The National Cancer Institute estimates that about 76,250 new cases of melanomas will be diagnosed in 2012 in the United States leading to at least 9810 related deaths. Metastasis of melanoma is the major challenge leading to the failure of its therapy. Hence, novel strategies to prevent metastasis are of prime importance. Anoikis is an anchorage independent cell death. Resistance to anoikis is one of the key features of a metastatic cell. In the current study, we show induction of anoikis by piperlongumine, a component of black pepper, by inhibition of STAT-3. Treatment of various melanoma cell lines in low attachment conditions with piperlongumine reduced the anoikis resistance in a concentration dependent manner. This decrease in anoikis resistance was associated with decrease in expression of STAT-3 and its phosphorylation at Y705. Significant down-regulation of Bcl-2 and Mcl-1, which are under the transcriptional regulation of STAT-3, was also observed by piperlongumine treatment indicating the role of STAT-3 in anoikis. Concentration dependent cleavage of poly (ADP-ribose) polymerase (PARP) was observed by piperlongumine treatment in melanoma cells. AG 490, an inhibitor of STAT-3 phosphorylation, alone induced anoikis in melanoma cells further indicating the role of STAT-3. IL-6 treatment not only increased the phophorylation of STAT-3 at Y05 but also abrogated the anoikis induced by piperlongumine. Silencing STAT-3 by shSTAT-3 sensitized the cells to piperlongumine treatment. On the other hand, over-expression of STAT-3 in SK-MEL28 and SK-MEL-2 cells conferred resistance to anoikis induced by piperlongumine. STAT-3 -/- SK-MEL-28 cells were highly sensitive to anoikis upon piperlongumine treatment. Finally, our in vivo studies established that melanoma cells treated with piperlongumine in suspension condition lost their potential to form tumors in mice. Taken together, our study suggests that the decrease in anoikis resistance induced by piperlongumine was mediated by STAT-3 inhibition. Notably, STAT-3 has been shown to be constitutively upregulated in melanoma rendering it resistant to chemotherapy and potential to metastasize. [Supported in part by R01 grant CA129038 (to S.K.S) awarded by the National Cancer Institute].

Citation Format: Neel M. Fofaria, Sanjay K. Srivastava. Inhibition of STAT-3 by piperlongumine induces anoikis in melanoma cells in vitro and blocks tumor formation potential in vivo. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5115. doi:10.1158/1538-7445.AM2013-5115