Hsp90 Inhibitor Ganetespib Sensitizes Non-Small Cell Lung Cancer to Radiation but Has Variable Effects with Chemoradiation

Mechanism of Musashi2 affecting radiosensitivity of lung cancer by modulating DNA damage repair

Identifying new targets for overcoming radioresistance is crucial for improving the efficacy of lung cancer radiotherapy, given that tumor cell resistance is a leading cause of treatment failure. Recent research has spotlighted the significance of Musashi2 (MSI2) in cancer biology. In this study, we first demonstrated that MSI2 plays a key function in regulating the radiosensitivity of lung cancer. The expression of MSI2 is negatively correlated with overall survival in cancer patients, and the knockdown of MSI2 inhibits tumorigenesis and increases radiosensitivity of lung cancer cells. Cellular radiosensitivity, which is closely linked to DNA damage, is influenced by MSI2 interaction with ataxia telangiectasia mutated and Rad3-related kinase (ATR) and checkpoint kinase 1 (CHK1) post-irradiation; moreover, knockdown of MSI2 inhibits the ATR-mediated DNA damage response pathway. RNA-binding motif protein 17 (RBM17), which is implicated in DNA damage repair, exhibits increased interaction with MSI2 post-irradiation. We found that knockdown of RBM17 disrupted the interaction between MSI2 and ATR post-irradiation and increased the radiosensitivity of lung cancer cells. Furthermore, we revealed the potential mechanism of MSI2 recruitment into the nucleus with the assistance of RBM17 to activate ATR to promote radioresistance. This study provides novel insights into the potential application of MSI2 as a new target in lung cancer radiotherapy.

Combination therapy involving HSP90 inhibitors for combating cancer: an overview of clinical and preclinical progress

The molecular chaperone heat shock protein 90 (HSP90) regulates multiple crucial signalling pathways in cancer by driving the maturation of key signalling components, thereby playing a crucial role in tumorigenesis and drug resistance in cancer. Inhibition of HSP90 results in metastable conformational collapse of its client proteins and their proteasomal degradation. Considerable efforts have been devoted to the development of small-molecule inhibitors targeting HSP90, and more than 20 inhibitors have been evaluated in clinical trials for cancer therapy. However, owing to disadvantages such as organ toxicity and drug resistance, only one HSP90 inhibitor has been approved for use in clinical settings. In recent years, HSP90 inhibitors used in combination with other anti-cancer therapies have shown remarkable potential in the treatment of cancer. HSP90 inhibitors work synergistically with various anti-cancer therapies, including chemotherapy, targeted therapy, radiation therapy and immunotherapy. HSP90 inhibitors can improve the pharmacological effects of the above-mentioned therapies and reduce treatment resistance. This review provides an overview of the use of combination therapy with HSP90 inhibitors and other anti-cancer therapies in clinical and preclinical studies reported in the past decade and summarises design strategies and prospects for these combination therapies. Altogether, this review provides a theoretical basis for further research and application of these combination therapies in the treatment of cancer.

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

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

Recent findings on the role of wild-type and mutant p53 in cancer development and therapy

The p53 protein is a tumor suppressor encoded by the TP53 gene and consists of 393 amino acids with four main functional domains. This protein responds to various cellular stresses to regulate the expression of target genes, thereby causing DNA repair, cell cycle arrest, apoptosis, metabolic changes, and aging. Mutations in the TP53 gene and the functions of the wild-type p53 protein (wtp53) have been linked to various human cancers. Eight TP53 gene mutations are located in codons, constituting 28% of all p53 mutations. The p53 can be used as a biomarker for tumor progression and an excellent target for designing cancer treatment strategies. In wild-type p53-carrying cancers, abnormal signaling of the p53 pathway usually occurs due to other unusual settings, such as high MDM2 expression. These differences between cancer cell p53 and normal cells have made p53 one of the most important targets for cancer treatment. In this review, we have dealt with various issues, such as the relative contribution of wild-type p53 loss of function, including transactivation-dependent and transactivation-independent activities in oncogenic processes and their role in cancer development. We also discuss the role of p53 in the process of ferroptosis and its targeting in cancer treatment. Finally, we focus on p53-related drug delivery systems and investigate the challenges and solutions.

P130cas-FAK interaction is essential for YAP-mediated radioresistance of non-small cell lung cancer

Based on the RNA-sequencing data, previous studies revealed that extracellular matrix receptor interaction and focal adhesion signaling pathways were enriched in radioresistant non-small cell lung cancer (NSCLC) cell lines. As the principal members of these signaling pathways, recent studies showed that FAK controlled YAP's nuclear translocation and activation in response to mechanical activation. However, the underlying mechanisms are largely unknown. This study was designed to determine whether P130cas plays a role in FAK-YAP axis-mediated radioresistance. We found that P130cas promoted proliferation, altered the cell cycle profile, and enhanced tumor growth using cell lines and xenograft mouse models. After treating the cell lines and xenograft models with a single dose of 5 Gy irradiation, we observed that P130cas effectively induced radioresistance in vitro and in vivo. We confirmed that P130cas interacted with and promoted YAP stabilization, thereby facilitating YAP's activation and nuclear translocation and downregulating the radiosensitivity of NSCLC. Our data also revealed that P130cas and FAK directly interacted with each other and worked together to regulate YAP's activation and nuclear translocation. Furthermore, the present study identified that P130cas, FAK and YAP formed a triple complex to induce radioresistance. Using P130cas-ΔSH3, FAK- P712/715A mutant, YAP-ΔSH3bm and YAP-ΔWW mutant, our results showed that targeting P130cas-FAK interaction may be a more cost-effective way to overcome the YAP activation mediated radioresistance in NSCLC. Using the data of the public database and our clinical samples, the present study suggested that the expression of P130cas correlated with YAP expression and indicated a poor overall response rate of NSCLC patients who underwent radiation therapy. Overall, our study extends the knowledge of FAK-YAP interaction and provides new insight into understanding the underlying mechanisms to overcome the radioresistance of NSCLC.

HSP90 promotes radioresistance of cervical cancer cells via reducing FBXO6 mediated CD147 polyubiquitination

HSP90 inhibition might be a promising strategy to overcome the radioresistance of some cancers. In the current study, we further explored the mechanisms of HSP90 in regulating the radiosensitivity of cervical cancer cells. Bioinformatic analysis was performed based on data from TCGA‐CESC. Cellular and molecular studies were conducted using CaSki and SiHa and the derived radioresistant (RR) subclones. Through a proteomics screen, we identified HSP90 chaperones (both HSP90α and HSP90β) as CD147‐binding partners supporting its stabilization. Targeting HSP90 sensitized CaSki‐RR and SiHa‐RR cancer cells to irradiation partially through CD147 destabilization. Mechanistically, HSP90 interacts with FBXO6 and reduces FBXO6‐mediated proteasomal degradation of CD147. Enforced FBXO6 overexpression also sensitized CaSki‐RR and SiHa‐RR cancer cells to irradiation. These effects were enhanced using 17‐AAG treatment but were weakened by CD147 overexpression. Survival analysis further confirmed the association between high FBXO6 expression and favorable progression‐free survival among patients with cervical cancer. In conclusion, this study showed that HSP90 promotes radioresistance of cervical cancer cells partially via reducing FBXO6 mediated CD147 polyubiquitination. These findings help to explain why HSP90 inhibitor exerts radio‐sensitizing effects in cervical cancer.

High-Content Clonogenic Survival Screen to Identify Chemoradiation Sensitizers

PURPOSE

The combination of cytotoxic chemotherapy with radiation therapy (CRT) has resulted in significant improvements in clinical outcomes for patients with many locally advanced unresectable cancers. Only a small proportion of patients achieve pathologic complete responses to CRT; combination of CRT with targeted agents offers the promise of further improving treatment responses. However, numerous clinical trials have failed to show an improvement in clinical outcomes with the addition of targeted agents. To increase the accessibility of our screening method and accelerate the pace at which novel combinations with CRT are identified and incorporated into standard practices for treatments, we report details on screening method optimization, data generation, and downstream data analysis.

METHODS

In part, the gap in translation to large, expensive, and ultimately unsuccessful clinical trials reflects the shortcomings of inconsistently designed, executed, and reported preclinical data on which these studies are based. In an effort to standardize the selection of agents for future clinical testing, we have designed, optimized and validated a high throughput, high content, clonogenic assay platform for step-wise progression of preclinical studies from in vitro to in vivo in non-small cell lung cancer and pancreatic ductal adenocarcinoma.

RESULTS

This highly stable in vitro method was standardized for identification of the most promising CTEP drugs that could best be combined with CRT from among as screen of multiple agents tested in an unbiased manner using 96-well plates. The methodology lends itself to seamless testing of multiple agents in a similar fashion allowing cross-comparisons, evaluation of CRT, or radiation therapy alone, and testing multiple concentrations of test agents sequenced at different times before and after radiation. The method identified Trametinib as a strong CRT sensitizer in KRAS-mutant non-small cell lung cancer and pancreatic ductal adenocarcinoma cell lines. This platform has enabled the screening and identification of several chemoradiation sensitizers.

CONCLUSIONS

High throughput, high content clonogenic drug screening assay allows for the rapid identification of targets and agents to be translated to the clinic to help improve the effectiveness of current standard of care CRT in various solid tumors.

Radiosensitivity-Specific Proteomic and Signaling Pathway Network of Non-Small Cell Lung Cancer (NSCLC)

PURPOSE

An unmet clinical need in non-small cell lung cancer (NSCLC) management is the accurate prediction of radiation response in patients receiving radical radiation therapy. We explored the intrinsic radiosensitivity of NSCLC from the proteomic profiles of NSCLC cell lines and paraffin-embedded human samples.

METHODS AND MATERIALS

To uncover radiosensitivity-specific proteomic and signaling pathways, we performed quantitative proteomics by data-independent acquisition mass spectrometry assay on 29 human NSCLC cell lines and 13 paraffin-embedded human NSCLC samples. We validated closely interacting radioresistant proteins by western blotting, immunofluorescence, real-time quantitative polymerase chain reaction in NSCLC cell lines, and immunohistochemistry in paraffin-embedded human samples. We validated the functions of 3 key hub proteins by lentivirus transfection, clonogenic survival assay, and flow cytometry.

RESULTS

The proteomic profiling of NSCLC showed that the intrinsic radiosensitivity of NSCLC is mainly modulated by signaling pathways of proteoglycans in cancer, focal adhesion, and regulation of the actin cytoskeleton. We identified 71 differentially expressed proteins and validated 8 closely interacting proteins as radioresistant proteins of NSCLC. Moreover, we also validated the functionality of integrin-linked protein kinase, p21-activated kinase 1, and Ras GTPase-activating-like protein IQGAP1 in the radiation response of NSCLC cell lines. Finally, with the NSCLC radiosensitivity-specific proteins, we delineated the atlas network of NSCLC radiosensitivity-related signaling pathways.

CONCLUSIONS

Radiosensitivity-specific proteins could guide individualized radiation therapy in clinical practice by predicting the radiation response of patients with NSCLC. Moreover, the NSCLC radiosensitivity-related signaling pathway atlas could guide further exploration of the underlying mechanism.

Moving Beyond the Standard of Care: Accelerate Testing of Radiation-Drug Combinations

Radiation therapy is a major treatment modality used in > 60% of cancer patients as definitive local treatment for inoperable locoregionally confined tumors and as palliative therapy. Although cytotoxic chemotherapy enhances the effectiveness of treatment, the benefit over radiation therapy alone is modest. There is a need to enhance the effectiveness of local tumor control over what sequentially or concurrently administered cytotoxic chemotherapy provides. Although many biological pathways are known to enhance the effectiveness of radiation therapy, there is currently a paucity of drugs approved for use in combination. Several clinical trials have tested the effectiveness of combining targeted agents or immunotherapies with radiation therapy, but the results of these trials have been negative, likely stemming from the relative lack of preclinical evidence using appropriate experimental standardization or model systems. Accelerating the identification of agents tested in an appropriate clinical context and experimental systems or models would greatly enhance the potential to bring forward early testing of drugs that would not only be safe but also more effective. This article provides an overview of the opportunities and challenges of developing therapeutics to combine with radiation therapy, and some guidance toward preclinical and early clinical testing to improve the chance that advanced phase testing of drug-radiation combinations would be successful in the long term.

Identification of Predictive Biomarkers of Response to HSP90 Inhibitors in Lung Adenocarcinoma

Heat shock protein 90 (HSP90) plays an essential role in lung adenocarcinoma, acting as a key chaperone involved in the correct functioning of numerous highly relevant protein drivers of this disease. To this end, HSP90 inhibitors have emerged as promising therapeutic strategies, even though responses to them have been limited to date. Given the need to maximize treatment efficacy, the objective of this study was to use isobaric tags for relative and absolute quantitation (iTRAQ)-based proteomic techniques to identify proteins in human lung adenocarcinoma cell lines whose basal abundances were correlated with response to HSP90 inhibitors (geldanamycin and radicicol derivatives). From the protein profiles identified according to response, the relationship between lactate dehydrogenase B (LDHB) and DNA topoisomerase 1 (TOP1) with respect to sensitivity and resistance, respectively, to geldanamycin derivatives is noteworthy. Likewise, rhotekin (RTKN) and decaprenyl diphosphate synthase subunit 2 (PDSS2) were correlated with sensitivity and resistance to radicicol derivatives. We also identified a relationship between resistance to HSP90 inhibition and the p53 pathway by glucose deprivation. In contrast, arginine biosynthesis was correlated with sensitivity to HSP90 inhibitors. Further study of these outcomes could enable the development of strategies to improve the clinical efficacy of HSP90 inhibition in patients with lung adenocarcinoma.

Low-Dose Hsp90 Inhibitor Selectively Radiosensitizes HNSCC and Pancreatic Xenografts

PURPOSE

Treatment approaches using Hsp90 inhibitors at their maximum tolerated doses (MTDs) have not produced selective tumor toxicity. Inhibition of Hsp90 activity causes degradation of client proteins including those involved in recognizing and repairing DNA lesions. We hypothesized that if DNA repair proteins were degraded by concentrations of an Hsp90 inhibitor below those required to cause nonspecific cytotoxicity, significant tumor-selective radiosensitization might be achieved.

EXPERIMENTAL DESIGN

Tandem mass tagged-mass spectrometry was performed to determine the effect of a subcytotoxic concentration of the Hsp90 inhibitor, AT13387 (onalespib), on global protein abundance. The effect of AT13387 on in vitro radiosensitization was assessed using a clonogenic assay. Pharmacokinetics profiling was performed in mice bearing xenografts. Finally, the effect of low-dose AT13387 on the radiosensitization of three tumor models was assessed.

RESULTS

A subcytotoxic concentration of AT13387 reduced levels of DNA repair proteins, without affecting the majority of Hsp90 clients. The pharmacokinetics study using one-third of the MTD showed 40-fold higher levels of AT13387 in tumors compared with plasma. This low dose enhanced Hsp70 expression in peripheral blood mononuclear cells (PBMCs), which is a biomarker of Hsp90 inhibition. Low dose monotherapy was ineffective, but when combined with radiotherapy, produced significant tumor growth inhibition.

CONCLUSIONS

This study shows that a significant therapeutic ratio can be achieved by a low dose of Hsp90 inhibitor in combination with radiotherapy. Hsp90 inhibition, even at a low dose, can be monitored by measuring Hsp70 expression in PBMCs in human studies.

KNK437 restricts the growth and metastasis of colorectal cancer via targeting DNAJA1/CDC45 axis

As an inhibitor of heat shock proteins (HSPs), KNK437 has been reported to play an anti-tumor role in several cancers. But its therapeutic effect and mechanisms in colorectal cancer (CRC) remain unclear. Here, KNK437 sharply inhibited the level of DnaJ heat shock protein family (Hsp40) member A1 (DNAJA1), followed by DNAJB1, but had little effect on the levels of HSP27, HSP105, HSP90, and HSP70 in CRC cells. DNAJA1 promoted CRC cell proliferation in vitro and tumor growth and metastasis in vivo. Mechanistically, DNAJA1 was activated by E2F transcription factor 1 (E2F1) and then promoted cell cycle by stabilizing cell division cycle protein 45 (CDC45), which could be reversed by KNK437. DNAJA1 was significantly upregulated in CRC tissues and positively correlated with serosa invasion, lymph node metastasis. High level of DNAJA1 predicted poor prognosis for CRC patients. Its expression was highly linked with E2F1 and CDC45 in CRC tissues. More importantly, KNK437 significantly suppressed the growth of DNAJA1 expressing tumor in vivo. The combined treatment of KNK437 with 5-FU/L-OHP chemotherapy reduced liver metastasis of CRC. These data reveal a novel mechanism of KNK437 in anti-tumor therapy of CRC and provides a newly therapeutic strategy with potential translation to the CRC patients.

Heat Shock Proteins: Agents of Cancer Development and Therapeutic Targets in Anti-Cancer Therapy

Heat shock proteins (HSPs) constitute a large family of molecular chaperones classified by their molecular weights, and they include HSP27, HSP40, HSP60, HSP70, and HSP90. HSPs function in diverse physiological and protective processes to assist in maintaining cellular homeostasis. In particular, HSPs participate in protein folding and maturation processes under diverse stressors such as heat shock, hypoxia, and degradation. Notably, HSPs also play essential roles across cancers as they are implicated in a variety of cancer-related activities such as cell proliferation, metastasis, and anti-cancer drug resistance. In this review, we comprehensively discuss the functions of HSPs in association with cancer initiation, progression, and metastasis and anti-cancer therapy resistance. Moreover, the potential utilization of HSPs to enhance the effects of chemo-, radio-, and immunotherapy is explored. Taken together, HSPs have multiple clinical usages as biomarkers for cancer diagnosis and prognosis as well as the potential therapeutic targets for anti-cancer treatment.

Cytotoxic activity of IMMUNEPOTENT CRP against non-small cell lung cancer cell lines

BACKGROUND

IMMUNEPOTENT-CRP® (I-CRP) is a bovine dialyzable leukocyte extract containing transfer factor. It is a cost-effective, unspecific active immunotherapy that has been used in patients with non-small cell lung cancer (NSCLC) as an adjuvant to reduce the side-effects of chemotherapy and radiotherapy, and has shown cytotoxic activity in vitro on different cancer cell lines. However, its mechanism of action against lung cancer cells has not been assessed. Therefore, the objective of this work was to assess the cytotoxic mechanism of I-CRP on lung cancer cell lines.

METHODS

We assessed cell viability through MTT assay on the NSCLC cell lines A549, A427, Calu-1, and INER-51 after treatment with I-CRP. To further understand the mechanisms of cell viability diminution we used fluorescence-activated cell sorting to evaluate cell death (annexin-V and propidium iodide [PI] staining), cell cycle and DNA degradation (PI staining), mitochondrial alterations (TMRE staining), and reactive oxygen species (ROS) production (DCFDA staining). Additionally, we evaluated caspase and ROS dependence of cell death by pretreating the cells with the pan-caspase inhibitor Q-VD-OPH and the antioxidant N-acetylcysteine (NAC), respectively.

RESULTS

Our data shows that I-CRP is cytotoxic to NSCLC cell lines in a dose and time dependent manner, without substantial differences between the four cell lines tested (A549, A427, Calu-1, and INER-51). Cytotoxicity is induced through regulated cell death and cell cycle arrest induction. I-CRP-induced cell death in NSCLC cell lines is characterized by DNA degradation, mitochondrial damage, and ROS production. Moreover, cell death is independent of caspases but relies on ROS production, as it is abrogated with NAC.

CONCLUSION

Altogether, these results improve the knowledge about the cytotoxic activity of I-CRP on NSCLC cells, indicating that cell death, cell cycle arrest, DNA degradation and mitochondrial damage are important features, while ROS play the main role for I-CRP mediated cytotoxicity in lung cancer cells.

Targeting CDK9 and MCL-1 by a new CDK9/p-TEFb inhibitor with and without 5-fluorouracil in esophageal adenocarcinoma

Background:

CDK9 inhibitors are antitumorigenic against solid tumors, including esophageal adenocarcinoma (EAC). However, efficacy of a CDK9 inhibitor combined with 5-fluorouracil (5-FU) and target proteins that are targeted by these agents in EAC are unknown.

Methods:

The anti-EAC efficacy of a new CDK9 inhibitor, BAY1143572, with and without 5-FU was assessed in vitro and in xenograft models in athymic nu/nu mice. Synergy between BAY1143572 and 5-FU in inhibiting cell proliferation was analyzed by calculating the combination index using CompuSyn software. Potential targets of BAY1143572 and 5-FU were identified by reverse-phase protein array. The effects of BAY1143572 and 5-FU on MCL-1 in vitro were analyzed by Western blotting, quantitative real-time polymerase chain reaction, and chromatin immunoprecipitation assay. MCL-1 protein expression in tumors from patients with locoregional EAC treated with chemoradiation and surgery was assessed by immunohistochemistry.

Results:

BAY1143572 had dose-dependent antiproliferative and proapoptotic effects and demonstrated synergy with 5-FU against EAC in vitro. The median volumes of FLO-1 and ESO-26 xenografts treated with 5-FU plus BAY114352 were significantly smaller than those of xenografts treated with either agent alone (p < 0.05). BAY1143572 downregulated MCL-1 by inhibiting HIF-1α binding to the MCL-1 promoter. 5-FU enhanced BAY1143572-induced MCL-1 downregulation and stable MCL-1 overexpression reduced the apoptosis induced by BAY1143572 and 5-FU in vitro. High patients’ tumor MCL-1 expression was correlated with shorter overall and recurrence-free survival.

Conclusions:

BAY1143572 and 5-FU have synergistic antitumorigenic effects against EAC. MCL-1 is a downstream target of CDK9 inhibitors and a predictor of response to neoadjuvant chemoradiation in EAC.

Targeting cyclin-dependent kinase 9 by a novel inhibitor enhances radiosensitization and identifies Axl as a novel downstream target in esophageal adenocarcinoma

Cyclin-dependent kinase 9 (CDK9) transcriptionally regulates several proteins and cellular pathways central to radiation induced tissue injury. We investigated a role of BAY1143572, a new highly specific CDK9 inhibitor, as a sensitizer to radiation in esophageal adenocarcinoma. In vitro synergy between the CDK9 inhibitor and radiation was evaluated by clonogenic assay. In vivo synergy between the CDK9 inhibitor and radiation was assessed in multiple xenograft models including a patient’s tumor derived xenograft (PDX). Reverse phase protein array (RPPA), western blotting, immunohistochemistry, and qPCR were utilized to identify and validate targets of the CDK9 inhibitor. The CDK9 inhibitor plus radiation significantly reduced growth of FLO-1, SKGT4, OE33, and radiation resistant OE33R xenografts and PDXs as compared to the cohorts treated with either single agent CDK9 inhibitor or radiation alone. RPPA identified Axl as a candidate target of CDK9 inhibition. Western blot and qPCR demonstrated reduced Axl mRNA (p = 0.02) and protein levels after treatment with CDK9 inhibitor with or without radiation in FLO-1 and SKGT4 cells. Axl protein expression in FLO-1 xenografts treated with combination of CDK9 inhibitor and radiation was significantly lower than the xenografts treated with radiation alone (p = 0.003). Clonogenic assay performed after overexpression of Axl in FLO-1 and SKGT4 cells enhanced radiosensitization by the CDK9 inhibitor, suggesting dependency of radiosensitization effects of the CDK9 inhibitor on Axl. In conclusion, these findings indicate that targeting CDK9 by BAY1143572 significantly enhances the effects of radiation and Axl is a novel downstream target of CDK9 in esophageal adenocarcinoma.

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.

Inhibition of HSP90 overcomes resistance to chemotherapy and radiotherapy in pancreatic cancer

Resistance of pancreatic ductal adenocarcinoma (PDAC) to radiotherapy and chemotherapy represents a significant clinical issue. Although the mechanisms of resistance are multi-faceted, client proteins of heat shock protein 90 (HSP90) such as hypoxia induced factor-1α (HIF-1α) have a central role in this process. The purpose of this investigation was to evaluate inhibition of HSP90 as a therapeutic strategy for radiosensitization in pancreatic cancer. Ganetespib, a selective inhibitor of HSP90, was evaluated as a radio-sensitizer in setting of PDAC. Inhibition of HSP90 by ganetespib potentiated the ability of radiation therapy to limit cell proliferation and colony formation in vitro. HIF-1α expression was upregulated by irradiation and HIF-1α-overexpressing stable cell lines were resistant to radiation. Inhibition of HSP90 with ganetespib reversed the effects of HIF-1α overexpression, by reducing signaling via proliferative, angiogenic and anti-apoptotic pathways. The potentiation of the antitumor effects of chemoradiotherapy by ganetespib and modulation of key pathways (e.g. HIF-1α, STAT3, and AKT) was confirmed in vivo in nude mice bearing HPAC xenograft tumors. These novel data highlight HIF-1α-mediated mechanisms of HSP90 inhibition that sensitize PDAC cells to chemoradiotherapy. This pathway and its pleiotropic effects warrant further evaluation in concert with conventional therapy in pancreatic cancer clinical trials.

Mutant LKB1 Confers Enhanced Radiosensitization in Combination with Trametinib in KRAS-Mutant Non-Small Cell Lung Cancer

Purpose: The MEK inhibitor trametinib radiosensitizes KRAS-mutant non-small cell lung cancer (NSCLC) and is being tested clinically with chemoradiation. However, variability in response to trametinib suggests that additional pathways are involved. The mechanism of resistance to trametinib radiosensitization is still unknown.Experimental Design: We used a panel of KRAS-mutant NSCLC cells and tested the radiosensitization effects of trametinib by clonogenic survival assay. Then, we investigated the mechanisms underlying the resistance to the combination therapy through several knockout and overexpression systems. Finally, we validated our findings in syngeneic mouse models in a treatment setting that mimicked the standard of care in the clinic.Results: Radiosensitization by trametinib was effective only in KRAS-LKB1-mutated cells with wild-type (WT) p53, and we found that restoring LKB1 expression in those cells blocked that sensitization. Trametinib and radiotherapy both induced senescence in a p53-dependent manner, but in WT LKB1 cells, the combination also activated the AMPK-autophagy pathway to rescue damaged cells from senescence. LKB1-knockout or autophagy inhibition in WT LKB1 cells potentiated trametinib radiosensitization. In syngeneic animal models of Kras-mutant lung tumors, Lkb1-knockout tumors were resistant to trametinib and chemoradiation given separately, but the combination greatly controlled tumor growth and prolonged survival.Conclusions: The LKB1 mutation in KRAS-mutant NSCLC conferred enhanced radiosensitization in combination with trametinib. The WT LKB1 could activate autophagy through AMPK pathway to induce resistance to the combination of trametinib and radiation. The KRAS-LKB1 mutation could potentially be a biomarker to select patients for trametinib and radiotherapy combination therapy. Clin Cancer Res; 24(22); 5744-56. ©2018 AACR.

Combining Immunotherapy and Radiotherapy for Cancer Treatment: Current Challenges and Future Directions

Since the approval of anti-CTLA4 therapy (ipilimumab) for late-stage melanoma in 2011, the development of anticancer immunotherapy agents has thrived. The success of many immune-checkpoint inhibitors has drastically changed the landscape of cancer treatment. For some types of cancer, monotherapy for targeting immune checkpoint pathways has proven more effective than traditional therapies, and combining immunotherapy with current treatment strategies may yield even better outcomes. Numerous preclinical studies have suggested that combining immunotherapy with radiotherapy could be a promising strategy for synergistic enhancement of treatment efficacy. Radiation delivered to the tumor site affects both tumor cells and surrounding stromal cells. Radiation-induced cancer cell damage exposes tumor-specific antigens that make them visible to immune surveillance and promotes the priming and activation of cytotoxic T cells. Radiation-induced modulation of the tumor microenvironment may also facilitate the recruitment and infiltration of immune cells. This unique relationship is the rationale for combining radiation with immune checkpoint blockade. Enhanced tumor recognition and immune cell targeting with checkpoint blockade may unleash the immune system to eliminate the cancer cells. However, challenges remain to be addressed to maximize the efficacy of this promising combination. Here we summarize the mechanisms of radiation and immune system interaction, and we discuss current challenges in radiation and immune checkpoint blockade therapy and possible future approaches to boost this combination.

RAD50 Expression Is Associated with Poor Clinical Outcomes after Radiotherapy for Resected Non-small Cell Lung Cancer

Purpose: Although postoperative radiotherapy is often used to maintain local control after surgical resection and chemotherapy for locally advanced non-small cell lung cancer (NSCLC), both locoregional failure and distant metastasis remain problematic. The mechanisms of therapeutic resistance remain poorly understood.Experimental Design: We used reverse-phase protein arrays (RPPA) to profile the baseline expression of 170 total and phosphorylated proteins in 70 NSCLC cell lines to categorize pathways that may contribute to radiation resistance. Significant markers identified by RPPA were further analyzed in tissue microarrays (TMA) of specimens from 127 patients with NSCLC who had received surgery before receiving postoperative radiotherapy. Cox regression analysis and log-rank tests were used to identify potential predictive factors. We then validated the biological function of the markers in NSCLC cell lines in vitroResults: Of the 170 proteins or phospho-proteins profiled, a subset of 12 proteins was found to correlate with radiation response parameters. TMA analysis of the 12 proteins showing the greatest differences in expression in the RPPA analysis demonstrated that RAD50 had the strongest correlation with distant relapse-free survival, locoregional relapse-free survival, and disease-free survival in patients with NSCLC. We confirmed that knockdown of RAD50 sensitized NSCLC cells to radiation and that upregulation of RAD50 increased radioresistance in in vitro experiments.Conclusions: Upregulated RAD50 may be a predictor of radioresistance in patients with lung cancer who received radiotherapy. Clin Cancer Res; 24(2); 341-50. ©2017 AACR.

Molecular mechanism and targeted therapy of Hsp90 involved in lung cancer: New discoveries and developments (Review)

The exploration of the molecular mechanisms and signaling pathways on lung cancer is very important for developing new strategies of diagnosis and treatment to this disease, such as finding valuable lung cancer markers and molecularly targeted therapies. Previously, a number of studies disclose that heat shock protein 90 (Hsp90) is upregulated in cancer cells, tissues and serum of lung cancer patients, and its upregulation intimately correlates with the occurrence, development and outcome of lung cancer. On the contrary, inhibition of Hsp90 can suppress cell proliferation, motility and metastasis of lung cancer and promote apoptosis of lung cancer cells via complex signaling pathways. In addition, a series of Hsp90 inhibitors have been investigated as effective molecular targeted therapy tactics fighting against lung cancer. This review, systematically summarizes the role of Hsp90 in lung cancer, the molecular mechanisms and development of anti-Hsp90 treatment in lung cancer.

Improving radiotherapy in cancer treatment: Promises and challenges

Effective radiotherapy for cancer has relied on the promise of maximally eradicating tumor cells while minimally killing normal cells. Technological advancement has provided state-of-the-art instrumentation that enables delivery of radiotherapy with great precision to tumor lesions with substantial reduced injury to normal tissues. Moreover, better understanding of radiobiology, particularly the mechanisms of radiation sensitivity and resistance in tumor lesions and toxicity in normal tissues, has improved the treatment efficacy of radiotherapy. Previous mechanism-based studies have identified many cellular targets that can affect radiation sensitivity, notably reactive oxygen species, DNA-damaging response signals, and tumor microenvironments. Several radiation sensitizers and protectors have been developed and clinically evaluated; however, many of these results are inconclusive, indicating that improvement remains needed. In this era of personalized medicine in which patients’ genetic variations, transcriptome and proteomics, tumor metabolism and microenvironment, and tumor immunity are available. These new developments have provided opportunity for new target discovery. Several radiotherapy sensitivity-associated “gene signatures” have been reported although clinical validations are needed. Recently, several immune modifiers have been shown to associate with improved radiotherapy in preclinical models and in early clinical trials. Combination of radiotherapy and immunocheckpoint blockade has shown promising results especially in targeting metastatic tumors through abscopal response. In this article, we succinctly review recent advancements in the areas of mechanism-driven targets and exploitation of new targets from current radio-oncogenomic and radiation-immunotherapeutic approaches that bear clinical implications for improving the treatment efficacy of radiotherapy.

Heat shock protein antagonists in early stage clinical trials for NSCLC

INTRODUCTION

Cancer cells have a higher need of chaperones than normal cells to prevent the toxic effects of intracellular protein misfolding and aggregation. Heat shock proteins (Hsps) belong to these chaperones; they are classified into families according to molecular size. Hsps are upregulated in many cancers and inhibition can inhibit tumor growth by destabilizing proteins necessary for tumor survival. In non-small cell lung cancer (NSCLC), there are three different Hsp antagonist classes that are in (early) clinical trials: Hsp90, Hsp70 and Hsp27 inhibitors. Areas covered: The rationale to use Hsp inhibitors in NSCLC will be summarized and phase I-III trials will be reviewed. Expert opinion: Several Hsp90 inhibitors have been tested in phase I-III trials, until now none was positive in unselected NSCLC; therefore development of AUY922, ganetespib and retaspimycin was halted. Results seem more promising in molecularly selected patients, especially in ALK-rearranged NSCLC. Hsp27 is overexpressed in squamous NSCLC and is a mechanism of chemotherapy resistance. The Hsp27 inhibitor apatorsen is now tested in squamous NSCLC. No phase II/III data are known for Hsp70 inhibitors. Combination of Hsp inhibitors with heat shock transcription factor 1 inhibitors or focal adhesion kinase inhibitors might be of interest for future trials.

HSP90 inhibition sensitizes head and neck cancer to platin-based chemoradiotherapy by modulation of the DNA damage response resulting in chromosomal fragmentation

BACKGROUND

Concurrent cisplatin radiotherapy (CCRT) is a current standard-of-care for locally advanced head and neck squamous cell carcinoma (HNSCC). However, CCRT is frequently ineffective in patients with advanced disease. It has previously been shown that HSP90 inhibitors act as radiosensitizers, but these studies have not focused on CCRT in HNSCC. Here, we evaluated the HSP90 inhibitor, AUY922, combined with CCRT.

METHODS

The ability of AUY922 to sensitize to CCRT was assessed in p53 mutant head and neck cell lines by clonogenic assay. Modulation of the CCRT induced DNA damage response (DDR) by AUY922 was characterized by confocal image analysis of RAD51, BRCA1, 53BP1, ATM and mutant p53 signaling. The role of FANCA depletion by AUY922 was examined using shRNA. Cell cycle checkpoint abrogation and chromosomal fragmentation was assessed by western blot, FACS and confocal. The role of ATM was also assessed by shRNA. AUY922 in combination with CCRT was assessed in vivo.

RESULTS

The combination of AUY922 with cisplatin, radiation and CCRT was found to be synergistic in p53 mutant HNSCC. AUY922 leads to significant alterations to the DDR induced by CCRT. This comprises inhibition of homologous recombination through decreased RAD51 and pS1524 BRCA1 with a corresponding increase in 53BP1 foci, activation of ATM and signaling into mutant p53. A shift to more error prone repair combined with a loss of checkpoint function leads to fragmentation of chromosomal material. The degree of disruption to DDR signalling correlated to chromosomal fragmentation and loss of clonogenicity. ATM shRNA indicated a possible rationale for the combination of AUY922 and CCRT in cells lacking ATM function.

CONCLUSIONS

This study supports future clinical studies combining AUY922 and CCRT in p53 mutant HNSCC. Modulation of the DDR and chromosomal fragmentation are likely to be analytical points of interest in such trials.