EFFECTS OF ENDOTHELIAL NITRIC-OXIDE SYNTHASE GENE-EXPRESSION ON THE TUMOR BIOLOGY OF HUMAN ORAL-CARCINOMA SCC-25 CELLS

Stable transfection of endothelial nitric oxide synthase (eNOS) cDNA i n human oral carcinoma SCC-25 cells was performed, Two eNOS-expressing clones were isolated, and both were shown to have increased eNOS expr ession as assayed by Northern and Western analyses, Furthermore, a nit rite assay indicated that nitric oxide production in eNOS-transfected cells was increased, The growth rate and plating efficiency of eNOS-tr ansfected cells in vitro were lower than that of the wild-type parenta l or vector control-transfected cells as assayed by growth curves, [H- 3]thymidine incorporation, and standard plating efficiency assays in L -arginine-rich medium. However, when these cancer cells were inoculate d into nude mice, tumor size of eNOS-transfected cells was smaller dur ing the first 25 days but increased later as compared to tumor size of parental and vector control-transfected cells, It is not clear whethe r the later increase in tumor size was due to an increase in SCC-25 ca ncer cell proliferation, normal stromal cell proliferation, or both. T hese results show significant effects of overexpression of eNOS on tum or growth in vitro and in vivo.