Abstract P6-20-03: Tumor epichaperome expression using 124I PU-H71 PET (PU-PET) as a biomarker of response for PU-H71 plus nab-paclitaxel in HER2 negative (HER2-) metastatic breast cancer (MBC)

Background: The epichaperome is a new cancer target required for tumor survival (Joshi et al. Nature Reviews Cancer 2018). PU-H71 is a synthetic, purine scaffold epichaperome inhibitor that binds to the ATP-binding site of HSP90 specifically when HSP90 is integrated into the epichaperome (Rodina et al. Nature 2016). It has demonstrated antitumor activity in multiple xenograft models. Furthermore, sequential administration of nab-paclitaxel and PU-H71 in TNBC xenograft models augmented epichaperome levels, and in turn resulted in super-synergistic drug action with ablation of xenografted tumors and cures in mice.

Methods: This is an open label phase1b study of PU-H71 + nab-paclitaxel in pts with HER2- MBC. Pts received nab-paclitaxel at a standard dose of 260mg/m2 IV Q 3weeks. PU-H71 was administered IV 6 hrs (+/-1 hr) post nab-paclitaxel Q3weeks in 2 escalating dose levels (225mg/m2 and 300 mg/m2). All pts underwent FDG PET/CT every 6 weeks. Additionally, patients had the option to enroll on a separate diagnostic PU-PET protocol to measure epichaperome expression prior to initiating treatment on the phase 1b study, wherein they received a single dose of up to 11mci of 124I-PU-H71 IV and underwent imaging at 3-4hrs and 20-24 hrs. Primary objective was to establish the MTD/RP2D of this regimen. Secondary objectives were to assess PK of PU-H71 + nab-paclitaxel and clinical efficacy. Exploratory analysis included correlation of epichaperome expression at baseline using PU-PET with tumor response.

Results: 12 patients (5 ER+/HER2- ; 7 TNBC) were enrolled (6 at 225mg/m2 of PU-H71 and 6 at 300mg/m2). Median Age: 54 yrs (range: 37-71). Median ECOG: 0. Median lines of therapy in the metastatic setting: 6 (range 1-11) including prior taxanes in 75% of pts. Most common toxicities included diarrhea G1 58%; G2 7%, G3 7%) that was easily managed with anti-diarrheal agents, G1 fatigue (25%), G1/2 peripheral neuropathy (17%), G1 hyperglycemia (67%), G1 increases in alk phos (58%), AST (50%) and ALT (42%). Hematological toxicities included G3 leukopenia (42%), G3/4 neutropenia (67%), G3 anemia (50%) and G2 thrombocytopenia (17%). There were no DLTs. 33% (4/12) had PR, 58% (7/12) achieved SD with only 1 PD at the time of first scan; 5 pts are currently ongoing including 2 TNBC pts with PR who have been on therapy > 7 months. PK data will be presented. 8/12 patients also underwent PU-PET at baseline. A higher tumor to muscle SUV ratio at 24 hrs on PU-PET predicted response and increased PU-H71 retention on PU-PET at 24 hrs correlated with a longer duration of response.

Conclusion: The RP2D of PU-H71 was 300mg/m2 with 260mg/m2 of nab-paclitaxel administered IV every 3 weeks. The regimen is well tolerated with promising clinical activity in this heavily pre-treated cohort. Tumor epichaperome expression at baseline using PU-PET has the potential to serve as a predictive biomarker of response. A Phase 2 trial of this combination along with baseline PU-PET is currently planned.

Citation Format: Jhaveri K, Dunphy M, Wang R, Comen E, Fornier M, Moynahan ME, Bromberg J, Ma W, Patil S, Taldone T, Rodina A, Sterlin V, Khoshi S, Lewis J, Norton L, Chiosis G, Modi S. Tumor epichaperome expression using 124I PU-H71 PET (PU-PET) as a biomarker of response for PU-H71 plus nab-paclitaxel in HER2 negative (HER2-) metastatic breast cancer (MBC) [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-20-03.

HSP90 stabilizes B-cell receptor kinases in a multi-client interactome: PU-H71 induces CLL apoptosis in a cytoprotective microenvironment

Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of B cells in the hematopoietic system and lymphoid tissues. Although inhibitors targeting the B-cell receptor (BCR) pathway have been successful in the treatment of the disease, the underlying mechanisms leading to BCR over-activity in CLL are not fully understood. In this study, we found that HSP90, a highly conserved molecular chaperone, is overexpressed in CLL compared with resting B cells. HSP90 overexpression is accompanied by the overexpression of several BCR kinases including LYN, spleen tyrosine kinase, Bruton tyrosine kinase and AKT. Chemical and immune-precipitation demonstrated that these BCR constituents are present in a multi-client chaperone complex with HSP90. Inhibition of HSP90 with PU-H71 destabilized the BCR kinases and caused apoptosis of CLL cells through the mitochondrial apoptotic pathway. Further, PU-H71 induced apoptosis in the presence of stromal co-culture or cytoprotective survival signals. Finally, genetic knockdown of HSP90 and its client AKT, but not BTK, reduced CLL viability. Overall, our study suggests that the chaperone function of HSP90 contributes to the over-activity of the BCR signaling in CLL and inhibition of HSP90 has the potential to achieve a multi-targeting effect. Thus, HSP90 inhibition may be explored to prevent or overcome drug resistance to single targeting agents.

Syntheses and discovery of a novel class of cinnamic hydroxamates as histone deacetylase inhibitors by multimodality molecular imaging in living subjects

Histone deacetylases (HDAC) that regulate gene expression are being explored as cancer therapeutic targets. In this study, we focused on HDAC6 based on its ability to inhibit cancerous Hsp90 chaperone activities by disrupting Hsp90/p23 interactions. To identify novel HDAC6 inhibitors, we used a dual-luciferase reporter system in cell culture and living mice by bioluminescence imaging (BLI). On the basis of existing knowledge, a library of hydrazone compounds was generated for screening by coupling cinnamic hydroxamates with aldehydes and ketones. Potency and selectivity were determined by in vitro HDAC profiling assays, with further evaluation to inhibit Hsp90(α/β)/p23 interactions by BLI. In this manner, we identified compound 1A12 as a dose-dependent inhibitor of Hsp90(α/β)/p23 interactions, UKE-1 myeloid cell proliferation, p21(waf1) upregulation, and acetylated histone H3 levels. 1A12 was efficacious in tumor xenografts expressing Hsp90(α)/p23 reporters relative to carrier control-treated mice as determined by BLI. Small animal (18)F-FDG PET/CT imaging on the same cohort showed that 1A12 also inhibited glucose metabolism relative to control subjects. Ex vivo analyses of tumor lysates showed that 1A12 administration upregulated acetylated-H3 by approximately 3.5-fold. Taken together, our results describe the discovery and initial preclinical validation of a novel selective HDAC inhibitor.

Interaction of heat-shock protein 90β isoform (HSP90β) with cellular inhibitor of apoptosis 1 (c-IAP1) is required for cell differentiation

Members of the inhibitor of apoptosis protein (IAP) family have demonstrated functions in cell death, cell signalling, cell migration and mitosis. Several of them are E3 enzymes in the ubiquitination of proteins that leads to their degradation by the proteosomal machinery. We previously reported that one of them, cellular inhibitor of apoptosis protein-1 (c-IAP1), migrated from the nucleus to the surface of the Golgi apparatus in cells undergoing differentiation. Here, we show that c-IAP1 is a client protein of the stress protein HSP90β. In three distinct cellular models, the two proteins interact and migrate from the nucleus to the cytoplasm along the differentiation process through a leptomycin B-sensitive pathway. Inhibition of HSP90 proteins by small chemical molecules and specific depletion of HSP90β isoform by siRNA both lead to auto-ubiquitination of c-IAP1 and its degradation by the proteasome machinery. This chaperone function of HSP90 towards c-IAP1 is specific of its β isoform as specific depletion of HSP90α does not affect c-IAP1 content. Chemical inhibition of HSP90 or siRNA-mediated depletion of HSP90β both inhibit cell differentiation, which can be reproduced by siRNA-mediated depletion of c-IAP1. Altogether, these results suggest that HSP90β prevents auto-ubiquitination and degradation of its client protein c-IAP1, whose depletion would be sufficient to inhibit cell differentiation.Cell Death and Differentiation advance online publication, 1 February 2008; doi:10.1038/sj.cdd.4402320.

Emerging Hsp90 inhibitors: from discovery to clinic

Hsp90 is a chaperone with important roles in maintaining transformation and in elevating the survival and growth potential of cancer cells. Activation of signaling pathways mediated by Hsp90 protein clients is necessary for cell proliferation, regulation of cell cycle progression and apoptosis. Additionally, gain-of-function mutations responsible for transformation often require Hsp90 for the maintenance of their folded, functionally active conformations. These characteristics promise Hsp90 as an important target in cancer therapy and prompt for the identification, development and clinical translation of small molecule inhibitors of the chaperone. This review intends to update the reader on the status of several existing and emerging classes of direct inhibitors of Hsp90 ATPase activity.

Selective cleavage of D-Ala-D-Lac by small molecules: re-sensitizing resistant bacteria to vancomycin

Pathogenic enterococci are becoming resistant to currently available antibiotics, including vancomycin, the drug of last resort for Gram-positive infections. Enterococci pose a significant public health threat, not least because of the risk of transferring vancomycin resistance to the ubiquitous Staphylococcus aureus. Vancomycin resistance is manifested by cell wall peptidoglycan precursors with altered termini that cannot bind the antibiotic. Small molecules with well-oriented nucleophile-electrophile assembly and complementary chirality to the peptidoglycan termini were identified as catalytic and selective cleavers of the peptidoglycan precursor depsipeptide. These molecules were tested in combination with vancomycin and were found to re-sensitize vancomycin-resistant bacteria to the antibiotic.

LY294002-geldanamycin heterodimers as selective inhibitors of the PI3K and PI3K-related family

Several LY294002-GM heterodimers were synthesized with the intent of modulating their activity in the presence of hsp90 and thereby creating selective inhibitors of PI3K and PI3K-related family.

A small molecule designed to bind to the adenine nucleotide pocket of Hsp90 causes Her2 degradation and the growth arrest and differentiation of breast cancer cells

BACKGROUND

The Hsp90s contain a conserved pocket that binds ATP/ADP and plays an important role in the regulation of chaperone function. Occupancy of this pocket by several natural products (geldanamycin (GM) and radicicol) alters Hsp90 function and results in the degradation of a subset of proteins (i.e. steroid receptors, Her2, Raf). We have used the structural features of this pocket to design a small molecule inhibitor of Hsp90.

RESULTS

The designed small molecule PU3 competes with GM for Hsp90 binding with a relative affinity of 15-20 microM. PU3 induces degradation of proteins, including Her2, in a manner similar to GM. Furthermore, PU3 inhibits the growth of breast cancer cells causing retinoblastoma protein hypophosphorylation, G1 arrest and differentiation.

CONCLUSIONS

PU3 is representative of a novel class of synthetic compounds that binds to Hsp90 and inhibits the proliferation of cancer cells. These reagents could provide a new strategy for the treatment of cancers.

Identification of a geldanamycin dimer that induces the selective degradation of HER-family tyrosine kinases

Geldanamycin (GM) is a natural antibiotic that binds Hsp90 and induces the degradation of receptor tyrosine kinases, steroid receptors, and Raf. It is a potent inhibitor of cancer cells that overexpress HER-kinases, but its effects on other important proteins may cause significant toxicity and limit its clinical use. We report the synthesis and identification of a GM dimer, GMD-4c, which had selective activity against HER-kinases. Selectivity was a function of linker length and required two intact GM moieties. GMD-4c is a potent inducer of G1 block and apoptosis of breast cancer cell lines that overexpress HER2, but does not appreciably inhibit the growth of 32D cells that lack HER-kinases. GMD-4c could be useful in the treatment of carcinomas dependent on HER-kinases.