The discovery of novel, potent and selective PDE5 inhibitors

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.

Investigation of PDE5/PDE6 and PDE5/PDE11 selective potent tadalafil-like PDE5 inhibitors using combination of molecular modeling approaches, molecular fingerprint-based virtual screening protocols and structure-based pharmacophore development

The essential biological function of phosphodiesterase (PDE) type enzymes is to regulate the cytoplasmic levels of intracellular second messengers, 3′,5′-cyclic guanosine monophosphate (cGMP) and/or 3′,5′-cyclic adenosine monophosphate (cAMP). PDE targets have 11 isoenzymes. Of these enzymes, PDE5 has attracted a special attention over the years after its recognition as being the target enzyme in treating erectile dysfunction. Due to the amino acid sequence and the secondary structural similarity of PDE6 and PDE11 with the catalytic domain of PDE5, first-generation PDE5 inhibitors (i.e. sildenafil and vardenafil) are also competitive inhibitors of PDE6 and PDE11. Since the major challenge of designing novel PDE5 inhibitors is to decrease their cross-reactivity with PDE6 and PDE11, in this study, we attempt to identify potent tadalafil-like PDE5 inhibitors that have PDE5/PDE6 and PDE5/PDE11 selectivity. For this aim, the similarity-based virtual screening protocol is applied for the “clean drug-like subset of ZINC database” that contains more than 20 million small compounds. Moreover, molecular dynamics (MD) simulations of selected hits complexed with PDE5 and off-targets were performed in order to get insights for structural and dynamical behaviors of the selected molecules as selective PDE5 inhibitors. Since tadalafil blocks hERG1 K channels in concentration dependent manner, the cardiotoxicity prediction of the hit molecules was also tested. Results of this study can be useful for designing of novel, safe and selective PDE5 inhibitors.

In silico design of novel hERG-neutral sildenafil-like PDE5 inhibitors

Cyclic nucleotide phosphodiesterase enzymes (PDEs) have functions in regulating the levels of intracellular second messengers, 3', 5'-cyclic adenosine monophosphate (cAMP) and 3', 5'-cyclic guanosine monophosphate (cGMP), via hydrolysis and decomposing mechanisms in cells. They take essential roles in modulating various cellular activities such as memory and smooth muscle functions. PDE type 5 (PDE5) inhibitors enhance the vasodilatory effects of cGMP in the corpus cavernosum and they are used to treat erectile dysfunction. Patch clamp experiments showed that the IC₅₀ values of the human ether-à-go-go-related gene (hERG1) potassium (K) ion channel blocking affinity of PDE5 inhibitors sildenafil, vardenafil, and tadalafil as 33, 12, and 100 μM, respectively. hERG1 channel is responsible for the regulation of the action potential of human ventricular myocyte by contributing the rapid component of delayed rectifier K⁺ current (I_Kr) component of the cardiac action potential. In this work, interaction patterns and binding affinity predictions of selected PDE5 inhibitors against the hERG1 channel are studied. It is attempted to develop PDE5 inhibitor analogs with lower binding affinity to hERG1 ion channel while keeping their pharmacological activity against their principal target PDE5 using in silico methods. Based on detailed analyses of docking poses and predicted interaction energies, novel analogs of PDE5 inhibitors with lower predicted binding affinity to hERG1 channels without loosing their principal target activity were proposed. Moreover, molecular dynamics (MD) simulations and post-processing MD analyses (i.e. Molecular Mechanics/Generalized Born Surface Area calculations) were performed. Detailed analysis of molecular simulations helped us to better understand the PDE5 inhibitor-target binding interactions in the atomic level. Results of this study can be useful for designing of novel and safe PDE5 inhibitors with enhanced activity and other tailored properties.

Multi-component one-pot synthesis and antimicrobial activities of 3-methyl-1,4-diphenyl-7-thioxo-4,6,8,9-tetrahydro-pyrazolo[5,4-b]pyrimidino[5,4-e]pyridine-5-one and related derivatives

The synthesis of 3-methyl-1,4-diphenyl-7-thioxo-4,6,8,9-tetrahydropyrazolo[5,4-b] pyrimidino[5,4-e]pyridine-5-one (6) was achieved by two different one-pot multi-component synthesis (one-pot three-component and one-pot four component synthesis). Mono and dialkylation of 6 under different conditions gave compounds 7–11. The hydrazine 12 produced from reaction of 9 with N₂H₄ was subjected to reactions with some aromatic aldehydes, ethyl acetoacetate, acetyl acetone, ethyl cyanoacetate and triethyl orthoformate to give 13–17, respectively. Compound 12 upon reaction with CS₂, nitrous acid, benzoin, chloroacetone and phenacyl bromide gave 18,20,21,22. Alkylation of 18 with ethyl iodide, ethyl chloroacetate and phenacyl bromide gave 19a–c. The antibacterial and antifungal activities of selected derivatives were evaluated.

Discovery of a 1,5-dihydrobenzo[b][1,4]diazepine-2,4-dione series of inhibitors of HIV-1 capsid assembly

The discovery of a 1,5-dihydrobenzo[b][1,4]diazepine-2,4-dione series of inhibitors of HIV-1 capsid assembly is described. Synthesis of analogs of the 1,5-dihydrobenzo[b][1,4]diazepine-2,4-dione hit established structure-activity relationships. Replacement of the enamine functionality of the hit series with either an imidazole or a pyrazole ring led to compounds that inhibited both capsid assembly and reverse transcriptase. Optimization of the bicyclic benzodiazepine scaffold to include a 3-phenyl substituent led to lead compound 48, a pure capsid assembly inhibitor with improved antiviral activity.

A new therapeutic approach in Parkinson's disease: some novel quinazoline derivatives as dual selective phosphodiesterase 1 inhibitors and anti-inflammatory agents

The increasing life expectancy in our population makes Parkinson's disease (PD) a growing public health problem. There is a great need to find a way to prevent and delay the disease. It was shown that selective phosphodiesterase 1 (PDE1) inhibitors and anti-inflammatory agents might be effective in treating PD. Therefore, a novel 1,2,9,11-tetrasubstituted-7H-thieno[2',3':4,5]pyrimido[6,1-b]-quinazolin-7-one (1-15) and 1,3,10,12-tetrasubstituted-8H-pyrido[2',3':4,5]pyrimido[6,1-b]quinazolin-8-one (16-36) derivatives were synthesized by reported method and investigated for their ability to inhibit PDE1. Most of the synthesized compounds have shown good activity against PDE1 and were less effective than 3-isobutyl-1-methylxanthine. All the compounds were also tested for their in vitro anti-inflammatory activity by carrageenan-induced oedema in rats. In addition, ulcerogenic activity was determined. The combined anti-inflammatory data from in vitro animal model showed that compounds, 9,11-dibromo-1-(2-furyl)-3-(4-tolyl)-8H-pyrido[2',3':4,5]pyrimido[6,1-b]quinazolin-8-one 23, 9,11-dibromo-1-(4-methoxy-phenyl)-3-phenyl-8H-pyrido[2',3':4,5]pyrimido[6,1-b]quinazolin-8-one 24, 9,11-dibromo-1-(4-chloro-phenyl)-3-(4-tolyl)-8H-pyrido[2',3':4,5]pyrimido[6,1-b]quinazolin-8-one 29 and 9-bromo-1-(4-chloro-phenyl)-3-(4-tolyl)-8H-pyrido[2',3':4,5]pyrimido[6,1-b]quinazolin-8-one 36 exhibited even more potent anti-inflammatory activity and low gastric ulceration incidence compare to reference standard Indomethacin. Since compound 23, 24, 29 and 36 exhibits both anti-inflammatory activity and PDE1 inhibition, it needs further detailed studies.

Assays for cyclic nucleotide-specific phosphodiesterases (PDEs) in the central nervous system (PDE1, PDE2, PDE4, and PDE10)

Since the identification of phosphodiesterase activity in brain tissue more than 40 years ago, 11 distinct gene families have been identified, differing with respect to localization, regulation, affinity for cAMP and cGMP, and distinct functions within cells. PDEs 1, 2, 4, and 10 are currently of special interest to CNS pharmacology because of their high expression in specific areas of the brain and the behavioral effects of inhibitors of these enzymes in rodents. Efficient high-throughput PDE enzyme assays are essential for PDE-targeted drug discovery, and this unit details two types of assays. The first method is relatively inexpensive and is based on separating radiolabeled cNMPs from degradation products on alumina columns. The second method is fluorescence-based; it is fast and better accommodates high-throughput screening, but is more expensive. Although these methods have successfully been used for PDEs 1, 2, 4 and 10, they could be readily adapted to other PDEs.

Phosphodiesterase 5 (PDE 5) inhibitors for the treatment of male erectile disorder: Attaining selectivity versus PDE6

The role of phosphodiesterase type 5 (PDE5) in the mechanism of male erection has been well understood, and several drugs inhibiting this enzyme are being used for the treatment of erectile dysfunction (ED). Discovery of inhibitors with improved selectivity versus other PDE isozymes could lead to drugs with improved safety profile. Achievement of selectivity versus PDE6, co-inhibition of which results in disturbances of color perception, remains the most challenging aspect of current drug discovery programs. The present review describes several case studies, where significant (>100 fold) selectivity versus PDE6 has been attained via investigation of structure-activity relationships (SAR). Special attention is given to the chemical routes leading to novel chemotypes and allowing efficient exploration of their SAR's. Strategies for attaining inhibitor selectivity discussed below may be applicable for other drug discovery programs.

Synthesis and phosphodiesterase 5 inhibitory activity of novel pyrido[1,2-e]purin-4(3H)-one derivatives

Synthesis and primary SAR of a novel series of 2-phenylpyrido[1,2-e]purin-4(3H)-one derivatives with piperazinyl sulfonamide substituents were described herein. As potential PDE5 inhibitors for erectile dysfunction (ED) treatment, representative compounds exhibit improved selectivity versus PDE1 and PDE6. Meanwhile, compound 3e demonstrated functional efficacy on rabbit corpus cavernosum strip in vitro.

SAR development of polycyclic guanine derivatives targeted to the discovery of a selective PDE5 inhibitor for treatment of erectile dysfunction

Development of structure-activity relationship of cyclic guanines I lead us to discovery of a potent and selective series of phosphodiesterase 5 inhibitors 52-59 (IC50=1.3-11.0 nM, PDE6/5=116-600).

Quinolines as extremely potent and selective PDE5 inhibitors as potential agents for treatment of erectile dysfunction

In a continuing effort to discover novel chemotypes as potent and selective PDE5 inhibitors for the treatment of male erectile dysfunction (ED), we have found that 4-benzylaminoquinoline derivatives are very potent and selective PDE5 inhibitors. Some compounds in this series had PDE5 IC(50)'s as low as 50 pM. While an electron withdrawing group at the C6-position of the quinoline substantially improved PDE5 potency, an ethyl group at the C8-position not only improved the PDE5 potency but also the isozyme selectivity. Substitutents at the C3-position can incorporate a variety of different groups. The synthesis and primary structure-activity relationship of this new series of potent PDE5 inhibitors are described.

Design and synthesis of xanthine analogues as potent and selective PDE5 inhibitors

We have discovered potent and selective xanthine PDE5 inhibitors. Compound 25 (PDE5 IC(50)=0.6 nM, PDE6/PDE5=101) demonstrated similar functional efficacy and PK profile to Sildenafil (PDE5 IC(50)=3.5 nM, PDE6/PDE5=7).

Phosphodiesterase 5 inhibitors: current status and potential applications

Phosphodiesterase enzymes convert cyclic GMP and cyclic AMP to the corresponding nucleotide monophosphates. Phosphodiesterase 5 (PDE5) inhibition is now a widely accepted and efficacious therapeutic option for the treatment of erectile dysfunction in men, as a result of extensive clinical experience with sildenafil and other new PDE5 inhibitors. Research in the field continues at a substantial level to identify new, selective PDE5 inhibitors and to investigate their usefulness and activity in other areas. This review summarizes recent clinical trials with PDE5 inhibitors, advances in medicinal chemistry, and other activities and potential applications of this class of compounds.