Background/Purpose: Our previous study demonstrated that Heat shock protein 90 (Hsp90) is overexpressed in the skin of patients with systemic sclerosis (SSc), in cultured SSc fibroblasts and preclinical models of SSc. HSP90 is a new regulator of canonical TGF-β signalling and its inhibition prevents the stimulatory effects of TGF-β on collagen synthesis and dermal fibrosis in three preclinical models of SSc. Herein, we aimed to evaluate the efficacy of Hsp90 inhibitor (17-DMAG) in the treatment of established experimental dermal fibrosis induced by bleomycin.

Methods: Design consisted of three control groups, I (NaCl-s.c./6 weeks), II (bleomycin-s.c./3w and NaCl-s.c./3w), III (bleomycin-s.c./6w), and 2 treatment groups (bleomycin-s.c./6w). During the last 3 weeks, one group was treated with 17-DMAG 0.5mg/kg-i.p. every third day, whereas one group (with nintedanib 50mg/kg-p.o. twice daily) served as a comparator with already published efficacy in this setting. Total of 40 BL6 mice were examined weekly for weight, activity and fur texture. The effects of 17-DMAG were determined by assessment of dermal thickness (HE-staining), collagen content (hydroxyproline assay), myofibroblast counts (α-SMA staining) and of 23 serum inflammatory cytokines/chemokines (Mouse-Cytokine-23-plex, Bio-Rad-Laboratories).

Results: 17-DMAG decreased dermal thickening by 53±3% (p< 0.001) (nintedanib by 46±2%,p< 0.001), collagen content by 48±5% (p=0.004) (nintedanib by 50±4%,p=0.003), myofibroblast counts by 42±9% (p< 0.001) (nintedanib by 44±7%,p< 0.001), and the count of CD3+ cells in the dermis by 46±7% (p< 0.001) and serum levels of IL-1a, IL-6, IL-12(p40), CXCL1, MCP-1, MIP-1a/b, RANTES (in all: p< 0.05) compared to vehicle-treated mice injected with bleomycin for 6w. Moreover, 17-DMAG also induced regression of pre-established fibrosis to below the levels of vehicle-treated mice injected with bleomycin for 3w and NaCl for 3w, i.e. the pre-treatment levels, (dermal thickness by 14±3%, collagen content by 20±5%, myofibroblast counts by 13±9%; whereas in nintedanib by 10±3%, 21±4%, 17±7%, respectively; in all: p< 0.05), and the count of CD3+ cells in the dermis by 22±7% (p=0.006) and levels of IL-12(p40), CXCL1, MCP-1, MIP-1b, RANTES (in all: p< 0.05). No significant weight loss, decrease in activity or changes in fur texture were observed upon 17-DMAG treatment.

Conclusion: This is the first study on effects of Hsp90 inhibitor 17-DMAG in the treatment of established dermal fibrosis. We demonstrate that 17-DMAG effectively prevents the progression and induces regression of established bleomycin-induced dermal fibrosis, in an extent that was comparable to nintedanib in this study (which was recently FDA approved for slowing the rate of decline in lung function in adults with SSc-ILD). 17-DMAG also reduced the T-cell infiltrate in the dermis and the systemic levels of inflammatory cytokines/chemokines. 17-DMAG was well tolerated without obvious clinical signs of toxicity. These data suggest that Hsp90 could be a novel potential target in the treatment of SSc dermal fibrosis.

Acknowledgement: Supported by AZV-16-33542A, MHCR00023728, SVV260373, Boehringer Ingelheim.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/hsp90-inhibition-effectively-prevents-progression-of-dermal-fibrosis-and-induces-regression-of-established-bleomycin-induced-dermal-fibrosis/