Screening Small Molecule Inhibitors of VLA-5 to Block the Interaction Between Acute Lymphoblastic Leukemia with Ph+ and Their Microenvironment.

Abstract 1027

Integrin VLA-5 (α5β1, CD49e/CD29) plays an important role in hematopoietic cells functioning as well as in promoting tumor angiogenesis and tumor metastasis. Molecules targeting VLA-5 can be rapidly developed into anti-inflammatory and anti-tumor pharmaceuticals. VLA-5 is highly expressed on Ph+ leukemia cells and VLA-5 inhibitory antibodies can significantly inhibit the adhesion of Ph+ leukemia cells to human fibronectin. We generated an atomic homology model of VLA-5 based on the crystal structure of the extracellular segment of integrin αVβ3 in complex with a cyclic peptide presenting the Arg-Gly-Asp sequence and utilized this structure-based approach to identify VLA-5 binding drug-like small molecules. We selected the Arg-Gly-Asp binding residues and the epitopes of VLA-5 antibody as the target for small molecule binding using SPHERE_SELECT in DOCK6. The grid-based scoring system was used for scoring with the non-bonded force field energy function. The 100 highest scoring small molecules were assayed in an in vitro adhesion assay using leukemia cell lines and solid phase assay. This approach identified several leading small-molecule compounds, V10, V20, V37 and L4. Their IC50 are respectively 22.5μM, 23.7μM, 32.0μM and 28.9μM. These compounds can inhibit the adhesion of VLA-5 expressing Philadelphia chromosome positive leukemia to both human fibronectin and bone marrow stromal cells. Compounds V10 and V20 also significantly inhibited the growth of Ph+ leukemia cells. These compounds can enhance the effect of imatinib and dasatinib to kill Ph+ leukemia cells when cultured contacting with bone marrow stromal cells. We are currently testing the synergistic effect of these compounds with tyrosine kinase inhibitors to treat the Ph+ acute lymphoblastic leukemia in NOD/SCID animal model.