Abstract 1668: Effect of folate and γ-glutamyl hydrolase modulation on in vivo chemosensitivity of colon cancer cells to 5-fluorouracil
Authors: Kim Sung-Eun , Ly Anna , Cho Robert C. , Sohn Kyoung-Jin , Croxford Ruth , Kamen Barton A. , Kim Young-In 
Published: June 2012

Background: γ-Glutamyl hydrolase (GGH) removes terminal glutamates of polyglutamylated folates, thereby facilitating hydrolysis and efflux of folates from the cell. GGH overexpression may affect chemosensitivity of colon cancer cells to 5-fluorouracil (5FU) by changing intracellular retention of a folate cofactor (5,10-methylenetetrahydrofolate) necessary for the cytotoxic effects of 5FU and by changing intracellular total and polyglutamylated folate concentrations. We have previously reported that the in vitro chemosensitivity of human HCT116 colon cancer cells overexpressing GGH to 5FU+leucovorin (LV) is decreased at high, whereas it is increased at physiologic, media concentrations of folate compared with the control. We investigated whether GGH overexpression and folate status would affect the in vivo chemosensitivity of HCT116 cells to 5FU+LV in nude mice.

Methods: Six-week-old male Balb/c nu/nu mice received s.c. injections in each flanks of HCT116 cells expressing endogenous GGH and sense GGH. When xenografts reached a volume of 80-200 mm3, mice were assigned to 2 (control) or 8 (supplemented) folic acid (FA) mg/kg diet and treated with 5FU (20 mg/kg/day) + LV (1 mg/kg/day) or saline for 5 consecutive days. The growth rate of xenografts was determined. At necropsy, plasma folate and homocysteine concentrations and xenograft folate concentrations, thymidylate synthase (TS) activity, epithelial proliferation and apoptosis were determined.

Results: Plasma folate concentration of the FA supplemented mice was significantly higher than that of mice on the control diet (p&lt;0.001) while plasma homocysteine concentrations did not differ between two diets groups. Total and polyglutamylated folate concentrations and TS activity of the xenografts generally reflected dietary FA levels but they were modulated by both 5FU+LV treatment and GGH status. The growth rate of xenografts expressing endogenous GGH was faster than those overexpressing GGH at both FA diets when treated with saline. The growth rate of colon cancer cells overexpressing GGH was inhibited less effectively by 5FU+LV at 8 mg FA supplemented diet and inhibited more effectively by 5FU+LV at 2 mg FA control diet compared with those expressing endogenous GGH (p&lt;0.05). For xenografts treated with 5FU+LV on the control diet, those expressing endogenous GGH had lower Ki-67 % and higher TUNEL % while those overexpressing GGH showed higher Ki-67 % and lower TUNEL % (p&lt;0.05).

Conclusions: The in vivo chemosensitivity results support the in vitro observations that both GGH modulation and folate status may increase chemosensitivity of colon cancer cells to 5FU-based chemotherapy. We provide proof-of-principle that GGH and folate status may be important clinical determinants for providing rational and effective tailored colon cancer chemotherapy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1668. doi:10.1158/1538-7445.AM2011-1668