The Role of the Aryl Hydrocarbon Receptor in DNA Methylation of the Immune Checkpoint Genes of Colon Cancer Stem Cells: In Vitro and Clinical Studies on Omani and Qatari Patients

Study rationale: Colorectal cancer (CRC) is a frequently diagnosed neoplasm and ranked second in women after breast cancer and third in men after prostate and lung cancer. In Qatar and Oman, CRC is third most commonly diagnosed cancer and a leading cause of cancer-related deaths in the country. In 2018, the annual incidence of colorectal cancer in Qatar was estimated to be 11.3%, with around two third of the cases were diagnosed at an advanced stage, regardless of the efficient treatment regimen. One of the recent theories for cancer recurrence and resistance is the development of a highly resistant to all therapies with self-renewal and infinite proliferation properties, known now as Cancer Stem Cells (CSCs). CSCs are driving tumor initiation, progression, metastasis and poor prognosis. Previous studies have linked the development of CSCs with the expression of Aryl hydrocarbon receptor (AhR) pathway in several cancer stem cells of breast and ovarian, but not colon cancer. On the other hand, recent advancements in research have been made to explore the modulation of immune checkpoint (ICP) on cancer development. Scientistic objectives and innovations: There are gaps in the knowledge with regard to the interaction and crosstalk between AhR and ICP in colon cancer stem cells. Thus, we hypothesize that blockade of the immune checkpoint pathway inhibits CSCs proliferation, development, and chemoresistance is an AhR-dependent mechanism, and thus considered as a novel biomarker and targeted therapy for the treatment of cancer. Systems. Methodology: To test our hypothesis, the study will be conducted in two phases. Phase 1 will be in vitro study, where we will first identify and characterize cancer stem cells from colon four different cancer cell lines caco-2, HCT116, SW480, and LS174T. Second, we will Explore the constitutive and inducible expression and function of AhR and ICP pathways in both colon cancer and their corresponding colon CSCs at the mRNA, protein and immunofluorescence levels. Third, we will investigate the impact of AhR activation/inhibition and ICP (PD-1, CTLA-4, and LAG3) inhibition on CSCs development, self-renewal and chemoresistance. Phase 2, in a Human-based study, where we will test hour hypothesis on human colon cancer tissues to validate our findings. In this phase, human colon cancer tissues and blood samples will be utilized to explore the expression of AhR and CTLA-4 and their impact on the aggressiveness and stages of the cancer. In addition, the role DNA methylation will be also investigated. Impact of the project: This detailed study on how AhR pathway regulates ICP system in CSCs driving the development of novel anti-cancer drugs potentially targeting AhR could be promising to overcome the existing challenges associated with colon cancer treatment. This study could help in identify a novel biomarker for early detection and open the gate for the development of a novel therapeutic target for CRC.