Mechanisms by which yield-difluoromethylornithine (DFMO)-induced polyamine depletion sensitizes human adenocarcinoma cells to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) will be studied. In addition, the in vivo utility of the drug combination will be evaluated using human adenocarcinoma xenografts in athymic (nude) mice. To investigate DNA and chromosomal damage as the target for the drugs' interaction, BCNU-induced sister chromatid exchanges will be measured in DFMO-pretreated and control cultures. Since depletion of O6-alkylguanine DNA alkyltransferase by streptozotocin (STZ) is known to increase DNA interstrand crosslinking in BCNU-resistant cells, further enhancement by DFMO plus STZ of cytotoxicity and crosslinks will be tested. If DFMO sensitizes cells to BCNU at targets other than DNA crosslinks, additive effects on cytotoxicity with no increase in crosslinks should be observed at sub-optimal doses of STZ. DFMO potentiation of nitrosoureas with different chemical mechanisms of action will be compared to determine if sensitization by DFMO is to the chloroethyl or the isocyanate portion of BCNU. If BCNU-induced DNA or chromosomal damage is enhanced in the polyamine-deficient cells, sensitivity of nuclear DNA to DNase-I digestion will be used to study DFMO effects on chromatin condensation. To investigate BCNU targets other than DNA which may be sensitized by DFMO, increased BCNU-mediated cell lysis in polyamine-depleted cells will be distinguished from further reduction of clonogenic potentials by BCNU after DFMO pretreatment. Inactivation of membrane transport systems by BCNU will be compared in polyamine-depleted and control cultures. The hypothesis that BCNU induces synthesis of heat-shock proteins (which are induced by other toxic agents and make cells resistant to thermal killing) will be tested. If BCNU induces the heat shock response, BCNU sensitivity of heat-shocked cells and BCNU induction of heat shock in polyamine-deficient cells will be studied further. To investigate in vivo sensitization, nude mice bearing human adenocarcinoma xenografts will be treated with BCNU, DFMO or their combination. Tumor growth will be monitored by volume estimates. Hematologic and pulmonary toxicity will also be evaluated. If antitumor efficacy is enhanced by more than toxicity is increased, the therapeutic index of BCNU may be improved by DFMO pretreatment.
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