S55746 (S 055746,BCL201) is a novel, orally active BCL-2 specific inhibitor (Ki = 1.3 nM) with poor affinity for BCL-XL and no significant binding to MCL-1, BFL-1 (BCL2A1/A1). The selectivity of S55746 for BCL-2 versus BCL-XL ranges from ~70 to 400 folds.
S55746 occupies the hydrophobic groove of BCL-2. In a panel of hematological cell lines, S55746 induces hallmarks of apoptosis including externalization of phosphatidylserine, caspase-3 activation and PARP cleavage. S55746 potently induces RS4;11 cell killing after 72 h of treatment with an IC50 of 71.6 nM and exhibits a much weaker activity in H146 (IC50 = 1.7 μM), a BCL-XL-dependent cell line, which expresses a low level of BCL-2 and high level of BCL-XL. It has no cytotoxic activity on BCL-XL-dependent cells, such as platelets[1].
S55746 administered by oral route daily in mice demonstrates robust anti-tumor efficacy in two hematological xenograft models (RS4;11 and Toledo models) with no weight lost and no change in behavior[1].
[1] Casara P, et al. Oncotarget. 2018, 9(28):20075-20088.