5-HT2B receptor antagonists inhibit fibrosis and protect from RV heart failure

Structure-Based Scaffold Repurposing for G Protein-Coupled Receptors: Transformation of Adenosine Derivatives into 5HT2B/5HT2C Serotonin Receptor Antagonists

Adenosine derivatives developed to activate adenosine receptors (ARs) revealed micromolar activity at serotonin 5HT_2B and 5HT_2C receptors (5HTRs). We explored the structure-activity relationship at 5HT₂Rs and modeled receptor interactions in order to optimize affinity and simultaneously reduce AR affinity. Depending on N⁶ substitution, small 5'-alkylamide modification maintained 5HT_2BR affinity, which was enhanced upon ribose substitution with rigid bicyclo[3.1.0]hexane (North (N)-methanocarba), e.g., N⁶-dicyclopropylmethyl 4'-CH₂OH derivative 14 (K_i 11 nM). 5'-Methylamide 23 was 170-fold selective as antagonist for 5HT_2BR vs 5HT_2CR. 5'-Methyl 25 and ethyl 26 esters potently antagonized 5HT₂Rs with moderate selectivity in comparison to ARs; related 6-N,N-dimethylamino analogue 30 was 5HT₂R-selective. 5' position flexibility of substitution was indicated in 5HT_2BR docking. Both 5'-ester and 5'-amide derivatives displayed in vivo t_1/2 of 3-4 h. Thus, we used G protein-coupled receptor modeling to repurpose nucleoside scaffolds in favor of binding at nonpurine receptors as novel 5HT₂R antagonists, with potential for cardioprotection, liver protection, or central nervous system activity.

Clinical signs of fibrosis in small intestinal neuroendocrine tumours

BACKGROUND

In patients with small intestinal neuroendocrine tumours (SI-NETs), serotonin and other cytokines released from tumour cells may induce fibrosis, leading to carcinoid heart disease and abdominal fibrotic reactions. The aim of this study was to assess the prevalence, clinical complications and management of this reaction in the abdomen.

METHODS

This was a retrospective cohort study of patients with SI-NETs diagnosed between 1985 and 2015. Clinical data, outcomes, radiological findings, and surgical and radiological interventions were reviewed.

RESULTS

A total of 824 patients were diagnosed with SI-NETs in the study interval. Clinically significant abdominal signs and symptoms of fibrosis occurred in 36 patients. Of these, 20 had critically symptomatic central mesenteric fibrosis causing obstruction of mesenteric vessels, and 16 had retroperitoneal fibrosis causing obstructive uropathy with hydronephrosis. Extensive fibrosis causing mesenteric vessel obstruction and/or obstructive uropathy was more often associated with symptomatic and advanced disease encompassing lymph node metastases in the mesenteric root, para-aortic lymph node metastases, as well as liver metastases and peritoneal carcinomatosis. Palliative intervention in terms of superior mesenteric vein stenting or resection of central mesenteric metastases and/or percutaneous nephrostomy and J stent treatment was beneficial in the majority of the patients.

CONCLUSION

Extensive abdominal fibrosis associated with clinically significant symptoms of intestinal ischaemia and/or obstructive uropathy was linked to advanced disease in patients with SI-NETs. Prompt recognition and minimally invasive intervention was effective in disease palliation.

Complications from carcinoid syndrome: review of the current evidence

Patients with well-differentiated neuroendocrine tumours may develop carcinoid syndrome (CS), which is characterised by flushing, abdominal cramps, diarrhoea, and bronchospasms. In this scenario, long-term secretion of vasoactive substances—serotonin, tachynins, and others, may induce fibrogenic responses in local or distant tissues, leading to complications such as carcinoid heart disease (CHD), mesenteric and/or retroperitoneal fibrosis. Rare cases of lung/pleural fibrosis and scleroderma have also been described. Despite it not being well described yet, current evidence suggests the pathogenesis of such fibrogenic complications relies on signalling through 5-HT_2B and TGF-β1. Medical management is still very limited and lacks prospective and randomised studies for definitive recommendations. Surgical procedures remain the best definitive treatment option for CHD and abdominal fibrosis. Recently, cognitive impairment has also been described as a potential consequence of CS. This review critically discusses the literature concerning the epidemiology, pathogenesis, clinical features, diagnosis, and treatment options for CS-related long-term complications.

Systemic sclerosis and localized scleroderma--current concepts and novel targets for therapy

Systemic sclerosis (SSc) is a chronic autoimmune disease with a high morbidity and mortality. Skin and organ fibrosis are key manifestations of SSc, for which no generally accepted therapy is available. Thus, there is a high unmet need for novel anti-fibrotic therapeutic strategies in SSc. At the same time, important progress has been made in the identification and characterization of potential molecular targets in fibrotic diseases over the recent years. In this review, we have selected four targeted therapies, which are tested in clinical trials in SSc, for in depths discussion of their preclinical characterization. Soluble guanylate cyclase (sGC) stimulators such as riociguat might target both vascular remodeling and tissue fibrosis. Blockade of interleukin-6 might be particularly promising for early inflammatory stages of SSc. Inhibition of serotonin receptor 2b signaling links platelet activation to tissue fibrosis. Targeting simultaneously multiple key molecules with the multityrosine kinase-inhibitor nintedanib might be a promising approach in complex fibrotic diseases such as SSc, in which many partially independent pathways are activated. Herein, we also give a state of the art overview of the current classification, clinical presentation, diagnostic approach, and treatment options of localized scleroderma. Finally, we discuss whether the novel targeted therapies currently tested in SSc could be used for localized scleroderma.

Novel Therapeutic Strategies for Reducing Right Heart Failure Associated Mortality in Fibrotic Lung Diseases

Fibrotic lung diseases carry a significant mortality burden worldwide. A large proportion of these deaths are due to right heart failure and pulmonary hypertension. Underlying contributory factors which appear to play a role in the mechanism of progression of right heart dysfunction include chronic hypoxia, defective calcium handling, hyperaldosteronism, pulmonary vascular alterations, cyclic strain of pressure and volume changes, elevation of circulating TGF-β, and elevated systemic NO levels. Specific therapies targeting pulmonary hypertension include calcium channel blockers, endothelin (ET-1) receptor antagonists, prostacyclin analogs, phosphodiesterase type 5 (PDE5) inhibitors, and rho-kinase (ROCK) inhibitors. Newer antifibrotic and anti-inflammatory agents may exert beneficial effects on heart failure in idiopathic pulmonary fibrosis. Furthermore, right ventricle-targeted therapies, aimed at mitigating the effects of functional right ventricular failure, include β-adrenoceptor (β-AR) blockers, angiotensin-converting enzyme (ACE) inhibitors, antioxidants, modulators of metabolism, and 5-hydroxytryptamine-2B (5-HT2B) receptor antagonists. Newer nonpharmacologic modalities for right ventricular support are increasingly being implemented. Early, effective, and individualized therapy may prevent overt right heart failure in fibrotic lung disease leading to improved outcomes and quality of life.