[Involvement of bcl-2 in multidrug resistance in human small cell lung cancer cell subline H446/DDP]

To study the mechanism of bcl-2 involvement in multidrug resistance in human small cell lung cancer (SCLC) cell subline H446/DDP.

After the construction of pLXSN-bcl-2, in which the full length of bcl-2 cDNA amplified from total RNA of H446/DDP cells was integrated into the mammalian expression vector pLXSN, allowing transcription of a bicistronic mRNA, and the synthesis in vitro of 20-mer ODNs targeting the coding region of bcl-2 mRNA and the scrambled ODNs used as the control, the cationic lipid DOTAP was used to transfect them into H446 and H446/DDP cells, respectively. When H446 cells were transfected with mammalian expression vector pLXSN, the cells were divided into 3 groups, including cells transfected with the recombinant pLXSN-bcl-2, cells transfected with the vector pLXSN and cells untransfected (control); when H446 cells and H446/DDP cells were transfected with PS-ODNs, the cells were divided into 3 groups, including cells transfected with AS-PS-ODNs, cells transfected with NS-PS-ODNs and cells untransfected (control), respectively. After transfection, Western blot were carried out to detect the expression level of bcl-2 in the control cells and the transfected cells, respectively. Meanwhile flow cytometry (FCM) was used to detect cell apoptosis in the control cells and the transfected cells.

(1) The data from Western blot showed that compared with the control H446 cells (gray-scale value 0.103 +/- 0.005), the expression level of bcl-2 in the pLXSN-bcl-2 transfected H446 cells (gray-scale value 0.854 +/- 0.016) was increased significantly (P < 0.01); and the apoptosis from DNA content analysis decreased significantly in the pLXSN-bcl-2 transfected H446 cells [(20.9 +/- 0.2)%] compared with that of the control H446 cells [(31.1 +/- 0.2)%] by DNA content analysis (P < 0.01). (2) The results from Western blot showed that bcl-2 expression in the AS-PS-ODNs transfected H446/DDP cells (gray-scale value 0.695 +/- 0.014) was significantly reduced compared with that of the control H446/DDP cells (gray-scale value 0.942 +/- 0.018), although not totally reduced to the level of the control H446 cells (P < 0.01); and the data from DNA content analysis indicated that the sensitivity of the AS-PS-ODNs transfected H446/DDP cells to 5 microg/ml DDP-induced apoptosis was strongly increased as compared with that of the control H446/DDP cells (P < 0.01).

Targeting to inhibit antiapoptotic mitochondrial gene Bcl-2 expression may be one of the important therapeutic approaches to overcoming chemoresistance in human SCLC.