The G protein-coupled receptor (GPCR) and chemokine receptor CXCR4 plays an essential role in tumor initiation and maintenance. This is exemplified in acute myeloid leukemia (AML), where CXCL12-mediated CXCR4 signaling plays a pivotal role for the crosstalk between leukemic stem cells and their microenvironmental niche. Despite the key role of CXCR4 in cancer, surprisingly little is known about endogenous mechanisms that specifically target CXCR4 and dampen its activity. Here, we demonstrate

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... t the naturally occurring peptide and CXCR4 antagonist EPI-X4 and its optimized derivatives effectively blocks CXCL12-mediated migration of AML cells towards a CXCL12 gradient and impairs growth of AML cells in vitro and in vivo in contrast to normal hematopoietic stem and progenitor cells. This anti-leukemic activity of EPI-X4 was accompanied by suppression of CXCR4-mediated MAPK signaling. Of note, EPI-X4 suppressed metabolic pathways and induced depletion of intracellular nicotinamide phosphoribosyltransferase (iNAMPT) in AML cells, linking anti-CXCR4 activity to shifts in NAD+ metabolism.