Synthesis and Biological Evaluation of Lactimidomycin and Its Analogues

Anticancer activities, structure-activity relationship, and mechanism of action of 12-, 14-, and 16-membered macrolactones

Cancer remains one of the major causes of death worldwide despite the encouraging breakthroughs in the discovery of novel chemotherapeutic agents in recent years. The development of new effective anticancer candidates still represents a challenging endeavor due to the severe anticancer demands and the emergence of drug-resistant, especially multidrug-resistant, cancers. Macrolactones could regulate multiple signaling pathways in cancer cells and demonstrated potential anticancer effects, including inhibition of proliferation, metastasis, and angiogenic activity. Accordingly, macrolactones possess excellent efficacy against both drug-sensitive and drug-resistant cancer cells, and the rational design of macrolactones may provide valuable therapeutic interventions for cancers. The purpose of this review is as follows: (1) outline the recent advances made in the development of 12-, 14-, and 16-membered macrolactones with anticancer potential; (2) summarize the structure-activity relationship; and (3) discuss their anticancer mechanisms.

Genomics-Driven Discovery of a Novel Glutarimide Antibiotic from Burkholderia gladioli Reveals an Unusual Polyketide Synthase Chain Release Mechanism

A gene cluster encoding a cryptic trans‐acyl transferase polyketide synthase (PKS) was identified in the genomes of Burkholderia gladioli BCC0238 and BCC1622, both isolated from the lungs of cystic fibrosis patients. Bioinfomatics analyses indicated the PKS assembles a novel member of the glutarimide class of antibiotics, hitherto only isolated from Streptomyces species. Screening of a range of growth parameters led to the identification of gladiostatin, the metabolic product of the PKS. NMR spectroscopic analysis revealed that gladiostatin, which has promising activity against several human cancer cell lines and inhibits tumor cell migration, contains an unusual 2‐acyl‐4‐hydroxy‐3‐methylbutenolide in addition to the glutarimide pharmacophore. An AfsA‐like domain at the C‐terminus of the PKS was shown to catalyze condensation of 3‐ketothioesters with dihydroxyacetone phosphate, thus indicating it plays a key role in polyketide chain release and butenolide formation.

Bioinformatic study to discover natural molecules with activity against COVID-19

Background: In 2020, the world has struggled to deal with coronavirus disease 2019 (COVID-19), which started in 2019 in China and has spread throughout the globe, affecting at least 31,175,835 humans globally and claiming 962,634 lives reported till 22nd September, 2020 by the World Health Organization. The main causative agent for this disease is known as severe acute respiratory syndrome coronavirus 2 (SARS-COV-2). So far, there is no cure or proven therapeutics available till date. Therefore, we undertook this study to find the most probable drug candidate through a bioinformatics study.

Methods: Thus, we virtually screened the Zinc natural database using HTVS tool through molecular docking studies to analyze molecules recommended for the treatment of COVID-19.

Results: Ramipril benzyl ester, propafenone dimer and Lariciresinol are three important drugs found from the present study due to their medicinal application which could be helpful in treating the disease. Stylopine, quillaic acid, cinobufagin, vitisinol C, segetalin A, scopolamine, 3-oxo glycyrrhetinic acid, conchinone B, lactimidomycin and cardinalins 4 are the other lead molecules that could be used as therapeutics against COVID-19 disease.

Conclusions: The studied molecules could act as an effective inhibitory drug against COVID-19.

The Natural Compound Homoharringtonine Presents Broad Antiviral Activity In Vitro and In Vivo

To complement traditional antivirals, natural compounds that act via host targets and present high barriers to resistance are of increasing interest. In the work reported here, we detected that homoharringtonine (HHT) presents effective antiviral activity. HHT completely inhibited infections of vesicular stomatitis virus (VSV), Newcastle disease virus (NDV), and porcine epidemic diarrhea virus (PEDV) at concentrations of 50, 100, and 500 nM in cell cultures, respectively. Treatment with HHT at doses of 0.05 or 0.2 mg/kg significantly reduced viral load and relieved severe symptoms in PEDV- or NDV-infected animals. HHT treatment, however, moderately inhibited avian influenza virus (AIV) infection, suggesting its potent antiviral action is restricted to a number of classes of RNA viruses. In this study, we also observed that HHT actively inhibited herpes simplex virus type 1 (HSV-1) replication with a 50% inhibitory concentration (IC50) of 139 nM; the treatment with HHT at 1000 nM led to reductions of three orders of magnitude. Moreover, HHT antagonized the phosphorylation level of endogenous and exogenous eukaryotic initiation factor 4E (p-eIF4E), which might regulate the selective translation of specific messenger RNA (mRNA). HHT provides a starting point for further progress toward the clinical development of broad-spectrum antivirals.

Broad-spectrum agents for flaviviral infections: dengue, Zika and beyond

Infections with flaviviruses, such as dengue, West Nile virus and the recently re-emerging Zika virus, are an increasing and probably lasting global risk. This Review summarizes and comments on the opportunities for broad-spectrum agents that are active against multiple flaviviruses. Broad-spectrum activity is particularly desirable to prepare for the next flaviviral epidemic, which could emerge from as-yet unknown or neglected viruses. Potential molecular targets for broad-spectrum antiflaviviral compounds include viral proteins, such as the viral protease or polymerase, and host targets that are exploited by these viruses during entry and replication, including α-glucosidase and proteins involved in nucleoside biosynthesis. Numerous compounds with broad-spectrum antiviral activity have already been identified by target-specific or phenotypic assays. For other compounds, broad-spectrum activity can be anticipated because of their mode of action and molecular targets.

Twelve-membered macrolactones: privileged scaffolds for the development of new therapeutics

Natural products commonly produced as secondary metabolites of various plants and micro-organisms represent a diverse chemical space of compounds. The diversity of natural products makes them an attractive target for interrogation by both chemists and biologists alike. Indeed, the study of 12-membered macrolactones has already led to the discovery of lead drug compounds and new biological targets, which has motivated the development of diverted total synthetic routes to libraries of analogs. This review explores the discovery, biological characterization, and synthesis of several 12-membered macrolactones, exploiting examples that underscore their importance in the drug discovery field. It is our hope that this review will motivate further interest in this class of natural products, a group of molecules that we think merit the classification of 'privileged scaffolds' within the medicinal chemistry community, to further investigate and develop novel compounds with promising bioactivity.

Lactimidomycin is a broad-spectrum inhibitor of dengue and other RNA viruses

Dengue virus, a member of the Flaviviridae family, is a mosquito-borne pathogen and the causative agent of dengue fever. Despite the nearly 400 million new infections estimated annually, no vaccines or specific antiviral therapeutics are currently available. We identified lactimidomycin (LTM), a recently established inhibitor of translation elongation, as a potent inhibitor of dengue virus 2 infection in cell culture. The antiviral activity is observed at concentrations that do not affect cell viability. We show that Kunjin virus and Modoc virus, two other members of the Flavivirus genus, as well as vesicular stomatitis virus and poliovirus 1, are also sensitive to LTM. Our findings suggest that inhibition of translation elongation, an obligate step in the viral replication cycle, may provide a general antiviral strategy against fast-replicating RNA viruses.