Figure 4.

Astrocytes protect melanoma cells from chemotherapy by a mechanism that requires direct physical contact. (A–C) Human melanoma cells were cultured alone or cocultured with GFP-expressing astrocytes (Ast.). After a 72-hour incubation with P-glycoprotein-sensitive (paclitaxel) or -insensitive (5-FU and cisplatin) chemotherapeutic drugs, the cells were harvested and ethanol-fixed, and the apoptotic index of the tumor cells (GFP-negative population) was determined by FACS using the propidium iodide protocol. (C) Physical separation of astrocytes and tumor cells using a transwell membrane (0.4-µm pore size) abolished the protective effect. (D) Astrocytes cultured alone or cocultured with human melanoma cells (TXM13) did not undergo apoptosis after incubation with chemotherapeutic drugs under conditions similar to that described above. (E) Substituting NIH3T3 fibroblasts for astrocytes in (A) and (B) failed to demonstrate protection of tumor cells from chemotherapy. Data are the mean of three experiments. Error bars represent SEM. *P < .01, **P > .05.