USE OF RETROVIRAL VECTORS ENCODING MURINE INDUCIBLE NITRIC-OXIDE SYNTHASE GENE TO SUPPRESS TUMORIGENICITY AND CANCER METASTASIS OF MURINE MELANOMA

The purpose of this study, was to determine whether retrovirus-mediate d transfer of murine macrophage inducible nitric oxide synthase (iNOS) can produce inhibition of tumorigenicity and metastasis. Retroviral v ectors encoding macrophage iNOS constructed in pLXSN, a retroviral vec tor with the iNOS gene under the control of a long terminal repeat pro moter, were stably transfected into PA317 cells. Medium harvested from confluent monolayers of the virus-producing cell lines was used for i nfection of the murine K-1735 melanoma cells. Expression of iNOS was c onfirmed by northern and Western blot analyses. Functional iNOS protei n expression was confirmed by bioassay of nitrite accumulation in the culture supernatant. Cells infected by a control iNOS-negative retrovi rus produced fast-growing subcutaneous tumors and many lung metastases in nude mice, whereas iNOS-transduced cells produced slow-growing tum ors and few lung metastases, showing that the infection of murine tumo r cells by retroviruses harboring the iNOS gene can suppress tumorigen icity and metastasis.