Inhibition of Fibrotic Contraction by Sirolimus (Rapamycin) in an Ex Vivo Model of Thyroid Eye Disease

Abstract

Background: Thyroid eye disease (TED) is characterized by orbital inflammation and complicated by extraocular muscle fibrosis. Treatment with rapamycin/sirolimus has been reported to improve ocular motility and disease manifestations in TED. Whether this resulted from a primary antifibrotic effect on fibroblasts or was secondary to immune-suppression is unclear. Methods: In vitro contractility studies of primary orbital fibroblasts. Cells from patients with TED and controls were treated with rapamycin [mechanistic target of rapamycin an (mTOR) inhibitor] and MHY1485 (an mTOR stimulator) as well as inhibitors upstream in the same signaling cascade (saracatinib and befatinib). Results: At concentrations consistent with the therapeutic dosing range in humans, rapamycin/sirolimus significantly reduces fibrosis in orbital fibroblasts from TED patients and controls in vitro. This effect is separate from, and in addition to, its immune suppressive effect. mTOR-driven fibrotic activity is greater in TED-derived fibroblasts and can be blocked also upstream of mTOR by inhibition of src. There was no adverse effect on cell survival. Conclusion: The authors present evidence for a direct antifibrotic effect of rapamycin/sirolimus in primary orbital fibroblasts. Targeting mTOR signaling presents a further and adjunctive treatment of TED alongside other immune-suppressive agents. By acting downstream of IGF1-R, sirolimus may offer a cost-effective alternative to teprotumumab therapy. Clinical case reports, now supplemented by this in vitro evidence, support the initiation of a clinical trial to treat the fibrotic sequelae of TED with this already-approved agent. Such an “off-the-shelf” therapy is a welcome prospect for TED treatment, particularly one available at a low price.

Rapamycin improves Graves’ orbitopathy by suppressing CD4+ cytotoxic T lymphocytes

“…Moreover, in vitro studies showed that rapamycin can directly suppress fibroblasts and preadipocytes, leading to reductions in fibrosis and adipogenesis, respectively (29,30). Thus, rapamycin is a plausible therapeutic agent for the management of GO and should be investigated in randomized clinical trials (31).…”

“…The rapid and effective suppression of GO-pathogenic CD4 + CTLs makes it one of the main mechanisms underlying the remarkable efficacy of rapamycin in GO, although Th1 cells, Th17 cells, and T regs are also reportedly potential targets ( 28 ). Moreover, in vitro studies showed that rapamycin can directly suppress fibroblasts and preadipocytes, leading to reductions in fibrosis and adipogenesis, respectively ( 29 , 30 ). Thus, rapamycin is a plausible therapeutic agent for the management of GO and should be investigated in randomized clinical trials ( 31 ).…”

Sirolimus as a second-line treatment for Graves’ orbitopathy

“…In vitro studies have shown that sirolimus-mediated inhibition of mTORC1 is followed by a block in adipogenesis in preadipocytes and fibroblasts from GO patients. In addition, by blocking the FRAP/mTOR signaling pathway, sirolimus reduces the synthesis of IL-16 promoted by circulating IgGs in orbital fibroblasts [18][19][20]. IL-16, together with the chemokine RANTES, represents one of the main mediators of "trafficking" of CD4-positive T lymphocytes in GO [21,22].…”

“…Given the molecular mechanisms of action of sirolimus, as teprotumumab, the drug may block IGF-1 signaling as well as other pathways involved in migration, proliferation, differentiation and cell activation, resulting in similar clinical effects, as we observed here. Furthermore, recent in vitro studies have shown that sirolimus affects tissue remodelling also by negatively regulating fibroblast migration and fibroblast transition into myofibroblasts, therefore reducing the production of collagen and extracellular matrix [20,23]. The anti-fibrotic effect of sirolimus has also been demonstrated in vivo in a murine model [24][25][26], and it has been proposed as one of the possible explanations for the efficacy of this drug in the two patients with GO reported previously [8,9].…”

Aktuelle Therapieansätze der endokrinen Orbitopathie – sind die zielgerichteten Therapien die Zukunft?

“…V.a. die Fibrose wird dabei adressiert [107].In einer Fall-Kontroll-Studie erhielten Patienten Sirolimus 2 mg oral am ersten Tag, gefolgt von 0,5 mg/Tag für 12 Wochen -Therapieeffekte wurden mit einer konsekutiven Kohorte verglichen, die kumulativ 4,5g IVGC erhielt. Es zeigte sich ein stärkerer Therapieeffekt für Sirolimus 86% versus 26% [73].…”