Background: AX-202 is a monoclonal antibody that inhibits the bioactivity of S100A4. S100A4 is an alarm signal that is released from cells in response to stress or injury and functions as an amplifying mechanism of inflammation and fibrosis in the diseased tissue microenvironment. Previous in vitro studies have found that S100A4 induces fibroblast activation, sensitizes fibroblasts to the effects of TGFβ, drives epithelial-mesenchymal transition, and stimulates monocyte cytokine release (1-3). Moreover, S100A4-/- mice are protected from fibrosis in several animal models (1). In patients with systemic sclerosis (SSc), S100A4 is elevated both in lesional tissue and systemically and correlates with skin involvement, disease activity, and pulmonary function.

Objectives: The aim of this study was to assess the antifibrotic effects of murine AX-202 in two pre-clinical models of SSs reflecting both inflammation-mediated and inflammation non-mediated fibrosis and confirm the in vivo activity of humanized AX-202.

Methods: We first evaluated the effects of murine AX-202 in the bleomycin-induced skin fibrosis model and the tight-skin 1 (Tsk-1) model. In the bleomycin (BLM) model, fibrosis was induced by 3 weeks of BLM s.c. injections followed by 3 weeks of AX-202 treatment in parallel with continued BLM s.c. injections. The control groups included NaCl s.c. injections for 6 weeks, BLM s.c. injections for 6 weeks, or BLM s.c. injections for 3 weeks, followed by NaCl s.c. injections for 3 weeks. Three dosing regimens of AX-202 were tested: 3.75, 7.5, or 12.5 mg/kg i.p. every 3^rd day. In the Tsk-1 model, treatment with 7.5 mg/kg i.p. every 3^rd day was administered from week 5 until week 10. The control groups included pa mice, Tsk-1 mice, and Tsk-1 mice treated i.p. with isotype IgG. We subsequently evaluated the effects of humanized AX-202 in the model of BLM-induced skin fibrosis in a similar design as used for the murine AX-202 study. Three dosing regimens were tested: 8 mg/kg and 16 mg/kg i.p. every 3^rd day and 24 mg/kg i.v. once weekly.

Results: In the BLM model, murine AX-202 (7.5 mg/kg) was effective both in the prevention of progression of pre-established skin fibrosis and in the induction of regression of fibrosis as assessed by the dermal thickness (-55%, p<0.0001 vs BLM for 6 weeks, and -23%, p<0.0001 vs BLM for 3 weeks), myofibroblast count and hydroxyproline content. Murine AX-202 also ameliorated fibrosis in the Tsk-1 model as assessed by the hypodermal thickness (-24%, p=0.01 vs Tsk-1 isotype control), myofibroblast count, and hydroxyproline content. In both models, the antifibrotic effects were associated with a reduction in pSMAD3 expression. Humanized AX-202 was effective in the prevention of progression of pre-established skin fibrosis in all doses tested across all endpoints (dermal thickness, myofibroblast counts, hydroxyproline content). In the two groups treated with 16 mg/kg i.p. and 24 mg/kg i.v., humanized AX-202 also induced regression of fibrosis (-83%, p<0.001, and -61%, p<0.001 vs BLM for 3 weeks, respectively). Both murine and humanized AX-202 were well tolerated in all study groups in both models.

Conclusion: We demonstrate that AX-202 confers potent antifibrotic effects in complementary models of SSc. These results confirm and expand previous data showing that inhibition of S100A4 by AX-202 is a promising potential therapeutic candidate for disease modification in SSc or other fibrotic conditions.

References: [1]Tomcik M et al. S100A4 amplifies TGF-beta-induced fibroblast activation in systemic sclerosis. Ann Rheum Dis. 2015;74(9):1748-55.

[2]Cerezo LA et al. The metastasis-associated protein S100A4 promotes the inflammatory response of mononuclear cells via the TLR4 signalling pathway in rheumatoid arthritis. Rheumatology (Oxford). 2014;53(8):1520-6.

[3]Fei F, et al. Role of metastasis-induced protein S100A4 in human non-tumor pathophysiologies. Cell Biosci. 2017;7:64.

Acknowledgements: The study was supported by Arxx Therapeutics and MHCR 023728.

Disclosure of Interests: Michal Tomčík: None declared, Thuong Trinh-Minh: None declared, Cuong Tran Manh: None declared, Hana Štorkánová: None declared, Lenka Štorkánová: None declared, Ladislav Šenolt: None declared, Jörg Klingelhöfer Employee of: Arxx Therapeutics, Rizwan I Hussain Employee of: Arxx Therapeutics, Jonas Hallén Employee of: Arxx Therapeutics, Jörg H.W. Distler Shareholder of: the stock owner of 4D Science, Consultant of: Actelion, Active Biotech, Anamar, ARXX, Bayer Pharma, Boehringer Ingelheim, Celgene, Galapagos, GSK, Inventiva, JB Therapeutics, Medac, Pfizer, RuiYi and UCB, Grant/research support from: Anamar, Active Biotech, Array Biopharma, ARXX, aTyr, BMS, Bayer Pharma, Boehringer Ingelheim, Celgene, Galapagos, GSK, Inventiva, Novartis, Sanofi-Aventis, RedX, UCB