Abstract C036: Cohesins and colorectal cancer (CRC): Modulation of CRC stem cells and chemoresistance by STAG1 with race-specific implications
Authors: Dela Cruz Mart , Zaworski Caroline , Datta Somenath , Chowdhury Sanjib , Roy Hemant K. 
Published: August 2020

Abstract
Despite advances in treatment and early detective measures for colorectal cancer (CRC), African-Americans (AAs) suffer disproportionately from CRC (~25% higher incidence and ~50% higher mortality) than Caucasians. Furthermore, AAs tend to receive earlier diagnoses in CRC and AA CRCs with high-grade differentiation were 3xs more likely to die within 5 yrs post-surgery as compared to whites (Alexander et al., Cancer 2005). The underlying mechanisms behind this more aggressive disease in AAs are poorly understood. Tomassati and Vogelstein postulate stem cell division correlates with risk of cancer (Science 2015). Addressing disease progression/aggressiveness, CRC stem cell markers are linked to chemoresistance; stem cell markers LGR5 and ALDH1a are established CRC stem cell markers. We have shown that the cohesin family member STAG1, a chromatin remodeler, is lost in the colonic epithelium of patients with premalignant lesions and AAs had a more profound loss (Cancer Prev Research 2016) through AA-specific STAG1 SNPs (Neoplasia 2018) and hypothesize that STAG1 loss is associated with poorer prognosis. Therefore, we wanted to investigate if STAG1 loss may lead to CRC stem cell induction as a potential mechanism of the racial disparities in CRC. RNA from rectal biopsies from 100 patients undergoing screening colonoscopies was processed for real-time PCR for CRC stem cell markers LGR5 and ALDH1a, as well as STAG1. To determine chemoresistance, STAG1 siRNA was transfected in CRC cell line HT29 and a CRISPR transfection of STAG1 SNP rs34149860 (found only in AAs) was transfected in CRC cell line RKO (possessing wildtype to SNP). Cell were treated with 5-FU and oxaliplatin and subjected to Annexin V Assay. Real-time PCR and analysis of STAG1 and CRC stem cell markers were performed for causation. AAs harboring neoplasias displayed a more robust loss of STAG1 mRNA (~50%, p&lt;0.007) vs Caucasians with neoplasias (~25%, p=0.1). In regard to CRC stem cell markers, AAs with adenomas showed a stronger increase of LGR5 (67%, p=0.14), and ALDH1a (73%, p&lt;0.007) vs Caucasians with neoplasias (LGR5 increased 59%, p=0.2; ALDH1a increased ~47%, p&lt;0.05). HT29 cells transfected with STAG1 siRNA showed 30% less apoptotic response to 5-FU vs scramble vector and a marked 74% less response with oxaliplatin. CRIPSR SNP transfection in RKO showed similar effects, with a 2-fold less apoptotic response to 5-FU and &gt;90% less response to oxaliplatin. PCR showed RKO STAG1-SNP transfected cells displayed a loss of STAG1(~40%, p&lt;0.05) and an upregulation of LGR5 (~50%, p&lt;0.05) and ALDH1a (~30%, p&lt;0.05). This shows, for the first time, that STAG1 loss is implicated in colon carcinogenesis through potentiation of cancer stem cells through early carcinogenesis/initiation as well as disease progression and aggressiveness as shown through chemoresistance. Our work provides a potential mechanism in CRC, thus providing a biomarker for cancer screening and therapeutics that could mitigate the racial disparity of CRC in AAs.
Citation Format: Mart Dela Cruz, Caroline Zaworski, Somenath Datta, Sanjib Chowdhury, Hemant K. Roy. Cohesins and colorectal cancer (CRC): Modulation of CRC stem cells and chemoresistance by STAG1 with race-specific implications [abstract]. In: Proceedings of the Eleventh AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2018 Nov 2-5; New Orleans, LA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(6 Suppl):Abstract nr C036.