Circumvention of 5-fluorouracil resistance in human stomach cancer cells by uracil phosphoribosyltransferase gene transduction

A human stomach cancer cell line,vith acquired resistance to 5-fluorouracil (5-FU), NUGC-3/5FU/L, has been found to possess reduced ability to convert 5-FU into active metabolites, We attempted in vitro gene therapy for this 5-FU-resistant cell line. NUGC-3 and NUGC-3/5FU/L cells were infected with recombinant adenovirus (Ad) containing Escherichia coli uracil phosphoribosyltransferase (UPRT) gene driven by CAG promoter (CA), AdCA-UPRT, and changes in their 5-FU metabolism and sensitivity were investigated. Activities of orotate phosphoribosyltransferase increased from 10.2 and 1.56 (nmol/mg protein/30 min) in the uninfected cells of NUGC-3 and NUGC-3/5FU/L to 216 and 237, respectively, after the transfection of UPRT gene, The 5-FU nucleotide level in the acid-insoluble fraction increased from 7.32 to 15.9 (pmol/mg protein) in NUGC-3 cells on infection with AdCA-UPRT, and in NUGC-3/5FU/L cells it increased from 1.91 to 21.4. The 50% growth-inhibition concentration (IC50) was 12.7 mu mol/liter for NUGC-3 and much higher than 100 mu mol/liter for NUGC-3/5FU/L, indicating over 8-fold resistance. NUGC-3/5FU/L transfected with the UPRT gene shelved very high sensitivity to 5-FU with an IC50 of 3.2 mu mol/liter. The high resistance in this metabolic activation-deficient cell line was thus completely reversed by transduction of an exogenous gene coding for a 5-FU-anabolizing enzyme.