Synergistic Anti-Tumor Effect of Cisplatin When Combined with an Anti-Src Kinase Integrin-Based Peptide

Background: It is known that active Src kinase promotes survival of ovarian cancer cell lines and inhibition of c-Src has been shown to restore sensitivity of drug-resistant human ovarian cancer cells to cisplatin. In this study we examined the effects of a 10 mer peptide on proliferation of human colon and ovarian cancer cells when used alone and in combination with cisplatin. Materials and Methods: A 10 mer peptide, RSKAKNPLYR, derived from a 15 mer ERK2 binding sequence present on the cytoplasmic domain of the β6 integrin subunit was tested for its effect on proliferation of HT29 colon cancer cells under serum-free conditions by means of the MTT assay. Cell proliferation studies to examine the effects of cisplatin combined with peptide were conducted in serum-containing medium using the 10 mer peptide fused to a hydrophobic signal peptide sequence. Drug combination studies were performed on HT29 cells and a cisplatin-resistant cell line (ADDP) derived from an ovarian cancer cell line A2780. The effects of peptides on Src kinase activity were assessed in a cell-free in vitro kinase assay. Results: The 10 mer peptide was as effective as the 15 mer parent compound at inhibiting proliferation of HT29 cells. Exposure of HT29 and ADDP cells to a combination of cisplatin and the fusion peptide resulted in synergistic inhibition of cell growth. Both the 10 mer peptide alone and when fused to the signal peptide sequence inhibited Src kinase activity. Conclusion: Our findings raise the possibility of combination therapy comprising peptide and cisplatin for cisplatin-resistant ovarian cancers and other cancers that are high expressors of c-Src.