ISOPRENIOD SYNTHESIS & TUMOR CELL GROWTH

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The long-term objectives of the project are the study of isoprenoid biosynthesis in relation to cell proliferation, and the development of new approaches to cancer chemotherapy based on inhibition of the regulatory enzyme in the isoprenoid pathway, 3hydroxy3methylglutaryl coenzyme A (HMG-CoA) reductase. This enzyme catalyzes the formation of mevalonate, an essential precursor of sterols and other isoprenoids such as ubiquinone, dolichol, and newly discovered isoprenoid proteins. The activity of HMGCoA reductase is elevated in many types of tumors, and data from the preceding project period showed that an inhibitor of this enzyme, mevinolin, suppresses the growth of subcutaneous neuroblastoma in mice. Continued evaluation of mevinolin during the next project period will establish whether this compound can suppress tumor growth in rat brain tumor models such as intracerebral C-6 glioma and intracisternal Walker 256 carcinoma. Several criteria will be used to assess the efficacy of mevinolin, including survival curves and clonogenic assays of residual tumors. Histological studies of normal brain, and colonyforming assays of bone marrow cells will identify potential toxic side effects of mevinolin. The results of these studies will indicate whether phaseI clinical trials of mevinolin are warranted. Cultured neuroblastoma and LM cells will be used in basic studies to determine why blocking mevalonate synthesis leads to arrest of cell cycling. These studies will focus specifically on a novel class of proteins which are modified post- translationally with isoprenoid prosthetic groups derived from mevalonate. One of these proteins, which is localized in the nucleus, will be purified by isoelectric focusing and SDSgel electrophoresis, and a monoclonal antibody will be raised by standard mouse hybridoma technology. The antibody will then be used to determine (1) whether the highmolecular weight nuclear isoprenoid protein is related antigenically to the lowermolecular weight isoprenoid proteins found in other subcellular compartments, (2) whether suppression of mevalonate synthesis by mevinolin results in a decreased synthesis of the polypeptide portion of the isoprenoid protein,, (3) whether the synthesis of the nuclear isoprenoid protein occurs during a specific phase of the cell cycle, and (4) whether the nuclear isoprenoid protein exhibits properties of a DNAbinding protein. These studies will provide new insight into the mechanism underlying the mevalonate requirement for cell growth.