New Class Of Potent Inhibitors Research Articles

Identification of 1,2,3-triazolium salt-based inhibitors of Leishmania infantum trypanothione disulfide reductase with enhanced antileishmanial potency in cellulo and increased selectivity

N-methylation of the triazole moiety present in our recently described triazole-phenyl-thiazole dimerization disruptors of Leishmania infantum trypanothione disulfide reductase (LiTryR) led to a new class of potent inhibitors that target different binding sites on this enzyme. Subtle structural changes among representative library members modified their mechanism of action, switching from models of classical competitive inhibition to time-dependent mixed noncompetitive inhibition. X-ray crystallography and molecular modeling results provided a rationale for this distinct behavior. The remarkable potency and selectivity improvements, particularly against intracellular amastigotes, of the LiTryR dimerization disruptors 4c and 4d reveal that they could be exploited as leishmanicidal agents. Of note, L. infantum promastigotes treated with 4c significantly reduced their low-molecular-weight thiol content, thus providing additional evidence that LiTryR is the main target of this novel compound.

Structural Optimization and Structure-Activity Relationship Studies of 6,6-Dimethyl-4-(phenylamino)-6H-pyrimido[5,4-b][1,4]oxazin-7(8H)-one Derivatives as A New Class of Potent Inhibitors of Pan-Trk and Their Drug-Resistant Mutants.

Tropomyosin receptor kinases (TrkA, TrkB, and TrkC) are attractive therapeutic targets for multiple cancers. Two first-generation small-molecule Trks inhibitors, larotrectinib and entrectinib, have just been approved to use clinically. However, the drug-resistance mutations of Trks have already emerged, which calls for new-generation Trks inhibitors. Herein, we report the structural optimization and structure-activity relationship studies of 6,6-dimethyl-4-(phenylamino)-6H-pyrimido[5,4-b][1,4]oxazin-7(8H)-one derivatives as a new class of pan-Trk inhibitors. The prioritized compound 11g exhibited low nanomolar IC50 values against TrkA, TrkB, and TrkC and various drug-resistant mutants. It also showed good kinase selectivity. 11g displayed excellent in vitro antitumor activity and strongly suppressed Trk-mediated signaling pathways in intact cells. In in vivo studies, compound 11g exhibited good antitumor activity in BaF3-TEL-TrkA and BaF3-TEL-TrkCG623R allograft mouse models without exhibiting apparent toxicity. Collectively, 11g could be a promising lead compound for drug discovery targeting Trks and deserves further investigation.

2-Sulfonylpyrimidines as Privileged Warheads for the Development of S. aureus Sortase A Inhibitors.

Staphylococcus aureus is one of the most frequent causes of nosocomial and community-acquired infections, with emerging multiresistant isolates causing a significant burden to public health systems. We identified 2-sulfonylpyrimidines as a new class of potent inhibitors against S. aureus sortase A acting by covalent modification of the active site cysteine 184. Series of derivatives were synthesized to derive structure-activity relationship (SAR) with the most potent compounds displaying low micromolar KI values. Studies on the inhibition selectivity of homologous cysteine proteases showed that 2-sulfonylpyrimidines reacted efficiently with protonated cysteine residues as found in sortase A, though surprisingly, no reaction occurred with the more nucleophilic cysteine residue from imidazolinium-thiolate dyads of cathepsin-like proteases. By means of enzymatic and chemical kinetics as well as quantum chemical calculations, it could be rationalized that the S N Ar reaction between protonated cysteine residues and 2-sulfonylpyrimidines proceeds in a concerted fashion, and the mechanism involves a ternary transition state with a conjugated base. Molecular docking and enzyme inhibition at variable pH values allowed us to hypothesize that in sortase A this base is represented by the catalytic histidine 120, which could be substantiated by QM model calculation with 4-methylimidazole as histidine analog.

Asymmetric Disulfanylbenzamides as Irreversible and Selective Inhibitors of Staphylococcus aureus Sortase A.

Staphylococcus aureus is one of the most frequent causes of nosocomial and community‐acquired infections, with drug‐resistant strains being responsible for tens of thousands of deaths per year. S. aureus sortase A inhibitors are designed to interfere with virulence determinants. We have identified disulfanylbenzamides as a new class of potent inhibitors against sortase A that act by covalent modification of the active‐site cysteine. A broad series of derivatives were synthesized to derive structure‐activity relationships (SAR). In vitro and in silico methods allowed the experimentally observed binding affinities and selectivities to be rationalized. The most active compounds were found to have single‐digit micromolar K i values and caused up to a 66 % reduction of S. aureus fibrinogen attachment at an effective inhibitor concentration of 10 μM. This new molecule class exhibited minimal cytotoxicity, low bacterial growth inhibition and impaired sortase‐mediated adherence of S. aureus cells.

Design, synthesis and biological evaluation of 2-alkoxycarbonyl-3-anilinoindoles as a new class of potent inhibitors of tubulin polymerization.

A new class of inhibitors of tubulin polymerization based on the 2-alkoxycarbonyl-3-(3',4',5'-trimethoxyanilino)indole molecular skeleton was synthesized and evaluated for antiproliferative activity, inhibition of tubulin polymerization and cell cycle effects. The results presented show that the methoxy substitution and location on the indole nucleus plays an important role in inhibition of cell growth, and the most favorable position for the substituent was at C-6. In addition, a small-size ester function (methoxy/ethoxycarbonyl) at the 2-position of the indole core was desirable. Also, analogues that were alkylated with methyl, ethyl or n-propyl groups or had a benzyl moiety on the N-1 indolic nitrogen retained activity equivalent to those observed in the parent N-1H analogues. The most promising compounds of the series were 2-methoxycarbonyl-3-(3',4'.5'-trimethoxyanilino)-5-methoxyindole 3f and 1-methyl-2-methoxycarbonyl-3-(3',4'.5'-trimethoxyanilino)-6-methoxy-indole 3w, both of which target tubulin at the colchicine site with antitubulin activities comparable to that of the reference compound combretastatin A-4.

Arylvinylpiperazine Amides, a New Class of Potent Inhibitors Targeting QcrB of Mycobacterium tuberculosis.

New drugs are needed to control the current tuberculosis (TB) pandemic caused by infection with Mycobacterium tuberculosis We report here on our work with AX-35, an arylvinylpiperazine amide, and four related analogs, which are potent antitubercular agents in vitro All five compounds showed good activity against M. tuberculosisin vitro and in infected THP-1 macrophages, while displaying only mild cytotoxicity. Isolation and characterization of M. tuberculosis-resistant mutants to the arylvinylpiperazine amide derivative AX-35 revealed mutations in the qcrB gene encoding a subunit of cytochrome bc1 oxidase, one of two terminal oxidases of the electron transport chain. Cross-resistance studies, allelic exchange, transcriptomic analyses, and bioenergetic flux assays provided conclusive evidence that the cytochrome bc1-aa3 is the target of AX-35, although the compound appears to interact differently with the quinol binding pocket compared to previous QcrB inhibitors. The transcriptomic and bioenergetic profiles of M. tuberculosis treated with AX-35 were similar to those generated by other cytochrome bc1 oxidase inhibitors, including the compensatory role of the alternate terminal oxidase cytochrome bd in respiratory adaptation. In the absence of cytochrome bd oxidase, AX-35 was bactericidal against M. tuberculosis Finally, AX-35 and its analogs were active in an acute mouse model of TB infection, with two analogs displaying improved activity over the parent compound. Our findings will guide future lead optimization to produce a drug candidate for the treatment of TB and other mycobacterial diseases, including Buruli ulcer and leprosy.IMPORTANCE New drugs against Mycobacterium tuberculosis are urgently needed to deal with the current global TB pandemic. We report here on the discovery of a series of arylvinylpiperazine amides (AX-35 to AX-39) that represent a promising new family of compounds with potent in vitro and in vivo activities against M. tuberculosis AX compounds target the QcrB subunit of the cytochrome bc1 terminal oxidase with a different mode of interaction compared to those of known QcrB inhibitors. This study provides the first multifaceted validation of QcrB inhibition by recombineering-mediated allelic exchange, gene expression profiling, and bioenergetic flux studies. It also provides further evidence for the compensatory role of cytochrome bd oxidase upon QcrB inhibition. In the absence of cytochrome bd oxidase, AX compounds are bactericidal, an encouraging property for future antimycobacterial drug development.

Microwave‐Assisted Synthesis of Novel Symmetric Bis‐1,2,4‐triazolin‐3‐ones as Potent Inhibitors of CYP51: An Antifungal Activity Study

AbstractImprovement of antifungal agents is a good solution to beat the drug‐resistance problems. In this context, a series of novel bis‐1,2,4‐triazolin‐3‐ones (5i‐t) were designed and synthesized by microwave irradiation (MWI), a convenient and efficient method. An effort was also made to get these bis‐1,2,4‐triazolin‐3‐ones (5i‐t) by one‐pot three‐component reaction (3CR) using 3‐aryl‐5‐methyl‐1,3,4‐oxadiazol‐2(3H)‐one (2a‐b), formamide and dibromo reagent (4c‐h) under microwave irradiation (MWI). In vitro antifungal activity was carried out against six pathogenic fungi. From the results it was observed that the newly synthesized bis‐1,2,4‐triazolin‐3‐ones (5i‐t) have shown excellent activity against all the tested pathogenic fungi with least MIC values in the range of 0.80 μg/ml to 0.20 μg/ml. Particularly, in comparison with the reference drug Fluconazole and mono‐1,2,4‐triazolin‐3‐ones (3a‐b) some of the bis‐1,2,4‐triazolin‐3‐ones (5i, 5j, 5 m, 5p and 5r) have shown broad spectrum of antifungal activity. Further, the molecular docking study has been performed for all the tested compounds with 14α‐demethylase (CYP51) as target enzyme and this study validated the experimental results. Thus, docking study has culminated in the identification of a new class of potent inhibitors of CYP51. The results provide significant information for the future design of more potent antifungal agents.

Screening of indeno[1,2-b]indoloquinones by MALDI-MS: a new set of potential CDC25 phosphatase inhibitors brought to light

Quinones and quinones-like compounds are potential candidates for the inhibition of CDC25 phosphatases. The combination of MALDI-MS analyses and biological studies was used to develop a rapid screening of a targeted library of indeno[1,2-b]indoloquinone derivatives. The screening protocol using MALDI-TOFMS and MALDI-FTICRMS highlighted four new promising candidates. Biological investigations showed that only compounds 5c–f inhibited CDC25A and -C phosphatases, with IC50 values around the micromolar range. The direct use of a screening method based on MALDI-MS technology allowed achieving fast scaffold identification of a new class of potent inhibitors of CDC25 phosphatases. These four molecules appeared as novel molecules of a new class of CDC25 inhibitors. Assessment of 5c–e in an MRC5 proliferation assay provided an early indicator of toxicity to mammalian cells. Compound 5d seems the most promising hit for developing new CDC25 inhibitors.

Discovery of indole-based tetraarylimidazoles as potent inhibitors of urease with low antilipoxygenase activity

A series of tetraarylimidazoles (5A-5O) were prepared by one pot four component condensation reactions of 2-arylindole-3-carbaldehydes, substituted anilines, benzil and ammonium acetate in acetic acid. The synthesized compounds exhibited potent antiurease activity with IC50 values ranging from 0.12 ± 0.06 μM to 29.12 ± 0.18 μM as compared with thiourea. However, low inhibition profiles were observed for lipoxygenase. The data show that tetraarylimidazoles containing a substituted 2-penylindole have emerged as a new class of potent inhibitors of urease enzyme.

Jatrophanes from Euphorbia squamosa as potent inhibitors of Candida albicans multidrug transporters.

A series of structurally related jatrophane diterpenoids (1-6), including the new euphosquamosins A-C (4-6), was purified from the Iranian spurge Euphorbia squamosa and evaluated for its capacity to inhibit drug efflux by multidrug transporters of Candida albicans. Three of these compounds showed an interesting profile of activity. In particular, deacetylserrulatin B (2) and euphosquamosin C (6) strongly inhibited the drug-efflux activity of the primary ABC-transporter CaCdr1p, an effect that translated, in a yeast strain overexpressing this transporter, into an increased sensitivity to fluconazole. These compounds were transported by CaCdr1p, as shown by the observation of an 11-14-fold cross-resistance of yeast growth, and could also inhibit the secondary MFS-transporter CaMdr1p. In contrast, euphosquamosin A (4) was selective for CaCdr1p, possibly as a result of a different binding mode. Taken together, these observations suggest jatrophane diterpenes to be a new class of potent inhibitors of multidrug transporters critical for drug resistance in pathogenic yeasts.

Antitumor Activity of 7-Aminocarboxycoumarin Derivatives, a New Class of Potent Inhibitors of Lactate Influx but Not Efflux

High lactate concentration in tumors is associated with bad prognosis. Lactate is released by glycolytic cells in tumors and recaptured by oxidative cancer cells to feed the tricarboxylic acid (TCA) cycle after conversion into pyruvate. Monocarboxylate transporters (MCT) mediate these fluxes of proton-linked lactate and represent attractive targets to interrupt lactate shuttle and to inhibit tumor growth. Here, we investigated the properties of 7-aminocarboxycoumarins (7ACC) developed to selectively interfere with lactate fluxes in the lactate-rich tumor microenvironment. The pharmacologic properties of two compounds of this family, including their effects on lactate influx and efflux and antitumor activity, were investigated using human cancer cell lines and mouse xenograft models. Contrary to the reference MCT1 inhibitor AR-C155858, 7ACC unexpectedly inhibited lactate influx but not efflux in tumor cells expressing MCT1 and MCT4 transporters. 7ACC delayed the growth of cervix SiHa tumors, colorectal HCT116 tumors, and orthoptopic MCF-7 breast tumors. MCT target engagement was confirmed by the lack of activity of 7ACC on bladder UM-UC-3 carcinoma that does not express functional MCT. 7ACC also inhibited SiHa tumor relapse after treatment with cisplatin. Finally, we found that contrary to AR-C155858, 7ACC did not prevent the cell entry of the substrate-mimetic drug 3-bromopyruvate (3BP) through MCT1, and contributed to the inhibition of tumor relapse after 3BP treatment. In conclusion, our results indicate that 7ACC selectively affects a single part of the MCT symporter translocation cycle, leading to strict inhibition of lactate influx. This singular activity is associated with antitumor effects less prone to resistance and side effects.

Mechanistic studies on the application of DNA aptamers as inhibitors of 2-oxoglutarate-dependent oxygenases.

The Escherichia coli (E. coli) AlkB protein and its functional human homologues belong to a subfamily of 2-oxoglutarate (2OG) dependent oxygenases (2OG oxygenases for simplicity) that enable the repair of cytotoxic methylation damage in nucleic acids and that catalyze t-RNA oxidations. DNA alkylation is a major mechanism of action for cytotoxic anticancer drugs. Thus, the inhibition of oxidative demethylation, catalyzed by these enzymes, has the potential to improve the efficacy of chemotherapies. Here we report that oligonucleotide aptamers constitute a new class of potent inhibitors of 2OG oxygenases. DNA aptamers can selectively bind to AlkB, with nanomolar affinity, and efficiently inhibit catalysis. The mechanism of inhibition was studied by capillary electrophoresis (CE) with laser-induced fluorescence (LIF) detection. Inhibition constants of the aptamers were determined and shown to correlate well with K(d) values. The results of kinetic analyses imply that the aptamers bind AlkB away from the active site. Our findings should stimulate the development of oligonucleotide aptamers for human homologues of AlkB and further their study as potential enhancers of chemotherapy efficiency.

Discovery of potent and orally bioavailable 17β-hydroxysteroid dehydrogenase type 3 inhibitors

We have previously reported the discovery of a new class of potent inhibitors of 17β-hydroxysteroid dehydrogenase type 3 (17β-HSD3) derived from benzylidene oxazolidinedione and thiazolidinedione scaffolds. In this study, these analogs were designed, synthesized, and evaluated in a human cell-based assay. The detailed structure–activity relationship (SAR) surrounding this pharmacophore were developed, and consequently a number of compounds from this series demonstrated single-digit nanomolar 17β-HDS3 inhibitory activity in vitro. Subsequent optimization work in pursuit of the improvement of oral bioavailability demonstrated in vivo proof-of-concept by prodrug strategy based on phosphate esters for these 17β-HSD3 inhibitors. When a phosphate ester 16 was administered orally at a high dose of 100mg/kg, 16 showed approximately two times more potent testosterone (T)-lowering effect against a positive control in the luteinizing hormone-releasing hormone (LH–RH)-induced T production assay. The T-lowering effect continued at ca 10% level of control over 4h after administration. The nonsteroidal molecules based on this series have the potential to provide unique and effective clinical opportunities for treatment of prostate cancer.

The central valine concept provides an entry in a new class of non peptide inhibitors of the p53–MDM2 interaction

Disrupting the interaction between the p53 tumor suppressor and its regulator MDM2 is a promising therapeutic strategy in anticancer drug research. In our search for non peptide inhibitors of this protein–protein interaction, we have devised a ligand design concept exploiting the central position of Val 93 in the p53 binding pocket of MDM2. The design of molecules based on this concept has allowed us to rapidly identify compounds having a 3-imidazolyl indole core structure as the first representatives of a new class of potent inhibitors of the p53–MDM2 interaction.

The macromolecular complex of ICP and falcipain-2 fromPlasmodium: preparation, crystallization and preliminary X-ray diffraction analysis

The malaria parasite Plasmodium depends on the tight control of cysteine-protease activity throughout its life cycle. Recently, the characterization of a new class of potent inhibitors of cysteine proteases (ICPs) secreted by Plasmodium has been reported. Here, the recombinant production, purification and crystallization of the inhibitory C-terminal domain of ICP from P. berghei in complex with the P. falciparum haemoglobinase falcipain-2 is described. The 1:1 complex was crystallized in space group P4(3), with unit-cell parameters a = b = 71.15, c = 120.09 Å. A complete diffraction data set was collected to a resolution of 2.6 Å.

Synthesis and 3D-QSARs Analyses of Herbicidal O,O-Dialkyl-1-phenoxyacetoxy-1-methylphosphonate Analogues as a New Class of Potent Inhibitors of Pyruvate Dehydrogenase

A series of O,O-dialkyl-1-phenoxyacetoxy-1-methylphosphonate analogues (1~22) as a new class of potent inhibitors of pyruvate dehydrogenase were synthesized and 3D-QSARs (three dimensional qantitative structure-activity relationships) models on the pre-emergency herbicidal activity against the seed of cucumber (Cucumus Sativa L.) were derived and discussed quantitatively using comparative molecular field analysis (CoMFA) and comparative molecular similarity indeces analysis (CoMSIA) methods. The statistical values of CoMSIA models were better predictability and fitness than those of CoMFA models. The inhibitory activities according to the optimized CoMSIA model I were dependent on the electrostatic field (41.4%), the H-bond acceptor field (26.0%), the hydrophobic field (20.8%) and the steric field (11.7%). And also, it was found that the optimized CoMSIA model I with the sensitivity to the perturbation (dq 2' /dr 2 yy' = 0.830) and the prediction (q 2 = 0.503) produced by a progressive scrambling analyses were not dependent on chance correlation. From the results of graphical analyses on the contour maps with the optimized CoMSIA model I, it is expected that the structural distinctions and descriptors that subscribe to herbicidal activities will be able to apply new an herbicide design.

Abstract 4279: Targeting Bmi1 in human prostate tumor initiating cells

Abstract Prostate cancer stem cells or tumor initiating cells (TICs) represent a barrier to effective treatment due to their intrinsic resistance to current therapeutic modalities. Recent studies identified Bmi-1 (B-cell specific MMLV insertion site-1), a member of the polycomb family of chromatin remodeling complexes, as a major oncogenic protein that is highly expressed in, and regulates stem cells and prostate TIC self-renewal. We found that shRNA specific targeting or pharmacological inhibition of the critical stem cell and TIC protein Bmi-1 in cultured prostate tumors resulted in cell death. These studies were extended to demonstrate that Bmi-1 plays an equally critical role in prostate TIC maintenance in patient tumors, and that targeting Bmi-1 eliminates the subpopulation of TICs resistant to hormone ablation and currently used chemotherapies. We utilized a novel zebrafish xenograft of primary human prostate tumor model to identify candidate Bmi-1 inhibitory drugs and other drugs targeting TIC pathways for further preclinical and clinical testing. First, we isolated and characterized TICs from fresh human prostate tissues from patients undergoing resection, and then utilized the zebrafish primary xenograft model to evaluate TIC growth, and to define Bmi-1 and other stem cell associated pathways as bonafide TIC targets. Next, we investigated Bmi-1 and other TIC inhibitors in enriched prostate stem cells and the zebrafish model, and the results were confirmed in the mouse xenograft model to determine efficacy and toxicity. Zebrafish bearing Du145 xenografts were compared to fish bearing fresh human TICs, and the combinations of Bmi-1 inhibitor(s) with taxotere, a drug approved for use in the treatment of advanced prostate cancer were synergistic. Our studies are extended to determine the features of prostate TICs in zebrafish xenograft assays, and to study the effects of Bmi-1 inhibitors in sensitized microenvironments lacking the downstream targets P16INK4a and p19Arf, in order to analyze the changes in Bmi-1 targets regulating survival, proliferation, and cancer stem cell maintenance. The novel aspects of these studies are the growth inhibition of human prostate TICs, and the use of zebrafish as an in vivo model to determine Bmi-1 inhibitor efficacy, doses and combinations with conventional therapies. Bmi-1 inhibitors that target prostate cancer TICs may provide a new class of potent inhibitors that when used alone and in combination with other targeted therapy would represent an effective therapeutic management for patients with prostate cancer. Moreover, the use of zebrafish would allow the rapid generation of response to therapy data that would facilitate the development of drugs targeted to prostate TICs. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4279.

Phosphaisocoumarins as a new class of potent inhibitors for pancreatic cholesterol esterase

Due to the importance of pancreatic cholesterol esterase (CEase) as a potential target in atherosclerosis and for the development of hypocholesterolemic agents, there are increasing interests in designing and synthesizing CEase inhibitors. In the present study, we prepared forty-five isocoumarin phosphorus analogues (i.e., phosphaisocoumarins) and investigated the inhibition of these compounds on the CEase. The results showed that some phosphaisocoumarins could act as potent inhibitors of CEase. The most potent inhibitors, compounds 9d, 10a and 12e give IC 50 values of 4.8 μM, 2.3 μM and 1.9 μM, respectively. The inhibition mechanism and kinetic characterization studies indicate that they are reversible competitive inhibitors.

Abstract C199: Development of potent, small-molecule inhibitors of ETK

Abstract Epithelial and endothelial tyrosine kinase (Etk) is a nonreceptor tyrosine kinase that plays a central role in the proliferation, differentiation, apoptosis, and tumorigenicity of epithelial cells. Inhibition of Etk signaling can result in impaired cellular transformation, down-regulation of angiogenesis, and increased apoptosis. Employing our proprietary CLIMB™ technology, a computationally driven drug discovery process, we designed and synthesized approximately 35 small molecules for ETK-inhibition testing in biochemical and cellular assays. Most of these compounds exhibited low nanomolar activity and selectivity across a wide panel of kinases. Five compounds were subsequently chosen for further evaluation in in vivo studies. As predicted from CLIMB™, all of the compounds showed sufficient tolerability and pharmacokinetics in mice to advance into tumor efficacy studies. Endometrial and hepatocellular cancers were selected for these studies based on previous in vitro results indicating high ETK expression and potent compound activity. All five compounds demonstrated marked activity in these models; in one cell line, two of the compounds inhibited tumor growth by more than 50% after less than two weeks of dosing. Using these same tumor lines in pharmacodynamic studies, the compounds also showed significant modulation of cellular transformation and anti-apoptotic markers consistent with ETK inhibition. Moreover, quantitative analysis of microvessel density, a key indicator of angiogenesis, demonstrated clear inhibition of blood vessel formation from tumors excised after treatment with the five compounds. Utilizing our CLIMB™ technology, we have rapidly developed a new class of potent inhibitors that consistently demonstrate in vivo activity against ETK-relevant tumor cell lines. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C199.

Beauvericin and enniatins H, I and MK1688 are new potent inhibitors of human immunodeficiency virus type-1 integrase

Some enniatins (ENs) reportedly exhibit antiretroviral activities in vivo. The potential inhibitory activities of cyclic hexadepsipeptides such as beauvericin (BEA) and ENs H, I and MK1688 were investigated in vitro against human immunodeficiency virus type-1 (HIV-1) integrase and Moloney murine leukemia virus reverse transcriptase. BEA, EN I and EN MK1688 exhibited strong inhibitory activities against HIV-1 integrase, whereas EN H showed relatively weak activity. None of the examined compounds showed anti-reverse transcriptase activity. BEA was the most effective inhibitor of the tested cyclic hexadepsipeptides in inhibiting HIV-1 integrase. These results indicate the potential of cyclic hexadepsipeptides as a new class of potent inhibitors of HIV-1 integrase.