N-Substituted Quinolinonyl Diketo Acid Derivatives as HIV Integrase Strand Transfer Inhibitors and Their Activity against RNase H Function of Reverse Transcriptase

Enhanced Selectivity in 4-Quinolone Formation: A Dual-Base System for Palladium-Catalyzed Carbonylative Cyclization with Fe(CO)5

The use of gaseous CO in Pd-catalyzed carbonylative quinolone synthesis presents challenges related to safety and precise pressure control. In response, a streamlined non-gaseous synthesis of 4-quinolone compounds has been developed. This study introduces a tunable CO-releasing system utilizing Fe(CO)5 activated by a dual-base system of piperazine and triethylamine. This alternative liquid CO resource facilitates the palladium-catalyzed carbonylative C-C coupling and subsequent intramolecular cyclization. By tuning the tandem kinetics of carbonylation and cyclization, this non-gaseous method achieves the successful synthesis of 22 distinct 4-quinolones with excellent yields. This is achieved through the three-component condensation of sub-stoichiometric amounts of Fe(CO)5 with 2-iodoaniline and terminal alkynes. Operando mechanistic studies have revealed a novel CO transfer mechanism that facilitates homogeneous carbonylative cyclization, distinguishing this method from traditional techniques. In addition to addressing safety concerns, this approach also provides precise control over selectivity, with significant implications for pharmaceutical research and the efficient synthesis of pharmaceutical and bioactive compounds.

Strategies in the Design and Development of Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTIs)

AIDS (acquired immunodeficiency syndrome) is a potentially life-threatening infectious disease caused by human immunodeficiency virus (HIV). To date, thousands of people have lost their lives annually due to HIV infection, and it continues to be a big public health issue globally. Since the discovery of the first drug, Zidovudine (AZT), a nucleoside reverse transcriptase inhibitor (NRTI), to date, 30 drugs have been approved by the FDA, primarily targeting reverse transcriptase, integrase, and/or protease enzymes. The majority of these drugs target the catalytic and allosteric sites of the HIV enzyme reverse transcriptase. Compared to the NRTI family of drugs, the diverse chemical class of non-nucleoside reverse transcriptase inhibitors (NNRTIs) has special anti-HIV activity with high specificity and low toxicity. However, current clinical usage of NRTI and NNRTI drugs has limited therapeutic value due to their adverse drug reactions and the emergence of multidrug-resistant (MDR) strains. To overcome drug resistance and efficacy issues, combination therapy is widely prescribed for HIV patients. Combination antiretroviral therapy (cART) includes more than one antiretroviral agent targeting two or more enzymes in the life cycle of the virus. Medicinal chemistry researchers apply different optimization strategies including structure- and fragment-based drug design, prodrug approach, scaffold hopping, molecular/fragment hybridization, bioisosterism, high-throughput screening, covalent-binding, targeting highly hydrophobic channel, targeting dual site, and multi-target-directed ligand to identify and develop novel NNRTIs with high antiviral activity against wild-type (WT) and mutant strains. The formulation experts design various delivery systems with single or combination therapies and long-acting regimens of NNRTIs to improve pharmacokinetic profiles and provide sustained therapeutic effects.

Targeting Metalloenzymes: The "Achilles' Heel" of Viruses and Parasites

Metalloenzymes are central to the regulation of a wide range of essential viral and parasitic functions, including protein degradation, nucleic acid modification, and many others. Given the impact of infectious diseases on human health, inhibiting metalloenzymes offers an attractive approach to disease therapy. Metal-chelating agents have been expansively studied as antivirals and antiparasitics, resulting in important classes of metal-dependent enzyme inhibitors. This review provides the recent advances in targeting the metalloenzymes of viruses and parasites that impose a significant burden on global public health, including influenza A and B, hepatitis B and C, and human immunodeficiency viruses as well as Trypanosoma brucei and Trypanosoma cruzi.

Quinolines and isoquinolines as HIV-1 inhibitors: Chemical structures, action targets, and biological activities

Human immunodeficiency virus type 1 (HIV-1), a lentivirus that causes acquired immunodeficiency syndrome (AIDS), poses a serious threat to global public health. Since the advent of the first drug zidovudine, a number of anti-HIV agents acting on different targets have been approved to combat HIV/AIDS. Among the abundant heterocyclic families, quinoline and isoquinoline moieties are recognized as promising scaffolds for HIV inhibition. This review intends to highlight the advances in diverse chemical structures and abundant biological activity of quinolines and isoquinolines as anti-HIV agents acting on different targets, which aims to provide useful references and inspirations to design and develop novel HIV inhibitors for medicinal chemists.

Recent advances on dual inhibitors targeting HIV reverse transcriptase associated polymerase and ribonuclease H

Reverse transcriptase (RT) plays an indispensable role in the replication of human immunodeficiency virus (HIV) through its associated polymerase and ribonuclease H (RNase H) activities during the viral RNA genome transformation into proviral DNA. Due to the fact that HIV is a highly mutagenic virus and easily resistant to single-target RT inhibitors, dual inhibitors targeting HIV RT associated polymerase and RNase H have been developed. These dual inhibitors have the advantages of increasing efficacy, reducing drug resistance, drug-drug interactions, and cytotoxicity, as well as improving patient compliance. In this review, we summarize recent advances in polymerase/RNase H dual inhibitors focusing on drug design strategies, and structure-activity relationships and share new insights into developing anti-HIV drugs.

Structure based design and evaluation of benzoheterocycle derivatives as potential dual HIV-1 protease and reverse transcriptase inhibitors

The development of dual inhibitors of HIV-1 protease and reverse transcriptase is an attractive strategy for multi-target therapeutic of AIDS, which may be privileged in delaying the occurrence of drug resistance. We herein designed a novel kind of dual inhibitors with benzofuran or indole cores. Biological results showed that a number of inhibitors displayed significant activity against both HIV-1 protease and reverse transcriptase. Among which, inhibitor 10f exhibited a good correlation with an approximate ratio of 1: 2 between the two enzymes. Furthermore, the dual inhibitors illustrated similar potency against both the wild-type virus and drug-resistant mutant. In addition, the molecular dynamic simulation studies verified the dual actions of such inhibitors.

Design, Synthesis and Docking Studies of Thioimidazolyl Diketoacid Derivatives Targeting HIV-1 Integrase

BACKGROUND

Integrase enzyme is a validated drug target to discover novel structures as anti-HIV-1 agents.

OBJECTIVE

Novel series of thioimidazolyl diketo acid derivatives characterizing various substituents at N-1 and 2-thio positions of central ring were developed as HIV-1 integrase inhibitors.

RESULTS

The obtained molecules were evaluated in the enzyme assay, displaying promising integrase inhibitory activity with IC50 values ranging from 0.9 to 7.7 M. The synthesized compounds were also tested for antiviral activity and cytotoxicity using HeLa cells infected by the single-cycle replicable HIV-1 NL4-3.

CONCLUSION

The most potent compound was 18i with EC50=19 µM, IC50 0.9 µM and SI= 10.5. Docking studies indicated that the binding mode of the active molecule is well aligned with the known HIV-1 integrase inhibitors.

HIV-1 Reverse Transcriptase/Integrase Dual Inhibitors: A Review of Recent Advances and Structure-activity Relationship Studies

The significant threat to humanity is HIV infection, and it is uncertain whether a definitive treatment or a safe HIV vaccine is. HIV-1 is continually evolving and resistant to commonly used HIV-resistant medications, presenting significant obstacles to HIV infection management. The drug resistance adds to the need for new anti-HIV drugs; it chooses ingenious approaches to fight the emerging virus. Highly Active Antiretroviral Therapy (HAART), a multi-target approach for specific therapies, has proved effective in AIDS treatment. Therefore, it is a dynamic system with high prescription tension, increased risk of medication reactions, and adverse effects, leading to poor compliance with patients. In the HIV-1 lifecycle, two critical enzymes with high structural and functional analogies are reverse transcriptase (RT) and integrase (IN), which can be interpreted as druggable targets for modern dual-purpose inhibitors. Designed multifunctional ligand (DML) is a new technique that recruited many targets to be achieved by one chemical individual. A single chemical entity that acts for multiple purposes can be much more successful than a complex multidrug program. The production of these multifunctional ligands as antiretroviral drugs is valued with the advantage that the viral-replication process may end in two or more phases. This analysis will discuss the RT-IN dual-inhibitory scaffolds' developments documented so far.

Flavonoids and Acid-Hydrolysis derivatives of Neo-Clerodane diterpenes from Teucrium flavum subsp. glaucum as inhibitors of the HIV-1 reverse transcriptase-associated RNase H function

Bioassay-guided fractionation of the ethyl acetate extract from Teucrium flavum subsp. glaucum, endowed with inhibitory activity towards the HIV-1 reverse transcriptase–associated RNase H function, led to the isolation of salvigenin (1), cirsimaritin (2) and cirsiliol (3) along with the neo-clerodanes teuflavin (4) and teuflavoside (5). Acid hydrolysis of the inactive teuflavoside provided three undescribed neo-clerodanes, flavuglaucins A-C (7-9) and one known neo-clerodane (10). Among all neo-clerodanes, flavuglaucin B showed the highest inhibitory activity towards RNase H function with a IC₅₀ value of 9.1 μM. Molecular modelling and site-directed mutagenesis analysis suggested that flavuglaucin B binds into an allosteric pocket close to RNase H catalytic site. This is the first report of clerodane diterpenoids endowed with anti-reverse transcriptase activity. Neo-clerodanes represent a valid scaffold for the development of a new class of HIV-1 RNase H inhibitors.

Quinolinonyl Non-Diketo Acid Derivatives as Inhibitors of HIV-1 Ribonuclease H and Polymerase Functions of Reverse Transcriptase

Novel anti-HIV agents are still needed to overcome resistance issues, in particular inhibitors acting against novel viral targets. The ribonuclease H (RNase H) function of the reverse transcriptase (RT) represents a validated and promising target, and no inhibitor has reached the clinical pipeline yet. Here, we present rationally designed non-diketo acid selective RNase H inhibitors (RHIs) based on the quinolinone scaffold starting from former dual integrase (IN)/RNase H quinolinonyl diketo acids. Several derivatives were synthesized and tested against RNase H and viral replication and found active at micromolar concentrations. Docking studies within the RNase H catalytic site, coupled with site-directed mutagenesis, and Mg²⁺ titration experiments demonstrated that our compounds coordinate the Mg²⁺ cofactor and interact with amino acids of the RNase H domain that are highly conserved among naïve and treatment-experienced patients. In general, the new inhibitors influenced also the polymerase activity of RT but were selective against RNase H vs the IN enzyme.

Design and biological evaluation of cinnamic and phenylpropionic amide derivatives as novel dual inhibitors of HIV-1 protease and reverse transcriptase

Upon the basis of both possible ligand-binding site interactions and the uniformity of key residues in active sites, a novel class of HIV-1 PR/RT dual inhibitors was designed and evaluated. Cinnamic acids or phenylpropionic acids with more flexible chain and smaller steric hindrance were introduced into the inhibitors, giving rise to significant improvement in HIV-1 RT inhibitory activity by one or two orders of magnitude, with comparable or even improved potency against PR at the same time, compared with coumarin anologues in our previous studies. Among these inhibitors, 38d displayed a 19-fold improvement in anti-PR activity with IC₅₀ value of 0.081 nM compared to the control DRV. In addition, inhibitor 38c exhibited an excellent anti-RT IC₅₀ value of 0.43 μM, only a 4.7-fold less potent activity than the control EFV. More significantly, the disparate ratio between HIV-1 PR and RT inhibition became more reasonable with ratio of 1: 10.4, just as 37b. Furthermore, the assays on HIV-1 late stage and early stage supported the rationality of designing dual inhibitors. The SAR data as well as molecular modeling studies provided new insight for further optimization of more potent HIV-1 PR/RT dual inhibitors.

Classification and Design of HIV-1 Integrase Inhibitors Based on Machine Learning

A key enzyme in human immunodeficiency virus type 1 (HIV-1) life cycle, integrase (IN) aids the integration of viral DNA into the host DNA, which has become an ideal target for the development of anti-HIV drugs. A total of 1785 potential HIV-1 IN inhibitors were collected from the databases of ChEMBL, Binding Database, DrugBank, and PubMed, as well as from 40 references. The database was divided into the training set and test set by random sampling. By exploring the correlation between molecular descriptors and inhibitory activity, it is found that the classification and specific activity data of inhibitors can be more accurately predicted by the combination of molecular descriptors and molecular fingerprints. The calculation of molecular fingerprint descriptor provides the additional substructure information to improve the prediction ability. Based on the training set, two machine learning methods, the recursive partition (RP) and naive Bayes (NB) models, were used to build the classifiers of HIV-1 IN inhibitors. Through the test set verification, the RP technique accurately predicted 82.5% inhibitors and 86.3% noninhibitors. The NB model predicted 88.3% inhibitors and 87.2% noninhibitors with correlation coefficient of 85.2%. The results show that the prediction performance of NB model is slightly better than that of RP, and the key molecular segments are also obtained. Additionally, CoMFA and CoMSIA models with good activity prediction ability both were constructed by exploring the structure-activity relationship, which is helpful for the design and optimization of HIV-1 IN inhibitors.

Investigation of Commiphora myrrha (Nees) Engl. Oil and Its Main Components for Antiviral Activity

The resinous exudate produced by Commiphora myrrha (Nees) Engl. is commonly known as true myrrh and has been used since antiquity for several medicinal applications. Hundreds of metabolites have been identified in the volatile component of myrrh so far, mainly sesquiterpenes. Although several efforts have been devoted to identifying these sesquiterpenes, the phytochemical analyses have been performed by gas-chromatography/mass spectrometry (GC-MS) where the high temperature employed can promote degradation of the components. In this work, we report the extraction of C. myrrha by supercritical CO₂, an extraction method known for the mild extraction conditions that allow avoiding undesired chemical reactions during the process. In addition, the analyses of myrrh oil and of its metabolites were performed by HPLC and GC-MS. Moreover, we evaluated the antiviral activity against influenza A virus of the myrrh extracts, that was possible to appreciate after the addition of vitamin E acetate (α-tocopheryl acetate) to the extract. Further, the single main bioactive components of the oil of C. myrrha commercially available were tested. Interestingly, we found that both furanodienone and curzerene affect viral replication by acting on different steps of the virus life cycle.

Search for new therapeutics against HIV-1 via dual inhibition of RNase H and integrase: current status and future challenges

Reverse transcriptase and integrase are key enzymes that play a pivotal role in HIV-1 viral maturation and replication. Reverse transcriptase consists of two active sites: RNA-dependent DNA polymerase and RNase H. The catalytic domains of integrase and RNase H share striking similarity, comprising two aspartates and one glutamate residue, also known as the catalytic DDE triad, and a Mg²⁺ pair. The simultaneous inhibition of reverse transcriptase and integrase can be a rational drug discovery approach for combating the emerging drug resistance problem. In the present review, the dual inhibition of RNase H and integrase is systematically discussed, including rationality of design, journey of development, advancement and future perspective.

2,4-Diketo esters: Crucial intermediates for drug discovery

Convenient structures such as 2,4-diketo esters have been widely used as an effective pattern in medicinal chemistry and pharmacology for drug discovery. 2,4-Diketonate is a common scaffold that can be found in many biologically active and naturally occurring compounds. Also, many 2,4-diketo ester derivatives have been prepared due to their suitable synthesis. These synthetic drugs and natural products have shown numerous interesting biological properties with clinical potential as a cure for the broad specter of diseases. This review aims to highlight the important evidence of 2,4-diketo esters as a privileged scaffold in medicinal chemistry and pharmacology. Herein, numerous aspects of 2,4-diketo esters will be summarized, including synthesis and isolation of their derivatives, development of novel synthetic methodologies, the evaluation of their biological properties as well as the mechanisms of action of the diketo ester derivates. This paperwork is expected to be a comprehensive, trustworthy, and critical review of the 2,4-diketo ester intermediate to the chemistry community.

Pyrrolyl Pyrazoles as Non-Diketo Acid Inhibitors of the HIV-1 Ribonuclease H Function of Reverse Transcriptase

Due to the biological liability of diketo acid (DKA) chain, we transferred this element of our previously reported anti-HIV-1 pyrrolyl derivatives to a non-DKA scaffold, obtaining a series of pyrrolyl-pyrazole carboxylic acids as new RNase H inhibitors. Among the newly synthesized derivatives, oxyphenylpyrrolyl-pyrazoles demonstrated inhibitory activities within the low micromolar/submicromolar range with compound 11b being the most potent. Interestingly, all tested compounds showed up to 2 orders of magnitude of selectivity for RNase H vs integrase. Docking studies within the RNase H catalytic site, coupled with site-directed mutagenesis, showed the key structural features that could confer the ability to establish specific interactions within RNase H. Furthermore, they proved the ability of our compounds to interact with amino acids highly conserved among HIV-1 subspecies isolated among patients carrying drug-resistant variants. In the end, the newly discovered pyrazole carboxylic acid derivatives feature promising serum stability with respect to their corresponding DKAs.

4-Oxoquinoline Derivatives as Antivirals: A Ten Years Overview

4-Oxoquinoline derivatives constitute an important family of biologically important substances, associated with different bioactivities, which can be synthesized by different synthetic methods, allowing the design and preparation of libraries of substances with specific structural variations capable of modulating their pharmacological action. Over the last years, these substances have been extensively explored by the scientific community in efforts to develop new biologically active agents, with greater efficiency for the treatment of a variety of diseases. Viral infections have been one of the targets of these studies, although to a lesser extent than other diseases such as cancer and bacterial infections. Nevertheless, the literature provides examples that corroborate with the fact that these substances may act on different pharmacological targets in different viral pathogens. This review provides a compilation of some of the major studies published in recent years showing the discovery and/or development of new antiviral oxoquinoline agents, highlighting, whenever possible, their mechanisms of action.

Rational design and Structure-Activity relationship of coumarin derivatives effective on HIV-1 protease and partially on HIV-1 reverse transcriptase

Since dual inhibitors may yield lower toxicity and reduce the likelihood of drug resistance, as well as inhibitors of HIV-1 PR and RT constitute the core of chemotherapy for AIDS treatment, we herein designed and synthesized new coumarin derivatives characterized by various linkers that exhibited excellent potency against PR and a weak inhibition of RT. Among which, compounds 6f and 7c inhibited PR with IC₅₀ values of 15.5 and 62.1 nM, respectively, and weakly affected also RT with IC₅₀ values of 241.8 and 188.7 μM, respectively, showing the possibility in the future of developing dual HIV-1 PR/RT inhibitors. Creative stimulation for further research of more potent dual HIV-1 inhibitors was got according to the molecular docking studies.

Evolution of HIV-1 reverse transcriptase and integrase dual inhibitors: Recent advances and developments

HIV infection is a major challenge to mankind and a definitive cure or a viable vaccine for HIV is still elusive. HIV-1 is constantly evolving and developing resistant against clinically used anti-HIV drugs thus posing serious hurdles in the treatment of HIV infection. This prompts the need to developed new anti-HIV drugs; preferentially adopting intelligent ways to counteract an evolving virus. Highly Active Anti-Retroviral Therapy (HAART): a strategy involving multiple targeting through various drugs has proven beneficial in the management of AIDS. However, it is a complex regimen with high drug load, increased risk of drug interactions and adverse effects, which lead to poor patient compliance. Reverse transcriptase (RT) and Integrase (IN) are two pivotal enzymes in HIV-1 lifecycle with high structural and functional analogy to be perceived as drug-able targets for novel dual-purpose inhibitors. Designed multi-functional ligand (DML) is a modern strategy by which multiple targets can be exploited using a single chemical entity. A single chemical entity acting on multiple targets can be much more effective than a complex multi-drug regimen. The development of such multifunctional ligands is highly valued in anti-HIV drug discovery with the proposed advantage of being able to stop two or more stages of viral replication cycle. This review will encompass the evolution of the RT-IN dual inhibitory scaffolds reported so far and the contribution made by the leading research groups over the years in this field.

Prediction of the binding mode and resistance profile for a dual-target pyrrolyl diketo acid scaffold against HIV-1 integrase and reverse-transcriptase-associated ribonuclease H

The rapid emergence of drug-resistant variants is one of the most common causes of highly active antiretroviral therapeutic (HAART) failure in patients infected with HIV-1. Compared with the existing HAART, the recently developed pyrrolyl diketo acid scaffold targeting both HIV-1 integrase (IN) and reverse transcriptase-associated ribonuclease H (RNase H) is an efficient approach to counteract the failure of anti-HIV treatment due to drug resistance. However, the binding mode and potential resistance profile of these inhibitors with important mechanistic principles remain poorly understood. To address this issue, an integrated computational method was employed to investigate the binding mode of inhibitor JMC6F with HIV-1 IN and RNase H. By using per-residue binding free energy decomposition analysis, the following residues: Asp64, Thr66, Leu68, Asp116, Tyr143, Gln148 and Glu152 in IN, Asp443, Glu478, Trp536, Lys541 and Asp549 in RNase H were identified as key residues for JMC6F binding. And then computational alanine scanning was carried to further verify the key residues. Moreover, the resistance profile of the currently known major mutations in HIV-1 IN and 2 mutations in RNase H against JMC6F was predicted by in silico mutagenesis studies. The results demonstrated that only three mutations in HIV-1 IN (Y143C, Q148R and N155H) and two mutations in HIV-1 RNase H (Y501R and Y501W) resulted in a reduction of JMC6F potency, thus indicating their potential role in providing resistance to JMC6F. These data provided important insights into the binding mode and resistance profile of the inhibitors with a pyrrolyl diketo acid scaffold in HIV-1 IN and RNase H, which would be helpful for the development of more effective dual HIV-1 IN and RNase H inhibitors.

Recent advances in the discovery of small-molecule inhibitors of HIV-1 integrase

AIDS caused by the infection of HIV is a prevalent problem today. Rapid development of drug resistance to existing drug classes has called for the discovery of new targets. Within the three major enzymes (i.e., HIV-1 protease, HIV-1 reverse transcriptase and HIV-1 integrase [IN]) of the viral replication cycle, HIV-1 IN has been of particular interest due to the absence of human cellular homolog. HIV-1 IN catalyzes the integration of viral genetic material with the host genome, a key step in the viral replication process. Several novel classes of HIV IN inhibitors have been explored by targeting different sites on the enzyme. This review strives to provide readers with updates on the recent developments of HIV-1 IN inhibitors.

AIDS is an epidemic disease that endangers the lives of millions of people across the world. The AIDS virus, also known as HIV, has developed resistance to the majority of available drugs on the market, thus requiring the need for new drugs. HIV integrase is one of the key viral enzymes required for viral cell proliferation. Since there is no similar enzyme in the human body, major emphasis is being made to develop therapeutics for this novel target. The drugs that are at various stages of development for this target are reviewed here.

Structure-Driven Discovery of α,γ-Diketoacid Inhibitors Against UL89 Herpesvirus Terminase

Human cytomegalovirus (HCMV) is an opportunistic pathogen causing a variety of severe viral infections, including irreversible congenital disabilities. Nowadays, HCMV infection is treated by inhibiting the viral DNA polymerase. However, DNA polymerase inhibitors have several drawbacks. An alternative strategy is to use compounds against the packaging machinery or terminase complex, which is essential for viral replication. Our discovery that raltegravir (1), a human immunodeficiency virus drug, inhibits the nuclease function of UL89, one of the protein subunits of the complex, prompted us to further develop terminase inhibitors. On the basis of the structure of 1, a library of diketoacid (α,γ-DKA and β,δ-DKA) derivatives were synthesized and tested for UL89-C nuclease activity. The mode of action of α,γ-DKA derivatives on the UL89 active site was elucidated by using X-ray crystallography, molecular docking, and in vitro experiments. Our studies identified α,γ-DKA derivative 14 able to inhibit UL89 in vitro in the low micromolar range, making 14 an optimal candidate for further development and virus-infected cell assay.

The Current Case of Quinolones: Synthetic Approaches and Antibacterial Activity

Quinolones are broad-spectrum synthetic antibacterial drugs first obtained during the synthesis of chloroquine. Nalidixic acid, the prototype of quinolones, first became available for clinical consumption in 1962 and was used mainly for urinary tract infections caused by Escherichia coli and other pathogenic Gram-negative bacteria. Recently, significant work has been carried out to synthesize novel quinolone analogues with enhanced activity and potential usage for the treatment of different bacterial diseases. These novel analogues are made by substitution at different sites--the variation at the C-6 and C-8 positions gives more effective drugs. Substitution of a fluorine atom at the C-6 position produces fluroquinolones, which account for a large proportion of the quinolones in clinical use. Among others, substitution of piperazine or methylpiperazine, pyrrolidinyl and piperidinyl rings also yields effective analogues. A total of twenty six analogues are reported in this review. The targets of quinolones are two bacterial enzymes of the class II topoisomerase family, namely gyrase and topoisomerase IV. Quinolones increase the concentration of drug-enzyme-DNA cleavage complexes and convert them into cellular toxins; as a result they are bactericidal. High bioavailability, relative low toxicity and favorable pharmacokinetics have resulted in the clinical success of fluoroquinolones and quinolones. Due to these superior properties, quinolones have been extensively utilized and this increased usage has resulted in some quinolone-resistant bacterial strains. Bacteria become resistant to quinolones by three mechanisms: (1) mutation in the target site (gyrase and/or topoisomerase IV) of quinolones; (2) plasmid-mediated resistance; and (3) chromosome-mediated quinolone resistance. In plasmid-mediated resistance, the efflux of quinolones is increased along with a decrease in the interaction of the drug with gyrase (topoisomerase IV). In the case of chromosome-mediated quinolone resistance, there is a decrease in the influx of the drug into the cell.

Anti-HIV Drug Discovery and Development: Current Innovations and Future Trends

The early effectiveness of combinatorial antiretroviral therapy (cART) in the treatment of HIV infection has been compromised to some extent by rapid development of multidrug-resistant HIV strains, poor bioavailability, and cumulative toxicities, and so there is a need for alternative strategies of antiretroviral drug discovery and additional therapeutic agents with novel action modes or targets. From this perspective, we first review current strategies of antiretroviral drug discovery and optimization, with the aid of selected examples from the recent literature. We highlight the development of phosphate ester-based prodrugs as a means to improve the aqueous solubility of HIV inhibitors, and the introduction of the substrate envelope hypothesis as a new approach for overcoming HIV drug resistance. Finally, we discuss future directions for research, including opportunities for exploitation of novel antiretroviral targets, and the strategy of activation of latent HIV reservoirs as a means to eradicate the virus.