Tumor Suppressor CHK2: Regulator of DNA Damage Response and Mediator of Chromosomal Stability: Figure 1

Functional genomics reveals an off-target dependency of drug synergy in gastric cancer therapy

BACKGROUND

Integrating molecular-targeted agents into combination chemotherapy is transformative for enhancing treatment outcomes in cancer. However, realizing the full potential of this approach requires a clear comprehension of the genetic dependencies underlying drug synergy. While the interactions between conventional chemotherapeutics are well-explored, the interplay of molecular-targeted agents with conventional chemotherapeutics remains a frontier in cancer treatment. Hence, we leveraged a powerful functional genomics approach to decode genomic dependencies that drive synergy in molecular-targeted agent/chemotherapeutic combinations in gastric adenocarcinoma, addressing a critical need in gastric cancer therapy.

METHODS

We screened pharmacological interactions between fifteen molecular-targeted agent/conventional chemotherapeutic pairs in gastric adenocarcinoma cells, and examined the genome-scale genetic dependencies of synergy integrating genome-wide CRISPR screening with the shRNA-based signature assay. We validated the synergy in cell death using fluorescence-based and lysis-dependent inference of cell death kinetics assay, and validated the genetic dependencies by single-gene knockout experiments.

RESULTS

Our combination screen identified SN-38/erlotinib as the drug pair with the strongest synergism. Functional genomics assays unveiled a genetic dependency signature of SN-38/erlotinib identical to SN-38. Remarkably, the enhanced cell death with improved kinetics induced by SN-38/erlotinib was attributed to erlotinib's off-target effect, inhibiting ABCG2, rather than its on-target effect on EGFR.

CONCLUSION

In the era of precision medicine, where emphasis on primary drug targets prevails, our research challenges this paradigm by showcasing a robust synergy underpinned by an off-target dependency. Further dissection of the intricate genetic dependencies that underlie synergy can pave the way to developing more effective combination strategies in gastric cancer therapy.

PARP inhibitors in prostate cancers, is it time for combinations?

Despite several improvements in outcomes, metastatic prostate cancer remains deadly. Alterations in the homologous recombination repair (HRR) pathway are associated with more aggressive disease. Olaparib and rucaparib, two poly-ADP-ribose polymerase (PARP) inhibitors, have received approval from the authorities of several countries for their anti-tumoral effects in patients with metastatic castration-resistant prostate cancers harboring HRR gene alterations, in particular BRCA2. More recently, it has been hypothesized that new hormonal therapies (NHTs) and PARP inhibitors (PARPi) could have synergistic actions and act independently of HRR deficiency. This review proposes to discuss the advantages and disadvantages of PARPi used as monotherapy or in combination with NHTs and whether there is a need for molecular selection.

Research advances in the molecular classification of gastric cancer

Gastric cancer (GC) is a malignant tumor with one of the lowest five-year survival rates. Traditional first-line treatment regimens, such as platinum drugs, have limited therapeutic efficacy in treating advanced GC and significant side effects, greatly reducing patient quality of life. In contrast, trastuzumab and other immune checkpoint inhibitors, such as nivolumab and pembrolizumab, have demonstrated consistent and reliable efficacy in treating GC. Here, we discuss the intrinsic characteristics of GC from a molecular perspective and provide a comprehensive review of classification and treatment advances in the disease. Finally, we suggest several strategies based on the intrinsic molecular characteristics of GC to aid in overcoming clinical challenges in the development of precision medicine and improve patient prognosis.

CHEK2 deficiency increase the response to PD-1 inhibitors by affecting the tumor immune microenvironment

Immune checkpoint blockade (ICB) therapy has improved treatment effects in multiple cancers. Gene mutations in the DNA damage repair pathway (DDR) may cause genomic instability and may relate to the efficacy of ICB. Checkpoint kinase 2 (CHEK2) and polymerase epsilon (POLE) are important genes in the DDR. In this study, we aimed to study the impact of CHEK2 deficiency mutations on the response to ICB. We found that tumors with CHEK2 mutations had a significantly higher tumor mutational burden (TMB) compared to those with CHEK2-WT in a pancancer database. We noted that CHEK2 deficiency mutations potentiated the anti-tumor effect of anti-PD-1 therapy in MC38 and B16 tumor-bearing mice with the decrease of tumor volume and tumor weight after anti-PD-1 treatment. Mechanistically, CHEK2 deficiency tumors were with the increased cytotoxic CD8+ T-cell infiltration, especially cytotoxic CD8+ T cells, and modulated the tumor-immune microenvironment with an upregulated immune inflammatory pathway and antigen presentation pathway after anti-PD-1 treatment. Furthermore, murine models with POLE mutations confirmed that CHEK2 deficiency shaped similar mutational and immune landscapes as POLE mutations after anti-PD-1 treatment. Taken together, our results demonstrated that CHEK2 deficiency mutations may increase the response to ICB (eg. anti-PD-1) by influencing the tumor immune microenvironment. This indicated that CHEK2 deficiency mutations were a potentially predictive biomarker and CHEK2 deficiency may potentiate response to immunotherapy.

Uncovering Cell Cycle Dysregulations and Associated Mechanisms in Cancer and Neurodegenerative Disorders: A Glimpse of Hope for Repurposed Drugs

The cell cycle is the sequence of events orchestrated by a complex network of cell cycle proteins. Unlike normal cells, mature neurons subsist in a quiescent state of the cell cycle, and aberrant cell cycle activation triggers neuronal death accompanied by neurodegeneration. The periodicity of cell cycle events is choreographed by various mechanisms, including DNA damage repair, oxidative stress, neurotrophin activity, and ubiquitin-mediated degradation. Given the relevance of cell cycle processes in cancer and neurodegeneration, this review delineates the overlapping cell cycle events, signaling pathways, and mechanisms associated with cell cycle aberrations in cancer and the major neurodegenerative disorders. We suggest that dysregulation of some common fundamental signaling processes triggers anomalous cell cycle activation in cancer cells and neurons. We discussed the possible use of cell cycle inhibitors for neurodegenerative disorders and described the associated challenges. We propose that a greater understanding of the common mechanisms driving cell cycle aberrations in cancer and neurodegenerative disorders will open a new avenue for the development of repurposed drugs.

In silico and structure-based evaluation of deleterious mutations identified in human Chk1, Chk2, and Wee1 protein kinase

Checkpoint kinases Chk1, Chk2, Wee1 are playing a key role in DNA damage response and genomic integrity. Cancer-associated mutations identified in human Chk1, Chk2, and Wee1 were retrieved to understand the function associated with the mutation and also alterations in the folding pattern. Therefore, an attempt has been made to identify deleterious effect of variants using in silico and structure-based approach. Variants of uncertain significance for Chk1, Chk2, and Wee1 were retrieved from different databases and four prediction servers were employed to predict pathogenicity of mutations. Further, Interpro, I-Mutant 3.0, Consurf, TM-align, and have (y)our protein explained were used for comprehensive study of the deleterious effects of variants. The sequences of Chk1, Chk2, and Wee1 were analyzed using Clustal Omega, and the three-dimensional structures of the proteins were aligned using TM-align. The molecular dynamics simulations were performed to explore the differences in folding pattern between Chk1, Chk2, Wee1 wild-type, and mutant protein and also to evaluate the structural integrity. Thirty-six variants in Chk1, 250 Variants in Chk2, and 29 in Wee1 were categorized as pathogenic using in silico prediction tools. Furthermore, 25 mutations in Chk1, 189 in Chk2, and 14 in Wee1 were highly conserved, possessing deleterious effect and also influencing the protein structure and function. These identified mutations may provide underlying genetic intricacies to serve as potential targets for therapeutic inventions and clinical management.

Functional genomics reveals an off-target dependency of drug synergy in gastric cancer therapy

The rational combination of anticancer agents is critical to improving patient outcomes in cancer. Nonetheless, most combination regimens in the clinic result from empirical methodologies disregarding insight into the mechanism of action and missing the opportunity to improve therapy outcomes incrementally. Deciphering the genetic dependencies and vulnerabilities responsible for synergistic interactions is crucial for rationally developing effective anticancer drug combinations. Hence, we screened pairwise pharmacological interactions between molecular-targeted agents and conventional chemotherapeutics and examined the genome-scale genetic dependencies in gastric adenocarcinoma cell models. Since this type of cancer is mainly chemoresistant and incurable, clinical situations demand effective combination strategies. Our pairwise combination screen revealed SN38/erlotinib as the drug pair with the most robust synergism. Genome-wide CRISPR screening and a shRNA-based signature assay indicated that the genetic dependency/vulnerability signature of SN38/erlotinib is the same as SN38 alone. Additional investigation revealed that the enhanced cell death with improved death kinetics caused by the SN38/erlotinib combination is surprisingly due to erlotinib's off-target effect that inhibits ABCG2 but not its on-target effect on EGFR. Our results confirm that a genetic dependency signature different from the single-drug application may not be necessary for the synergistic interaction of molecular-targeted agents with conventional chemotherapeutics in gastric adenocarcinoma. The findings also demonstrated the efficacy of functional genomics approaches in unveiling biologically validated mechanisms of pharmacological interactions.

Maintaining Genome Integrity: Protein Kinases and Phosphatases Orchestrate the Balancing Act of DNA Double-Strand Breaks Repair in Cancer

DNA double-strand breaks (DSBs) are the most lethal DNA damages which lead to severe genome instability. Phosphorylation is one of the most important protein post-translation modifications involved in DSBs repair regulation. Kinases and phosphatases play coordinating roles in DSB repair by phosphorylating and dephosphorylating various proteins. Recent research has shed light on the importance of maintaining a balance between kinase and phosphatase activities in DSB repair. The interplay between kinases and phosphatases plays an important role in regulating DNA-repair processes, and alterations in their activity can lead to genomic instability and disease. Therefore, study on the function of kinases and phosphatases in DSBs repair is essential for understanding their roles in cancer development and therapeutics. In this review, we summarize the current knowledge of kinases and phosphatases in DSBs repair regulation and highlight the advancements in the development of cancer therapies targeting kinases or phosphatases in DSBs repair pathways. In conclusion, understanding the balance of kinase and phosphatase activities in DSBs repair provides opportunities for the development of novel cancer therapeutics.

Determinants of outcome following PSMA-based radioligand therapy and mechanisms of resistance in patients with metastatic castration-resistant prostate cancer

[177Lu]Lu-PSMA has recently been approved for use in the post-taxane, post-novel hormonal-agent setting in patients with metastatic castration-resistant prostate cancer. As a beta-emitting radioligand targeting prostate-specific membrane antigen (PSMA), it delivers radiation to cells expressing PSMA on their surface. In pivotal clinical trials, patients were selected for this treatment based on positron emission tomography (PET)/CT imaging, requiring PSMA-avid disease with no evidence of discordant disease on 2-[18F]fluoro-2-deoxy-D-glucose PET/CT or contrast CT scan. Despite exhibiting an optimal imaging phenotype, the response for many patients is not durable, and a minority do not respond to [177Lu]Lu-PSMA at all. Disease progression is inevitable even for those who achieve an exceptional initial response. Reasons for both primary and acquired resistance are largely unknown; however, they are likely due to the presence of underlying PSMA-negative disease not identified on imaging, molecular factors conferring radioresistance, and inadequate delivery of lethal radiation, particularly to sites of micrometastatic disease. Biomarkers are urgently needed to optimize patient selection for treatment with [177Lu]Lu-PSMA by identifying those who are most and least likely to respond. Retrospective data support using several prognostic and predictive baseline patient- and disease-related parameters; however, robust prospective data is required before these can be translated into widespread use. Further, early on-treatment clinical parameters (in addition to serial prostate-specific antigen [PSA] levels and conventional restaging imaging) may serve as surrogates for predicting treatment response. With little known about the efficacy of treatments given after [177Lu]Lu-PSMA, optimal treatment sequencing is paramount, and biomarker-driven patient selection will hopefully improve treatment and survival outcomes.

Advances in PARP Inhibitors for Prostate Cancer

Poly-adenosine diphosphate-ribose polymerase plays an essential role in cell function by regulating apoptosis, genomic stability and DNA repair. PARPi is a promising drug class that has gained significant traction in the last decade with good outcomes in different cancers. Several trials have sought to test its effectiveness in metastatic castration resistant prostate cancer (mCRPC). We conducted a comprehensive literature review to evaluate the current role of PARPi in this setting. To this effect, we conducted queries in the PubMed, Embase and Cochrane databases. We reviewed and compared all major contemporary publications on the topic. In particular, recent phase II and III studies have also demonstrated the benefits of olaparib, rucaparib, niraparib, talazoparib in CRPC. Drug effectiveness has been assessed through radiological progression or overall response. Given the notion of synthetic lethality and potential synergy with other oncological therapies, several trials are looking to integrate PARPi in combined therapies. There remains ongoing controversy on the need for genetic screening prior to treatment initiation as well as the optimal patient population, which would benefit most from PARPi. PARPi is an important asset in the oncological arsenal for mCRPC. New combinations with PARPi may improve outcomes in earlier phases of prostate cancer.

Application of the CDK9 inhibitor FIT-039 for the treatment of KSHV-associated malignancy

Chronic infection with Kaposi's sarcoma-associated herpes virus (KSHV) in B lymphocytes causes primary effusion lymphoma (PEL), the most aggressive form of KSHV-related cancer, which is resistant to conventional chemotherapy. In this study, we report that the BCBL-1 KSHV⁺ PEL cell line does not harbor oncogenic mutations responsible for its aggressive malignancy. Assuming that KSHV viral oncogenes play crucial roles in PEL proliferation, we examined the effect of cyclin-dependent kinase 9 (CDK9) inhibitor FIT-039 on KSHV viral gene expression and KSHV⁺ PEL proliferation. We found that FIT-039 treatment impaired the proliferation of KSHV⁺ PEL cells and the expression of KSHV viral genes in vitro. The effects of FIT-039 treatment on PEL cells were further evaluated in the PEL xenograft model that retains a more physiological environment for the growth of PEL growth and KSHV propagation, and we confirmed that FIT-039 administration drastically inhibited PEL growth in vivo. Our current study indicates that FIT-039 is a potential new anticancer drug targeting KSHV for PEL patients.

The Role of E3 Ligase Pirh2 in Disease

The p53-dependent ubiquitin ligase Pirh2 regulates a number of proteins involved in different cancer-associated processes. Targeting the p53 family proteins, Chk2, p27Kip1, Twist1 and others, Pirh2 participates in such cellular processes as proliferation, cell cycle regulation, apoptosis and cellular migration. Thus, it is not surprising that Pirh2 takes part in the initiation and progression of different diseases and pathologies including but not limited to cancer. In this review, we aimed to summarize the available data on Pirh2 regulation, its protein targets and its role in various diseases and pathological processes, thus making the Pirh2 protein a promising therapeutic target.

Reciprocal regulation of p21 and Chk1 controls the Cyclin D1-RB pathway to mediate senescence onset after G2 arrest

Senescence is an irreversible proliferation withdrawal that can be initiated after DNA damage-induced cell cycle arrest in G2 phase to prevent genomic instability. Senescence onset in G2 requires p53 and RB family tumour suppressors, but how they are regulated to convert a temporary cell cycle arrest into a permanent one remains unknown. Here, we show that a previously unrecognised balance between the CDK inhibitor p21 and Chk1 controls D-type cyclin-CDK activity during G2 arrest. In non-transformed cells, p21 activates RB in G2 by inhibiting Cyclin D1-CDK2/CDK4. The resulting G2 exit, which precedes appearance of senescence markers, is associated with a mitotic bypass, Chk1 downregulation and DNA damage foci reduction. In p53/RB-proficient cancer cells, compromised G2 exit correlates with sustained Chk1 activity, delayed p21 induction, untimely Cyclin E1 re-expression and genome reduplication. Conversely, Chk1 depletion promotes senescence by inducing p21 binding to Cyclin D1 and Cyclin E1-CDK complexes and down-regulating CDK6, whereas Chk2 knockdown enables RB phosphorylation and delays G2 exit. In conclusion, p21 and Chk2 oppose Chk1 to maintain RB activity, thus promoting DNA damage-induced senescence onset in G2.

PARP Inhibitors as Monotherapy in Daily Practice for Advanced Prostate Cancers

Despite recent improvements in survival, metastatic castration-resistant prostate cancers (mCRPCs) remain lethal. Alterations in genes involved in the homologous recombination repair (HRR) pathway are associated with poor prognosis. Poly-ADP-ribose polymerase (PARP) inhibitors (PARPis) have demonstrated anti-tumoral effects by synthetic lethality in patients with mCRPCs harboring HRR gene alterations, in particular BRCA2. While both olaparib and rucaparib have obtained government approvals for use, the selection of eligible patients as well as the prescription of these treatments within the clinical urology community are challenging. This review proposes a brief review of the rationale and outcomes of PARPi treatment, then a pragmatic vision of PARPi use in terms of prescription and the selection of patients based on molecular screening, which can involve potential genetic counseling in the case of associated germinal alterations.

Pancreatic Neuroendocrine Neoplasms: Updates on Genomic Changes in Inherited Tumour Syndromes and Sporadic Tumours Based on WHO Classification

Pancreatic neuroendocrine neoplasms (PanNENs) are the neuroendocrine neoplasms with greatest rate of increase in incidence. Approximately 10% of PanNENs arise as inherited tumour syndromes which include multiple endocrine neoplasia type 1, multiple endocrine neoplasia type 4, von Hippel-Lindau syndrome, neurofibromatosis type1, tuberous sclerosis complex 1/2, Cowden syndrome, and Glucagon cell hyperplasia and neoplasia as well as familial insulinomatosis. In sporadic PanNENs, driver mutations in MEN1, DAXX/ATRX and mTOR pathway genes are associated with development and progression in pancreatic neuroendocrine tumours. The other changes are in VEGF pathway, Notch pathway, germline mutations in MUTYH, CHEK2, BRCA2, PHLDA3 as well as other genetic alterations. On the other hand, pancreatic neuroendocrine carcinomas share similar genetic alterations with ductal adenocarcinomas, e.g., TP53, RB1 or KRAS. In addition, microRNA and changes in immune microenvironment were noted in PanNENs. Updates on these genetic knowledges contribute to the development of management strategies for patients with PanNENs.

Susceptibility Genes and Chromosomal Regions Associated With Non-Syndromic Familial Non-Medullary Thyroid Carcinoma: Some Pathogenetic and Diagnostic Keys

Thyroid cancer is the malignant tumor that is increasing most rapidly in the world, mainly at the expense of sporadic papillary thyroid carcinoma. The somatic alterations involved in the pathogenesis of sporadic follicular cell derived tumors are well recognized, while the predisposing alterations implicated in hereditary follicular tumors are less well known. Since the genetic background of syndromic familial non-medullary carcinoma has been well established, here we review the pathogenesis of non-syndromic familial non-medullary carcinoma emphasizing those aspects that may be useful in clinical and pathological diagnosis. Non-syndromic familial non-medullary carcinoma has a complex and heterogeneous genetic basis involving several genes and loci with a monogenic or polygenic inheritance model. Most cases are papillary thyroid carcinoma (classic and follicular variant), usually accompanied by benign thyroid nodules (follicular thyroid adenoma and/or multinodular goiter). The possible diagnostic and prognostic usefulness of the changes in the expression and/or translocation of various proteins secondary to several mutations reported in this setting requires further confirmation. Given that non-syndromic familial non-medullary carcinoma and sporadic non-medullary thyroid carcinoma share the same morphology and somatic mutations, the same targeted therapies could be used at present, if necessary, until more specific targeted treatments become available.

Mitotic and DNA Damage Response Proteins: Maintaining the Genome Stability and Working for the Common Good

Cellular function is highly dependent on genomic stability, which is mainly ensured by two cellular mechanisms: the DNA damage response (DDR) and the Spindle Assembly Checkpoint (SAC). The former provides the repair of damaged DNA, and the latter ensures correct chromosome segregation. This review focuses on recently emerging data indicating that the SAC and the DDR proteins function together throughout the cell cycle, suggesting crosstalk between both checkpoints to maintain genome stability.

Proliferation Cycle Transcriptomic Signatures are Strongly associated With Gastric Cancer Patient Survival

Gastric cancer is one of the most heterogeneous tumors with multi-level molecular disturbances. Sustaining proliferative signaling and evading growth suppressors are two important hallmarks that enable the cancer cells to become tumorigenic and ultimately malignant, which enable tumor growth. Discovering and understanding the difference in tumor proliferation cycle phenotypes can be used to better classify tumors, and provide classification schemes for disease diagnosis and treatment options, which are more in line with the requirements of today's precision medicine. We collected 691 eligible samples from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) database, combined with transcriptome data, to explore different heterogeneous proliferation cycle phenotypes, and further study the potential genomic changes that may lead to these different phenotypes in this study. Interestingly, two subtypes with different clinical and biological characteristics were identified through cluster analysis of gastric cancer transcriptome data. The repeatability of the classification was confirmed in an independent Gene Expression Omnibus validation cohort, and consistent phenotypes were observed. These two phenotypes showed different clinical outcomes, and tumor mutation burden. This classification helped us to better classify gastric cancer patients and provide targeted treatment based on specific transcriptome data.

MicroRNAs and the DNA damage response: How is cell fate determined?

It is becoming clear that the DNA damage response orchestrates an appropriate response to a given level of DNA damage, whether that is cell cycle arrest and repair, senescence or apoptosis. It is plausible that the alternative regulation of the DNA damage response (DDR) plays a role in deciding cell fate following damage. MicroRNAs (miRNAs) are associated with the transcriptional regulation of many cellular processes. They have diverse functions, affecting, presumably, all aspects of cell biology. Many have been shown to be DNA damage inducible and it is conceivable that miRNA species play a role in deciding cell fate following DNA damage by regulating the expression and activation of key DDR proteins. From a clinical perspective, miRNAs are attractive targets to improve cancer patient outcomes to DNA-damaging chemotherapy. However, cancer tissue is known to be, or to become, well adapted to DNA damage as a means of inducing chemoresistance. This frequently results from an altered DDR, possibly owing to miRNA dysregulation. Though many studies provide an overview of miRNAs that are dysregulated within cancerous tissues, a tangible, functional association is often lacking. While miRNAs are well-documented in 'ectopic biology', the physiological significance of endogenous miRNAs in the context of the DDR requires clarification. This review discusses miRNAs of biological relevance and their role in DNA damage response by potentially 'fine-tuning' the DDR towards a particular cell fate in response to DNA damage. MiRNAs are thus potential therapeutic targets/strategies to limit chemoresistance, or improve chemotherapeutic efficacy.

Cellular Senescence in Traumatic Brain Injury: Evidence and Perspectives

Mild traumatic brain injury (mTBI) can lead to long-term neurological dysfunction and increase one's risk of neurodegenerative disease. Several repercussions of mTBI have been identified and well-studied, including neuroinflammation, gliosis, microgliosis, excitotoxicity, and proteinopathy – however the pathophysiological mechanisms activating these pathways after mTBI remains controversial and unclear. Emerging research suggests DNA damage-induced cellular senescence as a possible driver of mTBI-related sequalae. Cellular senescence is a state of chronic cell-cycle arrest and inflammation associated with physiological aging, mood disorders, dementia, and various neurodegenerative pathologies. This narrative review evaluates the existing studies which identify DNA damage or cellular senescence after TBI (including mild, moderate, and severe TBI) in both experimental animal models and human studies, and outlines how cellular senescence may functionally explain both the molecular and clinical manifestations of TBI. Studies on this subject clearly show accumulation of various forms of DNA damage (including oxidative damage, single-strand breaks, and double-strand breaks) and senescent cells after TBI, and indicate that cellular senescence may be an early event after TBI. Further studies are required to understand the role of sex, cell-type specific mechanisms, and temporal patterns, as senescence may be a pathway of interest to target for therapeutic purposes including prognosis and treatment.

Germline mutations in a DNA repair pathway are associated with familial colorectal cancer

Aiming to identify rare high-penetrance mutations in new genes for the underlying predisposition in familial colorectal cancer (CRC), we performed whole-exome sequencing in 24 familial CRCs. Mutations in genes that regulate DNA repair (RMI1, PALB2, FANCI) were identified that were related to the Fanconi anemia DNA repair pathway. In one pedigree, we found a nonsense mutation in CHEK2. CHEK2 played an essential role in cell cycle and DNA damage repair. Somatic mutation analysis in CHEK2 variant carriers showed mutations in TP53, APC, and FBXW7. Loss of heterozygosity was found in carcinoma of CHEK2 variant carrier, and IHC showed loss of Chk2 expression in cancer tissue. We identified a second variant in CHEK2 in 126 sporadic CRCs. A KO cellular model for CHEK2 (CHEK2^KO) was generated by CRISPR/Cas9. Functional experiments demonstrated that CHEK2^KO cells showed defective cell cycle arrest and apoptosis, as well as reduced p53 phosphorylation, upon DNA damage. We associated germline mutations in genes that regulate the DNA repair pathway with the development of CRC. We identified CHEK2 as a regulator of DNA damage response and perhaps as a gene involved in CRC germline predisposition. These findings link CRC predisposition to the DNA repair pathway, supporting the connection between genome integrity and cancer risk.

DNA damage response and repair in pancreatic cancer development and therapy

Pancreatic cancer (PC) is among fatal malignancies, with a dismal prognosis and a low survival rate of 5-10%. In both sporadic and inherited PC, gene alterations, such as BRCA1/2, PALB2, and ATM, can occur frequently. Currently, surgery, chemo- and radio-therapy are the most common therapeutic strategies for treating this cancer. DNA damage response (DDR) establishes multiple pathways that eliminate DNA damage sites to maintain genomic integrity. Various types of cancers and age-related diseases are associated with DDR machinery defects. According to the severity of the damage, DDR pathways respond appropriately to lesions through repairing damage, arresting the cell cycle, or apoptosis. Recently, novel agents, particularly those targeting DDR pathways, are being utilized to improve the response of many cancers to chemotherapy and radiotherapy. In this paper, we briefly reviewed DDR processes and their components, including DDR sensors, DDR mediators, and DDR transducers in the progression, prognosis, and treatment of PC.

Prostate cancer and PARP inhibitors: progress and challenges

Despite survival improvements achieved over the last two decades, prostate cancer remains lethal at the metastatic castration-resistant stage (mCRPC) and new therapeutic approaches are needed. Germinal and/or somatic alterations of DNA-damage response pathway genes are found in a substantial number of patients with advanced prostate cancers, mainly of poor prognosis. Such alterations induce a dependency for single strand break reparation through the poly(adenosine diphosphate-ribose) polymerase (PARP) system, providing the rationale to develop PARP inhibitors. In solid tumors, the first demonstration of an improvement in overall survival was provided by olaparib in patients with mCRPC harboring homologous recombination repair deficiencies. Although this represents a major milestone, a number of issues relating to PARP inhibitors remain. This timely review synthesizes and discusses the rationale and development of PARP inhibitors, biomarker-based approaches associated and the future challenges related to their prescription as well as patient pathways.

DNA damage repair as a target in pancreatic cancer: state-of-the-art and future perspectives

Complex rearrangement patterns and mitotic errors are hallmarks of most pancreatic ductal adenocarcinomas (PDAC), a disease with dismal prognosis despite some therapeutic advances in recent years. DNA double-strand breaks (DSB) bear the greatest risk of provoking genomic instability, and DNA damage repair (DDR) pathways are crucial in preserving genomic integrity following a plethora of damage types. Two major repair pathways dominate DSB repair for safeguarding the genome integrity: non-homologous end joining and homologous recombination (HR). Defective HR, but also alterations in other DDR pathways, such as BRCA1, BRCA2, ATM and PALB2, occur frequently in both inherited and sporadic PDAC. Personalised treatment of pancreatic cancer is still in its infancy and predictive biomarkers are lacking. DDR deficiency might render a PDAC vulnerable to a potential new therapeutic intervention that increases the DNA damage load beyond a tolerable threshold, as for example, induced by poly (ADP-ribose) polymerase inhibitors. The Pancreas Cancer Olaparib Ongoing (POLO) trial, in which olaparib as a maintenance treatment improved progression-free survival compared with placebo after platinum-based induction chemotherapy in patients with PDAC and germline BRCA1/2 mutations, raised great hopes of a substantially improved outcome for this patient subgroup. This review summarises the relationship between DDR and PDAC, the prevalence and characteristics of DNA repair mutations and options for the clinical management of patients with PDAC and DNA repair deficiency.

Concurrent germline BRCA1, BRCA2, and CHEK2 pathogenic variants in hereditary breast cancer: a case series

Background

Concurrent germline (g) pathogenic variants related to hereditary breast cancer represent a rare occurrence. While double heterozygosity in gBRCA1 and gBRCA2 has been reported in the past, herein we describe the first case of three known concurrent pathogenic variants identified in a family with a strong history of breast cancer.

Case presentation

The proband is a 55-year-old female diagnosed with synchronous bilateral breast cancers. She underwent a multi-gene panel testing indicating the presence of 3 concurrent heterozygous germline deleterious variants in BRCA1 (c.181T > G), BRCA2 (c.4398_4402delACATT), and CHEK2 (1100delC). The patient’s two daughters (34 and 29 years-old) were found to be transheterozygous for inherited pathogenic variants in BRCA1 (c.181T > G) and CHEK2 (1100delC) genes.

Conclusion

The cancer risk and phenotypic manifestations associated with transheterozygous or multiple concurrent deleterious germline variants in hereditary breast cancer requires further investigation. A personalized approach to counseling, screening, and risk reduction should be undertaken for these individuals.

Natural podophyllotoxin analog 4DPG attenuates EMT and colorectal cancer progression via activation of checkpoint kinase 2

Epithelial–mesenchymal transition (EMT) is critical for the metastatic dissemination of cancer cells and contributes to drug resistance. In this study, we observed that epithelial colorectal cancer (CRC) cells transiently exposed to 5-fluorouracil (5-FU) (a chemotherapeutic drug for CRC) as well as 5-FU-resistant cells (5-FU-R) develop EMT characters as evidenced by activation of Vimentin and augmented invasive properties. On the other hand, 4DPG (4′-demethyl-deoxypodophyllotoxin glucoside), a natural podophyllotoxin analog attenuates EMT and invadopodia formation abilities of HCT-116/5-FU-R and SW-620/5-FU-R cells. Treatment with 4DPG restrains Vimentin phosphorylation (Ser38) in 5-FU-R cells, along with downregulation of mesenchymal markers Twist1 and MMP-2 while augmenting the expression of epithelial markers E-cadherin and TIMP-1. Moreover, 4DPG boosts the tumor-suppressor protein, checkpoint kinase 2 (Chk2) via phosphorylation at Thr68 in a dose-dependent manner in 5-FU-R cells. Mechanistically, SiRNA-mediated silencing of Chk2, as well as treatment with Chk2-specific small-molecule inhibitor (PV1019), divulges that 4DPG represses Vimentin activation in a Chk2-dependent manner. Furthermore, immunoprecipitation analysis unveiled that 4DPG prevents complex formation between Vimentin and p53 resulting in the rescue of p53 and its nuclear localization in aggressive 5-FU-R cells. In addition, 4DPG confers suitable pharmacokinetic properties and strongly abrogates tumor growth, polyps formation, and lung metastasis in an orthotopic rat colorectal carcinoma model. In conclusion, our findings demonstrate 4DPG as a targeted antitumor/anti-metastatic pharmacological lead compound to circumvent EMT-associated drug resistance and suggest its clinical benefits for the treatment of aggressive cancers.

CHEK2 Germline Variants in Cancer Predisposition: Stalemate Rather than Checkmate

Germline alterations in many genes coding for proteins regulating DNA repair and DNA damage response (DDR) to DNA double-strand breaks (DDSB) have been recognized as pathogenic factors in hereditary cancer predisposition. The ATM-CHEK2-p53 axis has been documented as a backbone for DDR and hypothesized as a barrier against cancer initiation. However, although CHK2 kinase coded by the CHEK2 gene expedites the DDR signal, its function in activation of p53-dependent cell cycle arrest is dispensable. CHEK2 mutations rank among the most frequent germline alterations revealed by germline genetic testing for various hereditary cancer predispositions, but their interpretation is not trivial. From the perspective of interpretation of germline CHEK2 variants, we review the current knowledge related to the structure of the CHEK2 gene, the function of CHK2 kinase, and the clinical significance of CHEK2 germline mutations in patients with hereditary breast, prostate, kidney, thyroid, and colon cancers.

When Endoplasmic Reticulum Proteostasis Meets the DNA Damage Response

Sustaining both proteome and genome integrity (GI) requires the integration of a wide range of mechanisms and signaling pathways. These comprise, in particular, the unfolded protein response (UPR) and the DNA damage response (DDR). These adaptive mechanisms take place respectively in the endoplasmic reticulum (ER) and in the nucleus. UPR and DDR alterations are associated with aging and with pathologies such as degenerative diseases, metabolic and inflammatory disorders, and cancer. We discuss the emerging signaling crosstalk between UPR stress sensors and the DDR, as well as their involvement in cancer biology.

Proteome-scale analysis of phase-separated proteins in immunofluorescence images

Phase separation is an important mechanism that mediates the spatial distribution of proteins in different cellular compartments. While phase-separated proteins share certain sequence characteristics, including intrinsically disordered regions (IDRs) and prion-like domains, such characteristics are insufficient for making accurate predictions; thus, a proteome-wide understanding of phase separation is currently lacking. Here, we define phase-separated proteomes based on the systematic analysis of immunofluorescence images of 12 073 proteins in the Human Protein Atlas. The analysis of these proteins reveals that phase-separated candidate proteins exhibit higher IDR contents, higher mean net charge and lower hydropathy and prefer to bind to RNA. Kinases and transcription factors are also enriched among these candidate proteins. Strikingly, both phase-separated kinases and phase-separated transcription factors display significantly reduced substrate specificity. Our work provides the first global view of the phase-separated proteome and suggests that the spatial proximity resulting from phase separation reduces the requirement for motif specificity and expands the repertoire of substrates. The source code and data are available at https://github.com/cheneyyu/deepphase.

CHK2 is essential for spindle assembly and DNA repair during the first cleavage of mouse embryos

The quality of the early embryo is critical for embryonic development and implantation. Errors during cleavage lead to aneuploidy in embryos. As a cell cycle checkpoint protein, CHK2 participates in DNA replication, cell cycle arrest and spindle assembly. However, the functions of CHK2 in early development of the mouse embryo remain largely unknown. In this study, we show that CHK2 is localized on the spindle in metaphase and mainly accumulates at spindle poles in anaphase/telophase during the first cleavage of the mouse embryo. CHK2 inhibition led to cleavage failure in early embryonic development, accompanied by abnormal spindle assembly and misaligned chromosomes. Moreover, the loss of CHK2 activity increased the level of cellular DNA damage, which resulted in oxidative stress. Then, apoptosis and autophagy were found to be active in these embryos. In summary, our results suggest that CHK2 is an essential regulator of spindle assembly and DNA repair during early embryonic development in mice.

Patients Resistant Against PSMA-Targeting α-Radiation Therapy Often Harbor Mutations in DNA Damage-Repair-Associated Genes

Prostate-specific membrane antigen (PSMA)-targeting α-radiation therapy (TAT) is an emerging treatment modality for metastatic castration-resistant prostate cancer. There is a subgroup of patients with poor response despite sufficient expression of PSMA in their tumors. The aim of this work was to characterize PSMA-TAT-nonresponding lesions by targeted next-generation sequencing. Methods: Of 60 patients treated with ²²⁵Ac-PSMA-617, we identified 10 patients who presented with a poor response despite sufficient tumor uptake in PSMA PET/CT. We were able to perform CT-guided biopsies with histologic validation of the nonresponding lesions in 7 of these nonresponding patients. Specimens were analyzed by targeted next-generation sequencing interrogating 37 DNA damage-repair-associated genes. Results: In the 7 tumor samples analyzed, we found a total of 15 whole-gene deletions, deleterious or presumably deleterious mutations affecting TP53 (n = 3), CHEK2 (n = 2), ATM (n = 2), and BRCA1, BRCA2, PALB2, MSH2, MSH6, NBN, FANCB, and PMS1 (n = 1 each). The average number of deleterious or presumably deleterious mutations was 2.2 (range, 0-6) per patient. In addition, several variants of unknown significance in ATM, BRCA1, MSH2, SLX4, ERCC, and various FANC genes were detected. Conclusion: Patients with resistance to PSMA-TAT despite PSMA positivity frequently harbor mutations in DNA damage-repair and checkpoint genes. Although the causal role of these alterations in the patient outcome remains to be determined, our findings encourage future studies combining PSMA-TAT and DNA damage-repair-targeting agents such as poly(ADP-ribose)-polymerase inhibitors.

A new insight into the apoptotic effect of nitidine chloride targeting Checkpoint kinase 2 in human cervical cancer in vitro

Nitidine chloride (NC), a natural, bioactive, phytochemical alkaloid derived from the roots of Zanthoxylum nitidum, has been reported to exhibit anti-tumor activity against various types of cancer. However, the potential therapeutic role of NC in human cervical cancer has not yet been studied. We are the first to report that NC acts as a potential apoptosis-inducing agent for human cervical cancer in vitro. NC treatment of human cervical cancer cell lines induced caspase-mediated apoptosis, thereby reducing cell viability. Phospho-kinase proteome profiling using a human phospho-kinase array revealed that NC treatment phosphorylated Checkpoint kinase 2 (Chk2) at Thr68, which activates Chk2 in both cell lines. We also found that NC significantly affected the p53/Bim signaling axis, which was accompanied by mitochondrial membrane depolarization and cytochrome c release from the mitochondria into the cytosol. In addition, NC profoundly increased phosphorylation of the histone variant H2AX at Ser139, a typical marker of DNA damage. Taken together, these results provide in vitro evidence that NC can increase Chk2 activation, thereby acting as an attractive cell death inducer for treatment of human cervical cancer.

Unusual lymphoid malignancy and treatment response in two children with Down syndrome

BACKGROUND

Lymphoid malignancies other than acute lymphoblastic leukemia (ALL) are rare in children with Down syndrome (DS). Information about the toxicity of chemotherapy and prognosis is largely derived from the experience of children with DS and ALL or children without DS.

PROCEDURE

We describe the treatment and outcome of two unusual lymphoid malignancies in children with DS. One patient was diagnosed with Burkitt lymphoma (BL) and the second, after treatment for B precursor ALL, with T-cell EBV-positive proliferative disorder (LPD).

RESULTS

BL was treated with standard doses of LMB group B therapy subsequently intensified to group C therapy, including high-dose methotrexate (HD-MTX, 3-8 g/m² ). The patient did not experience excessive toxicity and remains in complete remission 13 months later. Despite presentation with disseminated disease the patient with T-cell EBV-positive LPD after treatment for B precursor ALL responded to dexamethasone and rituximab and remains in complete remission two years later.

CONCLUSIONS

Upfront reduction of the high treatment intensity, which is associated with excellent survival outcomes in BL, may not be warranted in all children with DS. Response to therapy and prognosis of T-cell EBV-positive LPD in a patient with DS was not predicted by reported experience in the absence of DS.

USP39 regulates DNA damage response and chemo-radiation resistance by deubiquitinating and stabilizing CHK2

The serine/threonine kinase, CHK2 (checkpoint kinase 2), is a key mediator in DNA damage response and a tumor suppressor, which is implicated in promoting cell cycle arrest, apoptosis and DNA repair. Accumulating evidence suggests that these functions are primarily exerted through phosphorylation downstream factors such as p53 and BRCA1. Recent studies have shown that ubiquitination is an important mode of regulation of CHK2. However, it remains largely unclear whether deubiquitinases participate in regulation of CHK2. Here, we report that a deubiquitinase, USP39, is a new regulator of CHK2. Mechanistically, USP39 deubiquitinates and stabilizes CHK2, which in turn enhances CHK2 stability. Short hairpin RNA (shRNA) mediated knockdown of USP39 led to deregulate CHK2, which resulted in compromising the DNA damage-induced G2/M checkpoint, decreasing apoptosis, and conferring cancer cells resistance to chemotherapy drugs and radiation treatment. Collectively, we identify USP39 as a novel regulator of CHK2 in the DNA damage response.

The TIA1 RNA-Binding Protein Family Regulates EIF2AK2-Mediated Stress Response and Cell Cycle Progression

TIA1 and TIAL1 encode a family of U-rich element mRNA-binding proteins ubiquitously expressed and conserved in metazoans. Using PAR-CLIP, we determined that both proteins bind target sites with identical specificity in 3' UTRs and introns proximal to 5' as well as 3' splice sites. Double knockout (DKO) of TIA1 and TIAL1 increased target mRNA abundance proportional to the number of binding sites and also caused accumulation of aberrantly spliced mRNAs, most of which are subject to nonsense-mediated decay. Loss of PRKRA by mis-splicing triggered the activation of the double-stranded RNA (dsRNA)-activated protein kinase EIF2AK2/PKR and stress granule formation. Ectopic expression of PRKRA cDNA or knockout of EIF2AK2 in DKO cells rescued this phenotype. Perturbation of maturation and/or stability of additional targets further compromised cell cycle progression. Our study reveals the essential contributions of the TIA1 protein family to the fidelity of mRNA maturation, translation, and RNA-stress-sensing pathways in human cells.

Whole-transcriptomic Profile of SK-MEL-3 Melanoma Cells Treated with the Histone Deacetylase Inhibitor: Trichostatin A

BACKGROUND

Malignant melanoma cells can rapidly acquire phenotypic properties making them resistant to radiation and mainline chemotherapies such as decarbonize or kinase inhibitors that target RAS-proto-oncogene independent auto-activated mitogen-activated protein kinases (MAPK)/through dual specificity mitogen-activated protein kinase (MEK). Both drug resistance and inherent transition from melanocytic nevi to malignant melanoma involve the overexpression of histone deacetylases (HDACs) and a B-Raf proto-oncogene (BRAF) mutation.

MATERIALS AND METHODS

In this work, the effects of an HDAC class I and II inhibitor trichostatin A (TSA) on the whole transcriptome of SK-MEL-3 cells carrying a BRAF mutation was examined.

RESULTS

The data obtained show that TSA was an extremely potent HDAC inhibitor within SK-MEL-3 nuclear lysates, where TSA was then optimized for appropriate sub-lethal concentrations for in vitro testing. The whole-transcriptome profile shows a basic phenotype dominance in the SK-MEL-3 cell line for i) synthesis of melanin, ii) phagosome acidification, iii) ATP hydrolysis-coupled proton pumps and iv) iron transport systems. While TSA did not affect the aforementioned major systems, it evoked a dramatic change to the transcriptome: reflected by a down-regulation of 810 transcripts and up-regulation of 833, with fold-change from -15.27 to +31.1 FC (p<0.00001). Largest differentials were found for the following transcripts: Up-regulated: Tetraspanin 13 (TSPAN13), serpin family i member 1 (SERPINI1), ATPase Na+/K+ transporting subunit beta 2 (ATP1B2), nicotinamide nucleotide adenylyl transferase 2 (NMNAT2), platelet-derived growth factor receptor-like (PDGFRL), cytochrome P450 family 1 subfamily A member 1 (CYP1A1), prostate androgen-regulated mucin-like protein 1 (PARM1), secretogranin II (SCG2), SYT11 (synaptotagmin 11), rhophilin associated tail protein 1 like (ROPN1L); down-regulated: polypeptide N-acetylgalactosaminyltransferase 3 (GALNT3), carbonic anhydrase 14 (CAXIV), BCL2-related protein A1 (BCL2A1), protein kinase C delta (PRKCD), transient receptor potential cation channel subfamily M member 1 (TRPM1), ubiquitin associated protein 1 like (UBAP1L), glutathione peroxidase 8 (GPX8), interleukin 16 (IL16), tumor protein p53 (TP53), and serpin family H member 1 (SERPINH1). There was no change to any of the HDAC transcripts (class I, II and IV), the sirtuin HDAC family (1-6) or the BRAF proto-oncogene v 599 transcripts. However, the data showed that TSA down-regulated influential transcripts that drive the BRAF-extracellular signal-regulated kinase (ERK)1/2 oncogenic pathway (namely PRKCD and MYC proto-oncogene which negatively affected the cell-cycle distribution. Mitotic inhibition was corroborated by functional pathway analysis and flow cytometry confirming halt at the G₂ phase, occurring in the absence of toxicity.

CONCLUSION

TSA does not alter HDAC transcripts nor BRAF itself, but down-regulates critical components of the MAPK/MEK/BRAF oncogenic pathway, initiating a mitotic arrest.

CHK2-mediated regulation of PARP1 in oxidative DNA damage response

Poly(ADP-ribose) polymerase 1 (PARP1) is a DNA damage sensor, which upon activation, recruits downstream proteins by poly(ADP-ribosyl)ation (PARylation). However, it remains largely unclear how PARP1 activity is regulated. Interestingly, the data obtained through this study revealed that PARP1 was co-immunoprecipitated with checkpoint kinase 2 (CHK2), and the interaction was increased after oxidative DNA damage. Moreover, CHK2 depletion resulted in a reduction in overall PARylation. To further explore the functional relationship between PARP1 and CHK2, this study employed H₂O₂ to induce an oxidative DNA damage response in cells. Here, we showed that CHK2 and PARP1 interact in vitro and in vivo through the CHK2 SCD domain and the PARP1 BRCT domain. Furthermore, CHK2 stimulates the PARylation activity of PARP1 through CHK2-dependent phosphorylation. Consequently, the impaired repair associated with PARP1 depletion could be rescued by re-expression of wild-type PARP1 and the phospho-mimic but not the phospho-deficient mutant. Mechanistically, we showed that CHK2-dependent phosphorylation of PARP1 not only regulates its cellular localization but also promotes its catalytic activity and its interaction with XRCC1. These findings indicate that CHK2 exerts a multifaceted impact on PARP1 in response to oxidative stress to facilitate DNA repair and to maintain cell survival.

Kaempferol Induces G2/M Cell Cycle Arrest via Checkpoint Kinase 2 and Promotes Apoptosis via Death Receptors in Human Ovarian Carcinoma A2780/CP70 Cells

Kaempferol is a widely distributed dietary flavonoid. Epidemiological studies have demonstrated kaempferol consumption lowers the risk of ovarian cancer. Our previous research proved that kaempferol suppresses human ovarian cancer cells by inhibiting tumor angiogenesis. However, the effects of kaempferol on the cell cycle and extrinsic apoptosis of ovarian cancer cells have not yet been studied. In the present study, we demonstrated that kaempferol induced G2/M cell cycle arrest via the Chk2/Cdc25C/Cdc2 pathway and Chk2/p21/Cdc2 pathway in human ovarian cancer A2780/CP70 cells. Chk2 was not responsible for kaempferol-induced apoptosis and up-regulation of p53. Kaempferol stimulated extrinsic apoptosis via death receptors/FADD/Caspase-8 pathway. Our study suggested that Chk2 and death receptors played important roles in the anticancer activity of kaempferol in A2780/CP70 cells. These findings provide more evidence of the anti-ovarian cancer properties of kaempferol and suggest that kaempferol could be a potential candidate for ovarian cancer adjuvant therapy.

Camptothecin induces G2/M phase arrest through the ATM-Chk2-Cdc25C axis as a result of autophagy-induced cytoprotection: Implications of reactive oxygen species

In the present study, we report that camptothecin (CPT) caused irreversible cell cycle arrest at the G₂/M phase, and was associated with decreased levels of cell division cycle 25C (Cdc25C) and increased levels of cyclin B1, p21, and phospho-H3. Interestingly, the reactive oxygen species (ROS) inhibitor, glutathione, decreased CPT-induced G₂/M phase arrest and moderately induced S phase arrest, indicating that the ROS is required for the regulation of CPT-induced G₂/M phase arrest. Furthermore, transient knockdown of nuclear factor-erythroid 2-related factor 2 (Nrf2), in the presence of CPT, increased the ROS’ level and further shifted the cell cycle from early S phase to the G₂/M phase, indicating that Nrf2 delayed the S phase in response to CPT. We also found that CPT-induced G₂/M phase arrest increased, along with the ataxia telangiectasia-mutated (ATM)-checkpoint kinase 2 (Chk2)-Cdc25C axis. Additionally, the proteasome inhibitor, MG132, restored the decrease in Cdc25C levels in response to CPT, and significantly downregulated CPT-induced G₂/M phase arrest, suggesting that CPT enhances G₂/M phase arrest through proteasome-mediated Cdc25C degradation. Our data also indicated that inhibition of extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) inhibited CPT-induced p21 and cyclin B1 levels; however, inhibition of ERK blocked CPT-induced G₂/M phase arrest, and inhibition of JNK enhanced apoptosis in response to CPT. Finally, we found that CPT-induced G₂/M phase arrest circumvented apoptosis by activating autophagy through ATM activation. These findings suggest that CPT-induced G₂/M phase arrest through the ROS-ATM-Chk2-Cdc25C axis is accompanied by the activation of autophagy.

Autophagy maintains stem cells and intestinal homeostasis in Drosophila

Intestinal homeostasis is maintained by tightly controlled proliferation and differentiation of tissue-resident multipotent stem cells during aging and regeneration, which ensures organismal adaptation. Here we show that autophagy is required in Drosophila intestinal stem cells to sustain proliferation, and preserves the stem cell pool. Autophagy-deficient stem cells show elevated DNA damage and cell cycle arrest during aging, and are frequently eliminated via JNK-mediated apoptosis. Interestingly, loss of Chk2, a DNA damage-activated kinase that arrests the cell cycle and promotes DNA repair and apoptosis, leads to uncontrolled proliferation of intestinal stem cells regardless of their autophagy status. Chk2 accumulates in the nuclei of autophagy-deficient stem cells, raising the possibility that its activation may contribute to the effects of autophagy inhibition in intestinal stem cells. Our study reveals the crucial role of autophagy in preserving proper stem cell function for the continuous renewal of the intestinal epithelium in Drosophila.

Low penetrance genetic polymorphisms as potential biomarkers for colorectal cancer predisposition

Colorectal cancer is a leading form of cancer in both males and females. Early detection of individuals at risk of colorectal cancer allows proper treatment and management of the disease to be implemented, which can potentially reduce the burden of colorectal cancer incidence, morbidity and mortality. In recent years, the role of genetic susceptibility factors in mediating predisposition to colorectal cancer has become more and more apparent. Identification of high-frequency, low-penetrance genetic polymorphisms associated with the cancer has therefore emerged as an important approach which can potentially aid prediction of colorectal cancer risk. However, the overwhelming amount of genetic epidemiology data generated over the past decades has made it difficult for one to assimilate the information and determine the exact genetic polymorphisms that can potentially be used as biomarkers for colorectal cancer. This review comprehensively consolidates, based primarily on results from meta-analyses, the recent progresses in the search of colorectal cancer-associated genetic polymorphisms, and discusses the possible mechanisms involved.

Regiospecific Synthesis of Ring A Fused Withaferin A Isoxazoline Analogues: Induction of Premature Senescence by W-2b in Proliferating Cancer Cells

Induction of premature senescence represents a novel functional strategy to curb the uncontrolled proliferation of malignant cancer cells. This study unveils the regiospecific synthesis of novel isoxazoline derivatives condensed to ring A of medicinal plant product Withaferin-A. Intriguingly, the cis fused products with β-oriented hydrogen exhibited excellent cytotoxic activities against proliferating human breast cancer MCF7 and colorectal cancer HCT-116 cells. The most potent derivative W-2b triggered premature senescence along with increase in senescence-associated β-galactosidase activity, G2/M cell cycle arrest, and induction of senescence-specific marker p21^Waf1/Cip1 at its sub-toxic concentration. W-2b conferred a robust increase in phosphorylation of mammalian checkpoint kinase-2 (Chk2) in cancer cells in a dose-dependent manner. Silencing of endogenous Chk2 by siRNA divulged that the amplification of p21 expression and senescence by W-2b was Chk2-dependent. Chk2 activation (either by ectopic overexpression or through treatment with W-2b) suppressed NM23-H1 signaling axis involved in cancer cell proliferation. Finally, W-2b showed excellent in vivo efficacy with 83.8% inhibition of tumor growth at a dose of 25 mg/kg, b.w. in mouse mammary carcinoma model. Our study claims that W-2b could be a potential candidate to limit aberrant cellular proliferation rendering promising improvement in the treatment regime in cancer patients.

Ape1 guides DNA repair pathway choice that is associated with drug tolerance in glioblastoma

Ape1 is the major apurinic/apyrimidinic (AP) endonuclease activity in mammalian cells, and a key factor in base-excision repair of DNA. High expression or aberrant subcellular distribution of Ape1 has been detected in many cancer types, correlated with drug response, tumor prognosis, or patient survival. Here we present evidence that Ape1 facilitates BRCA1-mediated homologous recombination repair (HR), while counteracting error-prone non-homologous end joining of DNA double-strand breaks. Furthermore, Ape1, coordinated with checkpoint kinase Chk2, regulates drug response of glioblastoma cells. Suppression of Ape1/Chk2 signaling in glioblastoma cells facilitates alternative means of damage site recruitment of HR proteins as part of a genomic defense system. Through targeting "HR-addicted" temozolomide-resistant glioblastoma cells via a chemical inhibitor of Rad51, we demonstrated that targeting HR is a promising strategy for glioblastoma therapy. Our study uncovers a critical role for Ape1 in DNA repair pathway choice, and provides a mechanistic understanding of DNA repair-supported chemoresistance in glioblastoma cells.

Associations between mutations of the cell cycle checkpoint kinase 2 gene and gastric carcinogenesis

Gastric cancer is the most common malignant tumor of the digestive system. The etiology of gastric cancer is complex, and susceptibility at the genetic level remains to be fully elucidated in genetic investigations. In the present study, mutations of the cell cycle checkpoint kinase 2 (CHEK2) gene and its association with gastric cancer were examined. Reverse transcription‑quantitative polymerase chain reaction technology was used to detect the expression of CHEK2 and it was found that the expression of CHEK2 was low in gastric cancer. Using sequencing analysis, it was found that the low expression level of CHEK2 was associated with expression of its mutation. The present study also established a CHEK2‑overexpressing mutant and confirmed that CHEK2 promoted gastric cancer cell proliferation. Overexpression of the CHEK2 mutation was confirmed to promote cancer cell migration and invasion. Furthermore, western blot analysis results revealed that overexpression of the CHEK2 mutation downregulated E‑cadherin and upregulated vimentin expression, indicating the mechanism underlying the altered biological behavior. These results suggested that there was a correlation between mutation of the CHEK2 gene and gastric cancer, and provided an experimental basis for antitumor drug investigation and development according to its mutation target.

Repurposing of nitroxoline as a potential anticancer agent against human prostate cancer: a crucial role on AMPK/mTOR signaling pathway and the interplay with Chk2 activation

Nitroxoline is an antibiotic by chelating Zn²⁺ and Fe²⁺ from biofilm matrix. In this study, nitroxoline induced G1 arrest of cell cycle and subsequent apoptosis in prostate cancer cells through ion chelating-independent pathway. It decreased protein levels of cyclin D1, Cdc25A and phosphorylated Rb, but activated AMP-activated protein kinase (AMPK), a cellular energy sensor and signal transducer, leading to inhibition of downstream mTOR-p70S6K signaling. Knockdown of AMPKα significantly rescued nitroxoline-induced inhibition of cyclin D1-Rb-Cdc25A axis indicating AMPK-dependent mechanism. However, cytoprotective autophagy was simultaneously evoked by nitroxoline. Comet assay and Western blot analysis demonstrated DNA damaging effect and activation of Chk2 other than Chk1 to nitroxoline action. Instead of serving as a DNA repair transducer, nitroxoline-mediated Chk2 activation was identified to function as a pro-apoptotic inducer. In conclusion, the data suggest that nitroxoline induces anticancer activity through AMPK-dependent inhibition of mTOR-p70S6K signaling pathway and cyclin D1-Rb-Cdc25A axis, leading to G1 arrest of cell cycle and apoptosis. AMPK-dependent activation of Chk2, at least partly, contributes to apoptosis. The data suggest the potential role of nitroxoline for therapeutic development against prostate cancers.

Targeting SOD1 induces synthetic lethal killing in BLM- and CHEK2-deficient colorectal cancer cells

Cancer is a major cause of death throughout the world, and there is a large need for better and more personalized approaches to combat the disease. Over the past decade, synthetic lethal approaches have been developed that are designed to exploit the aberrant molecular origins (i.e. defective genes) that underlie tumorigenesis. BLM and CHEK2 are two evolutionarily conserved genes that are somatically altered in a number of tumor types. Both proteins normally function in preserving genome stability through facilitating the accurate repair of DNA double strand breaks. Thus, uncovering synthetic lethal interactors of BLM and CHEK2 will identify novel candidate drug targets and lead chemical compounds. Here we identify an evolutionarily conserved synthetic lethal interaction between SOD1 and both BLM and CHEK2 in two distinct cell models. Using quantitative imaging microscopy, real-time cellular analyses, colony formation and tumor spheroid models we show that SOD1 silencing and inhibition (ATTM and LCS-1 treatments), or the induction of reactive oxygen species (2ME2 treatment) induces selective killing within BLM- and CHEK2-deficient cells relative to controls. We further show that increases in reactive oxygen species follow SOD1 silencing and inhibition that are associated with the persistence of DNA double strand breaks, and increases in apoptosis. Collectively, these data identify SOD1 as a novel candidate drug target in BLM and CHEK2 cancer contexts, and further suggest that 2ME2, ATTM and LCS-1 are lead therapeutic compounds warranting further pre-clinical study.

Cancer TARGETases: DSB repair as a pharmacological target

Cancer is a disease attributed to the accumulation of DNA damages due to incapacitation of DNA repair pathways resulting in genomic instability and a mutator phenotype. Among the DNA lesions, double stranded breaks (DSBs) are the most toxic forms of DNA damage which may arise as a result of extrinsic DNA damaging agents or intrinsic replication stress in fast proliferating cancer cells. Accurate repair of DSBs is therefore paramount to the cell survival, and several classes of proteins such as kinases, nucleases, helicases or core recombinational proteins have pre-defined jobs in precise execution of DSB repair pathways. On one hand, the proper functioning of these proteins ensures maintenance of genomic stability in normal cells, and on the other hand results in resistance to various drugs employed in cancer therapy and therefore presents a suitable opportunity for therapeutic targeting. Higher relapse and resistance in cancer patients due to non-specific, cytotoxic therapies is an alarming situation and it is becoming more evident to employ personalized treatment based on the genetic landscape of the cancer cells. For the success of personalized treatment, it is of immense importance to identify more suitable targetable proteins in DSB repair pathways and also to explore new synthetic lethal interactions with these pathways. Here we review the various alternative approaches to target the various protein classes termed as cancer TARGETases in DSB repair pathway to obtain more beneficial and selective therapy.

In vitro and in vivo single-agent efficacy of checkpoint kinase inhibition in acute lymphoblastic leukemia

BACKGROUND

Although progress in children, in adults, ALL still carries a dismal outcome. Here, we explored the in vitro and in vivo activity of PF-00477736 (Pfizer), a potent, selective ATP-competitive small-molecule inhibitor of checkpoint kinase 1 (Chk1) and with lower efficacy of checkpoint kinase 2 (Chk2).

METHODS

The effectiveness of PF-00477736 as single agent in B-/T-ALL was evaluated in vitro and in vivo studies as a single agent. The efficacy of the compound in terms of cytotoxicity, induction of apoptosis, and changes in gene and protein expression was assessed using different B-/T-ALL cell lines. Finally, the action of PF-00477736 was assessed in vivo using leukemic mouse generated by a single administration of the tumorigenic agent N-ethyl-N-nitrosourea.

RESULTS

Chk1 and Chk2 are overexpressed concomitant with the presence of genetic damage as suggested by the nuclear labeling for γ-H2A.X (Ser139) in 68 % of ALL patients. In human B- and T-ALL cell lines, inhibition of Chk1/2 as a single treatment strategy efficiently triggered the Chk1-Cdc25-Cdc2 pathway resulting in a dose- and time-dependent cytotoxicity, induction of apoptosis, and increased DNA damage. Moreover, treatment with PF-00477736 showed efficacy ex vivo in primary leukemic blasts separated from 14 adult ALL patients and in vivo in mice transplanted with T-ALL, arguing in favor of its future clinical evaluation in leukemia.

CONCLUSIONS

In vitro, ex vivo, and in vivo results support the inhibition of Chk1 as a new therapeutic strategy in acute lymphoblastic leukemia, and they provide a strong rationale for its future clinical investigation.