Synthesis and evaluation of Hsp90 inhibitors that contain the 1,4-naphthoquinone scaffold

Small molecule inhibitors targeting heat shock protein 90: An updated review

As a molecular chaperone, heat shock protein 90 (HSP90) plays important roles in the folding, stabilization, activation, and degradation of over 500 client proteins, and is extensively involved in cell signaling, proliferation, and survival. Thus, it has emerged as an important target in a variety of diseases, including cancer, neurodegenerative diseases, and viral infections. Therefore, targeted inhibition of HSP90 provides a valuable and promising therapeutic strategy for the treatment of HSP90-related diseases. This review aims to systematically summarize the progress of research on HSP90 inhibitors in the last five years, focusing on their structural features, design strategies, and biological activities. It will refer to the natural products and their derivatives (including novobiocin derivatives, deguelin derivatives, quinone derivatives, and terpenoid derivatives), and to synthetic small molecules (including resorcinol derivatives, pyrazoles derivatives, triazole derivatives, pyrimidine derivatives, benzamide derivatives, benzothiazole derivatives, and benzofuran derivatives). In addition, the major HSP90 small-molecule inhibitors that have moved into clinical trials to date are also presented here.

Structure-based discovery of potent myosin inhibitors to guide antiparasite drug development

Monogenea, a prevalent parasite in aquaculture, poses significant threats to the industry, leading to substantial losses. Current preventive measures have proven insufficient, necessitating the development of novel and effective anti-parasitic drugs. In this investigation, we obtained the full-length myosin cDNA sequence by analyzing three-generation transcriptome data, revealing a 5817-base sequence encoding 1938 amino acids. Subsequently, we modeled and analyzed the characteristics of the secondary and tertiary of myosin, pinpointing the crucial functional region within the motor domain (amino acids 1-768). The prokaryotic expression of this domain yielded a protein of 87.44 kDa, confirmed as myosin by Western Blotting. Molecular docking identified ASN439 as the key amino acid residue involved in arctigenin and myosin binding, a result corroborated by site-directed mutagenesis, affirming the active cavity of this interaction. Chalcone and shikonin were chosen from a virtual sieve of molecular library of natural drugs based on the active cavity. Chalcone and shikonin exhibited EC50 values of 1.085 mg/L and 0.371 mg/L, respectively, with corresponding IC50 values for myosin of 0.44 mM and 0.14 mM. Given its superior activity and structure, shikonin was selected for further optimization of drug molecule design, culminating in the discovery of 1,4-naphthoquinone as a potent antiparasitic agent. This compound demonstrated an EC50 of 0.047 mg/L, LC50 of 0.23 mg/L, and a TI index of 4.893. These findings collectively highlight the potential of shikonin and 1,4-naphthoquinone as alternative compounds to control Gyrodactylus infections. Further optimization of medicinal chemistry holds promise for the development of more potent 1,4-naphthoquinone analogues, offering prospects for future anthelmintic control through combinatorial or replacement strategies.

tert-Butylhydroperoxide mediated radical cyanoalkylation/cyanoalkenylation of 2-anilino-1,4-naphthoquinones with vinylarenes/arylalkynes and azobis(alkylcarbonitrile)s

A novel sustainable methodology based on one-pot cyanoalkylation/cyanoalkenylation of 2-anilino-1,4-naphthoquinones with vinylarenes/arylalkynes and azobis(alkylcarbonitrile)s involving a three-component radical cascade pathway has been achieved. Here, tert-butylhydroperoxide (TBHP) acts as an efficient oxidant, and it smoothly drives the reaction, producing the three-component products in very good to excellent yields. This cascade reaction eliminates the use of any base, additive, metal and hazardous cyanating agent. Additionally, this protocol exclusively delivers a stereospecific product in the case of arylalkynes. The involvement of radicals is evidenced through various radical trapping experiments.

Photochemical C-H Arylation of Napthoquinones Using Eosin Y

A visible-light-mediated C-H arylation of substituted 1,4-napthoquinones (1,4-SNQ) and 1,2-napthoquinone (1,2-NQ) with diazonium salt using a photocatalyst eosin Y at room temperature in a single step (isolated yield of ≥75%) is described in this report. The rate-determining step of the reaction is aryl radical generation, which was trapped by high-resolution mass spectrometry. Cost-effectiveness, operational simplicity, a short reaction time, high atom economy, and a good yield make this photoredox-mediated process a valuable alternative to the transition-metal (Fe, Cu, Pd, etc.)-catalyzed reaction.

Iron catalyzed C–C dehydrogenative coupling reaction: synthesis of arylquinones from quinones/hydroquinones

An atom-economical approach for the synthesis of arylquinones was achieved successfully via direct oxidative C–C dehydrogenative coupling reaction of quinones/hydroquinones with electron-rich arenes using an inexpensive Fe–I₂–(NH₄)₂S₂O₈ system. The efficiency of this catalytic approach was established with a broad scope of substrates involving quinones and hydroquinones to give high yields (60–89%) of several arylated quinones. The present protocol is simple, practical, and shows good functional group tolerance.

The synthesis of arylquinones was achieved via direct oxidative C–H/C–H cross-coupling of quinones/hydroquinones with electron-rich arenes using Fe–I₂–(NH₄)₂S₂O₈ system involving quinones/hydroquinones to give high yields (60–89%) of arylquinones.

New 2-Acetyl-3-aminophenyl-1,4-naphthoquinones: Synthesis and In Vitro Antiproliferative Activities on Breast and Prostate Human Cancer Cells

The reaction of 2-acyl-1,4-naphthoquinones with N,N-dimethylaniline and 2,5-dimethoxyaniline, promoted by catalytic amounts of CeCl₃·7H₂O under “open-flask” conditions, produced a variety of 2-acyl-3-aminophenyl-1,4-naphthoquinones structurally related to the cytotoxic 2-acetyl-3-phenyl-1,4-naphthoquinone, an inhibitor of the heat shock chaperone protein Hsp90. The members of the 2-acyl-3-aminophenyl-1,4-naphthoquinone series were isolated in good yields (63-98%). The cyclic voltammograms of the 2-acyl-3-aminophenyl-1,4-naphthoquinone exhibit two one-electron reduction waves to the corresponding radical-anion and dianion and two quasireversible oxidation peaks. The first and second half-wave potential values (E_1/2) of the members of the series are sensitive to the push-pull electronic effects of the substituents in the naphthoquinone scaffold. Furthermore, the in vitro antiproliferative properties of these new quinones were evaluated on two human cancer cells DU-145 (prostate) and MCF-7 (mammary) and a nontumorigenic HEK-293 (kidney) cell line, using the MTT colorimetric method. Two members, within the series, exhibited interesting cytotoxic activities on human prostate and mammary cancer cells.

Identification of the naphthoquinone derivative inhibitors binding site in heat shock protein 90: an induced-fit docking, molecular dynamics and 3D-QSAR study

The combination of molecular modeling methods to identify the putative binding site of inhibitors constitutes an important tool in drug discovery. In this work, we used these analyses to understand the potent inhibitory effect of naphthoquinone derivatives on heat shock protein 90 (Hsp90), one of the proteins involved in many types of cancer. Molecular docking results indicated that some favorable interactions of key amino acid residues at the binding site of Hsp90 with these quinones would be responsible for the inhibition of Hsp90 activity. Molecular docking and molecular dynamics simulation were carried out to further understand the binding modes and the interactions between the protein and these inhibitors. The main residues of the internal cavity were Val136, Phe138, Tyr139, Val150, Trp162 and Val186. The high concordance between the docking results and 3D-QSAR contour maps gives us helpful information about the environment of the binding site. Our results provide the bases for a rational modification of new molecules based in quinone scaffold, in order to design more potent Hsp90 inhibitors, which would exhibit highly potent antitumor activity.Communicated by Ramaswamy H. Sarma.

Oxidative radical coupling of hydroquinones and thiols using chromic acid: one-pot synthesis of quinonyl alkyl/aryl thioethers

An efficient, simple and practical protocol for one-pot sequential oxidative radical C–H/S–H cross-coupling of thiols with hydroquinones (HQs) and oxidation leading to the formation of quinonyl alkyl/aryl thioethers using H₂CrO₄ was developed. This cross-coupling of thiyl and aryl radicals offers mono thioethers in good to moderate yield and works well with a wide variety of thiols. Similarly, this method works well for coupling of 2-amino thiophenol and HQs to form phenothiazine-3-ones 5a–c. C–S bond formation via thioether synthesis was observed using a chromium reagent for the first time. Theoretical studies on the pharmacokinetic properties of compounds 5a–c revealed that due to drug-like properties, compound 5b strongly binds with Alzheimer's disease (AD) associated AChE target sites.

Oxidative radical C–H/S–H cross coupling of hydroquinones and thiols and oxidation to quinone using a H₂CrO₄ system was developed.

Vitamin K1 As A Potential Molecule For Reducing Single-Walled Carbon Nanotubes-Stimulated α-Synuclein Structural Changes And Cytotoxicity

Aims

Different kinds of vitamins can be used as promising candidates to mitigate the structural changes of proteins and associated cytotoxicity stimulated by NPs. Therefore, the structural changes of α-syn molecules and their associated cytotoxicity in the presence of SWCNTs either alone or co-incubated with vitamin K1 were studied by spectroscopic, bioinformatical, and cellular assays.

Methods

Intrinsic and ThT fluorescence, CD, and Congo red absorption spectroscopic approaches as well as TEM investigation, molecular docking, and molecular dynamics were used to explore the protective effect of vitamin K1 on the structural changes of α-syn induced by SWCNTs. The cytotoxicity of α-syn/SWCNTs co-incubated with vitamin K1 against SH-SY5Y cells was also carried out by MTT, LDH, and caspase-3 assays.

Results

Fluorescence spectroscopy showed that vitamin K1 has a significant effect in reducing SWCNT-induced fluorescence quenching and aggregation of α- syn. CD, Congo red adsorption, and TEM investigations determined that co-incubation of α- syn with vitamin K1 inhibited the propensity of α-syn into the structural changes and amorphous aggregation in the presence of SWCNT. Docking studies determined the occupation of preferred docked site of SWCNT by vitamin K1 on α- syn conformation. A molecular dynamics study also showed that vitamin K1 reduced the structural changes of α- syn induced by SWCNT. Cellular data exhibited that the cytotoxicity of α- syn co-incubated with vitamin K1 in the presence of SWCNTs is less than the outcomes obtained in the absence of the vitamin K1.

Conclusion

It may be concluded that vitamin K1 decreases the propensity of α- syn aggregation in the presence of SWCNTs and induction of cytotoxicity.

Novel Heat Shock Protein 90 Inhibitors Suppress P-Glycoprotein Activity and Overcome Multidrug Resistance in Cancer Cells

Heat Shock Protein 90 (Hsp90) chaperone interacts with a broad range of client proteins involved in cancerogenesis and cancer progression. However, Hsp90 inhibitors were unsuccessful as anticancer agents due to their high toxicity, lack of selectivity against cancer cells and extrusion by membrane transporters responsible for multidrug resistance (MDR) such as P-glycoprotein (P-gp). Recognizing the potential of new compounds to inhibit P-gp function and/or expression is essential in the search for effective anticancer drugs. Eleven Hsp90 inhibitors containing an isoxazolonaphtoquinone core were synthesized and evaluated in two MDR models comprised of sensitive and corresponding resistant cancer cells with P-gp overexpression (human non-small cell lung carcinoma and colorectal adenocarcinoma). We investigated the effect of Hsp90 inhibitors on cell growth inhibition, P-gp activity and P-gp expression. Structure-activity relationship analysis was performed in respect to cell growth and P-gp inhibition. Compounds 5, 7, and 9 directly interacted with P-gp and inhibited its ATPase activity. Their potential P-gp binding site was identified by molecular docking studies. In addition, these compounds downregulated P-gp expression in MDR colorectal carcinoma cells, showed good relative selectivity towards cancer cells, while compound 5 reversed resistance to doxorubicin and paclitaxel in concentration-dependent manner. Therefore, compounds 5, 7 and 9 could be promising candidates for treating cancers with P-gp overexpression.

Conjugation with polyamines enhances the antitumor activity of naphthoquinones against human glioblastoma cells

Glioblastoma multiform (GBM) is the most common and devastating type of primary brain tumor, being considered the deadliest of human cancers. In this context, extensive efforts have been undertaken to develop new drugs that exhibit both antiproliferation and antimetastasis effects on GBM. 1,4-Naphthoquinone (1,4-NQ) scaffold has been found in compounds able to inhibit important biological targets associated with cancer, which includes DNA topoisomerase, Hsp90 and monoamine oxidase. Among potential antineoplastic 1,4-NQs is the plant-derived lapachol (2-hydroxy-3-prenyl-1,4-naphthoquinone) that was found to be active against the Walker-256 carcinoma and Yoshida sarcoma. In the present study, we examined the effect of polyamine (PA)-conjugated derivatives of lapachol, nor-lapachol and lawsone on the growth and invasion of the human GBM cells. The conjugation with PA (a spermidine analog) resulted in dose-dependent and time-dependent increase of cytotoxicity of the 1,4-NQs. In addition, in-vitro inhibition of GBM cell invasion by lapachol was increased upon PA conjugation. Previous biochemical experiments indicated that these PA-1,4-NQs are capable of inhibiting DNA human topoisomerase II-α (topo2α), a major enzyme involved in maintaining DNA topology. Herein, we applied molecular docking to investigate the binding of PA-1,4-NQs to the ATPase site of topo2α. The most active molecules preferentially bind at the ATP-binding site of topo2α, which is energetically favored by the conjugation with PA. Taken together, these findings suggested that the PA-1,4-NQ conjugates might represent potential molecules in the development of new drugs in chemotherapy for malignant brain tumors.

Iron-mediated site-selective oxidative C–H/C–H cross-coupling of aryl radicals with quinones: synthesis of β-secretase-1 inhibitor B and related arylated quinones

Phenoxy radicals were converted intoparasite selectiveC-aryl radicals and coupled with quinones, using an inexpensive FeCl₃–K₂S₂O₈system, to obtain several arylated quinones, in good to moderate yields.

Synthesis, Characterization and In-vitro Evaluation of Novel Naphthoquinone Derivatives and Related Imines: Identification of New Anticancer Leads

Quinones such as 1,4-naphthoquinones are abundant in nature and naphthoquinone based natural products are known to possess anticancer activity. This pharmacophore is known to convey anticancer activity to some drugs such as streptonigrin, mitomycin A, etc. We synthesized and characterized different classes of naphthoquinone derivatives including bis naphthoquinone, 2-arylaminonaphthoquinone, benzoxantene-6,11-dione and benzoacridine-5,6-dione derivatives instead of the expected 2-hydroxy-3-(substituted phenyl(aryl amino)methyl)naphthalene-1,4-dione derivatives from the reaction of 2-hydroxy1,4-naphthoquinone (lawson) with different benzaldehydes and aryl amines. Benzoacridine-5,6-dione derivatives and related imines showed potent anti-breast cancer activity in MCF-7 cancer cells. The in-vitro results revealed that five compounds benzoacridinedione derivatives (6b and 7b) and imines (13, 14 and 15) by the IC₅₀ range of 5.4-47.99 μM are the most potent anti-breast cancer structures.

Antiproliferative and proapoptotic activities of aza-annulated naphthoquinone analogs

1,4-Naphthoquinone derivatives have been widely documented with regard to their biological properties, and particularly their anticancer activities. In the 9,10-anthraquinone family, aza-annulation involving one of the carbonyl oxygen atoms has afforded more potent, possibly less toxic analogues. We recently carried out different modifications on the naphthoquinone skeleton to generate 3-chloro-2-amino- and 3-chloro-2-(N-acetamido)-1,4-naphthoquinone and 3,4-dihydrobenzo[f]quinoxalin-6(2H)-one derivatives. These three series of compounds were now tested against normal human fibroblasts and six human cancer cell lines. Some of the dihydrobenzoquinoxalinone derivatives were not only more potent than their 1,4-naphthoquinone counterparts, but also exhibited 10- to 14-fold selectivity between bladder carcinoma and normal cells and were equipotent with the non-selective reference drug used (etoposide). The fusion of an additional azaheterocycle to the 1,4-naphthoquinone nucleus modulates both the activity, selectivity and mechanism of action of the compounds. The electrochemical properties of selected compounds were evaluated in an attempt to correlate them with cytotoxic activity and mechanism of action. Finally, 3D-QSAR CoMFA and CoMSIA models were built on the AGS, J82, and HL-60 cell lines. The best models had values of r²_pred = 0.815; 0.823 and 0.925. The main structural relationships found, suggest that acetylation and alkylation of the amino group with large groups would be beneficial for cytotoxic activity.

Benzimidazoisoquinoline derivatives inhibit glioblastoma cell proliferation through down-regulating Raf/MEK/ERK and PI3K/AKT pathways

Background

Recent studies showed that benzimidazoleisoquinolinone derivatives exhibit anticancer activity against human cancer cell lines. The aim of this study is to evaluate the anti-tumor effects and mechanisms of benzimidazoleisoquinolinones in isocitrate dehydrogenase-wildtype subtype of human glioblastoma (GBM) cells.

Methods

Human U87 and LN229 cell lines were used to perform the experiments. MTT was applied to screen the effective small molecular inhibitors suppressing growth of GBM cells. Colony formation and BrdU staining assays were performed to assess the inhibition effect of compound-1H on the proliferation of GBM cells. The cell cycle and apoptosis were measured by flow cytometry and western blot to analyze the changes of the relative protein expressions and their signal pathways.

Results

Compound-1H could suppress GBM cells in a time- and dose-dependent manner. Treatment of compound-1H could arrest cell cycle in S phase through up-regulating P21 and P53, and down-regulating cyclin A and E in a dose-dependent manner. Compound-1H also induced mitochondrial-dependent apoptosis by increasing Bax, cleaved caspase-3, cleaved caspase-9 and poly ADP-ribose polymerase expression, and decreasing Bcl-2 expression. Moreover, phosphorylated (p)-AKT and p-ERK levels relating to cell proliferation were dramatically decreased in U87 and LN229 cells.

Conclusions

Our results suggest that it is the first time to report the compound-1H with benzimidazoleisoquinolinone core playing antitumor activity in human glioblastoma cells by inhibiting Raf/MEK/ERK and PI3K/AKT signaling pathways, and it could be as a lead compound for the further development of targeted glioblastoma cancer therapy.

Synthesis and Evaluation of the Tumor Cell Growth Inhibitory Potential of New Putative HSP90 Inhibitors

Background: Heat shock protein 90 (HSP90) is a well-known target for cancer therapy. In a previous work, some of us have reported a series of 3-aryl-naphtho[2,3-d]isoxazole-4,9-diones as inhibitors of HSP90. Methods: In the present work, various compounds with new chromenopyridinone and thiochromenopyridinone scaffolds were synthesized as potential HSP90 inhibitors. Their binding affinity to HSP90 was studied in vitro. Selected compounds (5 and 8) were further studied in various tumor cell lines regarding their potential to cause cell growth inhibition, alter the cell cycle profile, inhibit proliferation, and induce apoptosis. Their effect on HSP90 client protein levels was also confirmed in two cell lines. Finally, the antitumor activity of compound 8 was studied in A431 squamous cell carcinoma xenografts in nude mice. Results: Our results indicated that treatment with compounds 5 and 8 decreased the proliferation of tumor cell lines and compound 8 induced apoptosis. In addition, these two compounds were able to downregulate selected proteins known as “clients” of HSP90. Finally, treatment of xenografted mice with compound 5 resulted in a considerable dose-dependent inhibition of tumor growth. Conclusions: Our results show that two new compounds with a chromenopyridinone and thiochromenopyridinone scaffold are promising putative HSP90 inhibitors causing tumor cell growth inhibition.

Targeting Akt as strategy to kill cancer cells using 3-substituted 5-anilinobenzo[c]isoxazolequinones: A preliminary study

Several new 3-substituted 5-anilinobenzo[c]isoxazolequinones were synthesized from 1,4-benzoquinone and alkyl- or arylcarbaldehydes by a three-step synthetic sequence. The new compounds (3a-h) were tested in vitro in normal human fibroblasts and two cancer cell lines for their cytotoxic activity. The range of IC₅₀ values obtained for the compounds was from 3.4 to 74.2μM. Five members of the series (3b, 3d, 3e, 3f, 3g) were further selected and evaluated as inhibitors of the Hsp90 chaperoning function taking Akt as example of Hsp90 client proteins. We also evaluated the changes of intracellular levels of GSH and ATP as markers of cellular metabolic status in response to these compounds in T24 cells. One of such isoxazolquinones (3b) decreased the expression of Akt, PARP and Hsp90. Compounds 3b and 3d decreased the amount of ATP but caused no effect on GSH levels. These compounds also activated caspase-3 but an apoptosis-like type of cell death was unlike since PARP protein was not cleaved and caspase activation was substantially lower than its activation induced by staurosporine, a known caspase-3 activator in T24 cells. Taken together, preliminary results led to the discovery of an original lead compound (3b) which can be used as model to obtain new Akt inhibitors.

Enhanced tau pathology via RanBP9 and Hsp90/Hsc70 chaperone complexes

Accumulation of amyloid β (Aβ) and tau represent the two major pathological hallmarks of Alzheimer's disease (AD). Despite the critical importance of Aβ accumulation as an early event in AD pathogenesis, multiple lines of evidence indicate that tau is required to mediate Aβ-induced neurotoxic signals in neurons. We have previously shown that the scaffolding protein Ran-binding protein 9 (RanBP9), which is highly elevated in brains of AD and AD mouse models, both enhances Aβ production and mediates Aβ-induced neurotoxicity. However, it is unknown whether and how RanBP9 transmits Aβ-induced neurotoxic signals to tau. Here we show for the first time that overexpression or knockdown of RanBP9 directly enhances and reduces tau levels, respectively, in vitro and in vivo. Such changes in tau levels are associated with the ability of RanBP9 to physically interact with tau and heat shock protein 90/heat shock cognate 70 (Hsp90/Hsc70) complexes. Meanwhile, both RanBP9 and tau levels are simultaneously reduced by Hsp90 or Hsc70 inhibitors, whereas overexpression or knockdown of RanBP9 significantly diminishes the anti-tau potency of Hsp90/Hsc70 inhibitors as well as Hsc70 variants (WT & E175S). Further, RanBP9 increases the capacity for Hsp90 and Hsc70 complexes to bind ATP and enhances their ATPase activities in vitro. These observations in vitro and cell lines are recapitulated in primary neurons and in vivo, as genetic reduction in RanBP9 not only ameliorates tauopathy in Tau-P301S mice but also rescues the deficits in synaptic integrity and plasticity.

A Scaffold Merging Approach to Hsp90 C-terminal Inhibition: Synthesis and Evaluation of a Chimeric Library

Inhibition of the Hsp90 C-terminus is an attractive therapeutic paradigm for the treatment of cancer, however the developmental space of C-terminal inhibitors is limited. It was hypothesized that the combination of two previously identified scaffolds into a single structure could provide a platform for which to probe the three-dimensional space within the Hsp90 C-terminal binding pocket. The resulting chimeric compounds displayed anti-proliferative activity at low micromolar concentrations and manifested inhibitory activity in an Hsp90-dependent rematuration assay. Initial structure-activity relationships suggest that this new scaffold binds Hsp90 in a conformation different from that of the parent compounds, and consequently, provides a new opportunity to develop more efficacious inhibitors of the Hsp90 C-terminal binding pocket.

Synthetic approaches and in vitro cytotoxic evaluation of 2-acyl-3-(3,4,5-trimethoxyanilino)-1,4-naphthoquinones

2-Acyl-1,4-naphthoquinones react with 3,4,5-trimethoxyaniline, under aerobic conditions, to give benzophenanthridinequinone, benzocarbazole and 2-acyl-3-(3,4,5-trimethoxyanilino)-1,4-naphthoquinone derivatives.

An Efficient and Facile Method for the Synthesis of Benzimidazoisoquinoline Derivatives via a Multicomponent Reaction

Two series of benzimidazoisoquinoline and fused benzimidazoisoquinoline-benzimidazole derivatives have been synthesized using an efficient one-pot procedure. This process involves an intramolecular nucleophilic substitution reaction and provides facile access to two series of complexes and potentially interesting biologically active scaffolds.

An efficient approach to bis-benzoquinonylmethanes on water under catalysis of the bio-derived O-carboxymethyl chitosan

O-Carboxymethyl chitosan was found to simulate an enzyme-like catalytic activity in the one-pot pseudo-three-component synthesis of bis-benzoquinonylmethane dyes in water.

Synthesis, characterization and biological activities of 3-aryl-1,4-naphthoquinones – green palladium-catalysed Suzuki cross coupling

Antifungal and trypanocidal aryl-1,4-naphthoquinones were prepared through an aqueous Suzuki protocol with reflux or microwave irradiation.

Synthesis and anti-proliferative activity evaluation of novel 1,4-naphthoquinones possessing pyrido[2,3-d]pyrimidine scaffolds

A series of novel 1,4-naphthoquinones possessing pyrido[2,3-d]pyrimidine scaffolds were synthesized and most of the compounds exhibited excellent anti-proliferative activities.

Biosynthesis and molecular actions of specialized 1,4-naphthoquinone natural products produced by horticultural plants

The 1,4-naphthoquinones (1,4-NQs) are a diverse group of natural products found in every kingdom of life. Plants, including many horticultural species, collectively synthesize hundreds of specialized 1,4-NQs with ecological roles in plant-plant (allelopathy), plant-insect and plant-microbe interactions. Numerous horticultural plants producing 1,4-NQs have also served as sources of traditional medicines for hundreds of years. As a result, horticultural species have been at the forefront of many basic studies conducted to understand the metabolism and function of specialized plant 1,4-NQs. Several 1,4-NQ natural products derived from horticultural plants have also emerged as promising scaffolds for developing new drugs. In this review, the current understanding of the core metabolic pathways leading to plant 1,4-NQs is provided with additional emphasis on downstream natural products originating from horticultural species. An overview on the biochemical mechanisms of action, both from an ecological and pharmacological perspective, of 1,4-NQs derived from horticultural plants is also provided. In addition, future directions for improving basic knowledge about plant 1,4-NQ metabolism are discussed.

Design, synthesis, and biological evaluation of ring-constrained novobiocin analogues as hsp90 C-terminal inhibitors

Hsp90 C-terminal inhibitors represent a novel and alternative chemotherapeutic approach for the treatment of cancer. Novobiocin was the first natural product identified as an Hsp90 C-terminal inhibitor; however, it manifests poor antiproliferative activity. In contrast to N-terminal inhibitors, novobiocin does not induce the pro-survival heat shock response. Structural investigations on novobiocin have elucidated some structure-activity relationships and several promising compounds. On the basis of structure-activity relationships and computational studies, a library of ring-constrained novobiocin analogues was designed, synthesized, and evaluated in antiproliferative assays. Results obtained from these studies provide insights into the Hsp90 C-terminal binding site, and new analogues that were developed manifest low micromolar to mid-nanomolar antiproliferative activity resulting from Hsp90 inhibition.

l-Proline catalyzed three-component synthesis of para-naphthoquinone–4-aza-podophyllotoxin hybrids as potent antitumor agents

A series of novelpara-naphthoquinone embodied 4-aza-podophyllotoxin hybrids were synthesized and some of the compounds exhibited excellent antitumor activities.

High-throughput screen of natural product libraries for hsp90 inhibitors

Hsp90 has become the target of intensive investigation, as inhibition of its function has the ability to simultaneously incapacitate proteins that function in pathways that represent the six hallmarks of cancer. While a number of Hsp90 inhibitors have made it into clinical trials, a number of short-comings have been noted, such that the search continues for novel Hsp90 inhibitors with superior pharmacological properties. To identify new potential Hsp90 inhibitors, we have utilized a high-throughput assay based on measuring Hsp90-dependent refolding of thermally denatured luciferase to screen natural compound libraries. Over 4,000 compounds were screen with over 100 hits. Data mining of the literature indicated that 51 compounds had physiological effects that Hsp90 inhibitors also exhibit, and/or the ability to downregulate the expression levels of Hsp90-dependent proteins. Of these 51 compounds, seven were previously characterized as Hsp90 inhibitors. Four compounds, anthothecol, garcinol, piplartine, and rottlerin, were further characterized, and the ability of these compounds to inhibit the refolding of luciferase, and reduce the rate of growth of MCF7 breast cancer cells, correlated with their ability to suppress the Hsp90-dependent maturation of the heme-regulated eIF2α kinase, and deplete cultured cells of Hsp90-dependent client proteins. Thus, this screen has identified an additional 44 compounds with known beneficial pharmacological properties, but with unknown mechanisms of action as possible new inhibitors of the Hsp90 chaperone machine.

Synthesis and characterization of novel unsymmetrical and symmetrical 3-halo- or 3-methoxy-substituted 2-dibenzoylamino-1,4-naphthoquinone derivatives

Symmetrical and unsymmetrical 3-halo- or 3-methoxy- substituted 2-dibenzoylamino- 1,4-naphthoquinone analogs were synthesized with an average yield of 45% via sodium hydride promoted bis-acylation of 2-amino-3-chloro-1,4-naphthoquinone, 2-amino-3-bromo-1,4-naphthoquinone and 2-amino-3-methoxy-1,4-naphthoquinone.

Vitamins K interact with N-terminus α-synuclein and modulate the protein fibrillization in vitro. Exploring the interaction between quinones and α-synuclein

In the last decades, a series of compounds, including quinones and polyphenols, has been described as having anti-fibrillogenic action on α-synuclein (α-syn) whose aggregation is associated to the pathogenesis of Parkinson's disease (PD). Most of these molecules act as promiscuous anti-amyloidogenic agents, interacting with the diverse amyloidogenic proteins (mostly unfolded) through non-specific hydrophobic interactions. Herein we investigated the effect of the vitamins K (phylloquinone, menaquinone and menadione), which are 1,4-naphthoquinone (1,4-NQ) derivatives, on α-syn aggregation, comparing them with other anti-fibrillogenic molecules such as quinones, polyphenols and lipophilic vitamins. Vitamins K delayed α-syn fibrillization in substoichiometric concentrations, leading to the formation of short, sheared fibrils and amorphous aggregates, which are less prone to produce leakage of synthetic vesicles. In seeding conditions, menadione and 1,4-NQ significantly inhibited fibrils elongation, which could be explained by their ability to destabilize preformed fibrils of α-syn. Bidimensional NMR experiments indicate that a specific site at the N-terminal α-syn (Gly31/Lys32) is involved in the interaction with vitamins K, which is corroborated by previous studies suggesting that Lys is a key residue in the interaction with quinones. Together, our data suggest that 1,4-NQ, recently showed up by our group as a potential scaffold for designing new monoamine oxidase inhibitors, is also capable to modulate α-syn fibrillization in vitro.

Isoxazolo(aza)naphthoquinones: a new class of cytotoxic Hsp90 inhibitors

A series of 3-aryl-naphtho[2,3-d]isoxazole-4,9-diones and some of their 6-aza analogues were synthesized and found to inhibit the heat shock protein 90 (Hsp90). The compounds were tested for their binding to Hsp90 and for their effects on Hsp90 client proteins expression in a series of human tumour cell lines. Representative compounds (7f, 10c) downregulated the Hsp90 client proteins EGFR, Akt, Cdk4, Raf-1, and survivin, and upregulated Hsp70. Most of the compounds, in particular the alkylated 3-pyridyl derivatives, exhibited potent antiproliferative activity, down to two-digit nanomolar range. Preliminary results indicated in vivo activity of 7f against human epithelial carcinoma A431 model growing as tumour xenograft in nude mice, thus supporting the therapeutic potential of this novel series of Hsp90 inhibitors.

Effects of respiratory mechanical forces on the pharmacological response of lung cancer cells to chemotherapeutic agents

In vitro screening of chemotherapeutic agents is routinely carried out in static monolayer cell cultures. However, drugs administered to patients act in the presence of various microenvironments in vivo. For example, in lung tumors, mechanical forces are constantly present and do affect the physiological response of the lung tissue to a variety of therapeutic agents. We hypothesized that mechanical forces may affect the response of lung tumors to chemotherapeutic agents and studied the effects under simulated conditions. First, we examined the effects of simulated forces that approximate normal respiration on the proliferation and morphology of NCI-H358 and A549 cell lines. Then, we studied the effects of the simulated forces on the ability of Paclitaxel, Doxorubicin, Cisplatin, Zactima and an experimental drug to induce cytotoxicity in both cell lines. Cells were treated with the drugs in the presence or absence of simulated forces (20% maximum strain and 15 cycles/minute) that approximate human lung expansion and contraction. Cell proliferation and the effectiveness of the drugs were assessed. Using a standard exponential cell growth model, it was determined that mechanical forces significantly reduced the proliferation of both cell lines. Interestingly, forces also significantly lowered the effectiveness of all drugs except Zactima in A549 cells, while in NCI-H358 cells, Zactima was the only drug that demonstrated an increase in effectiveness owing to applied forces. Our results demonstrate that mechanical forces have significant impact on cell survival and chemotherapeutic efficacy and may be of significance in engineering improved screening assays for antitumor drug discovery.