Purpose: To study the radiation response-modifying effect of imatinib (Gleevec) in a squamous cell carcinoma line, PECA.
Material and methods: Cytotoxicity was determined by colony forming and multiplying capacity. Drug stability was shown by HPLC. Multidrug resistance phenotype was studied by rhodamine-123 efflux. Cell-cycle responses were measured by flow cytometry. Homologous recombination repair was determined by Rad51 immunohistochemistry.
Results: Inactivating 50% of the PECA cells required approximately 7 microM imatinib. The drug did not decay nor was it degraded during test periods. Drug efflux occurred only to a minor extent. Multiplying capacity but not survival fractions revealed a radioprotective effect of imatinib. There were only minor cell-cycle alterations in the presence of imatinib but the rate of Rad51-positive repair foci was significantly increased.
Conclusion: PECA cells apparently lack a highly specific target for imatinib. In cells surviving at high drug concentrations, imatinib may exert a radioprotective effect on multiplying capacity by inducing DNA repair. Under prolonged exposure, drug-resistant cells may show an accelerated recovery from acute or delayed radiation damage.