PIM2 chinasi è indotta dal cisplatino e limita l'efficacia del farmaco in cellule di cancro ovarico

Cisplatin is a powerful anticancer drug, used in the treatment of many tumors since 1970. The mechanism of action is based on adducts formation in DNA strands. Platinum-based chemotherapy is widely used to treat various kinds of cancer, but many patients ultimately relapse due to drug resistance. Moreover the feasibility of the treatment is often limited by the severe side effects that prevent the use of effective concentration of platinum drugs. Therefore, to find a strategy to lower the concentration of platinum in therapy and to develop a method to overcome resistance is crucial in modern research. In the laboratory where I worked for my thesis project phosphoproteomic data had been obtained with SILAC technology, in order to identify kinases induced or repressed by cisplatin treatment in the ovarian cancer cell line SK-OV-3. PIM2 was identified among kinases likely to be involved, and came out to be the most interesting not only because its role in CDDP response of ovarian cancer cells has never been described but also because it is "druggable". PIM kinases are described as weak oncogenes and they have been found upregulated in several hematological malignances. Thus, my work was focused on the role of PIM2 kinase in the response of ovarian cancer cells to CDDP, at first by validating PIM2 induction by CDDP at the protein and mRNA level with western blots and real-time quantitative PCRs, respectively, in several ovarian cancer cell lines. Then functional assays were carried out to study the role of PIM2 kinases in the response of ovarian cancer cells to the drug. A pan-PIM inhibitor was used to assess whether PIMs inhibition sensitizes cell to CDDP. A reduced cell growth could be detected in ovarian cancer cells treated with the drug. Moreover, an increased effectiveness of CDDP in malignant cells that received CDDP and PIMs-inhibitor could be observed. These results were confirmed overexpressing PIM2 and observing a decreased CDDP effectiveness. Many evidences in literature suggest that PIM kinases protect cells from apoptosis by direct phosphorylation of BAD on Ser75. Accordingly, a decreased BAD phosphorylation on Ser75 was observed in cells treated with pan-PIM inhibitors, as well as an increased BAD phosphorylation in cells overexpressing PIM2. PIM2 was silenced using shRNA, again, an increased CDDP effectiveness both in limiting cell growth and in increasing apoptosis was demonstrated. Finally, impaired colony formation and cell growth in semisolid medium were seen in PIM2-silenced cells. This suggests that PIM inhibition could be an effective approach also in in-vivo studies and in therapy. In conclusion we demonstrated that PIM2 expression is induced by cisplatin in several ovarian cancer cell lines and that its inhibition could be an effective and amenable strategy to lower platinum drugs concentration in ovarian cancer therapy, since several inhibitors are undergoing clinical trials.