Figure 5.

Chemoprotection requires constant contact with astrocytes. (A) The apoptotic index of PC14Br₄ cells cultured with astrocytes was 30.9% ± 3.3%, and with fibroblasts, it was 54.6% ± 0.6% (P > .01). Tumor cells initially cultured with astrocytes were harvested and reincubated with astrocytes or fibroblasts in the presence of taxol for another 72 hours. Tumor cells cocultured again with astrocytes maintained the relative resistance to taxol compared with tumor cells cocultured (second cycle) with fibroblasts. Tumor cells initially cultured with fibroblasts were not resistant to taxol, but if these tumor cells were then reincubated (second cycle) with astrocytes, they developed resistance compared with tumor cells cultured again with fibroblasts. (B) Gene expression of BCL2L1, GSTA5, and TWIST1 was determined in PC14Br₄ cells cultured with astrocytes or fibroblasts. Similar to data shown in Figure 3, the survival genes were highly expressed in tumor cells cocultured with astrocytes but not with fibroblasts (first cycle). We harvested surviving tumor cells and cocultured them for the second cycle with either astrocytes or fibroblasts. Once again, only tumor cells cocultured with astrocytes (second cycle) expressed higher levels of BCL2L1, GSTA5, and TWIST1.