Modulation of apoptosis and enhancement of chemosensitivity by decreasing cellular thiols in a mouse B-cell lymphoma cell line that overexpresses bcl-2

Purpose: To determine whether the difference in the apoptosis and clonogeni c survival responses to radiation observed between the murine lymphoma cell lines LY-ar, which expresses bcl-2, and LY-as, which does not, was also ev ident after treatment with chemotherapy agents; and to determine whether cl onogenic survival after chemotherapy agent exposure could be diminished by enhancing apoptosis through a decrease in cellular thiols. Methods: Cells w ere treated with cisplatin, VP-16, or Adriamycin, and apoptosis was determi ned using a DNA fragmentation assay. Cellular survival was quantified by li miting dilution assay, Intracellular thiols were decreased by maintaining L Y-ar cells in cystine/methionine-free medium (CMF medium) for 7 h after dru g treatment. Results: LY-as cells were approximately four times more likely to undergo apoptosis than LY-ar cells, having differences in apoptosis of 80% and 20%, respectively, for the agents used. LY-as cells were also more sensitive as measured by cellular survival, with a dose-modifying factor of about 1.8 measured at a 10% survival level. Incubation of LY-ar cells in C MF medium after drug treatment increased apoptosis and reduced clonogenic s urvival to the levels seen in LY-as cells, except after treatment with VP-1 6, where the reduction in cell survival was more modest. Conclusions: Decre asing intracellular thiols enhances apoptosis and cell killing in lymphoma cells after exposure to a variety of chemotherapy agents. This may be espec ially true for tumor cells that overexpress bcl-2, a gene that modifies cel lular thiol status and conveys resistance to apoptosis. In this case, decre asing cellular thiols allows killing independent of the expression of bcl-2 .