Pos1022 a newly developed small molecule cd38 inhibitor exerts therapeutic effects in a collagen-induced arthritis mouse model

Background CD38 is a NAD+ consuming enzyme ubiquitously expressed on immune cells and its expression increases in several pathological conditions, including Rheumatoid Arthritis (RA) [1, 2]. Pre-clinical studies in CD38 knock-out models have demonstrated that CD38 deficient animals develop an attenuated form of Collagen-Induced-Arthritis (CIA) characterized by reduced inflammation and damage at the joint level suggesting a causal role of CD38 in the pathogenesis of CIA and, potentially, RA [3-5]. Objectives This study investigated the efficacy of NTX-748, a newly developed, potent and orally available small molecule inhibiting the enzymatic activity of CD38, in reducing the inflammation, cartilage destruction, pannus formation, and bone resorption associated with developing CIA in mice, a well-established animal model for the study of RA. Methods Mice were injected intradermally (ID) with Freund’s complete adjuvant (CFA) containing bovine type II collagen to induce arthritis on study days 0 and 21. Beginning on study day 18, the animals were dosed twice daily (BID) by the oral route (PO) with vehicle or NTX-748 (3, 10, or 30 mg/kg), or dosed PO once daily (QD) with Methotrexate (1 mg/kg) (n=12/group) for 18 days. One group served as a naïve control group (n=4). Efficacy evaluation was based on animal body weights, clinical arthritis scores (CAS) based on daily clinical scores of the paws (right front, left front, right rear, left rear) expressed as area under the curve (AUC), summed histopathology scores based on histopathologic evaluation performed on fore paws, hind paws, and knees, analysis of NTX-748 plasma concentrations and tissue metabolomic profile. The primary endpoint was day 36 CAS. Results Treatment with NTX-748 at 10 and 30mg/kg showed a statistically significant dose-dependent beneficial effect reducing day 36 CAS by 37% and 50% respectively relative to vehicle (p=0.13 and p=0.047), without showing any toxicity, including body and spleen weights. Histopathology analysis of joints, paws and knees confirmed NTX-748 efficacy. Strikingly, NTX-748 reduces incidence of CAS up to 50% in a dose-dependent manner (p = 0.0015). Plasma concentrations of NTX-748 increased approximately in proportion to dose. Mass Spectrometry-based tissue metabolomic analysis (liver and spleen) confirmed target engagement with dose dependent increases of NAD+ levels, the main substrate of CD38-mediated NAD+ hydrolysis, and decreases of NAM and ADPR, both products of the same enzymatic reaction. Methotrexate 1mg/kg also demonstrated efficacy (98% reduction in CAS) however significant splenomegaly (3-fold increase) indicated toxicity at this dose. Conclusion Our results demonstrated that NTX-748, a small molecule inhibiting the NADase enzymatic activity of CD38, is efficacious in the mouse CIA model, and thus potentially RA. These data confirm the potential of CD38 as druggable target in the treatment of inflammation-driven autoimmune diseases such as RA. References [1] Cole, S., et al., Integrative analysis reveals CD38 as a therapeutic target for plasma cell-rich pre-disease and established rheumatoid arthritis and systemic lupus erythematosus. Arthritis Res Ther, 2018. 20 (1): p. 85. [2] Thevissen, K., et al., Diagnostic and prognostic value of synovial biopsy in adult undifferentiated peripheral inflammatory arthritis: a systematic review. J Rheumatol Suppl, 2011. 87 : p. 45-7. [3] Postigo, J., et al., Mice deficient in CD38 develop an attenuated form of collagen type II-induced arthritis. PLoS One, 2012. 7 (3): p. e33534. [4] Rosal-Vela, A., et al., Identification of multiple transferrin species in the spleen and serum from mice with collagen-induced arthritis which may reflect changes in transferrin glycosylation associated with disease activity: The role of CD38. J Proteomics, 2016. 134 : p. 127-137. [5] Du, Y., et al., CD38 Deficiency Downregulates the Onset and Pathogenesis of Collagen-Induced Arthritis through the NF-kappaB Pathway. J Immunol Res, 2019. 2019 : p. 7026067. Acknowledgements We thank Dr. Peter Bungay (Sympetrus Ltd) for the support with the pharmacokinetic analysis. Disclosure of Interests Rosalba Perrone Consultant of: Juvenescence Ltd, a company owning shares of Napa Therapeutics Ltd., Prasanna Vadhana Ashok Kumaar: None declared, Katrina Gore: None declared, Jacob Favret: None declared, Eric Verdin Shareholder of: Napa Therapeutics Ltd, Steve Felstead Employee of: Juvenescence Ltd, a company owning shares of Napa Therapeutics Ltd.