Sildenafil Suppresses Inflammation-Driven Colorectal Cancer in Mice

Rational Design and Optimization of Novel PDE5 Inhibitors for Targeted Colorectal Cancer Therapy: An In Silico Approach

Colorectal cancer (CRC) is one of the leading causes of cancer-related deaths globally. Current treatment options including chemotherapy and targeted therapies face challenges such as resistance and toxicity. Cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase 5 (PDE5) has emerged as a promising target for CRC therapy due to its role in regulating cellular processes like proliferation and apoptosis. This study focuses on the in silico design of a novel PDE5 inhibitor MS01 derived from the lead compound exisulind which has shown apoptotic effects but failed due to hepatotoxicity. Using Schrödinger's Induced Fit Docking (IFD) and molecular dynamic simulations, MS01 was designed to enhance binding affinity and reduce toxicity. The docking studies showed that MS01 exhibits stronger interactions with key PDE5 residues, particularly Gln817 and Phe820. ADMET predictions indicate favorable pharmacokinetic profiles, with reduced risk of drug-drug interactions and improved bioavailability. Toxicity assessments revealed that MS01 and its analogs have moderate toxicity, with MS20 and MS21 demonstrating lower hepatotoxicity compared to exisulind. These findings suggest that MS01 has the potential to be a more effective and safer PDE5 inhibitor for CRC treatment pending further experimental validation.

Cyclic nucleotide phosphodiesterases as drug targets

Cyclic nucleotides are synthesized by adenylyl and/or guanylyl cyclase, and downstream of this synthesis, the cyclic nucleotide phosphodiesterase families (PDEs) specifically hydrolyze cyclic nucleotides. PDEs control cyclic adenosine-3',5'monophosphate (cAMP) and cyclic guanosine-3',5'-monophosphate (cGMP) intracellular levels by mediating their quick return to the basal steady state levels. This often takes place in subcellular nanodomains. Thus, PDEs govern short-term protein phosphorylation, long-term protein expression, and even epigenetic mechanisms by modulating cyclic nucleotide levels. Consequently, their involvement in both health and disease is extensively investigated. PDE inhibition has emerged as a promising clinical intervention method, with ongoing developments aiming to enhance its efficacy and applicability. In this comprehensive review, we extensively look into the intricate landscape of PDEs biochemistry, exploring their diverse roles in various tissues. Furthermore, we outline the underlying mechanisms of PDEs in different pathophysiological conditions. Additionally, we review the application of PDE inhibition in related diseases, shedding light on current advancements and future prospects for clinical intervention. SIGNIFICANCE STATEMENT: Regulating PDEs is a critical checkpoint for numerous (patho)physiological conditions. However, despite the development of several PDE inhibitors aimed at controlling overactivated PDEs, their applicability in clinical settings poses challenges. In this context, our focus is on pharmacodynamics and the structure activity of PDEs, aiming to illustrate how selectivity and efficacy can be optimized. Additionally, this review points to current preclinical and clinical evidence that depicts various optimization efforts and indications.

Repurposing of phosphodiesterase-5 inhibitor sildenafil as a therapeutic agent to prevent gastric cancer growth through suppressing c-MYC stability for IL-6 transcription

Phosphodiesterase-5 (PDE5) inhibitors have shown promise as anti-cancer agents in malignancies. However, their specific effects on gastric cancer (GC) and the underlying mechanisms remain elusive. Our aim was to investigate this by combining evidence from population-based studies with data obtained from in vivo and in vitro experiments. By combing a couple of nationwide Swedish registers, GC patients who received PDE5 inhibitors were compared to matched controls while adjusting for confounding factors. The anti-tumor effect and mechanism of the PDE5 inhibitor sildenafil were evaluated via using tumor cells, patient-derived tumor organoids and xenograft animal models in GC. A total of 161 Swedish GC patients from a nationwide population-based cohort who received post-diagnostic PDE5 inhibitors demonstrated lower cancer-specific mortality compared to the controls (HR = 0.66, 95% CI = 0.47-0.92, P = 0.016). Functionally, the PDE5 inhibitor sildenafil exhibited the suppressive ability to prevent oncogenic growth in GC. Mechanistically, sildenafil restrained GC growth by directly activating PKG through PDE5 inhibition for regulating c-MYC expression via its phosphorylation and ubiquitination degradation, thereby suppressing c-MYC stability for IL-6 transcription within the downstream IL-6/JAK/STAT3 signalling pathway. The PDE5 inhibitor sildenafil may serve as a promising adjuvant for GC therapy if further randomized clinical trials confirm its efficacy.

Novel Celecoxib Derivative, RF26, Blocks Colon Cancer Cell Growth by Inhibiting PDE5, Activating cGMP/PKG Signaling, and Suppressing β-catenin-dependent Transcription

BACKGROUND

Previous studies have reported that the cGMP-specific PDE5 isozyme is overexpressed in colon adenomas and adenocarcinomas and essential for colon cancer cell proliferation, while PDE5 selective inhibitors (e.g., sildenafil) have been reported to have cancer chemopreventive activity.

AIM

This study aimed to determine the anticancer activity of a novel PDE5 inhibitor, RF26, using colorectal cancer (CRC) cells and the role of PDE5 in CRC tumor growth in vivo.

OBJECTIVE

The objective of this study was to characterize the anticancer activity of a novel celecoxib derivative, RF26, in CRC cells previously reported to lack COX-2 inhibition but have potent PDE5 inhibitory activity.

METHODS

Anticancer activity of RF26 was studied using human CRC cell lines. Effects on cell growth, cGMPdependent protein kinase (PKG) activity, β-catenin levels, TCF/LEF transcriptional activity, cell cycle distribution, and apoptosis were measured. CRISPR/cas9 PDE5 knockout techniques were used to determine if PDE5 mediates the anticancer activity of RF26 and validate PDE5 as a cancer target.

RESULTS

RF26 was appreciably more potent than celecoxib and sildenafil to suppress CRC cell growth and was effective at concentrations that activated PKG signaling. RF26 suppressed β-catenin levels and TCF/LEF transcriptional activity and induced G1 cell cycle arrest and apoptosis within the same concentration range. CRISPR/cas9 PDE5 knockout CRC cells displayed reduced sensitivity to RF26, proliferated slower than parental cells, and failed to establish tumors in mice.

CONCLUSION

Further evaluation of RF26 for the prevention or treatment of cancer and studying the role of PDE5 in tumorigenesis are warranted.

Rethinking of phosphodiesterase 5 inhibition: the old, the new and the perspective in human health

The phosphodiesterases type 5 (PDE5) are catalytic enzymes converting the second messenger cyclic guanosine monophosphate (cGMP) to 5' GMP. While intracellular cGMP reduction is associated with several detrimental effects, cGMP stabilization associates with numerous benefits. The PDE5 specific inhibitors, PDE5i, found their explosive fortune as first-line treatment for erectile dysfunction (ED), due to their powerful vasoactive properties. The favorable effect for ED emerged as side-effect when PDE5i were originally proposed for coronary artery disease (CAD). From that point on, the use of PDE5i captured the attention of researchers, clinicians, and companies. Indeed, PDE5-induced intracellular cGMP stabilization offers a range of therapeutic opportunities associated not only with vasoactive effects, but also with immune regulatory/anti-inflammatory actions. Chronic inflammation is acknowledged as the common link underlying most non-communicable diseases, including metabolic and cardiac diseases, autoimmune and neurodegenerative disorders, cancer. In this scenario, the clinical exploitation of PDE5i is undeniably beyond ED, representing a potential therapeutic tool in several human diseases. This review aims to overview the biological actions exerted by PDE5i, focusing on their ability as modulators of inflammation-related human diseases, with particular attention to inflammatory-related disorders, like cardiac diseases and cancer.

Long-term effects of phosphodiesterase-5 inhibitors on cardiovascular outcomes and death: a systematic review and meta-analysis

AIMS

Phosphodiesterase 5 inhibitors (PDE5i), which are widely used for the treatment of erectile dysfunction (ED), have been found to exhibit systemic vascular benefits by improving endothelial function. In this context, we sought to evaluate the effects of PDE5i on long-term cardiovascular outcomes and mortality.

METHODS AND RESULTS

A comprehensive search of electronic databases was conducted up to 30 May 2023. Cohort studies comparing PDE5i treatment at any dose with other ED treatment, placebo or no treatment and minimum follow-up duration of 6 months were considered eligible. The primary endpoints were: (1) major adverse cardiovascular events (MACE) and (2) all-cause mortality. Pooled risk ratios (RR) with 95% confidence intervals (CI) were calculated. Sixteen studies were included (1 257 759 subjects-10.5% treated with PDE5i). The majority of patients (99.4%) were men [median age 61.5 years (range 30-72.8)]. The median follow-up duration was 4.3 years (range 6 months-7.5 years). PDE5i use was associated with a significant reduction in the composite of MACE (RR 0.78, 95% CI 0.69-0.89). Moreover, the analysis of pooled data from 13 studies, demonstrated that the use of PDE5i was associated with a significantly lower risk of all-cause mortality (RR 0.70, 95% CI 0.56-0.87).

CONCLUSION

The use of PDE5i primarily in men with or without known coronary artery disease was associated with a lower risk for cardiovascular events and overall mortality. This information underlines that PDE5i could provide clinical benefit beyond ED treatment and could instigate the conduction of further, large-scale randomized clinical trials.

Sildenafil increases AAV9 transduction after a systemic administration and enhances AAV9-dystrophin therapeutic effect in mdx mice

Adeno-associated virus (AAV) vectors have been successfully used to deliver genes for treating rare diseases. However, the systemic administration of high AAV vector doses triggers several adverse effects, including immune response, the asymptomatic elevation of liver transaminase levels, and complement activation. Thus, improving AAV transduction and reducing AAV dosage for treatment is necessary. Recently, we found that a phosphodiesterase-5 inhibitor significantly promoted AAV9 transduction in vitro by regulating the caveolae and macropinocytosis pathways. When AAV9-Gaussian luciferase (AAV9-Gluc) and AAV9-green fluorescent protein (AAV9-GFP) were injected intravenously into mice pre-treated with sildenafil, the expressions of Gluc in the plasma and GFP in muscle tissues significantly increased (P < 0.05). Sildenafil also improved Evans blue permeation in tissues. Additionally, we found that sildenafil promoted Treg proliferation, inhibited B-cell activation, and decreased anti-AAV9 IgG levels (P < 0.05). Furthermore, sildenafil significantly promoted Duchenne muscular dystrophy gene therapy efficacy using AAV9 in mdx mice; it increased micro-dystrophin gene expression, forelimb grip strength, and time spent on the rotarod test, decreased serum creatine kinase levels, and ameliorated histopathology by improving muscle cell morphology and reducing fibrosis (P < 0.05). These results show that sildenafil significantly improved AAV transduction, suppressed the levels of anti-AAV9 IgG, and enhanced the efficacy of gene therapy.

Exploring the Multifaceted Potential of Sildenafil in Medicine

Phosphodiesterase type 5 (PDE5) is pivotal in cellular signalling, regulating cyclic guanosine monophosphate (cGMP) levels crucial for smooth muscle relaxation and vasodilation. By targeting cGMP for degradation, PDE5 inhibits sustained vasodilation. PDE5 operates in diverse anatomical regions, with its upregulation linked to various pathologies, including cancer and neurodegenerative diseases. Sildenafil, a selective PDE5 inhibitor, is prescribed for erectile dysfunction and pulmonary arterial hypertension. However, considering the extensive roles of PDE5, sildenafil might be useful in other pathologies. This review aims to comprehensively explore sildenafil's therapeutic potential across medicine, addressing a gap in the current literature. Recognising sildenafil's broader potential may unveil new treatment avenues, optimising existing approaches and broadening its clinical application.

Targeting beta-catenin signaling for prevention of colorectal cancer - Nutraceutical, drug, and dietary options

Progressive up-regulation of β-catenin signaling is very common in the transformation of colorectal epithelium to colorectal cancer (CRC). Practical measures for opposing such signaling hence have potential for preventing or slowing such transformation. cAMP/PKA activity in colon epithelium, as stimulated by COX-2-generated prostaglandins and β2-adrenergic signaling, boosts β-catenin activity, whereas cGMP/PKG signaling has the opposite effect. Bacterial generation of short-chain fatty acids (as supported by unrefined high-carbohydrate diets, berberine, and probiotics), dietary calcium, daily aspirin, antioxidants opposing cox-2 induction, and nicotine avoidance, can suppress cAMP production in colonic epithelium, whereas cGMP can be boosted via linaclotides, PDE5 inhibitors such as sildenafil or icariin, and likely high-dose biotin. Selective activation of estrogen receptor-β by soy isoflavones, support of adequate vitamin D receptor activity with UV exposure or supplemental vitamin D, and inhibition of CK2 activity with flavanols such as quercetin, can also oppose β-catenin signaling in colorectal epithelium. Secondary bile acids, the colonic production of which can be diminished by low-fat diets and berberine, can up-regulate β-catenin activity by down-regulating farnesoid X receptor expression. Stimulation of PI3K/Akt via insulin, IGF-I, TLR4, and EGFR receptors boosts β-catenin levels via inhibition of glycogen synthase-3β; plant-based diets can down-regulate insulin and IGF-I levels, exercise training and leanness can keep insulin low, anthocyanins and their key metabolite ferulic acid have potential for opposing TLR4 signaling, and silibinin is a direct antagonist for EGFR. Partially hydrolyzed phytate can oppose growth factor-mediated down-regulation of β-catenin by inhibiting Akt activation. Multifactorial strategies for safely opposing β-catenin signaling can be complemented with measures that diminish colonic mutagenesis and DNA hypomethylation - such as avoidance of heme-rich meat and charred or processed meats, consumption of phase II-inductive foods and nutraceuticals (e.g., Crucifera), and assurance of adequate folate status.

A Non-Systemic Phosphodiesterase-5 Inhibitor Suppresses Colon Proliferation in Mice

Phosphodiesterase-5 inhibitors (PDE5i) are under investigation for repurposing for colon cancer prevention. A drawback to conventional PDE5i are their side-effects and drug-drug interactions. We designed an analog of the prototypical PDE5i sildenafil by replacing the methyl group on the piperazine ring with malonic acid to reduce lipophilicity, and measured its entry into the circulation and effects on colon epithelium. This modification did not affect pharmacology as malonyl-sildenafil had a similar IC50 to sildenafil but exhibited an almost 20-fold reduced EC50 for increasing cellular cGMP. Using an LC-MS/MS approach, malonyl-sildenafil was negligible in mouse plasma after oral administration but was detected at high levels in the feces. No bioactive metabolites of malonyl-sildenafil were detected in the circulation by measuring interactions with isosorbide mononitrate. The treatment of mice with malonyl-sildenafil in the drinking water resulted in a suppression of proliferation in the colon epithelium that is consistent with results previously published for mice treated with PDE5i. A carboxylic-acid-containing analog of sildenafil prohibits the systemic delivery of the compound but maintains sufficient penetration into the colon epithelium to suppress proliferation. This highlights a novel approach to generating a first-in-class drug for colon cancer chemoprevention.

Uncoupled nitric oxide synthase activity promotes colorectal cancer progression

Increased levels of reactive oxygen/nitrogen species are one hallmark of chronic inflammation contributing to the activation of pro-inflammatory/proliferative pathways. In the cancers analyzed, the tetrahydrobiopterin:dihydrobiopterin ratio is lower than that of the corresponding normal tissue, leading to an uncoupled nitric oxide synthase activity and increased generation of reactive oxygen/nitrogen species. Previously, we demonstrated that prophylactic treatment with sepiapterin, a salvage pathway precursor of tetrahydrobiopterin, prevents dextran sodium sulfate-induced colitis in mice and associated azoxymethane-induced colorectal cancer. Herein, we report that increasing the tetrahydrobiopterin:dihydrobiopterin ratio and recoupling nitric oxide synthase with sepiapterin in the colon cancer cell lines, HCT116 and HT29, inhibit their proliferation and enhance cell death, in part, by Akt/GSK-3β-mediated downregulation of β-catenin. Therapeutic oral gavage with sepiapterin of mice bearing azoxymethane/dextran sodium sulfate-induced colorectal cancer decreased metabolic uptake of [18F]-fluorodeoxyglucose and enhanced apoptosis nine-fold in these tumors. Immunohistochemical analysis of both mouse and human tissues indicated downregulated expression of key enzymes in tetrahydrobiopterin biosynthesis in the colorectal cancer tumors. Human stage 1 colon tumors exhibited a significant decrease in the expression of quinoid dihydropteridine reductase, a key enzyme involved in recycling tetrahydrobiopterin suggesting a potential mechanism for the reduced tetrahydrobiopterin:dihydrobiopterin ratio in these tumors. In summary, sepiapterin treatment of colorectal cancer cells increases the tetrahydrobiopterin:dihydrobiopterin ratio, recouples nitric oxide synthase, and reduces tumor growth. We conclude that nitric oxide synthase coupling may provide a useful therapeutic target for treating patients with colorectal cancer.

Beyond Erectile Dysfunction: cGMP-Specific Phosphodiesterase 5 Inhibitors for Other Clinical Disorders

Cyclic guanosine monophosphate (cGMP), an important intracellular second messenger, mediates cellular functional responses in all vital organs. Phosphodiesterase 5 (PDE5) is one of the 11 members of the cyclic nucleotide phosphodiesterase (PDE) family that specifically targets cGMP generated by nitric oxide-driven activation of the soluble guanylyl cyclase. PDE5 inhibitors, including sildenafil and tadalafil, are widely used for the treatment of erectile dysfunction, pulmonary arterial hypertension, and certain urological disorders. Preclinical studies have shown promising effects of PDE5 inhibitors in the treatment of myocardial infarction, cardiac hypertrophy, heart failure, cancer and anticancer-drug-associated cardiotoxicity, diabetes, Duchenne muscular dystrophy, Alzheimer's disease, and other aging-related conditions. Many clinical trials with PDE5 inhibitors have focused on the potential cardiovascular, anticancer, and neurological benefits. In this review, we provide an overview of the current state of knowledge on PDE5 inhibitors and their potential therapeutic indications for various clinical disorders beyond erectile dysfunction.

Sildenafil attenuates intestinal injury in necrotizing enterocolitis independently of endothelial nitric oxide synthase

BACKGROUND

Necrotizing enterocolitis (NEC) is a devastating disease that impacts the intestine of premature infants. Sildenafil has shown benefit in colitis and ischemia/reperfusion models but has not been adequately studied in NEC. Sildenafil's best studied mechanism involves augmenting nitric oxide induced vasodilation. We hypothesized that sildenafil would improve outcomes during experimental NEC in an eNOS dependent manner.

MATERIALS

NEC was induced in five-day old mouse pups with gavage formula feeds plus intermittent hypoxia and hypothermia. Using wild type (WT) mice, the route of sildenafil administration was studied in the following groups: (1) breastfed controls, (2) NEC + oral (PO) sildenafil, (3) NEC + PO vehicle, (4) NEC + intraperitoneal (IP) sildenafil, (5) NEC + IP vehicle. The eNOS KO groups studied included: (1) breastfed controls, (2) NEC + PO sildenafil, (3) NEC + PO vehicle. Data were tested for normality and compared using t-tests or Mann-Whitney with a p-value <0.05 considered significant.

RESULTS

In WT mice, oral and IP sildenafil resulted in improved clinical outcomes compared to their respective vehicle group. Only orally administered sildenafil significantly improved perfusion to the intestine and protected it from macroscopic and histologic injury. When repeated in eNOS KO mice, oral sildenafil improved clinical scores and attenuated intestinal injury scores, despite no effect on intestinal perfusion.

CONCLUSIONS

Sildenafil, when administered orally, improves clinical outcomes and protects the intestine in a murine model of experimental necrotizing enterocolitis. While sildenafil requires eNOS to impact mesenteric perfusion, it does not appear to be dependent on eNOS to attenuate intestinal injury.

Inhibition of Colon Cancer Cell Growth by Phosphodiesterase Inhibitors Is Independent of cGMP Signaling

There is growing interest in the potential use of phosphodiesterase (PDE) inhibitors for colorectal cancer (CRC) prevention and treatment. The present study has tested the idea that PDE inhibitors inhibit growth and viability of CRC cell lines by increasing cyclic guanosine monophosphate (cGMP) and activating cGMP-dependent protein kinase (PKG). Colon cancer cell lines and those with ectopic PKG2 expression were treated with membrane-permeable 8Br-cGMP or inhibitors of PDE5, PDE9, and PDE10a. Levels of cGMP capable of activating PKG were measured by immunoblotting for phosphorylation of vasodilator-stimulated phosphoprotein (VASP). The effects of treatment on CRC cell proliferation and death were measured using hemocytometry with trypan blue. Treatment with 8Br-cGMP had no effect on CRC cell proliferation or death. Endogenous PKG activity was undetectable in any of the CRC cells, but expression of ectopic PKG2 conferred modest inhibition of proliferation but did not affect cell death. Extremely high concentrations of all the PDE inhibitors reduced proliferation in CRC cell lines, but none of them increased cGMP levels, and the effect was independent of PKG expression. The inability of the PDE inhibitors to increase cGMP was due to the lack of endogenous cGMP generating machinery. In conclusion, PDE inhibitors that target cGMP only reduce CRC growth at clinically unachievable concentrations, and do so independent of cGMP signaling through PKG. SIGNIFICANCE STATEMENT: A large number of in vitro studies have reported that PDE inhibitors block growth of colon cancer cells by activating cGMP signaling, and that these drugs might be useful for cancer treatment. Our results show that these drugs do not activate cGMP signaling in colon cancer cells due to a lack of endogenous guanylyl cyclase activity, and that growth inhibition is due to toxic effects of clinically unobtainable drug concentrations.

Construction of an Immune-Autophagy Prognostic Model Based on ssGSEA Immune Scoring Algorithm Analysis and Prognostic Value Exploration of the Immune-Autophagy Gene in Endometrial Carcinoma (EC) Based on Bioinformatics

BACKGROUND

Endometrial carcinoma (EC) is a malignant cancer spreading worldwide and in the fourth position among all other types of cancer in women. The purpose of this paper is to explore the prognostic value of the immune-autophagy gene in endometrial carcinoma (EC) based on bioinformatics, construct an immune-autophagy prognostic model of endometrial carcinoma, search for independent prognostic markers, and finally predict the potential therapeutic drugs of TCGA subgroup.

METHODS

The Cancer Genome Atlas (TCGA) database was used to extract transcriptome sequencing data of patients suffering from EC; 28 kinds of immune cells were scored by ssGSEA, and the immune subtypes were grouped by consistency cluster analysis. The accuracy and effectiveness of the grouping were verified by the analysis of differential gene expression and survival rate of immune checkpoints in the two groups to provide the premise and basis for the establishment of independent prognostic factors. The expression of different genes in high and low immune groups was analyzed. The analysis of various genes' expression in immune groups (high and low) has been performed. Go function annotation and KEGG pathway enrichment analysis were used to evaluate the difference of immune infiltration between high and low immune groups. The immune and autophagy genes were crossed, the key (hub) genes were selected, the risk was scored, the prognosis model was constructed, and the independent prognostic markers were established. CAMP and CTRP 2.0 were used to test the drug sensitivity.

RESULTS

According to the level of immune cell enrichment, the results have been subcategorized into two immune subtypes: high immunity group_ H and low immunity group_ L. Two immune subtypes, CD274, PDCD1, and CTLA4, were detected in the immune system_ H and immunity_L. A significant difference was detected between these two groups in the expression and survival rate. Few more differences were also detected between the two groups through the evaluation of immune infiltration, which proved the grouping's accuracy and effectiveness. Differential gene expression analysis showed that there were 721 DEGs and 3 hub genes. DEGs are mainly involved in lymphocyte activation, proliferation, differentiation, leukocyte proliferation, and other biological processes, mediate chemokines' activities, chemokine receptor binding, and other molecular functions, and are enriched in the outer plasma membrane, endoplasmic reticulum, and T cell receptor complex. The enriched pathways are allograft, complex, inflammatory, interferon-alpha, interferon-gamma, E2F, G2M, mitotic, etc.

CONCLUSION

Through bioinformatics analysis, we successfully constructed the immuno-autophagy prognosis model of endometrial cancer and identified three high-risk immunoautophagy genes, including VEGFA, CCL2, and Ifng. Four potential therapeutic drugs were predicted as sildenafil, sunitinib, TPCA-1, and etoposide.

Type-2 cGMP-dependent protein kinase suppresses proliferation and carcinogenesis in the colon epithelium

A large body of evidence has demonstrated that cyclic-guanosine monophosphate (cGMP), signaling has anti-tumor effects that might be used for colon cancer prevention. The tumor-suppressive mechanism and the signaling components downstream of cGMP remain largely unknown. The present study has characterized the expression of cGMP-dependent protein kinases (PKG1, PKG2) in normal and cancerous tissue from human colon. PKG1 was detected in both normal and tumor tissue, where it localized exclusively to the lamina propria and stroma (respectively). In contrast, PKG2 localized specifically to the epithelium where its expression decreased markedly in tumors compared to matched normal tissue. Neither PKG isoform was detected at the RNA or protein level in established colon cancer cell lines. To test for a potential tumor-suppressor role of PKG2 in the colon epithelium, Prkg2 knockout (KO) mice were subjected to azoxymethane/dextran sulfate-sodium (AOM/DSS) treatment. PKG2 deficiency was associated with crypt hyperplasia (Ki67) and almost twice the number of polyps per mouse as wild-type (WT) siblings. In vitro culture of mouse colon epithelium as organoids confirmed that PKG2 was the only isoform expressed, and it was detected in both proliferating and differentiating epithelial compartments. Colon organoids derived from Prkg2 KO mice proliferated more rapidly and exhibited a reduced ability to differentiate compared to WT controls. Taken together our results highlight PKG2 as the central target of cGMP in the colon, where it suppresses carcinogenesis by controlling proliferation in an epithelial-cell intrinsic manner.

Pulmonary artery targeted therapy in treatment of COVID-19 related ARDS. Literature review

INTRODUCTION

The most grievous complication of the COVID-19 is the acute respiratory distress syndrome. A specific, rescue treatment for rapidly deteriorating patients should emerge to improve respiratory function and help patients to survive the most challenging period. Drugs used in targeted therapy of pulmonary arterial hypertension (PAH) appears to be suitable for this task and this article describes their potential for treatment of severe cases of COVID-19.

METHODS

The authors reviewed the following databases for randomized controlled trials, reviews and meta-analyses published up to July 2020: Pubmed, Scopus, Google Scholar, Cochrane Database and ClinicalKey. The authors included every study contributory to the assessment of the potential of drugs used in targeted PAH therapy in treatment of COVID-19.

RESULTS

Endothelin receptor antagonists, phosphodiesterase 5 inhibitors, riociguat and prostacyclin have proven ani-inflammatory effect and reduce pulmonary artery blood pressure, lung oedema and remodelling. Bosentan shows antiviral properties and sildenafil, as well as epoprostenol, inhibits apoptosis of lung epithelial cells. Among patients with lung lesions the decrease of pulmonary blood pressure can lead to increase of ventilation/perfusion mismatch and decrease of blood oxygenation.

CONCLUSIONS

Among all assessed drugs bosentan, sildenafil and epoprostenol appear to be most promising and a combination of these drugs should be considered due to synergism. The targeted PAH therapy in treatment of COVID-19 associated ARDS could be a useful tool saving lives of patients with severe SARS-CoV-2 infection, however, its introduction should be investigated and monitored very carefully as it can lead to transient deterioration of patient condition.

Receptor Guanylyl Cyclase C and Cyclic GMP in Health and Disease: Perspectives and Therapeutic Opportunities

Receptor Guanylyl Cyclase C (GC-C) was initially characterized as an important regulator of intestinal fluid and ion homeostasis. Recent findings demonstrate that GC-C is also causally linked to intestinal inflammation, dysbiosis, and tumorigenesis. These advances have been fueled in part by identifying mutations or changes in gene expression in GC-C or its ligands, that disrupt the delicate balance of intracellular cGMP levels and are associated with a wide range of clinical phenotypes. In this review, we highlight aspects of the current knowledge of the GC-C signaling pathway in homeostasis and disease, emphasizing recent advances in the field. The review summarizes extra gastrointestinal functions for GC-C signaling, such as appetite control, energy expenditure, visceral nociception, and behavioral processes. Recent research has expanded the homeostatic role of GC-C and implicated it in regulating the ion-microbiome-immune axis, which acts as a mechanistic driver in inflammatory bowel disease. The development of transgenic and knockout mouse models allowed for in-depth studies of GC-C and its relationship to whole-animal physiology. A deeper understanding of the various aspects of GC-C biology and their relationships with pathologies such as inflammatory bowel disease, colorectal cancer, and obesity can be leveraged to devise novel therapeutics.

Gut Dysbiosis and Intestinal Barrier Dysfunction: Potential Explanation for Early-Onset Colorectal Cancer

Colorectal cancer (CRC) is a heterogeneous disease that commonly affects individuals aged more than 50 years old globally. Regular colorectal screening, which is recommended for individuals aged 50 and above, has decreased the number of cancer death toll over the years. However, CRC incidence has increased among younger population (below 50 years old). Environmental factors, such as smoking, dietary factor, urbanization, sedentary lifestyle, and obesity, may contribute to the rising trend of early-onset colorectal cancer (EOCRC) because of the lack of genetic susceptibility. Research has focused on the role of gut microbiota and its interaction with epithelial barrier genes in sporadic CRC. Population with increased consumption of grain and vegetables showed high abundance of Prevotella, which reduces the risk of CRC. Microbes, such as Fusobacterium nucleatum, Bacteroides fragilis and Escherichia coli deteriorate in the intestinal barrier, which leads to the infiltration of inflammatory mediators and chemokines. Gut dysbiosis may also occur following inflammation as clearly observed in animal model. Both gut dysbiosis pre- or post-inflammatory process may cause major alteration in the morphology and functional properties of the gut tissue and explain the pathological outcome of EOCRC. The precise mechanism of disease progression from an early stage until cancer establishment is not fully understood. We hypothesized that gut dysbiosis, which may be influenced by environmental factors, may induce changes in the genome, metabolome, and immunome that could destruct the intestinal barrier function. Also, the possible underlying inflammation may give impact microbial community leading to disruption of physical and functional role of intestinal barrier. This review explains the potential role of the interaction among host factors, gut microenvironment, and gut microbiota, which may provide an answer to EOCRC.

Pros and Cons of Pharmacological Manipulation of cGMP-PDEs in the Prevention and Treatment of Breast Cancer

The cyclic nucleotides, cAMP and cGMP, are ubiquitous second messengers responsible for translating extracellular signals to intracellular biological responses in both normal and tumor cells. When these signals are aberrant or missing, cells may undergo neoplastic transformation or become resistant to chemotherapy. cGMP-hydrolyzing phosphodiesterases (PDEs) are attracting tremendous interest as drug targets for many diseases, including cancer, where they regulate cell growth, apoptosis and sensitization to radio- and chemotherapy. In breast cancer, PDE5 inhibition is associated with increased intracellular cGMP levels, which is responsible for the phosphorylation of PKG and other downstream molecules involved in cell proliferation or apoptosis. In this review, we provide an overview of the most relevant studies regarding the controversial role of PDE inhibitors as off-label adjuvants in cancer therapy.

A β-Catenin-TCF-Sensitive Locus Control Region Mediates GUCY2C Ligand Loss in Colorectal Cancer

BACKGROUND & AIMS

Sporadic colorectal cancers arise from initiating mutations in APC, producing oncogenic β-catenin/TCF-dependent transcriptional reprogramming. Similarly, the tumor suppressor axis regulated by the intestinal epithelial receptor GUCY2C is among the earliest pathways silenced in tumorigenesis. Retention of the receptor, but loss of its paracrine ligands, guanylin and uroguanylin, is an evolutionarily conserved feature of colorectal tumors, arising in the earliest dysplastic lesions. Here, we examined a mechanism of GUCY2C ligand transcriptional silencing by β-catenin/TCF signaling.

METHODS

We performed RNA sequencing analysis of 4 unique conditional human colon cancer cell models of β-catenin/TCF signaling to map the core Wnt-transcriptional program. We then performed a comparative analysis of orthogonal approaches, including luciferase reporters, chromatin immunoprecipitation sequencing, CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats) knockout, and CRISPR epigenome editing, which were cross-validated with human tissue chromatin immunoprecipitation sequencing datasets, to identify functional gene enhancers mediating GUCY2C ligand loss.

RESULTS

RNA sequencing analyses reveal the GUCY2C hormones as 2 of the most sensitive targets of β-catenin/TCF signaling, reflecting transcriptional repression. The GUCY2C hormones share an insulated genomic locus containing a novel locus control region upstream of the guanylin promoter that mediates the coordinated silencing of both genes. Targeting this region with CRISPR epigenome editing reconstituted GUCY2C ligand expression, overcoming gene inactivation by mutant β-catenin/TCF signaling.

CONCLUSIONS

These studies reveal DNA elements regulating corepression of GUCY2C ligand transcription by β-catenin/TCF signaling, reflecting a novel pathophysiological step in tumorigenesis. They offer unique genomic strategies that could reestablish hormone expression in the context of canonical oncogenic mutations to reconstitute the GUCY2C axis and oppose transformation.

Sildenafil: From angina to SARS-CoV-2

Sildenafil was first examined as an alternative to nitrates for the management of angina pectoris and hypertension and eventually developed into an oral therapeutic agent used for the treatment of erectile dysfunction. There are appropriate indicators that PDE5 inhibitors may also modify the detrimental consequences of the immune system over-stimulation, supplying a new chance for their use in SARS-CoV2 patients. The use of sildenafil for the management of SARS-CoV2 has been suggested based on its several mechanisms of action and therapeutic effects and on the clinical features of SARS-CoV2 which similar to those of other pathologies treated with the PDE5 inhibitors. Here we review fundamental highlights in the enhancement of sildenafil for numerous scientific disorders and consider practicable new uses for this versatile drug.

Phosphodiesterase type 5 inhibitors use and risk of colorectal cancer: a systematic review and meta-analysis

BACKGROUND

Experimental evidence has revealed that phosphodiesterase five inhibitors (PDE5is) increase epithelial barrier function and suppress intestinal carcinogenesis. Few epidemiological studies have investigated the role of PDE5i in increasing the risk of colorectal cancer (CRC); however, these studies have proffered varying conclusions. We therefore aimed to perform a comprehensive review and meta-analysis to investigate whether PDE5i use is associated with the incidence of CRC.

METHODS

Databases, namely, PubMed, Scopus, Embase, and Web of Science, were used for literature search. Observational studies (published until January 31, 2021) that assessed the association of PDE5i use with CRC incidence were considered. Pooled relative risk (RR) estimates and corresponding 95% confidence intervals (CIs) were calculated using the DerSimonian-Laird random-effects model.

RESULTS

We identified four retrospective studies that involved 965,044 participants and 3,518 CRC cases detected during a mean follow-up of 12.7 years. Pooled results indicated a significantly reduced CRC risk among all PDE5i users (RR, 0.85; 95% CI, 0.76-0.95; P = 0.004, I² = 63%). Moreover, continuous use of PDE5i was associated with a significantly reduced risk of CRC (RR, 0.63; 95% CI, 0.59-0.68; P < 0.001, I² = 0.0%). However, the type of PDE5i exhibited no association with the risk of CRC (RR, 1.00; 95% CI, 0.98-1.02; I² = 84.7%).

CONCLUSION

Our findings suggest that continuous use of PDE5i was associated with a significantly reduced risk of CRC development. Future studies with a longitudinal design and adequate control of confounding factors are required to clarify whether a longer duration of PDE5i use alters the risk of CRC.

Research progress of phosphodiesterase inhibitors in inflammatory bowel disease treatment

Inflammatory bowel disease is a recurrent chronic intestinal inflammatory disease with unknown etiology and no effective treatment. Phosphodiesterase (PDE) regulates a variety of physiological and pathophysiological processes by mediating the hydrolysis of intracellular second messengers cyclic adenosine monophosphate and cyclic guanosine monophosphate. In recent years, a series of researches suggest that PDE inhibitors such as several PDE4 inhibitors, PDE5 inhibitors (sildenafil, tadalafil and vardenafil), PDE3 inhibitors (cilostazol), PDE9 inhibitor (PF-04447943) and PDE3/PDE4 double inhibitor (pumafentrine) have ameliorating effect on experimental colitis in animals. In clinical trials, PDE4 inhibitor apremilast showed more therapeutic advantage than tetomilast. This article reviews the recent research progress of PDE inhibitors in treatment of inflammatory bowel disease.

Sildenafil triggers tumor lethality through altered expression of HSP90 and degradation of PKD2

The repurposing of existing drugs has emerged as an attractive additional strategy to the development of novel compounds in the fight against cancerous diseases. Inhibition of phosphodiesterase 5 (PDE5) has been claimed as a potential approach to target various cancer subtypes in recent years. However, data on the treatment of tumors with PDE5 inhibitors as well as the underlying mechanisms are as yet very scarce. Here, we report that treatment of tumor cells with low concentrations of Sildenafil was associated with decreased cancer cell proliferation and augmented apoptosis in vitro and resulted in impaired tumor growth in vivo. Notably, incubation of cancer cells with Sildenafil was associated with altered expression of HSP90 chaperone followed by degradation of protein kinase D2, a client protein previously reported to be involved in tumor growth. Furthermore, the involvement of low doses of PU-H71, an HSP90 inhibitor currently under clinical evaluation, in combination with low concentrations of Sildenafil, synergistically and negatively impacted on the viability of cancer cells in vivo. Taken together, our study suggests that repurposing of already approved drugs, alone or in combination with oncology-dedicated compounds, may represent a novel cancer therapeutic strategy.

Guanylyl cyclase 2C (GUCY2C) in gastrointestinal cancers: recent innovations and therapeutic potential

INTRODUCTION

Gastrointestinal (GI) cancers account for the second leading cause of cancer-related deaths in the United States. Guanylyl cyclase C (GUCY2C) is an intestinal signaling system that regulates intestinal fluid and electrolyte secretion as well as intestinal homeostasis. In recent years, it has emerged as a promising target for chemoprevention and therapy for GI malignancies.

AREAS COVERED

The loss of GUCY2C signaling early in colorectal tumorigenesis suggests it could have a significant impact on tumor initiation. Recent studies highlight the importance of GUCY2C signaling in preventing colorectal tumorigenesis using agents such as linaclotide, plecanatide, and sildenafil. Furthermore, GUCY2C is a novel target for immunotherapy and a diagnostic marker for primary and metastatic diseases.

EXPERT OPINION

There is an unmet need for prevention and therapy in GI cancers. In that context, GUCY2C is a promising target for prevention, although the precise mechanisms by which GUCY2C signaling affects tumorigenesis remain to be defined. Furthermore, clinical trials are exploring its role as an immunotherapeutic target for vaccines to prevent metastatic disease. Indeed, GUCY2C is an emerging target across the disease continuum from chemoprevention, to diagnostic management, through the treatment and prevention of metastatic diseases.

Sildenafil in Combination Therapy against Cancer: A Literature Review

The concepts of drug repurposing and Sildenafil or blue pill are tightly linked over the years. Indeed, in addition to its initial clinical application as an anti-hypertensive drug in the pulmonary system, Sildenafil is also known for its beneficial effects in erectile dysfunction. Moreover, evidence has been accumulated to support its value in anti-cancer therapy, either alone or in combination with other clinically efficient chemotherapy drugs. In this review, we focused on the old and recent in vitro and in vivo studies demonstrating the cellular and molecular rationale for the application of Sildenafil in combination therapy in various types of cancer. We emphasized on the different molecular targets as well as the different signaling pathways involved in cancer cells. The pro-apoptotic effect of Sildenafil through nitric oxide (NO)/ phosphodiesterase type 5 (PDE5)-dependent manner seems to be one of the most common mechanisms. However, the activation of autophagy, as well as the modulation of the anti-tumor immunity, constitutes the other pathways triggered by Sildenafil. Overall, the studies converged to reveal the complexity of the anti-cancer potential of Sildenafil. Thus, through our review, we aimed to present an updated and simplified picture of such repurposing of Sildenafil in the field of oncology.

Effect of a three-piece inflatable penile prosthesis combined with a phosphodiesterase-5 inhibitor on erectile dysfunction

Objective

To investigate the therapeutic effect of implanting a three-piece inflatable penile prosthesis (IPP) combined with the phosphodiesterase-5 inhibitor sildenafil in severe erectile dysfunction (ED) patients.

Methods

This randomized controlled study included 123 ED patients. Sixty-two patients received the IPP implantation and 61 patients received the IPP implantation and the phosphodiesterase-5 inhibitor sildenafil. Erectile function and sexual life quality were evaluated using the five-item International Index of Erectile Function (IIEF) and modified Sexual Life Quality Questionnaire–Quality of Life domain (mSLQQ-QoL), respectively. Serum interleukin (IL)-6, IL-8, tumor necrosis factor (TNF)-α, vascular cell adhesion molecule (VCAM)-1, and intercellular adhesion molecule (ICAM)-1 levels were assessed. Kaplan–Meier curves were used to assess the overall IPP survival.

Results

Implantation of the three-piece IPP with sildenafil improved erectile function and sexual life quality, alleviated the inflammatory response, reduced the complication rate, and improved overall IPP survival.

Conclusion

Implantation of the three-piece IPP combined with a phosphodiesterase-5 inhibitor significantly improved clinical outcomes and the prognosis in ED patients.

The Association Between Phosphodiesterase-5 Inhibitors and Colorectal Cancer in a National Cohort of Patients

To examine the association between phosphodiesterase-5 (PDE-5) inhibitor use and incidence of colorectal cancer among patients with erectile dysfunction treated in the Veterans Affairs (VA) Healthcare System.

Sildenafil 4.0-Integrated Synthetic Chemistry, Formulation and Analytical Strategies Effecting Immense Therapeutic and Societal Impact in the Fourth Industrial Era

Sildenafil is a potent selective, reversible inhibitor of phosphodiesterase type 5 (PDE5) approved for the treatment of erectile dysfunction and pulmonary arterial hypertension. Whilst twenty years have passed since its original approval by the US Food and Drug Administration (USFDA), sildenafil enters the fourth industrial era catalyzing the treatment advances against erectile dysfunction and pulmonary hypertension. The plethora of detailed clinical data accumulated and the two sildenafil analogues marketed, namely tadalafil and vardenafil, signify the relevant therapeutic and commercial achievements. The pharmacokinetic and pharmacodynamic behavior of the drug appears complex, interdependent and of critical importance whereas the treatment of special population cohorts is considered. The diversity of the available formulation strategies and their compatible administration routes, extend from tablets to bolus suspensions and from per os to intravenous, respectively, inheriting the associated strengths and weaknesses. In this comprehensive review, we attempt to elucidate the multi-disciplinary elements spanning the knowledge fields of chemical synthesis, physicochemical properties, pharmacology, clinical applications, biopharmaceutical profile, formulation approaches for different routes of administration and analytical strategies, currently employed to guide the development of sildenafil-based compositions.

Repurposing of sildenafil as antitumour; induction of cyclic guanosine monophosphate/protein kinase G pathway, caspase-dependent apoptosis and pivotal reduction of Nuclear factor kappa light chain enhancer of activated B cells in lung cancer

OBJECTIVES

Lung cancer is one of the most frequent types of cancers that lead to death. Sildenafil is a potent inhibitor of phosphodiesterase-5 and showed potential anticancer effects, which has not yet been fully evaluated. Thus, this study aims to investigate the potential anticancer effect of sildenafil in urethane-induced lung cancer in BALB/c mice.

METHODS

Five-week-old male BALB/c mice were treated with either (i) normal saline only, (ii) sildenafil only 50 mg kg-1/ P.O every other day for the last four successive weeks, (iii) urethane 1.5 gm kg-1 i.p (at day 1 and day 60), (iv) carboplatin after urethane induction, or (v) sildenafil after urethane induction.

KEY FINDINGS

It was shown that sildenafil significantly increased the levels of cGMP and Caspase-3 with a reduction of NF-κB, Bcl-2, Cyclin D1, intercellular adhesion molecule 1, matrix metalloproteinase-2 levels and normalisation of Nrf2 along with pronounced improvement in the histological patterns.

CONCLUSIONS

These results indicated that sildenafil markedly induces cell cycle arrest, apoptosis and inhibits the metastatic activity through activation of cyclic guanosine monophosphate/protein kinase G pathway and down-regulation of cyclin D1 and nuclear factor kappa light chain enhancer of activated B cells with downstream anti-apoptotic gene Bcl-2, which underscores the critical importance of future using sildenafil in the treatment of lung cancer.

PDE9 Inhibitor PF-04447943 Attenuates DSS-Induced Colitis by Suppressing Oxidative Stress, Inflammation, and Regulating T-Cell Polarization

Ulcerative colitis (UC) is a form of inflammatory bowel disease, which manifests as irritation or swelling and sores in the large intestine in a relapsing and remitting manner. In a dextran sulfate sodium sulfate (DSS)-induced UC model in female mice, we found that the levels of cyclic guanosine monophosphate (cGMP) are reduced, while the expression of phosphodiesterase 9A (PDE9A) is highest among all phosphodiesterase (PDEs). Since PDE9 has the highest affinity toward cGMP, we evaluated the selective PDE9 inhibitor PF-04447943 (PF) as a potential candidate for UC treatment. PF has been extensively studies in cognitive function and in sickle cell disease, but not in models for inflammatory bowel disease (IBD). Therefore, we used female C57BL/6 mice treated with 3% DSS alone or co-treated with PF or sulfasalazine (SASP) to study the body weight, colon length, histopathology, and measure superoxide dismutase (SOD), malondialdehyde (MDA), and cGMP level, as well as cytokines such as tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), interleukin-17 (IL-17), interleukin-12/23 (IL-12/23), interleukin-10 (IL-10), and pathways including nuclear factor kappa B (NF-κB), signal transducer and activator of transcription 3 (STAT3), and inflammasome activation. In addition, the number of dendritic cells (DC) and regulatory T cells (Treg cell) was assessed in the spleen, lymph node, and colon using flow cytometry. DSS reduced the number of goblet cells, decreased colon lengths and body weights, all of them were attenuated by PF treatment. It also suppressed the elevated level of inflammatory cytokines and increased level the anti-inflammatory cytokine, IL-10. PF treatment also reduced the DSS-induced inflammation by suppressing oxidative stress, NF-κB, STAT3, and inflammasome activation, by upregulating nuclear factor erythroid 2-related factor 2 (Nrf-2) and its downstream proteins via extracellular signal-regulated kinase (ERK) phosphorylation. Importantly, PF reversed imbalance in Treg/T helper 17 cells (Th17) cells ratio, possibly by regulating dendritic cells and Treg developmental process. In summary, this study shows the protective effect of a PDE9A inhibitor in ulcerative colitis by suppressing oxidative stress and inflammation as well as reversing the Treg/Th17 cells imbalance.

Sildenafil beyond erectile dysfunction and pulmonary arterial hypertension: Thinking about new indications

Sildenafil, approved two decades ago, is the inhibitor of phosphodiesterase 5 (PDE5). First of all, it was designated for angina pectoris, but soon it showed a wonderful efficacy in erectile dysfunction (ED) and then pulmonary arterial hypertension (PAH). Due to the distribution of phosphodiesterase (PDE) in almost all organs, maybe it effects other diseases. Hence, a great number of investigations began to understand the role of PDEi in different organs. Preliminary research on sildenafil in cell culture and animal models has yielded promising results. Soon, a greater number of animal researches and clinical trials joined them. The results disclosed sildenafil can have beneficial effects in each organ such as heart, liver, kidney, brain, and intestines. Furthermore, it has significantly improved the prognosis of organ ischemia in various animal models. Clinical trials in several diseases, such as recurrent spontaneous miscarriage, fatty liver disease, bronchopulmonary dysplasia (BPD), heart failure, and premature ejaculation (PE) brought promising results. Although some clinical trials are available on the effects of sildenafil on various diseases, further studies on humans are needed to consolidate the ultimate effects of sildenafil. The aim of this review was to describe the effects of sildenafil on each organ and explain its mechanisms of action. Further, other PDE inhibitors such as tadalafil and vardenafil have been briefly discussed in parts of this review.

Approaches to inhibiting oncogenic K-Ras

Activating somatic K-Ras mutations are associated with >15% all human tumors and up to 90% of specific tumor types such as pancreatic cancer. Successfully inhibiting abnormal K-Ras signaling would therefore be a game changer in cancer therapy. However, K-Ras has long been considered an undruggable target for various reasons. This view is now changing by the discovery of allosteric inhibitors that directly target K-Ras and inhibit its functions, and by the identification of new mechanisms to dislodge it from the plasma membrane and thereby abrogate its cellular activities. In this review, we will discuss recent progresses and challenges to inhibiting aberrant K-Ras functions by these two approaches. We will also provide a broad overview of other approaches such as inhibition of K-Ras effectors, and offer a brief perspective on the way forward.

New Approaches in Oncology for Repositioning Drugs: The Case of PDE5 Inhibitor Sildenafil

The use of already-approved drugs to treat new or alternative diseases has proved to be beneficial in medicine, because it reduces both drug development costs and timelines. Most drugs can be used to treat different illnesses, due their mechanisms of action are not restricted to one molecular target, organ or illness. Diverging from its original intent offers an opportunity to repurpose previously approved drugs to treat other ailments. This is the case of sildenafil (Viagra), a phosphodiesterase-5 (PDE5) inhibitor, which was originally designed to treat systemic hypertension and angina but is currently commercialized as erectile dysfunction treatment. Sildenafil, tadalafil, and vardenafil are PDE5 inhibitors and potent vasodilators, that extend the physiological effects of nitric oxide and cyclic guanosine monophosphate (cGMP) signaling. Although most of the biological implications of these signaling regulations remain unknown, they offer a large therapeutic potential for several diseases. In addition, some PDE5 inhibitors' molecular effects seem to play a key role in different illnesses such as kidney disease, diabetes mellitus, and cancer. In this review, we discuss the molecular effects of PDE5 inhibitors and their therapeutic repurposing in different types of cancer.

Guanylyl cyclase C as a biomarker for immunotherapies for the treatment of gastrointestinal malignancies

Gastrointestinal cancers encompass a diverse class of tumors arising in the GI tract, including esophagus, stomach, pancreas and colorectum. Collectively, gastrointestinal cancers compose a high fraction of all cancer deaths, highlighting an unmet need for novel and effective therapies. In this context, the transmembrane receptor guanylyl cyclase C (GUCY2C) has emerged as an attractive target for the prevention, detection and treatment of many gastrointestinal tumors. GUCY2C is an intestinally-restricted protein implicated in tumorigenesis that is universally expressed by primary and metastatic colorectal tumors as well as ectopically expressed by esophageal, gastric and pancreatic cancers. This review summarizes the current state of GUCY2C-targeted modalities in the management of gastrointestinal malignancies, with special focus on colorectal cancer, the most incident gastrointestinal malignancy.

The inhibition of colorectal cancer growth by the natural product macrocarpal I

BACKGROUND

Presently, few small molecule compounds are used as targeted therapy drugs in the treatment of colorectal cancer (CRC). It is important to identify new small molecule compounds, which can be used in the treatment of CRC.

METHODS

In this study, we selected four protein molecules as drug targets: PRL-3 (Phosphatase of regenerating liver 3), CLIC4 (Chloride intracellular channel 4), THBS2 (Thrombospondin 2), and BGN (Biglycan). These protein molecules were associated with the growth and metastasis of CRC cells. Small molecular compounds were screened on the basis of their target structures. Thus, five small molecule compounds were screened from each target structure, and three small molecule compounds (macrocarpal I, sildenafil, and neoandrographolide) were found to bind with two drug targets at the same time. Further experiments revealed that the inhibition rate of macrocarpal I was the highest in CRC cells. Therefore, we determined the effects of macrocarpal I on proliferation, apoptosis, cytoskeleton of CRC cells, and subcutaneous tumorigenesis in nude mice. Furthermore, RNA-seq analysis was performed to determine the molecular mechanism through which macrocarpal I inhibited the progression of CRC.

RESULTS

We found that macrocarpal I could effectively inhibit proliferation, colony formation of CRC cells, and subcutaneous tumorigenesis in nude mice. Moreover, it also destroyed the cytoskeleton of CRC cells and promoted apoptosis. The effects on kinase activity, cytoskeleton, and DNA repair is the mechanism of macrocarpal I to inhibiting CRC growth.

CONCLUSION

Macrocarpal I is a small molecule compound that can effectively inhibit the progression of CRC. Thus, macrocarpal I is a therapeutic compound that shows promising results in the treatment of advanced CRC.

An update on guanylyl cyclase C in the diagnosis, chemoprevention, and treatment of colorectal cancer

Introduction: Colorectal cancer remains the second leading cause of cancer death in the United States, underscoring the need for novel therapies. Despite the successes of new targeted agents for other cancers, colorectal cancer suffers from a relative scarcity of actionable biomarkers. In this context, the intestinal receptor, guanylyl cyclase C (GUCY2C), has emerged as a promising target.Areas covered: GUCY2C regulates a tumor-suppressive signaling axis that is silenced through loss of its endogenous ligands at the earliest stages of tumorigenesis. A body of literature supports a cancer chemoprevention strategy involving reactivation of GUCY2C through FDA-approved cGMP-elevating agents such as linaclotide, plecanatide, and sildenafil. Its limited expression in extra-intestinal tissues, and retention on the surface of cancer cells, also positions GUCY2C as a target for immunotherapies to treat metastatic disease, including vaccines, chimeric antigen receptor T-cells, and antibody-drug conjugates. Likewise, GUCY2C mRNA identifies metastatic cells, enhancing colorectal cancer detection, and staging. Pre-clinical and clinical programs exploring these GUCY2C-targeting strategies will be reviewed.Expert opinion: Recent mechanistic insights characterizing GUCY2C ligand loss early in tumorigenesis, coupled with results from the first clinical trials testing GUCY2C-targeting strategies, continue to elevate GUCY2C as an ideal target for prevention, detection, and therapy.

Sildenafil Potentiates the Therapeutic Efficacy of Docetaxel in Advanced Prostate Cancer by Stimulating NO-cGMP Signaling

PURPOSE

Docetaxel plays an indispensable role in the management of advanced prostate cancer. However, more than half of patients do not respond to docetaxel, and those good responders frequently experience significant cumulative toxicity, which limits its dose duration and intensity. Hence, a second agent that could increase the initial efficacy of docetaxel and maintain tolerability at biologically effective doses may improve outcomes for patients.

EXPERIMENTAL DESIGN

We determined phosphodiesterase 5 (PDE5) expression levels in human and genetically engineered mouse (GEM) prostate tissues and tumor-derived cell lines. Furthermore, we investigated the therapeutic benefits and underlying mechanism of PDE5 inhibitor sildenafil in combination with docetaxel using in vitro, Pten conditional knockout (cKO), derived tumoroid and xenograft prostate cancer models.

RESULTS

PDE5 expression was higher in both human and mouse prostate tumors and cancer cell lines compared with normal tissues/cells. In GEM prostate-derived cell lines, PDE5 expression increased from normal prostate (wild-type) epithelial cells to androgen-dependent and castrated prostate-derived cell lines. The addition of physiologically achievable concentrations of sildenafil enhanced docetaxel-induced prostate cancer cell growth inhibition and apoptosis in vitro, reduced murine 3D tumoroid growth, and in vivo tumorigenicity as compared with docetaxel alone. Furthermore, sildenafil enhanced docetaxel-induced NO and cGMP levels thereby augmenting antitumor activity.

CONCLUSIONS

Our results demonstrate that sildenafil's addition could sensitize docetaxel chemotherapy in prostate cancer cells at much lesser concentration than needed for inducing cell death. Thus, the combinatorial treatment of sildenafil and docetaxel may improve anticancer efficacy and reduce chemotherapy-induced side-effects among patients with advanced prostate cancer.

Phosphodiesterase-5 inhibitors use and risk for mortality and metastases among male patients with colorectal cancer

Phosphodiesterase-5 (PDE5) inhibitors are suggested to have anti-tumor effects and to inhibit surgery-induced immunosuppression. We aimed to explore whether post-diagnostic use of PDE5 inhibitors was associated with a better prognosis among male patients with colorectal cancer (CRC) and the role of open surgery in the association. Here we show that post-diagnostic use of PDE5 inhibitors is associated with a decreased risk of CRC-specific mortality (adjusted HR = 0.82, 95% CI 0.67-0.99) as well as a decreased risk of metastasis (adjusted HR = 0.85, 95% CI 0.74-0.98). Specifically, post-operative use of PDE5 inhibitors has a strong anti-cancer effect. The reduced risk of metastasis is mainly due to distant metastasis but not regional lymphatic metastasis. PDE5 inhibitors have the potential to be an adjuvant drug for patients with CRC to improve prognosis, especially those who have undergone open surgery.

Phosphodiesterase-5 (PDE5) inhibitors have been suggested to have an anti-tumor effect and block surgery-induced immunosuppression. Here, the authors show that postdiagnostic use of PDE5 inhibitors is associated with a decreased risk of colorectal cancerspecific mortality as well as a decreased risk of metastasis.

PDE5 and PDE10 inhibition activates cGMP/PKG signaling to block Wnt/β-catenin transcription, cancer cell growth, and tumor immunity

Although numerous reports conclude that nonsteroidal anti-inflammatory drugs (NSAIDs) have anticancer activity, this common drug class is not recommended for long-term use because of potentially fatal toxicities from cyclooxygenase (COX) inhibition. Studies suggest the mechanism responsible for the anticancer activity of the NSAID sulindac is unrelated to COX inhibition but instead involves an off-target, phosphodiesterase (PDE). Thus, it might be feasible develop safer and more efficacious drugs for cancer indications by targeting PDE5 and PDE10, which are overexpressed in various tumors and essential for cancer cell growth. In this review, we describe the rationale for using the sulindac scaffold to design-out COX inhibitory activity, while improving potency and selectivity to inhibit PDE5 and PDE10 that activate cGMP/PKG signaling to suppress Wnt/β-catenin transcription, cancer cell growth, and tumor immunity.

Repurposing of drugs: An attractive pharmacological strategy for cancer therapeutics

Human malignancies are one of the major health-related issues though out the world and anticipated to rise in the future. The development of novel drugs/agents requires a huge amount of cost and time that represents a major challenge for drug discovery. In the last three decades, the number of FDA approved drugs has dropped down and this led to increasing interest in drug reposition or repurposing. The present review focuses on recent concepts and therapeutic opportunities for the utilization of antidiabetics, antibiotics, antifungal, anti-inflammatory, antipsychotic, PDE inhibitors and estrogen receptor antagonist, Antabuse, antiparasitic and cardiovascular agents/drugs as an alternative approach against human malignancies. The repurposing of approved non-cancerous drugs is an effective strategy to develop new therapeutic options for the treatment of cancer patients at an affordable cost in clinics. In the current scenario, most of the countries throughout the globe are unable to meet the medical needs of cancer patients because of the high cost of the available cancerous drugs. Some of these drugs displayed potential anti-cancer activity in preclinic and clinical studies by regulating several key molecular mechanisms and oncogenic pathways in human malignancies. The emerging pieces of evidence indicate that repurposing of drugs is crucial to the faster and cheaper discovery of anti-cancerous drugs.

New drugs are not enough‑drug repositioning in oncology: An update

Drug repositioning refers to the concept of discovering novel clinical benefits of drugs that are already known for use treating other diseases. The advantages of this are that several important drug characteristics are already established (including efficacy, pharmacokinetics, pharmacodynamics and toxicity), making the process of research for a putative drug quicker and less costly. Drug repositioning in oncology has received extensive focus. The present review summarizes the most prominent examples of drug repositioning for the treatment of cancer, taking into consideration their primary use, proposed anticancer mechanisms and current development status.

Rapamycin for longevity: opinion article

From the dawn of civilization, humanity has dreamed of immortality. So why didn't the discovery of the anti-aging properties of mTOR inhibitors change the world forever? I will discuss several reasons, including fear of the actual and fictional side effects of rapamycin, everolimus and other clinically-approved drugs, arguing that no real side effects preclude their use as anti-aging drugs today. Furthermore, the alternative to the reversible (and avoidable) side effects of rapamycin/everolimus are the irreversible (and inevitable) effects of aging: cancer, stroke, infarction, blindness and premature death. I will also discuss why it is more dangerous not to use anti-aging drugs than to use them and how rapamycin-based drug combinations have already been implemented for potential life extension in humans. If you read this article from the very beginning to its end, you may realize that the time is now.

Therapeutic targeting of 3',5'-cyclic nucleotide phosphodiesterases: inhibition and beyond

Phosphodiesterases (PDEs), enzymes that degrade 3',5'-cyclic nucleotides, are being pursued as therapeutic targets for several diseases, including those affecting the nervous system, the cardiovascular system, fertility, immunity, cancer and metabolism. Clinical development programmes have focused exclusively on catalytic inhibition, which continues to be a strong focus of ongoing drug discovery efforts. However, emerging evidence supports novel strategies to therapeutically target PDE function, including enhancing catalytic activity, normalizing altered compartmentalization and modulating post-translational modifications, as well as the potential use of PDEs as disease biomarkers. Importantly, a more refined appreciation of the intramolecular mechanisms regulating PDE function and trafficking is emerging, making these pioneering drug discovery efforts tractable.

Use of Phosphodiesterase 5 Inhibitors Is Associated With Lower Risk of Colorectal Cancer in Men With Benign Colorectal Neoplasms

BACKGROUND & AIMS

Phosphodiesterase 5 (PDE5) inhibitors have been proposed to have chemopreventative effects on colorectal cancer (CRC), although data are needed from population-based studies. We performed a nationwide cohort study to investigate the association between the use of PDE5 inhibitors and the risk of CRC in men with benign colorectal neoplasms.

METHODS

We identified men who received a diagnosis of benign colorectal neoplasm from July 2005 through March 2015 who were listed in the Swedish Hospital Discharge Register. We linked data with those from other national Swedish registers to obtain information about the prescription of PDE5 inhibitors and CRC diagnoses. Cox regression was used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs).

RESULTS

A total of 4823 patients were prescribed PDE5 inhibitors during the study period; the incidence rate of CRC was 2.64 per 1000 person-years for men prescribed PDE5 inhibitors compared with 4.46 per 1000 person-years for men without a prescription. We found a significant negative association between PDE5 inhibitor use and risk of CRC (adjusted HR, 0.65; 95% CI, 0.49-0.85); the decreased risk of CRC was associated with an increased cumulative dose of PDE5 inhibitors (P = .003). PDE5 prescription was associated with greater reduction in risk of advanced-stage CRC (adjusted HR, 0.61; 95% CI, 0.37-1.00) than early-stage CRC (adjusted HR, 0.70; 95% CI, 0.50-0.98), but the difference was not significant.

CONCLUSIONS

In a nationwide population-based study of men with a diagnosis of benign colorectal neoplasm in Sweden, we found evidence that use of PDE5 inhibitors is associated with a reduced risk of CRC. Further studies are needed to confirm the observed association.