SODIUM PHENYLACETATE INDUCES GROWTH-INHIBITION AND BCL-2 DOWN-REGULATION AND APOPTOSIS IN MCF7RAS CELLS IN-VITRO AND IN NUDE-MICE

Using a highly tumorigenic human breast cancer model (Ha-ras-transfect ed MCF7 cell line) we analyzed the efficacy of the differentiation-ind ucing agent sodium phenylacetate (NaPA), both in vitro and in vivo. Na PA-treated MCF7ras cells showed dose-dependent growth inhibition from 2.5 to 15 mM without apparent toxicity. Western blot analysis showed a Bel-2 down-regulation after 48 h treatment with 5 mar NaPA, together with apparition of apoptotic nuclei by DAPI staining. Mice bearing MCF 7ras xenografts (n = 40) were treated for 2 weeks through s.c.-deliver ing osmotic pumps, followed by 6 weeks of daily i.p. NaPA administrati on. After 3 weeks, the treated tumors showed growth arrest without reg ression for the whole observation time, e.g., 12 weeks. Immunohistoche mical analysis showed Bel-2 down-regulation and differentiation patter ns: decrease of Ki-67 and increase of steroid receptors (estrogen and progesterone receptors) compared to controls. Cells cultured from trea ted tumors (II.b) displayed pseudotrabecular disposition as MCF7ras ce lls treated in vitro. They also showed a higher NaPA sensitivity, toge ther with 70% Bel-2 down-regulation as compared to the derived cells o f untreated tumors (IL.a). When reinjected into nude mice, Il.b cells induced only one poorly vascularized, noninvasive tumor (8%) with lowe r proliferation index, 100% progesterone receptor positive cells, and 35% terminal deoxynucleotidyltransferase-mediated dUTP-X nick end labe ling (+) nuclei, as compared to 100% induction of highly vascularized and invasive tumors with 3% terminal deoxynucleotidyltransferase-media ted dUTP-X nick end labeling (+) nuclei induced by II.a cells.