Investigating the mechanism of ITGA4/6-mediated chemoprotection of ALL cells

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DESCRIPTION (provided by applicant): Acute lymphoblastic leukemia is the most common childhood cancer and the 10th most common adult cancer in the United States. Drug resistance remains a major problem in the treatment of acute lymphoblastic leukemia (ALL). The bone marrow (BM) environment, consisting of endosteal and perivascular niches, has been shown to promote cell adhesion-mediated drug resistance (CAM-DR) in leukemia cells. Incomplete response to chemotherapy results in persistence of resistant clones and minimal residual disease (MRD). The exact mechanisms for CAM-DR leading to MRD and approaches to address this problem remain elusive. Integrin ¿4 mediates adhesion of hematopoietic cells onto bone marrow cells and has been implicated in CAM- DR of leukemia cells. We have determined that integrins ¿4 and ¿6 are the most upregulated integrins in pre-B ALL. We hypothesize that ¿4 and ¿6 integrin-mediated adhesion of ALL cells to bone marrow stromal niches contributes to the persistence of MRD. Integrin ¿4 and ¿6 loss-of-function studies in a BCR-ABL1+ pre-B ALL mouse model resulted in loss of adhesion, increased chemo-sensitivity and decreased self-renewal capacity of ALL cells. Using FDA approved Natalizumab as ¿4 blocking antibody, we demonstrated in a xenogeneic ALL model that ¿4-blockade with chemotherapy can eradicate leukemia. Delineating the mechanistic basis for this concept will enable us to validate and further develop this treatment approach towards patient care.