JAK inhibitors: a new choice for diabetes mellitus?

Abstract

Altered tyrosine kinase signaling is associated with a variety of diseases. Tyrosine kinases can be classified into two groups: receptor type and nonreceptor type. Nonreceptor-type tyrosine kinases are subdivided into Janus kinases (JAKs), focal adhesion kinases (FAKs) and tec protein tyrosine kinases (TECs). The beneficial effects of receptor-type tyrosine kinase inhibitors (TKIs) for the treatment of diabetes mellitus (DM) and the mechanisms involved have been previously described. Recently, several clinical cases involving the reversal of type 1 diabetes mellitus (T1DM) during treatment with JAK inhibitors have been reported, and clinical studies have described the improvement of type 2 diabetes mellitus (T2DM) during treatment with JAK inhibitors. In vivo and in vitro experimental studies have elucidated some of the mechanisms behind this effect, which seem to be based mainly on the reduction in β-cell disruption and the improvement of insulin resistance. In this review, we briefly describe the beneficial effects of JAK inhibitors among nonreceptor tyrosine kinase inhibitors for the treatment of DM and attempt to analyze the mechanisms involved.

Introduction

Diabetes mellitus (DM) is a common endocrine disease. Currently, the incidence of DM is rapidly increasing globally, and acute and chronic complications, especially chronic complications involving multiple organs and high rates of disability and death, seriously affect the physical and mental health of patients; thus, the increasing disease burden of DM is a major public health concern. DM can be classified into various types, but the most common types are type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM). T1DM is caused by autoimmune β-cell destruction, which usually results in absolute insulin deficiency, including potential autoimmune diabetes mellitus during adulthood. T2DM is caused by a gradual decrease in β-cell insulin secretion, which is often accompanied by insulin resistance [1]. JAK-STAT(Janus kinase-signal transducer and activator of transcription) is a newly discovered intracellular signaling pathway closely related to cytokines in recent years and is involved in many important biological processes, such as cell proliferation, differentiation, apoptosis, and immunomodulation. Cytokine receptor binding transmits signals to tyrosine to phosphorylate and activate receptor-associated JAK, which then phosphorylates and activates STATs. Tyrosine-phosphorylated STATs (pSTATs) form dimers that are translocated to the nucleus, where they bind to target DNA sequences and regulate gene expression (the pSTAT canonical pathway). Unphosphorylated STATs also form dimers that enter the nucleus and regulate transcription (uSTAT non-canonical pathway). Multiple inducible negative feedback systems are used to constrain signaling circuits, including suppressor of cytokine signaling (SOCS) family proteins, inhibitor of activated STAT protein (PIAS) family proteins, tyrosine phosphatase proteins (PTPs), USP18 and ISG15 [2]. This pathway has been shown to be integral to both type I (IFN-α/β) and type II (IFNγ) interferons (collectively also known as type II cytokines) and to all cytokines whose receptors are members of the cytokine receptor superfamily, also known as type I cytokine receptors. These type I cytokines include the short-chain cytokines interleukin (IL)−2, IL-3, IL-4, IL-5, GM-CSF, IL-7, IL-9, IL-13, and IL-15 and the long-chain cytokines IL-6, IL-11, OSM, CNTF, CT-1, growth hormone, prolactin, erythropoietin, and thrombopoietin [3]. In mammals, the JAK family consists of four members: JAK1, JAK2, JAK 3, and Tyk2 [4]. Targeting JAK-associated pathways through the use of JAK inhibitors has rapidly entered the clinical arena in a wide range of disease states, including myeloproliferative neoplasms, rheumatoid arthritis, other immune-mediated joint diseases, and numerous inflammatory skin diseases and inflammatory bowel diseases [5]. At present, DM is mainly treated with medication and insulin replacement therapy to achieve good glycemic control. Conventional medications in diabetes treatment focus on insulin secretion and insulin sensitization, thus causing unwanted side effects and leading to both patient noncompliance and treatment failure [6]. With respect to insulin replacement therapy, insulin is an anabolic hormone that stimulates a large number of cellular responses. Simple insulin replacement therapy has difficulty in stably controlling the blood insulin concentration, thereby increasing the risk of obesity and cardiovascular disease [7]. In addition, neither of the two therapies above can improve the basic pathological mechanism of DM and the function of the pancreatic islets. Therefore, in addition to delaying the progression of diabetes by controlling blood sugar, improving pancreatic islet function through the preservation of β-cells is crucial in diabetes mellitus, which includes both type 1 and type 2 diabetes. β-cell dysfunction, reduced mass, and apoptosis are central to insufficient insulin secretion in both types [8]. The destruction of β-cells is generally thought to be T-cell-mediated [9]. Teplizumab is a humanized immunoglobulin G1 monoclonal antibody that binds with high affinity to the ε chain of CD3 (the signaling hexamer CD3 is a T-cell co-receptor indispensable for the activity of the T-cell receptor). Teplizumab is the only FDA-approved drug for the treatment of T1DM [10], and its mechanism of action is that teplizumab binds to CD3 to induce Tregs tolerance in autoimmune diseases [11], thereby reducing the destruction of β-cells. Therefore, the prevention or delay of β-cell destruction has an important role in the treatment of diabetes. Recently, several clinical studies have been reported the reversal of T1DM during JAK inhibitor treatment [12,13,14] (Table 1), and a small number of clinical studies have reported the benefit of JAK inhibitors in the treatment of T2DM [15, 16] (Table 1). Several basic studies to elaborate on its mechanism, mainly focusing on reducing the destruction of β cells and improving insulin resistance (Table 2). In the present study, we attempt to analyze the possible mechanisms (Fig. 1) behind such effects from basic experimental studies and discuss their potential role as a new therapeutic paradigm for diabetes.

Table 1 Relevant case reports and clinical studies in the article

Table 2 Relevant basic experiments in the article

Fig. 1

The most likely mechanism of protection against diabetes by JAK inhibitors

T1DM

Data from animal models and in vitro studies

AZD1480 (Table 3) is an ATP-competitive inhibitor with specificity for JAK1 and JAK2 that targets the same active site as clinically approved drugs (ruxolitinib and baricitinib). Therefore, it can be used as a proof of principle for the use of JAK inhibitors in the treatment of diabetes. It was found that AZD1480, a JAK1/JAK2 inhibitor, blocked or delayed T-cell destruction of β-cells (reducing immune cell infiltration into pancreatic islets) by inhibiting β-cell MHC class I upregulation and reversed newly diagnosed diabetes in NOD mice (and reversed autoimmune insulinitis in NOD mice) [17]. Upadacitinib (ABT494) (Table 3) is also a JAK inhibitor that competes with adenosine triphosphate (ATP), which potently inhibits JAK1 and weakly inhibits the other isoforms JAK2, JAK3 and TYK2 [18]. Another study showed that upadacitinib (ABT494) could block β-cell MHC class 1 upregulation and inhibit the effects of common γ-chain cytokines on T-cell proliferation and effector T-cell and memory T-cell production, thereby reversing T1DM [19]. In addition, the lead compound JANEX-1 (Table 3) is a rationally designed potent and specific JAK3 inhibitor that does not affect the enzymatic activity of other protein tyrosine kinases [20, 21]. Targeting JAK3 with JANEX-1 in a NOD mouse model was able to block the development of insulin and diabetes in NOD-scid mice following splenocyte overgrafting in diabetic NOD mice. Most importantly, JANEX-1 was able to prevent the development of spontaneous autoimmune diabetes in a NOD type 1 diabetic mouse model [22]. Finally, deucravacitinib (Table 3) is an oral Tyk2 inhibitor that binds to the regulatory (JH2 pseudokinase) structural domain of Tyk2, is highly selective for Tyk2, and has little to no activity against JAK1-3 [23]. It has been shown that deucravacitinib can be used for the prevention or treatment of early T1DM by protecting β-cells from the deleterious effects of proinflammatory cytokines without affecting β-cell function or survival [24]. Thus, despite the paucity of basic experiments, the benefit of JAK inhibitors for T1DM can also be seen.

Table 3 JAK inhibitors and their targets related in the article

Clinical observations

In addition to basic experiments, evidence from clinical studies further elucidates the beneficial role of JAK inhibitors in T1DM. There is evidence that JAK inhibitors may have some therapeutic benefit in T1DM. First, a female patient with T1DM treated with baricitinib (Table 3) for rheumatoid arthritis (RA) experienced a rapid decrease in the daily insulin dose required (17 → 11 units), as well as a decrease in HbA1c levels (7.4% → 6.4%), and the patient's ability to secrete insulin was maintained for more than one year [13]. In addition, in a neonate with STAT3-GOF combined with IDDM, ruxolitinib (Table 3), as an off-label treatment, resulted in an immediate and significant decrease in insulin requirements (reduced from 6 to 0.6 IU/kg/day), and ruxolitinib insulin requirements remained low for more than 1 year of monotherapy (0.6 IU/kg/day); HbA1c that stabilized at 6.8% also confirmed continued diabetes control, and insulin autoantibody (IAA antibody) levels improved significantly with ruxolitinib [14]. Finally, in a 15-year-old adolescent with STAT1 gain of function combined with T1DM, 21 months after the diagnosis of T1DM and 12 months after the initiation of ruxolitinib (well beyond the "honeymoon" period of T1DM), exogenous insulin was discontinued, and the patient remained in a normoglycemic state. The patient also remained normal without insulin for more than a year [12]. Recently, Michaela Waibel et al. conducted a clinical study enrolling 91 patients with T1DM, in which patients diagnosed with T1DM within the 100 days prior to the start of the study were randomized to receive either baricitinib (4 mg once daily) or a matching placebo orally for 48 weeks, with a 2-h mixed-meal tolerance test performed at week 48. The ability of baricitinib to maintain β-cell function in patients with T1DM was evaluated by mean C-peptide levels determined from the area under the concentration‒time curve, as well as change from baseline in glycosylated hemoglobin levels, daily insulin doses, and measures of glycemic control assessed via continuous glucose monitoring. The study revealed that at 48 weeks, the median mean C-peptide level resulting from mixed dietary stimulation was greater in the baricitinib group than in the placebo group, the mean daily insulin dose was lower in the baricitinib group than in the placebo group, and the glycated hemoglobin levels were similar in the two trial groups. Estimates of mean C-peptide levels based on mixed dietary stimuli suggest that daily administration of baricitinib for more than 48 weeks appears to preserve β-cell function in patients with recent-onset T1DM [25]. The above data from different clinical observations support data from animal models of T1DM, suggesting that JAK inhibitors may all be useful in treating T1DM by preserving β-cell function and quality.

T2DM

Data from animal models and in vitro studies

Recently,Hauwa'u Yakubu Bako et al. conducted a basic study in which a rat model of T2DM was treated with different doses of tofacitinib (10, 20 mg/kg BW), aspirin (100, 200 mg/kg BW) and two doses of both drugs in combination for 9 weeks. The study revealed that T2DM resulted in a significant decrease in the serum insulin concentration and a significant reversal in all the tofacitinib-treated diabetic groups. Compared with those in the T2DM model group, the HOMA-IR values were significantly lower in all the diabetes groups treated with tofacitinib alone, the HOMA-β values were significantly greater, and the weekly blood glucose levels were lower [26]. Thus, although there are limited basic experiments, the concept that JAK inhibitors treat T2DM by improving insulin resistance emerges.

Clinical observations

In addition to basic experiments, evidence from clinical observations has further elucidated the therapeutic role of JAK inhibitors in T2DM. Claudia Di Muzio et al. conducted a clinical study enrolling 40 patients with RA with T2DM given tofacitinib (Table 3) at the appropriate dose according to the manufacturer's instructions. Glucose-lowering therapy was also maintained during the follow-up period, with the primary endpoint being the change in the 1998 update of the Homeostatic IR Model Assessment (HOMA2-IR) in patients with RA combined with T2DM, who were treated with tofacitinib for 6 months. The study revealed a gradual decrease in HOMA2-IR, i.e., a gradual reduction in the level of insulin resistance, and an increase in HOMA2-β, i.e., an improvement in insulin sensitivity, in patients treated with tofacitinib; a trend toward a decrease in glycosylated hemoglobin was also documented [15]. In addition, Cristina Martinez-Molina et al. conducted a clinical study that included 13 patients with T2DM combined with RA, six of whom were treated with tofacitinib and seven of whom were treated with baricitinib. The primary endpoint was glycated hemoglobin(HbA1c) after 6 months of treatment with JAK inhibitors. The study found a significant reduction in HbA1c in the treated baricitinib group, with 57.1% of patients treated with baricitinib having HbA1c values < 7%; in addition, 28.6% of patients treated with baricitinib required a reduction in the OAD dosee. However, there was no significant reduction in the tofacitinib group [16]. These studies support the findings of basic experiments suggesting that JAK inhibitors counteract T2DM by improving insulin resistance.

The respective possible mechanisms

JAK1

The JAK1 pathway is important for cytokines that share the common γ chain for type 1 cytokine receptors (e.g., IL-2, IL-6, and IL-21). JAK1 is also part of the canonical signaling pathway for type 1 and type 2 interferons [27]. The pathology of T1DM in NOD mice and humans is characterized by the presence of autoreactive cytotoxic CD8⁺T lymphocytes (CTLs) that mediate β-cell destruction. These cells acquire effector functions in pancreatic islets, a process that is dependent on the action of cytokines [28, 29]. Among these cytokines, IL-2, IL-7, and IL-15 have been shown to be three cytokines with indispensable roles in CD8⁺ T-cell memory generation and maintenance [30]. IL-2 and IL-21 are major cytokines required for CTL growth and differentiation [31, 32]. It has been shown that a selective inhibitor of JAK1 (ABT 317) blocks IL-2-, IL-7-, and IL-15-mediated phosphorylation of STAT5 and IL-21-mediated phosphorylation of STAT3, which inhibits the effects of common γ-chain cytokines on T-cell proliferation and effector and memory T-cell production, and thus reduces the destruction of β-cells by CTLs [19]. On the other hand, the overexpression of human leukocyte antigen class I (HLA-I) molecules on pancreatic β-cells is widely recognized as a hallmark feature of the pathogenesis of T1DM [33], this may increase the visibility of β-cells to self-reactive CD8⁺ T cells, thereby accelerating β-cell destruction. The presence of residual β-cells is critical for HLA-I overexpression in islet cells at all stages of the disease. The most likely drivers are interferons released by β-cells (type I or type III interferons) or produced from the influx of autoreactive immune cells (type II interferon). In both cases, the JAK/STAT pathway would be activated to induce downstream expression of interferon-stimulated genes [34]. This study also revealed that in NOD mice, a JAK1 selective inhibitor (ABT 317) reduced IFN-γ signaling in β-cells and prevented the upregulation of β-cell MHC class I, which reduced β-cell destruction [19].

JAK2

JAK2 plays an important role in signaling events that mediate innate and adaptive immunity. In the cytoplasm, the tyrosine protein kinase JAK2 plays a key role in signaling through association with type I receptors such as GHR, erythropoietin (EPOR), leptin (LEPR), prolactin (PRLR), and thrombopoietin (THPO) or type II receptors such as interferon-γ (IFN-γ), granulocyte/macrophage colony-stimulating factor (GM-CSF) and various interleukins (IL)-IL-3, IL-5, and IL-12 [35]. Basic experimental and clinical studies on the treatment of diabetes with a separate JAK2-selective inhibitor have not been reported. Sorafenib is an anticancer drug approved by the United States Food and Drug Administration (US FDA) for the treatment of unresectable hepatocellular carcinoma and advanced renal cell carcinoma. Sorafenib inhibits tumor growth and angiogenesis through targeting both the RAF/MEK/ERK pathway and receptor tyrosine kinases [36]. In vitro studies have shown that sorafenib indirectly inhibits the IL-12-induced phosphorylation of JAK2 and STAT4, thereby inhibiting Th1 cell differentiation. The Th1 cell population is a key mediator in the pathogenesis of T1DM. In the context of DM, β-cells are destroyed by cytotoxic T-lymphocytes (CTLs) and macrophages, both of which are regulated by helper T-lymphocytes (Th)1 cells [37]. In addition, since both JAK1 and JAK2 associate with IFN-γ and play key roles in IFN-γ signaling, they may have similar mechanisms. Interferon-γ-inducible protein 10 (CXCL10, also called IP-10) is considered an important chemokine in TIDM [38] and is required for the transportation of CTLs to sites of inflammation. It has been shown that AZD1480 (JAK1/JAK2 inhibitor) blocked IFN-γ-induced HLA-class I upregulation in β-cells and inhibited CXCL10 secretion in pancreatic islets; this resulted in a decrease in chemoattraction, migration, and accumulation of autoreactive CTLs in pancreatic islets, which led to attenuated interactions of autoreactive CTLs with AZD1480-treated β-cells and a reduction in the synaptic residence time, thereby reducing immune cell infiltration of pancreatic islets [17]. However, since JAK2 signaling is located downstream of EPO, GM-CSF, and TPO, JAK1-selective inhibitors have a better safety profile and lower risk of anemia than do JAK1/JAK2 inhibitors or JAK2-selective inhibitors [39].

JAK3

JAK3, a member of the JAK family, plays a crucial role in T-cell development and the homeostasis of the immune system homeostasis due to its association with the common γ chain (γc) of cytokine receptors [40] . PHA is a mitogenic agent obtained from the seed extract of cauliflower bean that can induce erythrocyte agglutination and stimulate mitosis in progressive lymphocytes in cell culture. It has been shown that JANEX-1 (JAK3-selective inhibitor) inhibits JAK3 dependent, IL-2-induced STAT5 tyrosine phosphorylation and alters the cytokine secretion pattern of T cells from diabetes-susceptible NOD mice with or without PHA stimulation. Furthermore, treatment with the JANEX-1 results in a significant increase in IL-10 secretion, a significant decrease in IL-2 secretion, and inhibition of the response of the PHA and proliferative responses to antigens (including the diabetic autoantigen GAD65) [22]. Therefore, there is a decrease in T-cell accumulation and a decrease in β-cell destruction. And it has been shown that exogenous IL-10 prevents insulitis or diabetes in NOD mice [41, 42]. Regulatory T cells are among the important factors involved in maintaining the immune tolerance of an organism, and regulate the immunity of the organism by inhibiting the activation and proliferation of potentially autoreactive T cells present in normal organisms via active regulation. It has been found that WHI-P131 (a JAK3-selective inhibitor) promotes TGF-β secretion by CD4 + T cells both in vivo and in vitro and significantly reduces IL-4, IFN-γ, and IL-2 production by CD4⁺ T cells. Induction of these cells may be a potential mechanism for the antidiabetic effects of JAK3-selective inhibitors in NOD mice [43]. In addition, tofacitinib is a JAK1/JAK3 inhibitor, and studies in rats with induced insulin resistance have shown that high levels of proinflammatory cytokines produced by the JAK-STAT and NF-κB signaling pathways lead to chronic inflammation and that high levels of proinflammatory cytokines increase the synthesis of cytokine inhibitory coactivators (SOCS) to inhibit insulin signaling, leading to insulin resistance. While tofacitinib can inhibit the production of high-level proinflammatory cytokines by inhibiting the JAK-STAT and NF-κB signaling pathways, it can also reduce SOCS and ultimately alleviate insulin resistance [26]; therefore, this may be a similar mechanism for inhibiting JAK or JAK3 to reduce insulin resistance.

TYK 2

Tyrosine kinase 2 (TYK2) is also an intracellular signaling tyrosine kinase that regulates signaling through a limited number of cytokines, including IL-12, IL-23, and type I IFNs (IFN-α and IFN-β), and plays a central role in the pathophysiology of IMID. Deucravacitinib is a novel orally-administered and selective TYK2 inhibitor with a unique binding mode to the regulatory (pseudokinase) structural domain rather than to the highly conserved ATP-binding site in the catalytic structural domain. TYK2 binds via a metastable mechanism that locks the regulatory structural domain in an inhibitory conformation with the catalytic structural domain, thereby trapping TYK2 in an inactive state and blocking receptor-mediated activation and downstream signaling [44, 45]. IFN-α is present in the pancreatic islets of T1DM patients [46] IFN-α plays a central role in the early stages of diabetes, and in human β-cells, IFN-α induces endoplasmic reticulum (ER) stress and prolonged the overexpression of HLA class I through the activation of the TYK2 signaling and STAT pathways. In addition, IFN-α synergizes with IL-1β to induce β-cell apoptosis [47, 48]. In mature stem cell pancreatic islets, the deletion or inhibition of TYK2 prevents IFN-α-induced antigen processing and presentation, including MHC class I and class II expression, which enhances their survival in response to CD8⁺ T-cell cytotoxicity [49]. Furthermore, in a study using deucravacitinib-mediated inhibition of TYK2 to analyze its effect on T1DM, it was found that deucravacitinib blocked the effect of IFN-α in a dose-dependent manner, i.e., it inhibited, among other factors, STAT1 and STAT2 activation and MHC class I overexpression, without affecting β-cell survival and function. In addition, decucravacitinib partially reduced apoptosis and inflammation in IFN-α + IL-1β or IFNγ + IL-1β-pretreated cells. However, it had no significant effect on ER stress [24].

Conclusion

In summary, case reports, clinical studies, and experimental animal and in vitro studies provide some evidence that JAK inhibitors improve the clinical performance of T1DM; in contrast, although there are two clinical studies in which JAK inhibitors improve the clinical performance of T2DM, few related experimental animal and in vitro studies exist. In this review, we found that JAK inhibitors act mainly against two major defects in diabetes, i.e., improvement of insulin resistance and reduction of β-cell dysfunction. One of the most common mechanisms is to block IFN and associated cytokine signaling by inhibiting JAK, which reduces T-cell activation, proliferation, accumulation, etc., and thus reduces β-cell destruction. In this work, we summarize previous related studies and highlight the possible mechanisms of the beneficial effects of JAK on DM; however, several limitations remain. First, the deep mechanism of action between related molecules and pathways is not fully understood. Second, the efficacy and safety of each molecule after inhibition have not been determined. Third, because the current research in this area is being explored, there are some limitations in this paper, as the number of relevant studies included is small. Therefore, owing to the potential benefits of JAK inhibitors on DM, we urgently need more basic experimental and clinical studies on JAK inhibitors and DM, including more clinical studies on JAK3 inhibitors and T1DM, experimental animal studies and then clinical studies on TYK2 inhibitors and T1DM, as well as studies on the molecular mechanism of action of JAK inhibitors on the benefits of T2DM. Currently, JAK inhibitors have been approved for use in many autoimmune diseases, and we believe that through more in-depth studies in the future, JAK inhibitors will inject newer and more powerful energy into the treatment and management of DM.