SUPPRESSION OF TUMORIGENICITY AND METASTASIS OF HUMAN RENAL-CARCINOMACELLS BY INFECTION WITH RETROVIRAL VECTORS HARBORING THE MURINE INDUCIBLE NITRIC-OXIDE SYNTHASE GENE

The purpose of this study was to determine whether retrovirus-mediated transfer of the murine macrophage inducible nitric oxide synthase (iN OS) gene can inhibit tumorigenicity and metastasis of human renal canc er cells. Retroviral vectors encoding murine macrophage iNOS were cons tructed in the pLXSN retroviral vector with the iNOS gene under the co ntrol of a long terminal repeat promoter and a neomycin resistance gen e under the control of an internal simian virus 40 promoter. Highly me tastatic human renal carcinoma SN12PM6 cells were infected with contro l or iNOS retrovirus, Expression of iNOS was confirmed by Northern and Western blot analyses, and expression of the functional iNOS protein, i.e., production of nitric oxide (NO), was determined by measuring ni trite accumulation in culture supernatants, Noninfected or control cel ls produced large orthotopic tumors in the kidney of nude mice and a l arger number of experimental lung metastases, whereas iNOS-infected ce lls produced small tumors in the kidneys and few to no lung metastases , The data indicate that the infection of human renal cancer cells by retroviruses harboring the murine iNOS gene can induce the production of high levels of NO, which is associated with autocytotoxicity, suppr ession of tumorigenicity, and abrogation of metastasis.