FLT3 internal tandem duplication (ITD) mutations are the most common alterations in acute myeloid leukemia (AML) and are associated with poor disease prognosis. Targeted therapy using FLT3-ITD inhibitors showed limited effect in reducing leukemia blasts in bone marrow (BM) than that in peripheral blood. The BM microenvironment is enriched with cytokines and adhesion molecules, such as CXCR4 and E-selectin, which are believed to provide AML cells protection against chemotherapeutic agents. Therefore, blocking CXCR4 and E-selectin concomitantly with FLT3 inhibition could theoretically eliminate the protection in FLT3-mutant AML patients. We recently reported that targeting CXCR4/E-selectin with the dual inhibitor GMI-1359 showed significant prolongation of survival of mice engrafted with FLT3-ITD mutant MV4-11 leukemia cells. In the present study, we further investigated anti-leukemia effects of dual CXCR4/E-selectin inhibition. Results indicate efficient mobilization of leukemia cells into the circulation by GMI-1359 in a MOLM14-engrafted murine model 2h after drug treatment, which was 3.3-fold (± 0.3) higher compared with the CXCR4 antagonist plerixafor, and 7.4-fold (± 2.7) higher compared with controls. In addition, GMI-1359 also mobilized normal murine leukocytes from the BM, suggesting that GMI-1359 may block interactions of leukemia cells with various BM components. Combination therapy of GMI-1359 and sorafenib significantly reduced leukemia burden (1.9e7 vs. 2.3e9, 1.0e9 and 8.5e7 photons/sec in the combination group versus control, GMI-1359 and sorafenib groups, respectively, at day 20 as determined by Xenogen IVIS bioluminescence Imaging; p < 0.001). Moreover, the combination treatment profoundly reduced leukemia burden in the BM of leukemic mice after a 15-day treatment (1.7e7 vs. 1.6e9, 6.3e8 and 7.0e7 photons/sec, p < 0.01; and 1.76% vs. 70.96%, 72.8% and 33.8%.leukemia cell engraftment measured as GFP positive leukemic cells in BM by flow cytometry, in the combination group vs. vehicle, GMI-1359 and Sorafenib groups, respectively, p < 0.01). Of note, the combination therapy profoundly extended the median survival of the leukemia-bearing mice from 27 days in the control group to 46.5 days in the combination treatment groups (p < 0.001). Mechanistically, we demonstrated that direct blockade of the interaction of E-selectin-CXCR4/SDF-1α with GMI-1359 was critical for leukemic cell mobilization via the disruption of adhesion to stromal cells. Furthermore, the presence of GMI-1359 enhanced sorafenib-induced apoptosis in FLT3-ITD mutated leukemic cells co-cultured with stromal cells. This effect occurred even under hypoxia, which is characteristic for the leukemic BM microenvironment. These findings provide the pre-clinical basis for the evaluation of GMI-1359 in patients with FLT3-mutant AML.

Citation Format: Weiguo Zhang, Hong Mu, Qi Zhang, Nalini B. Patel, William E. Fogler, John L. Magnani, Michael Andreeff. Targeting E-selectin/CXCR4 with GMI-1359 effectively mobilizes bone marrow leukemia cells and enhances FLT3 inhibitor-induced anti-leukemia efficacy in a murine acute myeloid leukemia model. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3284.