J Cancer 2016; 7(9):1142-1151. doi:10.7150/jca.10047
Liver Label Retaining Cancer Cells Are Relatively Resistant to the Reported Anti-Cancer Stem Cell Drug Metformin
1. Surgery Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA;
2. Laboratory of Molecular Oncology, Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education), Peking University Cancer Hospital and Institute, Beijing 100142, China;
3. Collaborative Protein Technology Resource, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA;
4. Laboratory for Experimental Carcinogenesis, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA;
5. Department of Surgery, Uniformed Services University of the Health Sciences, Bethesda, MD, USA;
6. Department of Surgery, Saint Peter's Healthcare System, Rutgers University, New Brunswick, NJ 08901, USA.
*Authors contributed equally.
Xin HW, Ambe CM, Miller TC, Chen JQ, Wiegand GW, Anderson AJ, Ray S, Mullinax JE, Hari DM, Koizumi T, Godbout JD, Goldsmith PK, Stojadinovic A, Rudloff U, Thorgeirsson SS, Avital I. Liver Label Retaining Cancer Cells Are Relatively Resistant to the Reported Anti-Cancer Stem Cell Drug Metformin. J Cancer 2016; 7(9):1142-1151. doi:10.7150/jca.10047. Available from http://www.jcancer.org/v07p1142.htm
Background & Aims: Recently, we reported that liver Label Retaining Cancer Cells (LRCC) can initiate tumors with only 10 cells and are relatively resistant to the targeted drug Sorafenib, a standard of practice in advanced hepatocellular carcinoma (HCC). LRCC are the only cancer stem cells (CSC) isolated alive according to a stem cell fundamental function, asymmetric cell division. Metformin has been reported to preferentially target many other types of CSC of different organs, including liver. It's important to know if LRCC, a novel class of CSC, are relatively resistant to metformin, unlike other types of CSC. As metformin inhibits the Sorafenib-Target-Protein (STP) PI3K, and LRCC are newly described CSC, we undertook this study to test the effects of Metformin on Sorafenib-treated HCC and HCC-derived-LRCC.
Methods: We tested various STP levels and phosphorylation status, associated genes' expression, proliferation, viability, toxicity, and apoptosis profiles, before and after treatment with Sorafenib with/without Metformin.
Results: Metformin enhances the effects of Sorafenib on HCC, and significantly decreased viability/proliferation of HCC cells. This insulin-independent effect was associated with inhibition of multiple STPs (PKC, ERK, JNK and AKT). However, Metformin increased the relative proportion of LRCCs. Comparing LRCC vs. non-LRCC, this effect was associated with improved toxicity and apoptosis profiles, down-regulation of cell death genes and up-regulation of cell proliferation and survival genes in LRCC. Concomitantly, Metformin up-regulated pluripotency, Wnt, Notch and SHH pathways genes in LRCC vs. non-LRCC.
Conclusions: Metformin and Sorafenib have enhanced anti-cancer effects. However, in contradistinction to reports on other types of CSC, Metformin is less effective against HCC-derived-CSC LRCC. Our results suggest that combining Metformin with Sorafenib may be able to repress the bulk of tumor cells, but as with other anti-cancer drugs, may leave LRCC behind leading to cancer recurrence. Therefore, liver LRCC, unlike other types of CSC, are relatively resistant to the reported anti-cancer stem cell drug metformin. This is the first report that there is a type of CSC that is not relatively resistant to the CSC-targeting drug. Our findings suggest that a drug targeting LRCC may be critically needed to target CSC and prevent cancer recurrence. These may significantly contribute to the understanding of Metformin's anti-cancer effects and the development of novel drugs targeting the relatively resistant LRCC.
Keywords: Metformin, sorafenib, PKC/ERK/JNK/AKT phosphorylation, MAPK, stem-like label-retaining cancer cells, LRCC, HCC, cancer-stem-cells.