ACIDIFICATION OF HUMAN MELANOMA XENOGRAFTS

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Hyperglycemia reduces the pHe of transplantable rodent tumors by 0.1 - 0.4 pH unit. Human tumors are acidified by an average of 0.17 pH unit. Extracellular acidification of 0.2 unit is unlikely to sensitize human tumors to hyperthermia since the average pHe is 7.15. The goal of this research is to significantly acidify tumors for the purpose of hyperthermia. The hypothesis to be tested is that hyperglycemia-induced acidification of human melanoma xenografts can be increased by inhibition of mitochondrial respiration or by inhibition of membrane proton pumps to enhance the therapeutic gain. Inhibition of respiration will shift glucose metabolism toward glycolysis and the production of lactic acid, and inhibition of the membrane proton pumping. Inhibition of respiration will shift glucose metabolism toward glycolysis and the production of lactic art, and inhibition of the membrane protein pumping mechanism will allow the inflow of extracellular hydrogen ions. In these studies respiration will be inhibited during hyperglycemia with meta-iodobenzylguanide (MIBG), and membrane proton pumps will be inhibited during hyperglycemia by Cariporide mesilate (Hoechst HOE642 to inhibit the Na+/H+ exchanger, NHE1) and DIDS (to inhibit the Cl-HCO3-exchanger). The hypothesis will be tested in F2 human melanoma xenografts. By using both invasive and non-invasive MRS techniques we will determine: 1. Therapeutic gain by tumor growth delay compared to bone marrow proliferative potential (CFU-GM); 2. Tumor versus normal tissue (brain muscle) intracellular and extracellular acidification; 3. Tumor and normal tissue lactic acid levels; 4. Tumor and normal tissue blood flow; 5. Relationship of tumor vasculature distribution and glucose distribution; 6. Tumor pO2 distribution and 7. Tumor Glut-1, hexokinase activity and rate of respiration. Hyperglycemia will be induced by oral or i.v. glucose administration to SCID mice bearing 8-10 mm diameter melanomas selected from our melanoma frozen tumor bank on the basic of metabolic parameters. MIBG or HOE642 and/or DIDS will be administered i.p. at the time of peak blood glucose concentration followed by hyperthermia (1 hour at 42 degrees Celsius by leg immersion). MRS will be performed by Dr. Jerry Glickson, University of Pennsylvania. Explanted tumor cells will be provided to Projects 1, 2 & 3. The kinetics of adaptation of melanoma cells to growth at low pHe and the effect of hyperthermia response will be determined in culture. The in vitro characterization of the human melanomas will provide critical information for Projects 1, 2 & 3 and will provide a cellular basis for the hyperthermia response of xenografts. Furthermore, in vivo results will validate findings from Projects 1, 2, & 3. These results will provide the preclinical data required for the design and implementation of a phase I/II clinical trial to acutely acidify human tumors in association with therapy.