Effect Of Pregnane X Receptor (PXR) Expression On Chemotherapeutic Sensitivity To CPT-11

BackgroudsColon cancer is a common gastrointestinal malignancy and chemotherapy is an important treatment for colon cancer.The multidrug resistance of cancer cells is lead to the failure of treatments for colon cancer,so how to reverse multidrug resistance of cancer cells is very important in the treatments for cancers.PXR is an important member of the nuclear receptor superfamily and regulates the expression of CYP3A4、CYP3A5、CYP2B、CYP2C、UGT1A1、GST、P-gp、 MDR1、MRP,et al.As a result,PXR plays an importang role in drug metabolism and multidrug resistance of cancer cells.The present study was designed to investigate the effects of PXR expression changes in human colon cancer cell on chemotherapeutic sensitivity to CPT-11by oberserving the influence of CPT-11on the proliferation of colon cancer cells in which the expression of PXR was downregulated or upregulated.ObjectiveThis study was to observe the influence of CPT-11on the proliferation of the untreated and treated colon cancer cells LS174T in which PXR expression were downregulated or upregulated by sulforaphane or rifampicin, so as to investigate the effects of PXR expression changes in human colon cancer cell on chemotherapeutic sensitivity to CPT-11.MethodsThe protein levels of PXR in human colon cancer cells LS174T, HT29and HCT116were measured by Westernblot and the protein level of PXR in LS174T cells was the highest which was choosen to be further researched.Then, the levels of PXR expression in LS174T cells were downregulated or upregulated by sulforaphane or rifampicin.After being treated with lOμg/mL CTP-11from24h to96h, Cell growth was studied by MTT assay.Results1. The protein levels of PXR in three cells were measured by WesternblotThe protein levels of PXR in human colon cancer cells LS174T、HT29and HCT116were0.6090±0.0865、0.1117±0.0245、0.1023±0.0232, respectively. The protein level of PXR in LS174T cell was the highest and the difference was statistically significant (P=0.000)2. The protein levels of PXR in treated LS174T cell were measured by WesternblotThe protein levels of PXR in LS174T cells treated with sulforaphane and rifampicin were0.0209±0.0136,1.4533±0.1785, respectively,which in untreated LS174T cells was0.5197±0.0914.Compared with untreated group,the protein level of PXR in sulforaphane group was downregulated,the protein level of PXR in rifampicin group was upregulated and the difference was statistically significant (P=0.000)3. The results of MTTAfter being treated with10μg/mL CTP-11from24h to96h,the OD mean of the sulforaphane and rifampicin groups in24、48、72、96h followed as:0.7001±0.137、0.8640±0.1905、1.0123±0.1641、1.3352±0.1366,1.1554±0.2131、1.6020±0.1511、1.9603±0.1317、2.4603±0.1635,respectively,which in untreated groups as:0.8217±0.1676、1.2420±0.1378、1.6193±0.2146、1.9917±0.1622. Compared with untreated groups,the cell proliferation in sulforaphane groups was suppressed,so the chemotherapeutic sensitivity of LS174T cell to CPT-11was significantly increased and the difference was statistically significant (P=0.013), the cell proliferation in rifampicin groups was enhanced, so the chemotherapeutic sensitivity to CPT-11was significantly decreased and the difference was statistically significant (P=0.019)ConclusionAfter downregulation of PXR expression by sulforaphane,the chemotherapeutic sensitivity of colon cancer cells LS174T to CPT-11is increased,by contrast,after upregulation of PXR expression by rifampicin,the chemotherapeutic sensitivity of LS174T cells to CPT-11is decreased.The expression changes of PXR in human colon cancer cell have significant effect on chemotherapeutic sensitivity to CPT-11,and this mechanism may play an important role in multi-drug resistance and reversing multi-drug resistance mechanisms of human colon cancer.