Alterations of Chk1 and Chk2 expression in colon cancer

From Crypts to Cancer: A Holistic Perspective on Colorectal Carcinogenesis and Therapeutic Strategies

Colorectal cancer (CRC) represents a significant global health burden, with high incidence and mortality rates worldwide. Recent progress in research highlights the distinct clinical and molecular characteristics of colon versus rectal cancers, underscoring tumor location's importance in treatment approaches. This article provides a comprehensive review of our current understanding of CRC epidemiology, risk factors, molecular pathogenesis, and management strategies. We also present the intricate cellular architecture of colonic crypts and their roles in intestinal homeostasis. Colorectal carcinogenesis multistep processes are also described, covering the conventional adenoma-carcinoma sequence, alternative serrated pathways, and the influential Vogelstein model, which proposes sequential APC, KRAS, and TP53 alterations as drivers. The consensus molecular CRC subtypes (CMS1-CMS4) are examined, shedding light on disease heterogeneity and personalized therapy implications.

Nanoparticle-Mediated PRDX2 Inhibition for Specific Targeting of CHK2-Null Colorectal Cancer

Synthetic lethality is a pragmatic targeted cancer therapy approach in which cancer cells harboring genetic alterations are exploited for the specific killing of cancer cells. Earlier, we have established a synthetic lethal (SL) interaction between two genes that are CHK2 and PRDX2 in colorectal cancer (CRC) cells. The SL interaction between CHK2 and PRDX2 resulted in selective targeting of CHK2-defective CRC cells. N-Carbamoyl alanine (NCA) is a PRDX2 inhibitor and is a peptide-like organic compound, which degrades after oral administration in harsh gastric pH. To overcome the limitations of NCA, a chitosan-based nanocarrier was developed for the entrapment of NCA. In this study, we targeted the SL interaction between PRDX2 and CHK2 using NCA-loaded chitosan nanoparticles (NCA-Chit NPs) to selectively inhibit the CHK2-null HCT116 cells. NCA-Chit NPs were assessed for various physicochemical characterizations such as the hydrodynamic diameter (size), zeta potential, and polydispersity index using a Zetasizer. Additionally, morphological studies for the shape and size of NPs were confirmed by transmission electron microscopy, scanning electron microscopy, and atomic force microscopy. Cellular uptake of NPs was confirmed using confocal microscopy, which exhibited that nanoparticles were able to internalize into the HCT116 cells. Blank Chit NPs were found to be cytocompatible as they did not exert any cytotoxic effects on hTERT, L929, and Caco-2 cells (intestinal epithelial cells). Importantly, NCA-Chit NPs were quite hemocompatible also. In the form of an NCA-chitosan nanoformulation, the efficacy was enhanced by about 8 times compared to free form of NCA towards selective killing of CHK2-null HCT116 cells as compared to HCT116 cells. The chitosan-based nanoformulation for NCA was developed to augment the efficacy of the NCA for enhanced cell death of colorectal cancer cells having CHK2 defects.

Induction of Mitosis Delay and Apoptosis by CDDO-TFEA in Glioblastoma Multiforme

Background: Glioblastoma multiforme (GBM) is the vicious malignant brain tumor in adults. Despite advances multi-disciplinary treatment, GBM constinues to have a poor overall survival. CDDO-trifluoroethyl-amide (CDDO-TEFA), a trifluoroethylamidederivative of CDDO, is an Nrf2/ARE pathway activator. CDDO-TEFEA is used to inhibit proliferation and induce apoptosis in glioma cells. However, it not clear what effect it may have on tumorigenesis in GBM. Methods: This in vitro study evaluated the effects of CDDO-TFEA on GBM cells. To do this, we treated GBM8401 cell lines with CDDO-TFEA and assessed apoptosis, cell cycle. DNA content and induction of apoptosis were analyzed by flow cytometry and protein expression by Western blot analysis. Results: CDDO-TFEA significantly inhibited the cell viability and induced cell apoptosis on GBM 8401 cell line. The annexin-FITC/PI assay revealed significant changes in the percentage of apoptotic cells. Treatment with CDDO-TFEA led to a significant reduction in the GBM8401 cells' mitochondrial membrane potential. A significant rise in the percentage of caspase-3 activity was detected in the treated cells. In addition, treatment with CDDO-TFEA led to an accumulation of G2/M-phase cells. In addition, these results suggest that regarding increased protein synthesis during mitosis in the MPM-2 staining, indicative of a delay in the G2 checkpoint. An analysis of Cyclin B1, CDK1, Cyclin B1/CDK1 complex and CHK1 and CHK2 expression suggested that cell cycle progression seems also to be regulated by CDDO-TFEA. Therefore, CDDO-TFEA may not only induce cell cycle G2/M arrest, it may also exert apoptosis in established GBM cells. Conclusion: CDDO-TFEA can inhibit proliferation, cell cycle progression and induce apoptosis in GBM cells in vitro, possibly though its inhibition of Cyclin B1, CDK1 expression, and Cyclin B1/CDK1 association and the promotion of CHK1 and CHK2 expression.

RTA404, an Activator of Nrf2, Activates the Checkpoint Kinases and Induces Apoptosis through Intrinsic Apoptotic Pathway in Malignant Glioma

Background: Malignant glioma (MG) is an aggressive malignant brain tumor. Despite advances in multidisciplinary treatment, overall survival rates remain low. A trifluoroethyl amide derivative of 2-cyano-3-,12-dioxoolean-1,9-dien-28-oic acid (CDDO), CDDO-trifluoroethyl amide (CDDO-TFEA) is a nuclear erythroid 2-related factor 2/antioxidant response element pathway activator. RTA404 is used to inhibit proliferation and induce apoptosis in cancer cells. However, its effect on tumorigenesis in glioma is unclear. Methods: This in vitro study evaluated the effects of RTA404 on MG cells. We treated U87MG cell lines with RTA404 and performed assessments of apoptosis and cell cycle distributions. DNA content and apoptosis induction were subjected to flow cytometry analysis. The mitotic index was assessed based on MPM-2 expression. Protein expression was analyzed through Western blotting. Results: RTA404 significantly inhibited the cell viability and induced cell apoptosis on the U87MG cell line. The Annexin-FITC/PI assay revealed significant changes in the percentage of apoptotic cells. Treatment with RTA404 led to a significant reduction in the U87MG cells' mitochondrial membrane potential. A significant rise in the percentage of caspase-3 activity was detected in the treated cells. In addition, these results suggest that cells pass the G2 checkpoint without cell cycle arrest by RTA404 treatment in the MPM-2 staining. An analysis of CHK1, CHK2, and p-CHK2 expression suggested that the DNA damage checkpoint system seems also to be activated by RTA404 treatment in established U87MG cells. Therefore, RTA404 may not only activate the DNA damage checkpoint system, it may also exert apoptosis in established U87MG cells. Conclusions: RTA404 inhibits the cell viability of gliomas and induces cancer cell apoptosis through intrinsic apoptotic pathway in Malignant glioma. In addition, the DNA damage checkpoint system seems also to be activated by RTA404. Taken together, RTA404 activated the DNA damage checkpoint system and induced apoptosis through intrinsic apoptotic pathways in established U87MG cells.

Role of Stress-Survival Pathways and Transcriptomic Alterations in Progression of Colorectal Cancer: A Health Disparities Perspective

Every year, more than a million individuals are diagnosed with colorectal cancer (CRC) across the world. Certain lifestyle and genetic factors are known to drive the high incidence and mortality rates in some groups of individuals. The presence of enormous amounts of reactive oxygen species is implicated for the on-set and carcinogenesis, and oxidant scavengers are thought to be important in CRC therapy. In this review, we focus on the ethnicity-based CRC disparities in the U.S., the negative effects of oxidative stress and apoptosis, and gene regulation in CRC carcinogenesis. We also highlight the use of antioxidants for CRC treatment, along with screening for certain regulatory genetic elements and oxidative stress indicators as potential biomarkers to determine the CRC risk and progression.

Predictive and Prognostic Value of DNA Damage Response Associated Kinases in Solid Tumors

Dysfunctional DNA repair with subsequent genome instability and high mutational burden represents a major hallmark of cancer. In established malignant tumors, increased DNA repair capacity mediates resistance to DNA-damaging therapeutics, including cytotoxic drugs, radiotherapy, and selected small molecules including inhibitors of poly (ADP-ribose) polymerase (PARP), Ataxia Telangiectasia Mutated (ATM), ataxia telangiectasia and Rad3-related protein (ATR), and Wee1 kinase (Wee1). In addition, DNA repair deficiency is not only associated with sensitivity to selected anticancer drugs, but also with increased mutagenicity and increased neoantigen load on tumor cells, resulting in increased immunogenicity and improved response to CTLA4- or PD-(L)1 targeting monoclonal antibodies. DNA damage response (DDR) is composed of complex signalling pathways, including the sensing of the DNA damage, signal transduction, cellular response pathways to DNA damage, and activation of DNA repair. DNA double strand breaks (DSBs) are the most dangerous form of DNA damage. Tumor cells are characterised by frequent accumulation of DSBs caused by either endogenous replication stress or the impact of cancer treatment, most prominently chemotherapy and radiotherapy. Therefore, response of cancer cells to DSBs represents a crucial mechanism for how tumors respond to systemic treatment or radiotherapy, and how resistance develops. Ample clinical evidence supports the importance of DDR associated kinases as predictive and prognostic biomarkers in cancer patients. The ATM-CHK2 and ATR-CHK1-WEE1 pathways initiate DNA DSB repair. In the current review, we focus on major DDR associated kinases including ATM, ATR, CHK1, CHK2, and WEE1, and discuss their potential prognostic and predictive value in solid malignancies.

FadA promotes DNA damage and progression of Fusobacterium nucleatum-induced colorectal cancer through up-regulation of chk2

Background

Globally, colorectal cancer (CRC) affects more than 1 million people each year. In addition to non-modifiable and other environmental risk factors, Fusobacterium nucleatum infection has been linked to CRC recently. In this study, we explored mechanisms underlying the role of Fusobacterium nucleatum infection in the progression of CRC in a mouse model.

Methods

C57BL/6 J-Adenomatous polyposis coli (APC) Min/J mice [APC (Min/+)] were treated with Fusobacterium nucleatum (10⁹ cfu/mL, 0.2 mL/time/day, i.g., 12 weeks), saline, or FadA knockout (FadA−/−) Fusobacterium nucleatum. The number, size, and weight of CRC tumors were determined in isolated tumor masses. The human CRC cell lines HCT29 and HT116 were treated with lentiviral vectors overexpressing chk2 or silencing β-catenin. DNA damage was determined by Comet assay and γH2AX immunofluorescence assay and flow cytometry. The mRNA expression of chk2 was determined by RT-qPCR. Protein expression of FadA, E-cadherin, β-catenin, and chk2 were determined by Western blot analysis.

Results

Fusobacterium nucleatum treatment promoted DNA damage in CRC in APC (Min/+) mice. Fusobacterium nucleatum also increased the number of CRC cells that were in the S phase of the cell cycle. FadA−/− reduced tumor number, size, and burden in vivo. FadA−/− also reduced DNA damage, cell proliferation, expression of E-cadherin and chk2, and cells in the S phase. Chk2 overexpression elevated DNA damage and tumor growth in APC (Min/+) mice.

Conclusions

In conclusion, this study provided evidence that Fusobacterium nucleatum induced DNA damage and cell growth in CRC through FadA-dependent activation of the E-cadherin/β-catenin pathway, leading to up-regulation of chk2.

The role of CDC25C in cell cycle regulation and clinical cancer therapy: a systematic review

One of the most prominent features of tumor cells is uncontrolled cell proliferation caused by an abnormal cell cycle, and the abnormal expression of cell cycle-related proteins gives tumor cells their invasive, metastatic, drug-resistance, and anti-apoptotic abilities. Recently, an increasing number of cell cycle-associated proteins have become the candidate biomarkers for early diagnosis of malignant tumors and potential targets for cancer therapies. As an important cell cycle regulatory protein, Cell Division Cycle 25C (CDC25C) participates in regulating G2/M progression and in mediating DNA damage repair. CDC25C is a cyclin of the specific phosphatase family that activates the cyclin B1/CDK1 complex in cells for entering mitosis and regulates G2/M progression and plays an important role in checkpoint protein regulation in case of DNA damage, which can ensure accurate DNA information transmission to the daughter cells. The regulation of CDC25C in the cell cycle is affected by multiple signaling pathways, such as cyclin B1/CDK1, PLK1/Aurora A, ATR/CHK1, ATM/CHK2, CHK2/ERK, Wee1/Myt1, p53/Pin1, and ASK1/JNK-/38. Recently, it has evident that changes in the expression of CDC25C are closely related to tumorigenesis and tumor development and can be used as a potential target for cancer treatment. This review summarizes the role of CDC25C phosphatase in regulating cell cycle. Based on the role of CDC25 family proteins in the development of tumors, it will become a hot target for a new generation of cancer treatments.

Cell-type-specific role of CHK2 in mediating DNA damage-induced G2 cell cycle arrest

Cancer is a life-threatening disease that affects one in three people. Although most cases are sporadic, cancer risk can be increased by genetic factors. It remains unknown why certain genes predispose for specific forms of cancer only, such as checkpoint protein 2 (CHK2), in which gene mutations convey up to twofold higher risk for breast cancer but do not increase lung cancer risk. We have investigated the role of CHK2 and the related kinase checkpoint protein 1 (CHK1) in cell cycle regulation in primary breast and lung primary epithelial cells. At the molecular level, CHK1 activity was higher in lung cells, whereas CHK2 was more active in breast cells. Inhibition of CHK1 profoundly disrupted the cell cycle profile in both lung and breast cells, whereas breast cells were more sensitive toward inhibition of CHK2. Finally, we provide evidence that breast cells require CHK2 to induce a G2–M cell cycle arrest in response of DNA damage, whereas lung cells can partially compensate for the loss of CHK2. Our results provide an explanation as to why CHK2 germline mutations predispose for breast cancer but not for lung cancer.

Overview of the oncogenic signaling pathways in colorectal cancer: Mechanistic insights

Colorectal cancer is a multifaceted disease which is therapeutically challenging. Based on insights gleaned from almost a quarter century of research, it is obvious that deregulation of spatio-temporally controlled signaling pathways play instrumental role in development and progression of colorectal cancer. High-throughput technologies have helped to develop a sharper and broader understanding of the wide ranging signal transduction cascades which also contribute to development of drug resistance, loss of apoptosis and, ultimately, of metastasis. In this review, we have set the spotlight on role of JAK/STAT, TGF/SMAD, Notch, WNT/β-Catenin, SHH/GLI and p53 pathways in the development and progression of colorectal cancer. We have also highlighted recent reports on TRAIL-mediated pathways and molecularly distinct voltage-gated sodium channels in colorectal cancer.

Evaluation of CHK1 activation in vulvar squamous cell carcinoma and its potential as a therapeutic target in vitro

CHK1 is an important regulator of the cell cycle and DNA damage response, and its altered expression has been identified in various tumors. Chk1 inhibitors are currently being evaluated as monotherapy and as potentiators of chemotherapy in clinical settings. However, to our knowledge, no previous study has investigated either the activation status or the therapeutic potential of CHK1 targeting in vulvar cancer. Therefore, we examined the expression status of activated CHK1 forms pCHK1^Ser345, pCHK1^Ser317, pCHK1^Ser296, and pCHK1^Ser280 in 294 vulvar squamous cell carcinomas (VSCC) using immunohistochemistry and analyzed their relationships with various clinicopathological variables and clinical outcome. To aid translation of preclinical studies, we also assessed cell sensitivity to the Chk1 inhibition in two vulvar cancer cell lines. Compared to the levels of pCHK1^Ser345, pCHK1^Ser317, pCHK1^Ser296, and pCHK1^Ser280 in normal vulvar squamous epithelium, high nuclear pCHK1^Ser345 expression was found in 57% of vulvar carcinomas, whereas low nuclear pCHK1^Ser317, pCHK1^Ser296, and pCHK1^Ser280 expressions were observed in 58%, 64%, and 40% of the cases, respectively. Low levels of pCHK1^Ser317 and pCHK1^Ser280 in the nucleus correlated significantly with advanced tumor behaviors and aggressive features. None of pCHK1^Ser345, pCHK1^Ser317, pCHK1^Ser296, and pCHK1^Ser280 forms were identified as prognostic factors. In vitro inhibition of CHK1 by small molecular inhibitors or siRNA reduced viability by inducing DNA damage and apoptosis of vulvar cancer cell lines. In summary, we conclude that cellular functions regulated by CHK1 are phosphorylation/localization‐dependent and deregulation of CHK1 function occurs in VSCC and might contribute to tumorigenesis. Targeting CHK1 might represent as a useful antitumor strategy for the subgroup of VSCC harboring p53 mutations.

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.

Experimental colitis in mice is attenuated by topical administration of chlorogenic acid

Epidemiological data suggest that the consumption of polyphenol-rich foods reduces the incidence of cancer, coronary heart disease, and inflammation. Chlorogenic acid (CGA), an ester of caffeic and quinic acids, is one of the most abundant polyphenol compounds in human diet with proven biological effectiveness both in vitro and in vivo. The aim of the study is to investigate the possible anti-inflammatory effect of CGA in the gastrointestinal (GI) tract and its mechanism of action. We used a well-established model of colitis, induced by intracolonic (i.c.) administration of trinitrobenzenesulfonic acid (TNBS) in mice. The anti-inflammatory effect of CGA in the colon was evaluated based on the clinical and macroscopic and microscopic parameters. To investigate the mechanism of protective action of CGA, myeloperoxidase (MPO), H2O2, and NF-κB levels were assessed in the colon tissue. CGA administered i.c. at the dose of 20 mg/kg (two times daily) protected against TNBS-induced colitis more effectively than the same dose administered orally (p.o.), as evidenced by significantly lower macroscopic and ulcer scores. Furthermore, CGA (20 mg/kg, i.c.) reduced neutrophil infiltration, as demonstrated by decreased MPO activity. Moreover, CGA suppressed activation of NF-κB, as evidenced by lower levels of phospho-NF-κB/NF-κB ratio in the tissue. CGA did not affect the oxidative stress pathways. CGA exhibits anti-inflammatory properties through reduction of neutrophil infiltration and inhibition of NF-κB-dependent pathways. Our results suggest that CGA may have the potential to become a valuable supplement in the treatment of GI diseases.

Novel orally available salvinorin A analog PR-38 protects against experimental colitis and reduces abdominal pain in mice by interaction with opioid and cannabinoid receptors

BACKGROUND

Salvinorin A (SA) is a potent anti-inflammatory diterpene isolated from the Mexican plant S. divinorum. Recently we showed that the novel SA analog, PR-38 has an inhibitory effect on mouse gastrointestinal (GI) motility mediated by opioid and cannabinoid (CB) receptors. The aim of the study was to characterize possible anti-inflammatory and antinociceptive action of PR-38 in the mouse GI tract.

METHODS

Macro- and microscopic colonic damage scores and myeloperoxidase activity were determined after intraperitoneal (i.p.), intracolonic (i.c.), and per os (p.o.) administration of PR-38 in the trinitrobenzene sulfonic acid (TNBS) and dextran sodium sulfate (DSS) models of colitis in mice. Additionally, MOP, KOP and CB1 protein expression was determined using Western blot analysis of mouse colon samples. The antinociceptive effect of PR-38 was examined based on the number of behavioral responses to i.c. instillation of mustard oil (MO).

RESULTS

The i.p. (10 mg/kg, twice daily), i.c. (10 mg/kg, twice daily) and p.o. (20 mg/kg, once daily) administration of PR-38 significantly attenuated TNBS- and DSS-induced colitis in mice. The effect of PR-38 was partially blocked by the KOP antagonist nor-binaltorphimine and CB1 antagonist AM 251. Western blot analysis showed a significant increase of MOP, KOP and CB1 receptor expression during colonic inflammation, which was reversed to the control levels by the administration of PR-38. PR-38 significantly decreased the number of pain responses after i.c. instillation of MO in the TNBS-treated mice.

CONCLUSIONS

Our results suggest that PR-38 has the potential to become a valuable anti-inflammatory and analgesic therapeutic for the treatment of GI inflammation.

Importance of DNA damage checkpoints in the pathogenesis of human cancers

All forms of life on earth must cope with constant exposure to DNA-damaging agents that may promote cancer development. As a biological barrier, known as DNA damage response (DDR), cells are provided with both DNA repair mechanisms and highly conserved cell cycle checkpoints. The latter are responsible for the control of cell cycle phase progression with ATM, ATR, Chk1, and Chk2 as the main signaling molecules, thus dealing with both endogenous and exogenous sources of DNA damage. As cell cycle checkpoint and also DNA repair genes, such as BRCA1 and BRCA2, are frequently mutated, we here discuss their fundamental roles in the pathogenesis of human cancers. Importantly, as current evidence also suggests a role of MAPK's (mitogen activated protein kinases) in cell cycle checkpoint control, we describe in this review both the ATR/ATM-Chk1/Chk2 signaling pathways as well as the regulation of cell cycle checkpoints by MAPK's as molecular mechanisms in DDR, and how their dysfunction is related to cancer development. Moreover, since damage to DNA might be the common underlying mechanism for the positive outcome of chemotherapy, we also discuss targeting anticancer treatments on cell cycle checkpoints as an important issue emerging in drug discovery.

Impaired DNA damage response--an Achilles' heel sensitizing cancer to chemotherapy and radiotherapy

Despite the progress in targeting particular molecular abnormalities specific to different cancers (targeted therapy), chemo- and radiotherapies are still the most effective of all anticancer modalities. Induction of DNA damage and inhibition of cell proliferation are the objects of most chemotherapeutic agents and radiation. Their effectiveness was initially thought to be due to the high rate of proliferation of cancer cells. However, normal cell proliferation rate in some tissues often exceeds that of curable tumors. Most tumors have impaired DNA damage response (DDR) and the evidence is forthcoming that this confers sensitivity to chemo- or radiotherapy. DDR is a complex set of events which elicits a plethora of molecular interactions engaging signaling pathways designed to: (a) halt cell cycle progression and division to prevent transfer of DNA damage to progeny cells; (b) increase the accessibility of the damaged sites to the DNA repair machinery; (c) engage DNA repair mechanisms and (d) activate the apoptotic pathway when DNA cannot be successfully repaired. A defective DDR makes cancer cells unable to effectively stop cell cycle progression, engage in DNA repair and/or trigger the apoptotic program when treated with DNA damaging drugs. With continued exposure to the drug, such cells accumulate DNA damage which leads to their reproductive death that may have features of cell senescence. Cancers with nonfunctional BRCA1 and BRCA2 are particularly sensitive to combined treatment with DNA damaging drugs and inhibitors of poly(ADP-ribose) polymerase. Antitumor strategies are being designed to treat cancers having particular defects in their DDR, concurrent with protecting normal cells.

Role of CHK2 in cancer development

DNA repair pathways enable tumour cells to survive DNA damage induced by external agents such as therapeutic treatments. Signalling cascades involved in these pathways comprise the DNA-dependent protein kinase (DNA-PK), Ataxia-telangiectasia mutated (ATM), ATM and Rad3 related (ATR) and checkpoint kinases I and 2 (Chk1/Chk2), among others. ATM and ATR phosphorylate, respectively, Chk2 and Chk1, leading to activation of checkpoints. Chk2 acts as a signal distributor, dispersing checkpoint signal to downstream targets such as p53, Cdc25A, Cdc25C, BRCA1 and E2F1. A role of Chk2 as a candidate tumour suppressor has been suggested based on both mouse genetics and somatic tumour studies. We will discuss here the possible role of this kinase in human carcinogenesis and the possibility to use it as a target to increment DNA damage in cancer cells in response to DNA-damaging therapies.