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, smallmolecule 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. [Cancer Res 2008;68(9):3421-8]

ABT-737 is a novel and potent Bcl-2 antagonist with singleagent 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. [Cancer Res 2007;67(3):1176-83]

1,25-dihydroxyvitamin D3 (1,25(OH)2D3) and its analogues have been shown to inhibit proliferation of human cancer cells mediated by vitamin D receptor (VDR). The over-expression of 25-hydroxyvitamin D-24-hydroxylase (CYP24A1), an enzyme involved in the metabolism of 1,25(OH)2D3 and its analogues, is associated with poor prognosis of some human cancers. In this study, we employed real-time reverse transcription PCR to examine the expression of VDR and CYP24A1 mRNA in a cohort of human breast, lung, colon and ovary tumor samples. We found that CYP24A1 mRNA was significantly up-regulated in colon, ovary and lung tumors, but down-regulated in breast tumor relative to the analogous normal tissues. As a comparison, VDR mRNA was modestly down-regulated in colon, breast and lung tumors, but highly up-regulated in ovarian tumors. Treatment of two breast cancer cell lines, SW-620 and MCF-7, and one colon cancer cell line, HT-29, by 1,25(OH)2D3 for 48 h profoundly stimulated CYP24A1 mRNA expression (EC50=0.6, 0.8 and 29.5 nM in SW-620, HT-29 and MCF-7, respectively), but did not significantly affect VDR mRNA expression. Growth as assessed by DNA synthesis was modestly arrested by 1,25(OH)2D3 after 72 h of incubation, but was not altered after a 5-day incubation period. These data suggest that the VDR signaling pathway may be compromised via the modulation of CYP24A1 and VDR in human tumors.

Despite the importance of the oncogene in many malignancies, clinical strategies targeting c-Met have benefitted only small subsets of patients with tumors driven by signaling through the c-Met pathway, thereby necessitating selection of patients with amplification and/or c-Met activation most likely to respond. An ADC targeting c-Met could overcome these limitations with potential as a broad-acting therapeutic. ADC ABBV-399 was generated with the c-Met-targeting antibody, ABT-700. Antitumor activity was evaluated in cancer cells with overexpressed c-Met or amplified and in xenografts including patient-derived xenograft (PDX) models and those refractory to other c-Met inhibitors. The correlation between c-Met expression and sensitivity to ABBV-399 in tumor and normal cell lines was assessed to evaluate the risk of on-target toxicity. A threshold level of c-Met expressed by sensitive tumor but not normal cells is required for significant ABBV-399-mediated killing of tumor cells. Activity extends to c-Met or amplified cell line and PDX models where significant tumor growth inhibition and regressions are observed. ABBV-399 inhibits growth of xenograft tumors refractory to other c-Met inhibitors and provides significant therapeutic benefit in combination with standard-of-care chemotherapy. ABBV-399 represents a novel therapeutic strategy to deliver a potent cytotoxin to c-Met-overexpressing tumor cells enabling cell killing regardless of reliance on signaling. ABBV-399 has progressed to a phase I study where it has been well tolerated and has produced objective responses in c-Met-expressing non-small cell lung cancer (NSCLC) patients..

The human T-cell leukemia virus type I (HTLV-I) Tax protein increases the DNA binding activity of a number of different host cell transcription factors, including the cyclic AMP response element binding protein (CREB). We have performed quantitative studies of CREB binding in the presence and absence of Tax in an attempt to gain insight into the mechanism of the Tax effect. Enhancement of binding occurred over a wide range of CREB concentrations, but sharply increased at the lowest concentrations tested. The data are best explained by a two-step binding model where Tax changes the apparent equilibrium constants for both a CREB-CREB dimerization step and a (CREB)2-DNA binding step. We used the model to perform a quantitative analysis of the binding of CREB to DNA that had been mutated at positions flanking the core CREB recognition site. Results suggest that there are altered or more extensive DNA-protein contacts at these positions in the presence of Tax. We also used the model to analyze differences in the interaction of Tax with nonphosphorylated and protein kinase A-phosphorylated CREB protein. There was no significant change in the behavior of CREB upon phosphorylation.