The results of the present study seem to support the safety and efficacy of Filgotinib for the management of articular and visceral involvement in SSc.
Despite the availability of several new agents, SSc treatment must still be considered as an unmet need. The efficacy of standard immunosuppressive therapies is currently limited, and no drugs have proved to be effective for fibrotic skin involvement. Moreover, drug-related side effects are common and often limit the use of newer molecules.
Compared to single-target drugs, Filgotinib has a wider spectrum of action, by modulating several cytokine receptors, implicated in inflammation and fibrogenic processes (16).
In our population the greater effectiveness was seen on articular involvement. An initial clinical effect had already been noticed after 12 weeks and a significant improvement with both reduction of TJ and SJ and an improvement of CDAI, SDAI and DAS28-CRP, was confirmed after 52 weeks of treatment. According to DAS28-CRP, 80% of our patients obtained remission of articular disease at the end of the follow-up. Moreover, the absence of subclinical inflammation was confirmed with PDUS after 6 and 12 months of treatment.
At the end of the follow-up, a considerable improvement of quality of life, defined by a reduction of HAQ, had also been observed.
Filgotinib treatment also led to a significant reduction of mRSS in patients with diffuse cutaneous subset. A concomitant clinically significant improvement of symptoms related to cutaneous disease activity, namely melanoderma, pruritus, skin tightening was observed. No patients developed DUs during follow-up, even in patients with a history of recurrent DUs, acrosteolysis and amputations. A stabilization of ILD detected in 2 patients, assessed through HRCT and PFTs, was observed. Finally, an overall clinical improvement in patients with dcSSc was confirmed by the CRISS score.
Filgotinib is an oral second-generation preferential JAK1 inhibitor, already approved for use in Europe, UK and Japan for the treatment of Rheumatoid Arthritis (AR) and ulcerative colitis (UC)(16) on the basis of the results of FINCH(17) and SELECTION trial (18), respectively. It also displayed a promising clinical profile in the FITZROY study(19) in patients with Crohn Disease (CD) and TORTUGA study(20) in patients with SpA.
In biochemical assays, Filgotinib demonstrated an high selective inhibition profile for JAK1 and showed > 5-fold higher potency for JAK1 over JAK2, JAK3, and tyrosine kinase. In vitro assay also showed that Filgotinib inhibited erythroid progenitor expansion, carried out by JAK2 through GM-CSF, less potently than the other JAKi (10). This may explain the better safety profile in relation to the laboratory abnormalities observed in the trials conducted for RA patients (21).
JAK1 is fundamental for the signalling of several cytokines, namely IL-6, IL-2, IL-4, IL-10, IL-11, IL-19, IL-20, IL-22, and interferon (IFN) alpha, IFN-beta, and IFN-gamma, which play a key role in inflammatory and fibrogenic processes (10).
There is growing evidence that JAK/STAT pathway plays a pivotal role in SSc pathogenesis (22). Recent in vitro studies have shown that the JAK/STAT pathway is activated in SSc and JAKi are effective in modulating inflammation and fibrogenic process, acting on mesenchymal and epithelial cells, lymphocytes and macrophages (23–25). JAKi exhibit both anti-inflammatory and anti-fibrotic properties, linked to the modulation of the activation state of pro-inflammatory M1 macrophages, but also limiting M2a activation of macrophages (23, 26).
Therefore, JAK/STAT appears to be relevant therapeutic target to evaluate in potential treatments for SSc.
To our knowledge, this is the first description of Filgotinib use in SSc.
Descriptions of JAKi usage for SSc in clinical practice are sparse and characterized by heterogeneity of population and low quality of evidences. In particular, descriptions are limited to few case reports (27–33), one single-center, open-label clinical trial (34), one pilot study (35) and a prospective observational study (36). A total of 60 SSc patients were globally recruited in these studies, 2 of whom with defined overlap syndrome with RA (28, 29) and one with SpA (30).
The presence of articular involvement represents the main indication for the use of Filgotinib in our study, and for the use of JAKi in general in patients with SSc (28–31, 35, 37). This is not surprising considering the established role of Filgotinib in RA (17).
The main study on the use of JAKi in SSc, in a pilot study performed by Karalilova et al. in 2021 (35). They compared treatment regimen with methotrexate and JAKi in 66 scleroderma patients, randomized in two arms. After 52 weeks of treatment, JAKi demonstrated greater efficacy than methotrexate in the improvement of musculoskeletal involvement, assessed through US in 10 joints.
The efficacy of Filgotinib in RA can mainly be explained by its anti-inflammatory action, through the inhibition of IL-6 and IFN type I signaling. Moreover, in vitro studies demonstrate that Filgotinib dosage dependently inhibits Th1 and Th2 differentiation, and limits, to a lower degree, the differentiation of Th17 cells (38).
Other than the aforementioned anti-inflammatory effects, JAKi also displayed anti-fibrotic properties, making its use challenging in fibrosing diseases (23).
Indeed, several in vitro studies on SSc patients and murine fibrotic model have shown that JAKi could be effective in ameliorating or preventing fibrogenesis, by modulating inflammation and the fibrogenic process, acting on mesenchymal and epithelial cells, lymphocytes and macrophages (23–25, 39–42).
Interestingly, Karalilova et al. had also observed a greater reduction of mRSS and skin thickness, assessed through US in 5 anatomical sites, and a significantly lower number of cumulative DUs in the JAKi arm than methotrexate one (35). Globally, a significant cutaneous response (decrease in the mRSS of > 5 points and ≥ 25% from baseline) was reported in 88% (52 patients) of the scleroderma patients treated with JAKi (43). An improvement of “salt and pepper” skin and digital ulcers was also described (27, 33).
Indeed, the results of the present study seem to confirm the poor data from the literature, especially regarding the treatment of skin and articular involvement. In the present work, the improvement of skin sclerosis and skin disease related symptoms was clearly observed in patients with dcSSc.
Remarkably, in our small cohort of patients a functional and radiological stabilization of ILD, assessed through PFTs and HRCT, and a significant improvement of dyspnea, has been observed.
Despite the development, over the last two decades, of a wide range of biological therapies, SSc-ILD still represents a major cause of death in scleroderma patients (2, 13).
Based on the first RCTs in scleroderma-ILD (3, 4) cyclophosphamide is the accepted standard of care with micophenolate mofetil for individuals with severe or progressive CTD-related ILD. More recently, RCTs for the use of Tocilizumab (5) and Rituximab (9) have shown positive effect in the management of SSC-ILD. Finally, Nintedanib, a Tyrosine Kinase Inhibitor, has been approved for treatment of SSc-ILD, based on the results of the SENSCISS and INBUILD trial (6–8). However the overall efficacy of new therapies is limited, and side effects may be common and debilitating.
JAKi could represent a pioneering treatment for SSc-ILD due to combined anti-fibrotic and anti-inflammatory properties that have been showed in vivo and in vitro (23).
In fact, JAKi and Filgotinib have already demonstrated to be a safe therapeutic option for the management of RA-associated ILD (44).
Finally, a recent literary review on the use of JAKi for the treatment of SSc-ILD (37) concluded that JAKi might lead to stabilisation or improvement of SSc-ILD in the majority of cases, with the exception of only 2 cases reporting a worsening of ILD. Nevertheless, it is usually well tolerated, with no cardiovascular events described in any study.
Considering PH, some authors discussed recent novel targets of therapies that have been developed, however, these are still in a pre-clinical phase and RCTs are clearly not available. While in recent years substantial progress has been made in targeting key molecular pathways, PH still remains without a definitive cure, and these novel therapies provide an important conceptual framework for categorizing patients on the basis of molecular phenotypes and subsets for effective treatment of the disease (45).
Some recent studies have also suggested that JAK/STAT pathway could be targeted for treating pulmonary arterial hypertension (PAH), a severe and frequent SSc complication (46, 47), although evidences are controversial (48–50).
In the present work no patients of our cohort experienced worsening of pre-existing PH.
Moreover, despite the recent FDA warning regarding the increased risk of major adverse cardiovascular events, malignancy, thrombosis and mortality correlated with the use of JAKi, no events were reported during the follow-up. Preferential inhibition of JAK1 modulates a subset of proinflammatory cytokines, which differ from those inhibited by JAK2 or JAK3 and could explain the favorable safety profile of Filgotinib compared to pan-JAKi (10, 16). Nevertheless, evaluation of cardiovascular risk factors is strongly suggested for patients applying for Filgotinib therapy.
Evaluation of drug efficacy may be challenging in SSc due to the heterogeneity of skin and organ involvement, as well as the lack of well-assessed disease activity scale. Therefore, the American College of Rheumatology (ACR) has recently proposed the CRISS score as a new composite response index to assess the likelihood of improvement in patients with dcSSc after 52 weeks of treatment with new pharmacologic agents (15). In the present study a clinical improvement, defined CRISS score > 0.6, was confirmed in the patients with dcSSc.