Integrins are key mediators of cell state and tumour heterogeneity

Human cancers display a high degree of intratumoural heterogeneity (ITH), largely driven by heterogeneous genetic/epigenetic alterations and interactions with the cellular microenvironment resulting in functionally diverse cell subpopulations with differing clinical implications. In order to better isolate, study and potentially target clinically relevant tumour subpopulations, I developed a methodology for simultaneous target discovery and synthetic antibody generation, coined CellectAb. This approach allowed me to discover, develop and characterize antibodies against CD133 positive colorectal cancer initiating cells (CICs). Surprisingly, two of the three antibodies I discovered and characterized recognize members of the integrin family of cell adhesion molecules: integrins alpha (α) 7 and beta (β) 6. These antibodies enrich for self-renewing CICs, and genetic ablation of integrin β6 impedes colorectal CIC function. Together, these findings validate the CellectAb approach, identify two integrins as novel colorectal CIC markers, and provide a rational for therapeutic targeting of integrin β6. Integrins play critical roles in many cancer biological processes including survival, proliferation, invasion and metastasis. While seven drugs targeting leukocyte/platelet integrins have progressed to market, drugs against solid tissue integrins, especially αV, fail to show clinical efficacy despite promising preclinical results. In chapter 3, I hypothesize that a contributing reason for this failure may be that without αV function, cells relate very differently to the extra cellular matrix (ECM) microenvironment. Specifically, loss of αV robustly mediates the loss of adherent growth and switch to a viable three dimensional sphere state in cell types ranging from fibroblasts to epithelial cancers. Surprisingly, this phenotype is completely reversed when exogenous ECM is provided or metabolic redox conditions are perturbed. This unexpected discovery stemmed from parallel functional genetic screen approaches to identify genes regulating proliferative interaction with the ECM. Together, my thesis contributes to a better understanding of how cancer cells functionally interact with their microenvironment through various integrins, and provides a new technology for marker discovery on rare cell populations.Ph.D.2020-07-11 00:00:0