Adriamycin, a clinical widely used anti-tumor agent, is thought to work as most other cancer chemotherapeutic drugs by affecting the replicating machinery of actively dividing tumor and normal cells. Unfortunately, this agent also affects the non-dividing cells of the heart. In addition, Adriamycin is recognized by a specific cellular mechanism, termed multi- drug resistance (MDR). In vitro systems have been developed in our laboratories in which cardiotoxic as well as tumoricidal and MDR mechanisms of drugs can be studied, at the cellular and subcellular level. We have uncovered fundamental differences in the electronegative membrane potentials of these cells that may in part explain differential cellular attraction of, and sensitivity to, Adriamycin, which is positively- charged. We propose to study how charge and lipophilicity of Adriamycin and related analogs affect their selective accumulation and toxicity in cardiac-muscle cells (MDR-) and in MDR- and MDR+ tumor cell lines. These anthracyclines however, are complex in structure which makes their use difficult for investigational structure/function studies of cardiotoxicity and MDR. We therefore plan to use a series of simple lipophilic-cationic compounds (guanidiniums and pyridiniums) as a model to explore mechanisms of drug selectivity in MDR- and MDR+ cells. Recently, utilizing this strategy we found (Cancer Research 52:6385-6389, 1992) that an aromatic moiety and a certain degree of lipophilicity are required for these simple cationic compounds to be recognized by MDR + cells. This information will be used to further characterize the physical/chemical requirements for MDR recognition as well as for MDR induction and modulation.
The specific aims of this proposal are to clarify the effects that chemical charge and lipophilicity impact on these simple compounds as well as on anthracyclines, to explain their differential accumulation and consequent cytotoxicity in MDR- and MDR+ cells. The overall goal of these studies is to increase understanding of the underlying mechanisms involved in both ADM-induced cardiotoxicity and multiple drug resistance, which could eventually translate into new designs of clinical protocols using anthracyclines with maximal activity toward MDR + tumor cells and minimal detrimental effects on cardiac cells. Our video-computerized system will be used to assay effects of drugs on sensitive (non-MDR) cardiac cell function and viability in vitro. Fluorescence microscopy, high pressure liquid chromatography and radioactive probes will be used to measure intracellular drug accumulation and transmembrane potentials.
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