Modulation of apoptosis and enhancement of chemosensitivity by decreasing cellular thiols in a mouse B-cell lymphoma cell line that overexpresses bcl-2.
OBJECTIVE
To determine whether the difference in the apoptosis and clonogenic 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 evident after treatment with chemotherapy agents; and to determine whether clonogenic survival after chemotherapy agent exposure could be diminished by enhancing apoptosis through a decrease in cellular thiols.


METHODS
Cells were treated with cisplatin, VP-16, or Adriamycin, and apoptosis was determined using a DNA fragmentation assay. Cellular survival was quantified by limiting dilution assay. Intracellular thiols were decreased by maintaining LY-ar cells in cystine/methionine-free medium (CMF medium) for 7 h after drug 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 CMF medium after drug treatment increased apoptosis and reduced clonogenic survival to the levels seen in LY-as cells, except after treatment with VP-16, where the reduction in cell survival was more modest.


CONCLUSIONS
Decreasing intracellular thiols enhances apoptosis and cell killing in lymphoma cells after exposure to a variety of chemotherapy agents. This may be especially true for tumor cells that overexpress bcl-2, a gene that modifies cellular thiol status and conveys resistance to apoptosis. In this case, decreasing cellular thiols allows killing independent of the expression of bcl-2.
Story
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MD
Department of Experimental Radiation Oncology, The University of Texas M.D. Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030, USA. mstory@mdanderson.org
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D000818:Animals; D000970:Antineoplastic Agents / Q000633:toxicity*; D017209:Apoptosis / Q000187:drug effects*; D002470:Cell Survival / Q000187:drug effects; D002945:Cisplatin / Q000633:toxicity; D053938:DNA Fragmentation; D004305:Dose-Response Relationship, Drug; D004317:Doxorubicin / Q000633:toxicity; D005047:Etoposide / Q000633:toxicity; D015972:Gene Expression Regulation, Neoplastic; D019254:Genes, bcl-2; D016393:Lymphoma, B-Cell / Q000235:genetics* / Q000473:pathology*; D051379:Mice; D014407:Tumor Cells, Cultured; D014410:Tumor Stem Cell Assay
D000970:Antineoplastic Agents; D005047:Etoposide; D004317:Doxorubicin; D002945:Cisplatin