Targeting of CXCR4 by the naturally occurring CXCR4 antagonist EPI-X 4 in Waldenström’s Macroglobulinemia

Abstract

CXCR4 expression and downstream signaling have been identified as key factors in malignant hematopoiesis. Thus, up to 40% of all patients with Waldenstrom Macroglobulinemia carry an activating mutation of CXCR4 that leads to a more aggressive clinical course and inferior outcome upon treatment with the Bruton's tyrosine kinase inhibitor ibrutinib. Nevertheless, little is known about physiological mechanisms counteracting CXCR4 signaling in hematopoietic neoplasms. Recently, the endogenous human peptide EPI-X4 was identified as a natural CXCR4 antagonist that effectively blocks CXCL12-mediated receptor internalization and suppresses the migration and invasion of cancer cells towards a CXCL12 gradient. Here, we demonstrate that EPI-X4 efficiently impairs growth of WM cells in vitro and in vivo and blocks their migration towards CXCL12. The CXCR4 inhibitory activity of EPI-X4 is accompanied by decreased expression of genes involved in MAPK signaling and energy metabolism. Notably, the anti-WM activity of EPI-X4 could be further augmented by the rational design of EPI-X4 derivatives showing higher binding affinity to CXCR4. In summary, these data demonstrate that a naturally occurring anti-CXCR4 peptide is able to interfere with WM growth, and that optimized derivatives of EPI-X4 may represent a promising approach in suppressing growth promoting CXCR4 signaling in WM.

Acute myeloid leukemia cells are targeted by the naturally occurring CXCR4 antagonist EPI-X4

“…Thus, beside downregulation of CXCR4–dependent signaling, our data point to another yet unknown effect of EPI-X4 and that is to change metabolism, linking its anti-cancer activity to metabolic shifts. These alterations in metabolism seem not to be cancer subtype-specific as we observed the modulation of metabolic pathways also in WM, an indolent B-cell lymphoma, for which activating CXCR4 mutations are a major driver of tumor growth 3,29 . In recent years, there has been growing interest into metabolism of cancer, also with the aim to identify metabolic vulnerabilities in malignant cells.…”

“…Inhibition of ERK and AKT signaling was performed as previously described 29 : briefly, cells were seeded in 100 μl starvation medium (RPMI, 1% FCS) and starved for 2 hours. 5 μl compound in PBS was added and cells were further incubated for 15 min.…”

Absence of the CXCR4 Antagonist EPI-X4 from Pharmaceutical Human Serum Albumin Preparations

“…EPI-X4 is a natural endogenous cleavage product of albumin that antagonizes CXCR4 and might play an important regulatory role in CXCR4 signaling. As a pharmacological compound, EPI-X4 behaves like a typical CXCR4 antagonist and blocks CXCL12 mediated signaling and cancer cell migration in vitro and mobilizes stem cells in vivo [13,17,18]. Moreover, EPI-X4 also acts as inverse agonist of CXCR4 and downregulates the intrinsic signaling activity of the receptor [13].…”

Absence of the CXCR4 antagonist EPI-X4 from pharmaceutical human serum albumin preparations

“…EPI-X4 is a natural endogenous cleavage product of albumin that antagonizes CXCR4 and might play an important regulatory role in CXCR4 signaling. As a pharmacological compound, EPI-X4 behaves like a typical CXCR4 antagonist and blocks CXCL12 mediated signaling and cancer cell migration in vitro and mobilizes stem cells in vivo [13,17,18]. Moreover, EPI-X4 also acts as inverse agonist of CXCR4 and downregulates the intrinsic signaling activity of the receptor [13].…”

“…Like AMD3100, EPI-X4 binds CXCR4 and prevents interaction with its most important ligand, chemokine CXCL12, and thereby blocks CXCL12-evoked responses such as cell migration [ 13 , 16 ]. Furthermore, synt, hetic EPI-X4 shows therapeutic effects in mouse models of asthma, atopic dermatitis and Waldenström’s Macroglobulinemia, and mobilizes hematopoietic stem cells in mice [ 13 , 17 , 18 ]. EPI-X4 can be generated in vivo and is for example present at µg/mL concentrations in urine of patients with chronic kidney disease [ 13 ], but the peptide is not detectable at relevant concentrations in human plasma [ 19 ] and its physiological role in vivo remains to be clarified.…”