Abstract 741: Lactic acid, hyperacidic media, and hypoxia diminish 4-hydroxyanisole-induced toxicity in melanoma cell lines

Abstract

Abstract Lack of in-vitro in-vivo correlation in drug efficacy is a major problem in anticancer drug discovery, which may be attributed to hypoxia and lactic acid production in tumor. In current work, we evaluated the effect of hypoxia, lactic acid and hyper-acidic condition on efficacy of 4-hydroxyanisole (4-HA) as an anti-melanoma prodrug in human SK-MEL-28 cells. Lactic acid concentrations and pH were determined in tumor and compared with liver, lung, kidney and serum in skin melanoma tumor model in mice. The pH of tumor and blood was measured using pH meter. The lactic acids were measured by a microdialysis analyzer. Modular incubator chamber was used to maintain hypoxic condition. MTT assay was used for IC50 (48h) determination and cell viability measurement. Male C57BL/6 mice (n=3) were inoculated s.c. at right flank with 1×106 B16-F0 melanoma cells. The pH of tumor and serum was 6.8-6.9 and 7.4-7.6, respectively, indicating that pH was significantly lower in tumor. The lactic acid concentrations in tumor increased from 10.8 to 19.4mM during day 8 through 13 post melanoma cell inoculation, whereas in serum, liver, lung and kidney remained within 5.5-7.8mM, 11.1-14.4mM, 3.5-6.9mM and 6.6-7.5mM, respectively. Normoxia results: The IC50 (48h) of 4-HA in SK-MEL-28 was 50µM. Lactic acid demonstrated a concentration dependent toxicity towards melanoma cell lines with an IC50 (48h) of 20mM. 4-HA (50µM) led to 50% toxicity in the presence of lactic acid (5-20mM) as well. A decrease in pH of the media was observed with an increase in lactic acid concentration. Hypoxia results: The IC50 (48h) of 4-HA remained 50µM in hypoxia. Lactic acid was less toxic to the cells under hypoxia. 4-HA (50µM) showed no toxicity in presence of lactic acid (5-20mM) under hypoxic condition. The effect of pyruvic acid, HCl and NaCl on 4-HA toxicity were also investigated in normoxia and hypoxia conditions. Our results suggest that lactic acid, hyper-acidic media and hypoxia may play major roles in diminishing 4-HA toxicity in melanoma cells, however, the role of hypoxia was found to be more prominent. Lactic acid provided protective effect against 4-HA induced toxicity under hypoxic condition. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 741.