Synthesis and anti-HIV activity of some novel diaryl phosphate derivatives of AZT

Synthesis, in silico and in vitro anti-cancer studies of phosphorylated derivatives of didanosine targeting MDA-MB-231 breast cancer cell lines

A series of new phosphorylated derivatives of didanosine were designed, synthesized and evaluated their anticancer effects on human breast cancer cells. Their binding affinities were evaluated against aromatase enzyme and the molecular docking studies demonstrated that 9a, 9h and 9i exhibited high binding interactions than the parent molecule (ddI) and other derivatives; evaluated the aromatase enzyme inhibition. The cell viability, cell proliferation, lactate dehydrogenase showed potential anti-proliferative in dose dependent manner, these results were well correlated with hoesch stain and DNA fragmentation on MDA-MB-231 breast cancer cell lines. Cytotoxicity results disclosed that tryptophan amino acid ester substituted derivative 9i showed potential cell death against MDA-MB-231 cancer cell lines. Furthermore, compound 9i has great potential significance for further investigations (in vivo).

Progress toward an amplifiable metabolic label for DNA: conversion of 4-thiothymidine (4sT) to 5-methyl-2′-deoxycytidine and synthesis of a 4sT phosphorodiamidate prodrug

The ability to metabolically label DNA in a way that produces a latent change from one nucleobase to another would create a signal that can be amplified by PCR — this in turn would allow studies of newly synthesized DNA using high-throughput sequencing. To function as an amplifiable metabolic label, a nucleotide analogue would need to be taken up by cells and incorporated into cellular DNA; after purification of DNA, it could be converted into a different nucleobase with a different base pairing pattern. We selected 4-thiothymidine (4sT) as a candidate metabolic label: 4sT is readily taken up by a large number of polymerases in vitro, and we present a method that allows 4sT to be converted into 5-methyl-2′-deoxycytidine (5mC) after incorporation into DNA. Encouraged by these results, we treated cells with 4sT nucleoside; however, we found that 4sT is not incorporated into DNA in bacterial, yeast, or mammalian cells to useful levels under the conditions we tested. A phosphorodiamidate prodrug of 4sTMP was successfully synthesized but did not measurably improve incorporation into cellular DNA.

The ProTide Prodrug Technology: From the Concept to the Clinic

The ProTide technology is a prodrug approach developed for the efficient intracellular delivery of nucleoside analogue monophosphates and monophosphonates. In this approach, the hydroxyls of the monophosphate or monophosphonate groups are masked by an aromatic group and an amino acid ester moiety, which are enzymatically cleaved-off inside cells to release the free nucleoside monophosphate and monophosphonate species. Structurally, this represents the current end-point of an extensive medicinal chemistry endeavor that spans almost three decades. It started from the masking of nucleoside monophosphate and monophosphonate groups by simple alkyl groups and evolved into the sophisticated ProTide system as known today. This technology has been extensively employed in drug discovery, and it has already led to the discovery of two FDA-approved (antiviral) ProTides. In this work, we will review the development of the ProTide technology, its application in drug discovery, and its role in the improvement of drug delivery and efficacy.

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.

Phosphoramidate and phosphate prodrugs of (−)-β-d-(2R,4R)-dioxolane-thymine: Synthesis, anti-HIV activity and stability studies

A series of phosphoramidate and phosphate prodrugs of DOT were synthesized via dichlorophosphate or H-phosphonate chemistry and evaluated for their anti-HIV activity against LAI M184V mutants in PBM cells as well as for their cytotoxicity. The antiviral and cytotoxic profiles of the prodrugs were compared with that of the parent compound (DOT), and it was found that four aryl phosphoramidates 5, 18, 20, and 26 showed a significant enhancement (8- to 12-fold) in anti-HIV activity without cytotoxicity. Chemical stability of these prodrugs was evaluated in phosphate buffer at pH values of biological relevance (i.e., pH 2.0 and 7.4). Enzymatic hydrolysis was also studied in esterase or lipase in buffer solution. Chemical stability studies indicate that the phosphoramidates have good chemical stability at pH 2.0 and at pH 7.4 phosphate buffer. Phosphoramidate prodrugs were hydrolyzed in vitro by esterase or lipase and found to be better substrates for lipases than for esterases. 1,3-Diol cyclic phosphates showed potent anti-HIV activity without increasing the cytotoxicity compared with that of DOT and have good chemical and enzymatic stability. Long-chain lipid phosphates, although showed potent anti-HIV activity, exhibited increased cytotoxicity.

Zidampidine, an aryl phosphate derivative of AZT: in vivo pharmacokinetics, metabolism, toxicity, and anti-viral efficacy against hemorrhagic fever caused by Lassa virus

The pharmacokinetics, metabolism, and toxicity of Zidampidine, an aryl phosphate derivative of AZT, 3'-azidothymidine-5'-[p-bromophenyl methoxyalaninyl phosphate] were investigated in CD-1 mice. Following iv injection, Zidampidine was rapidly converted to its metabolites Ala-AZT-MP and AZT. Zidampidine was not toxic to mice at doses up to 250mg/kg. We next examined the therapeutic effect of Zidampidine in CBA mice challenged with intracerebral injections of the Josiah strain of Lassa virus. Mice were treated either with vehicle or non-toxic doses of Zidampidine administered intraperitoneally 24h prior, 1h prior, and 24, 48, 72, and 96h after virus inoculation. The probability of survival following the Lassa challenge was significantly improved for Zidampidine-treated mice (Kaplan Meier, Log-Rank p value<0.0001). This pilot study provides the basis for future preclinical evaluation of Zidampidine and its potential as a new agent for the treatment of viral hemorrhagic fevers caused by Lassa virus.

Stereospecific chemical and enzymatic stability of phosphoramidate triester prodrugs of d4T in vitro

The phosphoramidate triester prodrug approach is widely used to deliver nucleotide forms of nucleoside analogues into target cells. We investigated the stereoselective stability of a series of prodrugs of the anti-HIV agent 2',3'-didehydro-2',3'-dideoxythymidine (d4T). Chemical stability was evaluated in phosphate buffer at pH values of biological relevance (i.e. pH 2.0, 4.6, 7.4). Enzymatic stability was tested in human plasma, in Caco-2 cell homogenates and monolayers and in rat liver. The compounds were relatively stable to chemical hydrolysis. Between 50 and 70% of unchanged prodrug was recovered after 16h incubation in human plasma, with no stereoselective preference for phosphate diastereoisomers. The p-OMe phenyl derivative, however, was an exception and only 5% of one diastereoisomer was recovered. In Caco-2 cells the stability and stereoselectivity largely depended on the experimental conditions: high enzymatic activity and stereoselectivity was observed in cell homogenates, but not in monolayers. In rat liver S9 fractions the stability profile was similar to that in Caco-2 cells and carboxyl ester cleavage appeared to be the sole mechanism of degradation in both media. The large and unpredictable differences in stereoselective metabolic rate of the pronucleotide series here presented suggest that in vivo circulating levels of intact prodrug could exert profoundly different activity or toxicity due to preferential body distribution of one diastereoisomeric form.

Advances in QSAR studies of HIV-1 reverse transcriptase inhibitors

A review is presented of the recent advances in quantitative structure-activity relationship (QSAR) studies of HIV-1 reverse transcriptase (RT) inhibitors. These inhibitors have been put into two classes: nucleoside RT inhibitors (NRTIs), which are 2',3'-dideoxynucleoside analogues (ddNs), and non-nucleoside RT inhibitors (NNRTIs). For NRTIs (ddNs), which act as competitive inhibitors or alternate substrates of RT and hence interact at the substrate binding site of the enzyme, QSARs have pointed out the major role of the electronic factors governing their activity. For NNRTIs, which bind to a site entirely distinct from the substrate binding site, the activity has been shown to be largely dependent upon the hydrophobic nature of the compounds or substituents. The hydrophobic nature of the active site in the receptor with which the NNRTIs interact provides relatively few possibilities for the molecules to have polar interactions or hydrogen bondings, but QSARs have indicated that NNRTIs do involve some polar interactions and hydrogen bondings with some pockets of the enzyme. QSARs also indicate the significant roles of steric interactions and conformational shape of the molecule.

Synthesis and anti-HIV activity of some novel arylphosphate and H-phosphonate derivatives of 3'-azido-2',3'-dideoxythymidine and 2',3'-didehydro-2',3'-dideoxythymidine

Phosphate and H-phosphonate derivatives of anti-HIV nucleoside analogues (AZT and d4T) were prepared as potential prodrugs of the bio-active free nucleotide and they were evaluated for their inhibitory effects on the replication of HIV-1 in several cell culture systems. One compound exhibited an important anti-HIV-1 activity and proved to be significantly more efficient than the parent nucleoside.

Aryl phosphoramidate derivatives of d4T have improved anti-HIV efficacy in tissue culture and may act by the generation of a novel intracellular metabolite

New phosphate derivatives of the anti-HIV nucleoside analogue d4T were prepared as potential membrane-soluble prodrugs of the bioactive free nucleotide. The enhanced antiviral potency and/or reduced cytotoxicity of the derivatives leads to an increase in selectivity relative to the parent nucleoside analogue. Moreover, the derivatives appear to bypass the dependence of the nucleoside on thymidine kinase-mediated activation, retaining full activity in thymidine kinase-deficient cells. This strongly suggests the successful intracellular delivery of free nucleotides by the masked phosphate triester prodrugs. This is further confirmed by studies using radiolabeled compound which clearly demonstrate the generation of d4T mono-, di- and triphosphates from the prodrug, even in thymidine kinase-deficient cells. Moreover, we herein report the generation of a new metabolite, a partially hydrolyzed phosphate diester, alaninyl d4T monophosphate. We suggest that at least part of the antiviral action of the prodrugs derives from the intracellular generation of such novel diesters which may add considerable weight to the suggested further preclinical development of the phosphate prodrugs.