Small Molecule Hsp90 Inhibitors Research Articles

Abstract 6053: Mechanism of action of tumor-selective, chaperone-mediated protein degraders (CHAMPs)

Abstract HSP90 mediates the folding of many important cancer-associated proteins, but it can also direct its substrates towards degradation via the ubiquitin-proteasome system. Furthermore, in tumor tissues, HSP90 complexes are in an activated state relative to normal tissues, and small molecule HSP90 inhibitors display unique tumor-selective pharmacokinetics. To take advantage of these attributes, we have developed a novel targeted protein degradation technology, termed Chaperone-Mediated Protein Degradation (CHAMP), and present here an in-depth characterization of the CHAMP mechanism of action. Initially, from a chemical library of greater than 1000 linkered HSP90 binders, hetero-bifunctional CHAMPs were synthesized in which target protein binders and HSP90 binders were covalently coupled together by short linkers. The resulting compounds were screened for target protein degradation and cancer cell cytotoxicity to identify promising leads for further optimization. We found that CHAMPs can degrade a wide variety of target proteins. This included proteins that are known to be regulated by HSP90, such as transcription factor BRD4 or ERK5 kinase. However, proteins that are normally independent of HSP90 function can also be degraded, including mutated KRAS and SHP2 phosphatase. In vitro, CHAMP treatment of cells resulted in formation of a ternary complex between the target protein, CHAMP compound and HSP90. Moreover, an X-ray crystal structure was solved for a mKRAS-CHAMP-HSP90 ternary complex. CHAMP-mediated degradation required both the target- and HSP90-binding moieties to be covalently coupled and involved ubiquitination of the target protein. Multiple ubiquitin E3 ligases were present in ternary complexes, and depending on the target protein, NEDD8 inhibition or CRISPR knockouts of individual E3 ligases could suppress proteasome-dependent target degradation. In vivo, irrespective of target, CHAMPs displayed prolonged exposure in tumors relative to plasma and normal tissues, resulting in prolonged target degradation in tumors and strong tumor growth inhibition at well-tolerated doses. CHAMP technology can be applied to a diversity of cancer-associated targets and has potential advantages relative to other protein degradation approaches, including an improved safety margin due to preferential accumulation in tumor tissues. Citation Format: Xiangcai Yang, Yan Dai, Qinglin Ding, Feng Du, Jinhua Li, Chuhe Liu, Chunyang Lv, Liang Ma, Thomas L. Prince, Yuetong Sun, Mingkai Wang, Rong Wang, Yaya Wang, Zhiyong Wang, Min Wu, Mengmeng Xu, Zimo Yang, Long Ye, Wei Yin, Chenghao Ying, Haoxin Zhou, Guoqiang Wang, Weiwen Ying, Kevin P. Foley. Mechanism of action of tumor-selective, chaperone-mediated protein degraders (CHAMPs) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6053.

Abstract 5879: Role of the inner mitochondrial membrane protein (Mic60) in MAPKi-resistant melanoma

Abstract Introduction: Metastatic melanoma is one of the most aggressive cancers, despite recent improvements in therapy. The rising melanoma incidence and mortality, along with its high propensity for metastasis highlights the urgency to find more effective therapeutic targets. The efficacy of targeted MAPK signaling pathway inhibitors (MAPKi) in metastatic melanoma therapy is limited by the development of resistance mechanisms that result in disease relapse. This situation necessitates alternative treatments for melanoma patients who develop resistance to targeted therapy. We have recently found out that there exists a group of human tumors that express lower levels of Mic60, a mitochondrial structural protein also known as mitofilin or inner membrane mitochondrial protein (IMMT). In a model of prostate cancer, we showed that Mic60-low tumors have lower mitochondrial fitness, but increased cell motility, invasion, and propensity to metastasize. However, a potential differential expression of Mic60 in melanoma has not been investigated and whether reduced mitochondrial fitness in Mic60-low tumors can expose new therapeutic vulnerabilities in combination with targeted therapies has not been determined. Experimental Procedures: We analyzed melanoma-specific TMA for differential expression of Mic60 in tumor vs. adjacent normal tissue by IHC. Differential mRNA expression levels were examined by single-cell RNA-Seq and quantified by bioinformatics analysis. Differential therapeutic vulnerabilities of Mic60-low melanoma cell lines to mitochondrial-targeted small molecule Hsp90 inhibitor, Gamitrinib, were assessed for cell death induction and mitochondrial dysfunction. Results: We identified subsets of melanoma patients with constitutively reduced or outright undetectable expression of Mic60, in vivo. By single-cell RNA-Seq, Mic60-low melanomas were characterized by reduced oxidative phosphorylation and decreased ATP production, slower cell cycle progression but paradoxically increased cell motility and invasion. Loss of Mic60 exposed new, actionable therapeutic vulnerabilities, and the combination of Gamitrinib plus MAPKi potently induced mitochondrial cell death in MAPKi-resistant melanoma cell lines. Conclusion: Mic60 is heterogeneously expressed and often reduced in melanoma. Although this is associated with increased cell invasion and metastatic propensity, the combination of Gamitrinib plus MAPKi restored mitochondrial cell death in therapy-resistant, Mic60-low melanoma cells. Citation Format: Jagadish C. Ghosh, Segundo Del Aguila, Haiyin Li, Jessie Villanueva, Dario C. Altieri. Role of the inner mitochondrial membrane protein (Mic60) in MAPKi-resistant melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5879.

Abstract 1814: Development and evaluation of Hsp90β-selective inhibitors to overcome the safety challenges associated with pan-Hsp90 inhibitors

Abstract The 90 kD heat shock proteins (Hsp90) are molecular chaperones that are responsible for the folding of select proteins, many of which are directly associated with cancer progression. Consequently, inhibition of the Hsp90 protein folding machinery results in a combinatorial attack on numerous oncogenic pathways. More than 20 small-molecule inhibitors of Hsp90 have entered clinical trials for the treatment of cancer, all of which bind the Hsp90 N-terminus and exhibit pan-inhibitory activity against all four Hsp90 isoforms (Hsp90a, Hsp90β, Grp94 and TRAP-1). Most of these clinical trials have failed as pan-Inhibition of Hsp90 appears to be detrimental with toxicities reported alongside induction of the pro-survival heat shock response, which leads to additional dosing challenges/toxicities. The cytosolic Hsp90 isoforms Hsp90a and Hsp90β are the major contributors to cancer growth/survival. It has been established that inhibition of Hsp90a is associated with cardiac toxicity, retinal toxicity, and induction of the heat shock response. Therefore, the development of Hsp90β -selective inhibitors represents an alternative approach for the treatment of cancer with limited side effects. Towards this goal, Hsp90β-selective inhibitors that exhibit >150-fold selectivity over Hsp90a have been developed, which exhibit efficacy against select cancers while overcoming the safety challenges associated with previous Hsp90 inhibitors. The results from such studies will be presented. Citation Format: Sanket Mishra, Tyelor Reynolds, Brian Blagg. Development and evaluation of Hsp90β-selective inhibitors to overcome the safety challenges associated with pan-Hsp90 inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1814.

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.

Rational design, synthesis and structural characterization of peptides and peptidomimetics to target Hsp90/Cdc37 interaction for treating hepatocellular carcinoma

Heat shock protein 90 (Hsp90) and cell division cycle 37 (Cdc37) work together as a molecular chaperone complex to regulate the activity of a multitude of client protein kinases. These kinases belong to a wide array of intracellular signaling networks that mediate multiple cellular processes including proliferation. As a result, Hsp90 and Cdc37 represent innovative therapeutic targets in various cancers (such as leukemia, multiple myeloma, and hepatocellular carcinoma (HCC)) in which their expression levels are elevated. Conventional small molecule Hsp90 inhibitors act by blocking the conserved adenosine triphosphate (ATP) binding site. However, by targeting less conserved sites in a more specific manner, peptides and peptidomimetics (modified peptides) hold potential as more efficacious and less toxic alternatives to the conventional small molecule inhibitors. Using a rational approach, we herein developed bioactive peptides targeting Hsp90/Cdc37 interaction. A six amino acid linear peptide derived from Cdc37, KTGDEK, was designed to target Hsp90. We used in silico computational docking to first define its mode of interaction, and binding orientation, and then conjugated the peptide with a cell penetrating peptide, TAT, and a fluorescent dye to confirm its ability to colocalize with Hsp90 in HCC cells. Based on the parent linear sequence, we developed a peptidomimetics library of pre-cyclic and cyclic derivatives. These peptidomimetics were evaluated for their binding affinity to Hsp90, and bioactivity in HCC cell lines. Among them, a pre-cyclic peptidomimetic demonstrates high binding affinity and bioactivity in HCC cells, causing reduced cell proliferation that is associated with induction of cell apoptosis, and down-regulation of phosphorylated MEK1/2. Overall, this generalized approach of rational design, structural optimization, and cellular validation of ‘drug-like’ peptidomimetics against Hsp90/Cdc37 offers a feasible and promising way to design novel therapeutic agents for malignancies and other diseases that are dependent on this molecular chaperone complex.

A novel small molecule Hsp90 inhibitor, C-316-1, attenuates acute kidney injury by suppressing RIPK1-mediated inflammation and necroptosis

Acute kidney injury (AKI) is marked by a fast deterioration of the kidney function that may be caused by a variety of factors. Recently, although our group found that PPBICA alleviated programmed cell death in AKI, poor water solubility limited its bioavailability. In this research, we screened a series of derivatives and found that C-316-1 had the best suppressive effect on preventing necroptosis and inflammation in cisplatin- and ischemia/reperfusion-induced AKI in vitro and in vivo with lower toxicity and better water solubility. Mass spectrometry results showed that C-316-1 bound to heat shock protein 90 (Hsp90), which was further confirmed by molecular docking and surface plasmon resonance. Additionally, the Hsp90 expression was upregulated in the blood and tissues of AKI patients. We discovered that C-316-1 decreased the RIPK1 protein level without affecting its mRNA expression. The proteasome inhibitor, MG132 restored the level of RIPK1 reduced by C-316-1, suggesting that C-316-1 limits necroptosis by promoting the degradation of RIPK1 rather than by reducing its production. Immunoprecipitation further showed that pretreatment with C-316-1 disrupted the Hsp90-Cdc37 protein–protein Interactions (PPIs). Thereby, C-316-1 inhibited the Hsp90-Cdc37 complex formation and led to a significant decrease in RIPK1, which in turn reduced necroptosis. Moreover, C-316-1 treatment did not protect against kidney injury in vivo and in vitro when Hsp90 was knocked down and R46, E47, and S50 in Cdc37 binding site of Hsp90 might form an important active pocket with C-316-1. These findings suggest that C-316-1 is a potential therapeutic agent against RIPK1-Mediated Necroptosis in AKI.

Feasibility and safety of targeting mitochondria for cancer therapy – preclinical characterization of gamitrinib, a first-in-class, mitochondriaL-targeted small molecule Hsp90 inhibitor

ABSTRACT Mitochondria are key tumor drivers, but their suitability as a therapeutic target is unknown. Here, we report on the preclinical characterization of Gamitrinib (GA mitochondrial matrix inhibitor), a first-in-class anticancer agent that couples the Heat Shock Protein-90 (Hsp90) inhibitor 17-allylamino-geldanamycin (17-AAG) to the mitochondrial-targeting moiety, triphenylphosphonium. Formulated as a stable (≥24 weeks at −20°C) injectable suspension produced by microfluidization (<200 nm particle size), Gamitrinib (>99.5% purity) is heavily bound to plasma proteins (>99%), has intrinsic clearance from liver microsomes of 3.30 mL/min/g and minimally penetrates a Caco-2 intestinal monolayer. Compared to 17-AAG, Gamitrinib has slower clearance (85.6 ± 5.8 mL/min/kg), longer t1/2 (12.2 ± 1.55 h), mean AUC0-t of 783.1 ± 71.3 h∙ng/mL, and unique metabolism without generation of 17-AG. Concentrations of Gamitrinib that trigger tumor cell killing (IC50 ~1-4 µM) do not affect cytochrome P450 isoforms CYP1A2, CYP2A6, CYP2B6, CYP2C8 or ion channel conductance (Nav1.5, Kv4.3/KChIP2, Cav1.2, Kv1.5, KCNQ1/mink, HCN4, Kir2). Twice weekly IV administration of Gamitrinib to Sprague-Dawley rats or beagle dogs for up to 36 d is feasible. At dose levels of up to 5 (rats)- and 12 (dogs)-fold higher than therapeutically effective doses in mice (10 mg/kg), Gamitrinib treatment is unremarkable in dogs with no alterations in clinical-chemistry parameters, heart function, or tissue histology, and causes occasional inflammation at the infusion site and mild elevation of serum urea nitrogen in rats (≥10 mg/kg/dose). Therefore, targeting mitochondria for cancer therapy is feasible and well tolerated. A publicly funded, first-in-human phase I clinical trial of Gamitrinib in patients with advanced cancer is ongoing (ClinicalTrials.gov NCT04827810)

A Novel Small Molecule Hsp90 Inhibitor, C-316-1, Attenuates Acute Kidney Injury by Suppressing Ripk1-Mediated Necroptosis

A Novel Small Molecule Hsp90 Inhibitor, C-316-1, Attenuates Acute Kidney Injury by Suppressing Ripk1-Mediated Necroptosis

The Potential of Hsp90 in Targeting Pathological Pathways in Cardiac Diseases

Heat shock protein 90 (Hsp90) is a molecular chaperone that interacts with up to 10% of the proteome. The extensive involvement in protein folding and regulation of protein stability within cells makes Hsp90 an attractive therapeutic target to correct multiple dysfunctions. Many of the clients of Hsp90 are found in pathways known to be pathogenic in the heart, ranging from transforming growth factor (TGF-) and mitogen activated kinase (MAPK) signaling to tumor necrosis factor (TNF), Gs and Gq g-protein coupled receptor (GPCR) and calcium (Ca2+) signaling. These pathways can therefore be targeted through modulation of Hsp90 activity. The activity of Hsp90 can be targeted through small-molecule inhibition. Small-molecule inhibitors of Hsp90 have been found to be cardiotoxic in some cases however. In this regard, specific targeting of Hsp90 by modulation of post-translational modifications (PTMs) emerges as an attractive strategy. In this review, we aim to address how Hsp90 functions, where Hsp90 interacts within pathological pathways, and current knowledge of small molecules and PTMs known to modulate Hsp90 activity and their potential as therapeutics in cardiac diseases.

The Development of Hsp90β-Selective Inhibitors to Overcome Detriments Associated with pan-Hsp90 Inhibition.

The 90 kD heat shock proteins (Hsp90) are molecular chaperones that are responsible for the folding of select proteins, many of which are directly associated with cancer progression. Consequently, inhibition of the Hsp90 protein folding machinery results in a combinatorial attack on numerous oncogenic pathways. Seventeen small-molecule inhibitors of Hsp90 have entered clinical trials for the treatment of cancer, all of which bind the Hsp90 N-terminus and exhibit pan-inhibitory activity against all four Hsp90 isoforms, which may lead to adverse effects. The development of Hsp90 isoform-selective inhibitors represents an alternative approach toward the treatment of cancer and may limit some of these detriments. Described herein, is a structure-based approach to develop isoform-selective inhibitors of Hsp90β, which induces the degradation of select Hsp90 clients without concomitant induction of Hsp90 levels. Together, these initial studies support the development of Hsp90β-selective inhibitors as a method for overcoming the detriments associated with pan-inhibition.

EXTH-54. ENHANCED SENSITIVITY OF HUMAN GLIOMA CELLS FOR TEMOZOLOMIDE (TMZ) BY COMBINING THERAPY WITH HEAT SHOCK PROTEIN 90

Abstract BACKGROUND Heat-shock protein 90 (HSP90) is a molecular chaperone involved in the conformational maturation of many client proteins that regulate cell proliferation, survival, and apoptosis. Due to the limited solubility of natural Hsp90 inhibitors, synthetic inhibitors with a more potent impact are being developed. In this study we examined the biological activity of a potent synthetic small molecule Hsp90 inhibitor, SNX-5422 (PF-04929113)and assessed its ability of to inhibit the growth of glioma and to synergize with temozolomide. We also examined the ability of SNX-5422 to cross the blood brain barrier (BBB) and to achieve target inhibition in vivo. METHODS Using a combination of in vitro techniques, the effect of SNX-5422 on the biological impact and HSP90 client protein signaling were studied in glioma lines and patient-derived glioma stem like cells. Its efficacy as a single agent or in combination with TMZ was also assessed in vitro. To assess SNX-5422 ability to cross blood brain barrier, brain and plasma pharmacokinetics was performed in non-tumor bearing mice. RESULTS SNX-5422 exhibited potent growth inhibition in both glioma cells and GSCs with an IC50 range of 100-500nM, and inhibited pro-survival signal kinases, phospho-Akt, p-ERK1/2 and p-S6 following treatment in GSC262 and GSC811. This was accompanied by accumulation of apoptotic cells following SNX-5422 exposure. Combination studies with TMZ showed a synergestic impact on glioma cell proliferation. Pharmacokinetics studies showed a significant drug penetrance into the intact brain further supported by elevated levels of HSP70 (molecular maker for HSP90 inhibition) by IHC. CONCLUSIONS SNX-5422 is effective in downregulating Hsp90 client proteins required for glioma cell survival. In addition, SNX-5422 inhibits tumor growth by promoting apoptosis through modulation of several key signaling pathways and sensitizes glioma cells to TMZ. Given also that SNX-5422 crosses BBB, it warrants further investigation as a clinical agent for treatment of gliomas.

Gephyromycin C, a novel small-molecule inhibitor of heat shock protein Hsp90, induces G2/M cell cycle arrest and apoptosis in PC3 cells in vitro

Gephyromycin C (GC), a natural compound isolated from a marine-derived actinomycete Streptomyces sp. SS13I, which exerts anti-proliferative effect on PC3 cells. However, its underlying mechanism of the anti-cancer effect remains unknown. The results of SRB assays showed that GC inhibited the proliferation of PC3 cells with an IC50 value of 1.79 ± 0.28 μM. GC also induced G2/M cell cycle arrest which was accompanied by declining levels of cyclin proteins. Possible mechanisms were investigated and it was found that GC bound to Hsp90 and caused the degradation of Hsp90 client proteins (AKT, CHK1, P53, CDK4, Raf-b, and Raf-1). The fluorescent polarization assay with FITC-labeled geldanamycin (FITC-GA) demonstrated that GC was able to compete with FITC-GA in binding to wild type Hsp90 with an IC50 of 2.15 μM. Results of a docking study also suggested that GC interacted with the N-terminal domain of Hsp90. Our results showed that GC could bind to Hsp90, which resulted in down-regulation of Hsp90 client proteins and G2/M arrest in PC3 cells. Since the antitumor effects of this kind of angucycline via targeting Hsp90 has not been reported before, our results indicate that GC is a novel inhibitor of Hsp90 from marine resources and worthy of further study.

CTEP 9557: A dose-escalation trial of combination dabrafenib, trametinib, and AT13387 in patients with BRAF mutant solid tumors.

3609 Background: Combination BRAF and MEK inhibitor therapy is associated with response in patients (pts) with BRAF mutant (mut) solid tumors; however critical limitations for the durable activity of these agents remains. Preclinically, the addition of heat shock protein 90 (HSP90) inhibitors improves the efficacy of BRAF inhibitor (BRAFi) therapy in both BRAFi -sensitive and resistant mutant cell lines. Methods: CTEP study 9557 (NCT02097225) is a phase I study designed to determine the safety and efficacy of the small molecule HSP90inhibitor, AT13387, in combination with dabrafenib (dab) and trametinib (tram) in patients with BRAF V600E/K mut solid tumors. Prior chemotherapy, immunotherapy, BRAF and/or MEK exposure was permitted. The primary objective was to determine the maximum tolerated dose (MTD). Results: From July 2015 to June 2018, 22 patients with previously treated, metastatic BRAF V600E/K mut solid tumors were enrolled using a 3 + 3 design at four dose levels (DL) (Table). Pts were predominantly female (59%) with a median age of 57.5yrs (37 -75). The most common tumor type was BRAF V600Emut colon cancer (N=12). Dose limiting toxicities (DLTs) occurred in one patient in DL3 and one in DL4, specifically grade 3 myelosuppression and fatigue, respectively. The MTD was Dab 150mg [BID/PO], Tram 2mg [QD/PO] and AT1187 260mg/m2 [D1,8,15/IV]. Twenty-one of 22 pts were eligible for efficacy assessment. Best response, per RECIST 1.1, was partial response (PR) in 2 pts – one with colon ca (TKI-naïve), one with melanoma (TKI-resistant) - stable disease (SD) in 8 pts, and disease progression (PD) in 11 with a disease control rate (PR + SD) of 47.6% (90% CI: 29% - 67%). Median time to progression was significantly longer in DL3 (3.9 mths; 1.8-9.2) compared to DL1 (1.6mths; 0.9-1.7) or DL2 (1.5; 0.6-3.6). Median PFS and OS were 1.8mths (90% CI: 1.6 – 3.7mths) and 5.1 mths (90% CI: 2.5 -10.6mths), respectively. Median OS was not reached in DL3/4. Correlative data on the expression of the key signaling proteins relating to response will be presented at the meeting. Conclusions: HSP90 inhibition combined with BRAF/MEK inhibition was determined to be safe with evidence of disease control in a heavily pre-treated population of pts with BRAF V600E/K mut solid tumors. Clinical trial information: NCT02097225 . [Table: see text]

Heat shock protein 90-targeted photodynamic therapy enables treatment of subcutaneous and visceral tumors

Photodynamic therapy (PDT) ablates malignancies by applying focused near-infrared (nIR) light onto a lesion of interest after systemic administration of a photosensitizer (PS); however, the accumulation of existing PS is not tumor-exclusive. We developed a tumor-localizing strategy for PDT, exploiting the high expression of heat shock protein 90 (Hsp90) in cancer cells to retain high concentrations of PS by tethering a small molecule Hsp90 inhibitor to a PS (verteporfin, VP) to create an Hsp90-targeted PS (HS201). HS201 accumulates to a greater extent than VP in breast cancer cells both in vitro and in vivo, resulting in increased treatment efficacy of HS201-PDT in various human breast cancer xenografts regardless of molecular and clinical subtypes. The therapeutic index achieved with Hsp90-targeted PDT would permit treatment not only of localized tumors, but also more diffusely infiltrating processes such as inflammatory breast cancer.

Targeting Refractory Sarcomas and Malignant Peripheral Nerve Sheath Tumors in a Phase I/II Study of Sirolimus in Combination with Ganetespib (SARC023).

Purpose Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive soft tissue sarcomas. Combining Hsp90 inhibitors to enhance endoplasmic reticulum stress with mTOR inhibition results in dramatic MPNST shrinkage in a genetically engineered MPNST mouse model. Ganetespib is an injectable potent small molecule inhibitor of Hsp90. Sirolimus is an oral mTOR inhibitor. We sought to determine the safety, tolerability, and recommended dose of ganetespib and sirolimus in patients with refractory sarcomas and assess clinical benefits in patients with unresectable/refractory MPNSTs. Patients and Methods. In this multi-institutional, open-label, phase 1/2 study of ganetespib and sirolimus, patients ≥16 years with histologically confirmed refractory sarcoma (phase 1) or MPNST (phase 2) were eligible. A conventional 3 + 3 dose escalation design was used for phase 1. Pharmacokinetic and pharmacodynamic measures were evaluated. Primary objectives of phase 2 were to determine the clinical benefit rate (CBR) of this combination in MPNSTs. Patient-reported outcomes assessed pain. Results Twenty patients were enrolled (10 per phase). Toxicities were manageable; most frequent non-DLTs were diarrhea, elevated liver transaminases, and fatigue. The recommended dose of ganetespib was 200 mg/m2 intravenously on days 1, 8, and 15 with sirolimus 4 mg orally once daily with day 1 loading dose of 12 mg. In phase 1, one patient with leiomyosarcoma achieved a sustained partial response. In phase 2, no responses were observed. The median number of cycles treated was 2 (1–4). Patients did not meet the criteria for clinical benefit as defined per protocol. Pain ratings decreased or were stable. Conclusion Despite promising preclinical rationale and tolerability of the combination therapy, no responses were observed, and the study did not meet parameters for further evaluation in MPNSTs. This trial was registered with (NCT02008877).

The Right Tool for the Job: An Overview of Hsp90 Inhibitors.

Molecular chaperones are responsible for maintaining intracellular protein quality control by facilitating the conformational maturation of new proteins as well as the refolding of denatured proteins. While there are several classes of molecular chaperones in the cell, this chapter will focus solely on the small molecule modulation of Hsp90, the 90kDa heat shock protein. Hsp90 is not only responsible for folding nascent proteins, but it also regulates the triage of numerous client proteins through partnering with the ubiquitin-proteasome pathway. Consequently, Hsp90 plays critical role in maintaining the protein homeostasis (proteostasis) network within the cell and is required for the activation/maturation of more than 300 client protein substrates. Many of the clients that depend upon Hsp90 are overexpressed or mutated during malignant transformation. This often renders the clients thermodynamically unstable and dependent on Hsp90 for stability. This phenomenon results in an oncogenic 'addiction' to the Hsp90 protein folding machinery as Hsp90 maintains onco-client proteins. Furthermore, Hsp90-dependent substrates are associated with all ten hallmarks of cancer, making Hsp90 an attractive target for the development of cancer chemotherapeutics. In fact, 17 small molecule inhibitors of Hsp90 have been developed and clinically evaluated for the treatment of cancer. Unfortunately, most of these molecules have failed for various reasons, necessitating a new approach to modulate the Hsp90 protein folding machine.

350P - Phase Ib study of heat shock protein 90 inhibitor, onalespib in combination with paclitaxel in patients with advanced, triple negative breast cancer (NCT02474173)

BackgroundHeat shock protein 90 (HSP90) is a molecular chaperone required for proper folding and stabilization of proteins. Client proteins of HSP90 include many oncogenic proteins known to be over-activated in triple negative breast cancer (TNBC) such as AKT, EGFR and members of RAS/MAPK signaling pathway. Over-expression of HSP90 client proteins such as AKT and c-RAF has also been implicated in paclitaxel resistance. Onalespib (AT13387) is a potent non-ansamycin small molecule inhibitor of HSP90. MethodsPatients (pts) with inoperable or metastatic, TNBC were treated with onalespib and paclitaxel on days 1, 8, 15 every 28 days. Paclitaxel was given at a dose of 80mg/m2 while the dose of onalespib was gradually increased from 120mg/m2 to 260mg/m2 in dose levels (DL) 1-4 using standard 3+3 design. In order to assess the effect of each drug on pharmacokinetics (PK) of the other drug, onalespib was given on day -7 prior to cycle 1 and skipped on day 1 of cycle 1. The primary objective was to determine dose limiting toxicities (DLT) and maximum tolerated dose (MTD). The secondary objectives were PKs of each agent, overall response rate (ORR), response duration and progression-free survival. Results20 pts were enrolled to dose escalation part (5, 3, 7 and 6 to DL 1-4 respectively). One pt in DL 1 did not start therapy due history of severe paclitaxel hypersensitivity and 2 pts (DL1 and DL 3) had to be replaced due to disease progression in cycle 1. One DLT occurred in 1pt in DL3 (grade 3 nausea, vomiting and abdominal pain). No DLTs were noted in the highest DL testing onalespib at 260mg/m2. The most common grade 3 or higher adverse events included diarrhea (55%), fatigue (55%), anemia (14%), leukopenia (24%) and neutropenia (41%). Diarrhea was self limiting, lasting 24-48hrs post infusion and responded well to loperamide. ORR and clinical benefit rate in 16 evaluable pts was 25% and 62.5% respectively. Preliminary PK analysis showed no evidene of interaction between onalespib and paclitaxel. ConclusionsStudy regimen demonstrated acceptable safety profile. MTD of onalespib in combination with standard dose and schedule of paclitaxel was determined to be 260mg/m2. Dose expansion study at MTD is currently ongoing. Clinical trial identificationNCI 9876 (NCT02474173). Legal entity responsible for the studyRobert Wesolowski, MD. FundingCancer Therapy Evaluation Program at the National Cancer Institute. DisclosureAll authors have declared no conflicts of interest.

High-Throughput Targeted Quantitative Analysis of the Interaction between HSP90 and Kinases.

Kinases, which function in numerous cell signaling processes, are among the best characterized groups of client proteins for the 90-kDa heat shock protein (HSP90), a molecular chaperone that suppresses the aggregation and maintains the proper folding of its substrate proteins (i.e., clients). No high-throughput proteomic method, however, has been developed for the characterizations of the interactions between HSP90 and the human kinome. Herein, by employing a parallel-reaction monitoring (PRM)-based targeted proteomic method, we found that 99 out of the 249 detected kinase proteins display diminished expression in cultured human cells upon treatment with ganetespib, a small-molecule HSP90 inhibitor. PRM analysis of kinase proteins in the affinity pull-down samples showed that 86 out of the 120 detected kinases are enriched from the CRISPR-engineered cells where a tandem affinity tag was conjugated with the C-terminus of endogenous HSP90β protein over the parental cells. Together, our results from the two complementary quantitative proteomic experiments offer systematic characterizations about the HSP90-kinase interactions at the entire proteome scale and reveal extensive interactions between HSP90 and kinase proteins in human cells.

Abstract 3731: A novel heat shock protein 90-targeted photosensitizer (HS-201) enables enhanced tumor-specific photodynamic therapy of inflammatory breast cancers

Abstract Background: Photodynamic therapy (PDT) is an effective local anti-cancer modality applied for the treatment of early stage disease and palliation of advanced disease, and could be used in managing inflammatory breast cancer (IBC). Although PDT can be focused by limiting the area of near infrared (nIR) light exposure, normal tissue injury due to the photosensitizer (PS) uptake by non-tumor tissues remains a barrier to broader applicability. We reported that selective delivery of a compound to malignant cells by exploiting their heat shock protein 90 (Hsp90) activity could be used for imaging breast cancers. This work was extended by the development of an Hsp90 targeted PS (HS201), in which a well characterized PS, verteporfin (VP), has been chemically tethered to a small molecule Hsp90 inhibitor and assessed the tumor-specificity and antitumor efficacy of HS201-based PDT (HS201-PDT). Methods &amp; Results: HS201 was taken up by human breast cancer cell lines, including IBC in vitro more readily than VP, resulting in increased tumor killing in vitro after exposure to a laser with a 690 nm wavelength. The in vivo selectively of HS201 uptake in tumor tissue was confirmed in both human breast cancer xenograft models and spontaneous tumors from HER2-transgenic mice. HS201 accumulation in the tumor was dramatically enhanced after the first laser exposure due to the feed forward increase in Hsp90 expression in the treated tumor cells, and thus a repeated laser exposure was conducted to enhance antitumor effects. This strategy enhanced antitumor effects, as MDA-MB-231 tumors implanted into SCID-beige mice responded to HS201-PDT but not to VP-PDT. Human xenograft breast cancer cell lines, including the IBC cell lines SUM149 and KPL-4, as well as non-IBC cell line BT474M1 and the patient-derived breast cancer xenograft HCI-013, were also tested in SCID-beige mice and demonstrated significantly suppressed tumor growth by HS201-PDT. Conclusions: HS201 showed selective uptake and longer retention by tumor cells, including IBC, especially when the tumors were exposed to local laser treatment. Due to the advantage of this feed-forward control of HS201 distribution, HS201-PDT demonstrated superior anti-tumor effects compared to VP-PDT against various human breast cancer xenografts in mice. These results suggest that HS201-PDT may be used in managing IBC, and may have an important role in anti-cancer therapy. Citation Format: Kensuke Kaneko, Takuya Osada, Philip F. Hughes, Timothy A. Haystead, Michael A. Morse, Herbert K. Lyerly. A novel heat shock protein 90-targeted photosensitizer (HS-201) enables enhanced tumor-specific photodynamic therapy of inflammatory breast cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3731.

HSP90 Inhibitor, NVP-AUY922, Improves Myelination in Vitro and Supports the Maintenance of Myelinated Axons in Neuropathic Mice.

Hereditary demyelinating neuropathies linked to peripheral myelin protein 22 (PMP22) involve the disruption of normal protein trafficking and are therefore relevant targets for chaperone therapy. Using a small molecule HSP90 inhibitor, EC137, in cell culture models, we previously validated the chaperone pathway as a viable target for therapy development. Here, we tested five commercially available inhibitors of HSP90 and identified BIIB021 and AUY922 to support Schwann cell viability and enhance chaperone expression. AUY922 showed higher efficacy, compared to BIIB021, in enhancing myelin synthesis in dorsal root ganglion explant cultures from neuropathic mice. For in vivo testing, we randomly assigned 2–3 month old C22 and 6 week old Trembler J (TrJ) mice to receive two weekly injections of either vehicle or AUY922 (2 mg/kg). By the intraperitoneal (i.p.) route, the drug was well-tolerated by all mice over the 5 month long study, without influence on body weight or general grooming behavior. AUY922 improved the maintenance of myelinated nerves of both neuropathic models and attenuated the decline in rotarod performance and peak muscle force production in C22 mice. These studies highlight the significance of proteostasis in neuromuscular function and further validate the HSP90 pathway as a therapeutic target for hereditary neuropathies.