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Objective: An important issue in cancer therapy is to investigate the mechanism for cellular sensitivity to anticancer agents such as cisplatin. Cisplatin is one of the DNA-damaging agents and several factors including p53 are related to the sensitivity to cisplatin in cancer. Protein kinase C (PKC) δ is known as a positive regulator for cisplatin-induced cell death. In our present study, we examined whether overexpression of PKCδ and p53 increases the sensitivity of the human gastric cancer cell line, MKN28, which has a mutation of p53 gene, to cisplatin. Methods: Cell viability and DNA content were measured in MKN28 with adenovirus-mediated expression of PKCδ and p53 after exposure to cisplatin. In addition, the active form of caspase-3 was detected by Western blotting. Results: Overexpression of exogenous PKCδ did not induce cell death in MKN28 but inhibited cell growth at 1 µg/ml cisplatin as compared to that by cisplatin alone. Moreover, overexpression of both wild-type p53 and exogenous PKCδ in MKN28 increased cisplatin-induced cell death in MKN28. Conclusion: These results suggest that PKCδ, in cooperation with p53, possibly regulates cisplatin-induced caspase-3-mediated cell death in gastric cancer.

Integrins have become a target for novel therapeutic strategies against malignant gliomas. Cilengitide, a synthetic Arg-Gly-Asp (RGD)-motif peptide, interferes with ligand binding to avb3 and avb5 integrins and is currently investigated in clinical trials. Integrins may also be involved in the activation of transforming growth factor (TGF)-b, a mediator of invasiveness and immune escape of glioma cells. Using flow cytometry, we demonstrate that the target integrins of cilengitide are expressed not only in glioblastoma blood vessels, but also by tumor cells. After exposure of glioma cells to cilengitide, we noticed reduced phosphorylation of Smad2 in most glioma cell lines, including stem-like glioma cells. Phophorylation of Smad2, but not cilengitide-induced detachment, is rescued by addition of recombinant TGF-b. Administration of cilengitide to glioma cells results in reduced TGF-b-mediated reporter gene activity. Furthermore, exposure to cilengitide leads to decreased TGF-b 1 and TGF-b 2 mRNA and protein expression. These effects are mimicked by blocking av, b3 or b5 antibodies or by silencing of integrins av, b3, b5 or b8 using RNA interference. Treatment of mice bearing experimental LN-308 glioma xenografts with cilengitide results in reduced pSmad2 levels. Taken together, cilengitide may exert anti-invasive and immune stimulatory activity in human glioblastoma patients by its anti-TGF-b properties.

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