Small Molecule Inhibitors to Disrupt Protein-protein Interactions of Heat Shock Protein 90 Chaperone Machinery

Rational design of peptide inhibitors targeting HSP90-CDC37 protein-protein interaction

Background: Specifically blocking HSP90-CDC37 interaction is emerging as a prospective strategy for cancer therapy. Aim: Applying a kinase pseudopeptide rationale to the discovery of HSP90-CDC37 protein-protein interaction (PPI) inhibitors. Methods: Pseudosubstrates were identified through sequence alignment and evaluated by biolayer interferometry assay, co-immunoprecipitation assay and antiproliferation assay. Results: TAT-DDO-59120 was identified to disrupt HSP90-CDC37 PPI through directly binding to HSP90, both extracellularly and intracellularly. In addition, the identified peptide showed ideal antiproliferative activity against the colorectal cancer cell HCT116 (IC50 = 12.82 μM). Conclusion: Compared with the traditional method of screening a large compound library to identify PPI inhibitors, this method is rapid and efficient with strong purpose, which provides a novel strategy for designing HSP90-CDC37 PPI inhibitors.

Small-molecule dual inhibitors targeting heat shock protein 90 for cancer targeted therapy

Heat shock protein 90, also known as Hsp90, is an extensively preserved molecular chaperone that performs a critical function in organizing various biological pathways and cellular operations. As a potential drug target, Hsp90 is closely linked to cancer. Hsp90 inhibitors are a class of drugs that have been extensively studied in preclinical models and have shown promise in a variety of diseases, especially cancer. However, Hsp90 inhibitors have encountered several challenges in clinical development, such as low efficacy, toxicity, or drug resistance, few Hsp90 small molecule inhibitors have been approved worldwide. Nonetheless, combining Hsp90 inhibitors with other tumor inhibitors, such as HDAC inhibitors, tubulin inhibitors, and Topo II inhibitors, has been shown to have synergistic antitumor effects. Consequently, the development of Hsp90 dual-target inhibitors is an effective strategy in cancer treatment, as it enhances potency while reducing drug resistance. This article provides an overview of Hsp90's domain structure and biological functions, as well as a discussion of the design, discovery, and structure-activity relationships of Hsp90 dual inhibitors, aiming to provide insights into clinical drug research from a medicinal chemistry perspective and discover novel Hsp90 dual inhibitors.

Interaction of constituents of MDT regimen for leprosy with Mycobacterium leprae HSP18: impact on its structure and function

Mycobacterium leprae, the causative organism of leprosy, harbors many antigenic proteins, and one such protein is the 18-kDa antigen. This protein belongs to the small heat shock protein family and is commonly known as HSP18. Its chaperone function plays an important role in the growth and survival of M. leprae inside infected hosts. HSP18/18-kDa antigen is often used as a diagnostic marker for determining the efficacy of multidrug therapy (MDT) in leprosy. However, whether MDT drugs (dapsone, clofazimine, and rifampicin) do interact with HSP18 and how these interactions affect its structure and chaperone function is still unclear. Here, we report evidence of HSP18-dapsone/clofazimine/rifampicin interaction and its impact on the structure and chaperone function of HSP18. These three drugs interact efficiently with HSP18 (having submicromolar binding affinity) with 1 : 1 stoichiometry. Binding of these MDT drugs to the 'α-crystallin domain' of HSP18 alters its secondary structure and tryptophan micro-environment. Furthermore, surface hydrophobicity, oligomeric size, and thermostability of the protein are reduced upon interaction with these three drugs. Eventually, all these structural alterations synergistically decrease the chaperone function of HSP18. Interestingly, the effect of rifampicin on the structure, stability, and chaperone function of this mycobacterial small heat shock protein is more pronounced than the other two MDT drugs. This reduction in the chaperone function of HSP18 may additionally abate M. leprae survivability during multidrug treatment. Altogether, this study provides a possible foundation for rational designing and development of suitable HSP18 inhibitors in the context of effective treatment of leprosy.

HIF-1: structure, biology and natural modulators

Hypoxia-inducible factor 1 (HIF-1), as a main transcriptional regulator of metabolic adaptation to changes in the oxygen environment, participates in many physiological and pathological processes in the body, and is closely related to the pathogenesis of many diseases. This review outlines the mechanisms of HIF-1 activation, its signaling pathways, natural inhibitors, and its roles in diseases. This article can provide new insights in the diagnosis and treatment of human diseases, and recent progress on the development of HIF-1 inhibitors.

Antioxidant, Antidiabetic and Anticancer Activities of L-Phenylalanine and L-Tyrosine Ester Surfactants: In Vitro and In Silico Studies of their Interactions with Macromolecules as Plausible Mode of Action for their Biological Properties

Background:

Aromatic amino acid-based surfactants have been found to have interesting biological properties such as antibacterial and hemolytic activities. Recently, we have reported the antibacterial activity of a range of ester hydrochloride surfactants derived from L-Phenylalanine and LTyrosine. This study aims at assessing the antioxidant, α-glycosidase inhibitory and cytotoxic activities of a series of L-Phenylalanine and L-Tyrosine ester hydrochlorides. Molecular docking and BSA binding studies were also carried out in order to investigate their potential therapeutic targets.

Methods:

L-Phenylalanine and L-Tyrosine surfactants were tested as potential lipophilic antioxidants using the DPPH and ABTS assays. These surfactants were also tested for their α-glycosidase inhibitory activity using 4-nitrophenyl α -D-glucopyranoside (pNPG) as substrate. Their cytotoxicity effects were screened using HeLa and KB cell lines. Glide version 5.7 as implemented in Schrödinger suite 2013-1, was used for performing docking studies of L-Phenylalanine and L-Tyrosine dodecyl esters. The interaction of the ester hydrochlorides of L-Phenylalanine and L-Tyrosine with bovine serum albumin (BSA) was investigated using fluorometric titration.

Results:

The presence of the phenolic moiety in L-Tyrosine-based surfactants was found to enhance the antioxidant and α-glucosidase inhibitory activities compared to the L-Phenylalanine derivatives. The α- glucosidase and anticancer activities of the phenylalanine surfactants were found to increase with chain length up to C12 above which the activities exhibited a downward trend. In the case of the tyrosine series, an increase in chain length from C8 to C14 was found to decrease the α-glucosidase inhibitory activity and increase the anticancer activity of the surfactants. Binding studies with bovine serum albumin showed that the tyrosine surfactants displayed greater affinity for the serum albumin, owing to the presence of the phenolic group which altered the orientation of the surfactant molecule within the hydrophobic core of BSA.

Conclusion:

L-Tyrosine esters having a phenolic moiety were found to possess enhanced biological activity in terms of both the antioxidant and antidiabetic activities as well as also bind more strongly to Bovine serum albumin. Molecular docking studies of the phenylalanine and tyrosine surfactants of similar chain length with target proteins showed direct correlation with their anticancer and antidiabetic activity. Therefore, the findings show that these aromatic based surfactants derived from L-Tyrosine can act as promising antioxidant, antidiabetic and anticancer agents, and they can also be efficiently transported and eliminated in the body, making them useful candidates for drug designs.

Why Some Targets Benefit from beyond Rule of Five Drugs

Beyond rule-of-five (bRo5) compounds are increasingly used in drug discovery. Here we analyze 37 target proteins that have bRo5 drugs or clinical candidates. Targets can benefit from bRo5 drugs if they have "complex" hot spot structure with four or more hots spots, including some strong ones. Complex I targets show positive correlation between binding affinity and molecular weight. These targets are conventionally druggable, but reaching additional hot spots enables improved pharmaceutical properties. Complex II targets, mostly protein kinases, also have strong hot spots but show no correlation between affinity and ligand molecular weight, and the primary motivation for creating larger drugs is to increase selectivity. Each target considered as complex III has some specific reason for requiring bRo5 drugs. Finally, targets with "simple" hot spot structure, i.e., three or fewer weak hot spots, must use larger compounds that interact with surfaces beyond the hot spot region to achieve acceptable affinity.

Inhibiting protein-protein interactions of Hsp90 as a novel approach for targeting cancer

The ninety kilo Dalton molecular weight heat shock protein (Hsp90) is an attractive target for the discovery of novel anticancer agents. Several strategies have been employed for the development of inhibitors against this polypeptide. The most successful strategy is targeting the N-terminal ATP binding region of the chaperone. However, till date not a single molecule reached Phase-IV of clinical trials from this class of Hsp90 inhibitors. The other approach is to target the Cterminal region of the protein. The success with this approach has been limited due to lack of well-defined ligand binding pocket in this terminal. The other promising strategy is to prevent the interaction of client proteins/co-chaperones with Hsp90 protein, i.e., protein-protein interaction inhibitors of Hsp90. The review focuses on advantage of this approach along with the recent advances in the discovery of inhibitors by following this strategy. Additionally, the biology of the client protein/co-chaperone binding site of Hsp90 is also discussed.

Gain-of-Function (GOF) Mutant p53 as Actionable Therapeutic Target

p53 missense mutant alleles are present in nearly 40% of all human tumors. Such mutated alleles generate aberrant proteins that not only lose their tumor-suppressive functions but also frequently act as driver oncogenes, which promote malignant progression, invasion, metastasis, and chemoresistance, leading to reduced survival in patients and mice. Notably, these oncogenic gain-of-function (GOF) missense mutant p53 proteins (mutp53) are constitutively and tumor-specific stabilised. This stabilisation is one key pre-requisite for their GOF and is largely due to mutp53 protection from the E3 ubiquitin ligases Mdm2 and CHIP by the HSP90/HDAC6 chaperone machinery. Recent mouse models provide convincing evidence that tumors with highly stabilized GOF mutp53 proteins depend on them for growth, maintenance, and metastasis, thus creating exploitable tumor-specific vulnerabilities that markedly increase lifespan if intercepted. This identifies mutp53 as a promising cancer-specific drug target. This review discusses direct mutp53 protein-targeting drug strategies that are currently being developed at various preclinical levels.

Stress-induced phosphoprotein-1 maintains the stability of JAK2 in cancer cells

Overexpression of stress-induced phosphoprotein 1 (STIP1) − a co-chaperone of heat shock protein (HSP) 70/HSP90 – and activation of the JAK2-STAT3 pathway occur in several tumors. Combined treatment with a HSP90 inhibitor and a JAK2 inhibitor exert synergistic anti-cancer effects. Here, we show that STIP1 stabilizes JAK2 protein in ovarian and endometrial cancer cells. Knock-down of endogenous STIP1 decreased JAK2 and phospho-STAT3 protein levels. The N-terminal fragment of STIP1 interacts with the N-terminus of JAK2, whereas the C-terminal DP2 domain of STIP1 mediates the interaction with HSP90 and STAT3. A peptide fragment in the DP2 domain of STIP1 (peptide 520) disrupted the interaction between STIP1 and HSP90 and induced cell death through JAK2 suppression. In an animal model, treatment with peptide 520 inhibited tumor growth. In summary, STIP1 modulates the function of the HSP90-JAK2-STAT3 complex. Peptide 520 may have therapeutic potential in the treatment of JAK2-overexpressing tumors.

Disrupting effects of antibiotic sulfathiazole on developmental process during sensitive life-cycle stage of Chironomus riparius

Antibiotics in the environment are a concern due to their potential to harm humans and interrupt ecosystems. Sulfathiazole (STZ), a sulfonamide antibiotic, is commonly used in aquaculture and is typically found in aquatic ecosystems. We evaluated the ecological risk of STZ by examining biological, molecular and biochemical response in Chironomus riparius. Samples were exposed to STZ for 12, 24 and 96 h, and effects of STZ were evaluated at the molecular level by analyzing changes in gene expression related to the endocrine system, cellular stress response and enzyme activity of genes on antioxidant and detoxification pathways. STZ exposure induced significant effects on survival, growth and sex ratio of emergent adults and mouthpart deformity in C. riparius. STZ caused concentration and time-dependent toxicity in most of the selected biomarkers. STZ exposure leads to significant heat-shock response of protein genes (HSP70, HSP40, HSP90 and HSP27) and to disruption by up-regulating selected genes, including the ecdysone receptor gene, estrogen-related receptors, ultraspiracle and E74 early ecdysone-responsive gene. Furthermore, STZ induced alteration of enzyme activities on antioxidant and detoxification responses (catalase, superoxide dismutase, glutathione peroxidase and peroxidase) in C. riparius. By inducing oxidative stress, antibiotic STZ disturbs the endocrine system and produces adverse effects in growth processes of invertebrates.

Optimization and bioevaluation of Cdc37-derived peptides: An insight into Hsp90-Cdc37 protein-protein interaction modulators

Targeting Hsp90-Cdc37 protein-protein interaction (PPI) is becoming an alternative approach for future anti-cancer drug development. We previously reported the discovery of an eleven-residue peptide (Pep-1) with micromolar activity for the disruption of Hsp90-Cdc37 PPI. Efforts to improve upon the Pep-1 led to the discovery of more potent modulators for Hsp90-Cdc37 PPI. Through the analysis of peptides binding patterns, more peptides were designed for further verification which resulted in Pep-5, the shortest peptide targeting Hsp90-Cdc37, exerting the optimal structure and the most efficient binding mode. Subsequent MD simulation analysis also confirmed that Pep-5 could perform more stable binding ability and better ligand properties than Pep-1. Under the premise of retentive binding capacity, Pep-5 exhibited lower molecular weight and higher ligand efficiency with a K_d value of 5.99μM (Pep-1 K_d=6.90μM) in both direct binding determination and biological evaluation. The optimal and shortest Pep-5 might provide a breakthrough and a better model for the future design of small molecule inhibitors targeting Hsp90-Cdc37 PPI.

Y-632 inhibits heat shock protein 90 (Hsp90) function by disrupting the interaction between Hsp90 and Hsp70/Hsp90 organizing protein, and exerts antitumor activity in vitro and in vivo

Heat shock protein 90 (Hsp90) stabilizes a variety of proteins required for cancer cell survival and has been identified as a promising drug target for cancer treatment. To date, several Hsp90 inhibitors have entered into clinical trials, but none has been approved for cancer therapy yet. Thus, exploring new Hsp90 inhibitors with novel mechanisms of action is urgent. In the present study, we show that Y-632, a novel pyrimidine derivative, inhibited Hsp90 in a different way from the conventional Hsp90 inhibitor geldanamycin. Y-632 induced degradation of diverse Hsp90 client proteins through the ubiquitin-proteasome pathway, as geldanamycin did; however, it neither directly bound to Hsp90 nor inhibited Hsp90 ATPase activity. Y-632 inhibited Hsp90 function mainly through inducing intracellular thiol oxidation, which led to disruption of the Hsp90-Hsp70/Hsp90 organizing protein complex and further induced cell adhesion inhibition, G0 /G1 cell cycle arrest, and apoptosis. Moreover, Y-632 efficiently overcame imatinib resistance mediated by Bcr-Abl point mutations both in vitro and in vivo. We believe that Y-632, acting as a novel small-molecule inhibitor of the Hsp90-Hsp70/Hsp90 organizing protein complex, has great potential to be a promising Hsp90 inhibitor for cancer therapy, such as for imatinib-resistant leukemia.

Hsp90: A New Player in DNA Repair?

Heat shock protein 90 (Hsp90) is an evolutionary conserved molecular chaperone that, together with Hsp70 and co-chaperones makes up the Hsp90 chaperone machinery, stabilizing and activating more than 200 proteins, involved in protein homeostasis (i.e., proteostasis), transcriptional regulation, chromatin remodeling, and DNA repair. Cells respond to DNA damage by activating complex DNA damage response (DDR) pathways that include: (i) cell cycle arrest; (ii) transcriptional and post-translational activation of a subset of genes, including those associated with DNA repair; and (iii) triggering of programmed cell death. The efficacy of the DDR pathways is influenced by the nuclear levels of DNA repair proteins, which are regulated by balancing between protein synthesis and degradation as well as by nuclear import and export. The inability to respond properly to either DNA damage or to DNA repair leads to genetic instability, which in turn may enhance the rate of cancer development. Multiple components of the DNA double strand breaks repair machinery, including BRCA1, BRCA2, CHK1, DNA-PKcs, FANCA, and the MRE11/RAD50/NBN complex, have been described to be client proteins of Hsp90, which acts as a regulator of the diverse DDR pathways. Inhibition of Hsp90 actions leads to the altered localization and stabilization of DDR proteins after DNA damage and may represent a cell-specific and tumor-selective radiosensibilizer. Here, the role of Hsp90-dependent molecular mechanisms involved in cancer onset and in the maintenance of the genome integrity is discussed and highlighted.

Organelle-specific Hsp90 inhibitors

Heat shock protein 90 (Hsp90) is an ATP-dependent molecular chaperone that is involved in the folding, activation, and stabilization of numerous oncogenic proteins. It has become an attractive therapeutic target, especially for eradicating malignant cancers and overcoming chemotherapy resistance. The Hsp90 family in mammalian cells is composed of four major homologs: Hsp90α, Hsp90β, 94-kDa glucose-regulated protein (Grp94), and TNF receptor-associated protein 1 (Trap1). Hsp90α and Hsp90β are mainly localized in the cytoplasm, while Grp94 and Trap1 reside in the endoplasmic reticulum and the mitochondria, respectively. Additionally, some Hsp90 s are secreted from the cytoplasm, commonly called extracellular Hsp90. Interestingly, each Hsp90 isoform is localized in a particular organelle, possesses a unique biological function, and participates in various physiological and pathological processes. To inhibit the organelle-specific Hsp90 chaperone function, there have been significant efforts to accumulate Hsp90 inhibitors in particular cellular compartments. This review introduces current studies regarding the delivery of Hsp90 inhibitors to subcellular organelles, particularly to the extracellular matrix and the mitochondria, and discusses their biological insights and therapeutic implications.