A novel small molecule CXCR4 antagonist improves anticancer therapy by blocking the interaction of malignant cells with their associated niches

Acute myeloid leukemia (AML) is a blood cancer characterized by uncontrolled proliferation of leukemic stem/progenitor cells. The retention and chemoresistance of AML cells in the bone marrow microenvironment are mediated by stromal cell-derived factor-1(SDF-1)/C-X-C chemokine receptor type 4 (CXCR4) axis. We recently developed a novel small molecule CXCR4 antagonist (designated HF51116) with a higher affinity than AMD3100 specifically for improving AML chemotherapy. Competitive binding assays confirmed that HF51116 bound to the surface of malignant U937 and HL60 cells with high affinities. Transwell assay results demonstrated that HF51116 blockade inhibited the SDF-1induced migration of U937 and HL60 cells with a concentration-dependent manner, as well as the migration induced by BMSCs. The mechanism for HF51116 in U937 and HL-60 cells migration appeared to involve attenuation of the SDF-1induced cytoskeletal re-arrangement and phosphorylation of AKT (S437) and ERK1/2 (Thr202/Tyr204). In addition, HF51116 reversed the chemoresistance of U937 cells co-cultured with BMSCs by increasing Annexin V expression and caspase-3 activity, resulting in decreased cell viability. In vivo experiments on AML xenograft mice revealed that subcutaneous administration of HF51116 mobilized the engrafted U937-Luc/EGFP cells from the bone marrow and spleen into the peripheral blood. Co-administrating HF51116 and cytarabine (Ara-C) further reduced the in vivo AML burden and expanded the lifespan of AML xenograft mice beyond that seen with Ara-C monotherapy. These results demonstrated that the novel CXCR4 antagonist HF51116 has potent anti-leukemic effects both in vitro and in vivo.