PO-503 The cohesin stromal antigen 1 (SA-1) modulates colonic and colorectal cancer (CRC) stem cells: mechanism for racial disparities

Abstract

IntroductionCRC disproportionately impacts African-Americans (incidence and mortality increased by ~25% and~50%, respectively). While mechanisms remain unclear, Vogelstein posited that the number of stem cell divisions determine CRC risk Science 2015. CRC stem cells may impact mortality via chemoresistance. LGR5, aldehyde dehydrogenase (ALDH1a3) and DCAMKL1 are markers of both intestinal and CRC stem cells. We have noted loss of SA-1 (a chromatin remodeler) occurred during colonic field carcinogenesis was markedly accentuated in Blacks (Cancer Prev Res 2016) via specific SNPs (Neoplasia 2018). SA-1 loss was also associated with poorer CRC prognosis. We hypothesised that SA-1 loss leads to stem cell induction and hence CRC disparities.Material and methodsRectal biopsies were obtained from endoscopically normal mucosa from ~200 patients undergoing screening colonoscopy with an IRB approved protocol. SA-1 was assessed by RT-PCR normalised to β-actin. We modulated SA-1 in human CRC cell line HT29 and tested efficacy of chemotherapy 5 fluorouracil (5-FU) and oxaliplatin via annexin V apoptosis assay.Results and discussionsAdenoma-harbouring subjects had ~50% increase in LGR5, ALD1a3 and DCAMKL1 (p<0.05) with concomitant suppression of SA-1. Causality was indicated by demonstrating that SiRNA SA-1 knockdowns (KD) in HT29 cells caused stem cell marker induction (LGR5=380%, ALD1a3=30% and DCAMKL1=85%, p<0.05). SA-1 overexpression resulted in reciprocal effects downregulation of all 3 stem cell markers. Functionally, SA-1 KD suppressed 5-FU and oxaliplatin induced apoptosis by 56% and 72% respectively versus scramble vector (p<0.0001). Underscoring racial disparities relevance was the observation that Blacks have a 31% greater SA1 loss vs. Whites (p<0.0004) which mirrored a 35% higher upregulation in LGR5 and ALDH1a3 (p<0.05). CRISPR editing of RKO cells to have the SNP rs34149860 (found only in Blacks) resulted in SA1 loss (41% loss, p<0.005) and concomitant ~45% LGR5 and ALDH1a3 upregulation (p<0.05).ConclusionThis novel finding that the proneoplastic effects of SA-1 loss may be transduced through intestinal/colonic stem cell (CRC incidence) and also augmenting CRC stem cells resulting in chemotherapy resistance (CRC mortality). Future studies may mitigate CRC disparities in Blacks through development of effective biomarkers and therapeutic.