Astrocytomas are the most common central nervous system tumors in both children and adults and are also the group most poorly controlled with conventional therapies. Recent studies have indicated that overexpression and excessive activation of protein kinase C (PKC) may play a significant role in mediating the growth of these tumors and, conversely, that inhibition of this second messenger may provide a novel strategy for blocking astrocytoma proliferation. The goals of the present study are to characterize the patterns of PKC isoenzyme expression in neoplastic and non-neoplastic astrocytes in order to determine whether one or more isoforms are differentially overexpressed in astrocytoma cells; these data will then form the basis for developing and examining the efficacy of therapeutic strategies directed at inhibiting PKC as a means for blocking astrocytoma growth in vitro and in vivo. The hypotheses to be evaluated in this study are that astrocytic tumor cells demonstrate overexpression of specific PKC isoforms in comparison to non-neoplastic astrocytes, that such isoforms play a role in mediating the growth of these tumors, and that the proliferation of astrocytic tumors may be inhibited by blocking PKC-mediated pathways. The experimental strategy is designed to identify which PKC isoenzymes are overexpressed in neoplastic astrocytes in comparison to non-neoplastic astrocytes using immunohistochemical and Western blotting studies on a series of established and low-passage astrocytoma and non-neoplastic astrocyte cell lines, and surgical tumor and nonneoplastic brain specimens. Antisense-mediated inhibition of the expression of such isoenzymes will then be employed to determine whether a selective decrease in the levels of individual isoforms inhibits basal and/or mitogen- stimulated cell proliferation in vitro. In addition, a series of well characterized PKC-selective inhibitors, which have been well tolerated in animal model studies of non-glial tumors, will be used to determine whether a more generalized inhibition of PKC activity is effective in blocking basal and mitogen-stimulated cell proliferation in vitro. Since excessive activation of PKC has been associated with resistance to a variety of conventional chemotherapeutic agents in non-glial tumor model systems, and this resistance may be reversed by inhibition of PKC, attention will also be focused on determining whether PKC inhibition potentiates the efficacy of conventional chemotherapeutic agents in gliomas, which characteristically show poor responsiveness to such agents. Based on the results of the in vitro experiments, subsequent studies will examine the efficacy of PKC inhibition both alone and in conjunction with conventional chemotherapeutic agents as a therapeutic strategy in a nude mouse glioma model. Taken together, these studies will provide fundamental information on the biology astrocytomas and would form the basis for future clinical application of PKC inhibition in the treatment of astrocytic neoplasms.
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