Comparison of the primary rat spinal cord cell (RSC) assay and the mouse bioassay for botulinum neurotoxin type A potency determination

IntroductionBotulinum neurotoxin (BoNT) type A is increasingly used in humans for pharmaceutical and cosmetic purposes. Currently, the standard assay used to determine potency of clinical samples, and the only assay approved by the FDA, is the in vivo mouse bioassay (MBA). However, due to several drawbacks of this assay (relatively large error, high cost, no standardization, requirement of high technical expertise, and use of large numbers of mice), there is an increasing need to replace this assay. A cell-based assay using primary rat spinal cord cells (RSC assay) has been previously reported to sensitively detect purified botulinum neurotoxin type A, and requires all biological properties of the toxin for detection.MethodsThis study presents data on quantitative detection of potency of purified BoNT/A by a cell-based assay, using primary rat spinal cord cells (RSC assay). The sensitivity and error rate of the RSC assay was directly compared to the currently used mouse bioassay by repeated testing of the same purified BoNT/A sample by both assays. In addition, the potency of several samples of purified BoNT/A of unknown activity was determined in parallel by RSC assay and MBA.ResultsThe results indicate sensitivity of the RSC assay similar to the mouse bioassay, high reproducibility, and a lower error rate than the mouse bioassay. Direct comparison of potency determination of several purified BoNT/A samples by RSC assay and MBA resulted in very similar values, indicating very good correlation.DiscussionThese data support the use of a cell-based assay for potency determination of purified BoNT/A as an alternative to the mouse bioassay.