCYP.HEK293-AAVR cells were seeded at 1 × 104 cells/well and transduced with rAAV-hCYP4V2 across an MOI gradient (1.17 × 103–2.4 × 106). After incubating at 37 °C for 72 h, medium was replaced with Opti-MEM containing 20 µM Luciferin-MultiCYP and incubated for 90 min ± 30 min. Next, cell supernatants were mixed with luciferase reagent, and bioluminescence was measured. Methodological validation results revealed that the method has good specificity, with an accuracy recovery rate of 100.94% ± 2.84% (RSD = 2.81%). Repeatability (GCV%) was 4.21%, and intermediate precision (RSD) was 6.16%. Linearity was good within the MOI range of 1.17 × 103 to 2.4 × 106 (R2 = 0.9902 ± 0.0061, n = 9). Lastly, the method was successfully applied to activity testing the products of three AAV serotypes (AAV8, AAV2/8, and AAV2). This bioluminescent method meets regulatory potency assay requirements and serves as an effective QC tool for process development, batch release, and stability evaluation of rAAV-hCYP4V2 products.