The role of nitric oxide in apoptosis and cancer metastasis

The purpose of these studies was to investigate the role of nitric oxide (NO) in tumor metastasis. K-1735 Metastatic cells survived in blood circulation to produce experimental lung metastases, whereas nonmetastatic cells did not. After incubation with combination cytokines or lipopolysaccharide (LPS), nonmetastatic cells exhibited high levels of inducible nitric oxide synthase (iNOS) activity and NO production, whereas metastatic cells did not. The production of NO directly correlated with cytotoxic effects of cytokines or LPS. To provide direct evidence for the inverse correlation between the production of endogenous NO and the ability of K-1735 cells to survive in syngeneic mice to produce lung metastases, highly metastatic K-1735 clone 4 cells (C4.P), which express low levels of iNOS, were transfected with a functional iNOS (C4.L8), inactive-mutated iNOS (C4.S2), or neomycin-resistance (C4.Neo) genes in medium containing 3 mM NMA. C4.P, C4.Neo.3, and C4.S2.3 cells were highly metastatic whereas C4.L8.5 cells were not metastatic. The C4.L8.5 cells produced slow growing subcutaneous tumors in nude mice, whereas the other three lines produced fast growing tumors. In vitro studies indicated that the expression of iNOS in C4.L8.5 cells induced apoptosis. Collectively, these data demonstrate that the expression of recombinant iNOS in melanoma cells is associated with apoptosis, suppression of tumorigenicity, and abrogation of metastasis.^ Furthermore, multiple systemic administrations of multilamellar vesicle-liposomes (MLV) containing the lipopeptide CGP 31362 (MLV-31362) or MLV-31362 combined with murine interferon-gamma (IFN-$\gamma$) eradicated the metastases by M5076 reticular cell sarcoma. Tumor regression correlated with iNOS expression within the tumor lesions and with increased NO production. The administration of NMA significantly decreased NO production and diminished the antitumor activities. These data imply that the activation of iNOS can serve as a target for immunotherapeutic agents for treatment of murine reticulum cell sarcoma metastases. ^