Background: As well as being an established oncoprotein and a therapeutic target in cancer, Proviral Integration site for murine Moloney leukemia virus-1 (pim-1) has been implicated in human autoimmunity. We previously confirmed this serine-threonine protein kinase to be strikingly upregulated in circulating CD4+ T cells of untreated rheumatoid arthritis (RA) patients as a consequence of IL-6 signalling ^1-2 . Evidence for the relevance of pim-1 signalling in the disruption of RA synovial fibroblast (RASF) homeostasis ³ further supports its candidacy as a therapeutic target.

Objectives: To investigate PIM1 and its family members (PIM2 and PIM3) as potential candidates for drug repurposing in RA.

Methods: A flow cytometric assay for PIM1 transcript measurement in circulating CD4+ T cells of early arthritis patients was validated against real-time PCR in paired cells isolated by bead selection. Synovial protein expression in tissue from the same cohort of untreated RA patients and disease controls was determined by quantitative multiplex immunofluorescence. The functional consequences of manipulating pim kinase family expression in freshly purified T cell receptor (TCR)-stimulated CD4+ T cells from early RA patients was explored. The impact of pim-1 specific and pim-1-3 (pan-pim) kinase inhibition on progression of the IL-6 dependent collagen-induced arthritis (CIA) model was assessed.

Results: The percentage of circulating CD4+ T cells positive for PIM1 transcript by flow cytometry proved a faithful surrogate for gene expression in early arthritis ( Figure 1 A ), distinguishing RA from other pathologies ( Figure 1 B ). Pim-1 protein expression was increased in the synovium of untreated RA compared with disease controls, including amongst infiltrating CD4+ T cells ( Figure 1 C-D ). In vitro , exposure of TCR-stimulated early RA CD4+ T cells to pim kinase inhibitors restrained their activation and proliferative capacity; diminished pro-inflammatory cytokine production (IFN-g and IL-17) and an expanded CD25 ^hi FoxP3+ regulatory T cell (Treg) fraction were also observed in treated versus un-treated cells. Finally, administration of pim inhibitors robustly attenuated clinical scores of arthritis in the CIA model, with reduced cartilage loss observed in animals treated with a pan-PIM inhibitor compared with vehicle control ( Figure 2 ).

Conclusion: Our data highlight pim kinases as plausible therapeutic targets for a subgroup of early RA patients that may be identifiable using tractable in vitro assays. Pim kinase inhibitors could simultaneously target immune inflammation and RASF dysregulation; consideration should now be given to their repurposing for this condition.

REFERENCES:

[1] Anderson AE et al Annals of the Rheumatic Diseases 2016; 75:466-73.

[2] Anderson AE et al Rheumatology 2019; 58:1250-1258

[3] Ha YJ et al Rheumatology 2019; 58:154-64

Disclosure of Interests: Nicola Maney Consultant of: Current employee of Eli Lilly, Henrique De Paula-Lemos: None declared, Ben Barron-Millar: None declared, Andrew Mellor Shareholder of: NewLink Genetics PLC, and has received patent licensing income from this source., John D Isaacs Consultant of: AbbVie, Bristol-Myers Squibb, Eli Lilly, Gilead, Janssen, Merck, Pfizer, Roche, Amy Anderson: None declared, Arthur Pratt Grant/research support from: Pfizer, GlaxoSmithKlein