The objective of this research is to test the hypothesis that the plasma membrane may represent a sensitive site for anticancer drug action. The work focuses on adriamycin and related anthracyclines. Damage to nuclear DNA has been considered to be a primary target for adriamycin action, but there is also a large body of evidence suggesting that the structure and functions of biological membranes are also sensitive to adriamycin disruption. This laboratory has shown that adriamycin immobilized on large polymers can be actively cytoxic under conditions where it does not enter the cell and bind to DNA, but only accesses the cell surface. Experiments are proposed to put this finding to a practical test by using the immobilized drug as a direct therapeutic agent in animals. The polymer bound drug will be used as an intracavitary agent to treat ovarian epithelial malignancies, mesothelioma, and ascites tumors. Preliminary results show that immobilization retains the anticancer activity of adriamycin, and intraperitoneal administration lacks significant toxic side effects. The second major aim of this research is to study the role of phosphatidyl inositol (PI) turnover in mediating the cytotoxic action of free adriamycin. Drug treatment enhances PI turnover, leading to the generation of two second messengers- inositol trisphosphate (Ip3) and diacylglycerol (DG). The function of Ip3 is to mobilize intracellular free Ca++, but these processes appear to be decoupled in the presence of adriamycin. The other messenger, DG, activates protein kinase C (PKC). The activity of this enzyme appears to be linked to the induction of adriamycin cytotoxicity, so experiments are proposed to determine the role of the following properties in drug mechanism: (1) cofactor requirements, (2) translocation between cytoplasm and membrane, (3) isozyme distribution, (4) phosphorylation of topoisomerase II and other substrates. These experiments will provide a detailed understanding of how the PI/PKC signal transduction pathway functions to mediate the cytotoxic cascade induced by adriamycin.
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