The Effect of the Combined Action of Roscovitine and Paclitaxel on the Apoptotic and Cell Cycle Regulatory Mechanisms in Colon and Anaplastic Thyroid Cancer Cells
Aim. To study the significance of cyclin-dependent kinases (Cdks) in paclitaxel-dependent apoptosis in colon and undifferentiated thyroid cancer cells. Materials and Methods. Experiments were performed on undifferentiated thyroid carcinoma (KTC-2) and colon carcinoma (ARO) cell lines. Cells were treated with paclitaxel (Ptx) and inhibitor of Cdk, roscovitine. Cell survival test and Western blotting were used for characterization of the effects of paclitaxel and roscovitine on cancer cells. Results. It was shown that not c-Jun N-terminal kinase, but cyclin-dependent kinases are responsible for antiapoptotic Bcl-2 phosphorylation. Cdk inhibition enhanced the cytotoxic effects of Ptx at low drug concentrations. There was antagonism between Ptx and roscovitine at higher (25？nM) paclitaxel concentrations. Conclusion. Using of paclitaxel at low (2.5 to 5？nM) concentrations and roscovitine is a promising combination for further preclinical trials for the development of new therapeutic approaches to the treatment of colon and anaplastic thyroid cancer. 1. Introduction Compounds that stabilize microtubules (MSA), which include taxanes (paclitaxel, docetaxel), are effective anticancer drugs. It is known that the therapeutic effect of these drugs is associated with cell cycle arrest, followed by initiation of apoptotic processes [1]. However, the exact mechanism that links cell division impairment with apoptosis induced by drugs is still poorly understood. The mammalian cell cycle is controlled by cyclin-dependent kinases, whose activity is modulated by several activators and inhibitors [2]. Cdks are serine/threonine kinases that play a key role in regulating both cell cycle and transcription through the phosphorylation of transcription factors and tumor suppressor proteins involved in DNA replication and cell division [2]. The Cdk modulators include a 2, 6, 9-substituted purine analogue, roscovitine (CYC202), which inhibits Cdk activity directly by competing for the ATP-binding sites of Cdk and causing apoptosis within various tumor cells. A study of clinical utility of roscovitine showed its anticancer effects and limited toxicity for humans in clinical trials [3]. The aim of this study was to establish a connection between the effect of paclitaxel on cell cycle and induction of apoptotic processes in colon (CC) and anaplastic thyroid cancer (ATC) cell lines ARO and KTC-2. 2. Materials and Methods 2.1. Cell Lines and Conditions of Culturing ATC cell lines KTC-2 were established at Kawasaki Medical School (Okayama, Japan). Human cancer cell line ARO (initially
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