CXCR4 is a chemokine receptor within the family of rhodopsin-like G Protein Coupled Receptors (GPCRs). The endogenous ligand, CXCL12, mainly activates Gi, G12/13 and β-arrestin2 mediated signalling through CXCR4. CXCR4 is one of the most researched chemokine receptors due to its importance in mobilizing hematopoietic stem cells, the ability to mediate metastasis of various cancers and role as a co-receptor for T-tropic (X4) HIV virus entry to CD4+ T cells. This research resulted in one FDA approved small molecule drug used to mobilize stem cells in cancer patients, plerixafor or AMD3100, a classical antagonist binding in CXCR4’s major pocket (see Figure). Before the start of this project, the team found a novel biological function of CXCR4 in immunology. Small molecules, more precisely natural monoamines (histamine, dopamine) or synthetic ones (clobenpropit (CB), IT1t), drive a profound anti-type I interferon (IFN-I) signal (1) in ex vivo innate immune cells such as plasmacytoid dendritic cells (pDC), in vitro in THP-1 cells, and in vivo in a lupus mouse model (2). These monoamines reverse resiquimod (R848) cell activation, a compound specifically activating Toll like receptor 7 (TLR7) and 8. Importantly, neither CXCL12 nor AMD3100 show the same inhibitory activity. Minor Pocket Ligands are postulated, through computational modelling and the CXCR4-IT1t crystal structure (3), to bind in the distinct minor pocket of CXCR4 thought to therefore be implicated in anti-inflammatory action. The ligands lose their activity when immune cells are treated with siRNA targeting CXCR4 or with the antagonist AMD3100 (1) probably due to binding competition. Additional small molecules were synthetized within the group and designed to target the CXCR4 minor pocket. These novel CB/IT1t derivative show improved broad spectrum anti-inflammatory properties on primary innate immune cells (pDCs, monocytes) compared to IT1t without blocking CXCL12’s natural functions thus reducing potential side effects in vivo.
While the team made substantial progress in identifying compounds with improved functional properties and understanding the consequences of CXCR4 activation through the ligands in immunology, the exact mode of action, the downstream signalling as well as the crosstalk between GPCR and TLR pathways remained unclear and represent the starting point of this project.
Moreover, at the end of the project there is a non-academic placement planned working in the immunology and inflammation cluster of Sanofi to utilise the researchers background in an industry setting and explore the differences in the working culture and methods in a more commercial focussed environment.
(1) Smith, N., et al. Nat Commun 8, 14253 (2017).
(2) Smith, N., et al. Sci Adv 5, eaav9019 (2019).
(3) Wu, B., et al. Science 330, 1066 (2010).
