Significant improvement of right ventricular function by imatinib mesylate in scleroderma-associated pulmonary arterial hypertension

Dasatinib-induced pulmonary arterial hypertension

Drug-induced (group 1) pulmonary hypertension (PH) is an important subgroup of PH involving dasatinib as a likely related agent, which is a second-generation tyrosine kinase inhibitor (TKI) used in the treatment of chronic myeloid leukaemia (CML). The mechanism of dasatinib-induced pulmonary arterial hypertension (PAH) is unclear. However, the occurrence of PAH with late onset in CML patients suggests a chronic pathological mechanism with an insidious onset rather than an acute inflammatory or cardiac aetiology. Dasatinib has a broader effect than other TKIs; the major known difference between dasatinib and other TKIs is the additional inhibition of Src family kinases. Therefore, Src inhibition was thought to play a role in the development of dasatinib-induced PAH. However, recently, it was also speculated that chronic dasatinib therapy may cause pulmonary endothelial damage, attenuate hypoxic pulmonary vasoconstriction responses and increase susceptibility to PAH independently of the Src family kinase-induced mechanism. Dasatinib-induced PAH usually seems to be reversible with the cessation of the drug, and sometimes with PAH-specific treatment strategies. Transthoracic echocardiography can be recommended as a routine screening prior to dasatinib initiation, and this non-invasive procedure can be utilized in patients having signs and symptoms attributable to PAH during dasatinib treatment.

Recent advances in animal models of systemic sclerosis

Systemic sclerosis (SSc) is a multisystem connective tissue disease characterized by the three cardinal pathological features, comprising aberrant immune activation, vasculopathy and tissue fibrosis, with unknown etiology. Although many inducible and genetic animal models mimicking the selected aspects of SSc have been well documented, the lack of models encompassing the full clinical manifestations hindered the development and preclinical testing of therapies against this disease. Under this situation, three new genetic animal models have recently been established, such as Fra2 transgenic mice, urokinase-type plasminogen activator receptor deficient mice and Klf5(+/-) ;Fli1(+/-) mice, all of which recapitulate the pathological cascade of SSc. The former two murine models demonstrate endothelial cell apoptosis and capillary loss followed by tissue fibrosis, whereas the immune systems show no remarkable abnormality. Klf5(+/-) ;Fli1(+/-) mice develop immune activation, vasculopathy and tissue fibrosis in this sequence, eventually resulting in the development of dermal fibrosis, interstitial lung disease and pulmonary vascular involvement resembling those of SSc. Because Krueppel-like factor (KLF)5 and Friend leukemia integration 1 transcription factor (Fli1) are the transcription factors epigenetically suppressed in SSc dermal fibroblasts, the reproduction of SSc manifestations in Klf5(+/-) ;Fli1(+/-) mice supports the canonical idea that environmental influences play a central role in the development of SSc in genetically predisposed individuals. These new animal models offer important clues for the better understanding of the underlying molecular mechanisms of SSc pathology and the identification of potential molecular targets for the treatment of this incurable disease.

[A Uuifying hypothesis for the pathogenesis of systemic sclerosis based on the deficiency of transcription factor Fli1 - the development of a new animal model of systemic sclerosis -]

Systemic sclerosis (SSc) is a multisystem connective tissue disease featured by immune abnormalities, vasculopathy and resultant fibrosis of the skin and various internal organs. Although the pathogenesis of SSc remains incompletely elucidated, it is currently accepted that this disease is caused by the complex interplay between hereditary and environmental factors. The deficiency of transcription factor Fli1, which is epigenetically suppressed in SSc dermal fibroblasts, potentially causes SSc-like phenotypical alteration in various cell types such as fibroblasts, endothelial cells, and macrophages, suggesting that Fli1 is a predisposing factor of SSc. KLF5 is another transcription factor which is suppressed in SSc dermal fibroblasts through an epigenetic mechanism. Importantly, double heterozygous mice for Fli1 and KLF5 develop three cardinal features of SSc, including immune abnormalities, vasculopathy and fibrosis. Therefore, these two transcription factors are likely to be critical predisposing factors regulating the development of SSc. Given that potential disease modifying drugs, bosentan and imatinib, reverse the expression and transcriptional activity of Fli1, the studies on the pathological process of double heterozygous mice and the impact of these transcription factors on various cell types may provide a new clue to further understand the pathogenesis of SSc leading to the development of new therapies.

Novel Targets of Drug Treatment for Pulmonary Hypertension

Biomedical advances over the last decade have identified the central role of proliferative pulmonary arterial smooth muscle cells (PASMCs) in the development of pulmonary hypertension (PH). Furthermore, promoters of proliferation and apoptosis resistance in PASMCs and endothelial cells, such as aberrant signal pathways involving growth factors, G protein-coupled receptors, kinases, and microRNAs, have also been described. As a result of these discoveries, PH is currently divided into subgroups based on the underlying pathology, which allows focused and targeted treatment of the condition. The defining features of PH, which subsequently lead to vascular wall remodeling, are dysregulated proliferation of PASMCs, local inflammation, and apoptosis-resistant endothelial cells. Efforts to assess the relative contributions of these factors have generated several promising targets. This review discusses recent novel targets of therapies for PH that have been developed as a result of these advances, which are now in pre-clinical and clinical trials (e.g., imatinib [phase III]; nilotinib, AT-877ER, rituximab, tacrolimus, paroxetine, sertraline, fluoxetine, bardoxolone methyl [phase II]; and sorafenib, FK506, aviptadil, endothelial progenitor cells (EPCs) [phase I]). While substantial progress has been made in recent years in targeting key molecular pathways, PH still remains without a cure, and these novel therapies provide an important conceptual framework of categorizing patients on the basis of molecular phenotype(s) for effective treatment of the disease.

Vasculopathy in scleroderma

Systemic sclerosis (SSc) is a multisystem connective tissue disorder featured by vascular injury and fibrosis of the skin and various internal organs with autoimmune background. Although the pathogenesis of SSc still remains elusive, it is generally accepted that initial vascular injury due to autoimmunity and/or environmental factors causes structural and functional abnormalities of vasculature which eventually result in the constitutive activation of fibroblasts in various organs. Structural alterations consist of destructive vasculopathy (loss of small vessels) and proliferative obliterative vasculopathy (occlusion of arterioles and small arteries with fibro-proliferative change) caused by impaired compensatory vasculogenesis and angiogenesis. Impaired function of SSc vasculature includes the altered expression of cell adhesion molecules predominantly inducing Th2 and Th17 cell infiltration, endothelial dysfunction primarily due to the low availability of nitric oxide, the activated endothelial-to-mesenchymal transition leading to fibro-proliferative vascular change and tissue fibrosis, and the impaired coagulation/fibrinolysis system promoting the formation of intravascular fibrin deposits. Recent new insights into the therapeutic mechanisms of intravenous cyclophosphamide pulse and bosentan and the establishment of a new SSc animal model (Klf5 (+/-);Fli1 (+/-) mice) provide us useful clues to further understand the development of vascular alterations characteristic of SSc. This article overviewed the present understanding of the pathogenesis of SSc vasculopathy.

Genetic Ablation of PDGF-Dependent Signaling Pathways Abolishes Vascular Remodeling and Experimental Pulmonary Hypertension

OBJECTIVE

Despite modern therapies, pulmonary arterial hypertension (PAH) harbors a high mortality. Vascular remodeling is a hallmark of the disease. Recent clinical studies revealed that antiremodeling approaches with tyrosine-kinase inhibitors such as imatinib are effective, but its applicability is limited by significant side effects. Although imatinib has multiple targets, expression analyses support a role for platelet-derived growth factor (PDGF) in the pathobiology of the disease. However, its precise role and downstream signaling events have not been established.

APPROACH AND RESULTS

Patients with PAH exhibit enhanced expression and phosphorylation of β PDGF receptor (βPDGFR) in remodeled pulmonary arterioles, particularly at the binding sites for phophatidyl-inositol-3-kinase and PLCγ at tyrosine residues 751 and 1021, respectively. These signaling molecules were identified as critical downstream mediators of βPDGFR-mediated proliferation and migration of pulmonary arterial smooth muscle cells. We, therefore, investigated mice expressing a mutated βPDGFR that is unable to recruit phophatidyl-inositol-3-kinase and PLCγ (βPDGFR(F3/F3)). PDGF-dependent Erk1/2 and Akt phosphorylation, cyclin D1 induction, and proliferation, migration, and protection against apoptosis were abolished in βPDGFR(F3/F3) pulmonary arterial smooth muscle cells. On exposure to chronic hypoxia, vascular remodeling of pulmonary arteries was blunted in βPDGFR(F3/F3) mice compared with wild-type littermates. These alterations led to protection from hypoxia-induced PAH and right ventricular hypertrophy.

CONCLUSIONS

By means of a genetic approach, our data provide definite evidence that the activated βPDGFR is a key contributor to pulmonary vascular remodeling and PAH. Selective disruption of PDGF-dependent phophatidyl-inositol-3-kinase and PLCγ activity is sufficient to abolish these pathogenic responses in vivo, identifying these signaling events as valuable targets for antiremodeling strategies in PAH.

Saudi Guidelines on the Diagnosis and Treatment of Pulmonary Hypertension: Pulmonary arterial hypertension associated with connective tissue diseases

The explosive growth of medical literature on pulmonary hypertension (PH) has led to a steady increase in awareness of this disease within the medical community during the past decade. The recent revision of the classification of PH is presented in in the main guidelines.

Group 1 PH or pulmonary arterial hypertension (PAH) is a heterogeneous group and includes PH due to inheritable, drug-induced, and toxin-induced causes and to such underlying systemic causes as connective tissue diseases, human immunodeficiency viral infection, portal hypertension, congenital heart disease, and schistosomiasis.

Systemic sclerosis (SSc) is an autoimmune multisystem disorder, which affects over 240 persons per million in the United States.[1] Its manifestations are not confined to the skin but may also involve the lungs, kidneys, peripheral circulation, musculoskeletal system, gastrointestinal tract, and heart.

The outcome of PAH associated with SSc is worse when compared to other subtypes of PAH.

In this review, we summarize available information about the pulmonary vascular and cardiac manifestations of SSc with special emphasis on their prognostic implications as well as the peculiarity of their detection.

Targeting the PDGF signaling pathway in the treatment of non-malignant diseases

Platelet-derived growth factor (PDGF) is a family of mesenchymal mitogens with important functions during the embryonal development and in the control of tissue homeostasis in the adult. The PDGF isoforms exert their effects by binding to α-and β-tyrosine kinase receptors. Overactivity of PDGF signaling has been linked to the development of certain malignant and non-malignant diseases, including atherosclerosis and various fibrotic diseases. Different types of PDGF antagonists have been developed, including inhibitory monoclonal antibodies and DNA aptamers against PDGF isoforms and receptors, and receptor tyrosine kinase inhibitors. Beneficial effects have been recorded using such inhibitors in preclinical models and in patients with certain malignant as well as non-malignant diseases. The present communication summarizes the use of PDGF antagonists in the treatment of non-malignant diseases.

Pharmacology and rationale for imatinib in the treatment of scleroderma

Systemic sclerosis (scleroderma) is a chronic, multisystem, fibrotic disease. Although the pathogenesis is not completely understood, early vascular damage leads to an inflammatory reaction and a severe fibrotic response. Therapy of systemic sclerosis is still not convincing and is mainly restricted to the management of organ complications. A wide choice of immunosuppressive and antifibrotic drugs has been used to try to modify the course of the disease, but significant breakthroughs are still lacking. Imatinib is a tyrosine kinase inhibitor known to regulate growth, proliferation, and differentiation as well as apoptosis of cells and is already widely used for several malignancies, eg, chronic myeloid leukemia and gastrointestinal stromal tumors. It has been used in preclinical as well as clinical studies to modulate the fibrotic process in patients with systemic sclerosis. This is based on its activity to interfere selectively with both the transforming growth factor-β and platelet-derived growth factor signaling pathway. Preclinical studies in mouse models of scleroderma showed significant anti-inflammatory and antifibrotic effects; however, several clinical, proof-of-concept trials have not yet confirmed these initially promising results.

Imatinib in active diffuse cutaneous systemic sclerosis: Results of a six-month, randomized, double-blind, placebo-controlled, proof-of-concept pilot study at a single center

OBJECTIVE

To better understand the feasibility of using imatinib, a tyrosine kinase inhibitor, to treat active diffuse cutaneous systemic sclerosis (dcSSc).

METHODS

We performed a 6-month, randomized, double-blind, placebo-controlled, proof-of-concept pilot study of imatinib in patients with active dcSSc. Data on safety, modified Rodnan skin thickness scores (MRSS), Health Assessment Questionnaire (HAQ) scores, patient's and physician's global assessments (100-mm visual analog scale), and biomarkers in serum and skin biopsy samples were collected. We used a 4:1 randomization strategy (imatinib 200 mg administered twice a day versus placebo), stratifying according to current use of methotrexate. The plan was to enroll 20 dcSSc patients.

RESULTS

After enrolling 10 patients (9 receiving active drug and 1 receiving placebo), we found poor tolerability and high rates of adverse events with imatinib, and study enrollment was discontinued. There was no significant difference in the mean MRSS in all patients who took imatinib (31.1 at baseline versus 29.4 at 6 months) or in only those who completed 6 months of imatinib (31.0 at baseline versus 30.3 at 6 months), and there was no difference in the C-reactive protein level, erythrocyte sedimentation rate, physician's global assessment, patient's global assessment, response to the Health Transition query, or the HAQ scores between those who did and those who did not complete 6 months of therapy. Side effects were edema, fluid retention, fatigue, nausea, cramps/myalgias, diarrhea, alopecia, and anemia. Most side effects occurred within the first week of treatment, and even when imatinib was reintroduced at a lower dosage (200 mg daily), it was poorly tolerated. Two patients were hospitalized because of side effects of the medication. In general, biomarker levels in plasma and skin did not change.

CONCLUSION

Imatinib was poorly tolerated, and this could limit its application in SSc. The study was too small to form conclusions about the efficacy of imatinib in SSc.

Pulmonary arterial hypertension in connective tissue diseases

Pulmonary arterial hypertension (PAH) may complicate diverse connective tissue diseases (CTDs). Approximately 10% of patients with systemic sclerosis develop PAH, the prevalence being much lower in other CTDs. However, PAH is an important contributor to morbidity and mortality in all forms of CTD. Despite similarities in presentation, hemodynamic perturbations, and pathogenesis, patients with CTD-associated PAH (CTD-PAH) usually have a poorer response to PAH-specific medications and poorer prognosis than patients with idiopathic PAH (IPAH). Select patients with CTD-PAH may be candidates for lung transplantation, but results are less favorable than for IPAH because of comorbidities and complications specifically associated with CTD.

Pulmonary arterial hypertension associated with systemic sclerosis: Current diagnostic approach and therapeutic strategies

Pulmonary arterial hypertension (PAH) represents a devastating vascular complication of systemic sclerosis (SSc) and is found in 10%-15% of cases carrying a severe prognosis. PAH has a dramatic impact on the clinical course and overall survival, being the single most common cause of death in patients with this entity. The clinical course and aggressive progression of PAH has led clinicians to perform annual screening for it, since early detection and diagnosis are the cornerstone of a prompt therapeutic intervention. The diagnosis of PAH can be challenging to clinicians, particularly in its early stages, since in the context of SSc, the multiple causes of dyspnea need to be assessed. Doppler echocardiography represents the best initial screening tool, however, right heart catheterization remains the gold standard and definitive diagnostic means. Remarkable advances have been achieved in elucidating the pathogenesis of PAH in the past two decades, leading to the development of disease-specific targeted therapies: prostacyclin analogues, endothelin receptor antagonists and inhibitors of five phosphodiesterase pathways. However, the clinical response to these therapies in SSc-associated PAH has not been as great as the one seen with idiopathic PAH. This review also focuses on the diagnosis and novel therapies that are currently available for PAH, as well as potential future therapeutic developments based on newly acquired knowledge of diverse pathogenic mechanisms.

Therapeutic inhibition of tyrosine kinases in systemic sclerosis: a review of published experience on the first 108 patients treated with imatinib

OBJECTIVE

Experimental and clinical evidence suggest a therapeutic role for the tyrosine kinase inhibitor imatinib in fibrosing conditions. We evaluated published data on the safety and efficacy of imatinib for patients with systemic sclerosis (SSc), a severe autoimmune disease with significant morbidity and mortality.

METHODS

A careful search for all original articles and abstracts on the use of imatinib in SSc published in English from 2008 through February 2012 was performed. Two additional patients from our center are also described.

RESULTS

Five small observational clinical trials on the use of imatinib in severe SSc have been conducted and case reports and small series of refractory to current approaches patients have been reported, adding to a total of 108 patients having received this drug to date. In most of these patients imatinib was given for skin or pulmonary fibrosis. Encouraging results were reported in 3 of 4 studies, whereas the fifth study was prematurely terminated for safety reasons. Overall, clinical results are highly variable, ranging from ineffective or toxic responses to extremely encouraging clinical improvements in some severely ill patients. These discrepancies could partly reflect imatinib-related safety issues, in particular, SSc patients or idiosyncratic resistance to imatinib, as happens in chronic myelogenous leukemia and gastrointestinal stromal tumors, the drug's approved indications.

CONCLUSIONS

The limited available experience suggests that imatinib could be considered as an individualized treatment approach in severe SSc and underscores the need to identify markers for selecting particular patients, who will safely respond to therapeutic inhibition of tyrosine kinases.

The pharmacological treatment of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a life-threatening and progressive disease of various origins characterized by pulmonary vascular remodeling that leads to increased pulmonary vascular resistance and pulmonary arterial pressure, most often resulting in right-sided heart failure. The most common symptom at presentation is breathlessness, with impaired exercise capacity as a hallmark of the disease. Advances in understanding the pathobiology over the last 2 decades have led to therapies (endothelin receptor antagonists, phosphodiesterase type 5 inhibitors, and prostacyclins or analogs) initially directed at reversing the pulmonary vasoconstriction and more recently directed toward reversing endothelial cell dysfunction and smooth muscle cell proliferation. Despite these advances, disease progression is common even with use of combination regimens targeting multiple mechanistic pathways. Overall 5-year survival for PAH has increased significantly from approximately 30% in the 1980s to approximately 60% at present, yet remains abysmal. This review summarizes the mechanisms of action, clinical data, and regulatory histories of approved PAH therapies and describes the latest agents in late-stage clinical development.

Reactivity of pulmonary circulation and right ventricle function to inhaled nitric oxide in systemic sclerosis patients

Systemic sclerosis (SSc) is complicated by pulmonary hypertension and right ventricle (RV) failure in approximately 10% of the patients. Factors influencing the reactivity of pulmonary circulation to vasodilators are not established, while the examination of vasoreactivity is important in determining the treatment, because systemic administration of oral vasodilators can induce severe adverse events in nonresponders. The mechanism of RV failure in SSc is unclear and may result either from increased RV afterload or intrinsic myocardial disease. The aim of the study was to assess the reactivity of pulmonary circulation to inhaled nitric oxide (iNO) and to evaluate its influence on RV function in SSc patients with elevated right ventricle systolic pressure (RVSP). In 60 SSc patients aged 24-73 (58 females, two males; 33 patients with limited SSc and 27 with diffuse SSc), echocardiographic examination with tissue Doppler echocardiography (TDE) was performed. RV function was measured by systolic (S) and early diastolic (E) velocity of tricuspid annulus by TDE. In patients with RVSP >45 mmHg, the reactivity of pulmonary circulation was assessed by iNO test. High-resolution computerized tomography (HRCT) was performed to assess the extent of pulmonary fibrosis. Of 14 SSc subjects with elevated RVSP (13 females, one male; RVSP 47-62 mmHg), positive reaction to iNO was observed in five (RVSP decreased from 51.6 ± 3.7 to 32.24 ± 2.3 mmHg); nine patients were not reactive (RVSP 53.5 ± 5.7 mmHg before iNO vs. 49.6 ± 6.7 mmHg). RV systolic function was decreased in patients with elevated RVSP as compared to the patients with normal pulmonary pressure (S velocity 13.2 ± 1.3 vs. 14.4 ± 1.6 cm/s, respectively, p < 0.05). Significant increase of RV systolic function during iNO test was found in reactive patients only (S velocity before iNO 12.8 ± 1.2 cm/s, during iNO 14.5 ± 1.5 cm/s, p < 0.01). RVSP decrease strongly correlated with S velocity increase (r = 0.95, p < 0.0001). Response to iNO was found only in limited form of SSc; diffuse SSc patients showed no response. Pulmonary fibrosis on HRCT was more frequent in subjects nonreactive to iNO (67% of patients) than in the reactive group (40% of patients). The reactivity of pulmonary circulation to iNO in SSc patients with elevated RVSP was found predominantly in limited form of the disease. Pulmonary fibrosis typical for diffuse SSc was more frequent in nonreactive subjects. Elevated pulmonary pressure plays an important role in RV systolic dysfunction. Pulmonary pressure decrease during iNO test leads to the improvement of RV systolic function. Therapy for right-heart failure in reactive SSc patients should be directed, if possible, at the decrease in pulmonary resistance.

Imatinib mesylate for the treatment of pulmonary arterial hypertension

INTRODUCTION

Despite recent advances, pulmonary arterial hypertension (PAH) remains a devastating disease which harbors a poor prognosis. Novel therapeutic approaches directly targeting pulmonary vascular remodeling are warranted.

AREAS COVERED

This review delineates the current limitations in the management of PAH and focuses on a novel, anti-proliferative therapeutic concept. It will help readers understand the mechanisms of receptor tyrosine kinase signaling, with a special focus on platelet-derived growth factor (PDGF) receptors and their role in the pathobiology of PAH. Furthermore, it provides a comprehensive summary regarding the rationale, efficacy and safety of the tyrosine kinase inhibitor imatinib mesylate , which potently inhibits the PDGF receptor, as an additional treatment option in PAH.

EXPERT OPINION

PDGF is a potent mitogen for pulmonary vascular smooth muscle cells and represents an important mediator of pulmonary vascular remodeling. Imatinib mesylate, a compound that inhibits the Bcr-Abl kinase and was developed for the treatment of chronic myeloid leukemia, also targets PDGF receptors. Both experimental and clinical data indicate that it reverses the vascular remodeling process even when it is fully established. Results from Phase II and III clinical trials suggest potent and prolonged efficacy in patients with severe PAH (i.e., pulmonary vascular resistance > 800 dynes*s*cm(-5)). Future studies should evaluate the long-term clinical efficacy and safety of imatinib, including patients with less impaired hemodynamics. Based on the current knowledge, this compound is likely to become an additional treatment option for patients with PAH and has the potential to at least partially correct the pathology of the disease.

Treatment with imatinib results in reduced IL-4-producing T cells, but increased CD4(+) T cells in the broncho-alveolar lavage of patients with systemic sclerosis

T cells, particularly those producing IL-4, are implicated in inflammation-mediated fibrosis. In our phase I/IIa open-label pilot study in 15 patients with scleroderma-interstitial lung disease (SSc-ILD), high-dose imatinib treatment showed modest improvement in lung function and skin score, but with several adverse events. Here, we investigated T cell phenotype and cytokine production in bronchoalveolar lavage (BAL) from patients enrolled in this trial. We found that IL-4(+) T cells showed a stronger correlation with ground glass opacity (GGO) than fibrosis scores on lung high-resolution computer tomography scans. Frequencies of IL-4(+) T cells also discriminated patients with high (≥20) versus low (<20) GGO scores. Functional annotation clustering of proteins that correlated with T cells identified two major clusters that belonged to immune/inflammatory and wounding response. Repeat analyses after 1 year of treatment in 10 BAL samples, one each from the right middle and lower lobes of lung from 5 patients, showed that post-imatinib, IL-4(+) T cells were profoundly reduced but CD4(+) T cells increased, except in one patient who showed worsening of SSc-ILD. Post-imatinib increase in CD4(+) T cells correlated with soluble ICAM-3 and PECAM-1 levels in BAL, which associated with the lack of worsening in SSc-ILD. Thus, imatinib might confer its therapeutic effect in fibrosis via re-directing T cell responses from type 2 to other, non-type 2 cytokine producing CD4(+) T cells.

Efficacy of low-dose imatinib mesylate for cutaneous involvement in systemic sclerosis: a preliminary report of three cases

In this pilot study, the effect of low-dose imatinib mesylate (100 mg/day) on cutaneous involvement in patients with systemic sclerosis (SSc) was analyzed. Three patients with SSc were treated with 100 mg/day of imatinib mesylate for 6 months because of pulmonary arterial hypertension refractory to conventional treatments, including beraprost, bosentan, sildenafil, and epoprostenol. Changes in cutaneous involvement were evaluated at 1, 3, and 6 months. During the treatment, the total skin score gradually improved in all of the patients. Contracture of phalanges was attenuated in two patients, one of whom also experienced the partial restoration of large-joint mobility. Nailfold bleeding, initially seen in two patients, was gradually attenuated and had completely disappeared at 6 months. In all patients, Raynaud's phenomenon was attenuated at around 3 months and had completely disappeared at 6 months. Although transient renal dysfunction was observed in one patient, none of the patients experienced common adverse effects of imatinib, such as edema, nausea, rash, and musculoskeletal pain. These clinical data indicate the tolerability and efficacy of low-dose imatinib in SSc, especially against cutaneous vascular involvement, including Raynaud's phenomenon and nailfold bleeding.

New perspectives for the treatment of pulmonary hypertension

Pulmonary hypertension (PH) is a debilitating disease with a poor prognosis. Therapeutic options remain limited despite the introduction of prostacyclin analogues, endothelin receptor antagonists and phosphodiesterase 5 inhibitors within the last 15 years; these interventions address predominantly the endothelial and vascular dysfunctionS associated with the condition, but simply delay progression of the disease rather than offer a cure. In an attempt to improve efficacy, emerging approaches have focused on targeting the pro-proliferative phenotype that underpins the pulmonary vascular remodelling in the lung and contributes to the impaired circulation and right heart failure. Many novel targets have been investigated and validated in animal models of PH, including modulation of guanylate cyclases, phosphodiesterases, tyrosine kinases, Rho kinase, bone morphogenetic proteins signalling, 5-HT, peroxisome proliferator activator receptors and ion channels. In addition, there is hope that combinations of such treatments, harnessing and optimizing vasodilator and anti-proliferative properties, will provide a further, possibly synergistic, increase in efficacy; therapies directed at the right heart may also offer an additional benefit. This overview highlights current therapeutic options, promising new therapies, and provides the rationale for a combination approach to treat the disease.

Pulmonary arterial hypertension associated with systemic sclerosis

Systemic sclerosis (SSc) is commonly complicated by pulmonary arterial hypertension (PAH), which is a leading cause of death in the SSc patient population. Owing to the fact that the risk of developing pulmonary hypertension is high, screening is important, although the optimal modality remains to be defined. Furthermore, despite recent advances in therapy for PAH, the response to these interventions in patients with PAH with SSc has been discouraging. The lack of clinical response to these therapies may merely reflect the limitations of traditionally employed PAH outcome measures in SSc-PAH patients or highlight the heterogeneity of the disease manifestations within SSc. Importantly, since extrapulmonary involvement of the GI tract and kidneys by SSc limit candidacy for lung transplantation, new therapies that target abnormal cellular proliferation in the pulmonary vasculature are currently under investigation and may be particularly relevant to SSc-PAH.

Lung involvement in systemic sclerosis

Scleroderma is a multisystem disease characterized by a severe inflammatory process and exuberant fibrosis. Lung involvement is a frequent complication and a leading cause of morbidity and mortality in this syndrome. Two major pulmonary syndromes are associated with scleroderma; a pulmonary vascular disorder evolving over time into relatively isolated pulmonary arterial hypertension (PAH), and interstitial lung disease (ILD). Each syndrome, when present, is a cause of morbidity and significantly reduces survival of scleroderma patients when compared to patients free of lung complication. When pulmonary hypertension and ILD are combined, survival is further reduced. Current therapy appears to have no meaningful effect on either condition and, thus, there is a need for better understanding of underlying pathogenic mechanisms. This review focuses on clinical, diagnostic, and therapeutic features of PAH and ILD as well as other frequent but less debilitating lung complications of scleroderma.

Serotonin transporter interacts with the PDGFβ receptor in PDGF-BB-induced signaling and mitogenesis in pulmonary artery smooth muscle cells

The serotonin transporter (SERT) and the platelet-derived growth factor receptor (PDGFR) have been implicated in both clinical and experimental pulmonary hypertension (PH) and the facilitation of pulmonary artery smooth muscle cell (PASMC) growth. To gain a better understanding of the possible relationship of these two cell surface molecules we have explored interactions between SERT and PDGFR. We have previously demonstrated that SERT transactivates PDGFRβ in serotonin-stimulated PASMC proliferation. We now provide evidence for a role for SERT in PDGF-BB signaling and PASMC proliferation by using pharmacological inhibitors, genetic ablation, and construct overexpression of SERT. The results show that four tested SERT blockers dose dependently inhibit PDGF-stimulated human and bovine PASMC proliferation with comparable efficacy to that of PDGFR inhibitors, whereas 5-HT1B or 5-HT2A receptor inhibitors had no effect. Combinations of the SERT and PDGFR inhibitors led to synergistic/additive inhibition. Similarly, PDGF-induced PASMC proliferation was attenuated by small interfering RNA downregulation of SERT. Inhibition of SERT in PASMCs attenuated PDGF-induced phosphorylation of PDGFRβ, Akt, and p38 but not Erk. Overexpression of SERT in HEK293 cells led to enhanced Akt phosphorylation by PDGF, which was blunted by a SERT PDZ motif mutant, indicating the mechanistic need for the PDZ motif of SERT in PDGF signaling. Furthermore, coimmunoprecipitation experiments showed that SERT and PDGFRβ become physically associated upon PDGF stimulation. In total, the data show for the first time an important interactive relationship between SERT and the PDGFRβ in the production of PASMC proliferation triggered by PDGF that may be important in PH.

Immunotherapy of systemic sclerosis

Scleroderma is a multisystem autoimmune disease characterized by an abnormal immune activation associated with the development of underlying vascular and fibrotic disease manifestations. This article highlights the current use of drugs targeting the immune system in scleroderma. Nonselective immunosuppression, and in particular cyclophosphamide, remains the main treatment for progressing skin involvement and active interstitial lung disease. Mycophenolate mofetil is a promising alternative to cyclophosphamide. The use of cyclosporine has been limited by modest efficacy and serious renal toxicity. Newer T-cell (sirolimus and alefacept) and B-cell (rituximab)-targeted therapies have provided some encouraging results in small pilot studies. Hematopoietic stem cell transplantation can be effective for severe fibrotic skin disease, but toxicity remains a concern. Clinical efficacy and safety of antifibrotic treatments (e.g., imatinib) await confirmation. Newer biological agents targeting key molecular or cellular effectors in scleroderma pathogenesis are now available for clinical testing.

The impact of Fli1 deficiency on the pathogenesis of systemic sclerosis

Systemic sclerosis (SSc) is an autoimmune inflammatory disease with unknown etiology characterized by microvascular injury and fibrosis of the skin and internal organs. A growing body of evidence suggests that deficiency of the transcription factor Fli1 (Friend leukemia integration-1) has a pivotal role in the pathogenesis of SSc. Fli1 is expressed in fibroblasts, endothelial cells, and immune cells, and has important roles in the activation, differentiation, development, and survival of these cells. Previous studies demonstrated that Fli1 is downregulated in SSc fibroblasts by an epigenetic mechanism and a series of experiments with Fli1-deficient animal models revealed that Fli1 deficiency in fibroblasts and endothelial cells reproduces the histopathologic features of fibrosis and vasculopathy in SSc, respectively. In this article, we review the impact of Fli1 deficiency on the pathogenesis of SSc and discuss a new therapeutic strategy for SSc by targeting the transcription factor Fli1.

Tyrosine kinases in inflammatory dermatologic disease

Tyrosine kinases (TKs) are enzymes that catalyze the phosphorylation of tyrosine residues on protein substrates. They are key components of signaling pathways that drive an array of cellular responses including proliferation, differentiation, migration, and survival. Specific TKs have recently been identified as critical to the pathogenesis of several autoimmune and inflammatory diseases. Small-molecule inhibitors of TKs are emerging as a novel class of therapy that may provide benefit in certain patient subsets. In this review, we highlight TK signaling implicated in inflammatory dermatologic diseases, evaluate strategies aimed at inhibiting these aberrant signaling pathways, and discuss prospects for future drug development.

Therapy for pulmonary arterial hypertension associated with systemic sclerosis

PURPOSE OF REVIEW

Systemic sclerosis is commonly complicated by pulmonary arterial hypertension (PAH-SSc) and is a leading cause of death in this population. We will review existing challenges and recent advances in the treatment of this disease.

RECENT FINDINGS

Traditionally employed outcome measures in pulmonary arterial hypertension research may not be applicable in PAH-SSc. Importantly, new therapies that target abnormal cellular proliferation in the pulmonary vasculature are currently under investigation and may be particularly relevant to PAH-SSc.

SUMMARY

Pulmonary arterial hypertension complicating systemic sclerosis occurs commonly and portends a poor prognosis. However, recent advances in our understanding of the disease in the context of systemic sclerosis may lead to novel diagnostic and therapeutic strategies that will ultimately improve quality of life and survival in this population.

Evaluation of imatinib mesylate in the treatment of pulmonary arterial hypertension

Imatinib mesylate is a small molecule inhibitor that selectively inhibits the PDGF receptor kinase as well the cKIT and Abl kinases, among other targets. Various studies have implicated the PDGF pathway in the pathogenesis of pulmonary arterial hypertension (PAH). Inhibition with imatinib mesylate has shown efficacy in human case reports and experimental models of PAH. Results from a Phase II trial of imatinib mesylate in PAH did not meet the primary end point but showed improvement in several secondary end points and in a subgroup analysis. As suggested by this study as well as a few case reports, imatinib may be effective in a subset of patients with more severe disease. However, this remains to be further validated through a Phase III study, which is already underway. In conclusion, it appears that imatinib mesylate may hold promise as an adjunct drug in PAH therapy, especially since it is directed at a pathway not previously targeted.