A Dual Bcl-2/x_L Inhibitor Induces Tumor Cell Apoptosis in a Hematopoietic Xenograft Model

Over-expression of the antiapoptotic proteins Bcl-2 and Bcl-xL provides a common mechanism through which cancer cells gain a survival advantage and become resistant to conventional standard of care therapies. Because Bcl-2 family members play key, but partially overlapping, roles as regulators of apoptosis, simultaneous inhibition of both Bcl-2 and Bcl-x_L could serve as a promising anticancer strategy. Clinical validation of this concept has been demonstrated with multiple agents targeting different Bcl2 family members. For example, recent Phase I/II trials of the dual Bcl-2 / Bcl-x_L inhibitor Navitoclax demonstrated a 20% response rate in relapsed, refractory CLL patients. However, in this study dosing was often limited by chronic thrombocytopenia, a well established side effect of inhibiting Bcl-x_L.

Here we disclose for the first time a novel and potent BH3 mimetic (Bcl2-32), with nanomolar binding affinity for Bcl-2 and Bcl-x_L, (K_i = 3.3 and 8.5nM respectively). In contrast to Navitoclax which requires daily oral administration for activity, Bcl2-32 has shown promising efficacy on an intermittent dosing schedule that allows full platelet recovery between doses. In this poster, we describe the in vitro and in vivo activity profile of Bcl2-32 in a variety of cell types that highlights its potential as a dual inhibitor of Bcl2 and BclX_L. In addition to exhibiting potent single agent anti-cancer activity in a sensitive Acute Lymphocytic Leukemia (RS4; 11) model with (TGI >100%, P < 0.001), Bcl2-32 also potentiates the effectiveness of standard chemotherapeutic agents in less sensitive DLBCL xenograft models. Taken together, these data suggest that Bcl2-32 represents an exciting development opportunity as single agent or in combination in a broad range of hematopoietic malignancies.