Aberrant activation of Wnt/NF-\#954;B signaling network has been observed in a third of melanomas. The prognosis of advanced melanoma exhibiting constitutive Wnt/NF-\#954;B activation is very poor. Recently, we showed that shRNA-mediated suppression of Wnt signaling causes the inhibition of NF-\#954;B signaling resulting in the apoptosis of human melanoma cells Mel 928 and Mel 1241 and suggested that the targeted disruption of Wnt/NF-\#954;B signaling could be a promising strategy for the treatment and prevention of these human melanoma subtypes (Oncogene 27; 5069-74, 2008). We set out a program to identify agents which could target Wnt as well as NF-\#954;B signaling in human melanoma cells. Based on earlier studies, we hypothesized that Lupeol, a dietary triterpene, could be such a multi-target agent. Recently, we showed that Lupeol (40-80 µM; 72 h) significantly decreases the viability of highly malignant human melanoma cells (451Lu) while sparing normal melanocytes at a similar dose (Clin Cancer Res 14; 2119-27, 2008). Our current study is aimed to (1) investigate the effect of Lupeol treatment on melanoma cells of varied Wnt signaling status and (2) evaluate its effect vis-à-vis NF-\#954;B signaling in these cells. To achieve our objective, we selected Mel 928 and Mel 1241 as prototype of human melanoma cells harboring constitutively active Wnt signaling and Mel 1011 cells which exhibits the least Wnt activation. We found that Lupeol inhibits the growth of all melanoma cells but the inhibitory effect was more pronounced in Mel 928 and Mel 1241 which exhibits constitutive Wnt activation. Next, we found that Lupeol (40-80 µM) resulted in significant inhibition of anchorage-independent colony formation of Mel 928 than in Mel 1011 cells. We then determined the effect of Lupeol treatment (40-80 µM; 72 h) on Wnt signaling pathway in Mel 928 cells. Lupeol treatment caused a decrease in levels of nuclear \#946;-catenin suggesting that it inhibits the translocation of \#946;-catenin to the nucleus thus inhibiting the activation of downstream targets. Next, we determined the effects of Lupeol on the downstream targets of Wnt signaling. We observed a dose-dependent decrease in the expression of CRD-BP, c-myc and MITF. We also measured the effect of Lupeol on the transcriptional activation of TCF responsive element, a marker for \#946;-catenin signaling, using TOP-Flash luciferase assay. We found that Lupeol inhibited the transcriptional activation of TCF responsive element (20 µM 24 h). Lupeol was also found to disrupt the NF-\#954;B signaling pathway. Lupeol treated melanoma cells exhibited a decrease in the transcriptional activation of p65-sub unit of NF-\#954;B with a decrease in levels of Bcl-2. We suggest that cell growth inhibition of melanoma cells by Lupeol is mediated, at least in part, by modulation of Wnt/NF-\#954;B signaling network. Lupeol could be used as a potential therapeutic agent for human melanomas exhibiting aberrations in the Wnt/NF-\#954;B signaling network.

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 3638.

100th AACR Annual Meeting-- Apr 18-22, 2009; Denver, CO

American Association for Cancer Research
2009