N-aryl-benzimidazolones as novel small molecule HSP90 inhibitors

We describe the development of a novel series of N-aryl-benzimidazolone HSP90 inhibitors (9) targeting the N-terminal ATP-ase site. SAR development was influenced by structure-based design based around X-ray structures of ligand bound HSP90 complexes. Lead compounds exhibited high binding affinities, ATP-ase inhibition and cellular client protein degradation.     

Synthesis of dual-action parthenolide prodrugs as potent anticancer agents

Cancer stem cells are responsible for the failure of a large number of cancer treatments and the re-emergence of cancer in patients. Parthenolide is a potent anticancer sesquiterpene lactone that is also able to kill cancer stem cells. The main problem with this compound is its poor solubility in water. To solve this problem, medicinal chemists have tried to prepare amino-derivatives of parthenolide, however, most amino-derivatives have less potency than that of parthenolide. In this paper, we proposed a new approach to synthesize parthenolide derivatives with better solubility and higher potency. We prepared novel parthenolide derivatives through the aza-Michael addition of nitrogen-containing anticancer drug molecules (cytarabine and melphalan) to the α-methylene-γ-lactone group of parthenolide. Different types of catalysts were used to catalyze the aza-Michael addition. Among all the used catalysts, 1,8-diazabicyclo [5.4.0] undec-7-ene (DBU) was found to have the highest catalytic activity. In addition, we examined the effects of parthenolide-anticancer drug hybrids on the growth and proliferation of three cancer cell lines (MCF-7, LNcaP, Hep G2) and CHO. The parthenolide prodrugs showed potent cytotoxic property with IC₅₀ values ranging from 0.2 to 5.2 μM, higher than those of parthenolide and anticancer drugs (cytarabine and melphalan).     

Synthesis and biological evaluation of C-ring truncated deguelin derivatives as heat shock protein 90 (HSP90) inhibitors

Based on the lead compound L-80 (compound 2), a potent heat shock protein 90 (HSP90) inhibitor, a series of C-ring truncated deguelin analogs were designed, synthesized and evaluated for Hypoxia Inducible Factor-1α (HIF-1α) inhibition as a primary screening method. Their structure–activity relationship was investigated in a systematic manner by varying the A/B ring, linker and D/E ring, respectively. Among the synthesized inhibitors, compound 5 exhibited potent HIF-1α inhibition in a dose-dependent manner and significant antitumor activity in human non-small cell lung carcinoma (H1299), with better activities than L-80. It also inhibited in vitro hypoxia-mediated angiogenic processes in human retinal microvascular endothelial cells (HRMEC). The docking study of 5 showed a similar binding mode as L-80: it occupied the C-terminal ATP-binding pocket of HSP90, indicating that the anticancer and antiangiogenic activities of 5 were derived from HIF-1α destabilization by inhibiting the C-terminal ATP-binding site of hHSP90.     

Identification of a new series of potent diphenol HSP90 inhibitors by fragment merging and structure-based optimization

Heat shock protein 90 (HSP90) is a molecular chaperone to fold and maintain the proper conformation of many signaling proteins, especially some oncogenic proteins and mutated unstable proteins. Inhibition of HSP90 was recognized as an effective approach to simultaneously suppress several aberrant signaling pathways, and therefore it was considered as a novel target for cancer therapy. Here, by integrating several techniques including the fragment-based drug discovery method, fragment merging, computer aided inhibitor optimization, and structure-based drug design, we were able to identify a series of HSP90 inhibitors. Among them, inhibitors 13, 32, 36 and 40 can inhibit HSP90 with IC₅₀ about 20–40 nM, which is at least 200-fold more potent than initial fragments in the protein binding assay. These new HSP90 inhibitors not only explore interactions with an under-studied subpocket, also offer new chemotypes for the development of novel HSP90 inhibitors as anticancer drugs.     

Anti-herpes simplex virus efficacies of 2-aminobenzamide derivatives as novel HSP90 inhibitors

After the widespread use of the acyclic purine nucleoside analogues for therapy of herpes simplex virus (HSV) infection since the 1980s, new antiviral strategies are urgently needed to counter the emergence of drug-resistant clinical isolates. In this report, we define the anti-HSV efficacies of three optimized 2-aminobenzamide derivatives in vitro and in vivo. The synthetic analogues SNX-25a, SNX-2112 and SNX-7081, which selectively bind to the N-terminal ATP pocket of heat shock protein 90 (HSP90), exhibited significant anti-HSV-1 and HSV-2 activities at non-cytotoxic concentrations in Vero cells, with EC(50) values close to that of acyclovir (ACV). The in vivo antiviral potentials were then confirmed using a herpes simplex keratitis (HSK) rabbit model, where eye gels containing 0.1% or 0.025% SNX-25a displayed the highest efficacies against HSV-1 infection, which were better than that obtained with 0.1% ACV. SNX-2112 and SNX-7081 gels were also effective against HSV-1 with different magnitude of activities. Our results for the first time confirmed the anti-HSV efficacies of these 2-aminobenzamide derivatives and suggest that with alternative mechanisms of action these novel HSP90 inhibitors, especially SNX-25a, could be potent as new anti-HSV clinical trial candidates.     

Synthesis of anilino-monoindolylmaleimides as potent and selective PKCbeta inhibitors

We report herein synthesis of PKCbeta-selective inhibitors possessing the novel pharmacophore of anilino-monoindolylmaleimide. Several compounds of this series exhibited IC50's as low as 50 nM against human PKCbeta2. One of the most potent compounds, 6l, inhibited PKCbeta1 and PKCbeta2 with IC50 of 21 and 5 nM, respectively, and exhibited selectivity of more than 60-fold in favor of PKCbeta2 relative to other PKC isozymes (PKCalpha, PKCgamma, and PKCepsilon).     

Synthesis of novel dual target inhibitors of PARP and HSP90 and their antitumor activities

Poly (ADP-ribose) polymerase (PARP) inhibitors have achieved great success in clinical application, especially for the prolonged survival of cisplatin-sensitive ovarian cancer patients. However, there are still many patients who do not respond to PARP inhibitors. Novel PARP inhibitors with higher activity are urgently needed. Herein we report a series of compounds by molecular hybridization PARP-1 inhibitor Olaparib (Ola) with HSP90 inhibitor C0817 (one curcumin derivative). All synthesized compounds were evaluated for their antiproliferative activity in vitro, and some were further assessed for their inhibitory activities of the PARP enzyme and HSP90 affinity. Our results indicated that compound 4 could bind to HSP90 and cause static quenching, indicating that compound 4 was able to bind to HSP90, moreover, downstream molecular breast cancer 1 (BRAC-1) was reduced. In conclusion, dual target inhibitors of PARP and HSP90 exhibited stronger selective cytotoxicities against cancer.     

Combination therapies with HSP90 inhibitors against colorectal cancer

Oncogene stability and homeostasis mediated by the HSP90 chaperone is a crucial protection trait of cancer cells. Therefore, HSP90 represents an attractive therapeutic target for many cancers, including colorectal cancer. Although monotherapy has limited clinical efficacy, preclinical and early-phase clinical studies indicate improved antitumor activity when HSP90 inhibitors are combined with chemotherapies or targeted agents. This may be further improved with a biomarker-guided approach based on oncogenic HSP90 clients, or stratification based on the consensus molecular subtypes of colorectal cancer, suggesting a synergistic activity with 5-fluorouracil in preclinical models of the chemorefractory mesenchymal subtype. Furthermore, HSP90 inhibition may activate mechanisms to turn non-immunogenic tumors hot and improve their recognition by the immune system, suggesting synergy with immune checkpoint blockade.     

Synthesis of tripeptides as potent Yersinia protein tyrosine phosphatase inhibitors

We report the synthesis of a series of monoanionic phosphotyrosyl (pTyr) mimetic-containing tripeptides based on 'Fmoc-Glu(OBn)-Xxx-Leu-amide' (where Xxx = pTyr mimetic) and their N-terminally modified derivatives. The inhibitory potencies of compounds were tested against YopH and human PTP1B enzymes. Several compounds exhibited noteworthy activity against both YopH and PTP1B. Among the N-terminally modified analogues, 5-methylindole derivative 30 was found to be the best moiety to replace base-labile Fmoc group. A mode of binding with YopH is proposed for tripeptides 21, 30, and 31.     

Synthesis of O-galactosyl aldoximes as potent LacNAc-mimetic galectin-3 inhibitors

A panel of anomeric oxime ether derivatives of beta-galactose were synthesized via the reaction of O-beta-D-galactopyranosylhydroxylamine with aldehydes. The oxime ethers were evaluated as inhibitors against galectin-3 in a competitive fluorescence polarization assay. The best inhibitor, [E]-O-(beta-D-galactopyranosyl)-indole-3-carbaldoxime (E-52), had a Kd value of 180 microM, which is 24 times better than methyl beta-D-galactopyranoside (Kd=4400 microM) and in the same range as methyl lactoside (Kd=220 microM).     

Synthesis of novel fenfuram-diarylether hybrids as potent succinate dehydrogenase inhibitors

Twelve novel fenfuram-diarylether hybrids were designed, synthesized and characterized by ¹H NMR and MS. Their in vitro antifungal activities were evaluated against five phytopathogenic fungi by mycelial growth inhibition method. Most compounds showed significant antifungal effect on Rhizoctonia solani and Sclerotinia sclerotiorum. Compound 1c exhibited the most potent antifungal effect on R. solani with an EC₅₀ value of 0.242 mg/L, superior to the commercial fungicide boscalid (EC₅₀ = 1.758 mg/L) and the lead fungicide fenfuram (EC₅₀ = 7.691 mg/L). Molecular docking revealed that compound 1c featured a higher affinity for succinate dehydrogenase (SDH) than fenfuram. Furthermore, it was shown that the 2-chlorophenyl group of compound 1c formed a π-π stacking with D/Tyr-128 and a Cl-π interaction with B/His-249, which made compound 1c more active than fenfuram against SDH.     

6-Hydrazinopurine 2'-methyl ribonucleosides and their 5'-monophosphate prodrugs as potent hepatitis C virus inhibitors

A series of 6-hydrazinopurine 2'-methyl ribonucleosides was synthesized and tested for its inhibitory activity against the hepatitis C virus (HCV). The lack of antiviral activity of these nucleosides was associated with a poor affinity for adenosine kinase, which prompted us to synthesize several of their 5'-monophosphate prodrugs. Some of these prodrugs exhibited more than 1000-fold improvement in anti-HCV activity when compared to their parent nucleosides (EC(50) of 24 nM vs 92 microM for the parent).     

Cyclic monophosphate prodrugs of base-modified 2'-C-methyl ribonucleosides as potent inhibitors of hepatitis C virus RNA replication

A new series of heterobase-modified 2'-C-methyl ribonucleosides was synthesized and tested as inhibitors of hepatitis C virus (HCV) RNA replication. The nucleosides showed a weak inhibitory activity in a HCV replicon system (EC(50)=92 microM) and did not exhibit any cytotoxicity (CC(50)>300 microM). Cyclic monophosphate (cMP) prodrugs of the same nucleosides were synthesized and also tested in the HCV replicon system. Prodrugs exhibited strong potency (EC(50)=0.008 microM) without significant cytotoxicity (CC(50)>50 microM).     

Discovery of novel anti-breast cancer agents derived from deguelin as inhibitors of heat shock protein 90 (HSP90)

A series of O-substituted analogues of the B,C-ring truncated scaffold of deguelin were designed as C-terminal inhibitors of heat shock protein 90 (HSP90) and investigated as novel antiproliferative agents against HER2-positive breast cancer. Among the synthesized compounds, compound 80 exhibited significant inhibition in both trastuzumab-sensitive and trastuzumab-resistant breast cancer cells, whereas compound 80 did not show any cytotoxicity in normal cells. Compound 80 markedly downregulated the expression of the major client proteins of HSP90 in both cell types, indicating that the cytotoxicity of 80 in breast cancer cells is attributed to the destabilization and inactivation of HSP90 client proteins and that HSP90 inhibition represents a promising strategy to overcome trastuzumab resistance. A molecular docking study of 80 with the homology model of a HSP90 homodimer showed that 80 fit nicely in the C-terminal domain with a higher electrostatic complementary score than that of ATP.     

Virtual screening and biophysical studies lead to HSP90 inhibitors

Heat shock protein 90 (HSP90) is a molecular chaperone that plays important functional roles in cells. The chaperone activity of HSP90 is regulated by the hydrolysis of ATP at the protein’s N-terminal domain. HSP90, in particular the N-terminal domain, is a current inhibition target for therapeutic treatments of cancers. This paper describes an application of virtual screening, thermal shift assaying and protein NMR spectroscopy leading to the discovery of HSP90 inhibitors that contain the resorcinol structure. The resorcinol scaffold can be found in a class of HSP90 inhibitors that are currently undergoing clinical trials. The proved success of the resorcinol moiety in HSP90 inhibitors validates this combined virtual screen and biophysical technique approach, which may be applied for future inhibitor discovery work for HSP90 as well as other targets.     

Synthesis and evaluation of novel prodrugs of caspase inhibitors

A novel type of caspase inhibitor prodrug that improves systemic exposure after oral administration in rats has been designed. Such a prodrug, based on a 6,6a-dihydrofuro[3,2-d]oxazol-5(3aH)-one motif, has the advantage of rapidly liberating the active inhibitor without producing any cleavage by-product. Prodrugs 6-8, are synthesised in a high yielding one-step transformation from the active parents with high diastereomeric excess.     

Synthesis of C2-symmetric guanidino-sugars as potent inhibitors of glycosidases

A series of enantiomerically pure C2-Symmetric guanidino-sugars was synthesized from D-mannitol. The first method described involves direct opening of a bis-epoxide by guanidine, whereas the second one deals with a mercury-catalyzed transformation of a cyclic thiourea into a N,N',N"-trisubstituted guanidine as a key step. The biological activity of these compounds towards several glycosidases has been evaluated. One of them (5) was found to selectively inhibit alpha-L-fucosidase of bovin kidney (2.8 microM).     

Synthesis and SAR of alpha-sulfonylcarboxylic acids as potent matrix metalloproteinase inhibitors

A series of novel carboxylic acid-based alpha-sulfone MMP inhibitors have been synthesized and the in vitro enzyme SAR is discussed. A potential binding mode in the active site of the MMP-9 homology model was highlighted. These compounds are potent MMP-9 inhibitors and are selective over MMP-1.     

Synthesis of proline analogues as potent and selective cathepsin S inhibitors

Cathepsin S is a potential target of autoimmune disease. A series of proline derived compounds were synthesized and evaluated as cathepsin S inhibitors. We discovered potent cathepsin S inhibitors through structure–activity relationship studies of proline analogues. In particular, compound 19-(S) showed promising in vitro/vivo pharmacological activities and properties as a selective cathepsin S inhibitor.