We have examined the influence of the
nitric oxide (NO)-modified anti-inflammatory
drug (S,R)-3-phenyl-4,5-dihydro-5-isoxasole
acetic acid (VGX-1027) named GIT-27NO or the NO-modified
antiviral drug saquinavir (Saq) named
Saq-NO on two
colon cancer cell lines, mouse CT26CL25 and human HCT116. The effects of the drugs on cell viability, apoptosis, proliferation, and metastatic potential were analyzed. The release of NO and
oxygen and
nitrogen species was also determined. The efficacy of the drugs was evaluated in vivo in BALB/c mice injected with CT26CL25 cells. Both agents suppressed the growth of
colon cancer cells in vitro and reduced
tumor volume in syngeneic BALB/c mice. However, their mechanisms of action were different because GIT-27NO released larger amounts of
nitrite than
Saq-NO in cell cultures and its antitumor action depended on the intracellular NO release inside the cells. On the contrary,
Saq-NO released barely detectable amounts of NO and its antitumor action was NO-independent. In fact, cotreatment with an NO-
peroxynitrite scavenger revealed that GIT-27NO but not
Saq-NO acts through
peroxynitrite-mediated cell destruction. At the cellular level, GIT-27NO prevalently induced proapoptotic signals followed by caspase-dependent apoptosis. In contrast,
Saq-NO blocked cell proliferation, changed the adhesive, migratory, and invasive properties of the cells, and decreased metastatic potential in vivo. In conclusion, differences in NO release and oxidative stress generation between GIT-27NO and
Saq-NO resulted in different mechanisms that caused cell death.