The application of the phosphoramidate ProTide approach confers micromolar potency against Hepatitis C virus on inactive agent 4′-azidoinosine: Kinase bypass on a dual base/sugar modified nucleoside

An overview of ProTide technology and its implications to drug discovery

Introduction: The ProTide technology is a phosphate (or phosphonate) prodrug method devised to deliver nucleoside monophosphate (or monophosphonate) intracellularly bypassing the key challenges of antiviral and anticancer nucleoside analogs. Three new antiviral drugs, exploiting this technology, have been approved by the FDA while others are in clinical studies as anticancer agents.Areas covered: The authors describe the origin and development of this technology and its incredible success in transforming the drug discovery of antiviral and anticancer nucleoside analogues. As evidence, discussion on the antiviral ProTides on the market, and those currently in clinical development are included. The authors focus on how the proven capacity of this technology to generate new drug candidates has stimulated its application to non-nucleoside-based molecules.Expert opinion: The ProTide approach has been extremely successful in delivering blockbuster antiviral medicines and it seems highly promising in oncology. Its application to non-nucleoside-based small molecules is recently emerging and proving effective in other therapeutic areas. However, investigations to explain the lack of activity of certain ProTide series and comprehensive structure activity relationship studies to identify the appropriate phosphoramidate motifs depending on the parent molecule are in our opinion mandatory for the future development of these compounds.

Synthesis, structural characterization and cytotoxicity of a new proton transfer compound based on 2,4-diamino-1,3,5-triazine: an experimental and computational study

A water-soluble proton transfer compound was synthesized and characterized. Non-covalent interactions were studied by X-ray crystallography and DFT calculations. Anticancer activities were investigated and supported by a molecular docking study.

Sonochemical synthesis of a nanodandelion tin(IV) complex with carbacylamidophosphate ligand as anti-Alzheimer agent: Molecular docking study

The dandelion-shaped nanostructure of an organotin complex with formula Sn(CH₃)₂Cl₂}NC₅H₄C(O)NHP(O)[NHC₆H₁₁]₂}₂ (C₁) was synthesized by means of a sonochemical method. Nano-structures were characterized by elemental analysis, NMR, SEM-EDS, XRD, UV-Vis, and FT-IR spectroscopy. The thermal stability of the complex C₁ has been studied by thermal gravimetric analysis (TGA), and compared to the bulk form (C₂). Both the morphology and the size of the ultrasound-assisted synthesized organotin complex have been investigated using scanning electron microscopy (SEM) by changing such parameters as the concentration of initial reactants and the sonication frequency. Two different forms of the organotin complex (C₁, C₂) and the corresponding ligand (L) were evaluated by a modified Ellman's method on acetyl- and butyrylcholinesterase enzymes. Nanodendalion C₁ and ligand L showed the best activity against AChE and BChE, respectively, with the IC₅₀ values being 326.59 μg/ml and 426.68 μg/ml. Further, Lineweaver Burk plots indicated that these compounds are mixed inhibitors. The synthesized compounds and cholinesterase enzymes were simulated by molecular docking for more details concerning the conformation and the orientations of these compounds in the active site of the receptor.

Phosphoramidates and phosphonamidates (ProTides) with antiviral activity

Following the first report on the nucleoside phosphoramidate (ProTide) prodrug approach in 1990 by Chris McGuigan, the extensive investigation of ProTide technology has begun in many laboratories. Designed with aim to overcome limitations and the key resistance mechanisms associated with nucleoside analogues used in the clinic (poor cellular uptake, poor conversion to the 5'-monophosphate form), the ProTide approach has been successfully applied to a vast number of nucleoside analogues with antiviral and anticancer activity. ProTides consist of a 5'-nucleoside monophosphate in which the two hydroxyl groups are masked with an amino acid ester and an aryloxy component which once in the cell is enzymatically metabolized to deliver free 5'-monophosphate, which is further transformed to the active 5'-triphosphate form of the nucleoside analogue. In this review, the seminal contribution of Chris McGuigan's research to this field is presented. His technology proved to be extremely successful in drug discovery and has led to two Food and Drug Administration-approved antiviral agents.

Thiophene-expanded guanosine analogues of Gemcitabine

The chemotherapeutic drug Gemcitabine, 2',2'-difluoro-2'-deoxycytidine, has long been the standard of care for a number of cancers. Gemcitabine's chemotherapeutic properties stem from its 2',2'-difluoro-2'-deoxyribose sugar, which mimics the natural nucleoside, but also disrupts nucleic acid synthesis, leading to cell death. As a result, numerous analogues have been prepared to further explore the biological implications for this structural modification. In that regard, a thieno-expanded guanosine analogue was of interest due to biological activity previously observed for the tricyclic heterobase scaffold. Several analogues were prepared, including the McGuigan ProTide, however the parent nucleoside exhibited the best chemotherapeutic activity, specifically against breast cancer cell lines (89.53% growth inhibition).

Bicyclic and Tricyclic "Expanded" Nucleobase Analogues of Sofosbuvir: New Scaffolds for Hepatitis C Therapies

Given the impressive success of Gilead's Sofosbuvir, many laboratories, including ours, have explored the unique 2'-sugar modification (2'-Me, 2'-F) of nucleoside analogues in the hopes of exploiting the biological activity that this unique modification has imparted to the nucleoside scaffold. In that regard, we have combined our tricyclic "expanded" purine base motif with the 2'-Me, 2'-F sugar modification. Although the synthesis of these complex molecules proved to be nontrivial, with the best results coming from a linear approach, the overall strategy resulted in highly promising biological results for several of the target compounds, including their corresponding McGuigan ProTides. Modest activity against HCV was observed with inhibitory concentrations of as low as 20 μM.

Synthesis of novel nucleoside analogue phosphorothioamidate prodrugs and in vitro anticancer evaluation against RKO human colon carcinoma cells

Novel phosphorothioamidates of pyrimidine nucleoside analogues have been prepared and evaluated in vitro against RKO human colon cancer cell by the MTT cytotoxicity assay. The parent nucleoside analogues were inactive in this assay, while the phosphorothioamidate prodrugs were active at low uM levels in some cases. The O-isopropyl phosphorothioamidate of 2 ',3 '-O-isopropylidene-uridine containing the L-phenylalanine ethyl ester 6f was the most active at 148 uM, a 10-fold enhancement in anticancer activity compared with the parent nucleoside 2 with no increase in cytotoxicity.

Chemical and enzymatic stability of amino acid derived phosphoramidates of antiviral nucleoside 5'-monophosphates bearing a biodegradable protecting group

Ribavirin and 2'-O-methylcytidine 5'-phosphoramidates derived from L-alanine methyl ester bearing either an O-phenyl or a biodegradable O-[3-(acetyloxy)-2,2-bis(ethoxycarbonyl)propyl] or O-[3-(acetyloxymethoxy)-2,2-bis(ethoxycarbonyl)propyl] protecting group were prepared. The kinetics of the deprotection of these pro-drugs by porcine liver esterase and by a whole cell extract of human prostate carcinoma was studied by HPLC-ESI-MS/MS. The 3-(acetyloxymethoxy)-2,2-bis(ethoxycarbonyl)propyl and 3-(acetyloxy)-2,2-bis(ethoxycarbonyl)propyl groups were readily removed releasing the l-alanine methyl ester phosphoramidate nucleotide, the deprotection of the 3-(acetyloxymethoxy) derivative being approximately 20 times faster. The chemical stability of the 2'-O-methylcytidine pro-drugs was additionally determined over a pH range from 7.5 to 10.

Aryloxy phosphoramidate triesters: a technology for delivering monophosphorylated nucleosides and sugars into cells

Prodrug technologies aimed at delivering nucleoside monophosphates into cells (protides) have proved to be effective in improving the therapeutic potential of antiviral and anticancer nucleosides. In these cases, the nucleoside monophosphates are delivered into the cell, where they may then be further converted (phosphorylated) to their active species. Herein, we describe one of these technologies developed in our laboratories, known as the phosphoramidate protide method. In this approach, the charges of the phosphate group are fully masked to provide efficient passive cell-membrane penetration. Upon entering the cell, the masking groups are enzymatically cleaved to release the phosphorylated biomolecule. The application of this technology to various therapeutic nucleosides has resulted in improved antiviral and anticancer activities, and in some cases it has transformed inactive nucleosides to active ones. Additionally, the phosphoramidate technology has also been applied to numerous antiviral nucleoside phosphonates, and has resulted in at least three phosphoramidate-based nucleotides progressing to clinical investigations. Furthermore, the phosphoramidate technology has been recently applied to sugars (mainly glucosamine) in order to improve their therapeutic potential. The development of the phosphoramidate technology, mechanism of action and the application of the technology to various monophosphorylated nucleosides and sugars will be reviewed.