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ABBV-075 is a potent and selective BET family bromodomain inhibitor that recently entered phase I clinical trials. Comprehensive preclinical characterization of ABBV-075 demonstrated broad activity across cell lines and tumor models, representing a variety of hematologic malignancies and solid tumor indications. In most cancer cell lines derived from solid tumors, ABBV-075 triggers prominent G 1 cell-cycle arrest without extensive apoptosis. In this study, we show that ABBV-075 efficiently triggers apoptosis in acute myeloid leukemia (AML), non-Hodgkin lymphoma, and multiple myeloma cells. Apoptosis induced by ABBV-075 was mediated in part by modulation of the intrinsic apoptotic pathway, exhibiting synergy with the BCL-2 inhibitor venetoclax in preclinical models of AML. In germinal center diffuse large B-cell lymphoma, BCL-2 levels or venetoclax sensitivity predicted the apoptotic response to ABBV-075 treatment. In vivo combination studies uncovered surprising benefits of low doses of ABBV-075 coupled with bortezomib and azacitidine treatment, despite the lack of in vitro synergy between ABBV-075 and these agents. The in vitro / in vivo activities of ABBV-075 described here may serve as a useful reference to guide the development of ABBV-075 and other BET family inhibitors for cancer therapy. Cancer Res; 77(11); 2976-89. ©2017 AACR ., (©2017 American Association for Cancer Research.)

Purpose: The purpose of this study was to characterize the activity of the Bcl-2 protein family inhibitor ABT-263 in a panel of small cell lung cancer (SCLC) xenograft models., Experimental Design: A panel of 11 SCLC xenograft models was established to evaluate the efficacy of ABT-263. Single agent activity was examined on a continuous dosing schedule in each of these models. The H146 model was used to further evaluate dose and schedule, comparison to standard cytotoxic agents, and induction of apoptosis., Results: ABT-263 exhibited a range of antitumor activity, leading to complete tumor regression in several models. Significant regressions of tumors as large as 1 cc were also observed. The efficacy of ABT-263 was also quite durable; in several cases, minimal tumor regrowth was noted several weeks after the cessation of treatment. Antitumor effects were equal or superior to that of several clinically approved cytotoxic agents. Regression of large established tumors was observed through several cycles of therapy and efficacy was retained in a Pgp-1 overexpressing line. Significant efficacy was observed on several dose and therapeutic schedules and was associated with significant induction of apoptosis., Conclusions: ABT-263 is a potent, orally bioavailable inhibitor of Bcl-2 family proteins that has recently entered clinical trials. The efficacy data reported here suggest that SCLC is a promising area of clinical investigation with this agent.

Overexpression of the prosurvival Bcl-2 family members (Bcl-2, Bcl-xL, and Mcl-1) is commonly associated with tumor maintenance, progression, and chemoresistance. We previously reported the discovery of ABT-737, a potent, small-molecule Bcl-2 family protein inhibitor. A major limitation of ABT-737 is that it is not orally bioavailable, which would limit chronic single agent therapy and flexibility to dose in combination regimens. Here we report the biological properties of ABT-263, a potent, orally bioavailable Bad-like BH3 mimetic (K(i)'s of <1 nmol/L for Bcl-2, Bcl-xL, and Bcl-w). The oral bioavailability of ABT-263 in preclinical animal models is 20% to 50%, depending on formulation. ABT-263 disrupts Bcl-2/Bcl-xL interactions with pro-death proteins (e.g., Bim), leading to the initiation of apoptosis within 2 hours posttreatment. In human tumor cells, ABT-263 induces Bax translocation, cytochrome c release, and subsequent apoptosis. Oral administration of ABT-263 alone induces complete tumor regressions in xenograft models of small-cell lung cancer and acute lymphoblastic leukemia. In xenograft models of aggressive B-cell lymphoma and multiple myeloma where ABT-263 exhibits modest or no single agent activity, it significantly enhances the efficacy of clinically relevant therapeutic regimens. These data provide the rationale for clinical trials evaluating ABT-263 in small-cell lung cancer and B-cell malignancies. The oral efficacy of ABT-263 should provide dosing flexibility to maximize clinical utility both as a single agent and in combination regimens.

ABT-737 is a novel and potent Bcl-2 antagonist with single-agent activity against small-cell lung cancer (SCLC) cell lines. Here, we evaluated the contribution of Bcl-2 family members to the in vitro cellular response of several SCLC cell lines to ABT-737. Relatively higher levels of Bcl-2, Bcl-X(L), Bim and Noxa, and lower levels of Mcl-1 characterized naïve SCLC cell lines that were sensitive to ABT-737. Conversely, a progressive decrease in the relative levels of Bcl-2 and Noxa and a progressive increase in Mcl-1 levels characterized the increased resistance of H146 cells following chronic exposure to ABT-737. Knockdown of Mcl-1 with small interfering RNA sensitized two resistant SCLC cell lines H196 and DMS114 to ABT-737 by enhancing the induction of apoptosis. Likewise, up-regulation of Noxa sensitized H196 cells to ABT-737. Combination treatment with DNA-damaging agents was extremely synergistic with ABT-737 and was associated with the down-regulation of Mcl-1 and the up-regulation of Noxa, Puma, and Bim in H196 cells. Thus, SCLC cells sensitive to ABT-737 expressed the target proteins Bcl-2 and Bcl-X(L), whereas Mcl-1 and factors regulating Mcl-1 function seem to contribute to the overall resistance of SCLC cells to ABT-737. Overall, these observations provide further insight as to the mechanistic bases for ABT-737 efficacy in SCLC and will be helpful for profiling patients and aiding in the rational design of combination therapies.

Inhibition of the prosurvival members of the Bcl-2 family of proteins represents an attractive strategy for the treatment of cancer. We have previously reported the activity of ABT-737, a potent inhibitor of Bcl-2, Bcl-X(L), and Bcl-w, which exhibits monotherapy efficacy in xenograft models of small-cell lung cancer and lymphoma and potentiates the activity of numerous cytotoxic agents. Here we describe the biological activity of A-385358, a small molecule with relative selectivity for binding to Bcl-X(L) versus Bcl-2 (K(i)'s of 0.80 and 67 nmol/L for Bcl-X(L) and Bcl-2, respectively). This compound efficiently enters cells and co-localizes with the mitochondrial membrane. Although A-385358 shows relatively modest single-agent cytotoxic activity against most tumor cell lines, it has an EC(50) of <500 nmol/L in cells dependent on Bcl-X(L) for survival. In addition, A-385358 enhances the in vitro cytotoxic activity of numerous chemotherapeutic agents (paclitaxel, etoposide, cisplatin, and doxorubicin) in several tumor cell lines. In A549 non-small-cell lung cancer cells, A-385358 potentiates the activity of paclitaxel by as much as 25-fold. Importantly, A-385358 also potentiated the activity of paclitaxel in vivo. Significant inhibition of tumor growth was observed when A-385358 was added to maximally tolerated or half maximally tolerated doses of paclitaxel in the A549 xenograft model. In tumors, the combination therapy also resulted in a significant increase in mitotic arrest followed by apoptosis relative to paclitaxel monotherapy.