The role of melanoma tumor-derived nitric oxide in the tumor inflammatory microenvironment: its impact on the chemokine expression profile, including suppression of CXCL10

Melanoma appears to be heterogeneous in terms of its molecular biology, etiology and epidemiology. We previously reported that the expression of inducible nitric-oxide synthase (iNOS) in melanoma tumor cells is strongly correlated with poor patient survival. Therefore, we hypothesized that nitric oxide (NO) produced by iNOS promotes the melanoma inflammatory tumor microenvironment associated with poor outcome. To understand the role of NO and iNOS in the melanoma inflammatory tumor microenvironment, polymerase chain reaction arrays of inflammatory and autoimmunity genes were performed on a series of stage III melanoma lymph node metastasis samples to compare the gene expression profiles of iNOS-expressing and nonexpressing tumor samples. The results indicate that expression of CXC chemokine ligand 10 (CXCL10) was inversely correlated with iNOS expression, and the high CXCL10-expressing cases had more favorable prognoses than the low CXCL10-expressing cases. Functional studies revealed that treating iNOS-negative/CXCL10-positive melanoma cell lines with a NO donor suppressed the expression of CXCL10. Furthermore, scavenging NO from iNOS-expressing cell lines significantly affected the chemokine expression profile. Culture supernatants from NO scavenger-treated melanoma cells promoted the migration of plasmacytoid dendritic cells, which was diminished when the cells were treated with a CXCL10-neutralizing antibody. CXCL10 has been reported to be an antitumorigenic chemokine. Our study suggests that the production of NO by iNOS inhibits the expression of CXCL10 in melanoma cells and leads to a protumorigenic tumor microenvironment. Inhibiting NO induces an antitumorigenic environment, and thus, iNOS should be considered to be an important therapeutic target in melanoma.