Enhanced Tumor Cell Radiosensitivity and Abrogation of G2 and S Phase Arrest by the Hsp90 Inhibitor 17-(Dimethylaminoethylamino)-17-demethoxygeldanamycin

Enhancement of colorectal cancer therapy through interruption of the HSF1-HSP90 axis by p53 activation or cell cycle inhibition

The stress-associated molecular chaperone system is an actionable target in cancer therapies. It is ubiquitously upregulated in cancer tissues and enables tumorigenicity by stabilizing hundreds of oncoproteins and disturbing the stoichiometry of protein complexes. Most inhibitors target the key component heat-shock protein 90 (HSP90). However, although classical HSP90 inhibitors are highly tumor-selective, they fail in phase 3 clinical oncology trials. These failures are at least partly due to an interference with a negative feedback loop by HSP90 inhibition, known as heat-shock response (HSR): in response to HSP90 inhibition there is compensatory synthesis of stress-inducible chaperones, mediated by the transcription factor heat-shock factor 1 (HSF1). We recently identified that wildtype p53 (p53) actively reduces the HSR by repressing HSF1 via a p21-CDK4/6-MAPK-HSF1 axis. Here we test the hypothesis that in HSP90-based therapies simultaneous p53 activation or direct cell cycle inhibition interrupts the deleterious HSF1-HSR axis and improves the efficiency of HSP90 inhibitors. Indeed, we find that the clinically relevant p53 activator Idasanutlin suppresses the HSF1-HSR activity in HSP90 inhibitor-based therapies. This combination synergistically reduces cell viability and accelerates cell death in p53-proficient colorectal cancer (CRC) cells, murine tumor-derived organoids and patient-derived organoids (PDOs). Mechanistically, upon combination therapy human CRC cells strongly upregulate p53-associated pathways, apoptosis, and inflammatory immune pathways. Likewise, in the chemical AOM/DSS CRC model in mice, dual HSF1-HSP90 inhibition strongly represses tumor growth and remodels immune cell composition, yet displays only minor toxicities in mice and normal mucosa-derived organoids. Importantly, inhibition of the cyclin dependent kinases 4 and 6 (CDK4/6) under HSP90 inhibition phenocopies synergistic repression of the HSR in p53-proficient CRC cells. Even more important, in p53-deficient (mutp53-harboring) CRC cells, an HSP90 inhibition in combination with CDK4/6 inhibitors similarly suppresses the HSF1-HSR system and reduces cancer growth. Likewise, p53-mutated PDOs strongly respond to dual HSF1-HSP90 pathway inhibition and thus, providing a strategy to target CRC independent of the p53 status. In sum, activating p53 (in p53-proficient cancer cells) or inhibiting CDK4/6 (independent of the p53 status) provide new options to improve the clinical outcome of HSP90-based therapies and to enhance colorectal cancer therapy.

CD98hc (SLC3A2) sustains amino acid and nucleotide availability for cell cycle progression

CD98 heavy chain (CD98hc) forms heteromeric amino acid (AA) transporters by interacting with different light chains. Cancer cells overexpress CD98hc-transporters in order to meet their increased nutritional and antioxidant demands, since they provide branched-chain AA (BCAA) and aromatic AA (AAA) availability while protecting cells from oxidative stress. Here we show that BCAA and AAA shortage phenocopies the inhibition of mTORC1 signalling, protein synthesis and cell proliferation caused by CD98hc ablation. Furthermore, our data indicate that CD98hc sustains glucose uptake and glycolysis, and, as a consequence, the pentose phosphate pathway (PPP). Thus, loss of CD98hc triggers a dramatic reduction in the nucleotide pool, which leads to replicative stress in these cells, as evidenced by the enhanced DNA Damage Response (DDR), S-phase delay and diminished rate of mitosis, all recovered by nucleoside supplementation. In addition, proper BCAA and AAA availability sustains the expression of the enzyme ribonucleotide reductase. In this regard, BCAA and AAA shortage results in decreased content of deoxynucleotides that triggers replicative stress, also recovered by nucleoside supplementation. On the basis of our findings, we conclude that CD98hc plays a central role in AA and glucose cellular nutrition, redox homeostasis and nucleotide availability, all key for cell proliferation.

The Nuclear and DNA-Associated Molecular Chaperone Network

Maintenance of a healthy and functional proteome in all cellular compartments is critical to cell and organismal homeostasis. Yet, our understanding of the proteostasis process within the nucleus is limited. Here, we discuss the identified roles of the major molecular chaperones Hsp90, Hsp70, and Hsp60 with client proteins working in diverse DNA-associated pathways. The unique challenges facing proteins in the nucleus are considered as well as the conserved features of the molecular chaperone system in facilitating DNA-linked processes. As nuclear protein inclusions are a common feature of protein-aggregation diseases (e.g., neurodegeneration), a better understanding of nuclear proteostasis is warranted.

Radiosensitization of HSF-1 Knockdown Lung Cancer Cells by Low Concentrations of Hsp90 Inhibitor NVP-AUY922

The inhibition of heat shock protein 90 (Hsp90) a molecular chaperone for multiple oncogenic client proteins is considered as a promising approach to overcome radioresistance. Since most Hsp90 inhibitors activate HSF-1 that induces the transcription of cytoprotective and tumor-promoting stress proteins such as Hsp70 and Hsp27, a combined approach consisting of HSF-1 knockdown (k.d.) and Hsp90 inhibition was investigated. A specific HSF-1 k.d. was achieved in H1339 lung cancer cells using RNAi-Ready pSIRENRetroQ vectors with puromycin resistance. The Hsp90 inhibitor NVP-AUY922 was evaluated at low concentrations—ranging from 1–10 nM—in control and HSF-1 k.d. cells. Protein expression (i.e., Hsp27/Hsp70, HSF-1, pHSF-1, Akt, ß-actin) and transcriptional activity was assessed by western blot analysis and luciferase assays and radiosensitivity was measured by proliferation, apoptosis (Annexin V, active caspase 3), clonogenic cell survival, alkaline comet, γH2AX, 53BP1, and Rad51 foci assays. The k.d. of HSF-1 resulted in a significant reduction of basal and NVP-AUY922-induced Hsp70/Hsp27 expression levels. A combined approach consisting of HSF-1 k.d. and low concentrations of the Hsp90 inhibitor NVP-AUY922 reduces the Hsp90 client protein Akt and potentiates radiosensitization, which involves an impaired homologous recombination mediated by Rad51. Our findings are key for clinical applications of Hsp90 inhibitors with respect to adverse hepatotoxic effects.

177Lu-octreotate therapy for neuroendocrine tumours is enhanced by Hsp90 inhibition

177Lu-octreotate is an FDA-approved radionuclide therapy for patients with gastroenteropancreatic neuroendocrine tumours (NETs) expressing somatostatin receptors. The 177Lu-octreotate therapy has shown promising results in clinical trials by prolonging progression-free survival, but complete responses are still uncommon. The aim of this study was to improve the 177Lu-octreotate therapy by means of combination therapy. To identify radiosensitising inhibitors, two cell lines, GOT1 and P-STS, derived from small intestinal neuroendocrine tumours (SINETs), were screened with 1,224 inhibitors alone or in combination with external radiation. The screening revealed that inhibitors of Hsp90 can potentiate the tumour cell-killing effect of radiation in a synergistic fashion (GOT1; false discovery rate <3.2×10-11). The potential for Hsp90 inhibitor ganetespib to enhance the anti-tumour effect of 177Lu-octreotate in an in vivo setting was studied in the somatostatin receptor-expressing GOT1 xenograft model. The combination led to a larger decrease in tumour volume relative to monotherapies and the tumour-reducing effect was shown to be synergistic. Using patient-derived tumour cells from eight metastatic SINETs, we could show that ganetespib enhanced the effect of 177Lu-octreotate therapy for all investigated patient tumours. Levels of Hsp90 protein expression were evaluated in 767 SINETs from 379 patients. We found that Hsp90 expression was upregulated in tumour cells relative to tumour stroma in the vast majority of SINETs. We conclude that Hsp90 inhibitors enhance the tumour-killing effect of 177Lu-octreotate therapy synergistically in SINET tumour models and suggest that this potentially promising combination should be further evaluated.

MEK-inhibitor PD184352 enhances the radiosensitizing effect of the Hsp90 inhibitor NVP-AUY922: the role of cell type and drug-irradiation schedule

Targeting MEK protein in cancer cells usually leads to acquired resistance to MEK inhibitors and activation of the prosurvival protein Akt. Since both MEK and Akt are clients of the Hsp90 chaperone system, the present study explores the responses of irradiated lung carcinoma A549 and glioblastoma SNB19 cell lines to combined MEK and Hsp90 inhibition. Unexpectedly, the MEK inhibitor PD184352 administered 24 h prior to irradiation, enhanced cell survival through upregulation of not only MEK and Erk1/2 but also of Akt. In contrast, PD184352 added 1 h before irradiation strongly reduced the expression of Erk and did not upregulate Akt in both cell lines. As a result, the MEK inhibitor increased the radiosensitizing effect of the Hsp90 inhibitor NVP-AUY922 in glioblastoma SNB19 cells. Possible reasons for the enhanced cell killing under this short-term pretreatment schedule may be a down-regulation of Erk during or directly after irradiation, increased DNA damage and/or a strong G₂/M arrest 24 h after irradiation. In addition, an 1-h pretreatment with PD184352 and/or NVP-AUY922 under schedule II induced neither G₁ arrest nor up-regulation of p-Akt in both cell lines as it did under schedule I. Yet, a long-term treatment with the MEK inhibitor alone caused a strong cytostatical effect. We conclude that the duration of drug pretreatment before irradiation plays a key role in the targeting of MEK in tumor cells. However, due to an aberrant activation of prosurvival proteins, the therapeutic window needs to be carefully defined, or a combination of inhibitors should be considered.

Sensitization of prostate cancer to radiation therapy: Molecules and pathways to target

Radiation therapy is used to treat cancer by radiation-induced DNA damage. Despite the best efforts to eliminate cancer, some cancer cells survive irradiation, resulting in cancer progression or recurrence. Alteration in DNA damage repair pathways is common in cancers, resulting in modulation of their response to radiation. This article focuses on the recent findings about molecules and pathways that potentially can be targeted to sensitize prostate cancer cells to ionizing radiation, thereby achieving an improved therapeutic outcome.

Hyperthermia-mediated drug delivery induces biological effects at the tumor and molecular levels that improve cisplatin efficacy in triple negative breast cancer

Triple negative breast cancer is an aggressive disease that accounts for at least 15% of breast cancer diagnoses, and a disproportionately high percentage of breast cancer related morbidity. Intensive research efforts are focused on the development of more efficacious treatments for this disease, for which therapeutic options remain limited. The high incidence of mutations in key DNA repair pathways in triple negative breast cancer results in increased sensitivity to DNA damaging agents, such as platinum-based chemotherapies. Hyperthermia has been successfully used in breast cancer treatment to sensitize tumors to radiation therapy and chemotherapy. It has also been used as a mechanism to trigger drug release from thermosensitive liposomes. In this study, mild hyperthermia is used to trigger release of cisplatin from thermosensitive liposomes in the vasculature of human triple negative breast cancer tumors implanted orthotopically in mice. This heat-triggered liposomal formulation of cisplatin resulted in significantly delayed tumor growth and improved overall survival compared to treatment with either non-thermosensitive liposomes containing cisplatin or free cisplatin, as was observed in two independent tumor models (i.e. MDA-MB-231 and MDA-MB-436). The in vitro sensitivity of the cell lines to cisplatin and hyperthermia alone and in combination was characterized extensively using enzymatic assays, clonogenic assays, and spheroid growth assays. Evaluation of correlations between the in vitro and in vivo results served to identify the in vitro approach that is most predictive of the effects of hyperthermia in vivo. Relative expression of several heat shock proteins and the DNA damage repair protein BRCA1 were assayed at baseline and in response to hyperthermia both in vitro and in vivo. Interestingly, delivery of cisplatin in thermosensitive liposomes in combination with hyperthermia resulted in the most significant tumor growth delay, relative to free cisplatin, in the less cisplatin-sensitive cell line (i.e. MDA-MB-231). This work demonstrates that thermosensitive cisplatin liposomes used in combination with hyperthermia offer a novel method for effective treatment of triple negative breast cancer.

Targeted cancer therapy through 17-DMAG as an Hsp90 inhibitor: Overview and current state of the art

Heat shock protein 90 (Hsp90) is an evolutionary preserved molecular chaperone which mediates many cellular processes such as cell transformation, proliferation, and survival in normal and stress conditions. Hsp90 plays an important role in folding, maturation, stabilization and activation of Hsp90 client proteins which all contribute to the development, and proliferation of cancer as well as other inflammatory diseases. Functional inhibition of Hsp90 can have a massive effect on various oncogenic and inflammatory pathways, and will result in the degradation of their client proteins. This turns it into an interesting target in the treatment of different malignancies. 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG) as a semi-synthetic derivative of geldanamycin, has several advantages over 17-Allylamino-17-demethoxygeldanamycin (17-AAG) such as higher water solubility, good bioavailability, reduced metabolism, and greater anti-tumour capability. 17-DMAG binds to the Hsp90, and inhibits its function which eventually results in the degradation of Hsp90 client proteins. Here, we reviewed the pre-clinical data and clinical trial data on 17-DMAG as a single agent, in combination with other agents and loaded on nanomaterials in various cancers and inflammatory diseases.

A novel HSP90 inhibitor with reduced hepatotoxicity synergizes with radiotherapy to induce apoptosis, abrogate clonogenic survival, and improve tumor control in models of colorectal cancer

The chaperone heat shock protein 90 (HSP90) crucially supports the maturation, folding, and stability of a variety of client proteins which are of pivotal importance for the survival and proliferation of cancer cells. Consequently, targeting of HSP90 has emerged as an attractive strategy of anti-cancer therapy, and it appears to be particularly effective in the context of molecular sensitization towards radiotherapy as has been proven in preclinical models of different cancer entities. However, so far the clinical translation has largely been hampered by suboptimal pharmacological properties and serious hepatotoxicity of first- and second-generation HSP90 inhibitors. Here, we report on NW457, a novel radicicol-derived member of the pochoxime family with reduced hepatotoxicity, how it inhibits the DNA damage response and how it synergizes with ionizing irradiation to induce apoptosis, abrogate clonogenic survival, and improve tumor control in models of colorectal cancer in vitro and in vivo.

Glioma progression through the prism of heat shock protein mediated extracellular matrix remodeling and epithelial to mesenchymal transition

Glial tumor is one of the intrinsic brain tumors with high migratory and infiltrative potential. This essentially contributes to the overall poor prognosis by circumvention of conventional treatment regimen in glioma. The underlying mechanism in gliomagenesis is bestowed by two processes- Extracellular matrix (ECM) Remodeling and Epithelial to mesenchymal transition (EMT). Heat Shock Family of proteins (HSPs), commonly known as "molecular chaperons" are documented to be upregulated in glioma. A positive correlation also exists between elevated expression of HSPs and invasive capacity of glial tumor. HSPs overexpression leads to mutational changes in glioma, which ultimately drive cells towards EMT, ECM modification, malignancy and invasion. Differential expression of HSPs - a factor providing cytoprotection to glioma cells, also contributes towards its radioresistance /chemoresistance. Various evidences also display upregulation of EMT and ECM markers by various heat shock inducing proteins e.g. HSF-1. The aim of this review is to study in detail the role of HSPs in EMT and ECM leading to radioresistance/chemoresistance of glioma cells. The existing treatment regimen for glioma could be enhanced by targeting HSPs through immunotherapy, miRNA and exosome mediated strategies. This could be envisaged by better understanding of molecular mechanisms underlying glial tumorigenesis in relation to EMT and ECM remodeling under HSPs influence. Our review might showcase fresh potential for the development of next generation therapeutics for effective glioma management.

Inhibiting heat shock protein 90 and the ubiquitin-proteasome pathway impairs metabolic homeostasis and leads to cell death in human pancreatic cancer cells

BACKGROUND

Heat shock protein 90 (HSP90) and the ubiquitin-proteasome pathway play crucial roles in the homeostasis of pancreatic cancer cells. This study combined for the first time the HSP90 inhibitor ganetespib (Gan) and the proteasome inhibitor carfilzomib (Carf) to target key mechanisms of homeostasis in pancreatic cancer. It was hypothesized that Gan plus Carf would elicit potent antitumor activity by modulating complementary homeostatic processes.

METHODS

In vitro and in vivo effects of this combination on mechanisms of cell growth and viability were evaluated with human pancreatic cancer cell lines (MIA PaCa-2 and HPAC).

RESULTS

Combined treatment with Gan and Carf significantly decreased cell viability. The mechanism varied by cell line and involved G₂ -M cell-cycle arrest accompanied by a consistent reduction in key cell-cycle regulatory proteins and concomitant upregulation of p27. Further studies revealed increased autophagy markers, including the upregulation of autophagy related 7 and light chain 3 cleavage, and evidence of apoptosis (increased Bax expression and processing of caspase 3). Immunoblot analyses confirmed the modulation of other pathways that influence cell viability, including phosphoinositide 3-kinase/Akt and nuclear factor κB. Finally, the treatment of athymic mice bearing HPAC tumors with Gan and Carf significantly reduced tumor growth in vivo. An immunoblot analysis of freshly isolated tumors from animals at the end of the study confirmed in vivo modulation of key signaling pathways.

CONCLUSIONS

The results reveal Gan plus Carf to be a promising combination with synergistic antiproliferative, apoptotic, and pro-autophagy effects in preclinical studies of pancreatic cancer and will further the exploration of the utility of this treatment combination in clinical trials. Cancer 2017;123:4924-33. © 2017 American Cancer Society.

Translational research in radiation-induced DNA damage signaling and repair

Radiotherapy is an effective tool in the fight against cancer. It is non-invasive and painless, and with advanced tumor imaging and beam control systems, radiation can be delivered to patients safely, generally with minor or no adverse side effects, accounting for its increasing use against a broad range of tumors. Tumors and normal cells respond to radiation-induced DNA damage by activating a complex network of DNA damage signaling and repair pathways that determine cell fate including survival, death, and genome stability. DNA damage response (DDR) proteins represent excellent targets to augment radiotherapy, and many agents that inhibit key response proteins are being combined with radiation and genotoxic chemotherapy in clinical trials. This review focuses on how insights into molecular mechanisms of DDR pathways are translated to small animal preclinical studies, to clinical studies of naturally occurring tumors in companion animals, and finally to human clinical trials. Companion animal studies, under the umbrella of comparative oncology, have played key roles in the development of clinical radiotherapy throughout its >100-year history. There is growing appreciation that rapid translation of basic knowledge of DNA damage and repair systems to improved radiotherapy practice requires a comprehensive approach that embraces the full spectrum of cancer research, with companion animal clinical trials representing a critical bridge between small animal preclinical studies, and human clinical trials.

Evaluation of the radiosensitizing potency of chemotherapeutic agents in prostate cancer cells

PURPOSE

Despite recent advances in the treatment of metastatic prostate cancer, survival rates are low and treatment options are limited to chemotherapy and hormonal therapy. Although ionizing radiation is used to treat localized and metastatic prostate cancer, the most efficient use of radiotherapy is yet to be defined. Our purpose was to determine in vitro the potential benefit to be gained by combining radiation treatment with cytotoxic drugs.

MATERIALS AND METHODS

Inhibitors of DNA repair and heat shock protein 90 and an inducer of oxidative stress were evaluated in combination with X-radiation for their capacity to reduce clonogenic survival and delay the growth of multicellular tumor spheroids.

RESULTS

Inhibitors of the PARP DNA repair pathway, olaparib and rucaparib, and the HSP90 inhibitor 17-DMAG, enhanced the clonogenic cell kill and spheroid growth delay induced by X-radiation. However, the oxidative stress-inducing drug elesclomol failed to potentiate the effects of X-radiation. PARP inhibitors arrested cells in the G₂/M phase when administered as single agents or in combination with radiation, whereas elesclomol and 17-DMAG did not affect radiation-induced cell cycle modulation.

CONCLUSION

These results indicate that radiotherapy of prostate cancer may be optimized by combination with inhibitors of PARP or HSP90, but not elesclomol.

Advances in HSP27 and HSP90-targeting strategies for glioblastoma

Glioblastoma (GBM) is the most common and malignant primary brain tumor in adults. There is a critical need for novel strategies to abolish the molecular mechanisms that support GBM growth, invasion and treatment resistance. The heat shock proteins, HSP27 and HSP90, serve these pivotal roles in tumor cells and have been identified as effective targets for developing therapeutics. Natural and synthetic inhibitors have been evaluated in clinical trials for several forms of systemic cancer but none as yet for GBM. This topic review summarizes the current preclinical evidence and rationale to define the potential of HSP27 and HSP90 inhibitors in GBM management.

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.

Increased activity of CHK enhances the radioresistance of MCF-7 breast cancer stem cells

The resistance of breast cancer to radiotherapy remains a major obstacle to successful cancer management. Radiotherapy may result in DNA damage and activate breast cancer stem cells. DNA damage may lead to activation of the checkpoint kinase (CHK) signaling pathway, of which debromohymenialdisine (DBH) is a specific inhibitor. Radiotherapy also increases the expression of phosphorylated CHK1/2 (pCHK1/2) in the breast cancer cell line, MCF-7, in vitro in a dose-dependent manner. DBH is a relatively stable effective inhibitor that significantly reduces pCHK1/2 expression and MCF-7 proliferation. Low-dose radiotherapy combined with DBH resulted in a higher MCF-7 inhibition rate compared with high-dose radiation alone. This result indicates that the inhibition of the CHK1/2 signal pathway may significantly reduce DNA damage within radiated cells. Radiotherapy may also regulate the proportion of CD44⁺/CD24⁻ MCF-7 cancer stem cells in a dose- and time-dependent manner. However, the stem cell proportion of MCF-7 cells was significantly reduced by treatment with DBH. The inhibition is relatively stable and time dependent. Significant reductions were observed after 3 days of culture (P<0.01). The results of the present study indicate that the DBH-induced downregulation of CHK may provide a novel method of enhancing the effect of radiotherapy and reducing stem cell survival in the MCF-7 cell line.

A high content clonogenic survival drug screen identifies mek inhibitors as potent radiation sensitizers for KRAS mutant non-small-cell lung cancer

INTRODUCTION

Traditional clonogenic survival and high throughput colorimetric assays are inadequate as drug screens to identify novel radiation sensitizers. We developed a method that we call the high content clonogenic survival assay (HCSA) that will allow screening of drug libraries to identify candidate radiation sensitizers.

METHODS

Drug screen using HCSA was done in 96 well plates. After drug treatment, irradiation, and incubation, colonies were stained with crystal violet and imaged on the INCell 6000 (GE Health). Colonies achieving 50 or more cells were enumerated using the INCell Developer image analysis software. A proof-of-principle screen was done on the KRAS mutant lung cancer cell line H460 and a Custom Clinical Collection (146 compounds).

RESULTS

Multiple drugs of the same class were found to be radiation sensitizers and levels of potency seemed to reflect the clinical relevance of these drugs. For instance, several PARP inhibitors were identified as good radiation sensitizers in the HCSA screen. However, there were also a few PARP inhibitors not found to be sensitizing that have either not made it into clinical development, or in the case of BSI-201, was proven to not even be a PARP inhibitor. We discovered that inhibitors of pathways downstream of activated mutant KRAS (PI3K, AKT, mTOR, and MEK1/2) sensitized H460 cells to radiation. Furthermore, the potent MEK1/2 inhibitor tramenitib selectively enhanced radiation effects in KRAS mutant but not wild-type lung cancer cells.

CONCLUSIONS

Drug screening for novel radiation sensitizers is feasible using the HCSA approach. This is an enabling technology that will help accelerate the discovery of novel radiosensitizers for clinical testing.

Characterization of the mammalian miRNA turnover landscape

Steady state cellular microRNA (miRNA) levels represent the balance between miRNA biogenesis and turnover. The kinetics and sequence determinants of mammalian miRNA turnover during and after miRNA maturation are not fully understood. Through a large-scale study on mammalian miRNA turnover, we report the co-existence of multiple cellular miRNA pools with distinct turnover kinetics and biogenesis properties and reveal previously unrecognized sequence features for fast turnover miRNAs. We measured miRNA turnover rates in eight mammalian cell types with a combination of expression profiling and deep sequencing. While most miRNAs are stable, a subset of miRNAs, mostly miRNA*s, turnovers quickly, many of which display a two-step turnover kinetics. Moreover, different sequence isoforms of the same miRNA can possess vastly different turnover rates. Fast turnover miRNA isoforms are enriched for 5′ nucleotide bias against Argonaute-(AGO)-loading, but also additional 3′ and central sequence features. Modeling based on two fast turnover miRNA*s miR-222-5p and miR-125b-1-3p, we unexpectedly found that while both miRNA*s are associated with AGO, they strongly differ in HSP90 association and sensitivity to HSP90 inhibition. Our data characterize the landscape of genome-wide miRNA turnover in cultured mammalian cells and reveal differential HSP90 requirements for different miRNA*s. Our findings also implicate rules for designing stable small RNAs, such as siRNAs.

Radiation sensitivity assay with a panel of patient-derived spheroids of small cell carcinoma of the cervix

Small cell carcinoma of the uterine cervix (SCCC) is a rare cancer with a poor prognosis for which no standard treatment exists. Here, we successfully established panels of patient-derived spheroid cultures from six SCCC patient samples by cancer tissue-originated spheroids (CTOS) method. To assess the intrinsic radiosensitivity and mechanism of radioresistance in individual SCCC patients, we further developed an in vitro sensitivity assay for radiation. Radiation sensitivity in the CTOS assay varied among individual cases and was consistent with in vivo radiation sensitivity using CTOS-derived xenograft tumors in the examined cases. Furthermore, by comparing gene expression in CTOSs with different radiosensitivity, we found that expression of hypoxia-inducible factor-1α (HIF-1α) target genes was upregulated in resistant CTOSs. HIF-1α protein levels increased several hours after irradiation. In a radioresistant CTOS, an inhibitor of heat shock protein 90 (HSP90) suppressed radiation-induced HIF-1α expression. Suppression of HIF-1α by small hairpin RNA significantly enhanced the effect of radiation, at least in part by promoting radiation-induced apoptosis. HSP90 inhibitor also increased radiation sensitivity. Our results indicate that radiation-induced HIF-1α upregulation was one mechanism of radioresistance in a radioresistant SCCC CTOS. Accumulating CTOS lines may provide a good platform to study characters of rare cancers like SCCC.

Hsp90 inhibitor as a sensitizer of cancer cells to different therapies (review)

Hsp90 is a molecular chaperone that maintains the structural and functional integrity of various client proteins involved in signaling and many other functions of cancer cells. The natural inhibitors, ansamycins influence the Hsp90 chaperone function by preventing its binding to client proteins and resulting in their proteasomal degradation. N- and C-terminal inhibitors of Hsp90 and their analogues are widely tested as potential anticancer agents in vitro, in vivo as well as in clinical trials. It seems that Hsp90 competitive inhibitors target different tumor types at nanomolar concentrations and might have therapeutic benefit. On the contrary, some Hsp90 inhibitors increased toxicity and resistance of cancer cells induced by heat shock response, and through the interaction of survival signals, that occured as side effects of treatments, could be very effectively limited via combination of therapies. The aim of our review was to collect the data from experimental and clinical trials where Hsp90 inhibitor was combined with other therapies in order to prevent resistance as well as to potentiate the cytotoxic and/or antiproliferative effects.

Irradiation facilitates the inhibitory effect of the heat shock protein 90 inhibitor NVP-BEP800 on the proliferation of malignant glioblastoma cells through attenuation of the upregulation of heat shock protein 70

The present study aimed to investigate the effect of NVP-BEP800, a novel heat shock protein (Hsp) 90 inhibitor of the 2-aminothieno[2,3-d]pyrimidine class, in combination with radiation on glioblastoma cells. T98G human glioblastoma cells were treated with dimethyl sulfoxide (DMSO), NVP-BEP800, NVP-BEP800 in combination with X-ray irradiation (10 Gy, 20 min), or X-ray irradiation only, and cultured for 40 h. Cell viability was measured upon completion of the treatments. In addition, apoptosis was measured and immunoblot analysis was performed to analyze the expression levels of cellular protein inhibitory κB kinase β (IKKβ). The combined treatment with NVP-BEP800 and X-ray irradiation resulted in the synergistic destruction of malignant cells. Furthermore, NVP-BEP800 significantly induced apoptosis in the human glioblastoma cells. The immunoblot analysis data indicated that NVP-BEP800 markedly reduced the expression level of IKKβ. The results also revealed that X-ray irradiation significantly attenuated the increase in the level of Hsp70 in cells treated with NVP-BEP800. Since elevated levels of Hsp70 are associated with drug resistance induced by Hsp90 inhibitors, the effects of X-ray irradiation on Hsp70 levels may be associated with the enhanced effect on cells of the presence of irradiation. The results of the current study suggest that irradiation enhances the inhibitory effect of NVP-BEP800 on the proliferation of malignant glioblastoma cells by downregulating the expression level of cellular signaling protein IKKβ and attenuating the upregulation of Hsp70 that is induced by NVP-BEP800.

Apoptosis and molecular targeting therapy in cancer

Apoptosis is the programmed cell death which maintains the healthy survival/death balance in metazoan cells. Defect in apoptosis can cause cancer or autoimmunity, while enhanced apoptosis may cause degenerative diseases. The apoptotic signals contribute into safeguarding the genomic integrity while defective apoptosis may promote carcinogenesis. The apoptotic signals are complicated and they are regulated at several levels. The signals of carcinogenesis modulate the central control points of the apoptotic pathways, including inhibitor of apoptosis (IAP) proteins and FLICE-inhibitory protein (c-FLIP). The tumor cells may use some of several molecular mechanisms to suppress apoptosis and acquire resistance to apoptotic agents, for example, by the expression of antiapoptotic proteins such as Bcl-2 or by the downregulation or mutation of proapoptotic proteins such as BAX. In this review, we provide the main regulatory molecules that govern the main basic mechanisms, extrinsic and intrinsic, of apoptosis in normal cells. We discuss how carcinogenesis could be developed via defective apoptotic pathways or their convergence. We listed some molecules which could be targeted to stimulate apoptosis in different cancers. Together, we briefly discuss the development of some promising cancer treatment strategies which target apoptotic inhibitors including Bcl-2 family proteins, IAPs, and c-FLIP for apoptosis induction.

Current concepts in clinical radiation oncology

Based on its potent capacity to induce tumor cell death and to abrogate clonogenic survival, radiotherapy is a key part of multimodal cancer treatment approaches. Numerous clinical trials have documented the clear correlation between improved local control and increased overall survival. However, despite all progress, the efficacy of radiation-based treatment approaches is still limited by different technological, biological, and clinical constraints. In principle, the following major issues can be distinguished: (1) The intrinsic radiation resistance of several tumors is higher than that of the surrounding normal tissue, (2) the true patho-anatomical borders of tumors or areas at risk are not perfectly identifiable, (3) the treatment volume cannot be adjusted properly during a given treatment series, and (4) the individual heterogeneity in terms of tumor and normal tissue responses toward irradiation is immense. At present, research efforts in radiation oncology follow three major tracks, in order to address these limitations: (1) implementation of molecularly targeted agents and 'omics'-based screening and stratification procedures, (2) improvement of treatment planning, imaging, and accuracy of dose application, and (3) clinical implementation of other types of radiation, including protons and heavy ions. Several of these strategies have already revealed promising improvements with regard to clinical outcome. Nevertheless, many open questions remain with individualization of treatment approaches being a key problem. In the present review, the current status of radiation-based cancer treatment with particular focus on novel aspects and developments that will influence the field of radiation oncology in the near future is summarized and discussed.

New treatment strategies for malignant gliomas

Malignant gliomas are the most prevalent type of primary brain tumor in adults. Despite progress in brain tumor therapy, the prognosis of malignant glioma patients remains dismal. The median survival of patients with glioblastoma multiforme, the most common grade of malignant glioma, is 10-12 months. Conventional therapy of surgery, radiation and chemotherapy is largely palliative. Essentially, tumor recurrence is inevitable. Salvage treatments upon recurrence are palliative at best and rarely provide significant survival benefit. Therapies targeting the underlying molecular pathogenesis of brain tumors are urgently required. Common genetic abnormalities in malignant glioma specimens are associated with aberrant activation or suppression of cellular signal transduction pathways and resistance to radiation and chemotherapy. Several low molecular weight signal transduction inhibitors have been examined in preclinical and clinical malignant glioma trials. The efficacy of these agents as monotherapies has been modest, at best; however, small subsets of patients who harbor specific genetic changes in their tumors may display favorable clinical responses to defined small molecule inhibitors. Multitargeted kinase inhibitors or combinations of agents targeting different mitogenic pathways may overcome the resistance of tumors to single-agent targeted therapies. Well designed studies of small molecule kinase inhibitors will include assessment of safety, drug delivery, target inhibition and correlative biomarkers to define mechanisms of response or resistance to these agents. Predictive biomarkers will enrich for patients most likely to respond in future clinical trials. Additional clinical studies will combine novel targeted therapies with radiation, chemotherapies and immunotherapies.

Radiosensitization of human lung cancer cells by the novel purine-scaffold Hsp90 inhibitor, PU-H71

The molecular chaperone heat shock protein 90 (Hsp90) is involved in the maturation and stabilization of a wide range of oncogenic client proteins for oncogenesis and malignant cell proliferation, which renders this protein a promising target in the development of cancer therapeutics. PU-H71 is a purine-scaffold Hsp90 inhibitor with less toxicity in normal cells than in cancer cells. In this study, we examined the in vitro radiosensitizing activity and molecular mechanisms of action of PU-H71 in human lung cancer cell lines. PU-H71 enhanced the sensitivity of the SQ-5 and A549 cancer cells to radiation. When the cancer cells were pre-treated with PU-H71, the repair of DNA double-strand breaks (DSBs) was markedly inhibited after irradiation compared with the cells that were not pre-treated with PU-H71, as evaluated by counting the foci of phosphorylated histone H2AX (γ-H2AX). We further demonstrated that post-irradiation, PU-H71 inhibited Rad51 foci formation, a critical protein for the homologous recombination pathway of DNA DSB repair. These data indicate that targeting Hsp90 with PU-H71 may be novel therapeutic strategy for radioresistant carcinomas.

Enhancing radiation therapy for patients with glioblastoma

Radiation therapy has been the foundation of therapy following maximal surgical resection in patients with newly diagnosed glioblastoma for decades and the primary therapy for unresected tumors. Using the standard approach with radiation and temozolomide, however, outcomes are poor, and glioblastoma remains an incurable disease with the majority of recurrences and progression within the radiation treatment field. As such, there is much interest in elucidating the mechanisms of resistance to radiation therapy and in developing novel approaches to overcoming this treatment resistance.

Radioprotective effects of oral 17-dimethylaminoethylamino-17-demethoxygeldanamycin in mice: bone marrow and small intestine

Background

Our previous research demonstrated that one subcutaneous injection of 17-Dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG) 24 hours (h) before irradiation (8.75 Gy) increased mouse survival by 75%. However, the protective mechanism of 17-DMAG is currently unknown. The present study aimed to investigate whether oral administration of 17-DMAG was also radioprotective and the potential role it may play in radioprotection.

Results

A single dose of orally pre-administered (24, 48, or 72 h) 17-DMAG (10 mg/kg) increased irradiated mouse survival, reduced body weight loss, improved water consumption, and decreased facial dropsy, whereas orally post-administered 17-DMAG failed. Additional oral doses of pre-treatment did not improve 30-day survival. The protective effect of multiple pre-administrations (2−3 times) of 17-DMAG at 10 mg/kg was equal to the outcome of a single pre-treatment. In 17-DMAG-pretreated mice, attenuation of bone marrow aplasia in femurs 30 days after irradiation with recovered expressions of cluster of differentiation 34, 44 (CD34, CD44), and survivin in bone marrow cells were observed. 17-DMAG also elevated serum granulocyte-colony stimulating factor (G-CSF), decreased serum fms-related tyrosine kinase 3 ligand, and reduced white blood cell depletion. 17-DMAG ameliorated small intestinal histological damage, promoted recovery of villus heights and intestinal crypts including stem cells, where increased leucine-rich repeat-containing G-protein coupled receptor 5 (Lgr5) was found 30 days after irradiation.

Conclusions

17-DMAG is a potential radioprotectant for bone marrow and small intestine that results in survival improvement.

Molecularly targeted agents as radiosensitizers in cancer therapy--focus on prostate cancer

As our understanding of the molecular pathways driving tumorigenesis improves and more druggable targets are identified, we have witnessed a concomitant increase in the development and production of novel molecularly targeted agents. Radiotherapy is commonly used in the treatment of various malignancies with a prominent role in the care of prostate cancer patients, and efforts to improve the therapeutic ratio of radiation by technologic and pharmacologic means have led to important advances in cancer care. One promising approach is to combine molecularly targeted systemic agents with radiotherapy to improve tumor response rates and likelihood of durable control. This review first explores the limitations of preclinical studies as well as barriers to successful implementation of clinical trials with radiosensitizers. Special considerations related to and recommendations for the design of preclinical studies and clinical trials involving molecularly targeted agents combined with radiotherapy are provided. We then apply these concepts by reviewing a representative set of targeted therapies that show promise as radiosensitizers in the treatment of prostate cancer.

Preclinical evaluation of radiosensitizing activity of Pluronic block copolymers

PURPOSE

Pluronic block copolymers are non-ionic surfactants with demonstrated sensitizing activity in chemotherapy and hyperthermia in various tumor cell lines. In the current study we investigated the potential activity of Pluronic as a radiosensitizing agent.

MATERIALS AND METHODS

As a possible mechanism, the effect of Pluronic on Hsp70 and Hsp90 was examined. Gli36 human glioma cells were treated with radiation alone as well as with a combination treatment of Pluronic and radiation.

RESULTS

Clonogenic cell survival assays show that Pluronic has an elevated effect on radiosensitization (50% high, p < 0.01), even with radiation doses as low as 2 Gy. The Hsp90 level was reduced 24 h after the combined treatment in both in vitro and in vivo. Similarly, Hsp70 levels were also decreased 24 h post treatment. When Gli36 cells were exposed to Pluronic before and during irradiation, DNA DSB: double-strand breaks repair was reduced, and elevated apoptosis was also seen in tumor xenografts.

CONCLUSION

Data suggest the potential use of L10 as a radiosensitizer. While the mechanism of sensitization requires additional investigation, the presented results indicate that the effect may be due, in part, to a decrease in Hsp90 and 70 levels and increased DNA damage.

Increased radiosensitivity and radiothermosensitivity of human pancreatic MIA PaCa-2 and U251 glioblastoma cell lines treated with the novel Hsp90 inhibitor NVP-HSP990

Background and purpose

Heat shock Protein 90 (Hsp90) is a molecular chaperone that folds, stabilizes, and functionally regulates many cellular proteins involved in oncogenic signaling and in the regulation of radiosensitivity. It is upregulated in response to stress such a heat. Hyperthermia is a potent radiosensitizer, but induction of Hsp90 may potentially limit its efficacy. Our aim was to investigate whether the new Hsp90 inhibitor NVP-HSP990 increases radiosensitivity, thermosensitivity and radiothermosensitivity of human tumor cell lines.

Material and methods

U251 glioblastoma and MIA PaCa-2 pancreatic carcinoma cells were used. To determine clonogenic survival, colony forming assays were performed. Cell viability and proliferation were assesed by Trypan blue staining. Cell cycle and apoptosis analyses were performed by flow cytometry. DAPI staining was used to detect mitotic catastrophe.

Results

NVP-HSP990 increased the thermosensitivity, radiosensitivity and radio-thermosensitivity of both cell lines in clonogenic assays. 72 hours after irradiation with 4 Gy, a significant reduction in cell number associated with considerable G2/M acumulation and mitotic catastrophe as well as cell death by apoptosis/necrosis was observed.

Conclusions

Treatment with NVP-HSP990 strongly sensitized U251 and MIA PaCa-2 cells to hyperthermia and ionizing radiation or combination thereof through augmentation of G2/M arrest, mitotic catastrophe and associated apoptosis.

Novel Hsp90 inhibitor NVP-AUY922 radiosensitizes prostate cancer cells

Outcomes for poor-risk localized prostate cancers treated with radiation are still insufficient. Targeting the "non-oncogene" addiction or stress response machinery is an appealing strategy for cancer therapeutics. Heat-shock-protein-90 (Hsp90), an integral member of this machinery, is a molecular chaperone required for energy-driven stabilization and selective degradation of misfolded "client" proteins, that is commonly overexpressed in tumor cells. Hsp90 client proteins include critical components of pathways implicated in prostate cancer cell survival and radioresistance, such as androgen receptor signaling and the PI3K-Akt-mTOR pathway. We examined the effects of a novel non-geldanamycin Hsp90 inhibitor, AUY922, combined with radiation (RT) on two prostate cancer cell lines, Myc-CaP and PC3, using in vitro assays for clonogenic survival, apoptosis, cell cycle distribution, γ-H2AX foci kinetics and client protein expression in pathways important for prostate cancer survival and radioresistance. We then evaluated tumor growth delay and effects of the combined treatment (RT-AUY922) on the PI3K-Akt-mTOR and AR pathways in a hind-flank tumor graft model. We observed that AUY922 caused supra-additive radiosensitization in both cell lines at low nanomolar doses with enhancement ratios between 1.4-1.7 (p < 0.01). RT-AUY922 increased apoptotic cell death compared with either therapy alone, induced G 2-M arrest and produced marked changes in client protein expression. These results were confirmed in vivo, where RT-AUY922 combination therapy produced supra-additive tumor growth delay compared with either therapy by itself in Myc-CaP and PC3 tumor grafts (both p < 0.0001). Our data suggest that combined RT-AUY922 therapy exhibits promising activity against prostate cancer cells, which should be investigated in clinical studies.

Hsp90: still a viable target in prostate cancer

Heat shock protein 90 (Hsp90) is a molecular chaperone that regulates the maturation, activation and stability of critical signaling proteins that drive the development and progression of prostate cancer, including the androgen receptor. Despite robust preclinical data demonstrating anti-tumor activity of first-generation Hsp90 inhibitors in prostate cancer, poor clinical responses initially cast doubt over the clinical utility of this class of agent. Recent advances in compound design and development, use of novel preclinical models and further biological insights into Hsp90 structure and function have now stimulated a resurgence in enthusiasm for these drugs as a therapeutic option. This review highlights how the development of new-generation Hsp90 inhibitors with improved physical and pharmacological properties is unfolding, and discusses the potential contexts for their use either as single agents or in combination, for men with metastatic prostate cancer.

Hsp90 Inhibitors NVP-AUY922 and NVP-BEP800 May Exert a Significant Radiosensitization on Tumor Cells along with a Cell Type-Specific Cytotoxicity

Targeting heat shock protein 90 (Hsp90) provides a promising therapeutic approach to enhance the sensitivity of tumor cells to ionizing radiation (IR). To explore the impact of scheduling drug-IR administration, in the present study, we analyzed the response of lung carcinoma A549 and glioblastoma SNB19 cells to simultaneous drug-IR treatment followed by a long-term drug administration. Cellular response was evaluated at different time intervals after IR-alone, drug-alone, or combined drug-IR treatments by colony counts and expression profiles of Hsp90 and its clients, along with several apoptotic markers and cell cycle-related proteins, as well as by IR-drug-induced cell cycle arrest, DNA damage, and repair. A short 30-minute exposure to either Hsp90 inhibitor did not affect the radiosensitivity of both tumor cell lines. Increasing the duration of post-IR-drug treatment progressively enhanced the sensitivity of SNB19 cells to IR. In contrast, the response of A549 cells to drug-IR combination was largely determined by the cytotoxic effects of both drugs without radiosensitization. Combined drug-IR treatment induced more severe DNA damage in both tumor cell lines than each treatment alone and also protracted the kinetics of DNA damage repair in SNB19 cells. In addition to large cell cycle disturbances, drug-IR treatment also caused depletion of the antiapoptotic proteins Akt and Raf-1 in both cell lines, along with a decrease of survivin in A549 cells in case of NVP-AUY922. The data show that simultaneous Hsp90 inhibition and irradiation may induce cell type-specific radiosensitization as well as cytotoxicity against tumor cells.

Hyperthermia-induced DNA repair deficiency suggests novel therapeutic anti-cancer strategies

Local hyperthermia is an effective treatment modality to augment radio- and chemotherapy-based anti-cancer treatments. Although the effect of hyperthermia is pleotropic, recent experiments revealed that homologous recombination, a pathway of DNA repair, is directly inhibited by hyperthermia. The hyperthermia-induced DNA repair deficiency is enhanced by inhibitors of the cellular heat-shock response. Taken together, these results provide the rationale for the development of novel anti-cancer therapies that combine hyperthermia-induced homologous recombination deficiency with the systemic administration of drugs that specifically affect the viability of homologous recombination deficient cells and/or inhibit the heat-shock response, to locally sensitise cancer cells to DNA damaging agents.

Synergistic effect of heat shock protein 90 inhibitor, 17-allylamino-17-demethoxygeldanamycin and X-rays, but not carbon-ion beams, on lethality in human oral squamous cell carcinoma cells

The purpose of this study is to clarify the effect of a heat shock protein 90 inhibitor, 17-allylamino-17-demethoxygeldanamycin (17-AAG), in combination with X-rays or carbon-ion beams on cell killing in human oral squamous cell carcinoma LMF4 cells. Cell survival was measured by colony formation assay. Cell-cycle distribution was analyzed by flow cytometry. Expression of DNA repair-related proteins was investigated by western blotting. The results showed 17-AAG to have synergistic effects on cell lethality with X-rays, but not with carbon-ion beams. The 17-AAG decreased G(2)/M arrest induced by X-rays, but not by carbon-ion beams. Both X-ray and carbon-ion irradiation up-regulated expression of non-homologous end-joining-associated proteins, Ku70 and Ku80, but 17-AAG inhibited only X-ray-induced up-regulation of these proteins. These results show that 17-AAG with X-rays releases G(2)/M phase arrest; cells carrying misrepaired DNA damage then move on to the G(1) phase. We demonstrate, for the first time, that the radiosensitization effect of 17-AAG is not seen with carbon-ion beams because 17-AAG does not affect these changes.

Darinaparsin: solid tumor hypoxic cytotoxin and radiosensitizer

PURPOSE

Hypoxia is an important characteristic of the solid tumor microenvironment and constitutes a barrier for effective radiotherapy. Here, we studied the effects of darinaparsin (an arsenic cytotoxin) on survival and radiosensitivity of tumor cells in vitro under normoxia and hypoxia and in vivo using xenograft models, compared to effects on normal tissues.

EXPERIMENTAL DESIGN

The cytotoxicity and radiosensitization of darinaparsin were first tested in vitro in a variety of solid tumor cell lines under both normoxia and hypoxia and compared with arsenic trioxide (ATO, an arsenical with reported cytotoxic and radiosensitizing activities on tumor cells). The effects were then tested in mouse models of xenograft tumors derived from tumor cell lines and clinical tumor specimens. The potential mechanisms of darinaparsin effects, including reactive oxygen species (ROS) generation, cellular damage, and changes in global gene expression, were also investigated.

RESULTS

In comparison with ATO, darinaparsin had significantly higher in vitro cytotoxic and radiosensitizing activities against solid tumor cells under both normoxia and hypoxia. In vivo experiments confirmed these activities at doses that had no systemic toxicities. Importantly, darinaparsin did not radiosensitize normal bone marrow and actually radioprotected normal intestinal crypts. The darinaparsin-mediated antitumor effects under hypoxia were not dependent on ROS generation and oxidative damage, but were associated with inhibition of oncogene (RAS and MYC)-dependent gene expression.

CONCLUSION

Darinaparsin has significant and preferential cytotoxic and radiosensitizing effects on solid tumors as compared with normal cells. Darinaparsin may therefore increase the therapeutic index of radiation therapy and has near term translational potential.

The HSP90 inhibitor NVP-AUY922 radiosensitizes by abrogation of homologous recombination resulting in mitotic entry with unresolved DNA damage

Background

Heat shock protein 90 (HSP90) is a molecular chaperone responsible for the conformational maintenance of a number of client proteins that play key roles in cell cycle arrest, DNA damage repair and apoptosis following radiation. HSP90 inhibitors exhibit antitumor activity by modulating the stabilisation and activation of HSP90 client proteins. We sought to evaluate NVP-AUY922, the most potent HSP90 inhibitor yet reported, in preclinical radiosensitization studies.

Principal Findings

NVP-AUY922 potently radiosensitized cells in vitro at low nanomolar concentrations with a concurrent depletion of radioresistance-linked client proteins. Radiosensitization by NVP-AUY922 was verified for the first time in vivo in a human head and neck squamous cell carcinoma xenograft model in athymic mice, as measured by delayed tumor growth and increased surrogate end-point survival (p = <0.0001). NVP-AUY922 was shown to ubiquitously inhibit resolution of dsDNA damage repair correlating to delayed Rad51 foci formation in all cell lines tested. Additionally, NVP-AUY922 induced a stalled mitotic phenotype, in a cell line-dependent manner, in HeLa and HN5 cell lines irrespective of radiation exposure. Cell cycle analysis indicated that NVP-AUY922 induced aberrant mitotic entry in all cell lines tested in the presence of radiation-induced DNA damage due to ubiquitous CHK1 depletion, but resultant downstream cell cycle effects were cell line dependent.

Conclusions

These results identify NVP-AUY922 as the most potent HSP90-mediated radiosensitizer yet reported in vitro, and for the first time validate it in a clinically relevant in vivo model. Mechanistic analysis at clinically achievable concentrations demonstrated that radiosensitization is mediated by the combinatorial inhibition of cell growth and survival pathways, ubiquitous delay in Rad51-mediated homologous recombination and CHK1-mediated G₂/M arrest, but that the contribution of cell cycle perturbation to radiosensitization may be cell line specific.

The Hsp90 inhibitor SNX-7081 synergizes with and restores sensitivity to fludarabine in chronic lymphocytic leukemia cells with lesions in the TP53 pathway: a potential treatment strategy for fludarabine refractory disease

Drug resistance in chronic lymphocytic leukemia (CLL) associated with lesions in the ATM/TP53 pathway represents a major challenge in clinical management. Evidence suggests that heat shock protein-90 (Hsp90) inhibitors may represent a therapeutic option in combination with more conventional therapies. We explored the effects of combining the Hsp90 inhibitor, SNX-7081, with fludarabine in vitro against CLL cells and hematological cell lines. In seven cell lines and 23 patient samples synergy between SNX-7081 and fludarabine (2-FaraA) was apparent in the three TP53 mutated cell lines and at significantly lower concentrations in TP53 or ATM dysfunctional patient cells. In 11/13 2-FaraA-resistant patient samples, SNX-7081 reduced the 50% inhibitory concentration to within a clinically achievable range. Synergy between SNX-7081 and 2-FaraA was evident in both the cell lines and patient samples as a significant decrease in cell viability. Our data suggest that combining SNX-7081 and fludarabine may be effective in the treatment of fludarabine-refractory CLL.

Design and synthesis of Hsp90 inhibitors: exploring the SAR of Sansalvamide A derivatives

Utilizing the structure-activity relationship we have developed during the synthesis of the first two generations and mechanism of action studies that point to the interaction of these molecules with the key oncogenic protein Hsp90, we report here the design of 32 new Sansalvamide A derivatives and their synthesis. Our new structures, designed from previously reported potent compounds, were tested for cytotoxicity on the HCT116 colon cancer cell line, and their binding to the biological target was analyzed using computational studies involving blind docking of derivatives using Autodock. Further, we show new evidence that our molecules bind directly to Hsp90 and modulate Hsp90's binding with client proteins. Finally, we demonstrate that we have integrated good ADME properties into a new derivative.

Novel HSP90 inhibitors, NVP-AUY922 and NVP-BEP800, radiosensitise tumour cells through cell-cycle impairment, increased DNA damage and repair protraction

Background:

Heat-shock protein 90 (Hsp90) has a crucial role in both the stabilisation and regulation of various proteins, including those related to radioresistance. Inhibition of Hsp90 may therefore provide a strategy for enhancing the radiosensitivity of tumour cells. This study explores the responses of four tumour cell lines (A549, GaMG, HT 1080 and SNB19) to combined treatment with ionising radiation (IR) and two novel inhibitors of Hsp90, NVP-AUY922 and NVP-BEP800. The techniques used included cell and colony counts, expression of Hsp90, Hsp70, Akt, survivin, cleaved caspase 3, p53, cell-cycle progression and associated proteins. DNA damage was analysed by histone γH2AX and Comet assays.

Results:

We found that NVP-AUY922 and NVP-BEP800 enhanced radiosensitivity in all tested cell lines. In contrast, only two cell lines (HT 1080 and GaMG) exhibited an increased rate of apoptosis after drug pretreatment, as revealed by western blot. In all tested cell lines, the expression of histone γH2AX, a marker of DNA double-strand breaks, after combined drug-IR treatment was higher and its decay rate was slower than those after each single treatment modality. Drug-IR treatment also resulted in impaired cell-cycle progression, as indicated by S-phase depletion and G2/M arrest. In addition, the cell cycle-associated proteins, Cdk1 and Cdk4, were downregulated after Hsp90 inhibition.

Interpretation:

These findings show that the novel inhibitors of Hsp90 can radiosensitise tumour cell lines of different entities through destabilisation and depletion of several Hsp90 client proteins, thus causing the depletion of S phase and G2/M arrest, increased DNA damage and repair protraction and, to some extent, apoptosis. The results might have important implications for the radiotherapy of solid tumours.

Inhibition of 90-kD heat shock protein potentiates the cytotoxicity of chemotherapeutic agents in human glioma cells

OBJECT

The introduction of temozolomide (TMZ) has advanced chemotherapy for malignant gliomas. A considerable number of glioblastoma cases are refractory to TMZ, however, and the development of novel chemotherapeutic regimens is needed. The authors of previous studies have revealed that hsp90 is expressed at higher levels in human neoplastic tissues, including gliomas, than in normal tissues. Heat shock protein 90 is involved in a cytoprotective mechanism against cellular stressors such as DNA damage, and the authors hypothesized that hsp90 inhibitors might act as antitumor agents against gliomas and potentiate the cytotoxicity of DNA-damaging agents.

METHODS

The authors examined the cytotoxicity of an hsp90 inhibitor, 17-(allylamino)-17-demethoxygeldanamycin (17-AAG), both alone and in combination with 1 of 3 DNA-damaging agents (cisplatin, 1,3-bis(2-chloroethyl)-1-nitrosourea, and TMZ) in human glioma cell lines. The cytotoxicity of these agents to glioma cells was measured using a colony formation assay. The cell cycle phase distribution, protein expression, and number of apoptotic cells were measured using a fluorescence-activated cell sorting assay, immunoblot assays, and double staining with annexin V and propidium iodide. In an in vivo experiment, 17-AAG, cisplatin, or 17-AAG and cisplatin were administered intraperitoneally to mice with xenografted U87MG cells, and the resulting tumor volumes were measured.

RESULTS

The authors found that 17-AAG reduced the clonogenicity of U87MG cells, and at a low concentration (< 100 nM) potentiated the cytotoxicity of the DNA-crosslinking agents cisplatin and 1,3-bis(2-chloroethyl)-1-nitrosourea, but not that of the DNA-methylating agent TMZ. This 17-AAG-induced potentiation of DNA crosslinking agent-induced cytotoxicity was a consequence of prolonged G(2)-M arrest accompanied by the suppression of cdc2 and cdc25C and of increased apoptotic cell death accompanied by the degradation of the antiapoptosis proteins Akt and survivin. Similar effects were observed when cells were treated with radicicol, another hsp90 inhibitor. The 17-AAG-induced enhancement of DNA crosslinking agent-induced cytotoxicity was also observed in other cell lines. In addition, 17-AAG sensitized xenografted U87MG cells to cisplatin in nude mice.

CONCLUSIONS

Heat shock protein 90-targeted therapy may be an effective strategy for potentiating chemotherapy using DNA-crosslinking agents for TMZ-refractory gliomas.