Effect of nitric oxide on the anticancer activity of the topoisomerase-active drugs etoposide and adriamycin in human melanoma cells

Abstract

Nitric oxide (×NO) was originally identified as an innate cytotoxin. However, in tumors it can enhance resistance to chemotherapy and exacerbate cancer progression. Our previous studies indicated that ×NO/×NO-derived species react with etoposide (VP-16) in vitro and form products that show significantly reduced activity toward HL60 cells and lipopolysaccharide (LPS)-induced mac-rophages. Here, we further confirm the hypothesis that 4NO generation contributes to VP-16 resistance by examining interactions of ×NO with VP-16 in inducible nitric-oxide synthase (iNOS)-expressing human melanoma A375 cells. Inhibition of iNOS catalysis by N6-(1-iminoethyl)-L-lysine dihydrochloride (L-NIL) in human melanoma A375 cells reversed VP-16 resistance, leading to increased DNA damage and apoptosis. Furthermore, we found that coculturing A375 melanoma cells with LPS-induced macrophage RAW cells also significantly reduced VP-16 cytotoxicity and DNA damage in A375 cells. We also examined the interactions of NO with another topoisomer-ase active drug, Adriamycin, in A375 cells. In contrast, to VP-16, NO caused no significant modulation of cytotoxicity or Adriamycin-dependent apoptosis, suggesting that NO does not interact with Adriamycin. Our studies support the hypothesis that NO oxidative chemistry can detoxify VP-16 through direct nitrogen oxide radical attack. Our results provide insights into the pharmacology and anticancer mechanisms of VP-16 that may ultimately contribute to increased resistance, treatment failure, and induction of secondary leukemia in VP-16-treated patients. Copyright © 2013 by The American Society for Pharmacology and Experimental Therapeutics.