| Objective: Diminished apoptosis play a critical role in tumor initiation, progressin,and grug resistance .Several proteins that inhibit apoptosis have been identified,including bcl-2family members bcl-2 and bcl-xL and the IAPS.Certain members of the latter family directly inhibit terminal effctor caspases engaged in the execution of cell death .The Survivin gene is expressed in the G2-M phase in a cell -regulated manner ,and its interaction with the mitotic spindle apparatus is essential for antiapoptotic function,its overexpression in tumors is implicated in the resistance to a variety of apoptotic stimuli,including chemotherapy.An in vitro study of the combined cytotoxicity of cisplatin (CDDP)and selenium dioxide was undertaken on a set of different ovarian carcinoma (COC1,COCI/DDP)cell lines so as to investigate possibility of overcoming the cisplatin resistance in human ovarian carcinoma cell line COC1/DDP induced by selenium dioxide (SeO2) and its probable mechanism.Methods :Growth inhibitions of cisplatin-sensitive human ovarian cancer cell(COC1) and cisplatin-resistant cell (COC1/DDP) induced by either selenium dioxide combined with cisplatin or selenium dioxide alone were measured by means of MTT in vitro .Apoptosis of COC1/DDP cell line induced by either selenium dioxide combined with cisplatin or selenium dioxide alone were determined by means of flow cytometry /electronic microscope. The expression of Survivin-an inhibitor of apoptosis protein in COC1/DDP cell line was detected by means of flow cytometry. Result: (1) Selenium dioxide-an selenium compound has significant anticarcinogenic activity. The growth inhibitions of COC1,COC1/DDP cell line induced by selenium dioxide alone were enhanced in dose-dependent pattern. Either the efficiency of 15 umol/L selenium dioxide or that of 30 umol/L selenium dioxide was similar to that of 10ug/ml cisplatin . The efficiency of 10 umol/L selenium dioxide is lower than that of 10ug/ml cisplatin. The inhibition rate in COC1 cell line is markedly higher than that in COC1/DDP cell line in the presence of each concentration of selenium dioxide . Taking into account the cytotoxicity of selenium dioxide itself, 10 umol/L appears to be the optimal concentration .(2) In all cases,the inhibition rates of COC1/DDP cell line induced by combined selenium dioxide and cisplatin ranged from 65%(SeO2+24h+DDP group) to79%(DDP+24h+SeO2 group and SeO2+DDP grpup),and that of the latter tow group was similar(P>0.05).(3)Compared with the control group (VRP +24h+DDP group),the inhibition rates of tow group (SeO2+DDP group ,DDP+24h+SeO2 group)were greatly higher than that of the former(P<0.05),whereas the inhibition rates of SeO2+24h+DDP group is similar to that of the control group (P>0.05). The SeO2-DDP associatiation is very efficient for the recovery of chemosensitivity in COC1/DDP. (4) Results obtained from flow cytometry showed that apoptosis rate of the test group ranged from 30.66%±2.34%(SeO2+DDP group),14.44%±6.31%(SeO2+24h+DDP group),15.84%±2.31%( only SeO2 group)to 8.54% ±2.31%(only DDPgroup),and that of the test group(SeO2+24h+DDP group) and another test group (only SeO2 group)were similar (P>0.05)(5)Electronic microscope confirmed apoptosis in COC1/DDP cells treated with either selenium dioxide combined with cisplatin or only selenium dioxide.(6) Results obtained from flowcytometry showed the expression of Survivin protein in the test group (SeO2+DDP group) was decreased from4.29% (the control group)to 0.64%.That of the test group (SeO2+24h+DDPgroup) was 1.116%,that of the test group treated only with SeO2( 1.57% )was similar to that of the test group treated only with cisplatin (2.01%)(P>0.05). Conclusion: In vitro slelnium dioxide alone has anticarcinogenic activity and can inhibit the growth of ovarian carcinoma (COC1 ,COCI/DDP)cell lines .Selenium dioxide can increase the sensitivity of COC1/DDP cell line to cisplatin and its efficiency of recovery of chemosensitivity to cisplatin was far more higher than that of VRP . Selenium dioxide (10umol/L) alone can induce apoptosis in ovarian carcinoma (COCI/DDP)cell lines. Our results show that the SeO2(10umol/L)-DDP association is more efficient in inducing apoptosis .The expression level of Survivin protein in COC1/DDP cell line is 4.29% .Our results comfirm that the high expression of Survivin protein play a critical role in the cisplatin resistance in human ovarian carcinoma cell line COC1/DDP . Selenium dioxide (10umol/L) alone could down-regulate Survivin protein expression level in COC1/DDP cell line. SeO2(10umol/L)-DDP association is more efficient in down-regulating Survivin protein expression level in COC1/DDP cell line.The mechanism of the recovery of chemosensitivity in COC1/DDP induced by selenium dioxide may correlate with down-regulation of Survivin protein expression level.
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