Sulindac selectively inhibits colon tumor cell growth by activating the cGMP/PKG pathway to suppress Wnt/β-catenin signaling

PDE5 inhibitors enhance the lethality of pemetrexed through inhibition of multiple chaperone proteins and via the actions of cyclic GMP and nitric oxide

Phosphodiesterase 5 (PDE5) inhibitors prevent the breakdown of cGMP that results in prolonged protein kinase G activation and the generation of nitric oxide. PDE5 inhibitors enhanced the anti-NSCLC cell effects of the NSCLC therapeutic pemetrexed. [Pemetrexed + sildenafil] activated an eIF2α – ATF4 – CHOP – Beclin1 pathway causing formation of toxic autophagosomes; activated a protective IRE1 – XBP-1 – chaperone induction pathway; and activated a toxic eIF2α – CHOP – DR4 / DR5 / CD95 induction pathway. [Pemetrexed + sildenafil] reduced the expression of c-FLIP-s, MCL-1 and BCL-XL that was blocked in a cell-type -dependent fashion by either over-expression of HSP90 / GRP78 / HSP70 / HSP27 or by blockade of eIF2α-CHOP signaling. Knock down of PKGI/II abolished the ability of sildenafil to enhance pemetrexed toxicity whereas pan-inhibition of NOS using L-NAME or knock down of [iNOS + eNOS] only partially reduced the lethal drug interaction. Pemetrexed reduced the ATPase activities of HSP90 and HSP70 in an ATM-AMPK-dependent fashion that was enhanced by sildenafil signaling via PKGI/II. The drug combination activated an ATM-AMPK-TSC2 pathway that was associated with reduced mTOR S2448 and ULK-1 S757 phosphorylation and increased ULK-1 S317 and ATG13 S318 phosphorylation. These effects were prevented by chaperone over-expression or by expression of an activated form of mTOR that prevented autophagosome formation and reduced cell killing. In two models of NSCLC, sildenafil enhanced the ability of pemetrexed to suppress tumor growth. Collectively we argue that the combination of [pemetrexed + PDE5 inhibitor] should be explored in a new NSCLC phase I trial.

Construction of a ceRNA network reveals potential lncRNA biomarkers in rectal adenocarcinoma

Competing endogenous RNAs (ceRNAs) render the functions of long non-coding RNAs (lncRNAs) more complicated during cancer processes. Potential lncRNA biomarkers and their roles as ceRNAs have not been clearly described for rectal adenocarcinoma (READ). In the present study, we extracted data from The Cancer Genome Atlas (TCGA) including data from 167 tumor samples and 10 adjacent non-tumor samples. A total of 202 lncRNAs, 190 microRNAs (miRNAs) and 1,530 mRNAs were identified as READ-specific RNAs [log₂(fold-change)>2, FDR<0.01]. The Gene Ontology (GO) biological processes and the Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathways were analysed for 1,530 specific mRNAs. Among 202 READ-specific lncRNAs, 7 lncRNAs were identified as being associated with overall survival of READ patients. Then, a ceRNA network was constructed with 34 key lncRNAs, 25 miRNAs and 65 mRNAs. A total of 7 lncRNAs from the network were revealed to be linked to clinical features. The results of qRT-PCR ascertained that our analysis was credible. Overall, this research provides a novel perspective from which to study the lncRNA-related ceRNA network in READ and assists in the identification of new potential biomarkers to be used for diagnostic and prognostic purposes.

RAC1 GTP-ase signals Wnt-beta-catenin pathway mediated integrin-directed metastasis-associated tumor cell phenotypes in triple negative breast cancers

The acquisition of integrin-directed metastasis-associated (ID-MA) phenotypes by Triple-Negative Breast Cancer (TNBC) cells is caused by an upregulation of the Wnt-beta-catenin pathway (WP). We reported that WP is one of the salient genetic features of TNBC. RAC-GTPases, small G-proteins which transduce signals from cell surface proteins including integrins, have been implicated in tumorigenesis and metastasis by their role in essential cellular functions like motility. The collective percentage of alteration(s) in RAC1 in ER+ve BC was lower as compared to ER-ve BC (35% vs 57%) (brca/tcga/pub2015). High expression of RAC1 was associated with poor outcome for RFS with HR=1.48 [CI: 1.15-1.9] p=0.0019 in the Hungarian ER-veBC cohort. Here we examined how WP signals are transduced via RAC1 in the context of ID-MA phenotypes in TNBC. Using pharmacological agents (sulindac sulfide), genetic tools (beta-catenin siRNA), WP modulators (Wnt-C59, XAV939), RAC1 inhibitors (NSC23766, W56) and WP stimulations (LWnt3ACM, Wnt3A recombinant) in a panel of 6-7 TNBC cell lines, we studied fibronectin-directed (1) migration, (2) matrigel invasion, (3) RAC1 and Cdc42 activation, (4) actin dynamics (confocal microscopy) and (5) podia-parameters. An attenuation of WP, which (a) decreased cellular levels of beta-catenin, as well as its nuclear active-form, (b) decreased fibronectin-induced migration, (c) decreased invasion, (d) altered actin dynamics and (e) decreased podia-parameters was successful in blocking fibronectin-mediated RAC1/Cdc42 activity. Both Wnt-antagonists and RAC1 inhibitors blocked fibronectin-induced RAC1 activation and inhibited the fibronectin-induced ID-MA phenotypes following specific WP stimulation by LWnt3ACM as well as Wnt3A recombinant protein. To test a direct involvement of RAC1-activation in WP-mediated ID-MA phenotypes, we stimulated brain-metastasis specific MDA-MB231BR cells with LWnt3ACM. LWnt3ACM-stimulated fibronectin-directed migration was blocked by RAC1 inhibition in MDA-MB231BR cells. In the light of our previous report that WP upregulation causes ID-MA phenotypes in TNBC tumor cells, here we provide the first mechanism based evidence to demonstrate that WP upregulation signals ID-MA tumor cell phenotypes in a RAC1-GTPase dependent manner involving exchange-factors like TIAM1 and VAV2. Our study demonstrates for the first time that beta-catenin-RAC1 cascade signals integrin-directed metastasis-associated tumor cell phenotypes in TNBC.

PDE5 inhibition eliminates cancer stem cells via induction of PKA signaling

Cancer stem cells (CSCs) are involved in metastasis and resistance development, thus affecting anticancer therapy efficacy. The underlying pathways required for CSC maintenance and survival are not fully understood and only a limited number of treatment strategies to specifically target CSCs have been identified. To identify novel CSC targeting compounds, we here set-up an aldehyde dehydrogenase (ALDH)-based phenotypic screening system that allows for an automated and standardized identification of CSCs. By staining cancer cells for ALDH activity and applying high-content-based single-cell population analysis, the proportion of a potential CSC subpopulation with significantly higher ALDH activity (ALDH_high) can be quantified in a heterogeneous cell population. We confirmed high ALDH activity as surrogate marker for the CSC subpopulation in vitro and validated Wnt signaling as an essential factor for the maintenance of CSCs in SUM149 breast cancer cells. In a small molecule screen, we identified phosphodiesterase type 5 (PDE5) inhibition as potential strategy to target CSC maintenance and survival in multiple cancer cell lines. CSC elimination by PDE5 inhibition was not dependent on PKG signaling, and we suggest a novel mechanism in which PDE5 inhibition leads to elevated cGMP levels that stimulate cAMP/PKA signaling to eliminate CSCs.

Identification of genomic expression differences between right-sided and left-sided colon cancer based on bioinformatics analysis

Introduction

More and more findings have demonstrated that right-sided colon cancers (RCC) and left-sided colon cancers (LCC) are distinct clinical and biological entities and suggest that they should be treated as different diseases. However, the reasons why RCC and LCC harbor different clinical and biological features remain unclear.

Materials and methods

To identify the genomic expression differences between RCC and LCC and uncover the mechanisms underlying these differences, we chose the gene expression profiles of GSE14333 from the Gene Expression Omnibus (GEO) database as an object of study. Then, a systematic and integrative bioinformatics analysis was performed to research the possible mechanism of the differentially expressed (DE) genes from the Gene Expression Omnibus dataset including gene ontology (GO) analysis, pathway enrichment analysis, protein-protein interaction (PPI) network construction, and module analysis. Totally, we extracted 3,793 DE genes from samples of colon cancer including 1,961 genes upregulated in RCC and 1,832 genes upregulated in LCC from the selected dataset.

Results

The results of GO and pathway enrichment analysis indicated that RCC and LCC could predispose to different pathways regulated by different genes. Based on the PPI network, PCNA, TP53, HSP90AA1, CSNK2A1, UBB, LRRK2, ABL1, PRKACA, CAV1, and JUN were identified as the key hub genes. Also, significant modules were screened from the PPI network.

Conclusion

In conclusion, the present study indicated that the identified genes and pathways may promote new insights into the underlying molecular mechanisms contributing to the difference between RCC and LCC and might be used as specific therapeutic targets and prognostic markers for the personalized treatment of RCC and LCC.

WNT Signaling in Cardiac and Vascular Disease

WNT signaling is an elaborate and complex collection of signal transduction pathways mediated by multiple signaling molecules. WNT signaling is critically important for developmental processes, including cell proliferation, differentiation and tissue patterning. Little WNT signaling activity is present in the cardiovascular system of healthy adults, but reactivation of the pathway is observed in many pathologies of heart and blood vessels. The high prevalence of these pathologies and their significant contribution to human disease burden has raised interest in WNT signaling as a potential target for therapeutic intervention. In this review, we first will focus on the constituents of the pathway and their regulation and the different signaling routes. Subsequently, the role of WNT signaling in cardiovascular development is addressed, followed by a detailed discussion of its involvement in vascular and cardiac disease. After highlighting the crosstalk between WNT, transforming growth factor-β and angiotensin II signaling, and the emerging role of WNT signaling in the regulation of stem cells, we provide an overview of drugs targeting the pathway at different levels. From the combined studies we conclude that, despite the sometimes conflicting experimental data, a general picture is emerging that excessive stimulation of WNT signaling adversely affects cardiovascular pathology. The rapidly increasing collection of drugs interfering at different levels of WNT signaling will allow the evaluation of therapeutic interventions in the pathway in relevant animal models of cardiovascular diseases and eventually in patients in the near future, translating the outcomes of the many preclinical studies into a clinically relevant context.

New cGMP analogues restrain proliferation and migration of melanoma cells

Melanoma is one of the most aggressive cancers and displays high resistance to conventional chemotherapy underlining the need for new therapeutic strategies. The cGMP/PKG signaling pathway was detected in melanoma cells and shown to reduce migration, proliferation and to increase apoptosis in different cancer types. In this study, we evaluated the effects on cell viability, cell death, proliferation and migration of novel dimeric cGMP analogues in two melanoma cell lines (MNT1 and SkMel28). These new dimeric cGMP analogues, by activating PKG with limited effects on PKA, significantly reduced proliferation, migration and increased cell death. No decrease in cell viability was observed in non-tumor cells suggesting a tumor-specific effect. These effects observed in melanoma are possibly mediated by PKG2 activation based on the decreased toxic effects in tumor cell lines not expressing PKG2. Finally, PKG-associated phosphorylation of vasodilator-stimulated-phosphoprotein (VASP), linked to cell death, proliferation and migration was found increased and with a change of subcellular localization. Increased phosphorylation of RhoA induced by activation of PKG may also contribute to reduced migration ability of the SkMel28 melanoma cell line when treated with cGMP analogues. These findings suggest that the cGMP/PKG pathway can be envisaged as a therapeutic target of novel dimeric cGMP analogues for the treatment of melanoma.

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.

New dimeric cGMP analogues reduce proliferation in three colon cancer cell lines

Activation of the cGMP-dependent protein kinase G (PKG) can inhibit growth and/or induce apoptosis in colon cancer. In this study we evaluated the effects on cell viability, cell death and proliferation of novel dimeric cGMP analogues, compared to a monomeric compound. Three colon cancer cell lines, which only express isoform 2 of PKG, were treated with these novel cGMP analogues and responded with increased PKG activity. cGMP analogues reduced cell viability in the three cell lines and this was due to a cytostatic rather than cytotoxic effect. These findings suggest that activation of PKG2 can be a therapeutic target in the treatment of colon cancer and, most importantly, that dimeric cGMP analogues can further improve the beneficial effects previously observed with monomeric cGMP analogues.

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.

Modulating the wnt signaling pathway with small molecules

Wnt signaling is a critical component during embryonic development and also plays an important role in regulating adult tissue homeostasis. Abnormal activation of Wnt signaling has been implicated in many cancers, while reduced activity of Wnt signaling leads to poor wound healing and structural formations. Thus, extensive efforts have been focused on developing small molecules that have potential to either inhibit or activate the pathway, hoping these molecules can offer leads for novel approaches in treating different human diseases. Many small-molecule inhibitors specifically target various elements, such as Frizzled, Disheveled, Porcupine, or Tankyrase, within the Wnt signaling pathways. These small molecules not only have the potential to be further developed as therapeutic reagents, but they may also be used as chemical probes to dissect the underlying mechanism of the Wnt signaling pathways. Therefore, their respective mechanisms and effective dosages are highly pertinent. Aiming to provide an overview of those molecules in a concise, easy-to-use manner, we summarize and organize the current research on them so that it may be helpful for utilization in different studies.

Bifunctional conjugates with potent inhibitory activity towards cyclooxygenase and histone deacetylase

We herein disclose a series of compounds with potent inhibitory activities towards histone deacetylases (HDAC) and cyclooxygenases (COX). These compounds potently inhibited the growth of cancer cell lines consistent with their anti-COX and anti-HDAC activities. While compound 2b showed comparable level of COX-2 selectivity as celecoxib, compound 11b outperformed indomethacin in terms of selectivity towards COX-2 relative to COX-1. An important observation with our lead compounds (2b, 8, 11b, and 17b) is their enhanced cytotoxicity towards androgen dependent prostate cancer cell line (LNCaP) relative to androgen independent prostate cancer cell line (DU-145). Interestingly, compounds 2b and 17b arrested the cell cycle progression of LNCaP in the S-phase, while compound 8 showed a G0/G1 arrest, similar to SAHA. Relative to SAHA, these compounds displayed tumor-selective cytotoxicity as they have low anti-proliferative activity towards healthy cells (VERO); an attribute that makes them attractive candidates for drug development.

β-catenin nuclear translocation in colorectal cancer cells is suppressed by PDE10A inhibition, cGMP elevation, and activation of PKG

Phosphodiesterase 10A (PDE10) is a cGMP and cAMP degrading PDE isozyme that is highly expressed in the brain striatum where it appears to play an important role in cognition and psychomotor activity. PDE10 inhibitors are being developed for the treatment of schizophrenia and Huntington's disease and are generally well tolerated, possibly because of low expression levels in most peripheral tissues. We recently reported high levels of PDE10 in colon tumors and that genetic silencing of PDE10 by siRNA or inhibition with small molecule inhibitors can suppress colon tumor cell growth with a high degree of selectivity over normal colonocytes (Li et al., Oncogene 2015). These observations suggest PDE10 may have an unrecognized role in tumorigenesis. Here we report that the concentration range by which the highly specific PDE10 inhibitor, Pf-2545920 (MP-10), inhibits colon tumor cell growth parallels the concentration range required to increase cGMP and cAMP levels, and activates PKG and PKA, respectively. Moreover, PDE10 knockdown by shRNA reduces the sensitivity of colon tumor cells to the growth inhibitory activity of Pf-2545920. Pf-2545920 also inhibits the translocation of β-catenin to the nucleus, thereby reducing β-catenin mediated transcription of survivin, resulting in caspase activation and apoptosis. PDE10 mRNA was also found to be elevated in colon tumors compared with normal tissues. These findings suggest that PDE10 can be targeted for cancer therapy or prevention whereby inhibition results in cGMP elevation and PKG activation to reduce β-catenin-mediated transcription of survival proteins leading to the selective apoptosis of cancer cells.

Phosphodiesterase-5 inhibition suppresses colonic inflammation-induced tumorigenesis via blocking the recruitment of MDSC

Phosphodiesterase 5 (PDE-5) is a major isoform of cGMP phosphodiesterase in diverse tissues and plays a critical role in regulating intracellular cGMP concentrations. However, the distribution and expression of PDE-5 in colitis-related colon cancer was still unclear, not even the function and mechanism. Western blotting and ELISA were performed to detect colonic PDE-5 expression in AOM/DSS-induced tumorigenesis model. Sildenafil, a specific PDE-5 inhibitor, was used to treat AOM/DSS-induced and AOM-induced colonic tumorigenesis model and DSS-induced colitis model. The leukocyte infiltration in colonic tissue was examined by flow cytometry and immunofluorescence staining. Further matrigel-based invasion assay was employed to determine the effects of Sildenafil on myeloid-derived suppressor cell (MDSC) in vitro. We first demonstrated the upregulation of colonic PDE-5 expression and the prevention role of PDE-5 inhibition in AOM/DSS-induced tumorigenesis model. More importantly, PDE-5 inhibitor Sildenafil inhibited colonic tumorigenesis dependent on inflammation and suppressed DSS-induced colitis. Molecular mechanism investigation indicated that Sildenafil regulated inflammation microenvironment via directly inhibiting MDSC infiltration in colonic tissue. The study provides solid evidence for the use of PDE-5 inhibitor in preventing and treating colonic inflammation-related tumorigenesis.

The interaction between the Wnt/β-catenin signaling cascade and PKG activation in cancer

The activation of the Wnt/β-catenin signaling cascade has been well studied and documented in colorectal cancer (CRC). The long-term use of non-steroidal anti-inflammatory drugs (NSAIDs) has been shown to reduce the incidence and risk of death from CRC in numerous epidemiological studies. The NSAID sulindac has also been reported to cause regression of precancerous adenomas in individuals with familial adenomatous polyposis who are at high risk of developing CRC. The mechanism responsible for cancer chemopreventive activity of NSAIDs is not well understood but may be unrelated to their cyclooxygenase inhibitory activity. Emerging evidence suggests that sulindac inhibits the growth of colon tumor cells by suppressing the activity of certain phosphodiesterase isozymes to activate cGMP-dependent protein kinase, PKG, through the elevation of the second messenger cyclic guanosine monophosphote, cGMP. PKG activation has been shown to inhibit the nuclear translocation of β-catenin, reduce β-catenin mRNA and protein levels, and suppress the transcriptional activity of β-catenin. This review describes the relationship between the Wnt/β-catenin signaling cascade and the activation of PKG through PDE inhibition and elevation of intracellular cGMP levels.

Soluble guanylate cyclase stimulators increase sensitivity to cisplatin in head and neck squamous cell carcinoma cells

Head and neck squamous cell carcinoma (HNSCC) is an aggressive and often fatal disease. Cisplatin is the most common chemotherapeutic drug in the treatment of HNSCC, but intrinsic and acquired resistance are frequent, and severe side effects occur at high doses. The second messenger cyclic GMP (cGMP) is produced by soluble guanylate cyclase (sGC). We previously reported that activation of the cGMP signaling cascade caused apoptosis in HNSCC cells, while others found that this pathway enhances cisplatin efficacy in some cell types. Here we found that sGC stimulators reduced HNSCC cell viability synergistically with cisplatin, and enhanced apoptosis by cisplatin. Moreover, the sGC stimulators effectively reduced viability in cells with acquired cisplatin resistance, and were synergistic with cisplatin. The sGC stimulator BAY 41-2272 reduced expression of the survival proteins EGFR and β-catenin, and increased pro-apoptotic Bax, suggesting a potential mechanism for the anti-tumorigenic effects of these drugs. The sGC stimulator Riociguat is FDA-approved to treat pulmonary hypertension, and others are being studied for therapeutic use in several diseases. These drugs could provide valuable addition or alternative to cisplatin in the treatment of HNSCC.

Consumption of Red/Processed Meat and Colorectal Carcinoma: Possible Mechanisms Underlying the Significant Association

Epidemiology and experimental studies provide an overwhelming support of the notion that diets high in red or processed meat accompany an elevated risk of developing pre-neoplastic colorectal adenoma and frank colorectal carcinoma (CRC). The underlying mechanisms are disputed; thus several hypotheses have been proposed. A large body of reports converges, however, on haem and nitrosyl haem as major contributors to the CRC development, presumably acting through various mechanisms. Apart from a potentially higher intestinal mutagenic load among consumers on a diet rich in red/processed meat, other mechanisms involving subtle interference with colorectal stem/progenitor cell survival or maturation are likewise at play. From an overarching perspective, suggested candidate mechanisms for red/processed meat-induced CRC appear as three partly overlapping tenets: (i) increased N-nitrosation/oxidative load leading to DNA adducts and lipid peroxidation in the intestinal epithelium, (ii) proliferative stimulation of the epithelium through haem or food-derived metabolites that either act directly or subsequent to conversion, and (iii) higher inflammatory response, which may trigger a wide cascade of pro-malignant processes. In this review, we summarize and discuss major findings of the area in the context of potentially pertinent mechanisms underlying the above-mentioned association between consumption of red/processed meat and increased risk of developing CRC.

Phosphodiesterases in non-neoplastic appearing colonic mucosa from patients with colorectal neoplasia

Background

Intracellular signaling through cyclic nucleotides, both cyclic AMP and cyclic GMP, is altered in colorectal cancer. Accordingly, it is hypothesized that an underlying mechanism for colorectal neoplasia involves altered function of phosphodiesterases (PDEs), which affects cyclic nucleotide degradation. Here we present an approach to evaluate the function of selected cyclic nucleotide-PDEs in colonic endoscopic biopsies from non-neoplastic appearing mucosa.

Methods

Biopsies were obtained from patients with and without colorectal neoplasia. Activities of PDEs were characterized functionally by measurements of transepithelial ion transport and their expression and localization by employing real-time qPCR and immunohistochemistry.

Results

In functional studies PDE subtype-4 displayed lower activity in colorectal neoplasia patients (p = 0.006). Furthermore, real-time qPCR analysis showed overexpression of subtype PDE4B (p = 0.002) and subtype PDE5A (p = 0.02) in colorectal neoplasia patients. Finally, immunohistochemistry for 7 PDE isozymes demonstrated the presence of all 7 isozymes, albeit with weak reactions, and with no differences in localization between colorectal neoplasia and control patients. Of note, quantification of PDE subtype immunostaining revealed a lower amount of PDE3A (p = 0.04) and a higher amount of PDE4B (p = 0.02) in samples from colorectal neoplasia patients.

Conclusion

In conclusion, functional data indicated lower activity of PDE4 subtypes while expressional and abundance data indicated a higher expression of PDE4B in patients with colorectal neoplasia. We suggest that cyclic nucleotide-PDE4B is overexpressed as a malfunctioning protein in non-neoplastic appearing colonic mucosa from patients with colorectal neoplasia. If a predisposition of reduced PDE4B activity in colonic mucosa from colorectal neoplasia patients is substantiated further, this subtype could be a potential novel early diagnostic risk marker and may even be a target for future medical preventive treatment of colorectal cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2980-z) contains supplementary material, which is available to authorized users.

Suppression of β-catenin/TCF transcriptional activity and colon tumor cell growth by dual inhibition of PDE5 and 10

Previous studies suggest the anti-inflammatory drug, sulindac inhibits tumorigenesis by a COX independent mechanism involving cGMP PDE inhibition. Here we report that the cGMP PDE isozymes, PDE5 and 10, are elevated in colon tumor cells compared with normal colonocytes, and that inhibitors and siRNAs can selectively suppress colon tumor cell growth. Combined treatment with inhibitors or dual knockdown suppresses tumor cell growth to a greater extent than inhibition from either isozyme alone. A novel sulindac derivative, ADT-094 was designed to lack COX-1/-2 inhibitory activity but have improved potency to inhibit PDE5 and 10. ADT-094 displayed >500 fold higher potency to inhibit colon tumor cell growth compared with sulindac by activating cGMP/PKG signaling to suppress proliferation and induce apoptosis. Combined inhibition of PDE5 and 10 by treatment with ADT-094, PDE isozyme-selective inhibitors, or by siRNA knockdown also suppresses β-catenin, TCF transcriptional activity, and the levels of downstream targets, cyclin D1 and survivin. These results suggest that dual inhibition of PDE5 and 10 represents novel strategy for developing potent and selective anticancer drugs.

Paracrine nitric oxide induces expression of cardiac sarcomeric proteins in adult progenitor cells through soluble guanylyl cyclase/cyclic-guanosine monophosphate and Wnt/β-catenin inhibition

AIM

Cardiac progenitor cells (CPC) from adult hearts can differentiate to several cell types composing the myocardium but the underlying molecular pathways are poorly characterized. We examined the role of paracrine nitric oxide (NO) in the specification of CPC to the cardiac lineage, particularly through its inhibition of the canonical Wnt/β-catenin pathway, a critical step preceding cardiac differentiation.

METHODS AND RESULTS

Sca1 + CPC from adult mouse hearts were isolated by magnetic-activated cell sorting and clonally expanded. Pharmacologic NO donors increased their expression of cardiac myocyte-specific sarcomeric proteins in a concentration and time-dependent manner. The optimal time window for NO efficacy coincided with up-regulation of CPC expression of Gucy1a3 (coding the alpha1 subunit of guanylyl cyclase). The effect of paracrine NO was reproduced in vitro upon co-culture of CPC with cardiac myocytes expressing a transgenic NOS3 (endothelial nitric oxide synthase) and in vivo upon injection of CPC in infarcted hearts from cardiac-specific NOS3 transgenic mice. In mono- and co-cultures, this effect was abrogated upon inhibition of soluble guanylyl cyclase or nitric oxide synthase, and was lost in CPC genetically deficient in Gucy1a3. Mechanistically, NO inhibits the constitutive activity of the canonical Wnt/β-catenin in CPC and in cell reporter assays in a guanylyl cyclase-dependent fashion. This was paralleled with decreased expression of β-catenin and down-regulation of Wnt target genes in CPC and abrogated in CPC with a stabilized, non-inhibitable β-catenin.

CONCLUSIONS

Exogenous or paracrine sources of NO promote the specification towards the myocyte lineage and expression of cardiac sarcomeric proteins of adult CPC. This is contingent upon the expression and activity of the alpha1 subunit of guanylyl cyclase in CPC that is necessary for NO-mediated inhibition of the canonical Wnt/β-catenin pathway.

A Second WNT for Old Drugs: Drug Repositioning against WNT-Dependent Cancers

Aberrant WNT signaling underlies cancerous transformation and growth in many tissues, such as the colon, breast, liver, and others. Downregulation of the WNT pathway is a desired mode of development of targeted therapies against these cancers. Despite the urgent need, no WNT signaling-directed drugs currently exist, and only very few candidates have reached early phase clinical trials. Among different strategies to develop WNT-targeting anti-cancer therapies, repositioning of existing drugs previously approved for other diseases is a promising approach. Nonsteroidal anti-inflammatory drugs like aspirin, the anti-leprotic clofazimine, and the anti-trypanosomal suramin are among examples of drugs having recently revealed WNT-targeting activities. In total, 16 human-use drug compounds have been found to be working through the WNT pathway and show promise for their prospective repositioning against various cancers. Advances, hurdles, and prospects of developing these molecules as potential drugs against WNT-dependent cancers, as well as approaches for discovering new ones for repositioning, are the foci of the current review.

C-type natriuretic peptide in combination with sildenafil attenuates proliferation of rhabdomyosarcoma cells

Rhabdomyosarcoma (RMS) is a malignant mesenchymal tumor and the most common soft tissue sarcoma in children. Because of several complications associated with intensive multimodal therapies, including growth disturbance and secondary cancer, novel therapies with less toxicity are urgently needed. C‐type natriuretic peptide (CNP), an endogenous peptide secreted by endothelial cells, exerts antiproliferative effects in multiple types of mesenchymal cells. Therefore, we investigated whether CNP attenuates proliferation of RMS cells. We examined RMS patient samples and RMS cell lines. All RMS clinical samples expressed higher levels of guanylyl cyclase B (GC‐B), the specific receptor for CNP, than RMS cell lines. GC‐B expression in RMS cells decreased with the number of passages in vitro. Therefore, GC‐B stable expression lines were established to mimic clinical samples. CNP increased cyclic guanosine monophosphate (cGMP) levels in RMS cells in a dose‐dependent manner, demonstrating the biological activity of CNP. However, because cGMP is quickly degraded by phosphodiesterases (PDEs), the selective PDE5 inhibitor sildenafil was added to inhibit its degradation. In vitro, CNP, and sildenafil synergistically inhibited proliferation of RMS cells stably expressing GC‐B and decreased Raf‐1, Mitogen‐activated protein kinase kinase (MEK), and extracellular signal‐regulated kinase (ERK) phosphorylation. These results suggested that CNP in combination with sildenafil exerts antiproliferative effects on RMS cells by inhibiting the Raf/MEK/ERK pathway. This regimen exerted synergistic effects on tumor growth inhibition without severe adverse effects in vivo such as body weight loss. Thus, CNP in combination with sildenafil represents a promising new therapeutic approach against RMS.

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.

The role of phosphodiesterase-5 inhibitors in prostatic inflammation: a review

Clinical and basic experimental evidence indicates that chronic inflammation is the greatest factor in benign prostatic hyperplasia (BPH) progression, which is the most common cause of Lower Urinary Tract Symptoms (LUTS). The use of anti-inflammatory agents such as steroids, cyclooxygenase-2 (COX-2) and phytotherapics have been investigated as forms of treatment for various prostate diseases. Recent evidence has demonstrated that PDE5 inhibitors (PDE5Is) improve symptoms of BPH/LUTS, possibly as a result of the relaxing of the smooth muscle fibers of the bladder and prostate by NO/cGMPc signaling, or by improving RhoA/Rho-kinase (ROCK), and reduction of the hyperactivity of the autonomic nervous system. However, some results have suggested that besides vasodilatation and their anti-proliferative effect, PDE5Is exert a direct anti-inflammatory effect, by raising cGMP. Given that inflammation is major factor in benign prostatic hyperplasia (BPH) progression, PDE5Is could act also restore prostatic function as they act as potent anti-inflammatory drugs. This review aims to provide a comprehensive summary of the use of phosphodiesterase-5 inhibitors to treat prostatic inflammation.

Sulindac metabolites decrease cerebrovascular malformations in CCM3-knockout mice

Cerebral cavernous malformation (CCM) is a disease of the central nervous system causing hemorrhage-prone multiple lumen vascular malformations and very severe neurological consequences. At present, the only recommended treatment of CCM is surgical. Because surgery is often not applicable, pharmacological treatment would be highly desirable. We describe here a murine model of the disease that develops after endothelial-cell-selective ablation of the CCM3 gene. We report an early, cell-autonomous, Wnt-receptor-independent stimulation of β-catenin transcription activity in CCM3-deficient endothelial cells both in vitro and in vivo and a triggering of a β-catenin-driven transcription program that leads to endothelial-to-mesenchymal transition. TGF-β/BMP signaling is then required for the progression of the disease. We also found that the anti-inflammatory drugs sulindac sulfide and sulindac sulfone, which attenuate β-catenin transcription activity, reduce vascular malformations in endothelial CCM3-deficient mice. This study opens previously unidentified perspectives for an effective pharmacological therapy of intracranial vascular cavernomas.

The Role of Nitric Oxide Synthase Uncoupling in Tumor Progression

Here, evidence suggests that nitric oxide synthases (NOS) of tumor cells, in contrast with normal tissues, synthesize predominantly superoxide and peroxynitrite. Based on high-performance liquid chromatography analysis, the underlying mechanism for this uncoupling is a reduced tetrahydrobiopterin:dihydrobiopterin ratio (BH4:BH2) found in breast, colorectal, epidermoid, and head and neck tumors compared with normal tissues. Increasing BH4:BH2 and reconstitution of coupled NOS activity in breast cancer cells with the BH4 salvage pathway precursor, sepiapterin, causes significant shifts in downstream signaling, including increased cGMP-dependent protein kinase (PKG) activity, decreased β-catenin expression, and TCF4 promoter activity, and reduced NF-κB promoter activity. Sepiapterin inhibited breast tumor cell growth in vitro and in vivo as measured by a clonogenic assay, Ki67 staining, and 2[18F]fluoro-2-deoxy-D-glucose-deoxyglucose positron emission tomography (FDG-PET). In summary, using diverse tumor types, it is demonstrated that the BH4:BH2 ratio is lower in tumor tissues and, as a consequence, NOS activity generates more peroxynitrite and superoxide anion than nitric oxide, resulting in important tumor growth-promoting and antiapoptotic signaling properties.

IMPLICATIONS

The synthetic BH4, Kuvan, is used to elevate BH4:BH2 in some phenylketonuria patients and to treat diseases associated with endothelial dysfunction, suggesting a novel, testable approach for correcting an abnormality of tumor metabolism to control tumor growth.

Atopic allergic conditions and colorectal cancer risk in the Multiethnic Cohort Study

Studies have provided evidence of an inverse association between atopic allergic conditions (AACs) and invasive colorectal cancer (CRC) incidence and mortality in predominantly white populations. We examined the association between AACs (asthma, hay fever, or allergy) and CRC among white, African-American, Native Hawaiian, Japanese-American, and Latino men and women in the Multiethnic Cohort Study within Hawaii and Los Angeles, California. The prospective analysis included 4,834 incident CRC cases and 1,363 CRC-related deaths ascertained between 1993 and 2010. We examined associations by ethnicity, location, stage, and potential effect modification by CRC risk factors. AACs were associated with a reduced risk of CRC incidence among both men and women (relative risk (RR) = 0.86, 95% confidence interval (CI): 0.80, 0.92). The reduction in risk was noted in all populations except Latinos and was significant in whites (RR = 0.85, 95% CI: 0.73, 0.98), African Americans (RR = 0.81, 95% CI: 0.70, 0.95), Native Hawaiians (RR = 0.72, 95% CI: 0.54, 0.96), and Japanese Americans (RR = 0.87, 95% CI: 0.78, 0.98). Individuals with AACs also had a 20% reduction in CRC-related mortality (P = 0.001). These findings provide evidence for the potential protective role of the reactive immune system in colorectal cancer.

Structural analysis of sulindac as an inhibitor of aldose reductase and AKR1B10

Aldose reductase (AR, AKR1B1) and AKR1B10 are enzymes implicated in important pathologies (diabetes and cancer) and therefore they have been proposed as suitable targets for drug development. Sulindac is the metabolic precursor of the potent non-steroidal anti-inflammatory drug (NSAID) sulindac sulfide, which suppresses prostaglandin production by inhibition of cyclooxygenases (COX). In addition, sulindac has been found to be one of the NSAIDs with higher antitumoral activity, presumably through COX inhibition. However, sulindac anticancer activity could be partially mediated through COX-independent mechanisms, including the participation of AR and AKR1B10. Previously, it had been shown that sulindac and sulindac sulfone were good AR inhibitors and the structure of the ternary complex with NADP(+) and sulindac was described (PDB ID 3U2C). In this work, we determined the three-dimensional structure of AKR1B10 with sulindac and established structure-activity relationships (SAR) of sulindac and their derivatives with AR and AKR1B10. The difference in the IC50 values for sulindac between AR (0.36 μM) and AKR1B10 (2.7 μM) might be explained by the different positioning and stacking interaction given by Phe122/Phe123, and by the presence of two buried and ordered water molecules in AKR1B10 but not in AR. Moreover, SAR analysis shows that the substitution of the sulfinyl group is structurally allowed in sulindac derivatives. Hence, sulindac and its derivatives emerge as lead compounds for the design of more potent and selective AR and AKR1B10 inhibitors.

Ciprofloxacin-Induced Antibacterial Activity Is Attenuated by Phosphodiesterase Inhibitors

Background

Ciprofloxacin is a commonly used antibiotic for urinary tract infection that interacts with bacterial topoisomerases leading to oxidative radicals generation and bacterial cell death. Phosphodiesterase inhibitors (PDEis), on the other hand, are commonly used drugs for the management of erectile dysfunction. The group includes agents such as sildenafil, vardenafil, and tadalafil.

Objectives

We investigated whether PDEi could interfere with the antibacterial activity of ciprofloxacin.

Methods

PDEis were tested in several reference bacteria, including Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Staphylococcus epidermidis, Acinetobacter baumannii, Proteus mirabilis, and Klebsiella pneumoniae utilizing a standard disc diffusion method and measuring both zones of inhibition and MIC.

Results

Results from both assays indicated that ciprofloxacin demonstrates potent activity against the tested reference bacteria. Additionally, when bacteria were treated with a combination of ciprofloxacin and sildenafil, tadalafil, or vardenafil, the zones of the combination inhibition were significantly reduced, whereas the MIC values were significantly greater than those of ciprofloxacin alone for all tested bacterial strains. In an attempt to examine the mechanism by which PDEis interfere with the action of ciprofloxacin, we utilized the in vitro E coli DNA gyrase cleavage assay. The results showed that PDEi drugs had no effect on ciprofloxacin’s inhibition of E coli gyrase activity.

Conclusions

Pretreatment of various reference bacterial cells with PDEis largely inhibited the antibacterial activity of ciprofloxacin.

Inhibition of phosphodiesterase 5 reduces bone mass by suppression of canonical Wnt signaling

Inhibitors of phosphodiesterase 5 (PDE5) are widely used to treat erectile dysfunction and pulmonary hypertension in clinics. PDE5, cyclic guanosine monophosphate (cGMP), and protein kinase G (PKG) are important components of the non-canonical Wnt signaling. This study aimed to investigate the effect of PDE5 inhibition on canonical Wnt signaling and osteoblastogenesis, using both in vitro cell culture and in vivo animal models. In the in vitro experiments, PDE5 inhibition resulted in activation of cGMP-dependent protein kinase 2 and consequent inhibition of glycogen synthase kinase 3β phosphorylation, destabilization of cytosolic β-catenin and the ultimate suppression of canonical Wnt signaling and reduced osteoblastic differentiation in HEK293T and C3H10T1/2 cells. In animal experiments, systemic inhibition of PDE5 suppressed the activity of canonical Wnt signaling and osteoblastogenesis in bone marrow-derived stromal cells, resulting in the reduction of bone mass in wild-type adult C57B/6 mice, significantly attenuated secreted Frizzled-related protein-1 (SFRP1) deletion-induced activation of canonical Wnt signaling and excessive bone growth in adult SFRP1^−/− mice. Together, these results uncover a hitherto uncharacterized role of PDE5/cGMP/PKG signaling in bone homeostasis and provide the evidence that long-term treatment with PDE5 inhibitors at a high dosage may potentially cause bone catabolism.

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.

Targeting the Wnt pathway in human cancers: therapeutic targeting with a focus on OMP-54F28

The Wnt signaling pathways are a group of signal transduction pathways that play an important role in cell fate specification, cell proliferation and cell migration. Aberrant signaling in these pathways has been implicated in the development and progression of multiple cancers by allowing increased proliferation, angiogenesis, survival and metastasis. Activation of the Wnt pathway also contributes to the tumorigenicity of cancer stem cells (CSCs). Therefore, inhibiting this pathway has been a recent focus of cancer research with multiple targetable candidates in development. OMP-54F28 is a fusion protein that combines the cysteine-rich domain of frizzled family receptor 8 (Fzd8) with the immunoglobulin Fc domain that competes with the native Fzd8 receptor for its ligands and antagonizes Wnt signaling. Preclinical models with OMP-54F28 have shown reduced tumor growth and decreased CSC frequency as a single agent and in combination with other chemotherapeutic agents. Due to these findings, a phase 1a study is nearing completion with OMP-54F28 in advanced solid tumors and 3 phase 1b studies have been opened with OMP-54F28 in combination with standard-of-care chemotherapy backbones in ovarian, pancreatic and hepatocellular cancers. This article will review the Wnt signaling pathway, preclinical data on OMP-54F28 and other Wnt pathway inhibitors and ongoing clinical trials.

Emerging role of the β-catenin-PPARγ axis in the pathogenesis of colorectal cancer

Multiple lines of evidence indicate that Wnt/β-catenin signaling plays a fundamental role in colorectal cancer (CRC) initiation and progression. Recent genome-wide data have confirmed that in CRC this pathway is one of the most frequently modified by genetic or epigenetic alterations affecting almost 90% of Wnt/β-catenin gene members. A major challenge is thus learning how the corrupted coordination of this pathway is tied to other signalings to enhance cell growth. Peroxisome proliferator activated receptor γ (PPARγ) is emerging as a growth-limiting and differentiation-promoting factor. In tumorigenesis it exerts a tumor suppressor role and is potentially linked with the Wnt/β-catenin pathway. Based on these results, the identification of new selective PPARγ modulators with inhibitory effects on the Wnt/β-catenin pathway is becoming an interesting perspective. Should, in fact, these molecules display such properties, new research avenues would be opened aimed at developing new molecular targeted drugs. Herein, we review the basic principles and present new hypotheses underlying the crosstalk between Wnt/β-catenin and PPARγ signaling. Furthermore, we discuss the advances in our understanding as to how their altered regulation can culminate in colon cancer and the efforts aimed at designing novel PPARγ agonists endowed with Wnt/β-catenin inhibitory effects to be used as therapeutic and/or preventive agents.

Phosphodiesterase 10A: a novel target for selective inhibition of colon tumor cell growth and β-catenin-dependent TCF transcriptional activity

The cyclic nucleotide phosphodiesterase 10A (PDE10) has been mostly studied as a therapeutic target for certain psychiatric and neurological conditions, although a potential role in tumorigenesis has not been reported. Here we show that PDE10 is elevated in human colon tumor cell lines compared with normal colonocytes, as well as in colon tumors from human clinical specimens and intestinal tumors from Apc(Min/+) mice compared with normal intestinal mucosa, respectively. An isozyme and tumor-selective role of PDE10 were evident by the ability of small-molecule inhibitors and small interfering RNA knockdown to suppress colon tumor cell growth with reduced sensitivity of normal colonocytes. Stable knockdown of PDE10 by short hairpin RNA also inhibits colony formation and increases doubling time of colon tumor cells. PDE10 inhibition selectively activates cGMP/cGMP-dependent protein kinase signaling to suppress β-catenin levels and T-cell factor (TCF) transcriptional activity in colon tumor cells. Conversely, ectopic expression of PDE10 in normal and precancerous colonocytes increases proliferation and activates TCF transcriptional activity. These observations suggest a novel role of PDE10 in colon tumorigenesis and that inhibitors may be useful for the treatment or prevention of colorectal cancer.

Autocrine fibroblast growth factor 18 signaling mediates Wnt-dependent stimulation of CD44-positive human colorectal adenoma cells

Expansion of a stem-like subpopulation with increased growth and survival potential is thought to drive colorectal tumor growth and progression. We investigated a CD44-positive (CD44((+))) subpopulation with extended growth and survival capacity in the human colon adenoma cell line LT97. This subpopulation expressed elevated levels of fibroblast growth factor 18 (FGF18) and fibroblast growth factor receptor FGFR3-IIIc. Expression levels of the FGFR3-IIIb, which does not bind FGF18, were similar in CD44((+)) and CD44((-)). Addition of FGF18 to the medium or its overexpression from an adenoviral vector increased the colony formation capacity of CD44((+)) threefold, and stimulated phosphorylation of ERK and GSK3β in both total LT97 populations and CD44((+)) cells. FGFR3 signaling blockade by expression of a dominant-negative FGFR3-IIIc mutant led to inhibition of both colony formation and down-stream signaling in the CD44((+)) cells. CD44((-)) cells did not respond. Blockade of the wnt-pathway by a dominant-negative Tcf4-mutant inhibited FGFR3 activation in LT97 cells as well as in HT29 colorectal cancer cells. The chemical wnt-inhibitor sulindac sulfide amide inhibited expression of FGF18 and FGFR3-IIIc and led to inhibition of receptor activation to less than 30% of control treated cells, both in LT97 and HT29 cultures. Our results demonstrate that an FGF18/FGFR3-IIIc autocrine growth and survival loop is up-regulated in a wnt-dependent manner and drives tumor cell growth in a subpopulation of colon adenoma cells. This subpopulation can be regarded as a precursor of colon cancer development and can be targeted for CRC-prevention by blocking either wnt- or FGFR3-signaling.

Anti-tumor activity of non-steroidal anti-inflammatory drugs: cyclooxygenase-independent targets

Non-steroidal anti-inflammatory drugs (NSAIDs) are used extensively for analgesic and antipyretic treatments. In addition, NSAIDs reduce the risk and mortality to several cancers. Their mechanisms in anti-tumorigenesis are not fully understood, but both cyclooxygenase (COX)-dependent and -independent pathways play a role. We and others have been interested in elucidating molecular targets of NSAID-induced apoptosis. In this review, we summarize updated literature regarding cellular and molecular targets modulated by NSAIDs. Among those NSAIDs, sulindac sulfide and tolfenamic acid are emphasized in this review because these two drugs have been well investigated for their anti-tumorigenic activity in many different types of cancer.

NSAIDs inhibit tumorigenesis, but how?

Numerous epidemiologic studies have reported that the long-term use of nonsteroidal anti-inflammatory drugs (NSAID) is associated with a significant decrease in cancer incidence and delayed progression of malignant disease. The use of NSAIDs has also been linked with reduced risk from cancer-related mortality and distant metastasis. Certain prescription-strength NSAIDs, such as sulindac, have been shown to cause regression of precancerous lesions. Unfortunately, the extended use of NSAIDs for chemoprevention results in potentially fatal side effects related to their COX-inhibitory activity and suppression of prostaglandin synthesis. Although the basis for the tumor growth-inhibitory activity of NSAIDs likely involves multiple effects on tumor cells and their microenvironment, numerous investigators have concluded that the underlying mechanism is not completely explained by COX inhibition. It may therefore be possible to develop safer and more efficacious drugs by targeting such COX-independent mechanisms. NSAID derivatives or metabolites that lack COX-inhibitory activity, but retain or have improved anticancer activity, support this possibility. Experimental studies suggest that apoptosis induction and suppression of β-catenin-dependent transcription are important aspects of their antineoplastic activity. Studies show that the latter involves phosphodiesterase inhibition and the elevation of intracellular cyclic GMP levels. Here, we review the evidence for COX-independent mechanisms and discuss progress toward identifying alternative targets and developing NSAID derivatives that lack COX-inhibitory activity but have improved antineoplastic properties.

Mechanisms of action of non-steroidal anti-inflammatory drugs (NSAIDs) and mesalazine in the chemoprevention of colorectal cancer

Colorectal cancer (CRC) is the third most common malignant neoplasm worldwide. Although conclusive evidence is still lacking, epidemiologic studies suggest that long-term use of non-steroidal anti-inflammatory drugs (NSAIDs) has chemopreventive properties against CRC. Similarly, regular consumption of mesalazine, a drug structurally related to NSAIDs, seems to reduce the risk of CRC in patients with ulcerative colitis. These observations are supported by a large body of experimental data showing the ability of such drugs to inhibit multiple pathways that sustain colon carcinogenesis. This review summarizes the current information on the molecular mechanisms by which NSAIDs and mesalazine could interfere with CRC cell growth and survival.

Mechanisms of action of non-steroidal anti-inflammatory drugs (NSAIDs) and mesalazine in the chemoprevention of colorectal cancer

Colorectal cancer (CRC) is the third most common malignant neoplasm worldwide. Although conclusive evidence is still lacking, epidemiologic studies suggest that long-term use of non-steroidal anti-inflammatory drugs (NSAIDs) has chemopreventive properties against CRC. Similarly, regular consumption of mesalazine, a drug structurally related to NSAIDs, seems to reduce the risk of CRC in patients with ulcerative colitis. These observations are supported by a large body of experimental data showing the ability of such drugs to inhibit multiple pathways that sustain colon carcinogenesis. This review summarizes the current information on the molecular mechanisms by which NSAIDs and mesalazine could interfere with CRC cell growth and survival.

COX-Independent Mechanisms of Cancer Chemoprevention by Anti-Inflammatory Drugs

Epidemiological and clinical studies suggest that non-steroidal anti-inflammatory drugs (NSAIDs), including cyclooxygenase (COX)-2 selective inhibitors, reduce the risk of developing cancer. Experimental studies in human cancer cell lines and rodent models of carcinogenesis support these observations by providing strong evidence for the antineoplastic properties of NSAIDs. The involvement of COX-2 in tumorigenesis and its overexpression in various cancer tissues suggest that inhibition of COX-2 is responsible for the chemopreventive efficacy of these agents. However, the precise mechanisms by which NSAIDs exert their antiproliferative effects are still a matter of debate. Numerous other studies have shown that NSAIDs can act through COX-independent mechanisms. This review provides a detailed description of the major COX-independent molecular targets of NSAIDs and discusses how these targets may be involved in their anticancer effects. Toxicities resulting from COX inhibition and the suppression of prostaglandin synthesis preclude the long-term use of NSAIDs for cancer chemoprevention. Furthermore, chemopreventive efficacy is incomplete and treatment often leads to the development of resistance. Identification of alternative NSAID targets and elucidation of the biochemical processes by which they inhibit tumor growth could lead to the development of safer and more efficacious drugs for cancer chemoprevention.