Abstract #1066: The specific targeting of liver cancer stem cells by lupeol through PTEN modulation

Current therapeutic strategies against hepatocellular carcinoma (HCC)mainly focus on targeting differentiated tumor cells. However, success of treatment is limited due to presence of primitive cancer stem cells (CSCs). There is an urgent need in search of novel therapeutic targets for liver CSCs, while sparing normal liver stem cells. Previously, our group has identified lupeol, a triterpene found rich in fruits and vegetables, to be able to reverse the EMT process of head and neck cancer. In accordance with epidemiologic studies attributing lower incidence of HCC to the high intake of fruits and vegetables, we hypothesized that lupeol might specifically target liver CSCs. In this study, we found that lupeol selectively induced substantial apoptosis of panels of HCC cell lines at high doses ranging from 80µM to 120µM, but exhibited only a minimal effect on an immortalized liver cell, MIHA in vitro.The ability to self-renew is one of the key characteristics of CSCs, we examined the effect of lupeol on CSCs by evaluating the number of spheroids developed by sphere formation assay upon addition of lupeol at low dose. Treatment with low dose lupeol (1µM to 15µM), which bears no growth inhibitory effect on Huh-7 and PLC cells, completely suppressed spheroid formation at 15µM. Consistently, lupeol was also found to suppress spheroid formation in five cases of HCC clinical samples. The inhibitory effect of lupeol on self-renewal was further confirmed in vivo by subcutaneously inoculation with HCC cell lines (Huh-7-luc and PLC-luc) either untreated or treated with lupeol for 3 days. All mice (6/6) either inoculated with untreated Huh-7-luc or PLC-luc exhibited tumor formation, while none of the mice (0/6) exhibited tumor formation after lupeol treatment. Given the chemoresistant nature of CSCs, we examined whether lupeol chemosensitized HCC cells to chemotherapeutic drugs. Using MHCCLM3 as a chemoresistant model, we found lupeol to chemosensitize MHCCLM3 cells to both cisplatin and doxorubicin through the down-regulation of ATP transporter proteins. Lupeol was found to target liver CSCs through transcriptional activation of PTEN and its down-stream signaling pathway. Recent evidence demonstrated PTEN inactivation has opposite effects on normal hematopoietic and leukemia-initiating cells, raising the possibility that drugs targeting this pathway could be more effective in eliminating CSCs while less effects on normal stem cells. The differential dependence on PTEN between normal liver stem cells and CSCs is currently being investigated. Western blot data from our group has found 58% down-regulation of PTEN in HCC samples when compared with their non-tumor, revealing lupeol as a potential specific agent to target liver CSCs. Our study provides evidence that inhibitors of CSCs may occur naturally in fruits and vegetables and its intake might have a surprising positive effect on cancer therapy.

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 1066.