bms-387032 and Carcinoma--Non-Small-Cell-Lung

In solid tumors, including non-small cell lung carcinomas (NSCLC) the existence of radioresistant subpopulations, such as quiescent or hypoxic tumor cells, is well established, thus posing a critical therapeutic problem. Although small-molecule inhibitors targeting cyclin-dependent kinases (CDK) were demonstrated to enhance cellular radiosensitivity preferentially in proliferating tumor cells, cell cycle-independent activities of these substances were recently suggested. In this study, the potential of a newer generation small-molecule CDK inhibitor, SNS-032, to sensitize radioresistant tumor cells to ionizing radiation was tested in vitro using two NSCLC cell lines (NCI-H460 and A549). Exposure of quiescent and hypoxic lung tumor cells to SNS-032 at a clinically achievable concentration (500 nM) prior to irradiation resulted in a significant increase in cellular radiosensitivity indicating cell cycle-unrelated mechanisms. The effect of SNS-032 on non-cycling cells was not attributed to an enhanced toxicity of the drug. A SNS-032 mediated delay in the resolution of radiation-induced gammaH2AX foci a surrogate for DNA double-strand breaks was determined in non-cycling cells, suggesting a modulation of DNA double-strand break repair. These results indicate a modulation of DNA double-strand break repair to be partially attributed to the radiosensitization effects of SNS-032 observed in hypoxic and quiescent lung tumor cells. Considering the importance of therapy resistance for the radiocurability of solid tumors, our findings may provide the basis for an improvement of the well-established treatment regimens in clinical oncology.

Topics: Antineoplastic Agents; Carcinoma, Non-Small-Cell Lung; Cell Cycle; Cell Hypoxia; Cell Line, Tumor; Cyclin-Dependent Kinases; Humans; Lung Neoplasms; Oxazoles; Radiation Tolerance; Thiazoles

Overexpression of cyclooxygenase-2 (COX-2) is frequently observed in several human cancers, including lung, colon, and head and neck. Malignancies are also associated with the dysregulation of cell cycle events and concomitant elevated activity of cyclin-dependent kinases (CDK). CDK2 is a key cell cycle regulatory protein that controls the transition of cells from G(1) to S phase. In this study, we furnish several lines of evidence that show a functional role for the CDK2 in interleukin-1beta (IL-1beta)-induced COX-2 expression in H358 human non-small cell lung carcinoma cell line by blocking CDK2 activity. First, we show that BMS-387032, a potent CDK2 inhibitor, blocks IL-1beta-induced expression as well as steady-state mRNA levels of COX-2. Second, we show that small interfering RNA that abrogates CDK2 expression also blocks IL-1beta-induced COX-2 expression. Third, results from in vitro kinase assays clearly show that IL-1beta induces CDK2 activity in H358 cells and this activity is significantly inhibited by BMS-387032. Moreover, CDK2 inhibition blocks IL-1beta-induced binding to the NF-IL6 element of the COX-2 promoter and inhibits transcription of the COX-2 gene. We also observed that BMS-387032 does not inhibit endogenous expression of COX-2 or prostaglandin synthesis in lung carcinoma cells. Finally, we provide evidence showing that IL-1beta-induced signaling events, such as p38 mitogen-activated protein kinase, phosphorylated stress-activated protein kinase/c-Jun NH(2)-terminal kinase, phosphorylated AKT, and phosphorylated extracellular signal-regulated kinase 1/2, are not inhibited by CDK2 inhibitor. Taken together, the data suggest that CDK2 activity may play an important event in the IL-1beta-induced COX-2 expression and prostaglandin E(2) synthesis and might represent a novel target for BMS-387032.

Topics: Carcinoma, Non-Small-Cell Lung; CCAAT-Enhancer-Binding Proteins; Cell Line, Tumor; Cyclin-Dependent Kinase 2; Cyclooxygenase 2; Dinoprostone; Down-Regulation; Enzyme Induction; Gene Expression Regulation, Enzymologic; Gene Expression Regulation, Neoplastic; Humans; Interleukin-1; Lung Neoplasms; Oxazoles; Promoter Regions, Genetic; RNA, Messenger; RNA, Small Interfering; Signal Transduction; Thiazoles; Transcription, Genetic; Transfection

E2F1 and E2F4 are known to have opposing roles in cell cycle control. In the present work, we examine the role of both E2F1 and E2F4 in apoptosis induced by three cyclin-dependent kinase inhibitors (roscovitine, BMS-387032, and flavopiridol) as well as by three established chemotherapeutic drugs (VP16, cisplatin and paclitaxel). We find that E2F4 levels are diminished following treatment with cyclin dependent kinase inhibitors (flavopiridol, roscovitine and BMS-387032) or with DNA damaging drugs (cisplatin and VP16). In contrast, each of these drugs induced E2F1. We find that mouse fibroblasts nullizygous for the E2F4 gene are more sensitive to apoptosis induced by roscovitine, flavopiridol, cisplatin, and VP16, whereas E2F1-deficient fibroblasts are less sensitive. Likewise, we find that RNAi-mediated reductions in E2F4 in human cancer cells results in increased drug sensitivity. Taken together, these results support a model in which E2F1 and E2F4 play opposing roles during drug-induced apoptosis.

Topics: Animals; Antineoplastic Agents; Apoptosis; Breast Neoplasms; Carcinoma, Non-Small-Cell Lung; Cell Cycle Proteins; DNA-Binding Proteins; E2F Transcription Factors; E2F1 Transcription Factor; E2F4 Transcription Factor; Fibroblasts; Flavonoids; Humans; Lung Neoplasms; Mice; Mice, Knockout; Oxazoles; Piperidines; Protein Kinase Inhibitors; Purines; RNA, Small Interfering; Roscovitine; Thiazoles; Transcription Factors; Tumor Cells, Cultured