Although the anthracyclines, particularly Adriamycin (ADM), have been shown to be useful in treating a broad spectrum of human tumors, cardiotoxicity, often leading to fatal congestive heart failure, remains a serious dose limiting side effect. In order to study the mechanism of ADM-induced cardiomyopathy, we developed a cardiac cell model in which several of the effect of ADM described in vivo can be simulated in vitro. Using this model we found that cardiac-muscle cells accumulate significantly greater amounts of ADM and undergo increased cellular damage as compared to cardiac-derived fibroblasts. This observation was coupled with our findings that cardiac-muscle and a number of carcinoma cell types and Friend leukemia cells preferentially accumulate the mitochondrial localizing dye, rhodamine 123. ADM and rhodamine 123 share in common that they are both positively-charged at physiologic pH. Our working hypothesis is that cardiac-muscle, a number of carcinoma cell types and Friend leukemia cells have similar mechanisms for enhanced accumulation of and sensitivity of positively-charged anthracyclines and rhodamines.
Our specific aims are to determine (1) why cardiac-muscle, a number of carcinoma cell lines and Friend leukemia cells accumulate high amounts of positively-charged lipophilic anthracyclines and rhodamines and (2) whether increased membrane potentials contribute to increased drug accumulation and sensitivity in these cell types. The ultimate goal is to identify mechanisms responsible for differential sensitivity to anthracyclines in order to prevent or reduce cardiotoxicity while improving the antitumor effectiveness of known or heretofore undiscovered anthracyclines and rhodamines. Using fluorescence microscopy, laser flow cytometry, high pressure liquid chromatography (HPLC), clonogenic assays and our computerized video cardiac cell function analyzer, we plan to investigate differential cellular accumulation and cytotoxicity of a variety of anthracyclines, rhodamines, and other related compounds. Using a number of modulators of resistance (calcium channel and calmodulin inhibitors), we plan to identify those with least effect on chronotropic and inotropic cardiac cell function and maximum effect on overcoming resistance to anthracyclines and rhodamines in cancer cells. By patch clamp technique, we will measure membrane potentials in cardiac-muscle, carcinoma and ADM- sensitive and resistant Friend leukemia cells and assess its importance relative to drug accumulation and chemosensitivity.
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