Ecific for BoNT/A, by the use of monoclonal antibodies specific for SNAP25197. The assay utilizes a stable cell line of neuronal origin [48] that can be differentiated in 48 h and a sensitive sandwich ELISA read-out that can be validated in a QC laboratory. This CBPA represents the multistep pharmacological mode of MedChemExpress 69-25-0 action of BoNT/A at pre-synaptic terminals [3,4,8]; it is accurate, robust, reproducible, amenable to validation, and can measure BoNT/A biological activity in pharmaceutical preparations (containing less than a nanogram of BoNT/A formulated with excipients). For over 25 years there has been a strong desire to replace the mouse bioassay with a fully in vitro assay that enables sensitive evaluation of all key steps in BoNT/A action [14,18,25]. It was the dogma that continuous cell lines lacked the sensitivity necessary to develop an assay that could replace the mouse bioassay [47], but at the same time the use of primary neurons or embryonic cell derived neurons pose their own challenges as they have to be freshly derived from animal tissue [39?2] or they requirecomplicated protocols and long time to be fully differentiated [44?6]. Moreover, when replacing a bioassay approved by regulatory agencies with a new in vitro assay, the sensitivity of the method is not the only consideration as the assay has to be validated and cross-validated against the mouse bioassay [18,25]. Our team set in place a rigorous evaluation process of continuous cell lines for their sensitivity to BoNT/A that culminated in the identification of several sensitive cell lines that could be amenable for developing potency assays, 1480666 with SiMa cells being the most sensitive even when undifferentiated (Figure 2). However, to achieve the sensitivity needed to replace the mouse bioassay (pM concentrations), optimization of the cells’ growth and differentiation conditions was essential. After the optimization process with Neuro-2a, PC12, LA1-55n, and SiMa cell lines, we achieved great sensitivity with EC50 values in the mid and low pM (Figure 3) that were excellent to develop BoNT/A activity assays. A breakthrough was achieved with the identification of the SiMa cells that were very sensitive (EC50 = 6.5 pM in WB and 3 pM in ELISA) to BoNT/A and produced excellent S/B at all doses tested, especially at sub-pM concentrations, comparable to the primary and embryonic cell derived neurons [40,41,44?7] while providing a continuous and reliable source of cells (allowing preparation of cell banks) for the CBPA. The development of a read-out for the FCCP cell-based assay that could be validated 1407003 in a QC environment was essential since Western blots, with intrinsic variability, are difficult to validate. Sandwich ELISA assays are robust, sensitive, and amenable to validation. The antibody binding affinity for the antigen is usually the main determinant of immunoassay sensitivity. The second breakthrough was achieved with the generation of a highly specific high affinity anti-SNAP25197 monoclonal antibody. The 2E2A6 antibody, displaying high affinity and a very low dissociation constant (Figure 1) was ideal to capture cleaved SNAP25197 from cell lysates treated with BoNT/A. The high specificity for SNAP25197 resulted in extremely low background signal from untreated lysates; excellent signal to background ratios, even at femtomolar amounts of BoNT/A; and Z9 values that support the use of the assay for screening. A very sensitive CBPA is needed for measuring BoNT/A biological activ.Ecific for BoNT/A, by the use of monoclonal antibodies specific for SNAP25197. The assay utilizes a stable cell line of neuronal origin [48] that can be differentiated in 48 h and a sensitive sandwich ELISA read-out that can be validated in a QC laboratory. This CBPA represents the multistep pharmacological mode of action of BoNT/A at pre-synaptic terminals [3,4,8]; it is accurate, robust, reproducible, amenable to validation, and can measure BoNT/A biological activity in pharmaceutical preparations (containing less than a nanogram of BoNT/A formulated with excipients). For over 25 years there has been a strong desire to replace the mouse bioassay with a fully in vitro assay that enables sensitive evaluation of all key steps in BoNT/A action [14,18,25]. It was the dogma that continuous cell lines lacked the sensitivity necessary to develop an assay that could replace the mouse bioassay [47], but at the same time the use of primary neurons or embryonic cell derived neurons pose their own challenges as they have to be freshly derived from animal tissue [39?2] or they requirecomplicated protocols and long time to be fully differentiated [44?6]. Moreover, when replacing a bioassay approved by regulatory agencies with a new in vitro assay, the sensitivity of the method is not the only consideration as the assay has to be validated and cross-validated against the mouse bioassay [18,25]. Our team set in place a rigorous evaluation process of continuous cell lines for their sensitivity to BoNT/A that culminated in the identification of several sensitive cell lines that could be amenable for developing potency assays, 1480666 with SiMa cells being the most sensitive even when undifferentiated (Figure 2). However, to achieve the sensitivity needed to replace the mouse bioassay (pM concentrations), optimization of the cells’ growth and differentiation conditions was essential. After the optimization process with Neuro-2a, PC12, LA1-55n, and SiMa cell lines, we achieved great sensitivity with EC50 values in the mid and low pM (Figure 3) that were excellent to develop BoNT/A activity assays. A breakthrough was achieved with the identification of the SiMa cells that were very sensitive (EC50 = 6.5 pM in WB and 3 pM in ELISA) to BoNT/A and produced excellent S/B at all doses tested, especially at sub-pM concentrations, comparable to the primary and embryonic cell derived neurons [40,41,44?7] while providing a continuous and reliable source of cells (allowing preparation of cell banks) for the CBPA. The development of a read-out for the cell-based assay that could be validated 1407003 in a QC environment was essential since Western blots, with intrinsic variability, are difficult to validate. Sandwich ELISA assays are robust, sensitive, and amenable to validation. The antibody binding affinity for the antigen is usually the main determinant of immunoassay sensitivity. The second breakthrough was achieved with the generation of a highly specific high affinity anti-SNAP25197 monoclonal antibody. The 2E2A6 antibody, displaying high affinity and a very low dissociation constant (Figure 1) was ideal to capture cleaved SNAP25197 from cell lysates treated with BoNT/A. The high specificity for SNAP25197 resulted in extremely low background signal from untreated lysates; excellent signal to background ratios, even at femtomolar amounts of BoNT/A; and Z9 values that support the use of the assay for screening. A very sensitive CBPA is needed for measuring BoNT/A biological activ.