The Bcl-2 Family Inhibitor ABT-263 Shows Significant Anti-Tumor Efficacy in Models of B Cell Non-Hodgkin’s Lymphoma.

ABT-263 is an orally bioavailable small molecule inhibitor of Bcl-2 family proteins with a K_i of ≤ 1 nM against Bcl-2, Bcl-X_L, and Bcl-w. Non-Hodgkin’s B-cell lymphomas represent clinically relevant disease targets for this molecule due, in part, to strong expression of Bcl-2 often associated with various types of NHL (frequently involving a t(14;18) translocation including the Bcl-2 locus). ABT-263 exhibits sub-micromolar in vitro activity against a variety of NHL cell lines. DoHH-2 and WSU-DLCL₂ are two B-cell NHL lines harboring the t(14;18) translocation that exhibit differential in vitro sensitivity to ABT-263. Granta-519 is a mantle cell lymphoma line with the characteristic t(11;14)(q13:q32) translocation resulting in overexpression of cyclin D1. ABT-263 has an EC₅₀ of approximately 150 nM in the Granta-519 cell line. Here we present efficacy data evaluating the activity of ABT-263 in several NHL xenograft models. ABT-263 has significant in vivo anti-tumor efficacy in established flank tumor models both as monotherapy and in combination with cytotoxic agents. The efficacy of ABT-263 at 100 mg/kg/day, p.o., q.d. ×21 was evaluated as monotherapy and in combination with etoposide, vincristine, modified CHOP, R-CHOP, bortezomib, rapamycin, and rituximab. Results show that ABT-263 significantly inhibits tumor growth as a monotherapy (~50–60% tumor growth inhibition) and enhances the efficacy of these cytotoxic agents in combination therapy. Statistically significant enhancement of tumor growth inhibition was observed for each combination relative to monotherapy treatment. Efficacy was maintained even when therapy was initiated on larger (~500 mm³) tumors. Combinations of ABT-263 + rapamycin and ABT-263 + rituximab result in complete regression of a significant percentage of established B cell lymphoma tumors for a sustained period of time in vivo. The combination of ABT-263 + R-CHOP resulted in complete regression of 100% of the tumors in the mantle cell lymphoma model. The strong in vitro potency and tumor regressions seen in vivo suggest that ABT-263 has great potential for the oral treatment of NHL B-cell lymphomas.