Abstract B19: The role of ABCB1 genotypes and targeting cancer stem cells in pancreatic cancer: Effects of metformin and dietary agents
Authors: Lyn-Cook Beverly D. , Word Beverly , Hammons George 
Published: December 2017

Pancreatic cancer carries a poor prognosis and survival rate. Developing effective agents or repurposing agents with low toxicity, such as metformin, an insulin-lowering drug, has recently been investigated for pancreatic cancer. Metformin has long been associated with decreased cancer risk, particularly in diabetic patients. Cancer stem cells have been identified in pancreatic tumors and have been shown to contribute to its progression and resistance to standard treatments. Pancreatic cancer stem cells are subject to regulation by key embryonic stem cell transcription factors that are known to be aberrantly expressed in pancreatic cancer, such as SOX2, OCT4 and NANOG. Overexpression of OCT4, SOX2 and NANOG together or separately leads to tumor transformation and tumor metastasis. These stem cell factors are known to promote self-renewal by interacting with other transcription factors. Using a human embryonic stem cell RT2 Profiler gene array, numerous stem cell genes were expressed in pancreatic cancer cell lines (MIAPaca2, Panc1). Both cell lines expressed high levels of SOX2, NANOG, CD44, GATA2, POU5F1 (OCT4) and other genes. Panc1 expressed high levels of SOX 17, while MIAPaCa2 expressed high levels of SOX 3, 15 and 17. Treatment of cells with the dietary agent, indole-3-carbinol alone at 100 or 200 µM inhibited or decreased the expression of SOX2, NANOG, CD44, SOX15 and STAT3. However, treatment with metformin alone increased expression of SOX15 and STAT3 in Panc1 cells but not in MIAPaCa2. Combination of metformin and indole-3-carbinol inhibited the expression of SOX2, NANOG, STAT3, and CD44. Expression levels of drug transporters in pancreatic tissue can also affect potential treatment of pancreatic cancer. High level of expression of ABCB1 causes multidrug-resistance. Metformin modulated the ATP-binding cassette gene, ABCB1, expression in pancreatic cancer cell lines with different ABCB1 genotypes. Metformin (100 µM or 200 µM) alone (p=0.0212 or p=0.0161) or in combination with gemcitabine (15nM) (p=0.0248 or p=0.0174) significantly decreased ABCB1 expression in MIAPaCa2 pancreatic cells after 24 hr or 72 hr treatments. This correlated to increased cell death. Metformin in combination with indole-3-carbinol also significantly (p=0.0317) decreased ABCB1 expression. However, a sex or genotype difference was noted when two female pancreatic cell lines, SU86.86 and AsPC1, were used. Metformin did not down-regulate ABCB1 expression and was chemoresistance in these two cell lines. AsPC1 and SU86.86 both carry the 2677GG-3435CC ABCB1 haplotype compared to MiaPaca-2, which carries the 2677TT-3134TT ABCB1 haplotype. The 2677TT and 3435TT genotypes/haplotypes are known to be associated with lower risk of developing pancreatic cancer. These data demonstrated that these genotypes are also more sensitive to metformin treatment compared to the 2677GG or 3435CC genotypes. Further research is needed to ascertain whether sex or genotype is contributing to different efficacy of metformin in pancreatic cancer cells with different genotypes. This study have shown that the dietary agent, indole-3-carbinol alone and in combination with metformin down-regulate critical stem cell genes involved in maintenance of pluripotency and self-renewal of cancer stem cells. Furthermore, downregulation of ABCB1 expression varied with treatment with specificity to certain genotypes.

Citation Format: Beverly D. Lyn-Cook, Beverly Word, George Hammons. The role of ABCB1 genotypes and targeting cancer stem cells in pancreatic cancer: Effects of metformin and dietary agents [abstract]. In: Proceedings of the AACR International Conference: New Frontiers in Cancer Research; 2017 Jan 18-22; Cape Town, South Africa. Philadelphia (PA): AACR; Cancer Res 2017;77(22 Suppl):Abstract nr B19.