Pancreatic cancer has the worst prognosis of all major cancers with 97% treatment failure. First-line systemic therapy for pancreatic cancer is the antimetabolite gemcitabine. Although, tumors may initially respond to the gemcitabine treatment, soon tumor resistance and excessive toxicity develops leading to treatment failure. Efforts to optimize and improve the efficacy of gemcitabine therapy through combination with other agents have little success. Previously, we demonstrated that N-acetyl-L-cysteine (NAC), a glutathione (GSH) precursor prevents NFκB activation and promotes pancreatic cancer cell death. The mechanism of inactivation of NFκB by NAC supplementation is a post-translational sulfhydryl modification called S-glutathionylation on p65-NFκB that inhibits its DNA-binding capacity and thus prevents activation of the survival genes. Mass spectrometric analysis indicated that four of the 9 cysteines of p65 are potentially S-glutathionylated. Our hypothesis is that chemoresistance against gemcitabine arises from a combination of hypoxia- and gemcitabine-induced NFκB activation. The objective of this study is to test the hypothesis and investigate if thiol donors like NAC can suppress NFκB signaling and augment a therapeutic response to gemcitabine in vivo. Here we determined the anti-tumor effect of gemcitabine and NAC on pancreatic tumors in mice. MIA PaCa-2 pancreatic cancer cells were injected into nude mice to grow subcutaneous tumors. Treatment groups were untreated, NAC, gemcitabine and gemcitabine+NAC. Results indicated that neither gemcitabine nor NAC by itself was effective in decreasing tumor growth. However, NAC and gemcitabine in combination inhibited tumor growth by 33%. Gemcitabine activates NFκB, although the mechanism for this phenomenon is unclear. NFκB activity was indeed increased in gemcitabine-treated tumors (3-fold) and combination with NAC treatment blunted this effect (p<0.005). The results confirm gemcitabine-induced NFκB activation and NAC bioavailability in tumors. To assess whether combined treatment of gemcitabine and NAC induces apoptosis, we performed TUNEL staining in tissues. Gemcitabine plus NAC increased apoptosis by 35-fold compared to gemcitabine alone. Taken together, our data suggest that NAC first inhibits NFκB activation arising from hypoxic regions of tumors and secondarily block gemcitabine-activated NFκB in hypoxic and normoxic regions of tumors, and therefore sensitizes cells to gemcitabine-induced killing. This could be used as an effective adjunct to gemcitabine chemotherapy of pancreatic cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1316. doi:1538-7445.AM2012-1316