AML-337: Targeting E-Selectin with GMI-1271 Overcomes Microenvironment-Mediated Resistance to Venetoclax/HMA Therapy

Acute myeloid leukemia (AML) is an aggressive heterogeneous hematologic disease with high mortality in patients older than 60 years. Clinical studies have proven that combinations of FDA-approved Bcl-2 inhibitor, venetoclax and hypomethylating agents (HMA) are highly effective in elderly patients with AML (DiNardo et al., 2019). Adhesion to the BM niche is critical for AML initiation, progression and LSC survival after induction therapy. The vascular adhesion molecule, E-selectin (E-sel) has crucial roles in BM homing and engraftment in leukemia (Krause et al, 2006). Here we elucidated the roles of E-sel in AML survival using human AML cell lines and patient-derived AML xenograft (PDX) models. In our experiments, E-sel decreased CDK4/6 expression and increased dormancy of AML cells in vitro. Pharmacological inhibition of E-sel by GMI-1271 increased expression of cell cycle regulating proteins including CDK4/6 and CyclinD1/2 in HUVEC co-cultured AML. To determine if E-sel has indispensable effects in BM niche component cells, we exposed healthy donor derived-mesenchymal stroma cells (MSC) to increasing concentrations of E-sel: E-sel upregulated surface expression of the most potent E-sel ligand, CD44 in human MSC and abrogation of E-sel binding by GMI-1271 diminished CD44 expression in vitro. Targeting E-sel with GMI-1271 attenuated eNOS phosphorylation in HUVEC co-cultured with AML cells, suggesting that E-sel inhibition may protect disruption of BM vasculatures during AML progression. Further, we found that targeting E-sel mobilized human AML cells and sensitized them to venetoclax/HMA in a PDX model derived from a patient who had developed resistance to venetoclax/HMA. The number of circulating leukemic cells was significantly reduced by combinatorial treatment of GMI-1271 with venetoclax/HMA compared to venetoclax/HMA alone (p<0.05). In addition, the combination of GMI-1271 and venetoclax/HMA significantly prolonged the survival of mice compared to vehicle control (p=0.015) as well as the venetoclax/HMA (p=0.0009) and GMI-1271 groups (p=0.03). The median survival of the vehicle control, GMI-1271, venetoclax/HMA, and combination-treated groups of mice was 86, 91, 81.5, and 106.5 days, respectively. Collectively, our results provide first evidence that an E-sel targeting strategy with GMI-1271 may overcome microenvironmental resistance to venetoclax/HMA-based therapy in AML by disrupting signaling pathways in the BM vascular niche.