Biased antagonism of CXCR4 avoids antagonist tolerance

Abstract

Repeated dosing of drugs targeting G protein–coupled receptors can stimulate antagonist tolerance, which reduces their efficacy; thus, strategies to avoid tolerance are needed. The efficacy of AMD3100, a competitive antagonist of the chemokine receptor CXCR4 that mobilizes leukemic blasts from the bone marrow into the blood to sensitize them to chemotherapy, is reduced after prolonged treatment. Tolerance to AMD3100 increases the abundance of CXCR4 on the surface of leukemic blasts, which promotes their rehoming to the bone marrow. AMD3100 inhibits both G protein signaling by CXCR4 and β-arrestin1/2–dependent receptor endocytosis. We demonstrated that biased antagonists of G protein–dependent chemotaxis but not β-arrestin1/2 recruitment and subsequent receptor endocytosis avoided tolerance. The peptide antagonist X4-2-6, which is derived from transmembrane helix 2 and extracellular loop 1 of CXCR4, limited chemotaxis and signaling but did not promote CXCR4 accumulation on the cell surface or cause tolerance. The activity of X4-2-6 was due to its distinct mechanism of inhibition of CXCR4. The peptide formed a ternary complex with the receptor and its ligand, the chemokine CXCL12. Within this complex, X4-2-6 released the portion of CXCL12 critical for receptor-mediated activation of G proteins but enabled the rest of the chemokine to recruit β-arrestins to the receptor. In contrast, AMD3100 displaced all components of the chemokine responsible for CXCR4 activation. We further identified a small molecule with similar biased antagonist properties to those of X4-2-6, which may provide a viable alternative to patients when antagonist tolerance prevents drugs from reaching efficacy.

Chemokines and galectins form heterodimers to modulate inflammation

“…Unexpectedly, the effect of Gal‐3 CRD was not accompanied by reduced internalization of CXCR4 (Fig D), which is mediated by β‐arrestin recruitment . However, it has been reported that chemokine receptors may signal in a biased fashion, with β‐arrestin recruitment and internalization being uncoupled .…”

β-Arrestin1 and β-Arrestin2 Are Required to Support the Activity of the CXCL12/HMGB1 Heterocomplex on CXCR4

“…So far, AMD3100 is the only CXCR4 unbiased antagonist approved for the use in the clinic, which blocks the activity of both G proteins and β-arrestins, and is also able to inhibit the function of the CXCL12/HMGB1 heterocomplex ( 6 ). To avoid development of tolerance induced by the use of AMD3100, other approaches to block the activity of CXCR4 have been exploited including the use of peptides with biased activity ( 17 ). In addition, the emerging concept that β-arrestins can support both G-protein-dependent and -independent signaling pathways ( 18 ) has fostered our research for a better understanding of the role of β-arrestins in promoting the activity of the CXCL12/HMGB1 heterocomplex.…”

Chemokines in COPD: From Implication to Therapeutic Use

“…Most strategies directly antagonize the GPCR (for excellent review, see Reference [108]). Although very successful in some cases, attested by the example of plerixafor [143] and maraviroc [144], the respective antagonists of CXCR4 and CCR5, most of the pharmacological agents that target chemokine receptors inhibit both G protein signaling and β-arrestins-mediated endocytosis, promoting receptor accumulation at cell surface, a process called “antagonist tolerance” [145]. As a result, the efficacy of this type of antagonist is reduced after a long time of treatment.…”