Recent advances toward the development of Hsp90 C-terminal inhibitors

Cemdomespib Therapy Slows the Progression of Neuromuscular Weakness and Demyelination in the R75W-Connexin 32 Animal Model of Charcot-Marie-Tooth 1X Disease

Mutations in connexin 32 (Cx32) are a common cause of Charcot-Marie-Tooth 1X (CMT1X) disease, an inherited peripheral neuropathy characterized by progressive neuromuscular weakness and demyelination. There are no approved pharmacologic therapies for CMT1X, and identifying new treatments that slow the onset and severity of neuromuscular decline may aid disease management. Cemdomespib is an orally bioavailable small molecule that improved demyelination and neuromuscular junction (NMJ) morphology in mice lacking Cx32 expression. However, whether a similar efficacy may manifest in models of CMT1X arising from Cx32 mutations that cause the organellar accumulation of the protein was unclear. Additionally, it was unclear whether cemdomespib therapy slowed the rate of demyelination/NMJ degeneration or stabilized nerve and NMJ morphology to levels present at the initiation of drug therapy. To address these issues, 4-month-old R75W-Cx32 mice, which accumulate the mutant Cx32 in golgi, were treated for 0, 10, or 20 weeks with 0 or 3 mg/kg cemdomespib. Grip strength, motor nerve conduction velocity (MNCV), femoral nerve myelination, and NMJ morphology were quantified. Daily drug therapy significantly slowed the decline in grip strength over the course of treatment, while 20 weeks of drug treatment significantly improved MNCV and decreased the g-ratio and the number of thinly myelinated femoral nerve axons. Similarly, 20 weeks of cemdomespib therapy improved the NMJ morphology and the overlap between presynaptic (synaptophysin) and postsynaptic (α-bungarotoxin) markers. These data show that cemdomespib therapy slows the rate of neuromuscular decline and demyelination and may present a disease-modifying approach for patients with gain-of-function Cx32 mutations.

Insights into the Allosteric Regulation of Human Hsp90 Revealed by NMR Spectroscopy

Human heat shock protein 90 (Hsp90) is one of the most important chaperones that play a role in the late stages of protein folding. Errors in the process of the chaperone cycle can lead to diseases such as cancer and neurodegenerative diseases. Therefore, the activity of Hsp90 must be carefully regulated. One of the possibilities is allosteric regulation by its natural allosteric modulators-nucleotides, co-chaperones and client proteins-and synthetic small-molecule allosteric modulators, such as those targeting the middle domain or the C-terminal domain (CTD) of Hsp90. Since no experimentally determined structure of a small-molecule allosteric modulator bound to the CTD of human Hsp90 has yet been obtained, the challenge for a structure-based design of allosteric modulators remains. Solution nuclear magnetic resonance (NMR) spectroscopy could be utilized to overcome these problems. The main aim of this review article is to discuss how solution NMR techniques, especially protein-based, and the advanced isotope labeling of proteins have been used to investigate the allosteric regulation of the cytosolic isoforms of human Hsp90 with allosteric modulators. This article provides the basis for planning future NMR experiments, with the aim of gaining insights into allosteric sites and the mechanisms of allosteric regulation.

The role of Aha1 in cancer and neurodegeneration

The 90 kDa Heat shock protein (Hsp90) is a family of ubiquitously expressed molecular chaperones responsible for the stabilization and maturation of >400 client proteins. Hsp90 exhibits dramatic conformational changes to accomplish this, which are regulated by partner proteins termed co-chaperones. One of these co-chaperones is called the activator or Hsp90 ATPase activity homolog 1 (Aha1) and is the most potent accelerator of Hsp90 ATPase activity. In conditions where Aha1 levels are dysregulated including cystic fibrosis, cancer and neurodegeneration, Hsp90 mediated client maturation is disrupted. Accumulating evidence has demonstrated that many disease states exhibit large hetero-protein complexes with Hsp90 as the center. Many of these include Aha1, where increased Aha1 levels drive disease states forward. One strategy to block these effects is to design small molecule disruptors of the Hsp90/Aha1 complex. Studies have demonstrated that current Hsp90/Aha1 small molecule disruptors are effective in both models for cancer and neurodegeration.

The Investigation of Hsp90C-Terminal Inhibitors Containing Amide Bioisosteres

Heat Shock Protein 90 (Hsp90) is responsible for the proper folding and maturation of ~400 client protein substrates, many of which are directly associated with the ten hallmarks of cancer. Hsp90 is a great target for cancer therapy including melanoma, since Hsp90 inhibition can disrupt multiple oncogenic pathways simultaneously. In this study, we report the synthesis and anti-proliferative activity manifested by a series of Hsp90 C-terminal inhibitors against mutant BRAF and wild-type BRAF melanoma cells. Furthermore, we explored structure-activity relationships (SAR) for the amide moiety of 6 (B1), a novel Hsp90C-terminal inhibitor via introduction of amide bioisosteres. Compound 6 displayed an IC50 of 1.01 μM, 0.782 μM, 0.607 μM and 1.413 μM against SKMel173, SKMel103, SKMel19 and A375 cells, respectively.

Hsp90α promotes lipogenesis by stabilizing FASN and promoting FASN transcription via LXRα in hepatocellular carcinoma

Excessive lipid accumulation promotes the occurrence and progression of hepatocellular carcinoma (HCC), accompanied by high levels of fatty acid synthetase (FASN) and more active lipogenesis. Heat shock protein 90 (Hsp90) acts as a chaperone to maintain the stability and activity of the client proteins. Studies have revealed that Hsp90 regulates the lipid metabolism of HCC, but the effect of Hsp90 on FASN still remains unknown. This study aims to discover the mechanism of Hsp90 inhibition on lipid accumulation and investigate the different effects of Hsp90 N-terminal domain inhibitor STA9090 and C-terminal domain inhibitor novobiocin on FASN protein stability and transcription pathway in HCC. We found that HCC cells tended to store lipids, which could be disrupted by Hsp90 inhibitors in vivo and in vitro. High levels of Hsp90α and FASN in tumor tissue had correlation with poor prognosis of HCC patients, and Hsp90α interacted with FASN to maintain its protein stability. Furthermore, N-terminal domain of Hsp90α was essential for process of sterol regulatory element binding protein 1 to activate FASN transcription and Hsp90α prevented proteasomal degradation of liver X receptor α to upregulate FASN transcription via liver X receptor α/sterol regulatory element binding protein 1 axis. Our data reveal that Hsp90α promotes lipid accumulation by increasing the protein stability and FASN mRNA transcription, and can be alleviated by Hsp90 inhibitors, which provides a theoretical basis for Hsp90-targeted therapy on lipid metabolism in HCC.

Ligand-based pharmacophore modelling, structure optimisation, and biological evaluation for the identification of 2-heteroarylthio-N-arylacetamides as novel HSP90 C-terminal inhibitors

Targeting Heat shock protein 90 (HSP90) C-terminus is an important strategy to develop HSP90 inhibitors without inducing heat shock response. The development of C-terminal inhibitors, however, is hampered by a lack of understanding regarding the interaction between the HSP90 C-terminus and the present inhibitors. We collected seven classical and structurally diverse HSP90 C-terminal inhibitors and constructed a ligand-based pharmacophore model. The subsequent virtual screening and structural optimisation led to the identification of 2-heteroarylthio-N-arylacetamides as novel HSP90 C-terminal inhibitors. 9 and 27 exhibited strong antitumour activity in vitro by inhibiting proliferation and inducing apoptosis in multiple cancer cell lines. These compounds disrupted the interaction between HSP90 C-terminus and peptidylprolyl isomerase D, exerting a stronger inhibitory effect than novobiocin. 27 significantly induced the degradation of HSP90 clients without triggering heat shock response. In an in vivo study using 4T1 mice breast cancer models, 9 showed a potent antitumour effect without obvious toxicity.

Extracellular heat shock protein 90 alpha (eHsp90α)'s role in cancer progression and the development of therapeutic strategies

Heat shock protein 90 alpha (Hsp90α) is an abundantly expressed and evolutionarily conserved molecular chaperone. Hsp90α is the inducible Hsp90 isoform, and its expression and secretion extracellularly (eHsp90α) can be triggered in response to a variety of cellular stresses to protect/activate client proteins and to facilitate cellular adjustment to the stress. As a result, cancers often have high expression levels of intracellular and extracellular (plasma) Hsp90α, allowing them to support their oncogenesis and progression. In fact, (e)Hsp90α has been implicated in regulating processes such as cell signaling transduction, DNA repair, promotion of the Epithelial-to-Mesenchymal Transition (EMT), promotion of angiogenesis, immune response, and cell migration. Hsp90α levels have been correlated with cancer progression and severity in several cancers, indicating that it may be a useful biomarker or drug-target for cancer. To date, the development of intracellular Hsp90α-targeted therapies include standard N-terminal ATP-competitive inhibitors and allosteric regulators that bind to Hsp90α's middle or C-terminal domain. On-target toxicities and dosing complications as a result of Hsp90α inhibition has driven the development of eHsp90α-targeted therapies. Examples include anti-Hsp90α monoclonal antibodies and cell-impermeable Hsp90α small molecule inhibitors. This review aims to discuss the many roles Hsp90α plays in cancer progression with a focus on the current development of Hsp90α-targeted therapies.

Discovery of indazole inhibitors for heat shock protein 90 as anti-cancer agents

A series of indazole analogs, derived from the B,C-ring-truncated scaffold of deguelin, were designed to function as C-terminal inhibitors of heat shock protein 90 (HSP90) and investigated as novel antitumor agents against HER2-positive breast cancer. Among the synthesized compounds, compound 12d exhibited substantial inhibitory effects in trastuzumab-sensitive (BT474) and trastuzumab-resistant (JIMT-1) breast cancer cells, with IC50 values of 6.86 and 4.42 μM, respectively. Notably, compound 12d exhibited no cytotoxicity in normal cells. Compound 12d markedly downregulated the expression of the major HSP90 client proteins in both cell types, attributing its cytotoxicity to the destabilization and inactivation of HSP90 client proteins. Molecular docking studies using the homology model of an HSP90 homodimer demonstrated that inhibitor 12d fit nicely into the C-terminal domain, boasting a higher electrostatic complementary score than ATP. In vivo pharmacokinetic study indicated the high oral bioavailability of compound 12 d at F = 66.9 %, while toxicological studies indicated its negligible impact on hERG channels and CYP isozymes. Genotoxicity tests further confirmed its safety profile. The findings collectively position compound 12d as a promising candidate for further development as an antitumor agent against HER2-positive breast cancer.

First dual inhibitors of human topoisomerase IIα and Hsp90 C-terminal domain inhibit the growth of Ewing sarcoma in vitro and in vivo

Heat shock protein 90 (Hsp90) and topoisomerase IIα (TopoIIα) are members of the GHKL protein superfamily, both with clinically validated roles as anticancer drug targets. We report the discovery of the first class of dual inhibitors targeting the ATP-binding site of TopoIIα and the C-terminal domain of Hsp90, displaying potent cancer growth inhibition both in vitro and in vivo. Initially, a known TopoIIα inhibitor, compound 3, was shown to bind to the C-terminal domain of Hsp90, but not to its ATP-binding N-terminal domain. Nineteen analogs were then prepared and evaluated to investigate the structure-activity relationships, several of which inhibited the growth of SK-N-MC Ewing sarcoma cells in vitro. Compound 3 emerged as one of the most potent growth inhibitors (IC50 = 0.33 ± 0.04 µM), demonstrating the ability to induce apoptosis and cell cycle arrest in SK-N-MC cells in vitro, and to slow the growth of Ewing sarcoma in vivo in a zebrafish model.

Misfolding and aggregation in neurodegenerative diseases: protein quality control machinery as potential therapeutic clearance pathways

The primary challenge in today's world of neuroscience is the search for new therapeutic possibilities for neurodegenerative disease. Central to these disorders lies among other factors, the aberrant folding, aggregation, and accumulation of proteins, resulting in the formation of toxic entities that contribute to neuronal degeneration. This review concentrates on the key proteins such as β-amyloid (Aβ), tau, and α-synuclein, elucidating the intricate molecular events underlying their misfolding and aggregation. We critically evaluate the molecular mechanisms governing the elimination of misfolded proteins, shedding light on potential therapeutic strategies. We specifically examine pathways such as the endoplasmic reticulum (ER) and unfolded protein response (UPR), chaperones, chaperone-mediated autophagy (CMA), and the intersecting signaling of Keap1-Nrf2-ARE, along with autophagy connected through p62. Above all, we emphasize the significance of these pathways as protein quality control mechanisms, encompassing interventions targeting protein aggregation, regulation of post-translational modifications, and enhancement of molecular chaperones and clearance. Additionally, we focus on current therapeutic possibilities and new, multi-target approaches. In conclusion, this review systematically consolidates insights into emerging therapeutic strategies predicated on protein aggregates clearance.

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

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

Exploration and optimisation of structure-activity relationships of new triazole-based C-terminal Hsp90 inhibitors towards in vivo anticancer potency

The development of new anticancer agents is one of the most urgent topics in drug discovery. Inhibition of molecular chaperone Hsp90 stands out as an approach that affects various oncogenic proteins in different types of cancer. These proteins rely on Hsp90 to obtain their functional structure, and thus Hsp90 is indirectly involved in the pathophysiology of cancer. However, the most studied ATP-competitive inhibition of Hsp90 at the N-terminal domain has proven to be largely unsuccessful clinically. Therefore, research has shifted towards Hsp90 C-terminal domain (CTD) inhibitors, which are also the focus of this study. Our recent discovery of compound C has provided us with a starting point for exploring the structure-activity relationship and optimising this new class of triazole-based Hsp90 inhibitors. This investigation has ultimately led to a library of 33 analogues of C that have suitable physicochemical properties and several inhibit the growth of different cancer types in the low micromolar range. Inhibition of Hsp90 was confirmed by biophysical and cellular assays and the binding epitopes of selected inhibitors were studied by STD NMR. Furthermore, the most promising Hsp90 CTD inhibitor 5x was shown to induce apoptosis in breast cancer (MCF-7) and Ewing sarcoma (SK-N-MC) cells while inducing cause cell cycle arrest in MCF-7 cells. In MCF-7 cells, it caused a decrease in the levels of ERα and IGF1R, known Hsp90 client proteins. Finally, 5x was tested in zebrafish larvae xenografted with SK-N-MC tumour cells, where it limited tumour growth with no obvious adverse effects on normal zebrafish development.

Heat Shock Protein 90 in Parkinson's Disease: Profile of a Serial Killer

Parkinson's disease (PD) is the second most common neurodegenerative disease, characterized by abnormal α-synuclein misfolding and aggregation, mitochondrial dysfunction, oxidative stress, as well as progressive death of dopaminergic neurons in the substantia nigra. Molecular chaperones play a role in stabilizing proteins and helping them achieve their proper structure. Previous studies have shown that overexpression of heat shock protein 90 (HSP90) can lead to the death of dopaminergic neurons associated with PD. Inhibiting HSP90 is considered a potential treatment approach for neurodegenerative disorders, as it may reduce protein aggregation and related toxicity, as well as suppress various forms of regulated cell death (RCD). This review provides an overview of HSP90 and its role in PD, focusing on its modulation of proteostasis and quality control of LRRK2. The review also explores the effects of HSP90 on different types of RCD, such as apoptosis, chaperone-mediated autophagy (CMA), necroptosis, and ferroptosis. Additionally, it discusses HSP90 inhibitors that have been tested in PD models. We will highlight the under-investigated neuroprotective effects of HSP90 inhibition, including modulation of oxidative stress, mitochondrial dysfunction, PINK/PARKIN, heat shock factor 1 (HSF1), histone deacetylase 6 (HDAC6), and the PHD2-HSP90 complex-mediated mitochondrial stress pathway. By examining previous literature, this review uncovers overlooked neuroprotective mechanisms and emphasizes the need for further research on HSP90 inhibitors as potential therapeutic strategies for PD. Finally, the review discusses the potential limitations and possibilities of using HSP90 inhibitors in PD therapy.

Recent developments of HSP90 inhibitors: an updated patent review (2020-present)

INTRODUCTION

The 90-kDa heat shock protein (HSP90) functions as a molecular chaperone, it assumes a significant role in diseases such as cancer, inflammation, neurodegeneration, and infection. Therefore, the research and development of HSP90 inhibitors have garnered considerable attention.

AREAS COVERED

The primary references source for this review is patents obtained from SciFinder, encompassing patents on HSP90 inhibitors from the period of 2020 to 2023.This review includes a thorough analysis of their structural attributes, pharmacological properties, and potential clinical utilities.

EXPERT OPINION

In the past few years, HSP90 inhibitors targeting ATP binding pocket are still predominate and one of them has been launched, besides, novel drug design strategies like C-terminal targeting, isoform selective inhibiting and bifunctional molecules are booming, aiming to improve the efficacy and safety. With expanded drug types and applications, HSP90 inhibitors may gradually becoming a sagacious option for treating various diseases.

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.

Enniatin A Analogues as Novel Hsp90 Inhibitors that Modulate Triple-Negative Breast Cancer

The 90 kilo-Dalton heat shock protein (Hsp90) is a molecular chaperone that facilitates the maturation of nascent polypeptides into their biologically active conformation. Because many of the >400 known client protein substrates are implicated in the development/progression of cancer, it is hypothesized that Hsp90 inhibition will simultaneously shut down numerous oncogenic pathways. Unfortunately, most of the small molecule Hsp90 inhibitors that have undergone clinical evaluation thus far have failed due to various toxicities. Therefore, the disruption of Hsp90 protein-protein interactions with cochaperones and/or client substrates has been proposed as an alternative way to achieve Hsp90 inhibition without such adverse events. The hexadepsipeptide Enniatin A (EnnA) has recently been reported to be one such inhibitor that also manifests immunogenic activity. Herein, we report preliminary structure-activity relationship (SAR) studies to determine the structural features that confer this unprecedented activity for an Hsp90 inhibitor. Our studies find that EnnA's branching moieties are necessary for its activity, but some structural modifications are tolerated.

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

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

Ginsenoside Rg5 enhances the radiosensitivity of lung adenocarcinoma via reducing HSP90-CDC37 interaction and promoting client protein degradation

Ginsenoside Rg5 is a rare ginsenoside showing promising tumor-suppressive effects. This study aimed to explore its radio-sensitizing effects and the underlying mechanisms. Human lung adenocarcinoma cell lines A549 and Calu-3 were used for in vitro and in vivo analysis. Bioinformatic molecular docking prediction and following validation by surface plasmon resonance (SPR) technology, cellular thermal shift assay (CETSA), and isothermal titration calorimetry (ITC) were conducted to explore the binding between ginsenoside Rg5 and 90 kD heat shock protein alpha (HSP90α). The effects of ginsenoside Rg5 on HSP90-cell division cycle 37 (CDC37) interaction, the client protein stability, and the downstream regulations were further explored. Results showed that ginsenoside Rg5 could induce cell-cycle arrest at the G1 phase and enhance irradiation-induced cell apoptosis. It could bind to HSP90α with a high affinity, but the affinity was drastically decreased by HSP90α Y61A mutation. Co-immunoprecipitation (Co-IP) and ITC assays confirmed that ginsenoside Rg5 disrupts the HSP90-CDC37 interaction in a dose-dependent manner. It reduced irradiation-induced upregulation of the HSP90-CDC37 client proteins, including SRC, CDK4, RAF1, and ULK1 in A549 cell-derived xenograft (CDX) tumors. Ginsenoside Rg5 or MRT67307 (an IKKε/TBK1 inhibitor) pretreatment suppressed irradiation-induced elevation of the LC3-II/β ratio and restored irradiation-induced downregulation of p62 expression. In A549 CDX tumors, ginsenoside Rg5 treatment suppressed LC3 expression and enhanced irradiation-induced DNA damage. In conclusion, ginsenoside Rg5 may be a potential radiosensitizer for lung adenocarcinoma. It interacts with HSP90α and reduces the binding between HSP90 and CDC37, thereby increasing the ubiquitin-mediated proteasomal degradation of the HSP90-CDC37 client proteins.

HSP90 C-terminal domain inhibition promotes VDAC1 oligomerization via decreasing K274 mono-ubiquitination in Hepatocellular Carcinoma

Voltage-dependent anion-selective channel protein 1 (VDAC1) is the most abundant protein in the mitochondrial outer membrane and plays a crucial role in the control of hepatocellular carcinoma (HCC) progress. Our previous research found that cytosolic molecular chaperone heat shock protein 90 (Hsp90) interacted with VDAC1, but the effect of the C-terminal and N-terminal domains of Hsp90 on the formation of VDAC1 oligomers is unclear. In this study, we focused on the effect of the C-terminal domain of Hsp90 on VDAC1 oligomerization, ubiquitination, and VDAC1 channel activity. We found that Hsp90 C-terminal domain inhibitor Novobiocin promoted VDAC1 oligomerization, release of cytochrome c, and activated mitochondrial apoptosis pathway. Atomic coarse particle modeling simulation revealed C-terminal domain of Hsp90α stabilized VDAC1 monomers. The purified VDAC1 was reconstituted into a planar lipid bilayer, and electrophysiology experiments of patch clamp showed that the Hsp90 C-terminal inhibitor Novobiocin increased VDAC1 channel conductance via promoting VDAC1 oligomerization. The mitochondrial ubiquitination proteomics results showed that VDAC1 K274 mono-ubiquitination was significantly decreased upon Novobiocin treatment. Site-directed mutation of VDAC1 (K274R) weakened Hsp90α-VDAC1 interaction and increased VDAC1 oligomerization. Taken together, our results reveal that Hsp90 C-terminal domain inhibition promotes VDAC1 oligomerization and VDAC1 channel conductance by decreasing VDAC1 K274 mono- ubiquitination, which provides a new perspective for mitochondria-targeted therapy of HCC.

Cytokine-Induced Killer Cells in Combination with Heat Shock Protein 90 Inhibitors Functioning via the Fas/FasL Axis Provides Rationale for a Potential Clinical Benefit in Burkitt's lymphoma

Constant efforts are being made to develop methods for improving cancer immunotherapy, including cytokine-induced killer (CIK) cell therapy. Numerous heat shock protein (HSP) 90 inhibitors have been assessed for antitumor efficacy in preclinical and clinical trials, highlighting their individual prospects for targeted cancer therapy. Therefore, we tested the compatibility of CIK cells with HSP90 inhibitors using Burkitt's lymphoma (BL) cells. Our analysis revealed that CIK cytotoxicity in BL cells was augmented in combination with independent HSP90 inhibitors 17-DMAG (17-dimethylaminoethylamino-17-demethoxygeldanamycin) and ganetespib. Interestingly, CIK cell cytotoxicity did not diminish after blocking with NKG2D (natural killer group 2, member D), which is a prerequisite for their activation. Subsequent analyses revealed that the increased expression of Fas on the surface of BL cells, which induces caspase 3/7-dependent apoptosis, may account for this effect. Thus, we provide evidence that CIK cells, either alone or in combination with HSP90 inhibitors, target BL cells via the Fas-FasL axis rather than the NKG2D pathway. In the context of clinical relevance, we also found that high expression of HSP90 family genes (HSP90AA1, HSP90AB1, and HSP90B1) was significantly associated with the reduced overall survival of BL patients. In addition to HSP90, genes belonging to the Hsp40, Hsp70, and Hsp110 families have also been found to be clinically significant for BL survival. Taken together, the combinatorial therapy of CIK cells with HSP90 inhibitors has the potential to provide clinical benefits to patients with BL.