Evaluation of PDE5 and PDE9 expression in benign and malignant breast tumors

What are the Optimal Systemic Treatment Options for Rhabdomyosarcoma?

OPINION STATEMENT

Rhabdomyosarcoma, a soft tissue sarcoma commonly observed in childhood, requires multidisciplinary treatment, including surgical tumor resection, chemotherapy, and radiation therapy. Although long-term survival can be expected in patients with localized rhabdomyosarcoma, the clinical outcomes in patients with metastatic or unresectable rhabdomyosarcoma remain unsatisfactory. To improve the outcomes of rhabdomyosarcoma, it is important to explore effective systemic treatments for metastatic rhabdomyosarcoma. Currently, multiagent chemotherapy comprising vincristine, actinomycin D, and ifosfamide/cyclophosphamide remains standard systemic treatment for rhabdomyosarcoma. On the other hand, new treatment, such as immune checkpoint inhibitors and molecular targeted drugs, have demonstrated superior clinical outcomes compared to those of standard treatments in various type of malignancies. Therefore, it is necessary to assess the efficacies of these treatments in patients with rhabdomyosarcoma. Recent clinical studies have shown efficacies and safeties of temozolomide combined with vincristine/irinotecan, olaratumab combined with doxorubicin or vincristine/irinotecan, and long-term maintenance therapy. Furthermore, basic researches demonstrated new therapeutic targets. Future studies using these approaches are required to assess their clinical significances.

A phase 1 study of regorafenib and sildenafil in adults with advanced solid tumors

The purpose of this study is to establish the recommended phase 2 dose for regorafenib in combination with sildenafil for patients with advanced solid tumors. Secondary outcomes included identification of antitumor effects of regorafenib and sildenafil, toxicity of the combination, determination of PDE5 expression in tumor samples, and the impact of sildenafil on the pharmacokinetics of regorafenib. This study was a phase 1, open-label single-arm dose-escalation trial using a 3 + 3 design. Additional patients were enrolled at the maximum tolerated dose (MTD) until a total of 12 patients were treated at the MTD. A total of 29 patients were treated in this study. The median duration of treatment was 8 weeks. The recommended phase 2 doses determined in this study are regorafenib 160 mg daily with sildenafil 100 mg daily. The most common toxicities included palmar-plantar erythrodysesthesia syndrome (20 patients, 69%) and hypophosphatemia (18 patients, 62%). Two patients (7%) experienced grade 4 lipase increase. Objective responses were not observed; however, 14 patients (48%) had a period of stable disease during the study. Stable disease for up to 12 months was observed in patients with ovarian cancer as well as up to 20 months for a patient with cervical cancer. The combination of regorafenib and sildenafil at the recommended phase 2 dose is safe and generally well tolerated. Disease control in patients with gynecologic malignancies was especially encouraging. Further evaluation of the combination of regorafenib and sildenafil in gynecologic malignancies is warranted. Clinical Trial Registration Number: NCT02466802.

Blockade of phosphodiesterase 5 by sildenafil reduces tumor growth and potentiates tumor-killing ability of cisplatin in vivo against T cell lymphoma: Implication of modulated apoptosis, reactive oxygen species homeostasis, glucose metabolism, and pH regulation

In the past years, PDE5 has emerged as a promising therapeutic target for many cancers due to its highly upregulated expression. Interestingly, a recent in vitro study by our group has shown the antitumor and chemopotentiating action of sildenafil against T cell lymphoma. Our study showed that lower doses of sildenafil (50 μM) and cisplatin (0.5 μg/mL) exhibited 4% and 23% cytotoxicity against HuT78 cells, respectively, which was dramatically increased up to 50% when treated with both. Hence, the present study was designed to evaluate the antitumor and chemo-potentiating action of sildenafil in a murine model of T cell lymphoma (popularly called as Dalton's lymphoma [DL]). In the present study, DL-bearing mice were administered with vehicle (PBS), sildenafil (5 mg/kg bw), cisplatin (5 mg/kg bw), and sildenafil and cisplatin followed by evaluation of their impact on tumor growth by analyzing various parameters. The apoptosis was assessed by Wright-Giemsa, annexin-V, and DAPI staining. Reactive oxygen species (ROS) level was examined through DCFDA staining. The expression of genes and proteins were estimated by RT-PCR and Western blotting, respectively. The experimental findings of the study demonstrate for the first time that sildenafil inhibits tumor growth and potentiates tumor inhibitory ability of cisplatin by altering apoptosis, glycolysis, ROS homeostasis, and pH regulation in T cell lymphoma-carrying host. In addition, our investigation also showed amelioration of tumor-induced liver and kidney damage by sildenafil. Overall, the experimental data of our study strongly advocate the use and repurposing of SDF in designing promising chemotherapeutic regimens against malignancies of T cells.

Cardio-oncology: Shared Genetic, Metabolic, and Pharmacologic Mechanism

PURPOSE OF REVIEW

The article aims to investigate the complex relationship between cancer and cardiovascular disease (CVD), with a focus on the effects of cancer treatment on cardiac health.

RECENT FINDINGS

Advances in cancer treatment have improved long-term survival rates, but CVD has emerged as a leading cause of morbidity and mortality in cancer patients. The interplay between cancer itself, treatment methods, homeostatic changes, and lifestyle modifications contributes to this comorbidity. Recent research in the field of cardio-oncology has revealed common genetic mutations, risk factors, and metabolic features associated with the co-occurrence of cancer and CVD. This article provides a comprehensive review of the latest research in cardio-oncology, including common genetic mutations, risk factors, and metabolic features, and explores the interactions between cancer treatment and CVD drugs, proposing novel approaches for the management of cancer and CVD.

Functional Axis of PDE5/cGMP Mediates Timosaponin-AIII-Elicited Growth Suppression of Glioblastoma U87MG Cells

Glioblastoma (GBM) is the most aggressive brain tumor, with high mortality. Timosaponin AIII (TIA), a steroidal saponin isolated from the medicinal plant Anemarrhena asphodeloides Bge., has been shown to possess anticancer properties in various cancer types. However, the effect of TIA on GBM is unknown. In this study, we reveal that TIA not only inhibited U87MG in vitro cell growth but also in vivo tumor development. Moreover, we found that the cause of TIA-induced cell growth suppression was apoptosis. When seeking to uncover antitumor mechanisms of TIA, we found that TIA diminished the expression of cGMP-specific phosphodiesterase 5(PDE5) while elevating the levels of guanylate cyclases (sGCβ), cellular cGMP, and phosphorylation of VASP^ser239. Following the knockdown of PDE5, PDE5 inhibitor tadalafil and cGMP analog 8-Bro-cGMP both inhibited cell growth and inactivated β-catenin; we reason that TIA elicited an antitumor effect by suppressing PDE5, leading to the activation of the cGMP signaling pathway, which, in turn, impeded β-catenin expression. As β-catenin is key for cell growth and survival in GBM, this study suggests that TIA elicits its anti-tumorigenic effect by interfering with β-catenin function through the activation of a PDE5/cGMP functional axis.

In Vitro Drug Repurposing: Focus on Vasodilators

Drug repurposing aims to identify new therapeutic uses for drugs that have already been approved for other conditions. This approach can save time and resources compared to traditional drug development, as the safety and efficacy of the repurposed drug have already been established. In the context of cancer, drug repurposing can lead to the discovery of new treatments that can target specific cancer cell lines and improve patient outcomes. Vasodilators are a class of drugs that have been shown to have the potential to influence various types of cancer. These medications work by relaxing the smooth muscle of blood vessels, increasing blood flow to tumors, and improving the delivery of chemotherapy drugs. Additionally, vasodilators have been found to have antiproliferative and proapoptotic effects on cancer cells, making them a promising target for drug repurposing. Research on vasodilators for cancer treatment has already shown promising results in preclinical and clinical studies. However, additionally research is needed to fully understand the mechanisms of action of vasodilators in cancer and determine the optimal dosing and combination therapy for patients. In this review, we aim to explore the molecular mechanisms of action of vasodilators in cancer cell lines and the current state of research on their repurposing as a treatment option. With the goal of minimizing the effort and resources required for traditional drug development, we hope to shed light on the potential of vasodilators as a viable therapeutic strategy for cancer patients.

Combination therapy of doxorubicin and Sildenafil inhibits the growth of pediatric rhabdomyosarcoma

BACKGROUND

Overexpression of phosphodiesterase type 5 (PDE5) has been detected in many types of malignant tumors. Sildenafil, a potent and selective inhibitor of a cGMP-specific PDE5, has been found to enhance the cytotoxic activity of different chemotherapeutic agents including doxorubicin. The combined therapy of doxorubicin with Sildenafil might reduce the possible side effects of chemotherapy while maintaining synergistic anticancer activity. The present study explored for the first time the effects of Sildenafil, alone and in combination with doxorubicin, on pediatric RMS cells.

METHODS

Human RMS cells lines RH30 and RD were used. Western blotting and RT-PCR were performed to analyze PDE5 expression in RMS cells. Cell viability was determined using MTT assay. Cell migration was analyzed via transwell chambers, clonal growth and mitotic cell death were analyzed using the clonogenic assay. FACS analysis was performed to evaluate reactive oxygen species (ROS) and apoptosis.

RESULTS

Sildenafil significantly decreased cell viability and migration of RD and RH30 cells. The exposure of RMS cells to doxorubicin resulted in a dose-dependent decrease in their viability. Simultaneous administration of Sildenafil enhanced this effect. The incubation of the RMS cells with Sildenafil in the presence of doxorubicin significantly increased the proportion of apoptotic cells and ROS production compared to the treatment with Sildenafil alone.

CONCLUSIONS

The results of our study indicate a link between PDE5 inhibition by Sildenafil and decreased calcium signalling leading to significantly impaired viability, migration, and colony forming of RMS cells. Increased ROS production and apoptosis are mechanisms relevantly contributing to this observation.

cAMP-specific phosphodiesterase 8A and 8B isoforms are differentially expressed in human testis and Leydig cell tumor

Cyclic adenosine monophosphate/Protein kinase A (cAMP/PKA) signaling pathway is the master regulator of endocrine tissue function. The level, compartmentalization and amplitude of cAMP response are finely regulated by phosphodiesterases (PDEs). PDE8 is responsible of cAMP hydrolysis and its expression has been characterized in all steroidogenic cell types in rodents including adrenal and Leydig cells in rodents however scarce data are currently available in humans. Here we demonstrate that human Leydig cells express both PDE8A and PDE8B isoforms. Interestingly, we found that the expression of PDE8B but not of PDE8A is increased in transformed Leydig cells (Leydig cell tumors-LCTs) compared to non-tumoral cells. Immunofluorescence analyses further reveals that PDE8A is also highly expressed in specific spermatogenic stages. While the protein is not detected in spermatogonia it accumulates nearby the forming acrosome, in the trans-Golgi apparatus of spermatocytes and spermatids and it follows the fate of this organelle in the later stages translocating to the caudal part of the cell. Taken together our findings suggest that 1) a specific pool(s) of cAMP is/are regulated by PDE8A during spermiogenesis pointing out a possible new role of this PDE8 isoform in key events governing the differentiation and maturation of human sperm and 2) PDE8B can be involved in Leydig cell transformation.

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.

Advances in Cyclic Nucleotide Phosphodiesterase-Targeted PET Imaging and Drug Discovery

Cyclic nucleotide phosphodiesterases (PDEs) control the intracellular concentrations of cAMP and cGMP in virtually all mammalian cells. Accordingly, the PDE family regulates a myriad of physiological functions, including cell proliferation, differentiation and apoptosis, gene expression, central nervous system function, and muscle contraction. Along this line, dysfunction of PDEs has been implicated in neurodegenerative disorders, coronary artery diseases, chronic obstructive pulmonary disease, and cancer development. To date, 11 PDE families have been identified; however, their distinct roles in the various pathologies are largely unexplored and subject to contemporary research efforts. Indeed, there is growing interest for the development of isoform-selective PDE inhibitors as potential therapeutic agents. Similarly, the evolving knowledge on the various PDE isoforms has channeled the identification of new PET probes, allowing isoform-selective imaging. This review highlights recent advances in PDE-targeted PET tracer development, thereby focusing on efforts to assess disease-related PDE pathophysiology and to support isoform-selective drug discovery.

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.

Synergistic growth inhibition effect of TiO2 nanoparticles and tris(1,3-dichloro-2-propyl) phosphate on earthworms in soil

The co-existence of organic pollutants and nanoparticles in the environment may lead to combined biological effects. The joint toxicity of pollutants and nanoparticles has been receiving increasing attention from researchers, but few studies have focused on soil biota due to the complexity of soil matrices. This study investigated the effects of tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) at 0, 5, and 25 mg/kg and nanoparticulate TiO₂ (nTiO₂) at 0, 500, and 2500 mg/kg in a 3 × 3 factorial arrangement of treatments for 28 days (d) on Eisenia fetida (earthworm). Compared with the control group (the 0 mg/kg TDCIPP + 0 mg/kg nTiO₂ treatment), all other single (TDCIPP or nTiO₂) and binary (TDCIPP + nTiO₂) treatments except for the single 500 mg/kg nTiO₂ treatment significantly reduced the weight gain rate of E. fetida. The binary treatments had significantly greater such effect than their corresponding single treatments, exhibiting a synergistic toxicity between TDCIPP and nTiO2 on the growth of E. fetida. Since TDCIPP and nTiO₂ had no significant effect on their concentrations in the soil or in E. fetida during binary exposure, the synergistic toxicity could be a result of the superimposition of the toxicity pathways of TDCIPP and nTiO₂. Transcriptomic analysis of E. fetida intestinal region revealed that exposure to 25 mg/kg TDCIPP or 2500 mg/kg nTiO₂ affected nutrient-related or cell apoptosis and DNA damage related genes, respectively; their co-exposure greatly inhibited genes related to nutrient digestion and absorption, while causing abnormal transcription of genes related to the development and maintenance of E. fetida's muscles, leading to synergistic toxicity. These findings provide new insights into the environmental risks of organophosphorus flame retardants, nanoparticles, and their co-exposure.

Nucleotide de novo synthesis increases breast cancer stemness and metastasis via cGMP-PKG-MAPK signaling pathway

Metabolic reprogramming to fulfill the biosynthetic and bioenergetic demands of cancer cells has aroused great interest in recent years. However, metabolic reprogramming for cancer metastasis has not been well elucidated. Here, we screened a subpopulation of breast cancer cells with highly metastatic capacity to the lung in mice and investigated the metabolic alternations by analyzing the metabolome and the transcriptome, which were confirmed in breast cancer cells, mouse models, and patients' tissues. The effects and the mechanisms of nucleotide de novo synthesis in cancer metastasis were further evaluated in vitro and in vivo. In our study, we report an increased nucleotide de novo synthesis as a key metabolic hallmark in metastatic breast cancer cells and revealed that enforced nucleotide de novo synthesis was enough to drive the metastasis of breast cancer cells. An increased key metabolite of de novo synthesis, guanosine-5'-triphosphate (GTP), is able to generate more cyclic guanosine monophosphate (cGMP) to activate cGMP-dependent protein kinases PKG and downstream MAPK pathway, resulting in the increased tumor cell stemness and metastasis. Blocking de novo synthesis by silencing phosphoribosylpyrophosphate synthetase 2 (PRPS2) can effectively decrease the stemness of breast cancer cells and reduce the lung metastasis. More interestingly, in breast cancer patients, the level of plasma uric acid (UA), a downstream metabolite of purine, is tightly correlated with patient's survival. Our study uncovered that increased de novo synthesis is a metabolic hallmark of metastatic breast cancer cells and its metabolites can regulate the signaling pathway to promote the stemness and metastasis of breast cancer.

Design and synthesis of novel pyrazolo[3,4-d]pyrimidin-4-one bearing quinoline scaffold as potent dual PDE5 inhibitors and apoptotic inducers for cancer therapy

PDE5 targeting represents a new and promising strategy for apoptosis induction and inhibition of tumor cell growth due to its over-expression in diverse types of human carcinomas. Accordingly, we report the synthesis of series of pyrazolo[3,4-d]pyrimidin-4-one carrying quinoline moiety (11a-r) with potential dual PDE5 inhibition and apoptotic induction for cancer treatment. These hybrids were structurally elucidated and characterized with variant spectroscopic techniques as ¹H NMR, ¹³C NMR and elemental analysis. The assessment of their anticancer activities has been declared. All the rationalized compounds 11a-r have been selected for their cytotoxic activity screening by NCI against 60 cell lines. Compounds 11a, 11b, 11j and 11k were the most active hybrids. Among all, compound 11j was further selected for five dose tesing and it displayed outstanding activity with strong antitumor activity against the nine tumor subpanels tested with selectivity ratios ranging from 0.019 to 8.3 at the GI₅₀ level. Further, the most active targets 11a, b, j and k were screened for their PDE5 inhibitory activity, compound 11j (with IC₅₀ 1.57 nM) exhibited the most potent PDE5 inhibitory activity. Moreover, compound 11j is also showed moderate EGFR inhibition with IC₅₀ of 5.827 ± 0.46 µM, but significantly inhibited the Wnt/β-catenin pathway with IC₅₀1286.96 ± 12.37 ng/mL. In addition, compound 11j induced the intrinsic apoptotic mitochondrial pathway in HepG2 cells as evidenced by the lower expression levels of the anti-apoptotic Bcl-2 protein, and the higher expression of the pro-apoptotic protein Bax, p53, cytochrome c and the up-regulated active caspase-9 and caspase-3 levels. All results confirmed by western blotting assay. Compound 11j exhibit pre G1 apoptosis and cell cycle arrest at G2/M phase. In conclusion, hybridization of quinoline moiety with the privileged pyrazolo[3,4-d]pyrimidinon-4-one structure resulted in highly potent anticancer agent, 11j, which deserves more study, in particular, in vivo and clinical investiagtions, and it is expected that these results would be applied for more drug discovery process.

Evaluation of LDL receptor and Scavenger Receptor, Class B, Type 1 in the malignant and benign breast tumors: The correlation with the expression of miR-199a-5p, miR-199b-5p and miR-455-5p

AIMS

The purpose of present study was to examine the correlations of LDL (LDLR) and HDL (SR-B1) receptors with lipoproteins, miR-199a-5p, miR-199b-5p, miR-455-5p in the malignant and benign breast tumors.

METHODS

Total cholesterol-rich-lipoproteins and the receptors were determined using enzymatic-homogeneous and ELISA methods. The expression levels of miRNAs were detected by qRT-PCR.

RESULTS

Receptor expressions and lipoproteins concentration were significantly higher in the malignant tumors (p < 0.05). Positive correlation was found for LDLR with Ki67% and Her2+. HDL-C content of TNBC tumors was higher than those of Non-TNBC (p < 0.05). The expression level of miR-199a-5p was found to be downregulated significantly in the malignant tumors of <2 cm, TNBC, HER2- or stage3. The expression of miR-199b-5p was downregulated in the malignant tumors and was negatively associated with TNBC, stage and Her2+. The expression of miR-455-5p was significantly correlated with Her2- (p < 0.05). A positive correlation was observed for SR-B1 or LDLR with HDL-C or LDL-C and also for SR-B1 with LDLR, although a reverse association was detected for the expression of miR-199b-5p with LDLR in the malignant tumors (p < 0.05). No significant correlations were found for miR-199a-5p or miR-455-5p with LDLR or SR-B1 expressions and also for LDL-C and SR-B1 with clinicopathological features (p ≥ 0.05).

CONCLUSIONS

Mechanisms potentially involved in the present findings may be due to the lipid internalization and lipoprotein consumption through LDLR and SR-B1 over expression. It is noteworthy that the expression of miR-199b-5p is negatively correlated with LDLR which may suggest it as a suppressor for LDLR expression in the breast cancer.

Phosphodiesterase 5 (PDE5) Is Highly Expressed in Cancer-Associated Fibroblasts and Enhances Breast Tumor Progression

The overexpression of phosphodiesterase (PDE) 5 is frequently found in various human cancers, such as those of the breast. However, PDE5’s role in the tumor microenvironment is still unknown. As PDE5 represents a high-value therapeutic target, we investigated whether the expression and function of PDE5 in breast cancer-associated fibroblasts (CAFs) may be clinically relevant to malignant progression. PDE5 expression was increased in human breast cancer stroma compared with normal stroma and was correlated to a shorter overall survival. Treatment of CAFs, isolated from breast tumor biopsies, with selective PDE5 inhibitors inhibited their proliferation, motility, and invasiveness, and negatively controlled tumor–stroma interactions in both ‘in vitro’ and ‘in vivo’ models. PDE5 stable overexpression transformed immortalized mouse embryonic fibroblasts (MEFs) towards an activated fibroblast phenotype, impacting their intrinsic characteristics and paracrine effects on breast cancer cell growth and migration through an enhanced production of the C-X-C motif chemokine 16 (CXCL16). On the other hand, CAF exposure to PDE5 inhibitors was associated with reduced CXCL16 expression and secretion. Importantly, CXCL16 levels in breast cancer stroma showed a strong correlation with PDE5 levels and poor patient outcomes. In conclusion, PDE5 is overexpressed in breast cancer stroma, enhances the tumor-stimulatory activities of fibroblasts, and impacts clinical outcomes; thus, we propose this enzyme as an attractive candidate for prognosis and a potential target for treatments in breast cancer patients.

Genetic and molecular biology of breast cancer among Iranian patients

Abstract

Background, Breast cancer (BC) is one of the leading causes of cancer related deaths in Iran. This high ratio of mortality had a rising trend during the recent years which is probably associated with late diagnosis.

Main body

Therefore it is critical to define a unique panel of genetic markers for the early detection among our population. In present review we summarized all of the reported significant genetic markers among Iranian BC patients for the first time, which are categorized based on their cellular functions.

Conclusions

This review paves the way of introducing a unique ethnic specific panel of diagnostic markers among Iranian BC patients. Indeed, this review can also clarify the genetic and molecular bases of BC progression among Iranians.

The Phosphodiesterase-5 Inhibitors and Prostate Cancer – What We Rely Know About It?

Phosphodiesterase-5 inhibitors (PDE5Is) represent a group of drugs that are registered for the treatment of erectile dysfunctions predominantly, but recently also for treatment of pulmonary hypertension and benign prostatic hypertrophy. However, more and more research deals with possible antitumor potential of PDE5Is in different types of cancers, including prostate cancer. Prostate cancer represents the one of the most common carcinoma in the male population, whose incidence is continuously increasing. Early detection combined with radical prostatectomy increases the survival rate, but also it is necessary to keep in mind the quality of life of patients undergoing prostatectomy in light of bladder control and erectile function. Authors of various clinical studies presented the results that often lead to totally opposing conclusions. For example, Chavez and colleagues have shown that use of PDE5Is in men with erectile dysfunction decreases the risk of developing prostate cancer, while, on the other hand, Michl and colleagues pointed out the adversely effect of PDE5Is on biochemical recurrence after bilateral nerve sparing radical prostatectomy. In that sense, the aim of this review was to present as many as possible of existing results dealing with of action of PDE5Is in the field of prostatic carcinoma. Taking into account all presented data, it can be concluded that eff ect of PDE5Is on formation, development and outcome of treatment in patients with prostate carcinoma is very intriguing question, whose response requires additional both experimental and clinical research.

Differential expression of alternative transcripts of soluble guanylyl cyclase, GYCY1a3 and GUCY1b3 genes, in the malignant and benign breast tumors

Extensive alterations in splicing is one of the molecular indicator for human cancers. Soluble guanylyl cyclase (sGC), an obligatory heterodimer, is composed of α1 and β1 subunits. Each subunit is encoded by a separate gene, GUCY1a3 and GUCY1b3, correspondingly. sGC activity has been regulated by an alternative splicing and it has an important effect on the breast cancer. sGC alternative splicing has been evaluated in the 55 malignant, 25 benign and 30 normal breast tissues using qRT-PCR and RT-PCR. The differences between groups were analyzed by Mann-Whitney U. The expression of six different splice forms have been detected, three for α1 and three for β1 sGC. Expressions of Tr1, Tr2 β1 sGC and Tr7, Tr6 α1 sGC mRNA in the malignant breast tumors were significantly lower than those of benign and normal breast tissues. However, the expression of Tr3 α1 sGC mRNA was significantly higher than that of benign and normal tissues. Present data have provided some evidences for an alteration in the expression of α1 and β1 sGC alternative splicing forms which may contribute to the loss of sGC functions in the breast cancer. The observed information might be discussed by the cGMP status.

Targeting cyclic nucleotide phosphodiesterase 5 (PDE5) in brain: Toward the development of a PET radioligand labeled with fluorine-18

With the aim to develop a specific radioligand for imaging the cyclic nucleotide phosphodiesterase 5 (PDE5) in brain by positron emission tomography (PET), seven new fluorinated inhibitors (3-9) were synthesized on the basis of a quinoline core. The inhibitory activity for PDE5 together with a panel of other PDEs was determined in vitro and two derivatives were selected for IC₅₀ value determination. The most promising compound 7 (IC₅₀ = 5.92 nM for PDE5A), containing a 3-fluoroazetidine moiety, was further radiolabeled by aliphatic nucleophilic substitution of two different leaving groups (nosylate and tosylate) using [¹⁸F]fluoride. The use of the nosylate precursor and tetra-n-butyl ammonium [¹⁸F]fluoride ([¹⁸F]TBAF) in 3-methyl-3-pentanol combined with the addition of a small amount of water proved to be the best radiolabeling conditions achieving a RCY of 4.9 ± 1.5% in an automated procedure. Preliminary biological investigations in vitro and in vivo were performed to characterize this new PDE5 radioligand. Metabolism studies of [¹⁸F]7 in mice revealed a fast metabolic degradation with the formation of radiometabolites which have been detected in the brain.

Repurposing drugs in oncology (ReDO)-selective PDE5 inhibitors as anti-cancer agents

Selective phosphodiesterase 5 inhibitors, including sildenafil, tadalafil and vardenafil, are widely-used in the treatment of erectile dysfunction and pulmonary arterial hypertension. They are also well-known as examples of successful drug repurposing in that they were initially developed for angina and only later developed for erectile dysfunction. However, these drugs may also be effective cancer treatments. A range of evidentiary sources are assessed in this paper and the case made that there is pre-clinical and clinical evidence that these drugs may offer clinical benefit in a range of cancers. In particular, evidence is presented that these drugs have potent immunomodulatory activity that warrants clinical study in combination with check-point inhibition.

Inhibitors of phosphodiesterase as cancer therapeutics

Phosphodiesterases (PDEs) are a class of enzymes that hydrolyze cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) which is involved in many physiological processes including visual transduction, cell proliferation and differentiation, cell-cycle regulation, gene expression, inflammation, apoptosis, and metabolic function. PDEs are composed of 11 different families and each family contains different subtypes. The distribution, expression, regulation mode and sensitivity to inhibitors of each subtype are different, and they are involved in cancer, inflammation, asthma, depression, erectile dysfunction and other pathological processes of development. A large number of studies have shown that PDEs play an important role in the development of tumors by affecting the intracellular level of cAMP and/or cGMP and PDEs could become diagnostic markers or therapeutic targets. This review will give a brief overview of the expression and regulation of PDE families in the process of tumorigenesis and their anti-tumor inhibitors, which may guide the design of novel therapeutic drugs targeting PDEs for anticancer agent.

Sildenafil citrate improves the delivery and anticancer activity of doxorubicin formulations in a mouse model of breast cancer

Sildenafil is an approved drug for the treatment of erectile dysfunction. The drug exerts its action through the relaxation of smooth muscles and the modulation of vascular endothelial permeability. In this work, we tested whether the aforementioned effects of sildenafil on tumour vasculatures could result in an improvement of anticancer drug concentration in tumour tissues and hence improves its anticancer effect. Sildenafil when added to doxorubicin showed synergistic anticancer activity against 4T1 breast cancer cells in vitro. Adding 1, 30 and 100 μM of Viagra to 1 μM of doxorubicin resulted in 1.8-fold, 6.2-fold and 21-fold statistically significant increases in its cytotoxic effect, respectively. As a result, 4T1 tumour-bearing mice showed up to 2.7-fold increase in drug concentrations of the fluorescent Dye DiI and doxorubicin in tumour tissues, as well as their nanoformulations. Animals treated with the combinations of both Sildenafil citrate and doxorubicin showed a statistically significant 4.7-fold reduction in tumour size compared to doxorubicin alone. This work highlights the effect of Sildenafil on tumour vasculatures and provides a rational for further testing the combination on breast cancer patients.

Phosphodiesterase type 5 and cancers: progress and challenges

Cancers are an extraordinarily heterogeneous collection of diseases with distinct genetic profiles and biological features that directly influence response patterns to various treatment strategies as well as clinical outcomes. Nevertheless, our growing understanding of cancer cell biology and tumor progression is gradually leading towards rational, tailored medical treatments designed to destroy cancer cells by exploiting the unique cellular pathways that distinguish them from normal healthy counterparts. Recently, inhibition of the activity of phosphodiesterase type 5 (PDE5) is emerging as a promising approach to restore normal intracellular cyclic guanosine monophosphate (cGMP) signalling, and thereby resulting into the activation of various downstream molecules to inhibit proliferation, motility and invasion of certain cancer cells. In this review, we present an overview of the experimental and clinical evidences highlighting the role of PDE5 in the pathogenesis and prevention of various malignancies. Current data are still not sufficient to draw conclusive statements for cancer patient management, but could provide further rational for testing PDE5-targeting drugs as anticancer agents in clinical settings.

Potential synergistic effect of phosphodiesterase inhibitors with chemotherapy in lung cancer

Purpose: Lung cancer remains the leading cause of cancer-related deaths worldwide and novel therapeutic approaches targeting crucial pathways are urgently needed to improve its treatment. Differentiation-based therapeutics (Methylxanthines) and phosphodiesterase inhibitors (type 4 and 5), have been implicated in cancer treatment. Our objectives were to capture any potential anti-tumor effect of these drug combinations with chemotherapeutic agents in vitro. Methods: Theophylline as Methylxanthines, Roflumilast as phosphodiesterase type 4 (PDE4) inhibitor and Sildenafil as phosphodiesterase type 5 (PDE5) inhibitor are the drugs that we combined with the chemotherapeutic agents (Docetaxel, Cisplatin and Carboplatin) in vitro. Lung cancer cell lines (NCI-H1048-Small cell lung cancer-SCLC, A549- Non-small cell lung cancer-NSCLC) were purchased from ATCC LGC Standards. At indicated time-point, following 24h and 48h incubation, cell viability and apoptosis were measured with Annexin V staining by flow cytometry. Statistical analysis was performed by GraphPad Prism. Results: In SCLC, following 48h incubation, platinum combinations of carboplatin with roflumilast and sildenafil (p<0.001) and carboplatin with theophylline and sildenafil showed increased apoptosis when compared to carboplatin alone. Concerning the combinations of cisplatin, when combined with roflumilast, theophylline and sildenafil appeared with increased apoptosis of that alone (p<0.001, 24h and 48h incubation). In NSCLC, the 24h incubation was not enough to induce satisfactory apoptosis, except for the combination of cisplatin with roflumilast and theophylline (p<0.05) when compared to cisplatin alone. However, following 48h incubation, carboplatin plus sildenafil, carboplatin plus sildenafil, theophylline and roflumilast showed more cytotoxicity when compared to carboplatin alone (p<0.001). Docetaxel combinations showed no statistically significant results. Conclusion: The synergistic effect of PDE inhibitors with platinum-based agents has been demonstrated in lung cancer. Our suggestion is that these combinations could be used as additive and maintenance treatment in combination to antineoplastic agents in lung cancer patients.

Phosphodiesterase 10A is overexpressed in lung tumor cells and inhibitors selectively suppress growth by blocking β-catenin and MAPK signaling

Phosphodiesterase 10A (PDE10) is a cyclic nucleotide (e.g. cGMP) degrading enzyme highly expressed in the brain striatum where it plays an important role in dopaminergic neurotransmission, but has limited expression and no known physiological function outside the central nervous system. Here we report that PDE10 mRNA and protein levels are strongly elevated in human non-small cell lung cancer cells and lung tumors compared with normal human airway epithelial cells and lung tissue, respectively. Genetic silencing of PDE10 or inhibition by small molecules such as PQ10 was found to selectively inhibit the growth and colony formation of lung tumor cells. PQ10 treatment of lung tumor cells rapidly increased intracellular cGMP levels and activated cGMP-dependent protein kinase (PKG) at concentrations that inhibit lung tumor cell growth. PQ10 also increased the phosphorylation of β-catenin and reduced its levels, which paralleled the suppression of cyclin D1 and survivin but preceded the activation of PARP and caspase cleavage. PQ10 also suppressed RAS-activated RAF/MAPK signaling within the same concentration range and treatment period as required for cGMP elevation and PKG activation. These results show that PDE10 is overexpressed during lung cancer development and essential for lung tumor cell growth in which inhibitors can selectively induce apoptosis by increasing intracellular cGMP levels and activating PKG to suppress oncogenic β-catenin and MAPK signaling.

Nitric Oxide Synthase-2-Derived Nitric Oxide Drives Multiple Pathways of Breast Cancer Progression

SIGNIFICANCE

Breast cancer is the second leading cause of cancer-related deaths among women in the United States. Development and progression of malignancy are associated with diverse cell signaling pathways that control cell proliferation, survival, motility, invasion, and metastasis. Recent Advances: An increasing number of clinical studies have implicated a strong relationship between elevated tumor nitric oxide synthase-2 (NOS2) expression and poor patient survival.

CRITICAL ISSUES

Herein, we review what we believe to be key mechanisms in the role(s) of NOS2-derived nitric oxide (NO) as a driver of breast cancer disease progression. High NO increases cyclooxygenase-2 activity, hypoxia inducible factor-1 alpha protein stabilization, and activation of important cell signaling pathways, including phosphoinositide 3-kinase/protein kinase B, mitogen-activated protein kinase, epidermal growth factor receptor, and Ras, through post-translational protein modifications. Moreover, dysregulated NO flux within the tumor microenvironment has other important roles, including the promotion of angiogenesis and modulation of matrix metalloproteinase/tissue inhibitor matrix metalloproteinase associated with tumor progression.

FUTURE DIRECTIONS

The elucidation of these and other NO-driven pathways implicates NOS2 as a key driver of breast cancer disease progression and provides a new perspective in the identification of novel targets that may be therapeutically beneficial in the treatment of estrogen receptor-negative disease. Antioxid. Redox Signal. 26, 1044-1058.

Inhibition of Phosphodiesterase 5 and Increasing the Level of Cyclic Guanosine 3',5' Monophosphate by Hydroalcoholic Achillea wilhelmsii C. Koch Extract in Human Breast Cancer Cell Lines MCF-7 and MDA-Mb-468

This study aimed to investigate the effect of hydroalcoholic Achillea wilhelmsii C. Koch extract (HAWE) on phosphodiesterase 5 (PDE5) gene expression and cyclic guanosine 3',5' monophosphate (cGMP) signaling in the MCF-7 and MDA-Mb-468 cell lines. The effective dose (ED50) of HAWE was examined in both cell lines using a 3-(4,5-dimethylhiazol-2-yl)-2,5-diphenyltetrazolium bromide viability test, and the type of cell death was detected by flow cytometry. The expression of PDE5 and the concentration of cGMP were measured in a time-dependent manner in the ED50 by real-time polymerase chain reaction and a colorimetric assay, respectively. Treatment with HAWE showed 25 µg/mL to be the ED50 for both cell lines, and HAWE led to a reduction in the PDE5 messenger RNA expression. The intracellular cGMP increased in a time-dependent manner. The results showed that HAWE has an antiproliferative property in MCF-7 and MDA-Mb-468 cell lines through the cGMP pathway. Therefore, HAWE is a potential source to effectively isolate inhibitory PDE5.

PDE5 Overexpression in Well-Differentiated Thyroid Carcinomas Is Associated with Lymph Node Metastasis

Overexpression of PDE5 is observed in certain human cancers, but PDE5 expression in well-differentiated thyroid carcinoma (WDTC) is unknown. We therefore examined PDE5 expression and its relationship with the clinicopathological features of WDTC. Real-time qPCR and Western blotting were performed to analyze the expression of PDE5 mRNA and protein in paired WDTC tumor and adjacent nontumor tissues. Immunohistochemistry was used to analyze the expression of PDE5 in paraffin-embedded tissues obtained from 103 cases of WDTC. Statistical analyses were performed to examine the correlation between PDE5 expression and clinicopathological features. The expression of PDE5 mRNA and protein was upregulated in WDTC lesions compared to their paired noncancerous tissues. The expression of PDE5 was significantly correlated with age (P = 0.032), regional lymph node status (P = 0.004), and the presence of distant metastasis (P = 0.020). High PDE5 expression was more closely associated with lymph node involvement in patients over 45 years (OR = 15.60, P ≤ 0.05). Thus, PDE5 may be a potential biomarker in WDTC, particularly in patients with regional lymph node metastasis, which is associated with disease recurrence, treatment failure, and morbidity. PDE5 expression may also help predict the prognosis and recurrence of WDTC after surgery.

Phosphodiesterase 5/protein kinase G signal governs stemness of prostate cancer stem cells through Hippo pathway

Cancer stem cells (CSC) are critical for initiation, metastasis, and relapse of cancers, however, the underlying mechanism governing stemness of CSC remains unknown. Herein, we have investigated the roles of phosphodiesterase 5 (PDE5) in stemness of prostate cancer cells. Both PDE5 and WW domain-containing transcription regulator protein-1 (TAZ), a core effector of Hippo pathway, are highly expressed in the PC3-derived cancer stem cells (PCSC). Either TAZ knockdown or inhibition of PDE5 activity attenuated colony formation, altered expression patterns of stem cell markers, and enhanced cisplatin cytotoxicity, resulting in attenuation of stemness in PCSC. In addition, inhibition of PDE5 activity by its specific inhibitors activates cGMP-dependent protein kinase G (PKG), which in turn induces MST/LATS kinases, resulting in cytosolic degradation of TAZ and activation of Hippo pathway. Accordingly, knockdown of TAZ almost completely abolished PDE5 inhibitor-induced attenuation in stemness in cultured PCSC, whereas knockdown of TAZ not only abolished PDE5 inhibitor-induced attenuation in stemness but also facilitated PDE5 inhibitor-induced trans-differentiation in PCSC xenografts. Together, the present study has uncovered that PDE/cGMP/PKG signal targets to Hippo/TAZ pathway in maintaining stemness of PCSC, and suggested that PDE5 inhibitors in combination with chemotherapeutic agents could effectively prevent initiation, metastasis, and relapse of prostate cancer.

The Role of PDE5 Inhibitors and the NO/cGMP Pathway in Cancer

INTRODUCTION

Phosphodiesterase 5 (PDE5) inhibitors (PDE5i) have been used clinically for the treatment of erectile dysfunction, acting on the nitric oxide/cyclic guanosine monophosphate (NO/cGMP) signaling pathway. Simultaneously, researchers have elucidated the roles that this pathway plays in the regulation of cell proliferation, tumor development, and progression. As a result, our knowledge of PDE5i and cancer biology has expanded and provides an integration that holds great promise for some, but concern for others.

AIM

This review evaluates the role of PDE5i and the NO/cGMP signaling pathway in the pathogenesis and prevention of various malignancies.

METHODS

A literature review was performed with regard to the role of NO/cGMP pathway in tumor formation and prevention in preclinical and clinical studies. Studies that utilized PDE5i to further explore the involvement of this pathway also were included.

MAIN OUTCOME MEASURES

To evaluate whether PDE5i provide a potential benefit for treating and/or preventing malignancies; or if they create potential harm leading to the development of these malignancies.

RESULTS

The best available data suggest that the interactions between PDE5i and cancer are tumor- and tissue-specific. Currently, the effect of PDE5i use on melanoma development is being debated. Further clinical controversy lies in PDE5i use for penile rehabilitation after nerve-sparing prostate cancer surgery. Preclinical studies suggest that PDE5 inhibition could lead to a decreased risk of developing colorectal and breast cancer, leukemia, and myeloma. PDE5i also may provide an additional antitumor immune response. Finally, researchers have demonstrated a synergistic effect from combining PDE5i with current chemotherapeutic regimens.

CONCLUSION

Currently, there are inadequate data to make any conclusive statements regarding the role of PDE5i in cancer pathogenesis and how to alter clinical management. In order to create appropriate clinical guidelines, further experimental and clinical evidence is required.

Expression and Function of Phosphodiesterase Type 5 in Human Breast Cancer Cell Lines and Tissues: Implications for Targeted Therapy

PURPOSE

By catalyzing cGMP hydrolysis, phosphodiesterase (PDE) 5 is a critical regulator of its concentration and effects in different (patho)physiologic processes, including cancers. As PDE5 is a known druggable target, we investigated the clinical significance of its expression in breast cancer and the underlying mechanisms by which it may contribute to tumor progression.

EXPERIMENTAL DESIGN

PDE5 expression was evaluated in seven breast cancer cell lines by RT-PCR and immunoblotting. To examine the impact of PDE5 on cancer phenotype, MCF-7 cells expressing lower levels of the enzyme were engineered to stably overexpress PDE5. Proliferation was evaluated by MTT assays, motility and invasion by wound-healing/transmigration/invasion assays, transcriptome-profiling by RNA-sequencing, and Rho GTPase signaling activation by GST-pulldown assays and immunoblotting. Clinical relevance was investigated by IHC on tissues and retrospective studies from METABRIC cohort.

RESULTS

PDE5 is differentially expressed in each molecular subtype of both breast cancer cell lines and tissues, with higher levels representing a startling feature of HER2-positive and triple-negative breast cancers. A positive correlation was established between elevated PDE5 levels and cancers of high histologic grade. Higher PDE5 expression correlated with shorter patient survival in retrospective analyses. On molecular level, stable PDE5 overexpression in Luminal-A-like MCF-7 cells resulted in enhanced motility and invasion through Rho GTPase signaling activation. Treatment of PDE5-stable clones with selective ROCK or PDE5 inhibitors completely restored the less motile and weak invasive behavior of control vector cells.

CONCLUSIONS

PDE5 expression enhances breast cancer cell invasive potential, highlighting this enzyme as a novel prognostic candidate and an attractive target for future therapy in breast cancers. Clin Cancer Res; 22(9); 2271-82. ©2015 AACR.

The cyclic GMP/protein kinase G pathway as a therapeutic target in head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is an aggressive disease with high mortality. Treatments, which can result in significant morbidity, have not substantially changed in three decades. The second messenger cyclic GMP (cGMP), which targets protein kinase G (PKG), is generated by guanylate cyclases (GCs), and is rapidly hydrolyzed by phosphodiesterases (PDEs). Activation of the cGMP/PKG pathway is antineoplastic in several cancer types, but its impact on HNSCC has not been fully exploited. We found differential expression of critical components of this pathway in four HNSCC cell lines. Several activators of soluble GC (sGC), as well as inhibitors of PDE5, increased intracellular cGMP, reduced cell viability, and induced apoptosis in HNSCC cells. The apoptotic effects of the sGC activator BAY 41-2272 and the PDE5 inhibitor Tadalafil (Cialis) were mediated by PKG. Furthermore, Tadalafil substantially reduced the growth of CAL27-derived tumors in athymic mice. Several drugs which either activate sGC or inhibit PDE5 are approved for treatment of nonmalignant conditions. These drugs could be repurposed as novel and effective therapeutics in patients with head and neck cancer.

GRP78/Dna K Is a Target for Nexavar/Stivarga/Votrient in the Treatment of Human Malignancies, Viral Infections and Bacterial Diseases

Prior tumor cell studies have shown that the drugs sorafenib (Nexavar) and regorafenib (Stivarga) reduce expression of the chaperone GRP78. Sorafenib/regorafenib and the multi‐kinase inhibitor pazopanib (Votrient) interacted with sildenafil (Viagra) to further rapidly reduce GRP78 levels in eukaryotes and as single agents to reduce Dna K levels in prokaryotes. Similar data were obtained in tumor cells in vitro and in drug‐treated mice for: HSP70, mitochondrial HSP70, HSP60, HSP56, HSP40, HSP10, and cyclophilin A. Prolonged ‘rafenib/sildenafil treatment killed tumor cells and also rapidly decreased the expression of: the drug efflux pumps ABCB1 and ABCG2; and NPC1 and NTCP, receptors for Ebola/Hepatitis A and B viruses, respectively. Pre‐treatment with the ‘Rafenib/sildenafil combination reduced expression of the Coxsackie and Adenovirus receptor in parallel with it also reducing the ability of a serotype 5 Adenovirus or Coxsackie virus B4 to infect and to reproduce. Sorafenib/pazopanib and sildenafil was much more potent than sorafenib/pazopanib as single agents at preventing Adenovirus, Mumps, Chikungunya, Dengue, Rabies, West Nile, Yellow Fever, and Enterovirus 71 infection and reproduction. ‘Rafenib drugs/pazopanib as single agents killed laboratory generated antibiotic resistant E. coli which was associated with reduced Dna K and Rec A expression. Marginally toxic doses of ‘Rafenib drugs/pazopanib restored antibiotic sensitivity in pan‐antibiotic resistant bacteria including multiple strains of bla_kpcKlebsiella pneumoniae. Thus, Dna K is an antibiotic target for sorafenib, and inhibition of GRP78/Dna K has therapeutic utility for cancer and for bacterial and viral infections. J. Cell. Physiol. 230: 2552–2578, 2015. © 2015 The Authors. Journal of Cellular Physiology published by Wiley Periodicals, Inc.

OSU-03012 and Viagra Treatment Inhibits the Activity of Multiple Chaperone Proteins and Disrupts the Blood-Brain Barrier: Implications for Anti-Cancer Therapies

We examined the interaction between OSU‐03012 (also called AR‐12) with phosphodiesterase 5 (PDE5) inhibitors to determine the role of the chaperone glucose‐regulated protein (GRP78)/BiP/HSPA5 in the cellular response. Sildenafil (Viagra) interacted in a greater than additive fashion with OSU‐03012 to kill stem‐like GBM cells. Treatment of cells with OSU‐03012/sildenafil: abolished the expression of multiple oncogenic growth factor receptors and plasma membrane drug efflux pumps and caused a rapid degradation of GRP78 and other HSP70 and HSP90 family chaperone proteins. Decreased expression of plasma membrane receptors and drug efflux pumps was dependent upon enhanced PERK‐eIF2α‐ATF4‐CHOP signaling and was blocked by GRP78 over‐expression. In vivo OSU‐03012/sildenafil was more efficacious than treatment with celecoxib and sildenafil at killing tumor cells without damaging normal tissues and in parallel reduced expression of ABCB1 and ABCG2 in the normal brain. The combination of OSU‐03012/sildenafil synergized with low concentrations of sorafenib to kill tumor cells, and with lapatinib to kill ERBB1 over‐expressing tumor cells. In multiplex assays on plasma and human tumor tissue from an OSU‐03012/sildenafil treated mouse, we noted a profound reduction in uPA signaling and identified FGF and JAK1/2 as response biomarkers for potentially suppressing the killing response. Inhibition of FGFR signaling and to a lesser extent JAK1/2 signaling profoundly enhanced OSU‐03012/sildenafil lethality. J. Cell. Physiol. 230: 1982–1998, 2015. © 2015 The Authors. Journal of Cellular Physiology Published by Wiley Periodicals, Inc.

GRP78/BiP/HSPA5/Dna K is a universal therapeutic target for human disease

The chaperone GRP78/Dna K is conserved throughout evolution down to prokaryotes. The GRP78 inhibitor OSU-03012 (AR-12) interacted with sildenafil (Viagra) or tadalafil (Cialis) to rapidly reduce GRP78 levels in eukaryotes and as a single agent reduce Dna K levels in prokaryotes. Similar data with the drug combination were obtained for: HSP70, HSP90, GRP94, GRP58, HSP27, HSP40 and HSP60. OSU-03012/sildenafil treatment killed brain cancer stem cells and decreased the expression of: NPC1 and TIM1; LAMP1; and NTCP1, receptors for Ebola/Marburg/Hepatitis A, Lassa fever, and Hepatitis B viruses, respectively. Pre-treatment with OSU-03012/sildenafil reduced expression of the coxsakie and adenovirus receptor in parallel with it also reducing the ability of a serotype 5 adenovirus or coxsakie virus B4 to infect and to reproduce. Similar data were obtained using Chikungunya, Mumps, Measles, Rubella, RSV, CMV, and Influenza viruses. OSU-03012 as a single agent at clinically relevant concentrations killed laboratory generated antibiotic resistant E. coli and clinical isolate multi-drug resistant N. gonorrhoeae and MRSE which was in bacteria associated with reduced Dna K and Rec A expression. The PDE5 inhibitors sildenafil or tadalafil enhanced OSU-03012 killing in N. gonorrhoeae and MRSE and low marginally toxic doses of OSU-03012 could restore bacterial sensitivity in N. gonorrhoeae to multiple antibiotics. Thus, Dna K and bacterial phosphodiesterases are novel antibiotic targets, and inhibition of GRP78 is of therapeutic utility for cancer and also for bacterial and viral infections. J. Cell. Physiol. 230: 1661–1676, 2015. © 2014 The Authors. Journal of Cellular Physiology Published by Wiley Periodicals, Inc.

PDE5 inhibitors as therapeutics for heart disease, diabetes and cancer

The phosphodiesterase 5 (PDE5) inhibitors, including sildenafil (Viagra™), vardenafil (Levitra™), and tadalafil (Cialis™) have been developed for treatment of erectile dysfunction. Moreover, sildenafil and tadalafil are used for the management of pulmonary arterial hypertension in patients. Since our first report showing the cardioprotective effect of sildenafil in 2002, there has been tremendous growth of preclinical and clinical studies on the use of PDE5 inhibitors for cardiovascular diseases and cancer. Numerous animal studies have demonstrated that PDE5 inhibitors have powerful protective effect against myocardial ischemia/reperfusion (I/R) injury, doxorubicin cardiotoxicity, ischemic and diabetic cardiomyopathy, cardiac hypertrophy, Duchenne muscular dystrophy and the improvement of stem cell efficacy for myocardial repair. Mechanistically, PDE5 inhibitors protect the heart against I/R injury through increased expression of nitric oxide synthases, activation of protein kinase G (PKG), PKG-dependent hydrogen sulfide generation, and phosphorylation of glycogen synthase kinase-3β - a master switch immediately proximal to mitochondrial permeability transition pore and the end effector of cardioprotection. In addition, PDE5 inhibitors enhance the sensitivity of certain types of cancer to standard chemotherapeutic drugs, including doxorubicin. Many clinical trials with PDE5 inhibitors have focused on the potential cardiovascular and anti-cancer benefits. Despite mixed results of these clinical trials, there is a continuing strong interest by basic scientists and clinical investigators in exploring their new clinical uses. It is our hope that future new mechanistic investigations and carefully designed clinical trials would help in reaping additional benefits of PDE5 inhibitors for cardiovascular disease and cancer in patients.

Cyclic nucleotide phosphodiesterases: important signaling modulators and therapeutic targets

By catalyzing hydrolysis of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), cyclic nucleotide phosphodiesterases are critical regulators of their intracellular concentrations and their biological effects. As these intracellular second messengers control many cellular homeostatic processes, dysregulation of their signals and signaling pathways initiate or modulate pathophysiological pathways related to various disease states, including erectile dysfunction, pulmonary hypertension, acute refractory cardiac failure, intermittent claudication, chronic obstructive pulmonary disease, and psoriasis. Alterations in expression of PDEs and PDE-gene mutations (especially mutations in PDE6, PDE8B, PDE11A, and PDE4) have been implicated in various diseases and cancer pathologies. PDEs also play important role in formation and function of multimolecular signaling/regulatory complexes, called signalosomes. At specific intracellular locations, individual PDEs, together with pathway-specific signaling molecules, regulators, and effectors, are incorporated into specific signalosomes, where they facilitate and regulate compartmentalization of cyclic nucleotide signaling pathways and specific cellular functions. Currently, only a limited number of PDE inhibitors (PDE3, PDE4, PDE5 inhibitors) are used in clinical practice. Future paths to novel drug discovery include the crystal structure-based design approach, which has resulted in generation of more effective family-selective inhibitors, as well as burgeoning development of strategies to alter compartmentalized cyclic nucleotide signaling pathways by selectively targeting individual PDEs and their signalosome partners.

Regulation of OSU-03012 toxicity by ER stress proteins and ER stress-inducing drugs

The present studies examined the toxic interaction between the non-coxib celecoxib derivative OSU-03012 and phosphodiesterase 5 (PDE5) inhibitors, and also determined the roles of endoplasmic reticulum stress response regulators in cell survival. PDE5 inhibitors interacted in a greater than additive fashion with OSU-03012 to kill parental glioma and stem-like glioma cells. Knockdown of the endoplasmic reticulum stress response proteins IRE1 or XBP1 enhanced the lethality of OSU-03012, and of [OSU-03012 + PDE5 inhibitor] treatment. Pan-caspase and caspase-9 inhibition did not alter OSU-03012 lethality but did abolish enhanced killing in the absence of IRE1 or XBP1. Expression of the mitochondrial protective protein BCL-XL or the caspase-8 inhibitor c-FLIP-s, or knockdown of death receptor CD95 or the death receptor caspase-8 linker protein FADD, suppressed killing by [OSU-03012 + PDE5 inhibitor] treatment. CD95 activation was blocked by the nitric oxide synthase inhibitor L-NAME. Knockdown of the autophagy regulatory proteins Beclin1 or ATG5 protected the cells from OSU-03012 and from [OSU-03012 + PDE5 inhibitor] toxicity. Knockdown of IRE1 enhanced OSU-03012/[OSU-03012 + PDE5 inhibitor]-induced JNK activation, and inhibition of JNK suppressed the elevated killing caused by IRE1 knockdown. Knockdown of CD95 blunted JNK activation. Collectively, our data demonstrate that PDE5 inhibitors recruit death receptor signaling to enhance OSU-03012 toxicity in glioblastoma multiforme (GBM) cells.

cGMP signaling as a target for the prevention and treatment of breast cancer

One in eight women in the United States will be diagnosed with invasive breast cancer in her lifetime. Advances in therapeutic strategies, diagnosis, and improved awareness have resulted in a significant reduction in breast cancer related mortality. However, there is a continued need for more effective and less toxic drugs for both the prevention and the treatment of breast cancer in order to see a continued decline in the morbidity and mortality associated with this disease. Recent studies suggest that the cGMP signaling pathway may be aberrantly regulated in breast cancer. As such, this pathway may serve as a source of novel targets for future breast cancer drug discovery efforts. This review provides an overview of cGMP signaling in normal physiology and in breast cancer as well as current strategies being investigated for targeting this pathway in breast cancer.

PDE5 inhibitors enhance the lethality of standard of care chemotherapy in pediatric CNS tumor cells

We determined whether clinically relevant phosphodiesterase 5 (PDE5) inhibitors interacted with clinically relevant chemotherapies to kill medulloblastoma cells. In medulloblastoma cells PDE5 inhibitors interacted in a greater than additive fashion with vincristine/etoposide/cisplatin to cause cell death. Knockdown of PDE5 expression recapitulated the combination effects of PDE5 inhibitor drugs with chemotherapy drugs. Expression of dominant negative caspase 9 did not significantly inhibit chemotherapy lethality but did significantly reduce enhanced killing in combination with the PDE5 inhibitor sildenafil. Overexpression of BCL-XL and c-FLIP-s suppressed individual and combination drug toxicities. Knockdown of CD95 or FADD suppressed drug combination toxicity. Treatment with PDE5 inhibitors and chemotherapy drugs promoted autophagy which was maximal at ~12 h post-treatment, and in a cell type-dependent manner knockdown of Beclin1 or ATG5 either suppressed or enhanced drug combination lethality. PDE5 inhibitors enhanced the induction of chemotherapy-induced DNA damage in a nitric oxide synthase-dependent fashion. In conclusion, our data demonstrate that the combination of PDE5 inhibitors with standard of care chemotherapy agents for medulloblastoma represents a possible novel modality for future treatment of this disease.

Phosphodiesterase 5 inhibitors enhance chemotherapy killing in gastrointestinal/genitourinary cancer cells

The present studies determined whether clinically relevant phosphodiesterase 5 (PDE5) inhibitors interacted with clinically relevant chemotherapies to kill gastrointestinal/genitourinary cancer cells. In bladder cancer cells, regardless of H-RAS mutational status, at clinically achievable doses, PDE5 inhibitors interacted in a greater than additive fashion with doxorubicin/mitomycin C/gemcitabine/cisplatin/paclitaxel to cause cell death. In pancreatic tumor cells expressing mutant active K-RAS, PDE5 inhibitors interacted in a greater than additive fashion with doxorubicin/gemcitabine/paclitaxel to cause cell death. The most potent PDE5 inhibitor was sildenafil. Knock down of PDE5 expression recapitulated the combination effects of PDE5 inhibitor drugs with chemotherapy drugs. Expression of cellular FLICE-like inhibitory protein-short did not significantly inhibit chemotherapy lethality but did significantly reduce enhanced killing in combination with sildenafil. Overexpression of B-cell lymphoma-extra large suppressed individual and combination drug toxicities. Knock down of CD95 or Fas-associated death domain protein suppressed drug combination toxicity. Combination toxicity was also abolished by necrostatin or receptor interacting protein 1 knock down. Treatment with PDE5 inhibitors and chemotherapy drugs promoted autophagy, which was maximal at ∼24 hour posttreatment, and 3-methyl adenine or knock down of Beclin1 suppressed drug combination lethality by ∼50%. PDE5 inhibitors enhanced and prolonged the induction of DNA damage as judged by Comet assays and γhistone 2AX (γH2AX) and checkpoint kinase 2 (CHK2) phosphorylation. Knock down of ataxia telangiectasia mutated suppressed γH2AX and CHK2 phosphorylation and enhanced drug combination lethality. Collectively our data demonstrate that the combination of PDE5 inhibitors with standard of care chemotherapy agents for gastrointestinal/genitourinary cancers represents a novel modality.