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Role of integrin alpha v beta 3 in tumor drug resistance and adenovirus mediated gene delivery

Integrins regulate adhesion-dependent growth, survival, and invasion of tumor cells. In particular, expression of integrin αvβ3 is associated with progression of a variety of human tumors. In addition, integrin αvβ3 is a molecule that promotes adenovirus internalization. We have found the upregulation of integrin αvβ3 in human laryngeal carcinoma cells (HEp2) resistant to cisplatin. In order to investigate relationship between integrin αvβ3 expression and cell sensitivity to antitumor drugs we isolated HEp2-derived αvβ3-expressing stable transfectants that were shown to be resistant to cisplatin, mitomycin C and doxorubicin. In αvβ3-expressing stable transfectants we showed increased level of glutathione compared with HEp2 cells and revealed that αvβ3 integrin-mediated drug resistance in HEp2 cells is caused by glutathione-dependent elimination of drug-induced reactive oxidative species. To investigate whether integrin αvβ3-mediated drug resistance represents a general phenomenon, we isolated two tongue squamous carcinoma cells (Cal27)-αvβ3 integrin stable transfectants that were also shown to be resistant to cisplatin, mitomycin C, doxorubicin, and even to etoposide. Surprisingly, Cal27-αvβ3 integrin expressing cells contained equal amount of glutathione implying different resistance mechanism. One option to increase targeting to tumor cells, especially those that express increased expression of integrin αvβ3, is the use of Ad5RGD4C, obtained by incorporation of RGD4C (CDCRGDCFC) motif into the HI-loop of fiber protein. We showed that integrin αvβ3 is an efficient adenovirus internalization receptor of wild type Ad5 and retargeted Ad5RGD4C, but cannot functionally replace αvβ5 in endosomal release. Others have demonstrated that cyclic RGD peptides bind with increased specificity to integrin αvβ3 in comparison with linear analogues. Up until now no one has investigated whether cysteines surrounding RGD targeting motif influence the retargeting potential of Ad5RGD4C. Using biochemical, genetic and spectroscopic methods we have shown that the cysteines surrounding the RGD motif in Ad5 indeed form disulphide bonds crucial for its retargeting potential. Our findings could have clinical importance in terms of identifying integrin αvβ3 as a drug resistance biomarker in tumor cells, as well as a tumor therapy target molecule. In addition, tumor cells that became drug resistant due to the integrin αvβ3 overexpression could be a better target for Ad5RGD4C gene therapy than the initial tumor.

integrin alpha v beta 3; tumor drug resistance; adenovirus

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