TARGETING ENDOGENOUS ANTIBODIES TO OVARIAN CARCINOMA

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DESCRIPTION (provided by applicant): Humans and Old World primates naturally produce a significant amount of antibodies which recognize a particular galactosyl epitope, GAL alpha 1-3GAL. We have been interested in testing if these anti-Gal antibodies can be targeted to undesirable cancerous cells. Specifically we wish to explore a possibility of redirecting these endogenous antibodies to ovarian carcinoma cells which overexpress folate receptor isotype alpha (FR-alpha) by means of chemical conjugates of folic acid to the galactosyl epitope. The end result should be the cytolysis of the target cell. Towards this goal, the present application is concerned with the total synthesis of the folate-digalactose conjugates and development of an ovarian cancer model in immune competent mice. Preparation of the conjugate which can mediate anti-Gal binding to FR+ cells with high avidity is the main chemistry goal of the project. Our strategy is to introduce multiple copies, 2 and 4 copies, of the epitopes to one molecule of folic acid at an optimal distance between them. Chemical synthesis will be carried out on a solid-phase support. The conjugates will be tested with FR+/Gal- human nasopharyngeal carcinoma KB cells for their ability of promoting the anti-Gal binding to FR on the cell surface. Specificity of the interaction will be tested in the presence of free folic acid or free disaccharide as well as with a conjugate that contains lactose instead of GAL alpha 1-3GAL. The antibody binding will be conveniently characterized by means of FACS procedure. The biological goal of this project is to develop a mouse model of ovarian cancer that is suitable for testing anti-tumor activity of our folate conjugates in vivo. Since normal mice express the galactosyl epitopes in their tissue, we will have to use alpha 1,3-GALactosyltransferase-knockout (GT/KO) mice. It is known that GT/KO mice produce anti-Gal as in humans. We plan to transform the ovarian epithelial cells harvested from these mice in culture to tumor-forming cell lines following a procedure we have recently developed. They will be then transfected with murine cDNA encoding full length FR-alpha. Finally these GAL-/FR+cells will be introduced into peritoneum of healthy GT/KO mice. Our current approach to immunotherapy of ovarian cancer is unique in that we are using naturally occurring endogenous antibodies. Immune modulators in this application are all small molecules with MW < 3 kDa, rendering pharmacokinetic properties most favorable for sustained activity in peritoneal cavity as well as reduced potential side effects.