Experimental Study On Growth Inhibition And Enhanced Radiation Effect By Selective Cyclooxygenase-2 Inhibitor In Prostate Cancer

Objective To investigate the effect of cyclooxygenase-2 inhibitor NS398 on growth and apoptosis in human prostate cancer cell line PC-3 in vitro. To observe the ability of NS398 on the radiosensitivity of human prostate cancer cell line PC-3 in vitro. To investigate the anti-tumor and radiation-enhancement effects of Celecoxib, a selective of cyclooxygenase-2 inhibitor, in human prostate cancer xenografts. The possible mechanisms of those effects were investigated in this study.Methods The proliferative inhibition of PC-3 cells was observed by methyl thiazol tetrazolium(MTT)rapid photocolorimetric assay;the expression of COX-2 mRNA in cultured PC-3 cells was examined by RT-PCR;the release levels of PGE2 was measured by enzyme linked immunosorbent assay(ELISA);PC-3 cells cultured in different concentrations of NS398 medium for 24h were marked with Annexin V-FITC and PI for the cell apoptosis assay by flow cytometry.PC-3 cell, highly expressing COX-2, had been incubated with NS398 at 0,10,100μmol/L for 24h before irradiation from 0 to 10Gy. Cell survival was measured by a standard clonogenic assay after 14 days of incubation.Suspension of PC-3 cells was injected into the right thigh of BALC/C male nude mice to make xenografts, and the xenografts were also cyclooxygenase-2 positive. The mice bearing tumors were divided into four groups: the control group, the group with Celecoxib alone, the group with radiation alone, the group with both celecoxib and radiation. The tumors were measured in the longest diameter everyday to calculate the tumor growth delay. The tumor tissues were taken out to detect the changes of cyclooxygense-2 mRNA by RT-PCR and prostaglandin E2 by ELISA. Results After treated with different concentrations of NS398,the inhibitory rate on proliferation increased with the increasing concentration and days. The expression of COX-2 mRNA and the release levels of PGE2 were decreased compared with control group.PC-3 cells cultured in 100,200μmol/L NS398 medium for 24h had significantly higher incidence of apoptosis.NS398 displayed radiosensitizing effect in PC-3 cells when at 100μmol/L of NS398 for 24h pre-incubation. The sensitation enhancement ratios(ratio of Dq) in PC-3 cell were 0.21 at 100μmol/L. While 0.99 at 10μmol/L of 24h pre-incubation, it did not displayed any radiosensitizing effect in PC-3 cells.The time that the longest diameters of all tumors grew from 8mm to 12mm was (6.18±0.72)d in the control group, (7.87±0.70)d in the group with celecoxib alone, (10.29±0.98)d in the group with radiation alone, (12.62±1.28) in the group combination both celecoxib and radiation. Analysis of variance showed that there was no significant difference in cyclooxygense-2 mRNA among these four groups. Prostaglandin E2 levels(pg/100mg) of tumors tissues were 68.4±10.2,29.7±8.2, 46.3±9.4,43.6±12.7,respectively contrast with control group(P<0.05).But Prostaglandin E2 levels in the group with radiation alone and in combination group had not significant difference(P>0.05).Conclusions NS398, a COX-2 inhibitor, can inhibit proliferation of human prostate cancer cell line PC-3 and induce its apoptosis in vitro,which may contributed to the COX-2 dependent pathway. NS398 can enhance the radiosensitivity of human prostate cancer cell line PC-3. Cyclooxygense-2 mRNA was not affected by celecoxib and 10Gy single dose irradiation, but prostaglandin E2 levels decreased. The fall of prostaglandin E2 may be a reason of the tumor growth delay by celecoxib.