SAT0370 PI3KΔ Pathway a Novel Therapeutic Target for Sjogren's Syndrome
Authors: S. Nayar, J. Campos, C. Buckley, R.A. Allen, W.A. Fahy, A. Payne, F. Barone
Journal: Annals of the Rheumatic Diseases (2015)

<h3>Background</h3> Sjögren9s syndrome (SS) is a chronic autoimmune disease characterized by B cell hyper-activation and exocrine gland infiltration that results in loss of glandular function, systemic manifestations and autoantibody production. The phosphatidylinositol 3–kinase delta isoform (PI3Kδ) belongs to a large family of intracellular lipid kinases that regulate metabolism, survival, proliferation, apoptosis, growth, and cell migration. The PI3Kδ pathway has been successfully targeted in B cell malignancies. <h3>Objectives</h3> Given the central role of the B cell in the pathogenesis of Sjögren9s syndrome we investigated evidence for the engagement of the PI3Kδ pathway in SS and the functional consequences of blocking PI3Kδ in an animal model of SS. <h3>Methods</h3> PI3K pathway activation was investigated in paraffin embedded salivary glands from patients with SS, non-specific chronic sialoadenitis (NSCS) and in tonsillar tissue. Staining for pS6 and pERK was performed in combination with several cellular markers and evaluated in the context of the histological organization of the inflammatory foci. UCB5857, a small molecule inhibitor of PI3Kδ, was used <i>in vivo</i> in an inducible model of ectopic lymphoneogenesis in murine salivary glands that mimics Sjögren9s syndrome. Wild type (C57BL/6) murine salivary glands were cannulated with AdV5 (10<sup>8</sup> p.f.u.) and sacrificed at specific time points post cannulation (p.c.). UCB5857, or vehicle control, was administered by daily gavage, both prophylactically and therapeutically, starting at either day 0 or day 3 p.c. 6 mice (12 salivary glands) were used per group. Flow cytometry on single cell flow suspension, immunofluorescence (IF) and quantitative real time PCR was used on the murine isolated salivary gland to evaluate the samples at day 15 p.c. <h3>Results</h3> IHC staining in human tissues showed significant expression of pS6 and pERK in SS samples, as compared to non-specific sialoadenitis control and tonsillar tissues, confirming engagement of the PI3K pathway. Both markers were detected within the lymphoid aggregates and on the periphery of the lymphoid foci in both T and B cell areas. pERK staining was also detected in non-infiltrated areas within the epithelium; pS6 staining was predominantly found on CD138<sup>+</sup> plasma cells. <i>In vivo</i>, we observed a marked decrease in the number of T and B cells in cannulated salivary glands of mice prophylactically treated with UCB5857, as compared to vehicle treated mice. This defect in lymphocyte infiltration was confirmed both by flow cytometry on isolated lymphocytes and IF. A reduction in total number of CD45<sup>+</sup>, CD3, (both CD8 and CD4<sup>+</sup> cells) and B cells was observed. The gene expression profile of tertiary lymphoid organ (TLO)-associated genes (CXCL13, CCL19, CCL21) was also significantly impaired in mice treated with UCB5857. This decrease was also observed in mice treated therapeutically from day 3 pc. <h3>Conclusions</h3> Preliminary data suggest that PI3Kδ is engaged in several cells present in the salivary glands of patients with SS and might contribute to disease pathogenesis. Accordingly, prophylactic and therapeutic blocking of PI3Kδ results in disaggregation of the inflammatory foci and resolution of salivary gland inflammation in an animal model of SS. <h3>Acknowledgements</h3> This research was funded by UCB Pharma. <h3>Disclosure of Interest</h3> S. Nayar Grant/research support from: UCB Pharma, J. Campos: None declared, C. Buckley: None declared, R. Allen Employee of: UCB Pharma, W. Fahy: None declared, A. Payne Employee of: UCB Pharma, F. Barone: None declared