The Application of Prodrugs as a Tool to Enhance the Properties of Nucleoside Reverse Transcriptase Inhibitors.

Antiretroviral Therapy (ART) is an effective treatment for human immunodeficiency virus (HIV) which has transformed the highly lethal disease, acquired immunodeficiency syndrome (AIDS), into a chronic and manageable condition. However, better methods need to be developed for enhancing patient access and adherence to therapy and for improving treatment in the long term to reduce adverse effects. From the perspective of drug discovery, one promising strategy is the development of anti-HIV prodrugs. This approach aims to enhance the efficacy and safety of treatment, promoting the development of more appropriate and convenient systems for patients. In this review, we discussed the use of the prodrug approach for HIV antiviral agents and emphasized nucleoside reverse transcriptase inhibitors. We comprehensively described various strategies that are used to enhance factors such as water solubility, bioavailability, pharmacokinetic parameters, permeability across biological membranes, chemical stability, drug delivery to specific sites/organs, and tolerability. These strategies might help researchers conduct better studies in this field. We also reported successful examples from the primary therapeutic classes while discussing the advantages and limitations. In this review, we highlighted the key trends in the application of the prodrug approach for treating HIV/AIDS.

Menthol carbonates as potent antiparasitic agents: synthesis and in vitro studies along with computer-aided approaches.

INTRODUCTION: Despite the number of deaths and the significant economic and social costs associated with Chagas, Leishmaniasis and Malaria diseases worldwide, available drugs are limited and have serious side effects and high toxicity for the patient. Therefore, there is an urgent need for safe, low-cost, and effective treatments. Natural products are an important source of bioactive compounds and there is current interest in finding natural bioactive molecules that can be used for treating these parasitic diseases. In the present study we proposed to evaluate the in vitro antiparasitic activity of new menthol derivatives against Trypanosoma cruzi, Leishmania braziliensis and Plasmodium falciparum; moreover, we propose to explore their mode of action through in silico approaches. MATERIAL AND METHODS: A series of carbonate prodrugs (1-9) were synthesized from menthol with different aliphatic alcohols. Spectroscopic techniques were used to confirm the structures of the synthesized compounds. The cytotoxicity of the compounds was assessed using U-937 cells. In vitro trypanocidal, leishmanicidal and antiplasmodial activity were evaluated using a T. cruzi, L. braziliensis and P. falciparum organism, respectively. In addition, in silico studies were also performed through molecular dynamics simulations and MM-PBSA analysis. RESULTS: The assay revealed that most of the compounds were highly active against intracellular amastigotes of T. cruzi and L. braziliensis, and had moderate activity against the total forms of P. falciparum. Compound 2 was one of the drugs that showed a high selectivity index (SI) for the three organisms evaluated. The prediction of the ADME properties suggests that all the compounds have drug-like molecular properties and the probability to be lead candidates. Finally, molecular dynamics simulations, and MM-PBSA studies indicate that menthol at the substrate binding site of TcDHODH, LbDHODH and PfDHODH is structurally stable in the same order as the natural substrate; also, interactions of menthol with residues involved in the inhibition of TcDHODH and PfDHODH proteins were predicted. CONCLUSIONS: The present study demonstrates that menthol prodrugs are promising antiparasitic agents; however, the mechanisms of action proposed in this study need to be experimentally verified by future enzymatic assays.

Do Drug-likeness Rules Apply to Oral Prodrugs?

This paper describes a comparative analysis of the physicochemical and structural properties of prodrugs and their corresponding drugs with regard to drug-likeness rules. The dataset used in this work was obtained from the DrugBank. Sixty-five pairs of prodrugs/drugs were retrieved and divided into the following categories: carrier-linked to increase hydrophilic character, carrier-linked to increase absorption, and bioprecursors. We compared the physicochemical properties related to drug-likeness between prodrugs and drugs. Our results show that prodrugs do not always follow Lipinski's Rule of 5, especially as we observed 15 prodrugs with more than 10 hydrogen bond acceptors and 18 with a molecular weight greater than 500 Da. This fact highlights the importance of extending Lipinski's rules to encompass other parameters as both strategies (filtering of drug-like chemical libraries and prodrug design) aim to improve the bioavailability of compounds. Therefore, critical reasoning is fundamental to determine whether a structure has drug-like properties or could be considered a potential orally active compound in the drug-design pipeline.

Drug-metabolizing enzymes: role in drug resistance in cancer.

Although continuous researches are going on for the discovery of new chemotherapeutic agents, resistance to these anticancer agents has made it really difficult to reach the fruitful results. There are many causes for this resistance that are being studied by the researchers across the world, but still, success is far because there are several factors that are going along unattended or have been studied less. Drug-metabolizing enzymes (DMEs) are one of these factors, on which less study has been conducted. DMEs include Phase I and Phase II enzymes. Cytochrome P450s (CYPs) are major Phase I enzymes while glutathione-S-transferases (GSTs), UDP-glucuronosyltransferases (UGTs), dihydropyrimidine dehydrogenases are the major enzymes belonging to the Phase II enzymes. These enzymes play an important role in detoxification of the xenobiotics as well as the metabolism of drugs, depending upon the tissue in which they are expressed. When present in tumorous tissues, they cause resistance by metabolizing the drugs and rendering them inactive. In this review, the role of these various enzymes in anticancer drug metabolism and the possibilities for overcoming the resistance have been discussed.

Is prodrug design an approach to increase water solubility?

Water solubility has been identified as a critical parameter and the main responsible by affecting poor performance of oral drug delivery. Poorly soluble drugs can originate unsatisfactory ADME properties leading to low oral bioavailability, insufficient chemical stability, low half-life, fast pre-systemic metabolism and difficulties in formulation. In this context, the prodrug design is an alternative in order to improve physicochemical, biopharmaceutical and pharmacokinetic properties such as permeability, solubility, bioavailability, chemical stability and metabolism of molecules presenting poor drug-like properties. In this article we highlight the importance of the prodrug design in the early stages of drug discovery and development process, in an attempt to diminish the attrition rate and end up falling into the valley of death. Selected examples of this strategy are provided in this review and they are classified by some basic functional groups that are amenable to the prodrug approach with the aim of increasing aqueous solubility of poorly water-soluble compounds. Over the past decade, the number of approved prodrugs is considerable among all drugs launched in the market, emphasizing the importance of this tool on drug design. It is reported that 10% of all marketed drug worldwide can be classified as prodrugs. Furthermore, prodrugs designed to be more water soluble launched in the past decade are summarized in a table to have a closer look and finally state that the prodrug design is an amenable approach to increase water solubility.

Prodrugs for targeted cancer therapy.

Introduction: Prodrugs have been used to improve the selectivity and efficacy of cancer therapy by targeting unique abnormal markers that are overexpressed by cancer cells and are absent in normal tissues. In this context, different strategies have been exploited and new ones are being developed each year. Areas covered: In this review, an integrated view of the potential use of prodrugs in targeted cancer therapy is provided. Passive and active strategies are discussed in light of the advantages of each one and some successful examples are provided, as well as the clinical status of several prodrugs. Among them, antibody-drug conjugates (ADCs) are the most commonly used. However, several drawbacks, including limited prodrug uptake, poor pharmacokinetics, immunogenicity problems, difficulties in selective targeting and gene expression, and optimized bystander effects limit their clinical applications. Expert opinion: Despite the efforts of different companies and research groups, several drawbacks, such as the lack of relevant in vivo models, complexity of the human metabolism, and economic limitations, have hampered the development of new prodrugs for targeted cancer therapy. As a result, we believe that the combination of prodrugs with cancer nanotechnology and other newly developed approaches, such as aptamer-conjugated nanomaterials, are efficient strategies.

The Role of the Phosphorus Atom in Drug Design.

Although the phosphorus atom is found in a variety of oxidation states, most of the phosphorus-containing molecules of pharmacological importance possess phosphorus in the form of phosphonate or phosphinate functional groups, or in a major oxidation state as a phosphate group. The most common occurrence of phosphorus in drugs is either in prodrugs or in compounds for which the phosphorus atom plays a role in the biological activity, such as in modified nucleotides, in metabolically stable analogues of metabolites bearing phosphate groups, and as bioisosteric analogues of carboxyl groups.

Stability and plasmatic protein binding of novel zidovudine prodrugs: Targeting site ii of human serum albumin.

Despite its vastly demonstrated clinical efficacy, zidovudine (AZT) exhibits several suboptimal pharmacokinetic properties. In particular, its short plasmatic half-life (t1/2 ~ 1 h) is related to its low bound fraction to whole plasmatic proteins and in particular to human serum albumin (HSA). The design of prodrugs constitutes a promising strategy to enhance AZT pharmacokinetic properties, including its affinity for HSA. Recently, we reported the synthesis and chemical stability evaluation of three novel prodrugs of AZT obtained by derivatization with dicarboxylic acids (1-3). In this work, we present the design, synthesis and evaluation of chemical and enzymatic stabilities of a novel series of double prodrugs of AZT obtained by derivatization of 1-3 with a methylated l-phenylalanine moiety (4-6). In addition, the plasmatic protein binding properties were studied both by experimental and theoretical techniques. Prodrugs 4-6 were found to be relatively stable at pH 7.4 (t1/2 between 4.1 and 57.8 h), while also demonstrated adequate stabilities in human plasma at 37 °C (t1/2 between 1.0 and 2.1 h). Also, prodrugs 4-6 were able to regenerate AZT at a rate that depended on the length of the alkyl chain in 1-3. Additionally, 4-6 exhibited a significantly increased binding to plasmatic proteins (between 52.1 and 72.5%) with respect to AZT (12%) and 1-3 (between 26 and 34%). It is noteworthy that the displacement experiments with HSA site I and II markers, demonstrated that 4-6 bound to a different site than that of AZT and 1-3. Molecular modeling studies (i.e. molecular docking and free energy of binding analysis) were applied to shed light at an atomistic level on the pharmacodynamic properties driving the interaction of 4-6 with HSA. Overall, the present work provides a state of the art contribution to the design and development of novel prodrugs of AZT with optimized pharmacokinetic properties.

Anti-Sporothrix brasiliensis activity of different pyrazinoic acid prodrugs: a repurposing evaluation

From drug repurposing studies, this work aimed to evaluate the activity of different pyrazinoic acid (POA) derivatives against Sporothrix brasiliensis. The POA esters were prepared and characterized as previously reported by classical esterification reactions, with good to excellent yields. Sporothrix brasiliensis isolates from cats (n=6) and standard strains of S. brasiliensis and S. schenckii were used to assess the antifungal activity of the POA derivatives through broth microdilution assay (CLSI M38-A2). Among the tested compounds, molecules 3 and 4 showed fungistatic and fungicidal activities against all Sporothrix spp. strains, and the obtained MIC and MFC values ranged from 2.12 to 4.24 mg/mL and from 1.29 to 5.15 mg/mL, respectively. Compound 2 and 5 were active as in vitro inhibitors of fungal growth, but showed weak fungicidal activity, while molecules 1 and POA itself were inactive. The results suggest the activity of POA derivatives against Sporothrix spp. may be dependent on the lipophilicity. In addition, the antifungal susceptibility of the isolates to itraconazole was performed, showing that two Sporothrix isolates from cats were itraconazole-resistant. Compounds 3 and 4 were also active against these itraconazole-resistant isolates, indicating a possible alternative route to the standard mode of action of itraconazole.

The latest advances in the discovery of nitric oxide hybrid drug compounds.

INTRODUCTION: There is a great interest in Nitric oxide (NO) within medicinal chemistry since it's involved in human signaling pathways. Prodrugs or hybrid compounds containing NO-donor scaffolds linked to an active compound are valuable, due to their potential for modulating many pathological conditions due to NO's biological properties when released in addition to the native drug. Compounds that selectively inhibit nitric oxide synthase isoforms (NOS) can also increase therapeutic capacity, particularly in the treatment of chronic diseases. However, search for bioactive compounds to efficiently and selectively modulate NO is still a challenge in drug discovery. Areas covered: In this review, the authors highlight the recent advances in the strategies used to discover NO-hybrid derivatives, especially those related to anti-inflammatory, cardiovascular, anticancer and anti-microorganism activities. They also focus on: nitric oxide synthase inhibitors, NO delivery materials and other related activities. Expert opinion: The process of molecular hybridization can be used to obtain NO-releasing compounds that also interact with different targets. The main problem with this approach is to control NO multiple actions in the right biological system. However, the use of NO-releasing groups with many different scaffolds leads to new molecular structures for bioactive compounds, suggesting synergies.

Dendrimer Prodrugs.

The main objective of this review is to describe the importance of dendrimer prodrugs in the design of new drugs, presenting numerous applications of these nanocomposites in the pharmaceutical field. Therefore, the use of dendrimer prodrugs as carrier for drug delivery, to improve pharmacokinetic properties of prototype, to promote drug sustained-release, to increase selectivity and, consequently, to decrease toxicity, are just some examples of topics that have been extensively reported in the literature, especially in the last decade. The examples discussed here give a panel of the growing interest dendrimer prodrugs have been evoking in the scientific community.

Synthesis and pharmaceutical properties of N-acyloxymethyl prodrugs of Allop with potential anti-trypanosomal activity.

We report herein the synthesis, and the physicochemical and pharmacokinetic properties of N-acyloxymethyl prodrugs of allopurinol (Allop) (2a-f). Allop is a compound with activity against Trypanosoma cruzi, a causative agent of Chagas disease. Its pathology leads to a huge number of infections and deaths per year, because in addition to many sufferers only having limited access to health services only an inefficient chemotherapy is available. Relevant pharmaceutical properties (pKa, stability, solubility, lipophilicity, in vitro permeability, binding protein, xanthine oxidase binding) were also determined. The results obtained showed that derivatives behave as prodrugs of Allop, since they exhibit improved physicochemical and pharmacokinetic properties relative to their precursor. This behavior turns these compounds into active reservoirs of Allop, and reduces its unfavorable characteristics, so 2a-f compounds are excellent candidates for the treatment of Chagas disease. This work is therefore an important contribution leading to the suppression of Chagas disease.

Biocatalytic approaches applied to the synthesis of nucleoside prodrugs.

Nucleosides are valuable bioactive molecules, which display antiviral and antitumour activities. Diverse types of prodrugs are designed to enhance their therapeutic efficacy, however this strategy faces the troublesome selectivity issues of nucleoside chemistry. In this context, the aim of this review is to give an overview of the opportunities provided by biocatalytic procedures in the preparation of nucleoside prodrugs. The potential of biocatalysis in this research area will be presented through examples covering the different types of nucleoside prodrugs: nucleoside analogues as prodrugs, nucleoside lipophilic prodrugs and nucleoside hydrophilic prodrugs.

The Prodrug Approach: A Successful Tool for Improving Drug Solubility.

Prodrug design is a widely known molecular modification strategy that aims to optimize the physicochemical and pharmacological properties of drugs to improve their solubility and pharmacokinetic features and decrease their toxicity. A lack of solubility is one of the main obstacles to drug development. This review aims to describe recent advances in the improvement of solubility via the prodrug approach. The main chemical carriers and examples of successful strategies will be discussed, highlighting the advances of this field in the last ten years.

Preformulation studies of novel 5'-O-carbonates of lamivudine with biological activity: solubility and stability assays.

As a part of preformulation studies, the aim of this work was to examine the solubility and stability of a series of 5'-O-carbonates of lamivudine with proven antihuman immunodeficiency virus activity. Solubility studies were carried out using pure solvents (water, ethanol and polyethylene glycol 400 [PEG 400]), as well as cosolvents in binary mixture systems (water-ethanol and water-PEG 400). These ionizable compounds showed that their aqueous solubility is decreasing as the carbon length of the substituent moiety increases, but being enhanced as the pH was reduced from 7.4 to 1.2. Thus, 3TC-Metha an active compound of the series, with an intrinsic solubility at 25 °C of 17 mg/mL, was about 70 times more soluble than 3TC-Octa (0.24 mg/mL), and at pHs of 1.2, 5.8 and 7.4 had intrinsic solubilities of 36.48, 19.20 and 15.40 mg/mL, respectively. In addition, the solubility was enhanced significantly by using ethanol and PEG 400 as cosolvents. A stability study was conducted in buffer solutions at pH 1.2, 5.8, 7.4 and 13.0 and in human plasma at 37 °C. Stability-indicating high-performance liquid chromatography procedure was found to be selective, sensitive and accurate for these compounds and good recovery, linearity and precision were also observed.

A study on the properties and reactivity of naphthoquinone-cobalt(III) prototypes for bioreductive prodrugs.

Our group has recently initiated a study on the development of new prototypes for bioreductive prodrugs, based on Co(III) complexes with the ligand 2,2'-bis(3-hydroxy-1,4-naphthoquinone), H2bhnq. The focus of this work is to investigate the dissociation of bhnq(-2) from the complex upon reduction, and the effects of pH, redox potential, oxygen concentration and nature of the auxiliary ligands on this reaction. The bhnq(2-) ligand is a "non-cytotoxic" agent that was chosen as a probe for the reactivity studies due to its suitable chromophoric properties, at the same time that it resembles more cytotoxic naphthoquinones relevant for cancer therapy. In this way, two Co(III) complexes [Co(bhnq)(L1)]BF4·H2O (1) and [Co(bhnq)(L2)]BF4·H2O (2) (L1=N,N'-bis(pyridin-2-ylmethyl)ethylenediamine and L2=N,N'-dimethyl-N,N'-bis(pyridin-2-ylmethyl)ethylenediamine) were synthesized and fully characterized. The gallium analogs [Ga(bhnq)(L1)]NO3·3H2O (3) and [Ga(bhnq)(L2)]NO3·3H2O (4) were also prepared for helping with the assignments of the redox properties of the cobalt complexes and the structure of 2. Cyclic voltammetry analysis revealed a pH-independent quasi-reversible Co(III)/Co(II) process at -0.22 and -0.08V vs NHE for 1 and 2, respectively. An O2-dependent dissociation of bhnq(2-) was observed for the reaction of 1 with ascorbic acid. For 2, the dissociation of bhnq(2-) was found to be independent on the concentration of O2 and faster than in 1, with little influence of the pH on both complexes. The difference in reactivity between 1 and 2 and their redox properties, among other factors, suggests that 1 undergoes redox cycling, pointed out as a key feature for a prodrug to achieve hypoxic selectivity.

Perfil comparativo do custo do tratamento entre pró-fármacos e os seus fármacos precursores / Comparative profile of the cost of treatment withdrugs and their prodrugs

A latenciação é uma importante ferramenta no processo de desenvolvimento de fármacos, pois através dela, diversas barreiras biológicas que limitam o uso de um agente terapêutico podem ser superadas. Assim, esta estratégia permite a reintrodução de substâncias anteriormente descartadas por suas propriedades indesejáveis e o aprimoramento de novos fármacos, antes mesmo que sejam lançados na terapêutica. Embora a latenciação apresente vantagens clínicas, não existem estudos demonstrando a vantagem econômica do uso de pró-fármacos em relação às substâncias precursoras. Dessa forma, o objetivo do presente trabalho foi elaborar um perfil comparativo do custo do tratamento entre pró-fármacos e seus respectivos fármacos precursores, disponíveis no mercado farmacêutico brasileiro, visando demonstrar a real importância da latenciação como ferramenta norteadora para o desenvolvimento de fármacos e, principalmente, a viabilidade financeira do uso de pró-fármacos. Constatou-se que seis do total de pró-fármacos analisados apresentaram-se financeiramente mais vantajosos que os seus precursores e, mesmo para os pró-fármacos que tiveram custo mais elevado, a vantagem clínica alcançada justifica sua utilização.

Prodrug design is an important tool in the drug discovery process, since many biological barriers that limit the use of a drug may be overcome by a prodrug precursor. This strategy allows the improvement of new drugs before they are marketed and also enables the reintroduction of substances previously discarded for their undesirable properties. Although clinical advantages of prodrug design are well-established, there are no studies demonstrating the economic benefits of using prodrugs rather than the intended drugs. The aim of this study was to elaborate a technical report on the relative cost of treatments carried out with prodrugs or with the related drugs. This study was intended to demonstrate the real importance of prodrug design as a guiding tool for drug development and the financial viability of the use of prodrugs. It was found that six of the analyzed prodrugs were financially advantageous compared to the actual drugs and that, even for the prodrugs that had a higher cost, the clinical advantage justified their therapeutic use.