The combination of gamma ionizing radiation and 8-Cl-cAMP induces synergistic cell growth inhibition and induction of apoptosis in human prostate cancer cells

The antiproliferative and cytotoxic potential of the nucleotide analog 8-Cl-cAMP was tested in PC-3 and DU145 metastatic human prostate cancer cells. The drug was examined as the only therapeutic agent and in combination with ionizing irradiation (IR). Highly synergistic effects of IR and 8-Cl-cAMP were observed in both cell lines when examined by the MTT viability and BrdU proliferation assays. The combination of IR and 8-Cl-cAMP at clinically relevant doses exerted substantial growth inhibition. The combination of IR and 8-Cl-cAMP caused a significant disturbance in the distribution of cell cycle phases. Cell cycle arrest in the sub-G0/G1 phase predominated in both cell lines. The most striking observation was a significant increase in apoptotic PC-3 and DU145 cells. The DU145 cells were three times more sensitive to the combined treatment than PC-3 cells. The initial resistance to IR-induced apoptosis in these p53-deficient prostate cancer cell lines was overcome through an alternative proapoptotic pathway induced by 8-Cl-cAMP. Considering the low effective doses of treatments, improved tumor eradication rates and minimal undesirable side effects, the combination of IR and 8-Cl-cAMP could be the therapy of choice in treating prostate cancer.