Roscovitine Modulates DNA Repair and Senescence: Implications for Combination Chemotherapy

Abstract

Purpose: Treatment of tumor cells by chemotherapy activates a series of responses ranging from apoptosis to premature senescence and repair. Survival responses are characterized by inhibition of cyclin-dependent kinases. Because inhibition of cyclin-dependent kinases represents a distinctive feature of DNA damage^induced prosurvival responses, we investigated the possibility that the cyclin-dependent kinase inhibitor roscovitine modulates drug-induced responses in human adenocarcinoma cells, favoring cell survival. Experimental Design: Sublethal concentrations of doxorubicin were used to induce premature senescence in human adenocarcinoma cells. The effect of the cyclin-dependent kinase inhibitor roscovitine on the doxorubicin-dependent cell cycle checkpoint activation and DNA repair pathways was evaluated. Results: Roscovitine reinforces doxorubicin-dependent G 1 checkpoint in A549 and HEC1B cells leading to decreased frequency of double-strand breaks and to the preferential induction of senescence and enhanced clonogenic survival. However, in other tumor cell lines, such as HCT116 and H1299, combined treatment with doxorubicin and roscovitine increases the frequency of doublestrand breaks and dramatically sensitizes to doxorubicin. This unexpected effect of roscovitine depends on a novel ability to inhibit DNA double-strand break repair processes and requires inactivation of the pRb pathway. Conclusions: Roscovitine, by hindering DNA repair processes, has the potential to inhibit recovery of mildly damaged tumor cells after doxorubicin treatment and to increase the susceptibility of tumor cells to chemotherapy. However, in some tumor cells, the cell cycle inhibitory function of roscovitine prevails over the DNA repair inhibitory activity, favoring premature senescence and clonogenic growth. These data indicate a novel mechanism underlying combined chemotherapy, which may have wide application in treatment of carcinomas.Chemotherapy is the primary form of treatment for human cancer. Conventional anticancer drugs damage several cellular components, triggering a series of cellular responses. At high doses of these drugs, the predominant effect is cell death, whereas at low doses tumor cells may repair damage and eventually resume normal proliferation (1). Cell death after DNA damage is largely the result of apoptosis, and accordingly, apoptosis is a key determinant of treatment outcome (2). However, although apoptosis represents the main response to chemotherapy in hematologic malignancies, the outcome of therapy in solid tumors does not correlate with the extent of programmed cell death (3). In solid tumors, treatment does not lead to tumor regression but rather results in so-called stable disease. The cytostatic effect of chemotherapeutic agents results from the activation of a premature senescence program (1). Accordingly, treatment of tumor cell lines with low doses of DNA-damaging agents readily induces features of senescence (4). More importantly, the induction of a senescent-like phenotype by anti...

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The Cyclin-Dependent Kinase Inhibitor Flavopiridol Potentiates the Effects of Topoisomerase I Poisons by Suppressing Rad51 Expression in a p53-Dependent Manner

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R-Roscovitine simultaneously targets both the p53 and NF-κB pathways and causes potentiation of apoptosis: implications in cancer therapy

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