Antimicrobial potential of quaternary phosphonium salt compounds: a review.

Given that mitochondrial dysregulation is a biomarker of many cancers, cationic quaternary phosphonium salt (QPS) conjugation is a widely utilized strategy for anticancer drug design. QPS-conjugated compounds exhibit greater cell permeation and accumulation in negatively charged mitochondria, and thus, show enhanced activity. Phylogenetic similarities between mitochondria and bacteria have provided a rationale for exploring the antibacterial properties of mitochondria-targeted compounds. Additionally, due to the importance of mitochondria in the survival of pathogenic microbes, including fungi and parasites, this strategy can be extended to these organisms as well. This review examines recent literature on the antimicrobial activities of various QPS-conjugated compounds and provides future directions for exploring the medicinal chemistry of these compounds.

The expanding repertoire of covalent warheads for drug discovery.

The reactive functionalities of drugs that engage in covalent interactions with the enzyme/receptor residue in either a reversible or an irreversible manner are called 'warheads'. Covalent warheads that were previously neglected because of safety concerns have recently gained center stage as a result of their various advantages over noncovalent drugs, including increased selectivity, increased residence time, and higher potency. With the approval of several covalent inhibitors over the past decade, research in this area has accelerated. Various strategies are being continuously developed to tune the characteristics of warheads to improve their potency and mitigate toxicity. Here, we review research progress in warhead discovery over the past 5 years to provide valuable insights for future drug discovery.

Elemental exchange: Bioisosteric replacement of phosphorus by boron in drug design.

Continuous efforts are being directed toward the employment of boron in drug design due to its advantages and unique characteristics including a plethora of target engagement modes, lower metabolism, and synthetic accessibility, among others. Phosphates are components of multiple drug molecules as well as clinical candidates, since they play a vital role in various biochemical functions, being components of nucleotides, energy currency- ATP as well as several enzyme cofactors. This review discusses the unique chemistry of boron functionalities as phosphate bioisosteres - "the boron-phosphorus elemental exchange strategy" as well as the superiority of boron groups over other commonly employed phosphate bioisosteres. Boron phosphate-mimetics have been utilized for the development of enzyme inhibitors as well as novel borononucleotides. Both the boron functionalities described in this review-boronic acids and benzoxaboroles-contain a boron connected to two oxygens and one carbon atom. The boron atom of these functional groups coordinates with a water molecule in the enzyme site forming a tetrahedral molecule which mimics the phosphate structure. Although boron phosphate-mimetic molecules - FDA-approved Crisaborole and phase II/III clinical candidate Acoziborole are products of the boron-phosphorus bioisosteric elemental exchange strategy, this technique is still in its infancy. The review aims to promote the use of this strategy in future medicinal chemistry projects.

Mitochondriotropic Derivative of Ethyl Ferulate, a Dietary Phenylpropanoid, Exhibits Enhanced Cytotoxicity in Cancer Cells via Mitochondrial Superoxide-Mediated Activation of JNK and AKT Signalling.

Specific targeting of anti-cancer drugs to mitochondria is an emerging strategy to enhance cancer cell killing whilst simultaneously overcoming the problem of drug resistance, low bioavailability and limited clinical success of natural products. We have synthesized a mitochondria targeted derivative of Ethyl Ferulate (EF, a naturally occurring ester of ferulic acid), by conjugating it with triphenylphosphonium ion and compared its cytotoxicity with the parent molecule. Mito-Ethyl Ferulate (M-EF) was found to be more potent than EF (~ 400-fold) in inhibiting the growth of A549 and MCF-7 cells and suppressing the clonogenic potential of A549 cells. Notably, M-EF did not induce any cytotoxicity in normal cells (mouse normal fibroblast cells) up to a concentration of 25 µM. Furthermore, M-EF treatment induced significantly higher cell death in MCF-7 and A549 cells, as compared to EF via induction of apoptosis. M-EF treatment increased mitochondrial superoxide production and induced mitochondrial DNA damage and phosphorylation of JNK and AKT in A549 cells. Furthermore, M-EF induced increase in mitochondrial superoxide production and cytotoxicity was attenuated on pre-treatment with mitochondria-targeted antioxidant (mitoTEMPO) indicating the involvement of mitochondrial ROS in the cytotoxic effects of M-EF. Finally, in silico prediction revealed putative mitochondrial targets of M-EF which are known to regulate mitochondrial ROS and cell viability. In conclusion, the improved cytotoxic efficacy of M-EF exemplifies the use of mitochondria-specific drug delivery in future development of natural product based mitochondrial pharmacology.

Mutations in SARS-CoV-2 nsp7 and nsp8 proteins and their predicted impact on replication/transcription complex structure.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA-dependent RNA polymerase (RdRp) has been identified to be a mutation hot spot, with the P323L mutation being commonly observed in viral genomes isolated from North America. RdRp forms a complex with nonstructural proteins nsp7 and nsp8 to form the minimal replication/transcription machinery required for genome replication. As mutations in RdRp may affect formation of the RdRp-nsp7-nsp8 supercomplex, we analyzed viral genomes to identify mutations in nsp7 and nsp8 protein sequences. Based on in silico analysis of predicted structures of the supercomplex comprising of native and mutated proteins, we demonstrate that specific mutations in nsp7 and nsp8 proteins may have a role in stabilization of the replication/transcription complex.

Tackling SARS-CoV-2: proposed targets and repurposed drugs.

The SARS-CoV-2 pandemic, declared as a global health emergency by the WHO in February 2020, has currently infected more than 6 million people with fatalities near 371,000 and increasing exponentially, in absence of vaccines and drugs. The pathogenesis of SARS-CoV-2 is still being elucidated. Identifying potential targets and repurposing drugs as therapeutic options is the need of the hour. In this review, we focus on potential druggable targets and suitable therapeutics, currently being explored in clinical trials, to treat SARS-CoV-2 infection. A brief understanding of the complex interactions of both viral as well as host targets, and the possible repurposed drug candidates are described with an emphasis on understanding the mechanisms at the molecular level.

Oxadiazole scaffolds in anti-tuberculosis drug discovery.

With the increasing number of cases of latent and drug resistant tuberculosis, there is an urgent need to develop new, potent molecules capable of combating this deadly disease. Molecules containing oxadiazoles are one such class that could be considered to fulfil this need. Oxadiazole regioisomers have been explored in drug discovery programs for their ability to act as effective linkers and also as pharmacophoric features. Oxadiazoles can act as bioisosteric replacements for the hydrazide moiety which can be found in first line anti-TB drugs, and some have been also reported to interact with newer anti-TB targets. In this context, the present review describes the potential of oxadiazoles as antituberculosis agents.

Synthesis and in-vivo taste assessment of meloxicam pivalate.

Meloxicam (MX), a nonsteroidal anti-inflammatory drug, widely used to treat arthritis, has a very bitter taste. Chemical modification of the bitter functionality was achieved by synthesis of a prodrug, meloxicam pivalate (MXP). Taste improvement was evaluated using single bottle-test rat model. It was found that palatability of MXP solution improved significantly as compared to MX.

Rational design of coumarin derivatives as antituberculosis agents.

AIM: A series of coumarin derivatives was designed as potential antituberculosis agents. RESULTS: The compounds were screened against active and dormant Mycobacterium tuberculosis (Mtb). Compounds 3k and 3n were found to have the most promising activity against replicating MtbH37Rv exhibiting minimum inhibitory concentration of 4.63 and 9.75 µM respectively. The compounds were also effective against dormant MtbH37Rv exhibiting more potency than the standard drugs, isoniazid and rifampicin. The compounds were found to be non-cytotoxic against human cell lines. CONCLUSION: This study provides promising antituberculosis agents that are effective against replicating as well as dormant Mtb and can thus act as potential leads for further development.

Microwave-Assisted Development of Orally Disintegrating Tablets by Direct Compression.

Orally disintegrating tablets (ODTs) are challenged by the need for simple technology to ensure good mechanical strength coupled with rapid disintegration. The objective of this work was to evaluate microwave-assisted development of ODTs based on simple direct compression tableting technology. Placebo ODTs comprising directly compressible mannitol and lactose as diluents, super disintegrants, and lubricants were prepared by direct compression followed by exposure to >97% relative humidity and then microwave irradiation for 5 min at 490 W. Placebo ODTs with hardness (>5 kg/cm2) and disintegration time (<60 s) were optimized. Palatable ODTs of Lamotrigine (LMG), which exhibited rapid dissolution of LMG, were then developed. The stability of LMG to microwave irradiation (MWI) was confirmed. Solubilization was achieved by complexation with beta-cyclodextrin (ß-CD). LMG ODTs with optimal hardness and disintegration time (DT) were optimized by a 23 factorial design using Design Expert software. Taste masking using sweeteners and flavors was confirmed using a potentiometric multisensor-based electronic tongue, coupled with principal component analysis. Placebo ODTs with crospovidone as a superdisintegrant revealed a significant increase in hardness from ∼3 to ∼5 kg/cm2 and a decrease in disintegration time (<60 s) following microwave irradiation. LMG ODTs had hardness >5 kg/cm2, DT < 30s, and rapid dissolution of LMG, and good stability was optimized by DOE and the design space derived. While ß-CD complexation enabled rapid dissolution and moderate taste masking, palatability, which was achieved including flavors, was confirmed using an electronic tongue. A simple step of humidification enabled MWI-facilitated development of ODTs by direct compression presenting a practical and scalable advancement in ODT technology.

Fragment Discovery for the Design of Nitrogen Heterocycles as Mycobacterium tuberculosis Dihydrofolate Reductase Inhibitors.

Fragment-based drug design was used to identify Mycobacterium tuberculosis (Mtb) dihydrofolate reductase (DHFR) inhibitors. Screening of ligands against the Mtb DHFR enzyme resulted in the identification of multiple fragment hits with IC50 values in the range of 38-90 µM versus Mtb DHFR and minimum inhibitory concentration (MIC) values in the range of 31.5-125 µg/mL. These fragment scaffolds would be useful for anti-tubercular drug design.

Identification of a novel class of quinoline-oxadiazole hybrids as anti-tuberculosis agents.

A series of novel quinoline-oxadiazole hybrid compounds was designed based on stepwise rational modification of the lead molecules reported previously, in order to enhance bioactivity and improve druglikeness. The hybrid compounds synthesized were screened for biological activity against Mycobacterium tuberculosis H37Rv and for cytotoxicity in HepG2 cell line. Several of the hits exhibited good to excellent anti-tuberculosis activity and selectivity, especially compounds 12m, 12o and 12p, showed minimum inhibitory concentration values<0.5µM and selectivity index>500. The results of this study open up a promising avenue that may lead to the discovery of a new class of anti-tuberculosis agents.

Design and Synthesis of a Focused Library of Diamino Triazines as Potential Mycobacterium tuberculosis DHFR Inhibitors.

We report design of a series of 2,4-diamino triazines as Mycobacterium tuberculosis (Mtb) dihydrofolate reductase inhibitors. The synthesized compounds were evaluated against Mtb (H37Rv and Dormant stage H37Ra), their cytotoxicity was assessed (HepG2 and A549 cell lines), and selectivity toward Mtb was evaluated by testing against other bacterial strains. Some derivatives showed promising activity along with low cytotoxicity. The most potent compound in the whole cell assay (MIC 0.325 µM against H37Rv) showed selectivity in the enzyme assay and exhibited synergy with second line anti-TB agent p-amino salicylic acid. This study therefore provides promising molecules for further development as antituberculosis DHFR inhibitors.

Antifolate Activity of Plant Polyphenols against Mycobacterium tuberculosis.

With the view of exploring phytochemicals as Mycobacterium tuberculosis (Mtb) dihydrofolate reductase inhibitors, known plant polyphenols from various classes were subjected to detailed docking studies. From this in-silico screening, seven polyphenols were selected and tested against Mtb H37 Rv in whole cell assays. The phytochemicals exhibited potential activity ranging from 3 to 183 µm. These molecules were then tested against the pathogenic and human enzymes in a high-throughput microtitre assay. Epigallocatechin gallate showed the best activity and selectivity. The in-silico analysis was in agreement with the assay results. Of these 7 polyphenols, 5 exhibiting minimum inhibitory concentration values of ≤15 µm were tested for synergistic activity with first line drug Ethambutol and second line folate inhibitor para-amino salicylic acid. Epigallocatechin gallate, Magnolol and Bakuchiol exhibited moderate synergistic association by lowering the minimum inhibitory concentration of these drugs. These simple phytochemicals could hence be considered as leads for further studies, or for preparation of semi-synthetic derivatives to be used in combination therapy, for increased anti-tuberculosis activity after validation in-vivo.

Rational drug design, synthesis and biological evaluation of dihydrofolate reductase inhibitors as antituberculosis agents.

BACKGROUND: A series of 2,4-diamino-s-triazines was designed, with potential for activity against Mycobacterium tuberculosis (Mtb) dihydrofolate reductase enzyme, on the basis of virtual screening results and structure-based drug design. RESULTS: The compounds were evaluated against Mtb (H37Rv) and their cytotoxicity was assessed using VERO cell lines. Of particular note, two compounds were found to have the most promising antituberculosis activity (6b minimum inhibitory concentration: 1.76 µM and 6i minimum inhibitory concentration: 1.57 µM) along with low cytotoxicity (CC50: >300 µM). The enzyme assay results of these two indicated significant inhibition of Mtb dihydrofolate reductase along with selectivity. Selected derivatives were tested against dormant tubercle bacilli in vivo and ex vivo indicating potential inhibition. CONCLUSION: This study provides promising antituberculosis dihydrofolate reductase inhibitors that can act as potential leads for further development.

Insights into the Interaction Mechanism of Ligands with Aß42 Based on Molecular Dynamics Simulations and Mechanics: Implications of Role of Common Binding Site in Drug Design for Alzheimer's Disease.

Aggregation of ß-amyloid (Aß) into oligomers and further into fibrils is hypothesized to be a key factor in pathology of Alzheimer's disease (AD). In this study, mapping and docking were used to study the binding of ligands to protofibrils. It was followed by molecular simulations to understand the differences in interactions of known therapeutic agents such as curcumin, fluorescence-based amyloid staining agents such as thioflavin T, and diagnostic agents such as florbetapir (AV45), with Aß protofibrils. We show that therapeutic agents bind to and distort the protofibrils, thus causing destabilization or prevention of oligomerization, in contrast to diagnostic agents which bind to but do not distort such structures. This has implications in the rational design of ligands, both for diagnostics and therapeutics of AD.

E84G mutation in dihydrofolate reductase from drug resistant strains of Mycobacterium tuberculosis (Mumbai, India) leads to increased interaction with Trimethoprim.

BACKGROUND: Dihydrofolate reductase (DHFR) (dfrA gene) is an essential enzyme for cell survival and an unexplored target in Mycobacterium tuberculosis (Mtb). This study was carried out to analyze mutations in the dfrA gene amongst 20 clinical DNA samples from Mtb isolates obtained from Mumbai, India. METHODS: Sequencing of the PCR amplified dfrA gene from these DNA isolates revealed a point mutation in one strain, leading to a glutamic acid to glycine change. In silico simulation studies revealed a surface alteration in the enzyme due to this E84G mutation. The amplified mutant gene was cloned and expressed. The mutant protein was assessed against known DHFR inhibitors: Methotrexate and Trimethoprim. RESULTS: An increased affinity for inhibitor Trimethoprim and native substrate dihydrofolate was observed with the mutant. Methotrexate did not vary in its activity with both the enzyme forms. CONCLUSIONS: The Glu84Gly point mutation may lead to a variation in the strain which may cause resistance in the future.

Isolation and evaluation of the enantiospecific antitubercular activity of a novel triazole compound.

Cyclohex-3-enyl(5-phenyl-4H-1,2,4-triazol-3-yl)methanol (MSDRT 12) is a novel triazole-based antitubercular compound with two chiral centers. To evaluate the enantiospecific antitubercular activity, the four stereoisomers were isolated using preparative chiral chromatography and the individual stereoisomers were evaluated using the resazurin microtiter assay method (REMA) and a microbroth dilution technique against the Mycobacterium tuberculosis H37Rv strain. Isomer III of MSDRT 12 was found to be the most potent with a minimum inhibitory concentration (MIC) of 0.78 µg/mL, Isomer II had a MIC of 12.5 µg/mL, and isomers I and IV showed no activity. The diastereomeric mixture of MSDRT 12 showed a MIC of 3.125 µg/mL and isoniazid, used as the standard drug, showed a MIC of 0.4 µg/mL. This confirms the necessity of screening individual enantiomers for their pharmacological activity early in the discovery phase to identify the most potent isomer for further development efforts.

Pharmacophore based 3DQSAR of phenothiazines as specific human butyrylcholinesterase inhibitors for treatment of Alzheimer's disease.

Quantitative three dimensional structure activity relationship (3D-QSAR) studies were performed on phenothiazine derivatives as Butyrylcholinesterase (BuChE) inhibitors. Pharmacophore Alignment and Scoring Engine (PHASE) was used to develop predictive Common Pharmacophore Hypotheses (CPHs). The alignment thus obtained was used for Comparative Molecular Field Analysis (CoMFA)/Comparative Molecular Similarity Indices Analysis (CoMSIA) model development. A fourpoint common pharmacophore hypothesis, comprising of one acceptor, one hydrophobic region and two aromatic ring centres was generated. A structurally diverse set of 80 molecules was used of which 56 were grouped into training set to develop the model and the rest 24 molecules into test set to validate the CoMFA/CoMSIA models. The models so developed showed a good r(2)predictive of 0.7587 for CoMFA and 0.7737 for CoMSIA. CoMFA and CoMSIA models had excellent Q(2) (cross-validated coefficient) of 0.7125 and 0.7093, respectively which showed high correlative and predictive abilities of the models. The 3-D contour maps of CoMFA/CoMSIA provided interpretable explanation of SAR for the compounds and also permitted interesting conclusions about the substituent effects on the phenothiazine derivatives. The outcomes of the study would help in the rational design of novel and potent therapeutic agents as specific BuChE inhibitors for symptomatic or disease modifying treatment of AD.

Rational drug design based synthesis of novel arylquinolines as anti-tuberculosis agents.

A series of novel arylquinoline derivatives was designed retaining significant pharmacophoric features and three dimensional geometry of bedaquiline. In silico ADME study was performed to assess drug likeness and toxicity profiles of the designed molecules. The compounds were evaluated for activity against Mycobacterium tuberculosis H37Rv using Resazurin Microtitre Assay (REMA) plate method and cytotoxicity in VERO C1008 cell line. Several of the synthesized compounds exhibited good antituberculosis activity and selectivity, especially compounds, 12i (MIC: 5.18 µM and MIC/CC50: 152.86) and 12l (MIC: 5.59 µM and MIC/CC50: 160.57). The study opens up a new platform for the development of arylquinoline based drugs for treating tuberculosis.