Suppression of Tumorigenicity and Metastasis of Human Renal Carcinoma Cells by Infection with Retroviral Vectors Harboring the Murine Inducible Nitric Oxide Synthase Gene

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Abstract
The purpose of this study was to determine whether retrovirus-mediated transfer of the murine macrophage inducible nitric oxide synthase (iNOS) gene can inhibit tumorigenicity and metastasis of human renal cancer cells. Retroviral vectors encoding murine macrophage iNOS were constructed in the pLXSN retroviral vector with the iNOS gene under the control of a long terminal repeat promoter and a neomycin resistance gene under the control of an internal simian virus 40 promoter. Highly metastatic human renal carcinoma SN12PM6 cells were infected with control 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 nitrite accumulation in culture supernatants. Noninfected or control cells produced large orthotopic tumors in the kidney of nude mice and a larger number of experimental lung metastases, whereas iNOS-infected cells 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, suppression of tumorigenicity, and abrogation of metastasis. We show here that highly metastatic human renal carcinoma cells (HRCCs) can produce nitric oxide (NO) subsequent to infection with a retroviral vector encoding the murine macrophage inducible nitric oxide synthase gene (iNOS) under the control of a long terminal repeat promoter and a neomycin resistance gene under the control of an internal simian virus 40 promoter. The production of NO by the HRCCs enhanced the rate of apoptosis, suppressed tumorigenicity at an orthotopic site (kidney of nude mice), and abrogated spontaneous lung metastasis. These data suggest that infection of human cancer cells with a retrovirus harboring the murine iNOS gene can be used for therapy of metastasis.