nitrophenols and Carcinoma--Small-Cell

Bcl-2 is a central regulator of cell survival that is overexpressed in the majority of small cell lung cancers (SCLC) and contributes to both malignant transformation and therapeutic resistance. We compared primary SCLC xenografts prepared from de novo human tumors with standard cell line-based xenografts in the evaluation of a novel and highly potent small molecule inhibitor of Bcl-2, ABT-737. ABT-737 induced dramatic regressions in tumors derived from some SCLC cell lines. In contrast, only one of three primary xenograft SCLC tumors showed significant growth inhibition with ABT-737. Explanations for this apparent dichotomy may include relatively low expression of Bcl-2 in the primary xenografts or inherent differences in the model systems. The addition of etoposide to ABT-737 in the primary xenografts resulted in significant decreases in tumor growth, underscoring the clinical potential of ABT-737 in combination therapy. To identify factors that may contribute to resistance to ABT-737 and related inhibitors, we isolated resistant derivatives of an initially sensitive cell line-based xenograft. Acquired resistance in this model was associated with decreases in the expression of the primary target Bcl-2, of proapoptotic partners of Bcl-2 (Bax and Bim), and of Bcl-2:Bim heterodimers. Expression profiling reveals 85 candidate genes demonstrating consistent changes in gene expression with acquired resistance. Taken together, these data have specific implications for the clinical development of Bcl-2 inhibitors for SCLC and broader implications for the testing of novel anticancer strategies in relevant preclinical models.

Topics: Animals; Antineoplastic Agents; Antineoplastic Combined Chemotherapy Protocols; Biphenyl Compounds; Carcinoma, Small Cell; Caspase 3; Cell Line, Tumor; Drug Resistance, Neoplasm; Drug Synergism; Enzyme Activation; Etoposide; Humans; Lung Neoplasms; Mice; Mice, Nude; Nitrophenols; Piperazines; Proto-Oncogene Proteins c-bcl-2; Sulfonamides; Xenograft Model Antitumor Assays

ABT-737 is a subnanomolar inhibitor of the antiapoptotic proteins Bcl-2, Bcl-X(L) and Bcl-w. Although ABT-737 triggers extensive cell death in many small-cell lung carcinoma (SCLC) cell lines, some of the SCLC cell lines and the majority of the cancer cell lines derived from other solid tumors were found to be resistant to ABT-737. To better understand the mechanism of resistance to ABT-737, we screened a short interfering RNA library consisting of short interfering RNA against 4000 'druggable' targets in an SCLC-derived cell line, NCI-H196. By comparing the knockdowns with phenotypes, all of the three top 'hits' from the screen were found to result from off-target gene silencing. Interestingly, the three off-target siRNAs were found to knock down an antiapoptotic Bcl-2 family protein Mcl-1 owing to the complementation between their seed regions with the 3' untranslated region (3' UTR) of Mcl-1. Furthermore, reducing the level of Mcl-1 using siRNAs or the small-molecule compounds Bay43-9006 and Seliciclib was sufficient to overcome the resistance to ABT-737 in the resistant SCLC cell line and cancer cell lines derived from other solid tumors. These results provide further evidence that Mcl-1 is the major factor that causes resistance to ABT-737 in cancer cells derived from diverse solid tumors, and the combination of Mcl-1 downregulating agents with ABT-737 could be potent therapeutic regimens for patient with ABT-737-resistant SCLC and many other types of solid tumors.

Topics: 3' Untranslated Regions; Antineoplastic Agents; Base Sequence; bcl-X Protein; Benzenesulfonates; Biphenyl Compounds; Blotting, Western; Carcinoma, Small Cell; Cell Line, Tumor; Cell Survival; DNA-Binding Proteins; Drug Resistance, Neoplasm; Humans; Lung Neoplasms; Myeloid Cell Leukemia Sequence 1 Protein; Neoplasm Proteins; Niacinamide; Nitrophenols; Phenylurea Compounds; Piperazines; Proto-Oncogene Proteins c-bcl-2; Purines; Pyridines; Receptor, Fibroblast Growth Factor, Type 2; RNA Interference; RNA, Small Interfering; Roscovitine; Sorafenib; Sulfonamides; Transmembrane Activator and CAML Interactor Protein; Zinc Fingers

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.

Topics: Antineoplastic Combined Chemotherapy Protocols; Apoptosis; Apoptosis Regulatory Proteins; Bcl-2-Like Protein 11; Biphenyl Compounds; Carboplatin; Carcinoma, Small Cell; Cell Growth Processes; Cell Line, Tumor; Down-Regulation; Drug Synergism; Etoposide; Humans; Lung Neoplasms; Membrane Proteins; Myeloid Cell Leukemia Sequence 1 Protein; Neoplasm Proteins; Nitrophenols; Piperazines; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-bcl-2; RNA, Small Interfering; Sulfonamides; Transfection; Up-Regulation

Proteins in the Bcl-2 family are central regulators of programmed cell death, and members that inhibit apoptosis, such as Bcl-X(L) and Bcl-2, are overexpressed in many cancers and contribute to tumour initiation, progression and resistance to therapy. Bcl-X(L) expression correlates with chemo-resistance of tumour cell lines, and reductions in Bcl-2 increase sensitivity to anticancer drugs and enhance in vivo survival. The development of inhibitors of these proteins as potential anti-cancer therapeutics has been previously explored, but obtaining potent small-molecule inhibitors has proved difficult owing to the necessity of targeting a protein-protein interaction. Here, using nuclear magnetic resonance (NMR)-based screening, parallel synthesis and structure-based design, we have discovered ABT-737, a small-molecule inhibitor of the anti-apoptotic proteins Bcl-2, Bcl-X(L) and Bcl-w, with an affinity two to three orders of magnitude more potent than previously reported compounds. Mechanistic studies reveal that ABT-737 does not directly initiate the apoptotic process, but enhances the effects of death signals, displaying synergistic cytotoxicity with chemotherapeutics and radiation. ABT-737 exhibits single-agent-mechanism-based killing of cells from lymphoma and small-cell lung carcinoma lines, as well as primary patient-derived cells, and in animal models, ABT-737 improves survival, causes regression of established tumours, and produces cures in a high percentage of the mice.

Topics: Animals; Antineoplastic Agents; Apoptosis; Biphenyl Compounds; Carcinoma, Small Cell; Cell Line, Tumor; Cytochromes c; Disease Models, Animal; Drug Synergism; Humans; Lymphoma; Magnetic Resonance Spectroscopy; Mice; Mitochondria; Models, Molecular; Neoplasms; Nitrophenols; Paclitaxel; Piperazines; Proto-Oncogene Proteins c-bcl-2; Structure-Activity Relationship; Sulfonamides; Survival Rate