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Signalling of Minor Pocket Agonists at CXCR4

Periodic Reporting for period 1 - SMiPAX4 (Signalling of Minor Pocket Agonists at CXCR4)

Reporting period: 2022-09-01 to 2025-02-28

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).
Within the project the interaction and signalling of the anti-inflammatory minor pocket ligands was explores in the context of GPCRs and TLRs after pin pointing potential important pathways via literature research. Using a BRET based proximity assay the binding of the compounds towards wild type and mutant CXCR4 was tested to pin point important residues for the mediation of the signal. Using a range of different techniques, mostly Western Blotting, BRET, and Luminescence reporter systems, the phosphorylation of the CXCR4 C-terminus, NFkB, IKK-β, AKT, ERK, G protein activation, the production of cAMP, effect on blocking PKA, β-arrestin recruitment and internalisation of the receptor were tested.
Moreover, a proteomics study was performed in collaboration with the Institute Pasteur looking at the changes of phosphorylation and ubiquitination status of all proteins to have an unbiased approach towards signalling outcomes.
Finally, the researcher spent the last 6 months at Sanofi working on method development for projects in immune regulation.
This project gives the scientific community a better understanding of the signalling cascade of minor pocket ligands at CXCR4 mediating an anti-inflammatory effect. The project was finished with the proteomics study opening the opportunity to following studies verifying the proteins that were altered significantly by the addition of the anti-inflammatory compounds. Ultimately, understanding the mode of action of these compounds could lead to the development of medicinal compounds used in auto-immune diseases.
In silico representation of CXCR4 binding sites; AMD3100 (blue) and IT1t (red)
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