Pharmacological characterization of a clinical candidate, TG-0054, a small molecule inverse agonist targeting CXCR4.

CXCR4 is an important therapeutic target for hematopoietic stem cell mobilization, which enhances the success of autologous stem cell transplantation for treating blood cancers such as lymphomas and myeloma. As CXCR4 has been shown to be involved in various inflammatory diseases, cancer progression, and cell entry by the human immunodeficiency virus, understanding the molecular mechanism of CXCR4 inhibitors has potential implications in a wide area of diseases. Here, we present an exploratory study which involves the molecular pharmacological characterization of TG-0054 (burixafor, GPC-100), a clinical candidate for hematopoietic stem cell mobilization. TG-0054 inhibited CXCL12 binding at CXCR4, and antagonized both Gα and β-arrestin2 recruitment as well as the downstream Gα-attenuation of cAMP signaling pathway, with pIC of 7.7, 8.0, and 7.9, respectively. Compared with the clinically used antagonist AMD3100 and the prototypical inverse agonist Isothiourea-1t (IT1t), TG-0054 displayed a unique pharmacological profile. Like IT1t, TG-0054 inhibited the constitutive Gα signaling of CXCR4. However, in contrast to IT1t and other reported inverse agonists, TG-0054 was not able to induce monomerization of CXCR4 oligomeric complexes. Considering the unique properties of TG-0054 on CXCR4, TG-0054 is an interesting tool compound for studying the relevance of inverse agonism as well as CXCR4 monomerization in various pathologies. SIGNIFICANCE STATEMENT: CXCR4-targeted therapeutics hold important potential for the treatment of blood cancers. TG-0054 has inverse agonistic properties and is a non-CXCR4-monomerizing small molecule antagonist, unlike other well studied CXCR4 small molecule antagonists.