Radiosensitizer effect of wortmannin in radioresistant bladder tumoral cell lines

This work analyzes the effectiveness of wortmannin in boosting the lethality induced by different doses of X-rays, using the colorimetric assay of MTT. Bladder tumoral cell lines differing in radiosensitivity and p53 status were used. Since wortmannin is able to inhibit DNA-dependent protein kinase (DNA-PK) and rejoining of double-strand breaks (DSBs), we have analyzed the constitutive contents and expression after irradiation of the catalytic subunit of DNA-PK (DNA-PKcs) in our cell lines with the aim of explaining the differential effect of wortmannin as radiosensitizer. Considering that DNA-PK is the main protein complex involved in DNA DSB repair, the ability to remove DSBs after irradiation (with or without wortmannin) was evaluated in the different cell lines by the use of pulse-field gel electrophoresis. Our results indicate a higher radiosensitization in the radio-resistant cell line that shows both high constitutive contents of DNA-PKcs and a high rate of DNA repair by the fast component. In contrast, no radiosensitizer effect of wortmannin was observed in the radiosensitive cell line, previously characterized as defective in DSB repair by a low repair fidelity, and - as our results show - with low constitutive contents and later post-irradiation expression of DNA-PKcs. No clear effect related to p53 status of the cell line was observed. These results suggest that high constitutive contents of DNA-PKcs are indicative of radio-resistant phenotypes, and analysis of the expression of this protein could be helpful in the optimal establishment of wortmannin as radiosensitizer in bladder tumoral cell lines.