Background: Lysophosphatidic acid (LPA) is increased in blood and tissues of the patients with systemic sclerosis, suggesting that LPA would be deeply involved in the pathogenesis of systemic sclerosis. LPA ₁ , one of the subtypes of LPA receptors, is highly expressed in fibroblasts and is closely involved in the pathogenesis of fibrosis. In addition, its antagonists have been shown to be effective in fibrosis. Another LPA receptor subtype, LPA ₃ , is highly expressed in keratinocytes and is suggested to be involved in skin homeostasis. Therefore, dual antagonism of LPA ₁ and LPA ₃ may be useful in improving the pathogenesis of skin fibrosis. However, the contribution of LPA ₃ to the pathogenesis of systemic sclerosis is unclear.

Objectives: We have developed a novel compound, TP0591108, which is a dual antagonist of LPA ₁ and LPA ₃ . To clarify the involvement of these receptors in the pathogenesis of systemic sclerosis, gene expression analysis of LPA-stimulated human primary cells and RNA-seq analysis of LPA-treated mouse skin tissue were performed with this compound. Furthermore, the anti-fibrotic effect of TP0591108 were evaluated compared to LPA ₁ selective antagonist in a mouse model of systemic sclerosis.

Methods: The antagonistic activities of TP0591108 against each LPA receptors were determined by calcium flux assays using cells over-expressing human and mouse LPA _1-5 receptors. The effect of TP0591108 on the change in mRNA expression were analyzed in LPA‐stimulated human fibroblasts and keratinocytes. The effects of TP0591108 on the skin fibrosis was evaluated orally administration of TP0591108 in bleomycin (BLM)-treated mice and the tight-skin (TSK-1) mice. Multiplex analysis was performed using the Luminex method for the protein levels in the plasma, and the RNA-seq method for the mRNA expression in the blood cells and skin tissue derived from LPA-stimulated mice and BLM-treated mice. In these evaluations, the LPA ₁ -selective antagonist AM095 was used as comparators.

Results: TP0591108 showed LPA ₁ and LPA ₃ receptor selective antagonistic activity. These antagonistic effects were sustained even after 1 hour from compound washout, suggesting that TP0591108 slowly dissociates from these receptors. The expressions of inflammation/fibrosis-related genes such as IL-6, IL-8 and CTGF were increased in LPA-stimulated human fibroblasts and keratinocytes. TP0591108 suppressed these gene expressions in both fibroblasts and keratinocytes, whereas AM095 was effective only in fibroblasts. The results of RNA-Seq analysis of the blood cells and skin tissue in LPA-stimulated mice revealed that gene expression changes in blood cells were suppressed by LPA ₁ inhibition alone, but those of in skin tissue were suppressed only in the TP0591108-treated mice, suggesting LPA ₃ involvement in skin tissue. In BLM-treated mice, TP0591108 suppressed the skin collagen overproduction as 79% at a dose of 1 mg/kg/day, whereas AM095 only suppressed it as 43% at a dose of 200 mg/kg/day. These drug effect is similar in TSK-1 mice, these results indicate that TP0591108 has more potent therapeutic effects on skin fibrosis than LPA ₁ -selective antagonists. In BLM-treated skin fibrosis mice, two of the blood fibrosis-related markers (Chitinase 3-like1, MMP-2) were significantly reduced in TP0591108-treated mice, and also the various inflammatory/fibrosis-related gene expressions were also suppressed by in the TP0591108-treated skin tissue.

Conclusion: TP0591108, a novel LPA _1/3 dual antagonist, is more effective than existing LPA ₁ selective antagonist and anti-fibrotic agent. In addition to the identified involvement of LPA ₁ in tissue fibrosis, these results suggest the involvement of LPA ₃ in skin inflammation and subsequent fibrosis in systemic sclerosis. TP0591108 may be a new therapeutic option in the treatment of systemic sclerosis.

REFERENCES: NIL.

Acknowledgements: NIL.

Disclosure of Interests: Takumi Naruse Taisho Pharmaceutical Co., Ltd., Taisho Pharmaceutical Co., Ltd., Lisa Okumura Taisho Pharmaceutical Co., Ltd., Taisho Pharmaceutical Co., Ltd., Hiromitsu Kajiyama Taisho Pharmaceutical Co., Ltd., Taisho Pharmaceutical Co., Ltd., Yuri Nagashima Taisho Pharmaceutical Co., Ltd., Taisho Pharmaceutical Co., Ltd., Takumi Sugawara Taisho Pharmaceutical Co., Ltd., Taisho Pharmaceutical Co., Ltd., Shohei Ito Taisho Pharmaceutical Co., Ltd., Taisho Pharmaceutical Co., Ltd., Teisuke Takahashi Taisho Pharmaceutical Co., Ltd., Taisho Pharmaceutical Co., Ltd., Hiroyuki Kakinuma Taisho Pharmaceutical Co., Ltd., Taisho Pharmaceutical Co., Ltd.

© The Authors 2025. This abstract is an open access article published in Annals of Rheumatic Diseases under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ). Neither EULAR nor the publisher make any representation as to the accuracy of the content. The authors are solely responsible for the content in their abstract including accuracy of the facts, statements, results, conclusion, citing resources etc.