A common Chk1-dependent phenotype of DNA double-strand break suppression in two distinct radioresistant cancer types

DNA damage response in breast cancer and its significant role in guiding novel precise therapies

DNA damage response (DDR) deficiency has been one of the emerging targets in treating breast cancer in recent years. On the one hand, DDR coordinates cell cycle and signal transduction, whose dysfunction may lead to cell apoptosis, genomic instability, and tumor development. Conversely, DDR deficiency is an intrinsic feature of tumors that underlies their response to treatments that inflict DNA damage. In this review, we systematically explore various mechanisms of DDR, the rationale and research advances in DDR-targeted drugs in breast cancer, and discuss the challenges in its clinical applications. Notably, poly (ADP-ribose) polymerase (PARP) inhibitors have demonstrated favorable efficacy and safety in breast cancer with high homogenous recombination deficiency (HRD) status in a series of clinical trials. Moreover, several studies on novel DDR-related molecules are actively exploring to target tumors that become resistant to PARP inhibition. Before further clinical application of new regimens or drugs, novel and standardized biomarkers are needed to develop for accurately characterizing the benefit population and predicting efficacy. Despite the promising efficacy of DDR-related treatments, challenges of off-target toxicity and drug resistance need to be addressed. Strategies to overcome drug resistance await further exploration on DDR mechanisms, and combined targeted drugs or immunotherapy will hopefully provide more precise or combined strategies and expand potential responsive populations.

DNA damage response-related signatures characterize the immune landscape and predict the prognosis of HCC via integrating single-cell and bulk RNA-sequencing

BACKGROUND

The occurrence and progression of hepatocellular carcinoma (HCC) are significantly affected by DNA damage response (DDR). Exploring DDR-related biomarkers can help predict the prognosis and immune characteristics of HCC.

METHODS

First, the single-cell RNA sequencing (scRNA-seq) dataset GSE242889 was processed and performed manual annotation. Then we found the marker genes of DDR-active subgroups based on "AUCell" algorithm. The "Limma" R package was used to identify differentially expressed genes (DEGs) between tumor and normal samples of HCC. The risk prognostic model was constructed by filtering genes using univariate Cox and LASSO regression analyses. Finally, the signatures were analyzed for immune infiltration, gene mutation, and drug sensitivity. Last but not least, KPNA2, which had the largest coefficient in our model was validated by experiments including western blot, MTT, colony formation and γ-H2AX assays.

RESULTS

We constructed a prognostic model based on 5 DDR marker genes including KIF2C, CDC20, KPNA2, UBE2S and ADH1B for HCC. We also proved that the model had an excellent performance in both training and validation cohorts. Patients in the high-risk group had a poorer prognosis, different immune features, gene mutation frequency, immunotherapy response and drug sensitivity compared with the low-risk group. Besides, our experimental results proved that KPNA2 was up-regulated in liver cancer cells than in hepatocytes. More importantly, the knockdown of KPNA2 significantly inhibited cell variability, proliferation and promoted DNA damage.

CONCLUSIONS

We innovatively integrated scRNA-seq and bulk RNA sequencing to construct the DDR-related prognostic model. Our model could effectively predict the prognosis, immune landscape and therapy response of HCC.

Targeting K-Ras-mediated DNA damage response in radiation oncology: Current status, challenges and future perspectives

Approximately 60% of cancer patients receive curative or palliative radiation. Despite the significant role of radiotherapy (RT) as a curative approach for many solid tumors, tumor recurrence occurs, partially because of intrinsic radioresistance. Accumulating evidence indicates that the success of RT is hampered by activation of the DNA damage response (DDR). The intensity of DDR signaling is affected by multiple parameters, e.g., loss-of-function mutations in tumor suppressor genes, gain-of-function mutations in protooncogenes as well as radiation-induced alterations in signal-transduction pathways. Therefore, the response to irradiation differs in tumors of different types, which makes the individualization of RT as a rational but challenging goal. One contributor to tumor cell radiation survival is signaling through the Ras pathway. Three RAS genes encode 4 Ras isoforms: K-Ras4A, K-Ras4B, H-Ras, and N-Ras. RAS family members are found to be mutated in approximately 19% of human cancers. Mutations in RAS lead to constitutive activation of the gene product and activation of multiple Ras-dependent signal-transduction cascades. Preclinical studies have shown that the expression of mutant KRAS affects DDR and increases cell survival after irradiation. Approximately 70% of RAS mutations occur in KRAS. Thus, applying targeted therapies directly against K-Ras as well as K-Ras upstream activators and downstream effectors might be a tumor-specific approach to overcome K-Ras-mediated RT resistance. In this review, the role of K-Ras in the activation of DDR signaling will be summarized. Recent progress in targeting DDR in KRAS-mutated tumors in combination with radiochemotherapy will be discussed.

Natural Baicalein-Rich Fraction as Radiosensitizer in Combination with Bismuth Oxide Nanoparticles and Cisplatin for Clinical Radiotherapy

PURPOSE

Chemotherapy has been used in conjunction with radiation therapy to improve the treatment outcomes of cancers. Cisplatin (Cis) is a standard treatment that has been used as a chemotherapeutic drug in medical settings. However, the possibility of complications constrains the treatment due to the exposure of healthy organs to unnecessary radiation and the drugs' toxicities. As a result, researchers have been looking for non-toxic chemotherapeutic agents which can be used as radiosensitizers, possibly produced from natural derivatives and nano sized materials.

METHODS

BRF, Cis, and BiONPs were irradiated individually and in combinations with 6 MV of photon beam and 6 MeV of electron beams with 0 to 10 Gy radiation doses on MCF-7, MDA-MB-231, and NIH/3T3 cell lines. Then, the experimental sensitization enhancement ratios (SER) of each treatment obtained were compared to the theoretical dose enhancement factor (DEF). The interactions within the BRF-BiONPs (BB) and BRF-Cis-BiONPs (BCB) combinations were also estimated using the Combination Index (CI).

RESULTS

BRF induced radiosensitization in all cells under 6 MV photon beam (SER of 1.06 to 1.35), and MDA-MB-231 cells only under 6 MeV electron beam (SER = 1.20). The highest SER values for BiONPs and Cis were obtained from MCF-7 cells under a 6 MeV electron beam (SER of 1.50 and 2.24, respectively). The theoretical DEFs were generally lower than the experimental SERs. Based on the SER and CI relationships, it was estimated that BB and BCB therapy methods interacted in either a synergistic or additive manner.

CONCLUSION

The BRF is found to induce relatively less radiosensitization effects compared to the BiONPs and Cis. The BB and BCB combinations have shown better effects with potential for becoming competently suitable radiosensitizers in breast cancer therapies.

Oleanolic acid combined with olaparib enhances radiosensitization in triple negative breast cancer and hypoxia imaging with 18F-FETNIM micro PET/CT

The heterogeneity of triple negative breast cancer (TNBC) results in the worst prognosis among breast cancer types, making its treatment strategy very challenging. A recent study showed that oleanolic acid (OA) has a radiosensitizing effect on tumor cells, but it does not show a good clinical effect when used alone in radiotherapy. The cytotoxicity of radiotherapy can be enhanced by modulating DNA repair, so new treatment options are being investigated to inhibit DNA repair pathways and sensitize tumors to radiation. Radiation induces DNA double-strand breaks (DSBs), and inhibition of Poly (ADP-Ribose) polymerase (PARP) can prevent the repair of these lesions. Hence, we evaluated the radiosensitization and the underlying mechanism of combination treatment with OA and olaparib in TNBC. Meanwhile, tumor hypoxia was monitored with ¹⁸F-Fluoroerythronitroimidazole (FETNIM) positron emission tomography/computed tomography (PET/CT) during radiosensitization therapy. Here, we found that OA and olaparib in combination with radiotherapy significantly inhibited cell proliferation compared with other groups. The results were observed using colony formation assays [sensitization enhancement ratios (SER) 1.16-1.65]. In vivo, tumor growth was significantly delayed in transplanted tumors receiving irradiation (IR) with OA and olaparib. ¹⁸F-FETNIM PET/CT can be utilized for tumor hypoxia monitoring and radiosensitization response evaluation. In conclusion, these results suggest that the combination of OA and olaparib with IR enhances the inhibition of MDA-MB-231 in cell culture and in mice, providing a potentially novel combination for the effective treatment of TNBC patients.

Overview and Lessons From the Preclinical Chemoradiotherapy Testing Consortium

PURPOSE

In the current molecular-targeted cancer treatment era, many new agents are being developed so that optimizing therapy with a combination of radiation and drugs is complex. The use of emerging laboratory technologies to further biological understanding of drug-radiation mechanisms of action will enhance the efficiency of the progression from preclinical studies to clinical trials. In 2017, the National Cancer Institute (NCI) solicited proposals through PAR 16-111 to conduct preclinical research combining targeted anticancer agents in the Cancer Therapy Evaluation Program's portfolio with chemoradiation.

METHODS AND MATERIALS

The Preclinical Chemo-Radiotherapy Testing Consortium (PCRTC) was formed with 4 U01 programs supported to generate validated high-quality preclinical data on the effects of molecular therapeutics when added to standard-of-care therapies with a concentration on cancers of the pancreas, lung, head and neck, gastrointestinal tract, and brain.

RESULTS

The PCRTC provides a rational basis for prioritizing NCI-supported investigational new drugs or agents most likely to have clinical activity with chemoradiotherapy and accelerate the pace at which combined modality treatments with greater efficacy are identified and incorporated into standard treatment practices.

CONCLUSIONS

Herein, we introduce and summarize the course of the PCRTC to date and report 3 preliminary observations from the consortium's work to date.

Radiotherapy role in non-seminomatous germ cell tumors, radiobiological and technical issues of an unexplored scenario

Historically, non-seminomatous germ cell tumor (NSGCT) has been considered a radio-resistant disease, excluding radiotherapy (RT) from curative strategies. However, case series exploring the use of radiation treatment in this setting are often outdated, and prospective ongoing studies testing new radiotherapeutic approaches in NSGCT are lacking. Considering that tremendous advances in radiotherapy technology have enabled improved precision in RT delivery as well as dose escalation while decreasing treatment-related morbidity, we overviewed the currently available literature to explore the radiobiological basis, the technical issues, and potential strategies for implementation of RT in the management of this clinical entity. The purpose of the present overview is to provide insight for future research in this unexplored scenario. In summary, the biological rationale for RT use and potential implementation with systemic therapies exist, especially considering the advantage of new technologies, which were unavailable in the era of early literature reports. The NSGCT radioresistance paradigm could be based only on the fact that effective treatment schedules were simply undeliverable with older RT techniques due to toxicity issues, but the availability of actual techniques may prompt further exploration to offer treatment alternatives to these patients. Ongoing trials on this issue are lacking, but potential areas of research are platinum-refractory disease and consolidation therapy for residual masses after PST.

Contemporary radiotherapy: present and future

Oncology care is increasingly a multidisciplinary endeavour, and radiation therapy continues to have a key role across the disease spectrum in nearly every cancer. However, the field of radiation oncology is still one of the most poorly understood of the cancer disciplines. In this Review, we attempt to summarise and contextualise developments within the field of radiation oncology for the non-radiation oncologist. We discuss advancements in treatment technologies and imaging, followed by an overview of the interplay with advancements in systemic therapy and surgical techniques. Finally, we review new frontiers in radiation oncology, including advances within the metastatic disease continuum, reirradiation, and emerging types of radiation therapy.

Targeting the DNA replication stress phenotype of KRAS mutant cancer cells

Mutant KRAS is a common tumor driver and frequently confers resistance to anti-cancer treatments such as radiation. DNA replication stress in these tumors may constitute a therapeutic liability but is poorly understood. Here, using single-molecule DNA fiber analysis, we first characterized baseline replication stress in a panel of unperturbed isogenic and non-isogenic cancer cell lines. Correlating with the observed enhanced replication stress we found increased levels of cytosolic double-stranded DNA in KRAS mutant compared to wild-type cells. Yet, despite this phenotype replication stress-inducing agents failed to selectively impact KRAS mutant cells, which were protected by CHK1. Similarly, most exogenous stressors studied did not differentially augment cytosolic DNA accumulation in KRAS mutant compared to wild-type cells. However, we found that proton radiation was able to slow fork progression and preferentially induce fork stalling in KRAS mutant cells. Proton treatment also partly reversed the radioresistance associated with mutant KRAS. The cellular effects of protons in the presence of KRAS mutation clearly contrasted that of other drugs affecting replication, highlighting the unique nature of the underlying DNA damage caused by protons. Taken together, our findings provide insight into the replication stress response associated with mutated KRAS, which may ultimately yield novel therapeutic opportunities.

DNA damage response inhibitors: An avenue for TNBC treatment

The DNA damage response (DDR) is critical for the maintenance of genomic stability by sensing DNA damage, regulating cell cycle and initiating DNA repair. Drugs targeting DDR pathways have been increasingly exploited in treating various tumors. Triple negative breast cancer (TNBC) is a highly heterogeneous and aggressive tumor with constitutive activation of oncogenes, inducing replication stress and DNA damage, which require the DDR for survival. In addition, emerging studies have demonstrated that TNBC harbors aberrant genetic alterations in DDR pathways, such as a high frequency of p53 dysfunction and BRCA1/2 mutations. DDR alterations force TNBC to rely on the existing DDR pathways for survival, and make TNBC particularly sensitive to specific DDR inhibitors, such as high sensitivity of TNBC with BRCA1/2 mutations to PARP inhibitors. This review first and comprehensively covers the current status of the development of DDR inhibitors and discusses the mechanism of targeting the DDR in TNBC. Preclinical and clinical studies on inhibitors of the ATR-CHK1-WEE1 pathway and PARP inhibitors, the most studied inhibitors, and some other DDR inhibitors as monotherapy or combination therapy in TNBC are summarized. We also highlight the possible predictive biomarkers for these DDR inhibitors and their potential combination strategies with chemotherapy, radiotherapy or other targeted agents to optimize the efficacy of DDR inhibitors in TNBC treatment. In conclusion, this review discussed the recent considerations related to the use of DDR inhibitors for TNBC and provides a perspective to address future directions and potential therapeutic strategies for patients with TNBC.

Histone methylation can either promote or reduce cellular radiosensitivity by regulating DNA repair pathways

Radiotherapy is one of the primary modalities for cancer treatment, and its efficiency usually relies on cellular radiosensitivity. DNA damage repair is a core content of cellular radiosensitivity, and the primary mechanism of which includes non-homologous end-joining (NHEJ) and homologous recombination (HR). By affecting DNA damage repair, histone methylation regulated by histone methyltransferases (HMTs) and histone demethylases (HDMs) participates in the regulation of cellular radiosensitivity via three mechanisms: (a) recruiting DNA repair-related proteins, (b) regulating the expressions of DNA repair genes, and (c) mediating the dynamic change of chromatin. Interestingly, both aberrantly high and low levels of histone methylation could impede DNA repair processes. Here we reviewed the mechanisms of the dual effects of histone methylation on cell response to radiation. Since some inhibitors of HMTs and HDMs are reported to increase cellular radiosensitivity, understanding their molecular mechanisms may be helpful in developing new drugs for the therapy of radioresistant tumors.

Phosphatase POPX2 interferes with cell cycle by interacting with Chk1

Protein-protein interaction network analysis plays critical roles in predicting the functions of target proteins. In this study, we used a combination of SILAC-MS proteomics and bioinformatic approaches to identify Checkpoint Kinase 1 (Chk1) as a possible POPX2 phosphatase interacting protein. POPX2 is a PP2C phosphatase that has been implicated in cancer cell invasion and migration. From the Domain-Domain Interaction (DDI) database, we first determined that the PP2C phosphatase domain interacts with Pkinase domain. Subsequently, 46 proteins with Pkinase domain were identified from POPX2 SILAC-MS data. We then narrowed down the leads and confirmed the biological interaction between Chk1 and POPX2. We also found that Chk1 is a substrate of POPX2. Chk1 is a key regulator of the cell cycle and is activated when the cell suffers DNA damage. Our approach has led us to identify POPX2 as a regulator of Chk1 and can interfere with the normal function of Chk1 at G1-S transition of the cell cycle in response to DNA damage.

Radiosensitization Effects by Bismuth Oxide Nanoparticles in Combination with Cisplatin for High Dose Rate Brachytherapy

PURPOSE

The aim of this study was to investigate the potential of the synergetic triple therapeutic combination encompassing bismuth oxide nanoparticles (BiONPs), cisplatin (Cis), and high dose rate (HDR) brachytherapy with Ir-192 source in breast cancer and normal fibroblast cell line.

METHODS

In vitro models of breast cancer cell lines (MCF-7, MDA-MB-231) and normal fibroblast cell line (NIH/3T3) were employed. Cellular localization and cytotoxicity studies were conducted prior to inspection on the radiosensitization effects and generation of reactive oxygen species (ROS) on three proposed radiosensitizers: BiONPs, Cis, and BiONPs-Cis combination (BC). The optimal, non-cytotoxic concentration of BiONPs (0.5 mM) and the 25% inhibitory concentration of Cis (1.30 µM) were applied. The radiosensitization effects were evaluated by using a 0.38 MeV Iridium-192 HDR brachytherapy source over a prescribed dose range of 0 Gy to 4 Gy.

RESULTS

The cellular localization of BiONPs was visualized by light microscopy and accumulation of the BiONPs within the vicinity of the nuclear membrane was observed. Quantification of the sensitization enhancement ratio extrapolated from the survival curves indicates radiosensitization effects for MCF-7 and MDA-MB-231 when treated with BiONPs, Cis, and BC. However, NIH/3T3 cells exhibited contradictive behavior as it only reacted towards the BC combination. Nonetheless, the MCF-7 cell line loaded with BC shows the highest SER of 4.29. ROS production analysis, on the other hand, shows that Cis and BC radiosensitizers generated the highest free radicals in comparison to BiONPs alone.

CONCLUSION

A BiONPs-Cis combination was unveiled as a novel approach that offers promising radiosensitization enhancement that will increase the efficiency of tumor control while preserving the normal tissue at a reduced dose. This data is the first precedent to prove the synergetic implication of BiONPs, Cis, and HDR brachytherapy that will be beneficial for future chemoradiotherapy strategies in cancer care.