Using JM and MOLT3, two human T-cell acute lymphoblastic leukemia cell lines, we investigated the ability of 24-h thymidine exposures to enhance the cytotoxicity of cis-diammine-1,1-cyclobutane dicarboxylate platinum(II) (carboplatin). Clinically achievable thymidine concentrations (for 24 h) significantly enhanced carboplatin killing. Unexpectedly, thymidine-carboplatin enhancement was as great at a relatively low 200-µg thymidine/ml as at the clinically much more toxic range of 1000 µg/ml. For a constant thymidine concentration (500 µg/ml), thymidine-carboplatin interaction increased with longer thymidine exposures until about 16 to 24 h. Thymidine and 41.8°C hyperthermia (for 1 h) together enhanced carboplatin killing significantly more than did hyperthermia-carboplatin or thymidine-carboplatin combinations. These results show that relatively brief, presumptively nonmyelosuppressive thymidine exposures can significantly increase carboplatin killing. Carboplatin-thymidine killing can then be further augmented by 41.8°C hyperthermia.

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Supported by Midwest Athletes Against Childhood Cancer, Inc.; The Thorton Fund for Neurooncology Research; and NIH Grant R01 CA 35464.

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