DNA damage response inhibitors: Mechanisms and potential applications in cancer therapy

Oxymestane, a cytostatic steroid derivative of exemestane with greater antitumor activity in non-estrogen-dependent cell lines

A new promising steroid derivative of Exemestane (Exe), the drug used for the treatment of estrogen-dependent breast cancer, was synthesized and evaluated against a set of human cancer cell lines. The new compound (Oxymestane-D1, Oxy) was tested comparatively with Exe against colon (C2BBe1, WiDr), liver (HepG2, HuH-7), lung (A549, H1299) and prostate (LNCaP, PC3) human cancer cell lines. Likewise, its effect on human colon normal cells (CCD-841 CoN) and human normal fibroblast cells (HFF-1) was studied. The cytostatic activity of Oxy was also compared with that of the reference cytostatic drugs used in chemotherapy protocols, namely carboplatin, cisplatin, doxorubicin, epirubicin, etoposide, flutamide, 5-fluorouracil, irinotecan, oxaliplatin and sorafenib. In all cell lines tested, Oxy proved to be more powerful cytostatic than Exe. Additionally, the IC₅₀ at 72 h showed a three-fold activity greater than 5-fluorouracil in the WiDr cell line, twice as high as cisplatin for cell line A549 and five times higher than cisplatin for cell line H1299. Also, Oxy surprisingly revealed to induce DNA damage and inhibit the DNA damage response (DDR) proteins ATM, ATR, CHK1 and CHK2. The results obtained allow concluding that Oxy can be a promising anticancer agent to be used in chemotherapy protocols. Furthermore, its ability to inhibit crucial components of DDR can also be useful for the monotherapy or for combination with chemo and/or radiotherapy of cancer.

Targeting Cellular DNA Damage Responses in Cancer: An In Vitro-Calibrated Agent-Based Model Simulating Monolayer and Spheroid Treatment Responses to ATR-Inhibiting Drugs

We combine a systems pharmacology approach with an agent-based modelling approach to simulate LoVo cells subjected to AZD6738, an ATR (ataxia–telangiectasia-mutated and rad3-related kinase) inhibiting anti-cancer drug that can hinder tumour proliferation by targeting cellular DNA damage responses. The agent-based model used in this study is governed by a set of empirically observable rules. By adjusting only the rules when moving between monolayer and multi-cellular tumour spheroid simulations, whilst keeping the fundamental mathematical model and parameters intact, the agent-based model is first parameterised by monolayer in vitro data and is thereafter used to simulate treatment responses in in vitro tumour spheroids subjected to dynamic drug delivery. Spheroid simulations are subsequently compared to in vivo data from xenografts in mice. The spheroid simulations are able to capture the dynamics of in vivo tumour growth and regression for approximately 8 days post-tumour injection. Translating quantitative information between in vitro and in vivo research remains a scientifically and financially challenging step in preclinical drug development processes. However, well-developed in silico tools can be used to facilitate this in vitro to in vivo translation, and in this article, we exemplify how data-driven, agent-based models can be used to bridge the gap between in vitro and in vivo research. We further highlight how agent-based models, that are currently underutilised in pharmaceutical contexts, can be used in preclinical drug development.

Inhibition of the DSB repair protein RAD51 potentiates the cytotoxic efficacy of doxorubicin via promoting apoptosis-related death pathways

The anthracycline derivative doxorubicin (Doxo) induces DNA double-strand breaks (DSBs) by inhibition of DNA topoisomerase type II. Defective mismatch repair (MMR) contributes to Doxo resistance and has been reported for colon and mammary carcinomas. Here, we investigated the outcome of pharmacological inhibition of various DNA repair-related mechanisms on Doxo-induced cytotoxicity employing MMR-deficient HCT-116 colon carcinoma cells. Out of different inhibitors tested (i.e. HDACi, PARPi, MRE11i, RAD52i, RAD51i), we identified the RAD51-inhibitor B02 as the most powerful compound to synergistically increase Doxo-induced cytotoxicity. B02-mediated synergism rests on pleiotropic mechanisms, including pronounced G2/M arrest, damage to mitochondria and caspase-driven apoptosis. Of note, B02 also promotes the cytotoxicity of oxaliplatin and 5-fluoruracil (5-FU) in HCT-116 cells and, furthermore, also increases Doxo-induced cytotoxicity in MMR-proficient colon and mammary carcinoma cells. Summarizing, pharmacological inhibition of RAD51 is suggested to synergistically increase the cytotoxic efficacy of various types of conventional anticancer drugs in different tumor entities. Hence, pre-clinical in vivo studies are preferable to determine the therapeutic window of B02 in a clinically oriented therapeutic regimen.

Roles of homologous recombination in response to ionizing radiation-induced DNA damage

PURPOSE

Ionizing radiation induces a vast array of DNA lesions including base damage, and single- and double-strand breaks (SSB, DSB). DSBs are among the most cytotoxic lesions, and mis-repair causes small- and large-scale genome alterations that can contribute to carcinogenesis. Indeed, ionizing radiation is a 'complete' carcinogen. DSBs arise immediately after irradiation, termed 'frank DSBs,' as well as several hours later in a replication-dependent manner, termed 'secondary' or 'replication-dependent DSBs. DSBs resulting from replication fork collapse are single-ended and thus pose a distinct problem from two-ended, frank DSBs. DSBs are repaired by error-prone nonhomologous end-joining (NHEJ), or generally error-free homologous recombination (HR), each with sub-pathways. Clarifying how these pathways operate in normal and tumor cells is critical to increasing tumor control and minimizing side effects during radiotherapy.

CONCLUSIONS

The choice between NHEJ and HR is regulated during the cell cycle and by other factors. DSB repair pathways are major contributors to cell survival after ionizing radiation, including tumor-resistance to radiotherapy. Several nucleases are important for HR-mediated repair of replication-dependent DSBs and thus replication fork restart. These include three structure-specific nucleases, the 3' MUS81 nuclease, and two 5' nucleases, EEPD1 and Metnase, as well as three end-resection nucleases, MRE11, EXO1, and DNA2. The three structure-specific nucleases evolved at very different times, suggesting incremental acceleration of replication fork restart to limit toxic HR intermediates and genome instability as genomes increased in size during evolution, including the gain of large numbers of HR-prone repetitive elements. Ionizing radiation also induces delayed effects, observed days to weeks after exposure, including delayed cell death and delayed HR. In this review we highlight the roles of HR in cellular responses to ionizing radiation, and discuss the importance of HR as an exploitable target for cancer radiotherapy.

Small-molecule screen reveals synergy of cell cycle checkpoint kinase inhibitors with DNA-damaging chemotherapies in medulloblastoma

Medulloblastoma (MB) consists of four core molecular subgroups with distinct clinical features and prognoses. Treatment consists of surgery, followed by radiotherapy and cytotoxic chemotherapy. Despite this intensive approach, outcome remains dismal for patients with certain subtypes of MB, namely, MYC-amplified Group 3 and TP53-mutated SHH. Using high-throughput assays, six human MB cell lines were screened against a library of 3208 unique compounds. We identified 45 effective compounds from the screen and found that cell cycle checkpoint kinase (CHK1/2) inhibition synergistically enhanced the cytotoxic activity of clinically used chemotherapeutics cyclophosphamide, cisplatin, and gemcitabine. To identify the best-in-class inhibitor, multiple CHK1/2 inhibitors were assessed in mice bearing intracranial MB. When combined with DNA-damaging chemotherapeutics, CHK1/2 inhibition reduced tumor burden and increased survival of animals with high-risk MB, across multiple different models. In total, we tested 14 different models, representing distinct MB subgroups, and data were validated in three independent laboratories. Pharmacodynamics studies confirmed central nervous system penetration. In mice, combination treatment significantly increased DNA damage and apoptosis compared to chemotherapy alone, and studies with cultured cells showed that CHK inhibition disrupted chemotherapy-induced cell cycle arrest. Our findings indicated CHK1/2 inhibition, specifically with LY2606368 (prexasertib), has strong chemosensitizing activity in MB that warrants further clinical investigation. Moreover, these data demonstrated that we developed a robust and collaborative preclinical assessment platform that can be used to identify potentially effective new therapies for clinical evaluation for pediatric MB.

A pilot study for colorectal carcinoma screening by instant metabolomic profiles using conductive polymer spray ionization mass spectrometry

BACKGROUND

The rapid and accurate discrimination of colorectal carcinoma (CRC) and polyps at the molecular level enables early intervention of CRC, which can greatly improve the 5-year survival rate of patients. Here we reported the potential of conductive polymer spray ionization mass spectrometry (CPSI-MS) in successfully screening CRC according to the serum metabolic profile.

METHODS

Trace intravenous blood (50 μL) was collected from 60 colorectal carcinoma (CRC) and 60 polyp patients, respectively. After centrifugation, serum (2 μL) was loaded onto the tip of conductive polymer to form a dried serum spot. When the 5 μL methanol-water (1:1, v/v) extraction solvent was spiked onto the dried serum spot followed with +4.5 kV high voltage applied on the polymer tip, the extracted components will be ionized and carried into the MS system for direct metabolic profiling.

FINDINGS

There were 51 metabolites discovered to be significantly changed in CRC serum compared to polyps. Combining these metabolites as the characteristic panel, the ideal diagnostic performance was achieved by Lasso regression model with the accuracy of 88.3%.

INTERPRETATION

This pilot study demonstrated the potential of CPSI-MS as a cost-effective tool in large-scale CRC screening in the high-risk population.

Overexpression of claspin promotes docetaxel resistance and is associated with prostate-specific antigen recurrence in prostate cancer

Although docetaxel (DTX) confers significant survival benefits in patients with castration‐resistant prostate cancer (CRPC), resistance to DTX inevitably occurs. Therefore, clarifying the mechanisms of DTX resistance may improve survival in patients with CRPC. Claspin plays a pivotal role in DNA replication stress and damage responses and is an essential regulator for the S‐phase checkpoint. CLSPN is an oncogenic gene that contributes to tumor proliferation in several human solid tumors. However, the clinical significance of claspin in prostate cancer (PCa) has not been examined. The present study aimed to elucidate the role of claspin and its relationship with DTX resistance in PCa. We immunohistochemically analyzed the expression of claspin in 89 PCa cases, of which 31 (35%) were positive for claspin. Claspin‐positive cases were associated with higher Gleason score, venous invasion, and perineural invasion. Kaplan–Meier analysis showed that high claspin expression was related to poor prostate‐specific antigen (PSA) relapse‐free prognosis. In a public database, high CLSPN expression was associated with poor PSA relapse‐free prognosis, Gleason score, T stage, lymph node metastasis, CRPC, and metastatic PCa. Claspin knockdown by siRNA decreased cell proliferation, upregulated DTX sensitivity, and suppressed the expression of Akt, Erk1/2, and CHK1 phosphorylation in DU145 and PC3 cell lines. Furthermore, claspin expression was much more upregulated in DTX‐resistant DU145 (DU145‐DR) than in parental DU145 cells. Claspin knockdown significantly upregulated the sensitivity to DTX in DU145‐DR cells. These results suggest that claspin plays an important role in PCa tumor progression and DTX resistance.

Usnic Acid Inhibits Proliferation and Migration through ATM Mediated DNA Damage Response in RKO Colorectal Cancer Cell

BACKGROUND

Usnic Acid (UA), also known as lichenol, has been reported to have inhibitory effects on a variety of cancer cells, but its specific mechanism remained to be elucidated. Tumor chemotherapy drugs, especially DNA damage chemotherapeutic drugs, target Chromosomal DNA, but their spontaneous and acquired drug resistance are also an urgent problem to be solved. Therefore, drug combination research has become the focus of researchers.

METHODS

Here, we evaluated the tumor-suppressing molecular mechanism of UA in colorectal cancer cells RKO from the perspective of the ATM-mediated DNA damage signaling pathway through H2O2 simulating DNA damage chemotherapeutic drugs. CCK8 cell proliferation assay was used to determine the inhibition of RKO cells by hydrogen peroxide and UA alone or in combination, and wound healing assay was applied to determine the effect of the drug on cell migration.

RESULTS

Transfected cells with miRNA18a-5p mimics and inhibitors, MDC and DCFH-DA staining for the measurement of autophagy and ROS, cell cycle and apoptosis were detected by flow cytometry, expressions of microRNA and mRNA were determined by fluorescence quantitative PCR, and protein by Western blot.

DISCUSSION

We found that UA can upregulate ATM via miR-18a to activate the DNA damage signaling pathway and inhibit the proliferation and migration of RKO cells in a concentration-dependent manner.

CONCLUSION

At the same time, DNA damage responses, including cell cycle, autophagy, apoptosis and ROS levels, are also regulated by UA. Therefore, UA combined with DNA damage chemotherapeutic drugs may be an effective treatment for cancer.

Dual PARP and RAD51 Inhibitory Drug Conjugates Show Synergistic and Selective Effects on Breast Cancer Cells

The genetic principle of synthetic lethality has most successfully been exploited in therapies engaging Poly-ADP-ribose-polymerase (PARP) inhibitors to treat patients with homologous recombination (HR)-defective tumors. In this work, we went a step further following the idea of a local molecular cooperation and designed hybrid compounds M1–M3. The drug conjugates M1–M3 combine Olaparib, the first PARP inhibitor approved for clinical use, with Cpd 1, an inhibitor of RAD51 that blocks its HR functions and yet permits RAD51 nucleoprotein filament formation on single-stranded DNA. While in M2 and M3, the parental drugs are linked by -CO-(CH₂)_n-CO-spacers (n = 2 and 4, respectively), they are directly merged omitting the piperazine ring of Olaparib in M1. Monitoring anti-survival effects of M1–M3 in six breast cancer cell lines of different molecular subtypes showed that in each cell line, at least one of the drug conjugates decreased viability by one to two orders of magnitude compared with parental drugs. While triple-negative breast cancer (TNBC) cells with frequent BRCA1 pathway dysfunction were sensitive to spacer-linked hybrid compounds M1 and M2 regardless of their HR capacities, non-TNBC cells were responsive to the merged drug conjugate M1 only, suggesting different spatial requirements for dual inhibition in these two groups of cell lines. These results demonstrate that, depending on chemical linkage, dual PARP1-RAD51 inhibitory drugs can either sensitize non-TNBC and re-sensitize TNBC cells, or discriminate between these groups of cells.

Inhibition of ATM Induces Hypersensitivity to Proton Irradiation by Upregulating Toxic End Joining

Proton Bragg peak irradiation has a higher ionizing density than conventional photon irradiation or the entrance of the proton beam profile. Whether targeting the DNA damage response (DDR) could enhance vulnerability to the distinct pattern of damage induced by proton Bragg peak irradiation is currently unknown. Here, we performed genetic or pharmacologic manipulation of key DDR elements and evaluated DNA damage signaling, DNA repair, and tumor control in cell lines and xenografts treated with the same physical dose across a radiotherapy linear energy transfer spectrum. Radiotherapy consisted of 6 MV photons and the entrance beam or Bragg peak of a 76.8 MeV spot scanning proton beam. More complex DNA double-strand breaks (DSB) induced by Bragg peak proton irradiation preferentially underwent resection and engaged homologous recombination (HR) machinery. Unexpectedly, the ataxia-telangiectasia mutated (ATM) inhibitor, AZD0156, but not an inhibitor of ATM and Rad3-related, rendered cells hypersensitive to more densely ionizing proton Bragg peak irradiation. ATM inhibition blocked resection and shunted more DSBs to processing by toxic ligation through nonhomologous end-joining, whereas loss of DNA ligation via XRCC4 or Lig4 knockdown rescued resection and abolished the enhanced Bragg peak cell killing. Proton Bragg peak monotherapy selectively sensitized cell lines and tumor xenografts with inherent HR defects, and the repair defect induced by ATM inhibitor coadministration showed enhanced efficacy in HR-proficient models. In summary, inherent defects in HR or administration of an ATM inhibitor in HR-proficient tumors selectively enhances the relative biological effectiveness of proton Bragg peak irradiation. SIGNIFICANCE: Coadministration of an ATM inhibitor rewires DNA repair machinery to render cancer cells uniquely hypersensitive to DNA damage induced by the proton Bragg peak, which is characterized by higher density ionization.See related commentary by Nickoloff, p. 3156.

Veliparib Is an Effective Radiosensitizing Agent in a Preclinical Model of Medulloblastoma

Medulloblastoma is the most common malignant childhood brain tumor, and 5-year overall survival rates are as low as 40% depending on molecular subtype, with new therapies critically important. As radiotherapy and chemotherapy act through the induction of DNA damage, the sensitization of cancer cells through the inhibition of DNA damage repair pathways is a potential therapeutic strategy. The poly-(ADP-ribose) polymerase (PARP) inhibitor veliparib was assessed for its ability to augment the cellular response to radiation-induced DNA damage in human medulloblastoma cells. DNA repair following irradiation was assessed using the alkaline comet assay, with veliparib inhibiting the rate of DNA repair. Veliparib treatment also increased the number of γH2AX foci in cells treated with radiation, and analysis of downstream pathways indicated persistent activation of the DNA damage response pathway. Clonogenicity assays demonstrated that veliparib effectively inhibited the colony-forming capacity of medulloblastoma cells, both as a single agent and in combination with irradiation. These data were then validated in vivo using an orthotopic implant model of medulloblastoma. Mice harboring intracranial D425 medulloblastoma xenografts were treated with vehicle, veliparib, 18 Gy multifractionated craniospinal irradiation (CSI), or veliparib combined with 18 Gy CSI. Animals treated with combination therapy exhibited reduced tumor growth rates concomitant with increased intra-tumoral apoptosis observed by immunohistochemistry. Kaplan–Meier analyses revealed a statistically significant increase in survival with combination therapy compared to CSI alone. In summary, PARP inhibition enhanced radiation-induced cytotoxicity of medulloblastoma cells; thus, veliparib or other brain-penetrant PARP inhibitors are potential radiosensitizing agents for the treatment of medulloblastoma.

Targeting WEE1 by adavosertib inhibits the malignant phenotypes of hepatocellular carcinoma

Targeting the cell cycle checkpoints and DNA damage response are promising therapeutic strategies for cancer. Adavosertib is a potent inhibitor of WEE1 kinase, which plays a critical role in regulating cell cycle checkpoints. However, the effect of adavosertib on hepatocellular carcinoma (HCC) treatment, including sorafenib-resistant HCC, has not been thoroughly studied. In this study, we comprehensively investigated the efficacy and pharmacology of adavosertib in HCC therapy. Adavosertib effectively inhibited the proliferation of HCC cells in vitro and suppressed tumor growth in HCC xenografts and patient-derived xenograft (PDX) models in vivo. Additionally, adavosertib treatment effectively inhibited the motility of HCC cells by impairing pseudopodia formation. Further, we revealed that adavosertib induced DNA damage and premature mitosis entrance by disturbing the cell cycle. Thus, HCC cells accumulating DNA damage underwent mitosis without G2/M checkpoint arrest, thereby leading to mitotic catastrophe and apoptosis under adavosertib administration. Given that sorafenib resistance is common in HCC in clinical practice, we also explored the efficacy of adavosertib in sorafenib-resistant HCC. Notably, adavosertib still showed a desirable inhibitory effect on the growth of sorafenib-resistant HCC cells. Adavosertib markedly induced G2/M checkpoint arrest and cell apoptosis in a dose-dependent manner, confirming the similar efficacy of adavosertib in sorafenib-resistant HCC. Collectively, our results highlight the treatment efficacy of adavosertib in HCC regardless of sorafenib resistance, providing insights into exploring novel strategies for HCC therapy.

Potential and promising anticancer drugs from adenosine and its analogs

In recent years, many studies have shown that adenosine has efficacy for treating cancer. More importantly, some adenosine analogs have been successfully marketed to fulfill anticancer purposes. In this review, we summarize the anticancer effects of adenosine and its analogs in clinical trials and preclinical studies, with focus on their anticancer mechanisms. In addition, we link the anticancer activities of adenosine analogs with their structures through structure-activity relationship (SAR) analysis, and highlight additional promising anticancer drug candidates. We hope that this review will be of help in understanding the importance of adenosine and its analogs with anticancer activities and directing future research and development of such compounds.

Clinical Efficacy and Molecular Response Correlates of the WEE1 Inhibitor Adavosertib Combined with Cisplatin in Patients with Metastatic Triple-Negative Breast Cancer

PURPOSE

We report results from a phase II study assessing the efficacy of the WEE1 inhibitor adavosertib with cisplatin in metastatic triple-negative breast cancer (mTNBC).

PATIENTS AND METHODS

Patients with mTNBC treated with 0-1 prior lines of chemotherapy received cisplatin 75 mg/m2 i.v. followed 21 days later by cisplatin plus adavosertib 200 mg oral twice daily for five doses every 21 days. The study had 90% power to detect the difference between null (20%) and alternative (40%) objective response rates (ORR) with a one-sided type I error of 0.1: an ORR >30% was predefined as making the regimen worthy of further study. RNA sequencing and multiplex cyclic immunofluorescence on pre- and post-adavosertib tumor biopsies, as well as targeted next-generation sequencing on archival tissue, were correlated with clinical benefit, defined as stable disease ≥6 months or complete or partial response.

RESULTS

A total of 34 patients initiated protocol therapy; median age was 56 years, 2 patients (6%) had BRCA2 mutations, and 14 (41%) had one prior chemotherapy. ORR was 26% [95% confidence interval (CI), 13-44], and median progression-free survival was 4.9 months (95% CI, 2.3-5.7). Treatment-related grade 3-5 adverse events occurred in 53% of patients, most commonly diarrhea in 21%. One death occurred because of sepsis, possibly related to study therapy. Tumors from patients with clinical benefit demonstrated enriched immune gene expression and T-cell infiltration.

CONCLUSIONS

Among patients with mTNBC treated with 0-1 prior lines, adavosertib combined with cisplatin missed the prespecified ORR cutoff of >30%. The finding of immune-infiltrated tumors in patients with clinical benefit warrants validation.

Role of Non-coding RNAs on the Radiotherapy Sensitivity and Resistance of Head and Neck Cancer: From Basic Research to Clinical Application

Head and neck cancers (HNCs) rank as the sixth common and the seventh leading cause of cancer-related death worldwide, with an estimated incidence of 600,000 cases and 40-50% mortality rate every year. Radiotherapy is a common local therapeutic modality for HNC mainly through the function of ionizing radiation, with approximately 60% of patients treated with radiotherapy or chemoradiotherapy. Although radiotherapy is more advanced and widely used in clinical practice, the 5-year overall survival rates of locally advanced HNCs are still less than 40%. HNC cell resistance to radiotherapy remains one of the major challenges to improve the overall survival in HNC patients. Non-coding RNAs (ncRNAs) are newly discovered functional small RNA molecules that are different from messenger RNAs, which can be translated into a protein. Many previous studies have reported the dysregulation and function of ncRNAs in HNC. Importantly, researchers reported that several ncRNAs were also dysregulated in radiotherapy-sensitive or radiotherapy-resistant HNC tissues compared with the normal cancer tissues. They found that ectopically elevating or knocking down expression of some ncRNAs could significantly influence the response of HNC cancer cells to radiotherapy, indicating that ncRNAs could regulate the sensitivity of cancer cells to radiotherapy. The implying mechanism for ncRNAs in regulating radiotherapy sensitivity may be due to its roles on affecting DNA damage sensation, inducing cell cycle arrest, regulating DNA damage repair, modulating cell apoptosis, etc. Additionally, clinical studies reported that in situ ncRNA expression in HNC tissues may predict the response of radiotherapy, and circulating ncRNA from body liquid serves as minimally invasive therapy-responsive and prognostic biomarkers in HNC. In this review, we aimed to summarize the current function and mechanism of ncRNAs in regulating the sensitivity of HNC cancer cells to radiotherapy and comprehensively described the state of the art on the role of ncRNAs in the prognosis prediction, therapy monitoring, and prediction of response to radiotherapy in HNC.

Overcoming PARPi resistance: Preclinical and clinical evidence in ovarian cancer

Ovarian cancer is the fifth cause of cancer-related deaths in women with high grade serous carcinoma (HGSOC) representing the most common histological subtype. Approximately 50 % of HGSOC are characterized by deficiency in homologous recombination (HR), one of the main cellular pathways to repair DNA double strand breaks and one of the well-described mechanisms is the loss of function of the BRCA1 or BRCA2 genes. Inhibition of the poly-ADP-ribose polymerase (PARP) is synthetic lethal with HR deficiency and the use of PARP inhibitors (PARPi) has significantly improved the outcome of patients with HGSOC with a greater benefit in patients with BRCA1/2 deficient tumors. However, intrinsic or acquired resistance to PARPi inevitably occurs in most HGSOC patients. Distinct heterogeneous mechanisms underlying the resistance to PARPi have been described, including a decrease in intracellular drug levels due to upregulation of multidrug efflux pumps, loss of expression/inactivating mutations in the PARP1 protein, restoration of HR and the protection of the replicative fork. Deciphering the molecular mechanisms of resistance to PARPi is of paramount importance towards the development of new treatment strategies and/or novel pharmacological agents to overcome this chemoresistance and optimize the treatment regimen for individual HGSOC patients. The current review summarizes the mechanisms underlying the resistance to PARPi, the available preclinical and clinical data on new combination treatment strategies (with chemotherapy, anti-angiogenic agents and immune checkpoint inhibitors) as well as agents under investigation which target the DNA damage response.

Progress towards a clinically-successful ATR inhibitor for cancer therapy

The DNA damage response (DDR) is now known to play an important role in both cancer development and its treatment. Targeting proteins such as ATR (Ataxia telangiectasia mutated and Rad3-related) kinase, a major regulator of DDR, has demonstrated significant therapeutic potential in cancer treatment, with ATR inhibitors having shown anti-tumour activity not just as monotherapies, but also in potentiating the effects of conventional chemotherapy, radiotherapy, and immunotherapy. This review focuses on the biology of ATR, its functional role in cancer development and treatment, and the rationale behind inhibition of this target as a therapeutic approach, including evaluation of the progress and current status of development of potent and specific ATR inhibitors that have emerged in recent decades. The current applications of these inhibitors both in preclinical and clinical studies either as single agents or in combinations with chemotherapy, radiotherapy and immunotherapy are also extensively discussed. This review concludes with some insights into the various concerns raised or observed with ATR inhibition in both the preclinical and clinical settings, with some suggested solutions.

Alkaloids as Anticancer Agents: A Review of Chinese Patents in Recent 5 Years

BACKGROUND

In recent years, many novel alkaloids with anticancer activity have been found in China, and some of them are promising for developing as anticancer agents.

OBJECTIVE

This review aims to provide a comprehensive overview of the information about alkaloid anticancer agents disclosed in Chinese patents, and discusses their potential to be developed as anticancer drugs used clinically.

METHODS

Anticancer alkaloids disclosed in Chinese patents in recent 5 years were presented according to their mode of actions. Their study results published on PubMed, and SciDirect databases were presented.

RESULTS

More than one hundred anticancer alkaloids were disclosed in Chinese patents and their mode of action referred to arresting cell cycle, inhibiting protein kinases, affecting DNA synthesis and p53 expression, etc. Conclusion: Many newly found alkaloids displayed potent anticancer activity both in vitro and in vivo, and some of the anticancer alkaloids acted as protein kinase inhibitors or CDK inhibitors possess the potential for developing as novel anticancer agents.

LncRNA linc00312 suppresses radiotherapy resistance by targeting DNA-PKcs and impairing DNA damage repair in nasopharyngeal carcinoma

Radioresistance is the main obstacle in the clinical management of nasopharyngeal carcinoma (NPC). linc00312 is deregulated in a number of human cancers, including NPC. However, the detailed functions and underlying mechanisms of linc00312 in regulating radiosensitivity of NPC remains unknown. In this study, cox regression analysis was used to assess the association between linc00312 and NPC patients’ survival after radiotherapy. Our results reveal that linc00312 is significantly down-regulated in NPC tissues and patients with higher expression of linc00312 are significantly associated with longer overall survival and better short-term radiotherapy efficacy. Overexpression of linc00312 could increase the sensitivity of NPC cells to ionizing radiation, as indicated by clonogenic survival assay, comet assay, and flow cytometry. Mechanistically, RNA pull down and RNA immunoprecipitation were performed to investigate the binding proteins of linc00312. linc00312 directly binds to DNA-PKcs, hinders the recruitment of DNA-PKcs to Ku80, and inhibits phosphorylation of AKT–DNA–PKcs axis, therefore inhibiting the DNA damage signal sensation and transduction in the NHEJ repair pathway. In addition, linc00312 impairs DNA repair and cell cycle control by suppressing MRN–ATM–CHK2 signal and ATR–CHK1 signal. In summary, we identified DNA-PKcs as the binding protein of linc00312 and revealed a novel mechanism of linc00312 in the DNA damage response, providing evidence for a potential therapeutic strategy in NPC.

Exploiting DNA repair pathways for tumor sensitization, mitigation of resistance, and normal tissue protection in radiotherapy

More than half of cancer patients are treated with radiotherapy, which kills tumor cells by directly and indirectly inducing DNA damage, including cytotoxic DNA double-strand breaks (DSBs). Tumor cells respond to these threats by activating a complex signaling network termed the DNA damage response (DDR). The DDR arrests the cell cycle, upregulates DNA repair, and triggers apoptosis when damage is excessive. The DDR signaling and DNA repair pathways are fertile terrain for therapeutic intervention. This review highlights strategies to improve therapeutic gain by targeting DDR and DNA repair pathways to radiosensitize tumor cells, overcome intrinsic and acquired tumor radioresistance, and protect normal tissue. Many biological and environmental factors determine tumor and normal cell responses to ionizing radiation and genotoxic chemotherapeutics. These include cell type and cell cycle phase distribution; tissue/tumor microenvironment and oxygen levels; DNA damage load and quality; DNA repair capacity; and susceptibility to apoptosis or other active or passive cell death pathways. We provide an overview of radiobiological parameters associated with X-ray, proton, and carbon ion radiotherapy; DNA repair and DNA damage signaling pathways; and other factors that regulate tumor and normal cell responses to radiation. We then focus on recent studies exploiting DSB repair pathways to enhance radiotherapy therapeutic gain.

An Escherichia coli Effector Protein EspF May Induce Host DNA Damage via Interaction With SMC1

Enterohemorrhagic Escherichia coli (EHEC) O157: H7 is an important foodborne pathogen that causes human diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome. EspF is one of the most important effector proteins injected by the Type III Secretion System. It can target mitochondria and nucleoli, stimulate host cells to produce ROS, and promote host cell apoptosis. However, the mechanism of the host-pathogen interaction leading to host oxidative stress and cell cytotoxic effects such as DNA damage remains to be elucidated. Here, we used Cell Counting Kit-8 (CCK-8) assays and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-OHdG) ELISA to study cell viability and DNA oxidative damage level after exposure to EspF. Western blot and immunofluorescence were also used to determine the level of the DNA damage target protein p-H2AX and cell morphology changes after EspF infection. Moreover, we verified the toxicity in intestinal epithelial cells mediated by EspF infection in vivo. In addition, we screened the host proteins that interact with EspF using CoIP-MS. We found that EspF may more depend on its C-terminus to interact with SMC1, and EspF could activate SMC1 phosphorylation and migrate it to the cytoplasm. In summary, this study revealed that EspF might mediate host cell DNA damage and found a new interaction between EspF and the DNA damage repair protein SMC1. Thus, EspF may mediate DNA damage by regulating the subcellular localization and phosphorylation of SMC1.

Bridging of nucleosome-proximal DNA double-strand breaks by PARP2 enhances its interaction with HPF1

Poly(ADP-ribose) Polymerase 2 (PARP2) is one of three DNA-dependent PARPs involved in the detection of DNA damage. Upon binding to DNA double-strand breaks, PARP2 uses nicotinamide adenine dinucleotide to synthesize poly(ADP-ribose) (PAR) onto itself and other proteins, including histones. PAR chains in turn promote the DNA damage response by recruiting downstream repair factors. These early steps of DNA damage signaling are relevant for understanding how genome integrity is maintained and how their failure leads to genome instability or cancer. There is no structural information on DNA double-strand break detection in the context of chromatin. Here we present a cryo-EM structure of two nucleosomes bridged by human PARP2 and confirm that PARP2 bridges DNA ends in the context of nucleosomes bearing short linker DNA. We demonstrate that the conformation of PARP2 bound to damaged chromatin provides a binding platform for the regulatory protein Histone PARylation Factor 1 (HPF1), and that the resulting HPF1•PARP2•nucleosome complex is enzymatically active. Our results contribute to a structural view of the early steps of the DNA damage response in chromatin.

Targeting DNA damage response kinases in cancer therapy

Cancer cells die when their decimated DNA damage response (DDR) unsuccessfully handles DNA damage. This notion has been successfully exploited when targeting PARP (poly ADP-ribose polymerase) in homologous recombination-deficient cells. With the greater understanding of DDR achieved in the last decade, new cancer therapy targets within the DDR network have been identified. Intriguingly, many of the molecules that have advanced into clinical trials are inhibitors of DDR kinases. This special issue is devoted to discussing the mechanism of cell killing and the level of success that such inhibitors have reached in pre-clinical and clinical settings.

Association of XRCC2 rs2040639 with the survival of patients with oral squamous cell carcinoma undergoing concurrent chemoradiotherapy

OBJECTIVE

To investigate the association between the variants of DNA double-strand break repair genes and the clinical outcomes of patients with oral squamous cell carcinoma (OSCC) undergoing concurrent chemoradiotherapy.

METHODS

Five variants of DNA double-strand break repair genes in samples from 319 patients with OSCC were genotyped using the Sequenom iPLEX MassARRAY system. Kaplan-Meier curves and Cox proportional hazards analysis were used to identify the factors associated with patient survival.

RESULTS

The XRCC2 rs2040639 (G3063A) polymorphism in the codominant model was associated with decreased recurrence risk (hazard ratio [HR] = 0.55, 95% confidence interval [CI] = 0.31-0.98; p = 0.042). A marginally significant interaction was observed between XRCC2 rs2040639 and PRKDC rs7003908 in patients carrying the AA and AA genotypes; these patients showed reduced recurrence risk (HR = 0.36, 95% CI = 0.17-0.79; p = 0.010).

CONCLUSION

The A-allele of XRCC2 rs2040639 is a favorable prognostic factor for disease-free survival. Patients with these genotypes may benefit from concurrent chemoradiotherapy. Additional confirmation from studies with larger samples or other ethnic populations is warranted.

Activation of ATM/Akt/CREB/eNOS Signaling Axis by Aphidicolin Increases NO Production and Vessel Relaxation in Endothelial Cells and Rat Aortas

Although DNA damage responses (DDRs) are reported to be involved in nitric oxide (NO) production in response to genotoxic stresses, the precise mechanism of DDR-mediated NO production has not been fully understood. Using a genotoxic agent aphidicolin, we investigated how DDRs regulate NO production in bovine aortic endothelial cells. Prolonged (over 24 h) treatment with aphidicolin increased NO production and endothelial NO synthase (eNOS) protein expression, which was accompanied by increased eNOS dimer/monomer ratio, tetrahydrobiopterin levels, and eNOS mRNA expression. A promoter assay using 5'-serially deleted eNOS promoters revealed that Tax-responsive element site, located at -962 to -873 of the eNOS promoter, was responsible for aphidicolin-stimulated eNOS gene expression. Aphidicolin increased CREB activity and ectopic expression of dominantnegative inhibitor of CREB, A-CREB, repressed the stimulatory effects of aphidicolin on eNOS gene expression and its promoter activity. Co-treatment with LY294002 decreased the aphidicolin-stimulated increase in p-CREB-Ser133 level, eNOS expression, and NO production. Furthermore, ectopic expression of dominant-negative Akt construct attenuated aphidicolin-stimulated NO production. Aphidicolin increased p-ATM-Ser1981 and the knockdown of ATM using siRNA attenuated all stimulatory effects of aphidicolin on p-Akt-Ser473, p-CREB-Ser133, eNOS expression, and NO production. Additionally, these stimulatory effects of aphidicolin were similarly observed in human umbilical vein endothelial cells. Lastly, aphidicolin increased acetylcholine-induced vessel relaxation in rat aortas, which was accompanied by increased p-ATM-Ser1981, p-Akt-Ser473, p-CREB-Ser133, and eNOS expression. In conclusion, our results demonstrate that in response to aphidicolin, activation of ATM/Akt/CREB/eNOS signaling cascade mediates increase of NO production and vessel relaxation in endothelial cells and rat aortas.

Proteolysis targeting chimera (PROTAC) in drug discovery paradigm: Recent progress and future challenges

Proteolysis targeting chimera (PROTAC), hijacking protein of interest (POI) and recruiting E3 ligase for target degradation via the ubiquitin-proteasome pathway, is a novel drug discovery paradigm which has been widely used as biological tools and medicinal molecules with the potential of clinical application value. Currently, ARV-110, an orally small molecule PROTAC was designed to specifically target Androgen receptor (AR), firstly enters clinical phase I trials for the treatment of metastatic castration-resistant prostate cancer, which turns a new avenue for the development of PROTAC. We herein provide a detail summary on the latest one year progress of PROTAC target various proteins and elucidate the advantages of PROTAC technology. Finally, the potential challenges of this vibrant field are also discussed.

Small molecule 2,3-DCPE induces S phase arrest by activating the ATM/ATR-Chk1-Cdc25A signaling pathway in DLD-1 colon cancer cells

In our previous study, it was reported that 2[[3-(2,3-dichlorophenoxy)propyl]amino]ethanol (2,3-DCPE) induces apoptosis and cell cycle arrest. The current study aimed to investigate the molecular mechanism involved in 2,3-DCPE-induced S phase arrest. The results demonstrated that 2,3-DCPE upregulated phosphorylated (p-)H2A histone family member X, a biomarker of DNA damage, in the DLD-1 colon cancer cell line. Western blotting revealed that 2,3-DCPE increased the checkpoint kinase (Chk)1 (Ser317 and Ser345) level and decreased the expression of M-phase inducer phosphatase 1 (Cdc25A) in a time-dependent manner. Subsequently, the results demonstrated that the ataxia-telangiectasia mutated (ATM) and ataxia-telangiectasia and Rad3-related (ATR) inhibitors wortmannin and caffeine had no effect on the cell cycle; however, the inhibitors partially abrogated 2,3-DCPE-induced S phase arrest. Flow cytometry assays revealed that caffeine (2 mM) reduced the proportion of S phase cells from 83 to 39.6% and that wortmannin (500 nM) reduced the proportion of S phase cells from 83 to 48.2%. Furthermore, wortmannin and caffeine inhibited the 2,3-DCPE-mediated phosphorylation of Chk1 and the degradation of Cdc25A. However, these ATM/ATR inhibitors had limited effect on 2,3-DCPE-induced apoptosis. Taken together, the data of the current study indicated that 2,3-DCPE caused DNA damage in colon cancer cells and that 2,3-DCPE-induced S phase arrest was associated with the activation of the ATM/ATR-Chk1-Cdc25A pathway.

Structure-activity relationships of Wee1 inhibitors: A review

Wee1 kinase plays an important role in regulating G2/M checkpoint and S phase, and the inhibition of it will lead to mitotic catastrophe in cancer cells with p53 mutation or deletion. Therefore, the mechanism of Wee1 kinase in cancer treatment and the development of its inhibitors have become a research hotspot. However, although a variety of Wee1 inhibitors with different scaffolds and considerable activity have been successfully identified, so far no one has systematically summarized the structure-activity relationships (SARs) of Wee1 inhibitors. Previous reviews mainly focused on its mechanism and clinical application. To facilitate the rational design and development of Wee1 inhibitors in the future, this paper systematically summarizes its structural types, SARs and binding modes according to the Wee1 inhibitors reported in scientific journals, and also summarizes the regulatory effect of Wee1 kinase on cell cycle and the progress of its inhibitors in clinical application.

DNA Damage Promotes TMPRSS2-ERG Oncoprotein Destruction and Prostate Cancer Suppression via Signaling Converged by GSK3β and WEE1

TMPRSS2-ERG gene fusion occurs in approximately 50% of cases of prostate cancer (PCa), and the fusion product is a key driver of prostate oncogenesis. However, how to leverage cellular signaling to ablate TMPRSS2-ERG oncoprotein for PCa treatment remains elusive. Here, we demonstrate that DNA damage induces proteasomal degradation of wild-type ERG and TMPRSS2-ERG oncoprotein through ERG threonine-187 and tyrosine-190 phosphorylation mediated by GSK3β and WEE1, respectively. The dual phosphorylation triggers ERG recognition and degradation by the E3 ubiquitin ligase FBW7 in a manner independent of a canonical degron. DNA damage-induced TMPRSS2-ERG degradation was abolished by cancer-associated PTEN deletion or GSK3β inactivation. Blockade of DNA damage-induced TMPRSS2-ERG oncoprotein degradation causes chemotherapy-resistant growth of fusion-positive PCa cells in culture and in mice. Our findings uncover a previously unrecognized TMPRSS2-ERG protein destruction mechanism and demonstrate that intact PTEN and GSK3β signaling are essential for effective targeting of ERG protein by genotoxic therapeutics in fusion-positive PCa.

NRIP3 upregulation confers resistance to chemoradiotherapy in ESCC via RTF2 removal by accelerating ubiquitination and degradation of RTF2

Esophageal squamous cell carcinoma (ESCC) is a common malignant cancer worldwide. Despite recent improvements in surgical techniques and adjuvant therapies, the prognosis of patients with advanced ESCC remains poor. Resistance to chemoradiotherapy (CRT) remains a major cause of treatment failure for advanced ESCC patients. Here, we report that NRIP3 (nuclear receptor interacting protein 3) promotes ESCC tumor cell growth and resistance to CRT in ESCC cells by increasing and binding to DDI1 (DNA-damage inducible 1 homolog 1) and RTF2 (homologous to Schizosaccharomyces pombe Rtf2), and accelerating the removal of RTF2, which is a key determinant for the ability of cells to manage replication stress. In addition, we found that NRIP3 could increase DDI1 expression via PPARα. The NRIP3-PPARα-DDI1-RTF2 axis represents a protective molecular pathway in ESCC cells that mediates resistance to replication stress signals induced by chemoradiotherapy. In addition, elevated NRIP3 is associated with the poor clinical outcome of ESCC patients receiving radiotherapy and/or cisplatin-based chemotherapy. Our study therefore reveals that NRIP3 is a prognostic factor in ESCC and could have some predictive value to select patients who benefit from CRT treatment. A common mechanism that protects ESCC tumor cells from DNA damage induced by CRT is also revealed in this study.

Enhanced radiotherapy using photothermal therapy based on dual-sensitizer of gold nanoparticles with acid-induced aggregation

The damaged DNA strands caused by radiotherapy (RT) can repair by themselves. A gold nanoparticles (GNPs) system with acid-induced aggregation was developed into a dual sensitizer owing to its high radioactive rays attenuation ability and enhanced photothermal heating efficiency after GNPs aggregation to achieve a combination therapy of RT and photothermal therapy (PTT). In this combination therapy, the formed GNP aggregates firstly showed a higher sensitize enhancement ratio (SER) value (1.52). Importantly, the self-repair of damaged DNA strands was inhibited by mild PTT through down-regulating the expression of DNA repair protein, thus resulting in a much higher SER value (1.68). Anti-tumor studies further demonstrated that this combination therapy exhibited ideal anti-tumor efficacy. Furthermore, the imaging signals of GNPs in computed tomography and photoacoustic were significantly improved following the GNPs aggregation. Therefore, a dual sensitizer with multimodal imaging was successfully developed and can be further applied as a new anti-tumor therapy.

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.

New strategies in ovarian cancer treatment

Insights from basic science dissecting carcinogenesis in the fallopian tube and ovary have led to a deeper understanding of the origin, molecular characteristics, and types of ovarian cancers. This logically then has led to the development of novel approaches to treat ovarian cancer. Increasingly, novel agents are being developed to target the different growth pathways. The identification of molecular markers associated with different histopathologies has resulted in newer clinical trial designs to capture both clinical and translational endpoints. Unique molecular characteristics in DNA damage and repair pathways and unique cell surface markers have driven new drug development, yielding promise for both patients with platinum-sensitive and platinum-resistant ovarian cancers. Specific examples described include the histology-selective mutations, such as ARID1A in clear cell and endometrioid ovarian cancers; the rationale for using cell cycle checkpoint inhibitors when there already is a p53-mediated loss of cell cycle checkpoint regulation or combinations of agents that will both induce neoantigen formation and unleash immune modulators; and techniques to enhance the therapeutic delivery of known agents. A systematic and thoughtful approach to combining agents in clinical trials is needed so that irrespective of the trial outcomes, the results inform both clinical and translational endpoints.

Expression and prognostic significance of the P53-related DNA damage repair proteins checkpoint kinase 1 (CHK1) and growth arrest and DNA-damage-inducible 45 alpha (GADD45A) in human oral squamous cell carcinoma

DNA damage repair is a key factor in the maintenance of cell genome stability, plays an important role in the regulation of tumour evolution, and can affect the prognosis of cancer patients. This study aimed to detect the protein expression of the DNA damage repair protein P53 and its upstream and downstream regulators, CHK1, GADD45A, and MDM2, in oral squamous cell carcinoma (OSCC), in order to analyse the association between the expression of these proteins and overall survival, and to assess their prognostic implications for OSCC patients. The expression of the above proteins was detected by immunohistochemistry in 80 human OSCC tissue samples and in non-cancerous tissue samples. Compared to that in the non-cancerous tissue, the expression of CHK1, GADD45A, and MDM2 in OSCC tissue was significantly increased. The protein expression of the tumour suppressor gene P53 was also increased. Patients with high CHK1 and MDM2 expression levels had a reduced survival time and a poor prognosis, whereas patients with high GADD45A expression levels had a good prognosis. Our results indicate that high CHK1 expression is an independent risk factor for poor OSCC prognosis, and that CHK1 may be a potential target for OSCC clinical treatment.

Digoxin Enhances the Anticancer Effect on Non-Small Cell Lung Cancer While Reducing the Cardiotoxicity of Adriamycin

Digoxin is widely used to treat heart failure. Epidemiological studies suggested it might be used as an anticancer drug or sensitizing agent for cancer therapy. Adriamycin is a well-known anticancer drug, but often causes cardiotoxicity which limits its use. We recently investigated the anticancer effects of digoxin alone or in combination with adriamycin on human non-small cell lung cancer in vitro and in vivo. Digoxin reduced the viability of A549 and H1299 cells in vitro, increased DNA damage by promoting ROS generation and inhibiting both DNA double strand break (DSB) and single strand break (SSB) repair. Combination with adriamycin showed synergistic antiproliferative effects at the ratios of 1/2IC50_DIG:IC50_ADR and IC50_DIG:IC50_ADR on A549 and H1299 cells, respectively. In vivo, digoxin potently inhibited A549 growth in both zebrafish and nude mouse xenograft model. Co-treatment with adriamycin not only enhanced the antitumor efficacy, but also reduced the cardiotoxicity. Our findings suggest that digoxin has the potential to be applied as an antitumor drug via inhibiting both DNA DSB and SSB repair, and combination with adriamycin for therapy of human non-small cell lung cancer is reasonable.

Targeting DNA-PK in cancer

DNA-dependent protein kinase (DNA-PK) is involved in many cellular pathways. It has a key role in the cellular response to DNA damage, in the repair of DNA double-strand break (DNA-DSBs) and as a consequence an important role in maintaining genomic integrity. In addition, DNA-PK has been shown to modulate transcription, to be involved in the development of the immune system and to protect telomeres. These pleotropic involvements and the fact that its expression is de-regulated in cancer have made DNA-PK an intriguing therapeutic target in cancer therapy, especially when combined with agents causing DNA-DSBs such as topoisomerase II inhibitors and ionizing radiation. Different small molecule inhibitors of DNA-PK have been recently synthesized and some are now being tested in clinical trials. This review discusses what is known about DNA-PK, its role in tumor biology, DNA repair and cancer therapy and critically discusses its inhibition as a potential therapeutic approach.

Olaparib Combined with an ATR or Chk1 Inhibitor as a Treatment Strategy for Acquired Olaparib-Resistant BRCA1 Mutant Ovarian Cells

OBJECTIVE

Despite the promise of PARP inhibitors (PARPi) for treating BRCA1/2 mutated ovarian cancer (OC), drug resistance invariably develops. We hypothesized rationale drug combinations, targeting key molecules in DNA repair pathways and the cell cycle may be synergistic and overcome acquired PARPi resistance.

METHODS

Drug sensitivity to PARPi alone and in combination with inhibitors of key DNA repair and cell cycle proteins, including ATR (VE-821), Chk1 (MK-8776), Wee1 (MK-1775), RAD51 (RI-1) was assessed in PARPi-sensitive (UWB1) and -resistant (UWB1-R) gBRCA1 mutant OC cell lines using a cell proliferation assay. The Bliss synergy model was used to estimate the two-drug combination effect and pharmacologic synergy (Bliss score ≥ 0) or antagonistic (Bliss score ≥ 0) response of the PARPi in combination with the inhibitors.

RESULTS

IC₅₀ for olaparib alone was 1.6 ± 0.9 µM compared to 3.4 ± 0.6 µM (p = 0.05) for UWB1 and UWB1-R cells, respectively. UWB1-R demonstrated increased sensitivity to ATRi (p = 0.04) compared to UWB1. Olaparib (0.3-1.25 µM) and ATRi (0.8-2.5 µM) were synergistic with Bliss scores of 17.2 ± 0.2, 11.9 ± 0.6 for UWB1 and UWB1-R cells, respectively. Olaparib (0.3-1.25 µM) and Chk1i(0.05-1.25 µM) were synergistic with Bliss scores of 8.3 ± 1.6, 5.7 ± 2.9 for UWB1 and UWB1-R cells, respectively.

CONCLUSIONS

Combining an ATRi or Chk1i with olaparib is synergistic in both PARPi-sensitive and -resistant BRCA1 mutated OC cell models, and are rationale combinations for further clinical development.

Aberrantly Expressed Timeless Regulates Cell Proliferation and Cisplatin Efficacy in Cervical Cancer

Timeless is a regulator of molecular clockwork in Drosophila and related to cancer development in mammals. This study aimed to investigate the effect of Timeless on cell proliferation and cisplatin sensitivity in cervical cancer. Timeless expression was determined by bioinformatics analysis, immunohistochemistry, and quantitative polymerase chain reaction (qPCR). Chromatin immunoprecipitation assays and reporter gene assays were applied to determine the transcriptional factor contributing to Timeless upregulation. The effects of Timeless depletion on cell proliferation and cisplatin sensitivity were determined through in vitro and in vivo experiments. Cell apoptosis and senescence were assessed by flow cytometry and β-galactosidase staining. DNA damage and DNA repair pathways were determined by comet assay, immunofluorescent staining, and Western blot analysis. Timeless is aberrantly expressed in ∼52.5% of cervical cancer tissues. E2F1 and E2F4 contribute to the transcriptional activation of Timeless. Timeless depletion inhibits cell proliferation and increases cisplatin sensitivity in vitro and in vivo. Knockdown of Timeless induces cell apoptosis and cell senescence. Mechanically, Timeless silencing leads to DNA damage and impairs the activation of the ATR/CHK1 pathway in response to cisplatin in cervical cancer. Timeless is overexpressed in cervical cancer and regulates cell proliferation and cisplatin sensitivity, presenting an attractive target for cisplatin sensitizer in cervical cancer.

A pan-cancer transcriptome analysis identifies replication fork and innate immunity genes as modifiers of response to the CHK1 inhibitor prexasertib

The combined influence of oncogenic drivers, genomic instability, and/or DNA damage repair deficiencies increases replication stress in cancer. Cells with high replication stress rely on the upregulation of checkpoints like those governed by CHK1 for survival. Previous studies of the CHK1 inhibitor prexasertib demonstrated activity across multiple cancer types. Therefore, we sought to (1) identify markers of prexasertib sensitivity and (2) define the molecular mechanism(s) of intrinsic and acquired resistance using preclinical models representing multiple tumor types. Our findings indicate that while cyclin E dysregulation is a driving mechanism of prexasertib response, biomarkers associated with this aberration lack sufficient predictive power to render them clinically actionable for patient selection. Transcriptome analysis of a pan-cancer cell line panel and in vivo models revealed an association between expression of E2F target genes and prexasertib sensitivity and identified innate immunity genes associated with prexasertib resistance. Functional RNAi studies supported a causal role of replication fork components as modulators of prexasertib response. Mechanisms that protect cells from oncogene-induced replication stress may safeguard tumors from such stress induced by a CHK1 inhibitor, resulting in acquired drug resistance. Furthermore, resistance to prexasertib may be shaped by innate immunity.

Targeting the DNA damage response (DDR) by natural compounds

Natural compounds (NC) are an important source of anticancer drugs. The genomic DNA of tumor cells is a major target of conventional anticancer therapeutics (cAT). DNA damage elicits a complex stress response programme termed DNA damage response (DDR), with the PI3-like kinase ATM and ATR being the key regulators. Since the DDR coordinates mechanisms of DNA repair and apoptosis, hence regulating the balance between death and survival, it is an attractive target of novel anticancer strategies. The aim of the study was to identify natural compounds derived from endophytic fungi, lichens, marine sponges or plants that interfere with mechanisms of the DDR. To this end, the cytotoxic and DDR modulating potency of 296 natural compounds, used alone or in combination with the cAT cisplatin (Cis) and doxorubicin (Doxo) was investigated by fluorescence-based analysis of the ATM/ATR-catalyzed S139 phosphorylation of histone 2AX (γH2AX), a surrogate marker of DNA damage-triggered DDR. After initial screening, a total of ten natural compounds were identified that were toxic in pancreatic carcinoma cells and activated the DDR on their own and/or promoted the DDR if used in combination with cAT. Their mode of action was shown to be independent of drug transport mechanisms. Based on their chemical structures, DDR modulatory activity and published data we suggest the marine NC 5-epi-nakijiquinone Q and 5-epi-ilimaquinone as well as the fungal compound secalonic acid F as most promising NC-based drug candidates for future synthesis of DDR-modulating chemical derivatives and their preclinical in vitro and in vivo testing.

Oncogenic Roles of RAD51AP1 in Tumor Tissues Related to Overall Survival and Disease-Free Survival in Hepatocellular Carcinoma

OBJECTIVE

This study aimed to investigate the associations between RAD51AP1 and the outcomes of hepatocellular carcinoma (HCC).

METHODS

RAD51AP1 expression levels were compared in Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA) datasets. The Liver Hepatocellular Carcinoma (TCGA, Provisional) and GSE36376 datasets were used for survival analysis. RAD51AP1 associations with clinicopathological features were determined with the GSE36376 dataset.

RESULTS

RAD51AP1 mRNA expression was significantly upregulated in advanced liver fibrosis samples (S3-4 vs. S0-2 and G3-4 vs. G0-2) from hepatitis B virus (HBV)-related liver fibrosis patients and in tumor tissues and peripheral blood mononuclear cells (PBMCs) from HCC patients (all P < 0.05). HCC patients with high RAD51AP1 expression had significantly worse overall survival (OS) and disease-free survival (DFS) than those with low RAD51AP1 expression (P = 0.0034 and P = 0.0012, respectively) in the TCGA dataset, and these findings were validated with the GSE36376 dataset (P = 0.0074 and P = 0.0003, respectively). A Cox regression model indicated that RAD51AP1 was a risk factor for OS and DFS in HCC patients in GSE36376 (HR = 1.54, 95% CI = 1.02-2.32, P = 0.04 and HR = 1.71, 95% CI = 1.22-2.39, P = 0.002, respectively). Moreover, RAD51AP1 mRNA expression increased gradually with increasing tumor stage, including stratification by American Joint Committee on Cancer (AJCC) stages, Barcelona Clinic Liver Cancer (BCLC) stages and Edmondson grades. In addition, RAD51AP1 was overexpressed in HCC patients with intrahepatic metastasis, major portal vein invasion, vascular invasion and/or an alpha-fetoprotein (AFP) level > 300 ng/ml.

CONCLUSIONS

Contributing to an advanced tumor stage, intrahepatic metastasis, vascular invasion and AFP level elevation, RAD51AP1 upregulation was significantly associated with OS and DFS in HCC patients.

Hyaluronan in the Tumor Microenvironment

The extracellular matrix is part of the microenvironment and its functions are associated with the physical and chemical properties of the tissue. Among the extracellular components, the glycosaminoglycan hyaluronan is a key component, defining both the physical and biochemical characteristics of the healthy matrices. The hyaluronan metabolism is strictly regulated in physiological conditions, but in the tumoral tissues, its expression, size and binding proteins interaction are dysregulated. Hyaluronan from the tumor microenvironment promotes tumor cell proliferation, invasion, immune evasion, stemness alterations as well as drug resistance. This chapter describes data regarding novel concepts of hyaluronan functions in the tumor. Additionally, we discuss potential clinical applications of targeting HA metabolism in cancer therapy.

Development and Characterization of a Wee1 Kinase Degrader

The G1/S cell cycle checkpoint is frequently dysregulated in cancer, leaving cancer cells reliant on a functional G2/M checkpoint to prevent excessive DNA damage. Wee1 regulates the G2/M checkpoint by phosphorylating CDK1 at Tyr15 to prevent mitotic entry. Previous drug development efforts targeting Wee1 resulted in the clinical-grade inhibitor, AZD1775. However, AZD1775 is burdened by dose-limiting adverse events, and has off-target PLK1 activity. In an attempt to overcome these limitations, we developed Wee1 degraders by conjugating AZD1775 to the cereblon (CRBN)-binding ligand, pomalidomide. The resulting lead compound, ZNL-02-096, degrades Wee1 while sparing PLK1, induces G2/M accumulation at 10-fold lower doses than AZD1775, and synergizes with Olaparib in ovarian cancer cells. We demonstrate that ZNL-02-096 has CRBN-dependent pharmacology that is distinct from AZD1775, which justifies further evaluation of selective Wee1 degraders.

Co-inhibition of HDAC and MLL-menin interaction targets MLL-rearranged acute myeloid leukemia cells via disruption of DNA damage checkpoint and DNA repair

While the aberrant translocation of the mixed-lineage leukemia (MLL) gene drives pathogenesis of acute myeloid leukemia (AML), it represents an independent predictor for poor prognosis of adult AML patients. Thus, small molecule inhibitors targeting menin-MLL fusion protein interaction have been emerging for the treatment of MLL-rearranged AML. As both inhibitors of histone deacetylase (HDAC) and menin-MLL interaction target the transcription-regulatory machinery involving epigenetic regulation of chromatin remodeling that governs the expression of genes involved in tumorigenesis, we hypothesized that these two classes of agents might interact to kill MLL-rearranged (MLL-r) AML cells. Here, we report that the combination treatment with subtoxic doses of the HDAC inhibitor chidamide and the menin-MLL interaction inhibitor MI-3 displayed a highly synergistic anti-tumor activity against human MLL-r AML cells in vitro and in vivo, but not those without this genetic aberration. Mechanistically, co-exposure to chidamide and MI-3 led to robust apoptosis in MLL-r AML cells, in association with loss of mitochondrial membrane potential and a sharp increase in ROS generation. Combined treatment also disrupted DNA damage checkpoint at the level of CHK1 and CHK2 kinases, rather than their upstream kinases (ATR and ATM), as well as DNA repair likely via homologous recombination (HR), but not non-homologous end joining (NHEJ). Genome-wide RNAseq revealed gene expression alterations involving several potential signaling pathways (e.g., cell cycle, DNA repair, MAPK, NF-κB) that might account for or contribute to the mechanisms of action underlying anti-leukemia activity of chidamide and MI-3 as a single agent and particularly in combination in MLL-r AML. Collectively, these findings provide a preclinical basis for further clinical investigation of this novel targeted strategy combining HDAC and Menin-MLL interaction inhibitors to improve therapeutic outcomes in a subset of patients with poor-prognostic MLL-r leukemia.

Challenges and Opportunities for Childhood Cancer Drug Development

Cancer in children is rare with approximately 15,700 new cases diagnosed in the United States annually. Through use of multimodality therapy (surgery, radiation therapy, and aggressive chemotherapy), 70% of patients will be "cured" of their disease, and 5-year event-free survival exceeds 80%. However, for patients surviving their malignancy, therapy-related long-term adverse effects are severe, with an estimated 50% having chronic life-threatening toxicities related to therapy in their fourth or fifth decade of life. While overall intensive therapy with cytotoxic agents continues to reduce cancer-related mortality, new understanding of the molecular etiology of many childhood cancers offers an opportunity to redirect efforts to develop effective, less genotoxic therapeutic options, including agents that target oncogenic drivers directly, and the potential for use of agents that target the tumor microenvironment and immune-directed therapies. However, for many high-risk cancers, significant challenges remain.

CRIF1 as a potential target to improve the radiosensitivity of osteosarcoma

Resistance to ionizing radiation (IR), which is a conventional treatment for osteosarcoma that cannot be resected, undermines the efficacy of this therapy. However, the mechanism by which IR induces radioresistance in osteosarcoma is not defined. Here, we report that CR6-interacting factor-1 (CRIF1) is highly expressed in osteosarcoma and undergoes nuclear-cytoplasmic shuttling of cyclin-dependent kinase 2 (CDK2) after IR. Osteosarcoma cells lacking CRIF1 show increased sensitivity to IR, which is associated with delayed DNA damage repair, inactivated G1/S checkpoint, and mitochondrial dysfunction. CRIF1 interacts with the DNA damage checkpoint regulator CDK2, and CRIF1 and CDK2 colocalize in the nucleus after IR. Nuclear localization of CDK2 is associated with phosphorylation changes that promote DNA repair and activation of the G1/S checkpoint. CRIF1 knockdown synergized with IR in an in vivo osteosarcoma model, leading to tumor regression. Based on these findings, we identify CRIF1 as a potential therapeutic target in osteosarcoma that can increase the efficacy of radiotherapy. More broadly, our findings may provide insights into the mechanism for other types of radioresistant cancers and be exploited for therapeutic ends.

Inhibition of Caspase-2 Translation by the mRNA Binding Protein HuR: A Novel Path of Therapy Resistance in Colon Carcinoma Cells?

An increased expression and cytoplasmic abundance of the ubiquitous RNA binding protein human antigen R (HuR) is critically implicated in the dysregulated control of post- transcriptional gene expression during colorectal cancer development and is frequently associated with a high grade of malignancy and therapy resistance. Regardless of the fact that HuR elicits a broad cell survival program by increasing the stability of mRNAs coding for prominent anti-apoptotic factors, recent data suggest that HuR is critically involved in the regulation of translation, particularly, in the internal ribosome entry site (IRES) controlled translation of cell death regulatory proteins. Accordingly, data from human colon carcinoma cells revealed that HuR maintains constitutively reduced protein and activity levels of caspase-2 through negative interference with IRES-mediated translation. This review covers recent advances in the understanding of mechanisms underlying HuR's modulatory activity on IRES-triggered translation. With respect to the unique regulatory features of caspase-2 and its multiple roles (e.g., in DNA-damage-induced apoptosis, cell cycle regulation and maintenance of genomic stability), the pathophysiological consequences of negative caspase-2 regulation by HuR and its impact on therapy resistance of colorectal cancers will be discussed in detail. The negative HuR-caspase-2 axis may offer a novel target for tumor sensitizing therapies.

ATM in DNA repair in cancer

Alterations in DNA damage response (DDR) pathways are hallmarks of cancer. Incorrect repair of DNA lesions often leads to genomic instability. Ataxia telangiectasia mutated (ATM), a core component of the DNA repair system, is activated to enhance the homologous recombination (HR) repair pathway upon DNA double-strand breaks. Although ATM signaling has been widely studied in different types of cancer, its research is still lacking compared with other DDR-involved molecules such as PARP and ATR. There is still a vast research opportunity for the development of ATM inhibitors as anticancer agents. Here, we focus on the recent findings of ATM signaling in DNA repair of cancer. Previous studies have identified several partners of ATM, some of which promote ATM signaling, while others have the opposite effect. ATM inhibitors, including KU-55933, KU-60019, KU-59403, CP-466722, AZ31, AZ32, AZD0156, and AZD1390, have been evaluated for their antitumor effects. It has been revealed that ATM inhibition increases a cancer cell's sensitivity to radiotherapy. Moreover, the combination with PARP or ATR inhibitors has synergistic lethality in some cancers. Of note, among these ATM inhibitors, AZD0156 and AZD1390 achieve potent and highly selective ATM kinase inhibition and have an excellent ability to penetrate the blood-brain barrier. Currently, AZD0156 and AZD1390 are under investigation in phase I clinical trials. Taken together, targeting ATM may be a promising strategy for cancer treatment. Hence, further development of ATM inhibitors is urgently needed in cancer research.