The cell cycle checkpoint kinase Chk2 is a negative regulator of mitotic catastrophe

Investigation into the Neuroprotective and Therapeutic Potential of Plant-Derived Chk2 Inhibitors

Nature provides us with a rich source of compounds with a wide range of applications, including the creation of innovative drugs. Despite advancements in chemically synthesized therapeutics, natural compounds are increasingly significant, especially in cancer treatment, a leading cause of death globally. One promising approach involves the use of natural inhibitors of checkpoint kinase 2 (Chk2), a critical regulator of DNA repair, cell cycle arrest, and apoptosis. Chk2's activation in response to DNA damage can lead to apoptosis or DNA repair, influencing glycolysis and mitochondrial function. In cancer therapy, inhibiting Chk2 can disrupt DNA repair and cell cycle progression, promoting cancer cell death and enhancing the efficacy of radiotherapy and chemotherapy. Additionally, Chk2 inhibitors can safeguard non-cancerous cells during these treatments by inhibiting p53-dependent apoptosis. Beyond oncology, Chk2 inhibition shows potential in treating hepatitis C virus (HCV) infections, as the virus relies on Chk2 for RNA replication in neurodegenerative diseases like amyotrophic lateral sclerosis (ALS), in which DNA damage plays a crucial role. Plant-derived Chk2 inhibitors, such as artemetin, rhamnetin, and curcumin, offer a promising future for treating various diseases with potentially milder side effects and broader metabolic impacts compared to conventional therapies. The review aims to underscore the immense potential of natural Chk2 inhibitors in various therapeutic contexts, particularly in oncology and the treatment of other diseases involving DNA damage and repair mechanisms. These natural Chk2 inhibitors hold significant promise for revolutionizing the landscape of cancer treatment and other diseases. Further research into these compounds could lead to the development of innovative therapies that offer hope for the future with fewer side effects and enhanced efficacy.

Targeting mTOR and survivin concurrently potentiates radiation therapy in renal cell carcinoma by suppressing DNA damage repair and amplifying mitotic catastrophe

BACKGROUND

Renal cell carcinoma (RCC) was historically considered to be less responsive to radiation therapy (RT) compared to other cancer indications. However, advancements in precision high-dose radiation delivery through single-fraction and multi-fraction stereotactic ablative radiotherapy (SABR) have led to better outcomes and reduced treatment-related toxicities, sparking renewed interest in using RT to treat RCC. Moreover, numerous studies have revealed that certain therapeutic agents including chemotherapies can increase the sensitivity of tumors to RT, leading to a growing interest in combining these treatments. Here, we developed a rational combination of two radiosensitizers in a tumor-targeted liposomal formulation for augmenting RT in RCC. The objective of this study is to assess the efficacy of a tumor-targeted liposomal formulation combining the mTOR inhibitor everolimus (E) with the survivin inhibitor YM155 (Y) in enhancing the sensitivity of RCC tumors to radiation.

EXPERIMENTAL DESIGN

We slightly modified our previously published tumor-targeted liposomal formulation to develop a rational combination of E and Y in a single liposomal formulation (EY-L) and assessed its efficacy in RCC cell lines in vitro and in RCC tumors in vivo. We further investigated how well EY-L sensitizes RCC cell lines and tumors toward radiation and explored the underlying mechanism of radiosensitization.

RESULTS

EY-L outperformed the corresponding single drug-loaded formulations E-L and Y-L in terms of containing primary tumor growth and improving survival in an immunocompetent syngeneic mouse model of RCC. EY-L also exhibited significantly higher sensitization of RCC cells towards radiation in vitro than E-L and Y-L. Additionally, EY-L sensitized RCC tumors towards radiation therapy in xenograft and murine RCC models. EY-L mediated induction of mitotic catastrophe via downregulation of multiple cell cycle checkpoints and DNA damage repair pathways could be responsible for the augmentation of radiation therapy.

CONCLUSION

Taken together, our study demonstrated the efficacy of a strategic combination therapy in sensitizing RCC to radiation therapy via inhibition of DNA damage repair and a substantial increase in mitotic catastrophe. This combination therapy may find its use in the augmentation of radiation therapy during the treatment of RCC patients.

The heterogeneous cancer phenotype of individuals with biallelic germline pathogenic variants in CHEK2

PURPOSE

Females with biallelic CHEK2 germline pathogenic variants (gPVs) more often develop multiple breast cancers than individuals with monoallelic CHEK2 gPVs. This study is aimed at expanding the knowledge on the occurrence of other malignancies.

METHODS

Exome sequencing of individuals who developed multiple primary malignancies identified 3 individuals with the CHEK2 (NM_007194.4) c.1100del p.(Thr367MetfsTer15) loss-of-function gPV in a biallelic state. We collected the phenotypes of an additional cohort of individuals with CHEK2 biallelic gPVs (n = 291).

RESULTS

In total, 157 individuals (53.4%; 157/294 individuals) developed ≥1 (pre)malignancy. The most common (pre)malignancies next to breast cancer were colorectal- (n = 19), thyroid- (n = 19), and prostate (pre)malignancies (n = 12). Females with biallelic CHEK2 loss-of-function gPVs more frequently developed ≥2 (pre)malignancies and at an earlier age compared with females biallelic for the CHEK2 c.470T>C p.(Ile157Thr) missense variant. Furthermore, 26 males (31%; 26/84 males) with CHEK2 biallelic gPVs developed ≥1 (pre)malignancies of 15 origins.

CONCLUSION

Our study suggests that CHEK2 biallelic gPVs likely increase the susceptibility to develop multiple malignancies in various tissues, both in females and males. However, it is possible that a substantial proportion of individuals with CHEK2 biallelic gPVs is missed as diagnostic testing for CHEK2 often is limited to individuals who developed breast cancer.

Targeting mTOR and Survivin Concurrently Potentiates Radiation Therapy in Renal Cell Carcinoma by Suppressing DNA Damage Repair and Amplifying Mitotic Catastrophe

Background

Renal cell carcinoma (RCC) was historically considered to be less responsive to radiation therapy (RT) compared to other cancer indications. However, advancements in precision high-dose radiation delivery through single-fraction and multi-fraction stereotactic ablative radiotherapy (SABR) have led to better outcomes and reduced treatment-related toxicities, sparking renewed interest in using RT to treat RCC. Moreover, numerous studies have revealed that certain therapeutic agents including chemotherapies can increase the sensitivity of tumors to RT, leading to a growing interest in combining these treatments. Here, we developed a rational combination of two radiosensitizers in a tumor-targeted liposomal formulation for augmenting RT in RCC. The objective of this study is to assess the efficacy of a tumor-targeted liposomal formulation combining the mTOR inhibitor everolimus (E) with the survivin inhibitor YM155 (Y) in enhancing the sensitivity of RCC tumors to radiation.

Experimental Design

We slightly modified our previously published tumor-targeted liposomal formulation to develop a rational combination of E and Y in a single liposomal formulation (EY-L) and assessed its efficacy in RCC cell lines in vitro and in RCC tumors in vivo. We further investigated how well EY-L sensitizes RCC cell lines and tumors toward radiation and explored the underlying mechanism of radiosensitization.

Results

EY-L outperformed the corresponding single drug-loaded formulations E-L and Y-L in terms of containing primary tumor growth and improving survival in an immunocompetent syngeneic mouse model of RCC. EY-L also exhibited significantly higher sensitization of RCC cells towards radiation in vitro than E-L and Y-L. Additionally, EY-L sensitized RCC tumors towards radiation therapy in xenograft and murine RCC models. EY-L mediated induction of mitotic catastrophe via downregulation of multiple cell cycle checkpoints and DNA damage repair pathways could be responsible for the augmentation of radiation therapy.

Conclusion

Taken together, our study demonstrated the efficacy of a strategic combination therapy in sensitizing RCC to radiation therapy via inhibition of DNA damage repair and a substantial increase in mitotic catastrophe. This combination therapy may find its use in the augmentation of radiation therapy during the treatment of RCC patients.

Role of Bile-Derived Extracellular Vesicles in Hepatocellular Proliferation after Partial Hepatectomy in Rats

Although liver regeneration has been extensively studied, the effects of bile-derived extracellular vesicles (bile EVs) on hepatocytes has not been elucidated. We examined the influence of bile EVs, collected from a rat model of 70% partial hepatectomy (PH), on hepatocytes. We produced bile-duct-cannulated rats. Bile was collected over time through an extracorporeal bile duct cannulation tube. Bile EVs were extracted via size exclusion chromatography. The number of EVs released into the bile per liver weight 12 h after PH significantly increased. Bile EVs collected 12 and 24 h post-PH, and after sham surgery (PH12-EVs, PH24-EVs, sham-EVs) were added to the rat hepatocyte cell line, and 24 h later, RNA was extracted and transcriptome analysis performed. The analysis revealed that more upregulated/downregulated genes were observed in the group with PH24-EVs. Moreover, the gene ontology (GO) analysis focusing on the cell cycle revealed an upregulation of 28 types of genes in the PH-24 group, including genes that promote cell cycle progression, compared to the sham group. PH24-EVs induced hepatocyte proliferation in a dose-dependent manner in vitro, whereas sham-Evs showed no significant difference compared to the controls. This study revealed that post-PH bile Evs promote the proliferation of the hepatocytes, and genes promoting cell cycles are upregulated in hepatocytes.

Chk1/2 inhibitor AZD7762 enhances the susceptibility of IDH-mutant brain cancer cells to temozolomide

The IDH mutation initially exhibits chemosensitive properties, progression-free survival cannot be achieved in the later grades, and malignant transformation occurs as a result of TMZ-induced hypermutation profile and adaptation to this profile. In this study, we evaluated the potential of the combination of TMZ and AZD7762 at molecular level, to increase the anticancer activity of TMZ in IDH-mutant U87-mg cells. We used the WST-1 test to evaluate cytotoxic effect of TMZ and AZD7762 combination with dose-effect and isobologram curves. The effects of the inhibitory and effective concentrations of the combination on apoptosis, cell cycle and γ-H2AX phosphorylation were analyzed with flow cytometry. The expression of genes responsible for the DNA damage response was analyzed with qRT-PCR. The combination showed a synergistic effect with high dose reduction index. Single and combined administrations of TMZ and AZD7762 increased in G₂/M arrest from 24 to 48 h, and cells in the G₂/M phase shifted towards octaploidy at 72 h. While no double-strand breaks were detected after TMZ treatment, AZD7762 and combination treatments caused a significant increase in γ-H2AX phosphorylation and increased apoptotic stimulation towards 72 h although TMZ did not cause apoptotic effect in IDH-mutant U87-mg cells. The genes controlling the apoptosis were determined to be upregulated in all three groups, and genes regarding cell cycle checkpoints were downregulated. Targeting Chk1/2 with AZD7762 simultaneously with TMZ may be a potential therapeutic strategy for both increasing the sensitivity of IDH-mutant glioma cells to TMZ and reducing the dose of TMZ. In IDH-mutant glioma cells, AZD7762, the Chk1/2 inhibitor, can increase the efficacy of Temozolomide by (i) increasing mitotic chaos, and (ii) inhibiting double-strand break repair, (iii) thereby inducing cell death.

Non-Canonical Programmed Cell Death in Colon Cancer

Simple Summary

Non-canonical PCD is an important player in colon cancer cell suicide. It influences colon cancer in many ways, such as through tumorigenesis, treatment, and prognosis. In this review, we present the mechanism, application, and prospect of different types of non-canonical PCD in colon cancer.

Abstract

Programmed cell death (PCD) is an evolutionarily conserved process of cell suicide that is regulated by various genes and the interaction of multiple signal pathways. Non-canonical programmed cell death (PCD) represents different signaling excluding apoptosis. Colon cancer is the third most incident and the fourth most mortal worldwide. Multiple factors such as alcohol, obesity, and genetic and epigenetic alternations contribute to the carcinogenesis of colon cancer. In recent years, emerging evidence has suggested that diverse types of non-canonical programmed cell death are involved in the initiation and development of colon cancer, including mitotic catastrophe, ferroptosis, pyroptosis, necroptosis, parthanatos, oxeiptosis, NETosis, PANoptosis, and entosis. In this review, we summarized the association of different types of non-canonical PCD with tumorigenesis, progression, prevention, treatments, and prognosis of colon cancer. In addition, the prospect of drug-resistant colon cancer therapy related to non-canonical PCD, and the interaction between different types of non-canonical PCD, was systemically reviewed.

N(6)-methyladenosine methylation-regulated polo-like kinase 1 cell cycle homeostasis as a potential target of radiotherapy in pancreatic adenocarcinoma

In pancreatic cancer, methyltransferase-like 3 (METTL3), a N(6)-methyladenosine (m6A) methyltransferase, has a favorable effect on tumors and is a risk factor for patients' prognosis. However, the details of what genes are regulated by METTL3 remain unknown. Several RNAs are methylated, and what genes are favored in pancreatic cancer remains unclear. By epitranscriptomic analysis, we report that polo-like kinase 1 (PLK1) is an important hub gene defining patient prognosis in pancreatic cancer and that RNA methylation is involved in regulating its cell cycle-specific expression. We found that insulin like growth factor 2 mRNA binding protein 2 (IGF2BP2) binds to m6A of PLK1 3' untranslated region and is involved in upregulating PLK1 expression and that demethylation of this site activates the ataxia telangiectasia and Rad3-related protein pathway by replicating stress and increasing mitotic catastrophe, resulting in increased radiosensitivity. This suggests that PLK1 methylation is essential for cell cycle maintenance in pancreatic cancer and is a new therapeutic target.

Circadian control of heparan sulfate levels times phagocytosis of amyloid beta aggregates

Alzheimer's Disease (AD) is a neuroinflammatory disease characterized partly by the inability to clear, and subsequent build-up, of amyloid-beta (Aβ). AD has a bi-directional relationship with circadian disruption (CD) with sleep disturbances starting years before disease onset. However, the molecular mechanism underlying the relationship of CD and AD has not been elucidated. Myeloid-based phagocytosis, a key component in the metabolism of Aβ, is circadianly-regulated, presenting a potential link between CD and AD. In this work, we revealed that the phagocytosis of Aβ42 undergoes a daily circadian oscillation. We found the circadian timing of global heparan sulfate proteoglycan (HSPG) biosynthesis was the molecular timer for the clock-controlled phagocytosis of Aβ and that both HSPG binding and aggregation may play a role in this oscillation. These data highlight that circadian regulation in immune cells may play a role in the intricate relationship between the circadian clock and AD.

SF3B1 homeostasis is critical for survival and therapeutic response in T cell leukemia

The production of noncanonical mRNA transcripts is associated with cell transformation. Driven by our previous findings on the sensitivity of T cell acute lymphoblastic leukemia (T-ALL) cells to SF3B1 inhibitors, we identified that SF3B1 inhibition blocks T-ALL growth in vivo with no notable associated toxicity. We also revealed protein stabilization of the U2 complex component SF3B1 via deubiquitination. Our studies showed that SF3B1 inhibition perturbs exon skipping, leading to nonsense-mediated decay and diminished levels of DNA damage response-related transcripts, such as the serine/threonine kinase CHEK2, and impaired DNA damage response. We also identified that SF3B1 inhibition leads to a general decrease in R-loop formation. We further demonstrate that clinically used SF3B1 inhibitors synergize with CHEK2 inhibitors and chemotherapeutic drugs to block leukemia growth. Our study provides the proof of principle for posttranslational regulation of splicing components and associated roles and therapeutic implications for the U2 complex in T cell leukemia.

A link between mitotic defects and mitotic catastrophe: detection and cell fate

Although the phenomenon of mitotic catastrophe was first described more than 80 years ago, only recently has this term been used to explain a mechanism of cell death linked to delayed mitosis. Several mechanisms have been suggested for mitotic catastrophe development and cell fate. Depending on molecular perturbations, mitotic catastrophe can end in three types of cell death, namely apoptosis, necrosis, or autophagy. Moreover, mitotic catastrophe can be associated with different types of cell aging, the development of which negatively affects tumor elimination and, consequently, reduces the therapeutic effect. The effective triggering of mitotic catastrophe in clinical practice requires induction of DNA damage as well as inhibition of the molecular pathways that regulate cell cycle arrest and DNA repair. Here we discuss various methods to detect mitotic catastrophe, the mechanisms of its development, and the attempts to use this phenomenon in cancer treatment.

Garlic Extract Alleviates Trastuzumab-Induced Hepatotoxicity in Rats Through Its Antioxidant, Anti-Inflammatory, and Antihyperlipidemic Effects

Background

Trastuzumab is a new biological drug that has been used to treat breast and gastric cancer; however, its cardiotoxicity and hepatotoxicity limit its use. Garlic has antioxidant, anti-inflammatory, antihyperlipidemic, and anticancer effects. The present study aimed to evaluate the effects of garlic on trastuzumab-induced hepatotoxicity in a rat model.

Methods

Twenty rats were divided into four equal groups as vehicle control (G1), garlic (G2), trastuzumab (G3), and trastuzumab+garlic (G4). All rats were sacrificed after eight weeks of treatment, followed by blood collection and excision of liver tissues for further analyses. The liver specimens were processed for histopathological (HP), immunohistochemical (expression of TNF-α and PCNA), immunofluorescent expression of Chk2 and p53, biochemical, and flow cytometry investigations to evaluate the extent of hepatocyte injury. The biochemical analysis was conducted for the activity of tissue antioxidants (GPX1, CAT, and SOD2), serum lipid profile, and liver enzymes, whereas ROS was performed by flow cytometry.

Results

The results revealed remarkable structural changes in hepatocytes of G3 with significant increases in the numbers of inflammatory cells and positive PCNA cells, area % of collagen fibers, and immuno-expression of TNF-α, as well as a significant reduction in the nuclear expression of Chk2. In addition, significant reductions were noticed in the antioxidant enzymes (SOD2, CAT, and GPX1) activity of G3. In contrast, the levels of lipid profile tests (triglycerides, total cholesterol, LDLC, and HDLC), liver enzymes (ALT, AST, and ALP), and ROS revealed significant increases in rats of G3. Likewise, garlic administration in G4 restored all mentioned changes to their average levels deviated by trastuzumab.

Conclusion

Based on the current results, garlic demonstrates hepatoprotective effects against trastuzumab-induced toxicity in rats. The study suggested for the first time that the coadministration of garlic with trastuzumab for treating breast or gastric cancer can augment their efficacy with minimal toxicity.

VALD-3, a Schiff base ligand synthesized from o-vanillin derivatives, induces cell cycle arrest and apoptosis in breast cancer cells by inhibiting the Wnt/β-catenin pathway

Schiff base compounds and their metal complexes have become important synthetic organic drugs due to their extensive biological activities, which include anticancer, antibacterial and antiviral effects. In this study, we investigated the cytotoxic and apoptotic effects of VALD-3, a Schiff base ligand synthesized from o-vanillin derivatives, on human breast cancer cells and the possible underlying mechanisms. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)-test was used to observe the proliferation of human breast cancer MCF-7 and MDA-MB-231 cells induced by VALD-3. Flow cytometry analysis showed that VALD-3 triggered cell cycle arrest and induced apoptosis of breast cancer cells. Western blot analysis revealed that VALD-3 upregulated pro-apoptotic proteins (Bad and Bax), downregulated anti-apoptotic proteins (Bcl-2, Bcl-xl, survivin and XIAP) and increased the expression of cleaved caspase-3, cleaved caspase-8, Cyto-c and cleaved PARP. VALD-3 also regulated the Wnt/β-catenin signaling pathway in breast cancer cells, inhibiting the activation of downstream molecules. By xenografting human breast cancer cells into nude mice, we found that VALD-3 significantly suppressed tumor cell growth while showing low toxicity against major organs. In addition, survival analysis showed that VALD-3 can significantly prolong the survival time of mice (P = 0.036). This study is the first to show that VALD-3 induces apoptosis and cell cycle arrest in human breast cancer cells by suppressing Wnt/β-catenin signaling, indicating that it could be a potential drug for the treatment of breast cancer.

Tau oligomers accumulation sensitizes prostate cancer cells to docetaxel treatment

PURPOSE

Human tau is a highly dynamic, multifunctional protein expressed in different isoforms and conformers, known to modulate microtubule turnover. Tau oligomers are considered pathologic forms of the protein able to initiate specific protein accumulation diseases, called tauopathies. In our study, we investigated the potential association between autophagy and tau oligomers accumulation and its role in the response of prostate cancer cells to docetaxel.

METHODS

We evaluated in vitro the expression of tau oligomers in prostate cancer cell lines, PC3 and DU145, in presence of autophagy inhibitors and investigated the role of tau oligomers accumulation in resistance to docetaxel treatment.

RESULTS

Tau protein was basally expressed in prostate cancer lines as several monomeric and oligomeric forms. The pharmacologic inhibition of autophagy induced in cancer cells the accumulation of tau protein, with a prevalent expression of oligomeric forms. Immunofluorescence analysis of untreated cells revealed that tau was visible mainly in dividing cells where it was localized on the mitotic spindle. Inhibition of autophagy determined an evident upregulation of tau signal in dividing cells and the presence of aberrant monoastral mitotic spindles. The accumulation of tau oligomers was associated with DNA DSB and increased cytotoxic effect by docetaxel.

CONCLUSIONS

Our data indicate that autophagy could exert a promoting role in cancer growth and during chemotherapy facilitating degradation of tau protein and thus blocking the antimitotic effect of accumulated tau oligomers. Thus, therapeutic strategies aimed at stimulating tau oligomers formation, such as autophagy inhibition, could be an effective adjuvant in cancer therapy.

Clonogenic Assays to Detect Cell Fate in Mitotic Catastrophe

Mitotic catastrophe (MC) is a cell death modality induced by DNA damage that involves the activation of cell cycle checkpoints such as the "DNA structure checkpoint" and "spindle assembly checkpoint" (SAC) leading to aberrant mitosis. Depending on the signal, MC can drive the cell to death or to senescence. The suppression of MC favors aneuploidy. Several cancer therapies, included microtubular poisons and radiations, trigger MC. The clonogenic assay has been used to study the capacity of single cells to proliferate and to generate macroscopic colonies and to evaluate the efficacy of anticancer drugs. Nevertheless, this method cannot analyze MC events. Here, we report an improved technique based on the use of human colon cancer HCT116 stable expressing histone H2B-GFP and DsRed-centrin proteins, allowing to determine the capacity of cells to proliferate, and to determine changes in the nucleus and centrosomes.

MicroRNA-107 enhances radiosensitivity by suppressing granulin in PC-3 prostate cancer cells

Prostate cancer is the second leading cause of cancer-related death worldwide. Radiotherapy is often applied for the treatment, but radioresistance is a challenge in some patients. MicroRNAs have been reported to be involved in the DNA damage response induced by ionizing radiation and recent studies have reported microRNA-mediated radiosensitivity. In the present study, we found microRNA-107 (miR-107) enhanced radiosensitivity by regulating granulin (GRN) in prostate cancer (PC-3) cells. MiR-107 was downregulated and GRN was upregulated in response to ionizing radiation in PC-3 cells. Overexpression of miR-107 and knockdown of GRN promoted the sensitivity of PC3 cells to ionizing radiation. By rescue experiments of GRN, we revealed that radiosensitivity enhanced by miR-107 can be attenuated by GRN overexpression in PC-3 cells. Furthermore, we showed miR-107 enhanced radiation-induced G1/S phase arrest and G2/M phase transit, and identify delayed apoptosis by suppressing p21 and phosphorylation of CHK2. Collectively, these results highlight an unrecognized mechanism of miR-107-mediated GRN regulation in response to ionizing radiation and may advance therapeutic strategies for the treatment of prostate cancer.

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.

Screening and authentication of molecular markers in malignant glioblastoma based on gene expression profiles

Glioblastoma (GBM) is a malignant tumor of the central nervous system with high mortality rates. Gene expression profiling may determine the chemosensitivity of GBMs. However, the molecular mechanisms underlying GBM remain to be determined. To screen the novel key genes in its occurrence and development, two glioma databases, GSE122498 and GSE104291, were analyzed in the present study. Bioinformatics analyses were performed using the Database for Annotation, Visualization and Integrated Discovery, the Search Tool for the Retrieval of Interacting Genes, Cytoscape, cBioPortal, and Gene Expression Profiling Interactive Analysis softwares. Patients with recurrent GBM showed worse overall survival rate. Overall, 341 differentially expressed genes (DEGs) were authenticated based on two microarray datasets, which were primarily enriched in ‘cell division’, ‘mitotic nuclear division’, ‘DNA replication’, ‘nucleoplasm’, ‘cytosol, nucleus’, ‘protein binding’, ‘ATP binding’, ‘protein C-terminus binding’, ‘the cell cycle’, ‘DNA replication’, ‘oocyte meiosis’ and ‘valine’. The protein-protein interaction network was composed of 1,799 edges and 237 nodes. Its significant module had 10 hub genes, and CDK1, BUB1B, NDC80, NCAPG, BUB1, CCNB1, TOP2A, DLGAP5, ASPM and MELK were significantly associated with carcinogenesis and the development of GBM. The present study indicated that the DEGs and hub genes, identified based on bioinformatics analyses, had significant diagnostic value for patients with GBM.

M2I-1 disrupts the in vivo interaction between CDC20 and MAD2 and increases the sensitivities of cancer cell lines to anti-mitotic drugs via MCL-1s

Background

Drugs such as taxanes, epothilones, and vinca alkaloids are widely used in the treatment of breast, ovarian, and lung cancers but come with major side effects such as neuropathy and loss of neutrophils and as single agents have a lack of efficacy. M2I-1 (MAD2 inhibitor-1) has been shown to disrupt the CDC20-MAD2 interaction, and consequently, the assembly of the mitotic checkpoint complex (MCC).

Results

We report here that M2I-1 can significantly increase the sensitivity of several cancer cell lines to anti-mitotic drugs, with cell death occurring after a prolonged mitotic arrest. In the presence of nocodazole or taxol combined with M2I-1 cell death is triggered by the premature degradation of Cyclin B1, the perturbation of the microtubule network, and an increase in the level of the pro-apoptotic protein MCL-1s combined with a marginal increase in the level of NOXA. The elevated level of MCL-1s and the marginally increased NOXA antagonized the increased level of MCL-1, a pro-survival protein of the Bcl-2 family.

Conclusion

Our results provide some important molecular mechanisms for understanding the relationship between the mitotic checkpoint and programmed cell death and demonstrate that M2I-1 exhibits antitumor activity in the presence of current anti-mitotic drugs such as taxol and nocodazole and has the potential to be developed as an anticancer agent.

Porcine epidemic diarrhea virus through p53-dependent pathway causes cell cycle arrest in the G0/G1 phase

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PEDV causes Vero cell cycle arrest in the G0/G1 phase.

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PEDV through p53-dependent pathway causes cell cycle arrest in the G0/G1 phase.

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Vero cells released from G0/G1 phase are advantageous for PEDV replication.

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This is the first report that PEDV through p53-dependent pathway causes cell cycle arrest in the G0/G1 phase.

Porcine epidemic diarrhea virus (PEDV), an enteropathogenic Alphacoronavirus, has caused enormous economic losses in the swine industry. p53 protein exists in a wide variety of animal cells, which is involved in cell cycle regulation, apoptosis, cell differentiation and other biological functions. In this study, we investigated the effects of PEDV infection on the cell cycle of Vero cells and p53 activation. The results demonstrated that PEDV infection induces cell cycle arrest at G0/G1 phase in Vero cells, while UV-inactivated PEDV does not cause cell cycle arrest. PEDV infection up-regulates the levels of p21, cdc2, cdk2, cdk4, Cyclin A protein and down-regulates Cyclin E protein. Further research results showed that inhibition of p53 signaling pathway can reverse the cell cycle arrest in G0/G1 phase induced by PEDV infection and cancel out the up-regulation of p21 and corresponding Cyclin/cdk mentioned above. In addition, PEDV infection of the cells synchronized in various stages of cell cycle showed that viral subgenomic RNA and virus titer were higher in the cells released from G0/G1 phase synchronized cells than that in the cells released from the G1/S phase and G2/M phase synchronized or asynchronous cells after 18 h p.i.. This is the first report to demonstrate that the p53-dependent pathway plays an important role in PEDV induced cell cycle arrest and beneficially contributes to viral infection.

Part III: Novel checkpoint kinase 2 (Chk2) inhibitors; design, synthesis and biological evaluation of pyrimidine-benzimidazole conjugates

Recently a dramatic development of the cancer drug discovery has been shown in the field of targeted cancer therapy. Checkpoint kinase 2 (Chk2) inhibitors offer a promising approach to enhance the effectiveness of cancer chemotherapy. Accordingly, in this study many pyrimidine-benzimidazole conjugates were designed and twelve feasible derivatives were selected to be synthesized to investigate their activity against Chk2 and subjected to study their antitumor activity alone and in combination with the genotoxic anticancer drugs cisplatin and doxorubicin on breast carcinoma, (ER+) cell line (MCF-7). The results indicated that the studied compounds inhibited Chk2 activity with high potency (IC₅₀ = 5.56 nM - 46.20 nM). The studied candidates exhibited remarkable antitumor activity against MCF-7 (IG₅₀ = 6.6  μM - 24.9 μM). Compounds 10a-c, 14 and 15 significantly potentiated the activity of the studied genotoxic drugs, whereas, compounds 9b and 20-23 antagonized their activity. Moreover, the combination of compound 10b with cisplatin revealed the best apoptotic effect as well as combination of compound 10b with doxorubicin led to complete arrest of the cell cycle at S phase where more than 40% of cells are in the S phase with no cells at G2/M. Structure-activity relationship was discussed on the basis of molecular modeling study using Molecular modeling Environment program (MOE).

Cell Death Pathways in Response to Antitumor Therapy

Failure to eliminate cancer cells that have been exposed to cytotoxic agents may contribute to the development of resistance to antitumor drugs. A widespread model in present day oncology is that antitumor therapy involves the triggering of tumor cells to undergo apoptosis, and cells that can avoid apoptosis will be resistant to such therapy. Apoptosis is a defined program of cell death that is markedly influenced by the fact that many routes leading to it are mutated or deregulated in human cancer. Mutations in the tumor suppressor protein p53, a common feature of many cancers, may decrease the sensitivity of cells to some antitumor agents. Moreover, it has been increasingly reported that antitumor therapy not only causes apoptosis, but other forms of cell death as well, such as mitotic catastrophe, necrosis and autophagy, or a permanent cell arrest with phenotype characteristics of senescence. Mitotic catastrophe is a form of cell death that results from abnormal mitosis, which does not seem to depend on wild-type p53. Sometimes mitotic catastrophe is used restrictively for faulty mitosis leading to cell death, which may occur via apoptosis or necrosis. We critically review herein how antitumor therapy may elicit the response of human cancers through different cell pathways leading to cell death.

Involvement of autophagy in the outcome of mitotic catastrophe

Evading cell death is a major driving force for tumor progression that is one of the main problems in current cancer research. Mitotic catastrophe (MC) represents attractive platform compromising tumor resistance to current therapeutic modalities. MC appeared as onco-suppressive mechanism and is defined as a stage driving the cell to an irreversible destiny, i.e. cell death via apoptosis or necrosis. Our study highlights that MC induction in colorectal carcinoma cell lines ultimately leads to the autophagy followed by apoptosis. We show that autophagy suppression in Atg 13 knockout non-small cell lung carcinoma cells lead to the dramatic decrease of MC rate. Furthermore, mitochondria-linked anti-apoptotic proteins Mcl-1 and Bcl-xL play a crucial role in the duration of MC and a cross-talk between autophagy and apoptosis. Thus, the suppression of apoptosis by overexpression of Mcl-1 or Bcl-xL affected MC and lead to a significant induction of autophagy in HCT116 wt and HCT116 14-3-3σ^-/- cells. Our data demonstrate that MC induction is a critical stage, in which a cell decides how to die, while mitochondria are responsible for the maintaining the balance between MC - autophagy - apoptosis.

Huwe1 Regulates the Establishment and Maintenance of Spermatogonia by Suppressing DNA Damage Response

Spermatogenesis is sustained by a heterogeneous population of spermatogonia that includes the spermatogonial stem cells. However, the mechanisms underlying their establishment from gonocyte embryonic precursors and their maintenance thereafter remain largely unknown. In this study, we report that inactivation of the ubiquitin ligase Huwe1 in male germ cells in mice led to the degeneration of spermatogonia in neonates and resulted in a Sertoli cell-only phenotype in the adult. Huwe1 knockout gonocytes showed a decrease in mitotic re-entry, which inhibited their transition to spermatogonia. Inactivation of Huwe1 in primary spermatogonial culture or the C18-4 cell line resulted in cell degeneration. Degeneration of Huwe1 knockout spermatogonia was associated with an increased level of histone H2AX and an elevated DNA damage response that led to apparent mitotic catastrophe but not apoptosis or senescence. Blocking this increase in H2AX prevented the degeneration of Huwe1-depleted cells. Taken together, these results reveal a previously undefined role of Huwe1 in orchestrating the physiological DNA damage response in the male germline that contributes to the establishment and maintenance of spermatogonia.

RA-Induced Transcriptional Silencing of Checkpoint Kinase-2 through Promoter Methylation by Dnmt3b Is Required for Neuronal Differentiation of P19 Cells

In a previous study, we identified several novel targets of Dnmt3b using a chromatin library from retinoic acid (RA)-treated P19 cells. The present study describes the regulation of expression and function of checkpoint kinase (Chk2), which was one of the target genes of Dnmt3b. Chromatin immunoprecipitation followed by quantitative PCR analysis showed that recruitment of Dnmt3b on Chk2 promoter is induced following RA treatment of P19 cells. Both bisulfite genomic sequence and COBRA analyses showed that the methylation level of Chk2 promoter is progressively increased during RA-induced neuronal differentiation of P19 cells. Concomitantly, both mRNA and protein expression of Chk2 are reduced as determined by real-time PCR and Western blot analysis, respectively. Suppression of Dnmt3b expression by lentiviral-mediated shRNA resulted in increased expression and reduced methylation of Chk2, which clearly showed that Dnmt3b is responsible for transcriptional silencing of Chk2 gene in RA-treated P19 cells. Neuronal differentiation of P19 cells was inhibited upon enforced Chk2 expression in P19 cells, which showed that the decrease in endogenous expression of Chk2 is essential for normal differentiation. Ectopic Chk2 expression also negatively regulated cell cycle arrest and apoptosis following RA treatment, which could also contribute to impaired neuronal differentiation. Together, this study described the regulation of Chk2 expression through promoter methylation and also presented a novel role of Chk2 during neuronal differentiation, which is independent of its previously known function in DNA damage response.

Inhibition of protein kinases by anticancer DNA intercalator, 4-butylaminopyrimido[4',5':4,5]thieno(2,3-b)quinoline

Targeting protein kinases (PKs) has been a promising strategy in treating cancer, as PKs are key regulators of cell survival and proliferation. Here in this study, we studied the ability of pyrimido[4′,5′:4,5]thieno(2,3-b)quinolines (PTQ) to inhibit different PKs by performing computational docking and in vitro screening. Docking studies revealed that 4-butylaminopyrimido[4′,5′:4,5]thieno(2,3-b)quinoline (BPTQ) has a higher order of interaction with the kinase receptors than other PTQ derivatives. In vitro screening confirms that BPTQ inhibits VEGFR1 and CHK2, with the IC₅₀ values of 0.54 and 1.70 µmol/L, respectively. Further, cytotoxicity of BPTQ was measured by trypan blue assay. Treatment with BPTQ decreased the proliferation of HL-60 cells with an IC₅₀ value of 12 µmol/L and induces apoptosis, as explicated by the fall in the mitochondrial membrane potential, annexin V labeling and increased expression of caspase-3. Taken together, these data suggest that BPTQ possess ability to inhibit PKs and to induce cell death in human promyelocytic leukemia cells.

Mitotic catastrophe and cell cycle arrest are alternative cell death pathways executed by bortezomib in rituximab resistant B-cell lymphoma cells

The ubiqutin-proteasome system (UPS) plays a role in rituximab-chemotherapy resistance and bortezomib (BTZ) possesses caspase-dependent (i.e. Bak stabilization) and a less characterized caspase-independent mechanism-of-action(s). Here, we define BTZ-induced caspase-independent cell death pathways. A panel of rituximab-sensitive (RSCL), rituximab-resistant cell lines (RRCL) and primary tumor cells derived from lymphoma patients (N = 13) were exposed to BTZ. Changes in cell viability, cell-cycle, senescence, and mitotic index were quantified. In resting conditions, RRCL exhibits a low-proliferation rate, accumulation of cells in S-phase and senescence. Exposure of RRCL to BTZ reduces cell senescence, induced G2-M phase cell-cycle arrest, and is associated with mitotic catastrophe. BTZ stabilized p21, CDC2, and cyclin B in RRCL and in primary tumor cells. Transient p21 knockdown alleviates BTZ-induced senescence inhibition, G2-M cell cycle blockade, and mitotic catastrophe. Our data suggest that BTZ can induce apoptosis or mitotic catastrophe and that p21 has a pivotal role in BTZ activity against RRCL.

Predicting and Overcoming Chemotherapeutic Resistance in Breast Cancer

Our understanding of breast cancer and its therapeutic approach has improved greatly due to the advancement of molecular biology in recent years. Clinically, breast cancers are characterized into three basic types based on their immunohistochemical properties. They are triple-negative breast cancer, estrogen receptor (ER) and progesterone receptor (PR)-positive-HR positive breast cancer, and human epidermal growth factor receptor 2 (HER2)-positive breast cancer. Even though these subtypes have been characterized, assessment of a breast cancer's receptor status is still widely used to determine whether or not a targeted therapy could be applied. Moreover, drug resistance is common in all breast cancer types despite the different treatment modalities applied. The development of resistance to different therapeutics is not mutually exclusive. It seems that tumor could be resistant to multiple treatment strategies, such as being both chemoresistant and monoclonal antibody resistant. However, the underlying mechanisms are complicated and need further investigation. In this chapter, we aim to provide a brief review of the different types of breast cancer and their respective treatment strategies. We also review the possible mechanisms of potential drug resistance associated with each treatment type. We believe that a better understanding of the drug resistance mechanisms can lead to a more effective and efficient therapeutic success.

Mitotic catastrophe and cancer drug resistance: A link that must to be broken

An increased tendency of genomic alterations during the life cycle of cells leads to genomic instability, which is a major driving force for tumorigenesis. A considerable fraction of tumor cells are tetraploid or aneuploid, which renders them intrinsically susceptible to mitotic aberrations, and hence, are particularly sensitive to the induction of mitotic catastrophe. Resistance to cell death is also closely linked to genomic instability, as it enables malignant cells to expand even in a stressful environment. Currently it is known that cells can die via multiple mechanisms. Mitotic catastrophe represents a step preceding apoptosis or necrosis, depending on the expression and/or proper function of several proteins. Mitotic catastrophe was proposed to be an onco-suppressive mechanism and the evasion of mitotic catastrophe constitutes one of the gateways to cancer development. Thus, stimulation of mitotic catastrophe appears to be a promising strategy in cancer treatment. Indeed, several chemotherapeutic drugs are currently used at concentrations that induce apoptosis irrespective of the cell cycle phase, yet are very efficient at triggering mitotic catastrophe at lower doses, significantly limiting side effects. In the present review we summarize current data concerning the role of mitotic catastrophe in cancer drug resistance and discuss novel strategies to break this link.

Targeted Therapies for Triple-Negative Breast Cancer: Combating a Stubborn Disease

Triple-negative breast cancers (TNBCs) constitute a heterogeneous subtype of breast cancers that have a poor clinical outcome. Although no approved targeted therapy is available for TNBCs, molecular-profiling efforts have revealed promising molecular targets, with several candidate compounds having now entered clinical trials for TNBC patients. However, initial results remain modest, thereby highlighting challenges potentially involving intra- and intertumoral heterogeneity and acquisition of therapy resistance. We present a comprehensive review on emerging targeted therapies for treating TNBCs, including the promising approach of immunotherapy and the prognostic value of tumor-infiltrating lymphocytes. We discuss the impact of pathway rewiring in the acquisition of drug resistance, and the prospect of employing combination therapy strategies to overcome challenges towards identifying clinically-viable targeted treatment options for TNBC.

Targeting the Mitotic Catastrophe Signaling Pathway in Cancer

Mitotic catastrophe, as defined in 2012 by the International Nomenclature Committee on Cell Death, is a bona fide intrinsic oncosuppressive mechanism that senses mitotic failure and responds by driving a cell to an irreversible antiproliferative fate of death or senescence. Thus, failed mitotic catastrophe can promote the unrestrained growth of defective cells, thereby representing a major gateway to tumour development. Furthermore, the activation of mitotic catastrophe offers significant therapeutic advantage which has been exploited in the action of conventional and targeted anticancer agents. Yet, despite its importance in tumour prevention and treatment, the molecular mechanism of mitotic catastrophe is not well understood. A better understanding of the signals that determine cell fate following failed or defective mitosis will reveal new opportunities to selectively target and enhance the programme for therapeutic benefit and reveal biomarkers to predict patient response. This review is focused on the molecular mechanism of mitotic catastrophe induction and signalling and highlights current strategies to exploit the process in cancer therapy.

Cyclin A/Cdk2 regulates Cdh1 and claspin during late S/G2 phase of the cell cycle

Whereas many components regulating the progression from S phase through G2 phase into mitosis have been identified, the mechanism by which these components control this critical cell cycle progression is still not fully elucidated. Cyclin A/Cdk2 has been shown to regulate the timing of Cyclin B/Cdk1 activation and progression into mitosis although the mechanism by which this occurs is only poorly understood. Here we show that depletion of Cyclin A or inhibition of Cdk2 during late S/early G2 phase maintains the G2 phase arrest by reducing Cdh1 transcript and protein levels, thereby stabilizing Claspin and maintaining elevated levels of activated Chk1 which contributes to the G2 phase observed. Interestingly, the Cyclin A/Cdk2 regulated APC/C(Cdh1) activity is selective for only a subset of Cdh1 targets including Claspin. Thus, a normal role for Cyclin A/Cdk2 during early G2 phase is to increase the level of Cdh1 which destabilises Claspin which in turn down regulates Chk1 activation to allow progression into mitosis. This mechanism links S phase exit with G2 phase transit into mitosis, provides a novel insight into the roles of Cyclin A/Cdk2 in G2 phase progression, and identifies a novel role for APC/C(Cdh1) in late S/G2 phase cell cycle progression.

Efficacy of Combined Histone Deacetylase and Checkpoint Kinase Inhibition in a Preclinical Model of Human Burkitt Lymphoma

Checkpoint kinase inhibition has been studied as a way of enhancing the effectiveness of DNA-damaging agents. More recently, histone deacetylase inhibitors have shown efficacy in several cancers, including non-Hodgkin lymphoma. To evaluate the effectiveness of this combination for the treatment of lymphoma, we examined the combination of AR42, a histone deacetylase inhibitor, and checkpoint kinase 2 (CHEK2) inhibitor II in vitro and in vivo. The combination resulted in up to 10-fold increase in potency in five Burkitt lymphoma cell lines when compared with either drug alone. Both drugs inhibited tumor progression in xenograft models, but the combination was more effective than either agent alone, resulting in regression of established tumors. No toxicity was observed. These results suggest that the combination of histone deacetylase inhibition and checkpoint kinase inhibition represent an effective and nontoxic treatment option that should be further explored in preclinical and clinical studies.

Stress-mediated Sin3B activation leads to negative regulation of subset of p53 target genes

The multiprotein SWI-independent 3 (Sin3)-HDAC (histone deacetylase) corepressor complex mediates gene repression through its interaction with DNA-binding factors and recruitment of chromatin-modifying proteins on to the promoters of target gene. Previously, an increased expression of Sin3B and tumour suppressor protein, p53 has been established upon adriamycin treatment. We, now provide evidence that Sin3B expression is significantly up-regulated under variety of stress conditions and this response is not stress-type specific. We observed that Sin3B expression is significantly up-regulated both at transcript and at protein level upon DNA damage induced by bleomycin drug, a radiomimetic agent. This increase in Sin3B expression upon stress is found to be p53-dependent and is associated with enhanced interaction of Sin3B with Ser(15) phosphorylated p53. Binding of Sin3-HDAC repressor complex on to the promoters of p53 target genes influences gene regulation by altering histone modifications (H3K9me3 and H3K27me3) at target genes. Furthermore, knockdown of Sin3B by shRNA severely compromises p53-mediated gene repression under stress conditions. Taken together, these results suggest that stress-induced Sin3B activation is p53-dependent and is essential for p53-mediated repression of its selective target genes. The present study has an implication in understanding the transrepression mechanism of p53 under DNA damaging conditions.

CHK2 kinase in the DNA damage response and beyond

The serine/threonine kinase CHK2 is a key component of the DNA damage response. In human cells, following genotoxic stress, CHK2 is activated and phosphorylates >20 proteins to induce the appropriate cellular response, which, depending on the extent of damage, the cell type, and other factors, could be cell cycle checkpoint activation, induction of apoptosis or senescence, DNA repair, or tolerance of the damage. Recently, CHK2 has also been found to have cellular functions independent of the presence of nuclear DNA lesions. In particular, CHK2 participates in several molecular processes involved in DNA structure modification and cell cycle progression. In this review, we discuss the activity of CHK2 in response to DNA damage and in the maintenance of the biological functions in unstressed cells. These activities are also considered in relation to a possible role of CHK2 in tumorigenesis and, as a consequence, as a target of cancer therapy.

siRNA targeting stathmin inhibits invasion and enhances chemotherapy sensitivity of stem cells derived from glioma cell lines

Glioma is one of the most highly angiogenic tumors, and glioma stem cells (GSCs) are responsible for resistance to chemotherapy and radiotherapy, as well as recurrence after operation. Stathmin is substantial for mitosis and plays an important role in proliferation and migration of glioma-derived endothelial cells. However, the relationship between stathmin and GSCs is incompletely understood. Here we isolated GSCs from glioma cell lines U87MG and U251, and then used siRNA targeting stathmin for silencing. We showed that silencing of stathmin suppressed the proliferation, increased the apoptosis rate, and arrested the cell cycle at G2/M phase in GSCs. Silencing of stathmin in GSCs also resulted in inhibited the migration/invasion as well as the capability of vasculogenic mimicry. The susceptibility of GSCs to temozolomide was also enhanced by stathmin silencing. Our findings suggest stathmin as a potential target in GSCs for glioma treatment.

Co-abrogation of Chk1 and Chk2 by potent oncolytic adenovirus potentiates the antitumor efficacy of cisplatin or irradiation

Mammalian checkpoint kinases 1 and 2 (Chk1 and Chk2) are essential kinases that are involved in cell cycle checkpoint control, and the abrogation of either has been proposed as one way to sensitize cancer cells to DNA-damaging agents. However, it remains unclear which kinase is the most therapeutically relevant target, and whether multiple kinases might need to be targeted to achieve the best efficacy because of their overlapping substrate spectra and redundant functions. To clarify this issue, we established asynchronous cell cycle arrest models to investigate the therapeutic outcomes of silencing Chk1 and Chk2 in the presence of irradiation or cisplatin. Our results showed that Chk1- and Chk2-targeting small interference RNAs (siRNAs) demonstrated synergistic effects when both siRNAs were used simultaneously. Interestingly, Chk1 and Chk2 co-expression occurred in ∼90% of neoplastic tissues examined and showed no difference in neoplastic versus non-neoplastic tissues. Therefore, the selective targeting of Chk1 and Chk2 by oncolytic adenovirus mutants was chosen to treat resistant tumor xenograft mice, and the maximum antitumoral efficacy was achieved with the combined co-abrogation of Chk1 and Chk2 in the presence of low-dose cisplatin. This work deepens our understanding of novel strategies that target checkpoint pathways and contributes to the development of novel, potent and safe checkpoint abrogators.

Chk2 regulates cell cycle progression during mouse oocyte maturation and early embryo development

As a tumor suppressor homologue during mitosis, Chk2 is involved in replication checkpoints, DNA repair, and cell cycle arrest, although its functions during mouse oocyte meiosis and early embryo development remain uncertain. We investigated the functions of Chk2 during mouse oocyte maturation and early embryo development. Chk2 exhibited a dynamic localization pattern; Chk2 expression was restricted to germinal vesicles at the germinal vesicle (GV) stage, was associated with centromeres at pro-metaphase I (Pro-MI), and localized to spindle poles at metaphase I (MI). Disrupting Chk2 activity resulted in cell cycle progression defects. First, inhibitor-treated oocytes were arrested at the GV stage and failed to undergo germinal vesicle breakdown (GVBD); this could be rescued after Chk2 inhibition release. Second, Chk2 inhibition after oocyte GVBD caused MI arrest. Third, the first cleavage of early embryo development was disrupted by Chk2 inhibition. Additionally, in inhibitor-treated oocytes, checkpoint protein Bub3 expression was consistently localized at centromeres at the MI stage, which indicated that the spindle assembly checkpoint (SAC) was activated. Moreover, disrupting Chk2 activity in oocytes caused severe chromosome misalignments and spindle disruption. In inhibitor-treated oocytes, centrosome protein γ-tubulin and Polo-like kinase 1 (Plk1) were dissociated from spindle poles. These results indicated that Chk2 regulated cell cycle progression and spindle assembly during mouse oocyte maturation and early embryo development.

Comparative analysis of radiosensitizers for K-RAS mutant rectal cancers

Approximately 40% of rectal cancers harbor activating K-RAS mutations, and these mutations are associated with poor clinical response to chemoradiotherapy. We aimed to identify small molecule inhibitors (SMIs) that synergize with ionizing radiation (IR) ("radiosensitizers") that could be incorporated into current treatment strategies for locally advanced rectal cancers (LARCs) expressing mutant K-RAS. We first optimized a high-throughput assay for measuring individual and combined effects of SMIs and IR that produces similar results to the gold standard colony formation assay. Using this screening platform and K-RAS mutant rectal cancer cell lines, we tested SMIs targeting diverse signaling pathways for radiosensitizing activity and then evaluated our top hits in follow-up experiments. The two most potent radiosensitizers were the Chk1/2 inhibitor AZD7762 and the PI3K/mTOR inhibitor BEZ235. The chemotherapeutic agent 5-fluorouracil (5-FU), which is used to treat LARC, synergized with AZD7762 and enhanced radiosensitization by AZD7762. This study is the first to compare different SMIs in combination with IR for the treatment of K-RAS mutant rectal cancer, and our findings suggest that Chk1/2 inhibitors should be evaluated in new clinical trials for LARC.

A novel role for the anti-senescence factor TBX2 in DNA repair and cisplatin resistance

The emergence of drug resistant tumours that are able to escape cell death pose a major problem in the treatment of cancers. Tumours develop resistance to DNA-damaging chemotherapeutic agents by acquiring the ability to repair their DNA. Combination therapies that induce DNA damage and disrupt the DNA damage repair process may therefore prove to be more effective against such tumours. The developmentally important transcription factor TBX2 has been suggested as a novel anticancer drug target, as it is overexpressed in several cancers and possesses strong anti-senescence and pro-proliferative functions. Importantly, we recently showed that when TBX2 is silenced, we are able to reverse several features of transformation in both breast cancer and melanoma cells. Overexpression of TBX2 has also been linked to drug resistance and we have shown that its ectopic expression results in genetically unstable polyploidy cells with resistance to cisplatin. Whether the overexpression of endogenous TBX2 levels is associated with cisplatin resistance in TBX2-driven cancers has, however, not been shown. To address this we have silenced TBX2 in a cisplatin-resistant breast cancer cell line and we show that knocking down TBX2 sensitises the cells to cisplatin by disrupting the ATM-CHK2-p53 signalling pathway. Cell cycle analyses demonstrate that when TBX2 is knocked down there is an abrogation of an S-phase arrest but a robust G2/M arrest that correlates with a reduction in phosphorylated CHK2 and p53 levels. This prevents DNA repair resulting in TBX2-deficient cells entering mitosis with damaged DNA and consequently undergoing mitotic catastrophe. These results suggest that targeting TBX2 in combination with chemotherapeutic drugs such as cisplatin could improve the efficacy of current anticancer treatments.

Curcumin suppresses multiple DNA damage response pathways and has potency as a sensitizer to PARP inhibitor

Inhibitors of poly(ADP-ribose) polymerase (PARP) are promising anticancer drugs, particularly for the treatment of tumors deficient in the DNA damage response (DDR). However, it is challenging to design effective therapeutic strategies for use of these compounds against cancers without DDR deficiencies. In this context, combination therapies in which PARP inhibitors are used alongside DDR inhibitors have elicited a great deal of interest. Curcumin, a component of turmeric (Curcuma longa), has been tested in clinical studies for its chemosensitizing potential; however, the mechanisms of chemosensitization by curcumin have not been fully elucidated. This study demonstrates that curcumin suppresses three major DDR pathways: non-homologous end joining (NHEJ), homologous recombination (HR) and the DNA damage checkpoint. Curcumin suppresses the histone acetylation at DNA double-strand break (DSB) sites by inhibiting histone acetyltransferase activity, thereby reducing recruitment of the key NHEJ factor KU70/KU80 to DSB sites. Curcumin also suppresses HR by reducing expression of the BRCA1 gene, which regulates HR, by impairing histone acetylation at the BRCA1 promoter. Curcumin also inhibits ataxia telangiectasia and Rad3-related protein (ATR) kinase (IC50 in vitro = 493 nM), resulting in impaired activation of ATR-CHK1 signaling, which is necessary for HR and the DNA damage checkpoint pathway. Thus, curcumin suppresses three DDR pathways by inhibiting histone acetyltransferases and ATR. Concordantly, curcumin sensitizes cancer cells to PARP inhibitors by enhancing apoptosis and mitotic catastrophe via inhibition of both the DNA damage checkpoint and DSB repair. Our results indicate that curcumin is a promising sensitizer for PARP inhibitor-based therapy.

Anticancer effect of Tamarix gallica extracts on human colon cancer cells involves Erk1/2 and p38 action on G2/M cell cycle arrest

Taking into account that oxidative stress is among the factors causing cancer-related death; chemoprevention which consists in using antioxidant substances such as phenolics could prevent cancer formation and progression. In the present study, phenolic contents and antioxidant activities of methanolic extracts from the halophyte Tamarix gallica shoots were determined. Moreover, the anticancer effect of this species on human colon cancer cells and the likely underlying mechanisms were also investigated. Shoot extracts showed an appreciable total phenolic content (85 mg GAE/g DW) and a high antioxidant activity (IC50 = 3.3 μg/ml for DPPH test). At 50 and 100 μg/ml, shoot, leaf, and flower extracts significantly inhibited Caco-2 cell growth. For instance, almost all plant part extracts inhibited cell growth by 62 % at the concentration 100 μg/ml. DAPI staining results revealed that these extracts decrease DNA synthesis and confirm their effect on Caco-2 cells proliferation, principally at 100 μg/ml. More importantly, cell mitosis was arrested at G2/M phase. The changes in the cell-cycle-associated proteins (cyclin B1, p38, Erk1/2, Chk1, and Chk2) are correlated with the changes in cell cycle distribution. Taken together, our data suggest that T. gallica is a promising candidate species to be used as a source of anticancer biomolecules.

Expression of cyclin A, B1 and D1 after induction of cell cycle arrest in the Jurkat cell line exposed to doxorubicin

Jurkat human lymphoblastoid cells were incubated in increasing concentrations of doxorubicin (0.05, 0.1 and 0.15 μM) to induce cell death, and their expression of cyclin A, B1 and D1 was evaluated by flow cytometry (cell cycle progression, Annexin V assay, percentages and levels of each of the cyclins), transmission electron microscopy (ultrastructure) and confocal fluorescence microscopy (expression and intracellular localization of cyclins). After low-dose doxorubicin treatment, Jurkat cells responded mainly by G2/M arrest, which was related to increased cyclin B1, A and D1 levels, a low level of apoptosis and/or mitotic catastrophe. The influence of doxorubicin on levels and/or localization of selected cyclins was confirmed, which may in turn contribute to the G2/M arrest induced by the drug.

MEK1/2 inhibition enhances the radiosensitivity of cancer cells by downregulating survival and growth signals mediated by EGFR ligands

The inhibition of the Ras/mitogen-activated protein kinase (Ras/MAPK) pathway through the suppression of mutated Ras or MAPK/extracellular signal-regulated kinase 1/2 (MEK1/2) has been shown to sensitize tumor cells to ionizing radiation (IR). The molecular mechanisms of this sensitization however, are not yet fully understood. In this study, we investigated the role of transforming growth factor-α (TGF-α) in the radiosensitizing effects of selumetinib, a selective inhibitor of MEK1/2. The expression of epidermal growth factor receptor (EGFR) ligands was assessed by ELISA in both Ras wild-type and Ras mutant cells that were exposed to radiation with or without selumetinib. The effects of selumetinib on the TGF-α/EGFR signaling cascade in response to radiation were examined by western blot analysis, clonogenic assay and by determing the yield of mitotic catastrophe. The treatment of cells with selumetinib reduced the basal and IR-induced secretion of TGF-α in both Ras wild-type and Ras mutant cell lines in vitro and in vivo. The reduction of TGF-α secretion was accompanied with a reduction in phosphorylated tumor necrosis factor-α converting enzyme (TACE) in the cells treated with selumetinib with or without IR. The treatment of cells with selumetinib with or without IR inhibited the phosphorylation of EGFR and check-point kinase 2 (Chk2), and reduced the expression of survivin. Supplementation with exogenous TGF-α partially rescued the selumetinib-treated cells from IR-induced cell death, restored EGFR and Chk2 phosphorylation and increased survivin expression. These data suggest that the inhibition of MEK1/2 with selumetinib may provide a mechanism to sensitize tumor cells to IR in a fashion that prevents the activation of the TGF-α autocrine loop following IR.

How many ways can a podocyte die?

Podocytes are highly specialized epithelial cells that line the urinary surface of the glomerular capillary tuft. To maintain kidney filtration, podocytes oppose the high intraglomerular hydrostatic pressure, form a molecular sieve, secrete soluble factors to regulate other glomerular cell types, and provide synthesis and maintenance of the glomerular basement membrane. Impairment of any of these functions after podocyte injury results in proteinuria and possibly renal failure. Loss of glomerular podocytes is a key feature for the progression of renal diseases, and detached podocytes can be retrieved in the urine of patients with progressive glomerular diseases. Thus, the concept of podocyte loss as a hallmark of progressive glomerular disease has been widely accepted. However, the nature of events that promote podocyte detachment and whether detachment is preceded by any kind of podocyte cell death, such as apoptosis, necroptosis, or necrosis, still remains unclear and is discussed in this review.

Resveratrol abrogates the temozolomide-induced G2 arrest leading to mitotic catastrophe and reinforces the temozolomide-induced senescence in glioma cells

Background

Temozolomide (TMZ) is the most widely used drug to treat glioblastoma (GBM), which is the most common and aggressive primary tumor of the Central Nervous System and one of the hardest challenges in oncotherapy. TMZ is an alkylating agent that induces autophagy, apoptosis and senescence in GBM cells. However, therapy with TMZ increases survival after diagnosis only from 12 to 14.4 months, making the development of combined therapies to treat GBM fundamental. One candidate for GBM therapy is Resveratrol (Rsv), which has additive toxicity with TMZ in several glioma cells in vitro and in vivo. However, the mechanism of Rsv and TMZ additive toxicity, which is the aim of the present work, is not clear, especially concerning cell cycle dynamics and long term effects.

Methods

Glioma cell lines were treated with Rsv and TMZ, alone or in combinations, and the induction and the role of autophagy, apoptosis, cell cycle dynamics, protein expression and phosphorylation status were measured. We further evaluated the long term senescence induction and clonogenic capacity.

Results

As expected, temozolomide caused a G2 cell cycle arrest and extensive DNA damage response. Rsv did not reduced this response, even increasing pATM, pChk2 and gammaH2Ax levels, but abrogated the temozolomide-induced G2 arrest, increasing levels of cyclin B and pRb(S807/811) and reducing levels of pWee1(S642) and pCdk1(Y15). This suggests a cellular state of forced passage through G2 checkpoint despite large DNA damage, a scenario that may produce mitotic catastrophe. Indeed, the proportion of cells with high nuclear irregularity increased from 6 to 26% in 48 h after cotreatment. At a long term, a reduction in clonogenic capacity was observed, accompanied by a large induction of senescence.

Conclusion

The presence of Rsv forces cells treated with TMZ through mitosis leading to mitotic catastrophe and senescence, reducing the clonogenic capacity of glioma cells and increasing the chronic effects of temozolomide.

The E3 ligase PIRH2 polyubiquitylates CHK2 and regulates its turnover

The serine threonine kinase checkpoint kinase 2 (CHK2) is a DNA damage checkpoint protein important for the ATM-p53 signaling pathway. In addition to its phosphorylation, CHK2 is also ubiquitylated, and both post-translational modifications are important for its function. However, although the mechanisms that regulate CHK2 phosphorylation are well established, those that control its ubiquitylation are not fully understood. In this study, we demonstrate that the ubiquitin E3 ligase PIRH2 (p53-induced protein with a RING (Really Interesting New Gene)-H2 domain) interacts with CHK2 and mediates its polyubiquitylation and proteasomal degradation. We show that the deubiquitylating enzyme USP28 forms a complex with PIRH2 and CHK2 and antagonizes PIRH2-mediated polyubiquitylation and proteasomal degradation of CHK2. We also provide evidence that CHK2 ubiquitylation by PIRH2 is dependent on its phosphorylation status. Cells deficient in Pirh2 displayed accumulation of Chk2 and enhanced hyperactivation of G1/S and G2/M cell-cycle checkpoints. This hyperactivation was, however, no longer observed in Pirh2-/-Chk2-/- cells, providing evidence for the importance of Chk2 regulation by Pirh2. These findings indicate that PIRH2 has central roles in the ubiquitylation of Chk2 and its turnover and in the regulation of its function.

Various modes of cell death induced by DNA damage

The consequences of DNA damage depend on the cell type and the severity of the damage. Mild DNA damage can be repaired with or without cell-cycle arrest. More severe and irreparable DNA injury leads to the appearance of cells that carry mutations or causes a shift towards induction of the senescence or cell death programs. Although for many years it was argued that DNA damage kills cells via apoptosis or necrosis, technical and methodological progress during the last few years has helped to reveal that this injury might also activate death by autophagy or mitotic catastrophe, which may then be followed by apoptosis or necrosis. The molecular basis underlying the decision-making process is currently the subject of intense investigation. Here, we review current knowledge about the response to DNA damage and subsequent signaling, with particular attention to cell death induction and the molecular switches between different cell death modalities following damage.