Engineering an antibiotic to fight cancer: optimization of the novobiocin scaffold to produce anti-proliferative agents

Synthesis of C3'-Foused Aryl/Penta-1,4-Dien-3-One/Amine Hybrids as HSP90C-Terminal Inhibitors

24 C3'-focused hybrids of aryl/penta-1,4-dien-3-one/amine (APDA) were designed and synthesized. Of these hybrids, 2 n demonstrated improved antiproliferative effects on HER2-positive breast cancer cells (SKBr3 and BT474) and triple-negative breast cancer (TNBC) cells (MDA-MB-231 and MDA-MB-468) with IC50 values ranging from 7.45 to 10.75 μM, but less toxicity to normal breast cells MCF-10A than the first generation of hybrid 1. Additionally, 2 n retained its ability to inhibit HSP90C-terminus, leading to the degradation of HSP90 client proteins HER2, EGFR, pAKT, AKT, and CDK4, without inducing a heat-shock response. Notably, 2 n also demonstrated improved thermostability compared to 1 and maintained in vitro metabolic stability in simulated intestinal fluid. These findings will provide a scientific basis for developing HSP90C-terminal inhibitors in the future.

Coumarin as an Elite Scaffold in Anti-Breast Cancer Drug Development: Design Strategies, Mechanistic Insights, and Structure-Activity Relationships

Breast cancer is the most common cancer among women. Currently, it poses a significant threat to the healthcare system due to the emerging resistance and toxicity of available drug candidates in clinical practice, thus generating an urgent need for the development of new potent and safer anti-breast cancer drug candidates. Coumarin (chromone-2-one) is an elite ring system widely distributed among natural products and possesses a broad range of pharmacological properties. The unique distribution and pharmacological efficacy of coumarins attract natural product hunters, resulting in the identification of numerous natural coumarins from different natural sources in the last three decades, especially those with anti-breast cancer properties. Inspired by this, numerous synthetic derivatives based on coumarins have been developed by medicinal chemists all around the globe, showing promising anti-breast cancer efficacy. This review is primarily focused on the development of coumarin-inspired anti-breast cancer agents in the last three decades, especially highlighting design strategies, mechanistic insights, and their structure-activity relationship. Natural coumarins having anti-breast cancer efficacy are also briefly highlighted. This review will act as a guideline for researchers and medicinal chemists in designing optimum coumarin-based potent and safer anti-breast cancer agents.

A silicon-containing aryl/penta-1,4-dien-3-one/amine hybrid exhibits antiproliferative effects on breast cancer cells by targeting the HSP90 C-terminus without inducing heat-shock response

A pharmacophore-hybridized strategy based on previously reported HSP90 C-terminal inhibitors was utilized to prepare 32 aryl/penta-1,4-dien-3-one/amine hybrids. Among them, a silicon-containing compound 1z exhibited remarkable broad-spectrum antiproliferative effects on various human breast cancer cell lines. Through fluorescence polarization and AlphaScreen-based assays, we demonstrated that 1z specifically inhibited the HSP90 C-terminus without affecting HSP90 N-terminus. Furthermore, 1z effectively inhibited the HSP90 C-terminus without inducing heat-shock response (HSR), leading to the degradation of its client proteins HER2, pAKT, AKT, and CDK4, causing G1 arrest of MCF-7 and SKBr3 cells, and ultimately contributing to apoptosis of these cells through caspase-3, caspase-8, and caspase-9 activation. Additionally, the penta-1,4-dien-3-one linker in the hybrid, a large bulky lipophilic substitution in the aryl fragment at the 3'-site, and the presence of N-methylpiperazine as the amine fragment were identified as crucial factors that significantly contributed to the observed antiproliferative activity through structure-activity relationship (SAR) analysis. Lastly, we found that 1z exhibited superior thermostability compared to vibsanin B derivatives and good in vitro metabolic stability in simulated intestinal fluid, representing one of the few reported silicon-containing HSP90 C-terminal inhibitors.

Ru(II)-Catalyzed Synthesis of Fused Imidazo[1,2-a]pyridine-chromenones and Methylene-Tethered Bis-imidazo[1,2-a]pyridines and Regioselective O-Acetoxylation of Imidazo[1,2-a]pyridines

Herein, we disclose an unprecedented protocol via ruthenium-catalyzed annulation for the synthesis of 6H-chromeno[4',3':4,5]imidazo[1,2-a]pyridin-6-one, and functionalized 2-(3-formylimidazo[1,2-a]pyridin-2-yl)phenyl acetate has been revealed by intramolecular chelation-assisted C-H activation. Additionally, a one-pot approach for creating bis(2-phenylimidazo[1,2-a]pyridin-3-yl)methane (BIP) has been realized through ruthenium catalysis with the use of formic acid. This method was used in gram-scale synthesis of BIP and step-economical late-stage functionalization of a marketed drug, zolimidine, in good yield.

Mono-ADP-ribosyltransferase 1 ( Artc1 )-deficiency decreases tumorigenesis, increases inflammation, decreases cardiac contractility, and reduces survival

Arginine-specific mono-ADP-ribosylation is a reversible post-translational modification; arginine-specific, cholera toxin-like mono-ADP-ribosyltransferases (ARTCs) transfer ADP-ribose from NAD ⁺ to arginine, followed by cleavage of ADP-ribose-(arginine)protein bond by ADP-ribosylarginine hydrolase 1 (ARH1), generating unmodified (arginine)protein. ARTC1 has been shown to enhance tumorigenicity as does Arh1 deficiency. In this study, Artc1 -KO and Artc1/Arh1 -double-KO mice showed decreased spontaneous tumorigenesis and increased age-dependent, multi-organ inflammation with upregulation of pro-inflammatory cytokine TNF- α . In a xenograft model using tumorigenic Arh1 -KO mouse embryonic fibroblasts (MEFs), tumorigenicity was decreased in Artc1 -KO and heterozygous recipient mice, with tumor infiltration by CD8 ⁺ T cells and macrophages, leading to necroptosis, suggesting that ARTC1 promotes the tumor microenvironment. Furthermore, Artc1/Arh1 -double-KO MEFs showed decreased tumorigenesis in nude mice, showing that tumor cells as well as tumor microenvironment require ARTC1. By echocardiography and MRI, Artc1 -KO and heterozygous mice showed male-specific, reduced myocardial contractility. Furthermore, Artc1 -KO male hearts exhibited enhanced susceptibility to myocardial ischemia-reperfusion-induced injury with increased receptor-interacting protein kinase 3 (RIP3) protein levels compared to WT mice, suggesting that ARTC1 suppresses necroptosis. Overall survival rate of Artc1 -KO was less than their Artc1 -WT counterparts, primarily due to enhanced immune response and inflammation. Thus, anti-ARTC1 agents may reduce tumorigenesis but may increase multi-organ inflammation and decrease cardiac contractility.

Mechanistic investigation on rhodium(III)-catalyzed cycloaddition of 2-vinylphenol derivatives with ethyne or carbon monoxide by DFT study

Rhodium-catalyzed cycloaddition reaction was calculated by density functional theory M06-2X method to directly synthesize benzoxepine and coumarin derivatives. In this work, we conducted a computational study of two competitive mechanisms in which the carbon atom of acetylene or carbon monoxide attacked and inserted from two different directions of the six-membered ring reactant to clarify the principle characteristics of this transformation. The calculation results reveal that: (i) the insertion process of alkyne or carbon monoxide is the key step of the reaction; (ii) for the (5+2) cycloaddition reaction of acetylene, higher energy is required to break the Rh−O bond of the reactant, and the reaction tends to complete the insertion from the side of the Rh−C bond; (iii) for the (5+1) cycloaddition of carbon monoxide, both reaction paths have lower activation free energy, and the two will generate a competition mechanism.

Synthesis and Evaluation of Small Molecule Disruptors of the Aha1/Hsp90 Complex for the Reduction of Tau Aggregation

KU-177 was recently shown to disrupt interactions between Hsp90 and Aha1 in vitro. Subsequent studies in recombinant thioflavin T (ThT) assays demonstrated that KU-177 ablates Aha1-driven enhancement of Hsp90-dependent tau aggregation, which was confirmed by TEM. Using KU-177 as a lead compound, derivatives of KU-177 were synthesized and evaluated for their ability to disrupt Aha1/Hsp90 interactions and inhibit P301L tau aggregation. Preliminary structure-activity relationships were revealed, which led to the identification of a new lead compound that contains a cis-like amide bond. The new lead compounds retain the ability to disrupt Aha1/Hsp90 interactions in SH-SY5Y and SK-BR-3 cells without direct inhibition of Hsp90, providing a new scaffold for subsequent drug discovery efforts.

Copper-mediated C-O/C-N Bond Formation: A Facile Synthesis of 3-Amidocoumarin, 3-amidoazacoumarin and N-Aeroylindole Derivatives

Three different heterocyclic systems, 3-amidocoumarins 1, 3-amidoazacoumarins 11, and N-benzoylindol-2-carboxamides 12 were synthesized based on the strikingly different selectivity of copper-mediated C-O/C-N bond formation from azlactones under conventional heating conditions. The results demonstrated that the stereochemistry of the double bond dictated the outcome of the products. The microwave irradiation played an important role in the isomerization of the trisubstituted olefin leading to the formation of 3-amidocoumarins 1 and 3-amidoazacoumarins 11. Compounds 1h, 1i, and 1l showed promising to good cytotoxic activity against a panel of cancer cell lines including HepG2 (hepatoblastoma) and MOLT-3 (T-lymphoblast acute lymphoblastic leukemia).

Recent progress in rare-earth metal-catalyzed sp2 and sp3 C–H functionalization to construct C–C and C–heteroelement bonds

The review presents rare-earth metal-catalyzed C(sp2/sp3)–H functionalization accessing C–C/C–heteroatom bonds and olefin (co)polymerization, highlighting substrate scope, mechanistic realization, and origin of site-, enantio-/diastereo-selectivity.

Transition metal-catalyzed synthesis of new 3-substituted coumarin derivatives as antibacterial and cytostatic agents

Aim: The aim of this study was to synthesize new coumarin-based compounds and evaluate their antibacterial and antitumor potential. Results: Using transition metal-catalyzed reactions, a series of 7-hydroxycoumarin derivatives were synthesized with aliphatic and aryl moiety attached directly at C-3 of the coumarin ring and through the ethynyl or 1,2,3-triazole linker. The 3-substituted coumarin derivative bearing bistrifluoromethylphenyl at the C-4 position of 1,2,3-triazole (33) showed strong and selective antiproliferative activity against cervical carcinoma cells. The 7-hydroxy-4-methylcoumarin with a phenyl ring directly attached to coumarin at C-3 (10) showed good potency against the methicillin-resistant Staphylococcus aureus and vancomycin-resistant strains. Conclusion: The most active coumarin derivatives owe their antiproliferative potential to the 3,5-ditrifluoromethylphenyl substituent (in 33) and antibacterial activity to the aromatic moiety (in 10); their structure can be optimized further for improved effect.

Non-carbohydrate strategies to inhibit lectin proteins with special emphasis on galectins

Lectins are a family of glycan-binding proteins, many of which have been established as key targets for therapeutic intervention. They play a central role in many physiological and cellular processes. With the advances in protein crystallography, NMR spectroscopy and computational power over the past couple of decades, the carbohydrate-receptor interactions are now well understood and characterized. Nevertheless, designing efficient carbohydrate inhibitors is a laborious endeavour. They are known to have weak affinities, unsuitable pharmacokinetic properties and highly cumbersome/complex synthetic routes. To circumvent these issues many non-carbohydrate strategies have been reported. Galectins are a sub-family of lectin proteins which have been recognized as crucial targets for a wide variety of diseases. Many candidates targeting galectins are currently in advanced stages of clinical trials. There have been a few reports of non-carbohydrate inhibitors targeting galectins which comprise of peptide-based inhibitors and a recent flourish of heterocyclic inhibitors. In this review, we have briefly highlighted the strategies like fragment-based drug-design and high-throughput screens utilized to identify non-carbohydrate based antagonists for proteins wherein the presence of a sugar was believed to be essential. Additionally, we have described the literature pertaining to non-carbohydrate inhibitors of galectins and how previous reports on rational substitution of a sugar motif could aid in design of heterocyclics that inhibit lectins/galectins. We have concluded with remarks on challenges, gap in our understanding and future perspectives concerned with rational design of non-carbohydrate molecules targeting lectins/galectins.

Visible-light promoted oxidative cyclization of cinnamic acid derivatives using xanthone as the photocatalyst

We have developed an efficient photocatalytic synthesis of coumarin derivatives via a tandem double bond isomerization/oxidative cyclization of cinnamic acids.

The quest for supernatural products: the impact of total synthesis in complex natural products medicinal chemistry

Covering: 2000 up to 2020This review presents select recent advances in the medicinal chemistry of complex natural products that are prepared by total synthesis. The underlying studies highlight enabling divergent synthetic strategies and methods that permit the systematic medicinal chemistry studies of key analogues bearing deep-seated structural changes not readily accessible by semisynthetic or biosynthetic means. Select and recent examples are detailed where the key structural changes are designed to improve defined properties or to overcome an intrinsic limitation of the natural product itself. In the examples presented, the synthetic efforts provided supernatural products, a term first introduced by our colleague Ryan Shenvi (Synlett, 2016, 27, 1145-1164), with properties superseding the parent natural product. The design principles and approaches for creating the supernatural products are highlighted with an emphasis on the properties addressed that include those that improve activity or potency, increase selectivity, enhance durability, broaden the spectrum of activity, improve chemical or metabolic stability, overcome limiting physical properties, add mechanisms of action, enhance PK properties, overcome drug resistance, and/or improve in vivo efficacy. Some such improvements may be regarded by some as iterative enhancements whereas others, we believe, truly live up to their characterization as supernatural products. Most such efforts are also accompanied by advances in synthetic organic chemistry, inspiring the development of new synthetic methodology and providing supernatural products with improved synthetic accessibility.

An updated patent review of anticancer Hsp90 inhibitors (2013-present)

INTRODUCTION

Heat shock protein 90 (Hsp90) is one of the most critical chaperones amenable to mediating the folding and maturation of more than 300 client proteins. In normal cells, Hsp90 chaperone cycle is required for regulating multiple cellular processes to maintain homeostasis. However, extremely overexpressed Hsp90 in neoplastic cells results in the dysregulation of client proteins, many of which are indispensable to the accumulation of cancer hallmarks, such as infinite proliferation and increased invasiveness. Consequently, modulation of Hsp90 activity has been considered as a potential strategy for cancer treatment.

AREAS COVERED

This review recapitulated recent patents' progress in the development of Hsp90 inhibitors with potent antitumor activities during 2013 to present. Besides, the structural-activity relationships of the patented inhibitors and their structural similarity were also discussed.

EXPERT OPINION

Hsp90, as an anticancer target, has been investigated for several decades. The first generation of Hsp90 inhibitors exhibited potent antitumor activities in preclinical trials but were trapped in different phases of clinical trials. The second generation of Hsp90 inhibitors has been identified with increased specificity and security through structure modification. Moreover, these inhibitors may offer opportunities for studies of Hsp90 chaperone and development of Hsp90 inhibition therapy.

Dissecting Molecular Principles of the Hsp90 Chaperone Regulation by Allosteric Modulators Using a Hierarchical Simulation Approach and Network Modeling of Allosteric Interactions: Conformational Selection Dictates the Diversity of Protein Responses and Ligand-Specific Functional Mechanisms

Conformational plasticity of the Hsp90 molecular chaperones underlies the diversity of functional mechanisms that these versatile molecular machines employ to coordinate their vast protein clientele in the cellular environment. Despite a steady progress in studies of the Hsp90 machinery, a great deal remains unknown about molecular principles and ligand-specific functional mechanisms of the Hsp90 regulation by allosteric modulators that attracted significant attention because of their therapeutic potential. Due to structural complexity and dynamic nature of the Hsp90 responses to allosteric modulators, the atomistic details about the mode of action of these small molecules continue to be fairly scarce and controversial. In this work, we employ an integrative strategy that encompassed atomistic simulations of the Hsp90 proteins and hierarchical modeling of Hsp90-ligand binding with network analysis to explore functional mechanisms of the Hsp90 regulation by a panel of allosteric modulators (novobiocin, KU-135, KU-174, and KU-32) with different models of action. The results show that functional mechanisms of allosteric modulation in the Hsp90 proteins may be driven by conformational selection principles in which ligands elicit pre-existing states of the unbound chaperone to drive ligand-specific protein responses and distinct scenarios of Hsp90 regulation. We found that novobiocin can selectively sequester an ensemble of open chaperone conformations and inhibit the progression of the functional cycle through a cascade of cumulative dynamic changes. In contrast, KU-32 displayed unique preferences toward partially closed dynamic states, inducing robust allosteric signaling and stimulation of the ATPase cycle. The proposed model of the Hsp90 regulation by allosteric modulators reconciled diverse experimental data and showed that allosteric modulators may operate via targeted exploitation of dynamic landscapes eliciting vastly different protein responses and diverse mechanisms of action.

A Significant Question in Cancer Risk and Therapy: Are Antibiotics Positive or Negative Effectors? Current Answers and Possible Alternatives

Cancer is predominantly considered as an environmental disease caused by genetic or epigenetic alterations induced by exposure to extrinsic (e.g., carcinogens, pollutants, radiation) or intrinsic (e.g., metabolic, immune or genetic deficiencies). Over-exposure to antibiotics, which is favored by unregulated access as well as inappropriate prescriptions by physicians, is known to have led to serious health problems such as the rise of antibiotic resistance, in particular in poorly developed countries. In this review, the attention is focused on evaluating the effects of antibiotic exposure on cancer risk and on the outcome of cancer therapeutic protocols, either directly acting as extrinsic promoters, or indirectly, through interactions with the human gut microbiota. The preponderant evidence derived from information reported over the last 10 years confirms that antibiotic exposure tends to increase cancer risk and, unfortunately, that it reduces the efficacy of various forms of cancer therapy (e.g., chemo-, radio-, and immunotherapy alone or in combination). Alternatives to the current patterns of antibiotic use, such as introducing new antibiotics, bacteriophages or enzybiotics, and implementing dysbiosis-reducing microbiota modulatory strategies in oncology, are discussed. The information is in the end considered from the perspective of the most recent findings on the tumor-specific and intracellular location of the tumor microbiota, and of the most recent theories proposed to explain cancer etiology on the notion of regression of the eukaryotic cells and systems to stages characterized for a lack of coordination among their components of prokaryotic origin, which is promoted by injuries caused by environmental insults.

Heat shock protein 90 inhibitors block the antinociceptive effects of opioids in mouse chemotherapy-induced neuropathy and cancer bone pain models

Heat shock protein 90 (Hsp90) is a ubiquitous signal transduction regulator, and Hsp90 inhibitors are in clinical development as cancer therapeutics. However, there have been very few studies on the impact of Hsp90 inhibitors on pain or analgesia, a serious concern for cancer patients. We previously found that Hsp90 inhibitors injected into the brain block opioid-induced antinociception in tail flick, paw incision, and HIV neuropathy pain. This study extended from that initial work to test the cancer-related clinical impact of Hsp90 inhibitors on opioid antinociception in cancer-induced bone pain in female BALB/c mice and chemotherapy-induced peripheral neuropathy in male and female CD-1 mice. Mice were treated with Hsp90 inhibitors (17-AAG, KU-32) by the intracerebroventricular, intrathecal, or intraperitoneal routes, and after 24 hours, pain behaviors were evaluated after analgesic drug treatment. Heat shock protein 90 inhibition in the brain or systemically completely blocked morphine and oxymorphone antinociception in chemotherapy-induced peripheral neuropathy; this effect was partly mediated by decreased ERK and JNK MAPK activation and by increased protein translation, was not altered by chronic treatment, and Hsp90 inhibition had no effect on gabapentin antinociception. We also found that the Hsp90 isoform Hsp90α and the cochaperone Cdc37 were responsible for the observed changes in opioid antinociception. By contrast, Hsp90 inhibition in the spinal cord or systemically partially reduced opioid antinociception in cancer-induced bone pain. These results demonstrate that Hsp90 inhibitors block opioid antinociception in cancer-related pain, suggesting that Hsp90 inhibitors for cancer therapy could decrease opioid treatment efficacy.

Dynamically Shaping Chaperones. Allosteric Modulators of HSP90 Family as Regulatory Tools of Cell Metabolism in Neoplastic Progression

Molecular chaperones have recently emerged as fundamental regulators of salient biological routines, including metabolic adaptations to environmental changes. Yet, many of the molecular mechanisms at the basis of their functions are still unknown or at least uncertain. This is in part due to the lack of chemical tools that can interact with the chaperones to induce measurable functional perturbations. In this context, the use of small molecules as modulators of protein functions has proven relevant for the investigation of a number of biomolecular systems. Herein, we focus on the functions, interactions and signaling pathways of the HSP90 family of molecular chaperones as possible targets for the discovery of new molecular entities aimed at tuning their activity and interactions. HSP90 and its mitochondrial paralog, TRAP1, regulate the activity of crucial metabolic circuitries, making cells capable of efficiently using available energy sources, with relevant implications both in healthy conditions and in a variety of disease states and especially cancer. The design of small-molecules targeting the chaperone cycle of HSP90 and able to inhibit or stimulate the activity of the protein can provide opportunities to finely dissect their biochemical activities and to obtain lead compounds to develop novel, mechanism-based drugs.

Theoretical study of rhodium(III)-catalyzed synthesis of benzoxepine and coumarin

The mechanisms of the rhodium-catalyzed cycloaddition of 2-vinylphenol with diphenylacetylene and carbon monoxide have been studied using density functional theory calculations at the B3LYP/6-31G (d, p) (Lanl2dz for Rh) level of theory. The SMD solvation model was used in MeCN solvents at M06-2X/6-311 ++ G (d, p) (Lanl2dz (f) for Rh) levels using a single-point calculation to consider the solvent effect. The calculation results show that there are two competitive reaction pathways for the cycloaddition reaction of rhodium-catalyzed synthesis of benzohexine and coumarin. Starting from the precursor reaction complex, the reaction channel is more favorable for the carbon atoms of diphenylacetylene and carbon monoxide to attack the Rh-C bond (the barriers of 9.88 and 10.01 kcal/mol) rather than attack the Rh-O bond (the barriers of 15.37 and 30.17 kcal/mol), and carbon monoxide in two different reaction channels has a greater energy difference than diphenylacetylene. The results show that the computational study of the rhodium-catalyzed cycloaddition reaction has a high catalytic activity consistent with the high yield of the experiment of Gulías et al.

Investigation of the cytotoxicity of bioinspired coumarin analogues towards human breast cancer cells

Abstract

Coumarins possess a wide array of therapeutic capabilities, but often with unclear mechanism of action. We tested a small library of 18 coumarin derivatives against human invasive breast ductal carcinoma cells with the capacity of each compound to inhibit cell proliferation scored, and the most potent coumarin analogues selected for further studies. Interestingly, the presence of two prenyloxy groups (5,7-diprenyloxy-4-methyl-coumarin, 4g) or the presence of octyloxy substituent (coumarin 4d) was found to increase the potency of compounds in breast cancer cells, but not against healthy human fibroblasts. The activity of potent compounds on breast cancer cells cultured more similarly to the conditions of the tumour microenvironment was also investigated, and increased toxicity was observed. Results suggest that tested coumarin derivatives could potentially reduce the growth of tumour mass. Moreover, their use as (combination) therapy in cancer treatment might have the potential of causing limited side effects.

Graphic abstract

Electronic supplementary material

The online version of this article (10.1007/s11030-020-10082-6) contains supplementary material, which is available to authorized users.

Carbohydrates: Potential Sweet Tools Against Cancer

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Cancer, one of the most devastating degenerative diseases nowadays, is one of the main targets in Medicinal Chemistry and Pharmaceutical industry. Due to the significant increase in the incidence of cancer within world population, together with the complexity of such disease, featured with a multifactorial nature, access to new drugs targeting different biological targets connected to cancer is highly necessary.

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Among the vast arsenal of compounds exhibiting antitumor activities, this review will cover the use of carbohydrate derivatives as privileged scaffolds. Their hydrophilic nature, together with their capacity of establishing selective interactions with biological receptors located on cell surface, involved in cell-to-cell communication processes, has allowed the development of an ample number of new templates useful in cancer treatment.

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Their intrinsic water solubility has allowed their use as of pro-drug carriers for accessing more efficiently the pharmaceutical targets. The preparation of glycoconjugates in which the carbohydrate is tethered to a pharmacophore has also allowed a better permeation of the drug through cellular membranes, in which selective interactions with the carbohydrate motifs are involved. In this context, the design of multivalent structures (e.g. gold nanoparticles) has been demonstrated to enhance crucial interactions with biological receptors like lectins, glycoproteins that can be involved in cancer progression.

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Moreover, the modification of the carbohydrate structural motif, by incorporation of metal complexes, or by replacing their endocyclic oxygen, or carbon atoms with heteroatoms has led to new antitumor agents.

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Such diversity of sugar-based templates with relevant antitumor activity will be covered in this review.

Bromocoumarinplatin, targeting simultaneously mitochondria and nuclei with p53 apoptosis pathway to overcome cisplatin resistance

Mitochondria as one of potential anticancer target, alternatively damaging mtDNA other than nDNA is a potential method for platinum-based anticancer drugs to overcome cisplatin resistance. We herein report that bromocoumarinplatin 1, a coumarin-Pt(IV) prodrug, targeted simultaneously mitochondria and nuclei with the contents of Pt in nDNA and mtDNA were 25.75% and 65.91%, respectively, which demonstrated mtDNA apoptosis played a key role in overcoming cisplatin resistance. Moreover, 1 promoted the expression of p53 gene and protein more effectively than cisplatin, leading to the increased anticancer activity of 1 through p53 pathway. The property of preferential accumulation in cancer cells (Snu-368 and Snu-739) compared to the matched normal cells (HL-7702 cells) demonstrated that 1 was potentially safe for clinical therapeutic use. In addition, the higher therapeutic indices of 1 for HCT-116 cells in vivo indicated that bromocoumarinplatin behaved a vital function in the treatment of colon cancer.

CO2 = CO + [O]: recent advances in carbonylation of C–H bonds with CO2

Carbon dioxide (CO₂) is an ideal one-carbon source owing to its nontoxicity, abundance, availability, and recyclability.

The Alpha Isoform of Heat Shock Protein 90 and the Co-chaperones p23 and Cdc37 Promote Opioid Anti-nociception in the Brain

Opioid activation of the mu opioid receptor (MOR) promotes signaling cascades that evoke both analgesic responses to pain and side effects like addiction and dependence. Manipulation of these cascades, such as by biased agonism, has great promise to improve opioid therapy. However, the signaling cascades of the MOR are in general poorly understood, providing few targets for drug development. In our earlier work, we identified Heat shock protein 90 (Hsp90) as a novel and crucial regulator of opioid anti-nociception in the brain by promoting ERK MAPK activation. In this study, we sought to identify the molecular isoforms and co-chaperones by which Hsp90 carried out this role, which could provide specific targets for future clinical intervention. We used novel selective small molecule inhibitors as well as CRISPR/Cas9 gene editing constructs delivered by the intracerebroventricular (icv) route to the brains of adult CD-1 mice to target Hsp90 isoforms (Hsp90α/β, Grp94) and co-chaperones (p23, Cdc37, Aha1). We found that inhibition of the isoform Hsp90α fully blocked morphine anti-nociception in a model of post-surgical paw incision pain, while blocking ERK and JNK MAPK activation, suggesting Hsp90α as the main regulator of opioid response in the brain. We further found that inhibition of the co-chaperones p23 and Cdc37 blocked morphine anti-nociception, suggesting that these co-chaperones assist Hsp90α in promoting opioid anti-nociception. Lastly, we used cycloheximide treatment in the brain to demonstrate that rapid protein translation within 30 min of opioid treatment is required for Hsp90 regulation of opioid response. Together these studies provide insight into the molecular mechanisms by which Hsp90 promotes opioid anti-nociception. These findings thus both improve our basic science knowledge of MOR signal transduction and could provide future targets for clinical intervention to improve opioid therapy.

Mitochondrial-targeted Hsp90 C-terminal inhibitors manifest anti-proliferative activity

The development of C-terminal heat shock protein 90 kDa (Hsp90) inhibitors has emerged as a potential treatment for cancer. Similarly, small molecules that target the mitochondria have proven to be efficacious towards cancer, as the reprogramming of mitochondrial function is often associated with oncogenic transformation. Herein, we report the development of triphenylphosphonium (TPP)-conjugated Hsp90 C-terminal inhibitors, their anti-proliferative activity, and accumulation in the mitochondria. In general, TPP-conjugated Hsp90 C-terminal inhibitors were found to manifest increased activity against various cancer cell lines when compared to the parent compounds.

An efficient, mild and metal freel-proline catalyzed construction of fused pyrimidines under microwave conditions in water

One-pot condensation of 4-hydroxy coumarins, aldehydes and urea/thiourea to build C–C and C–N bonds is described. Fused pyrimidines have been synthesized under mild reaction conditions using l-proline. The protocol has been performed rapidly and efficiently in water under metal free conditions. Heterocyclic derivatives have been synthesized using the present methodology and avoid the use of hazardous solvents over conventional organic solvents. A proposed mechanism could be established for three component reactions. The present study reveals the first case in which l-proline has been explored as a homogeneous catalyst in the synthesis of fused pyrimidines in water under microwave irradiation. This synthesis involves simple workup and acceptable efficiency. The most notable feature of this protocol is the ability of the catalyst to influence asymmetric induction in the reaction.

One-pot condensation of 4-hydroxy coumarins, aldehydes and urea/thiourea to build C–C and C–N bonds is described.

Novobiocin-ferrocene conjugates possessing anticancer and antiplasmodial activity independent of HSP90 inhibition

A series of tailored novobiocin-ferrocene conjugates was prepared in moderate yields and investigated for in vitro anticancer and antiplasmodial activity against the MDA-MB-231 breast cancer line and Plasmodium falciparum 3D7 strain, respectively. While the target compounds displayed moderate anticancer activity against the breast cancer cell line with IC₅₀ values in the mid-micromolar range, compounds 10a-c displayed promising antiplasmodial activity as low as 0.889 µM. Furthermore, the most promising compounds were tested for inhibitory effects against a postulated target, heat shock protein 90 (Hsp90). A selection of tailored novobiocin derivatives bearing the organometallic ferrocene unit were synthesized and characterized by common spectroscopic techniques. The target compounds were investigated for in vitro anticancer and antimalarial activity against the MDA-MB-231 breast cancer cell line and Plasmodium falciparum 3D7 strain, respectively.

Metal-Free Construction of Fused Pyrimidines via Consecutive C-C and C-N Bond Formation in Water

A facile and efficient protocol has been developed for mild construction of fused pyrimidines via l-proline-catalyzed reaction of 4-hydroxy coumarins, aldehydes, and 2-aminobenzothiazoles/urea. The reaction has been carried out rapidly and efficiently in water under mild and metal-free conditions. Current etiquette has efficiently synthesized the heterocycles and avoids the use of hazardous solvents over conventional organic solvents. A plausible reaction mechanism has been established in this study. This study represents the first case in which l-proline as a homogeneous catalyst has been explored in the synthesis of fused pyrimidines in water in view of simple procedure and acceptable efficiency. This method gives the target product in excellent yield with ease of workup.

Development of a novel Hsp90 inhibitor NCT-50 as a potential anticancer agent for the treatment of non-small cell lung cancer

Despite the development of advanced therapeutic regimens such as molecular targeted therapy and immunotherapy, the 5-year survival of patients with lung cancer is still less than 20%, suggesting the need to develop additional treatment strategies. The molecular chaperone heat shock protein 90 (Hsp90) plays important roles in the maturation of oncogenic proteins and thus has been considered as an anticancer therapeutic target. Here we show the efficacy and biological mechanism of a Hsp90 inhibitor NCT-50, a novobiocin-deguelin analog hybridizing the pharmacophores of these known Hsp90 inhibitors. NCT-50 exhibited significant inhibitory effects on the viability and colony formation of non-small cell lung cancer (NSCLC) cells and those carrying resistance to chemotherapy. In contrast, NCT-50 showed minimal effects on the viability of normal cells. NCT-50 induced apoptosis in NSCLC cells, inhibited the expression and activity of several Hsp90 clients including hypoxia-inducible factor (HIF)-1α, and suppressed pro-angiogenic effects of NSCLC cells. Further biochemical and in silico studies revealed that NCT-50 downregulated Hsp90 function by interacting with the C-terminal ATP-binding pocket of Hsp90, leading to decrease in the interaction with Hsp90 client proteins. These results suggest the potential of NCT-50 as an anticancer Hsp90 inhibitor.

Inhibitors and chemical probes for molecular chaperone networks

The molecular chaperones are central mediators of protein homeostasis. In that role, they engage in widespread protein-protein interactions (PPIs) with each other and with their "client" proteins. Together, these PPIs form the backbone of a network that ensures proper vigilance over the processes of protein folding, trafficking, quality control, and degradation. The core chaperones, such as the heat shock proteins Hsp60, Hsp70, and Hsp90, are widely expressed in most tissues, yet there is growing evidence that the PPIs among them may be re-wired in disease conditions. This possibility suggests that these PPIs, and perhaps not the individual chaperones themselves, could be compelling drug targets. Indeed, recent efforts have yielded small molecules that inhibit (or promote) a subset of inter-chaperone PPIs. These chemical probes are being used to study chaperone networks in a range of models, and the successes with these approaches have inspired a community-wide objective to produce inhibitors for a broader set of targets. In this Review, we discuss progress toward that goal and point out some of the challenges ahead.

Synthesis and evaluation of a ring-constrained Hsp90 C-terminal inhibitor that exhibits neuroprotective activity

KU-596 is a second-generation C-terminal heat shock protein 90 KDa (Hsp90) modulator based on the natural product, novobiocin. KU-596 has been shown to induce Hsp70 levels and manifest neuroprotective activity through induction of the heat shock response. A ring-constrained analog of KU-596 was designed and synthesized to probe its binding orientation and ability to induce Hsp70 levels. Compound 2 was found to exhibit comparable or increased activity compared to KU-596, which is under clinical investigation for the treatment of neuropathy.

Exploiting polarity and chirality to probe the Hsp90 C-terminus

Inhibition of the Hsp90 C-terminus is an attractive therapeutic approach for the treatment of cancer. Novobiocin, the first Hsp90 C-terminal inhibitor identified, contains a synthetically complex noviose sugar that has limited the generation of structure-activity relationships for this region of the molecule. The work described herein utilizes various ring systems as noviose surrogates to explore the size and nature of the surrounding binding pocket.

In silico identification and analysis of the binding site for aminocoumarin type inhibitors in the C-terminal domain of Hsp90

Hsp90 contains two Nucleotide Binding Sites (NBS): one each in its N-terminal domain (NTD) and C-terminal domain (CTD), respectively. Previously we used computational techniques to locate a nucleotide-binding site in the CTD. Nucleotide binding at this site stabilized the structurally labile region within this domain, thus providing a rationale for increased resistance to thermal denaturation and proteolysis. A scan for ligand-binding sites in CTD revealed four potential sites with the requisite volume to accommodate aminocoumarins and -derived inhibitors. Only one of these reproducibly formed docked complexes with inhibitors and showed excellent interactions with residues lining the site. Fortuitously, it was identical to the aforementioned nucleotide-binding site thus providing an explanation for the reported direct competition between inhibitors and nucleotides. Further studies with carefully chosen inhibitors and some inactive analogues provided an explanation for the known Structure-Activity Relationships (SAR) of aminocoumarin and -derived inhibitors. We also performed similar studies of the NTD to discern the reason(s) for its inability to bind aminocoumarins, given the family resemblance to prokaryotic Top-IV and Gyr-B. Our studies permitted the identification of the putative inhibitor binding site in the CTD, an explanation for increased resistance to thermal denaturation and proteolysis upon inhibitor binding as well as direct competition with ATP.

Designing novel inhibitors against falcipain-2 of Plasmodium falciparum

Coumarin containing pyrazoline derivatives have been synthesized and tested as inhibitors of in vitro development of a chloroquine-sensitive (MRC-02) and chloroquine-resistant (RKL-2) strain of Plasmodium falciparum and in vivo Plasmodium berghei malaria. Docking study was also done on cysteine protease falcipain-2 which showed that the binding pose of C-14 molecule and epoxysuccinate, inhibitor of falcipain-2, binds in the similar pattern. The most active antimalarial compound was 3-(1-benzoyl-5-(4-flurophenyl)-4,5-dihydro-1H-pyrazol-3yl)-7-(diethyamino)-2H-chromen-2-one C-14, with an IC₅₀ of 4.21 µg/ml provided complete protection to the infected mice at 24 mg/kg X 4 days respectively.

Development of noviomimetics that modulate molecular chaperones and manifest neuroprotective effects

Heat shock protein 90 (Hsp90) is a chaperone under investigation for the treatment of cancer and neurodegenerative diseases. Neuroprotective Hsp90 C-terminal inhibitors derived from novobiocin (novologues) include KU-32 and KU-596. These novologues modulate molecular chaperones and result in an induction of Heat Shock Protein 70 (Hsp70). "Noviomimetics" replace the synthetically complex noviose sugar with a simple cyclohexyl moiety to maintain biological efficacy as compared to novologues KU-596 and KU-32. In this study, we further explore the development of noviomimetics and evaluate their efficacy using a luciferase refolding assay, immunoblot analysis, a c-jun assay, and an assay measuring mitochondrial bioenergetics. These new noviomimetics were designed and synthesized and found to induce Hsp70 and improve biological activity. Noviomimetics 39e and 40a were found to induce Hsp70 and exhibit promising effects in cellular assays.

Synthesis and Biological Evaluation of Stilbene Analogues as Hsp90 C-Terminal Inhibitors

The design, synthesis, and biological evaluation of stilbene-based novobiocin analogues is reported. Replacement of the biaryl amide side chain with a triazole side chain produced compounds that exhibited good antiproliferative activities. Heat shock protein 90 (Hsp90) inhibition was observed when N-methylpiperidine was replaced with acyclic tertiary amines on the stilbene analogues that also contain a triazole-derived side chain. These studies revealed that ≈24 Å is the optimal length for compounds that exhibit good antiproliferative activity as a result of Hsp90 inhibition.