THU0214 THE PI3KΔ SELECTIVE INHIBITOR INCB050465 ABROGATES KIDNEY PATHOLOGY IN A SPONTANEOUS MURINE MODEL OF SYSTEMIC LUPUS ERYTHEMATOSUS
Authors: Brittany Fay, Monika Scuron, Niu Shin, Yan-Ou Yang, Eddy Yue, Andrew Combs, Eduardo Huarte, Melissa Parker, Paul Smith
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Background:</h3> Systemic lupus erythematosus (SLE) is an autoimmune disease that affects multiple organs, including the skin, joints and kidneys. Though SLE typically cycles through periods of flares and remission, patients often eventually succumb to end-stage kidney or cardiovascular damage<sup>1</sup>. SLE is characterized by the presence of autoantibodies that form immune complexes resulting in kidney deposition that significantly contribute to lupus nephritis pathogenesis. Phosphatidylinositol 3-kinases (PI3Ks) are divided into three classes (Class I, II, and III) according to their structure, regulation and substrate specificity. The Class I PI3K delta isoform (PI3Kδ) has been implicated in autoimmune diseases associated with aberrant B cell and antibody responses. INCB050465 is an oral small molecule PI3Kδ selective inhibitor currently being evaluated in clinical trials for the inflammatory indications Sjögren's syndrome and autoimmune hemolytic anaemia (NCT03627065 &amp; NCT03538041). <h3>Objectives:</h3> To quantify the efficacious potential of INCB050465, a selective PI3Kδ inhibitor, in a preclinical model of systemic lupus erythematosus with kidney pathology. <h3>Methods:</h3> The MRL/lpr mouse model spontaneously develops multiple inflammatory phenotypes that mimic human SLE pathologies, including kidney damage resulting in proteinuria, cutaneous skin lesions and anti-double stranded DNA (anti-dsDNA) antibodies. Kidney sections were stained with hematoxylin and eosin (H&amp;E) and assigned a composite score based on glomerulus, crescents, protein casts, interstitial inflammation and vasculitis by a rater unaware of the treatment groups<sup>2</sup>. Flow cytometry was performed on splenocytes to characterize B cell and T cell subsets. Anti-dsDNA antibodies were determined by commercial ELISA. <h3>Results:</h3> In vitro enzymatic selectivity screening revealed INCB050465 potently inhibited the PI3Kδ kinase enzyme (IC50 = 1.1 ± 0.5 nM), with ∼20,000-fold selectivity for the other PI3K family member enzymes. Proteinuria identified spontaneous kidney damage in 85%+ of vehicle treated mice by 21 weeks of age, and kidney histology revealed gross tissue enlargement associated with structural abnormalities. In contrast, therapeutic INCB050465 treatment (0.3 – 3.0 mg/kg, b.i.d.) dose-dependently reduced the incidence of proteinuria (p &lt; 0.01), and kidney structural integrity was normalized (p &lt; 0.0001). A feature of the MRL/lpr model is lymphocyte hyper-proliferation resulting in lymphadenopathy and splenomegaly. Therapeutic INCB050465 treatment dose-dependently reduced spleen (p &lt; 0.01) and lymph node (p &lt; 0.01) weight. Cutaneous skin lesions were unaffected by INCB050465 treatment. Splenocyte flow cytometry revealed no reduction in absolute lymphocyte, CD19<sup>+</sup> B cell, CD4<sup>+</sup> or CD8<sup>+</sup> T cell frequencies following INCB050465 treatment. However INCB050465 reduced the absolute counts of germinal center (CD19<sup>+</sup>GL7<sup>+</sup>) and marginal zone (CD19<sup>+</sup>CD21<sup>+</sup>) B cell subsets. Anti-dsDNA antibodies were abrogated by INCB050465 therapy (p &lt; 0.0001). <h3>Conclusion:</h3> INCB050465, a selective PI3Kδ inhibitor, was highly efficacious against immune-mediated mechanisms associated with lupus nephritis, but not cutaneous lupus disease manifestations in this preclinical model. Treatment-induced preservation of kidney tissue integrity corresponded to specific B cell subset modulation and autoantibody reduction. Selective PI3Kδ inhibitor treatment did not induce lymphocyte depletion. <h3>Reference:</h3> [1] Grande, et al. Experimental models of lupus nephritis. Contrib Nephrol. 2011; 169:183-97. [2] Chan, et al. The roles of B cells in MRL/lpr murine lupus. Ann N Y Acad Sci. 1997Apr5;815:75-87. <h3>Disclosure of Interests:</h3> Brittany Fay Shareholder of: The author is an employee and/or shareholder of Incyte Corporation., Employee of: The author is an employee and/or shareholder of Incyte Corporation., Monika Scuron Shareholder of: The author is an employee and/or shareholder of Incyte Corporation., Employee of: The author is an employee and/or shareholder of Incyte Corporation., Niu Shin Shareholder of: The author is an employee and/or shareholder of Incyte Corporation., Employee of: The author is an employee and/or shareholder of Incyte Corporation., Yan-ou Yang Shareholder of: The author is an employee and/or shareholder of Incyte Corporation., Employee of: The author is an employee and/or shareholder of Incyte Corporation., Eddy Yue Shareholder of: The author is an employee and/or shareholder of Incyte Corporation., Employee of: The author is an employee and/or shareholder of Incyte Corporation., Andrew Combs Shareholder of: The author is an employee and/or shareholder of Incyte Corporation., Employee of: The author is an employee and/or shareholder of Incyte Corporation., Eduardo Huarte Shareholder of: The author is an employee and/or shareholder of Incyte Corporation., Employee of: The author is an employee and/or shareholder of Incyte Corporation., Melissa Parker Shareholder of: The author is an employee and/or shareholder of Incyte Corporation., Employee of: The author is an employee and/or shareholder of Incyte Corporation., Paul Smith Shareholder of: The author is an employee and/or shareholder of Incyte Corporation., Employee of: The author is an employee and/or shareholder of Incyte Corporation.