DNA Damage Repair and the Emerging Role of Poly(ADP-ribose) Polymerase Inhibition in Cancer Therapeutics

Role of STING in the treatment of non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is a prevalent form of lung cancer. Patients with advanced NSCLC are currently being treated with various therapies, including traditional radiotherapy, chemotherapy, molecular targeted therapies and immunotherapy. However, a considerable proportion of advance patients who cannot benefit from them. Consequently, it is essential to identify a novel research target that offers an encouraging perspective. The stimulator of interferon genes (STING) has emerged as such a target. At present, it is confirmed that activating STING in NSCLC tumor cells can impede the proliferation and metastasis of dormant tumor cells. This review focuses on the role of STING in NSCLC treatment and the factors influencing its activation. Additionally, it explores the correlation between STING activation and diverse therapy modalities for NSCLC, such as radiotherapy, chemotherapy, molecular targeted therapies and immunotherapy. Furthermore, it proposes the prospect of innovative therapy methods involving nanoparticles, with the aim of using the features of STING to develop more strategies for NSCLC therapy.

PARP inhibitors combined with radiotherapy: are we ready?

PARP was an enzyme found in the nucleus of eukaryotic cells that played a crucial role in repairing damaged DNA. Recently, PARP inhibitors have demonstrated great potential in cancer treatment. Thus, the FDA has approved several small-molecule PARP inhibitors for cancer maintenance therapy. The combination of PARP inhibitors and radiotherapy relies on synthetic lethality, taking advantage of the flaws in DNA repair pathways to target cancer cells specifically. Studies conducted prior to clinical trials have suggested that the combination of PARP inhibitors and radiotherapy can enhance the sensitivity of cancer cells to radiation, intensify DNA damage, and trigger cell death. Combining radiotherapy with PARP inhibitors in clinical trials has enhanced the response rate and progression-free survival of diverse cancer patients. The theoretical foundation of PARP inhibitors combined with radiotherapy is explained in detail in this article, and the latest advances in preclinical and clinical research on these inhibitors for tumor radiotherapy are summarized. The problems in the current field are recognized in our research and potential therapeutic applications for tumors are suggested. Nevertheless, certain obstacles need to be tackled when implementing PARP inhibitors and radiotherapies in clinical settings. Factors to consider when using the combination therapy are the most suitable schedule and amount of medication, identifying advantageous candidates, and the probable adverse effects linked with the combination. The combination of radiotherapy and PARP inhibitors can greatly enhance the effectiveness of cancer treatment.

Design, synthesis, and biological evaluation of a series of benzofuran[3,2-d]pyrimidine-4(3H)-one derivatives containing thiosemicarbazone analogs as novel PARP-1 inhibitors

Poly ADP ribose polymerase-1 (PARP-1), one of the most important members of the PARP protein family, plays a crucial role in DNA damage repair, gene transcription, and apoptosis of cancer cells. In this work, benzofuran[3,2-d]pyrimidine-4(3H)-one was used as a framework to design and synthesize a series of novel PARP-1 inhibitors by introducing thiosemicarbazone or its derivatives into the scafford. Among all the target compounds, 19b and 19c were found to exhibit more potent inhibitory activity and higher selectivity against PARP-1 than Olaparib, especially the latter had an IC50 value of 0.026 μM against PARP-1 enzyme and a PARP-2/PARP-1 selectivity of 85.19-fold over Olapanib. Apart from strong cytotoxicity against the tested cancer cell lines, 19c was most sensitive to SK-OV-3 cells, with an IC50 value of 4.98 μM superior to Olaparib. Anti-cancer mechanism studies revealed that 19c could inhibit DNA single-strand breakage repair and aggravate DNA double-strand breakage by inhibiting PARP-1 activity, and promote the apoptosis of cancer cells through the mitochondrial apoptosis pathway.

Clinical application of PARP inhibitors in ovarian cancer: from molecular mechanisms to the current status

As a kind of gynecological tumor, ovarian cancer is not as common as cervical cancer and breast cancer, but its malignant degree is higher. Despite the increasingly mature treatment of ovarian cancer, the five-year survival rate of patients is still less than 50%. Based on the concept of synthetic lethality, poly (ADP- ribose) polymerase (PARP) inhibitors target tumor cells with defects in homologous recombination repair(HRR), the most significant being the target gene Breast cancer susceptibility genes(BRCA). PARP inhibitors capture PARP-1 protein at the site of DNA damage to destroy the original reaction, causing the accumulation of PARP-DNA nucleoprotein complexes, resulting in DNA double-strand breaks(DSBs) and cell death. PARP inhibitors have been approved for the treatment of ovarian cancer for several years and achieved good results. However, with the widespread use of PARP inhibitors, more and more attention has been paid to drug resistance and side effects. Therefore, further research is needed to understand the mechanism of PARP inhibitors, to be familiar with the adverse reactions of the drug, to explore the markers of its efficacy and prognosis, and to deal with its drug resistance. This review elaborates the use of PARP inhibitors in ovarian cancer.

Proteomic Analysis Reveals Low-Dose PARP Inhibitor-Induced Differential Protein Expression in BRCA1-Mutated High-Grade Serous Ovarian Cancer Cells

High-grade serous ovarian cancer (HGSOC) is the most common form of ovarian cancer diagnosed in patients worldwide. Patients with BRCA1/2-mutated HGSOC have benefited from targeted treatments such as poly(ADP-ribose) polymerase inhibitors (PARPi). Despite the initial success of PARPi-based ovarian cancer treatment regimens, approximately 70% of patients with ovarian cancer relapse and the 5-year survival rate remains at 30%. PARPi exhibit variable treatment efficacy and toxicity profiles. Furthermore, the off-target effects of PARP inhibition have not yet been fully elucidated, warranting further study of these classes of molecules in the context of HGSOC treatment. Highly reproducible quantitative mass spectrometry-based proteomic workflows have been developed for the analysis of tumor tissues and cell lines. To detect the off-target effects of PARP inhibition, we conducted a quantitative mass spectrometry-based proteomic analysis of a BRCA1-mutated HGSOC cell line treated with low doses of two PARPi, niraparib and rucaparib. Our goal was to identify PARPi-induced protein signaling pathway alterations toward a more comprehensive elucidation of the mechanism of action of PARPi beyond the DNA damage response pathway. A significant enrichment of nuclear and nucleoplasm proteins that are involved in protein binding was observed in the rucaparib-treated cells. Shared upregulated proteins between niraparib and rucaparib treatment demonstrated RNA II pol promoter-associated pathway enrichment in transcription regulation. Pathway enrichment analyses also revealed off-target effects in the Golgi apparatus and the ER. The results from our mass spectrometry-based proteomic analysis highlights notable off-target effects produced by low-dose treatment of BRCA1-mutated HGSOC cells treated with rucaparib or niraparib.

PD-1 Inhibitor Maintenance Therapy Combined Iodine-125 Seed Implantation Successfully Salvage Recurrent Cervical Cancer after CCRT: A Case Report

Cervical cancer is the fourth most common cancer in females worldwide. Patients with stage III and IV cervical cancer based on the Federation of Gynecology and Obstetrics (FIGO) classification have higher recurrence rates. Because of organs at risk (OAR) protection and the low indication rate of salvage surgery, the choice of treatment is always challenging. Systemic chemotherapy is palliative and can be performed in conjunction with surgery or radiotherapy; however, it has no significant benefit to survival. Brachytherapy and stereotactic body radiotherapy (SBRT) are characterized by extremely high radiation doses applied to tumor cells while sparing the normal tissues. Several studies have investigated the efficacy of these technologies in recurrent cervical cancer and showed promising results. The immune checkpoint inhibitors approach was also investigated and showed promising results too. Herein, we report a case of a patient with cervical cancer that recurred five months after adjuvant chemotherapy and concurrent chemoradiotherapy. The disease prognosis after interstitial implantation brachytherapy (IIB) was determined. Then, the patient underwent radioactive 125I-seed implantation combined with PD-1 inhibitor treatment. The patient exhibited a partial response after seed implantation, and up to now, the duration of this partial response was 24 months.

Human Mass Balance and Metabolite Profiling of [14 C]-Pamiparib, a Poly (ADP-Ribose) Polymerase Inhibitor, in Patients With Advanced Cancer

Pamiparib, a selective poly (ADP-ribose) polymerase 1/2 inhibitor, demonstrated tolerability and antitumor activity in patients with solid tumors at 60 mg orally twice daily. This phase 1 open-label study (NCT03991494; BGB-290-106) investigated the absorption, metabolism, and excretion (AME) of 60 mg [14 C]-pamiparib in 4 patients with solid tumors. The mass balance in excreta, blood, and plasma radioactivity and plasma pamiparib concentration were determined along with metabolite profiles in plasma, urine, and feces. Unchanged pamiparib accounted for the most plasma radioactivity (67.2% ± 10.2%). Pamiparib was rapidly absorbed with a median time to maximum plasma concentration (Cmax ) of 2.00 hours (range, 1.00-3.05 hours). After reaching Cmax , pamiparib declined in a biphasic manner, with a geometric mean terminal half-life (t1/2 ) of 28.7 hours. Mean cumulative [14 C]-pamiparib excretion was 84.7% ± 3.5%. Pamiparib was mainly cleared through metabolism, primarily via N-oxidation and oxidation of the pyrrolidine ring. A dehydrogenated oxidative product (M3) was the most abundant metabolite in biosamples. A mean of 2.11% and 1.11% of [14 C]-pamiparib was excreted as unchanged pamiparib in feces and urine, respectively, indicating near-complete absorption and low renal clearance of parent drug. Cytochrome P450 (CYP) phenotyping demonstrated CYP2C8 and CYP3A involvement in pamiparib metabolism. These findings provide an understanding of pamiparib AME mechanisms and potential drug-drug interaction liability.

Exploiting somatic alterations as therapeutic targets in advanced and metastatic cervical cancer

It is estimated that 604,127 patients were diagnosed with cervical cancer worldwide in 2020. While a small percentage of patients will have metastatic disease at diagnosis, a large percentage (15-61%) later develop advanced disease. For this cohort, treatment with systemic chemotherapy remains the standard of care, with a static 5-year survival rate over the last thirty years. Data on targetable molecular alterations in cervical cancer have lagged behind other more common tumor types thus stunting the development of targeted agents. In recent years, tumor genomic testing has been increasingly incorporated into our clinical practice, opening the door for a potential new era of personalized treatment for advanced cervical cancer. The interim results from the NCI-MATCH study reported an actionability rate of 28.4% for the cervical cancer cohort, suggesting a subset of patients may harbor mutations which that are targetable. This review sets out to summarize the key targeted agents currently under exploration either alone or in combination with existing treatments for cervical cancer.

PARP inhibitor niraparib as a radiosensitizer promotes antitumor immunity of radiotherapy in EGFR-mutated non-small cell lung cancer

BACKGROUND

Poly-(ADP-Ribose)-Polymerase inhibitors (PARPi) were reported as radiosensitizers in non-small cell lung cancer (NSCLC) with wide-type epidermal growth factor receptor (EGFR), but the effects of radiation combined with PARPi were not investigated in EGFR-mutated NSCLC. Moreover, the underlying mechanisms were not well examined. This study aimed to study the efficacy of radiation combined with niraparib in EGFR-mutated NSCLC and explore their influence on the immune system.

METHODS

Clone formation and apoptosis assay were conducted to explore the effects of niraparib and radiation. Immunofluorescence was conducted to detect the double-strand DNA breaks. Real-time PCR and immunoblotting were employed to evaluate the activation of STING/TBK1/TRF3 pathway and the expression levels of interferon β, CCL5 and CXCL10. Immunocompetent mice model bearing with subcutaneous Lewis lung cancer was established to confirm the results in vivo.

RESULTS

Niraparib and radiation were synergistic to inhibit tumor both in vitro and in vivo. Radiation plus niraparib could activate anti-tumor immunity, which appeared as increased CD8⁺ T lymphocytes and activated STING/TBK1/IRF3 pathway.

CONCLUSION

PARPi not only as a radiosensitizer inhibited EGFR-mutated NSCLC tumor growth, but also cooperated with radiation to promote anti-tumor immune responses.

The pharmacokinetics of pamiparib in the presence of a strong CYP3A inhibitor (itraconazole) and strong CYP3A inducer (rifampin) in patients with solid tumors: an open-label, parallel-group phase 1 study

Purpose

Pamiparib is an investigational, selective, oral poly(ADP-ribose) polymerase 1/2 (PARP1/2) inhibitor that has demonstrated PARP–DNA complex trapping and CNS penetration in preclinical models, as well as preliminary anti-tumor activity in early-phase clinical studies. We investigated whether the single-dose pharmacokinetic (PK) profile of pamiparib is altered by coadministration of a strong CYP3A inducer (rifampin) or a strong CYP3A inhibitor (itraconazole) in patients with solid tumors.

Methods

In this open-label, phase 1 study, adults with advanced solid tumors received either oral pamiparib 60 mg (days 1 and 10) and once-daily oral rifampin 600 mg (days 3–11) or oral pamiparib 20 mg (days 1 and 7) and once-daily oral itraconazole 200 mg (days 3–8). Primary endpoints included pamiparib maximum observed concentration (C_max), and area under the plasma concentration–time curve from zero to last quantifiable concentration (AUC_0–tlast) and infinity (AUC_0–inf). Secondary endpoints included safety and tolerability.

Results

Rifampin coadministration did not affect pamiparib C_max (geometric least-squares [GLS] mean ratio 0.94; 90% confidence interval 0.83–1.06), but reduced its AUC_0–tlast (0.62 [0.54–0.70]) and AUC_0–inf (0.57 [0.48–0.69]). Itraconazole coadministration did not affect pamiparib C_max (1.05 [0.95–1.15]), AUC_0–tlast (0.99 [0.91–1.09]), or AUC_0–inf (0.99 [0.90–1.09]). There were no serious treatment-related adverse events.

Conclusions

Pamiparib plasma exposure was reduced 38–43% with rifampin coadministration but was unaffected by itraconazole coadministration. Pamiparib dose modifications are not considered necessary when coadministered with CYP3A inhibitors. Clinical safety and efficacy data will be used with these results to recommend dose modifications when pamiparib is coadministered with CYP3A inducers.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00280-021-04253-x.

RAD51-Mediated DNA Homologous Recombination Is Independent of PTEN Mutational Status

Simple Summary

PTEN is an important tumor suppressor that is frequently mutated in malignancy. PTEN mutational loss has been associated with reduced RAD51 expression and homologous recombination deficiency (HRD), however; recent studies have failed to recapitulate these findings. Here, we show that RAD51 expression, foci formation and homologous recombination repair activity are unaltered in normal and tumorigenic PTEN-deficient cells and patient samples. Furthermore, we show that PTEN-deficient tumor cell lines do not synergize with the clinical PARP inhibitor olaparib, underscoring a need to discontinue its use in treating patients with PTEN-deficient tumors that do not otherwise exhibit HRD.

Abstract

PTEN mutation occurs in a variety of aggressive cancers and is associated with poor patient outcomes. Recent studies have linked mutational loss of PTEN to reduced RAD51 expression and function, a key factor involved in the homologous recombination (HR) pathway. However, these studies remain controversial, as they fail to establish a definitive causal link to RAD51 expression that is PTEN-dependent, while other studies have not been able to recapitulate the relationship between the PTEN expression and the RAD51/HR function. Resolution of this apparent conundrum is essential due to the clinically-significant implication that PTEN-deficient tumors may be sensitive to poly (ADP-ribose) polymerase (PARP) inhibitors (PARPi) commonly used in the clinical management of BRCA-mutated and other HR-deficient (HRD) tumors. Methods: Primary Pten-deficient (and corresponding wild-type) mouse embryonic fibroblasts (MEFs) and astrocytes and PTEN-null human tumor cell lines and primary cells were assessed for RAD51 expression (via the Western blot analysis) and DNA damage repair analyses (via alkali comet and γH2AX foci assays). RAD51 foci analysis was used to measure HR-dependent DNA repair. Xrcc2-deficient MEFs served as an HR-deficient control, while the stable knockdown of RAD51 (shRAD51) served to control for the relative RAD51/HR-mediated repair and the phospho-53BP1 foci analysis served to confirm and measure non-homologous end joining (NHEJ) activity in PTEN-deficient and shRAD51-expressing (HRD) lines. Cell proliferation studies were used to measure any potential added sensitivity of PTEN-null cells to the clinically-relevant PARPi, olaparib. RAD51 levels and DNA damage response signaling were assessed in PTEN-mutant brain tumor initiating cells (BTICs) derived from primary and recurrent glioblastoma multiforme (GBM) patients, while expression of RAD51 and its paralogs were examined as a function of the PTEN status in the RNA expression datasets isolated from primary GBM tumor specimens and BTICs. Results: Pten knockout primary murine cells display unaltered RAD51 expression, endogenous and DNA strand break-induced RAD51 foci and robust DNA repair activity. Defective HR was only observed in the cells lacking Xrcc2. Likewise, human glioblastoma multiforme (GBM) cell lines with known PTEN deficiency (U87, PTEN-mutated; U251 and U373, PTEN-null) show apparent expression of RAD51 and display efficient DNA repair activity. Only GBM cells stably expressing shRNAs against RAD51 (shRAD51) display dysfunctional DNA repair activity and reduced proliferative capacity, which is exacerbated by PARPi treatment. Furthermore, GBM patient-derived BTICs displayed robust RAD51 expression and intact DNA damage response signaling in spite of PTEN-inactivating mutations. RNA expression analysis of primary GBM tissue specimens and BTICs demonstrate stable levels of RAD51 and its paralogs (RAD51B, RAD51C, RAD51D, XRCC2, XRCC3, and DMC1), regardless of the PTEN mutational status. Conclusions: Our findings demonstrate definitively that PTEN loss does not alter the RAD51 expression, its paralogs, or the HR activity. Furthermore, deficiency in PTEN alone is not sufficient to impart enhanced sensitivity to PARPi associated with HRD. This study is the first to unequivocally demonstrate that PTEN deficiency is not linked to the RAD51 expression or the HR activity amongst primary neural and non-neural Pten-null cells, PTEN-deficient tumor cell lines, and primary PTEN-mutant GBM patient-derived tissue specimens and BTICs.

[Molecular pathways of autophagy regulation by BRCA1: Implications in cancer]

The BRCA1 protein contributes to maintain genomic integrity, through transcriptional regulation of proteins that control the cell cycle and DNA repair or by direct interaction with these proteins. The genetic instability caused by mutations that result in a deficit of BRCA1 activity, confers an increased risk of mainly breast and ovarian cancers. In recent years, it has been shown that autophagy has a dual role in tumor development, and chemical agents such as lucanthone, chloroquine, Z-ligustilide, spautin-1, tunicamycin, T-12, and olaparib, regulate tumor survival/death autophagy-dependent. Here we also review the different molecular pathways by which BRCA1 regulates (mostly negatively) autophagy, mainly in breast and ovarian cancers, and where the cellular redox state (ROS, GSH) and proteins mTOR, p53-Mdm2, STAT3, and Parkin, have been shown to play an essential role.

PARP Inhibitors in Biliary Tract Cancer: A New Kid on the Block?

Poly adenosine diphosphate-ribose polymerase inhibitors (PARPi) represent an effective therapeutic strategy for cancer patients harboring germline and somatic aberrations in DNA damage repair (DDR) genes. BRCA1/2 mutations occur at 1–7% across biliary tract cancers (BTCs), but a broader spectrum of DDR gene alterations is reported in 28.9–63.5% of newly diagnosed BTC patients. The open question is whether alterations in genes that are well established to have a role in DDR could be considered as emerging predictive biomarkers of response to platinum compounds and PARPi. Currently, data regarding PARPi in BTC patients harboring BRCA and DDR mutations are sparse and anecdotal; nevertheless, a variety of clinical trials are testing PARPi as monotherapy or in combination with other anticancer agents. In this review, we provide a comprehensive overview regarding the genetic landscape of DDR pathway deficiency, state of the art and future therapeutic implications of PARPi in BTC, looking at combination strategies with immune-checkpoint inhibitors and other anticancer agents in order to improve survival and quality of life in BTC patients.

The emerging role of PARP inhibitors in prostate cancer

INTRODUCTION

In prostate cancer , there has recently been an emerging interest in mutations in genes belonging to the homologous recombination repair (HRR) pathway and in the inhibition of poly (ADP-ribose) polymerase (PARP) proteins.

AREAS COVERED

Mutations in the HRR genes, including BRCA1, BRCA2, and Ataxia-Telangiesctasia mutated (ATM), have been reported in prostate cancer, with different incidence in the localized and advanced settings. The PARP enzyme complex is involved in repair of DNA damage and its inhibition causes the accumulation of DNA mutations in HRR deficient cells. Several PARP inhibitors (PARPi) are under development, such as olaparib, talazoparib, niraparib, rucaparib, and veliparib. In metastatic castration resistant prostate cancer (mCRPC), olaparib has been the most studied and its clinical efficacy has been validated in a phase III clinical trial. Rucaparib and niraparib have also shown promising results in the preliminary analyzes of two phase II trials, while talazoparib is currently under development.

EXPERT OPINION

PARPi have become part of the treatment of mCRPC. Early results of combination therapy with PARPi and new hormonal therapy are promising and are supported by a strong biological rationale. Current results need to be validated in randomized phase III-controlled trials in order to translate the use of PARPi into real world practice.

Design of potential anti-tumor PARP-1 inhibitors by QSAR and molecular modeling studies

Poly ADP-ribose polymerase-1 (PARP-1) inhibitors have been recognized as new agents for the treatment of patients with breast cancer type 1 (BRCA1) disorders. The quantitative structure-activity relationships (QSAR) technique was used in order to achieve the required medicines for anticancer activity easier and faster. In this study, the QSAR method was developed to predict the half-maximal inhibitory concentration (IC₅₀) of 51 1H-benzo[d]immidazole-4-carboxamide derivatives by genetic algorithm-multiple linear regression (GA-MLR) and least squares-support vector machine (LS-SVM) methods. Results in the best QSAR model represented the coefficient of leave-one-out cross-validation (Q _cv ² ) = 0.971, correlation coefficient (R²) = 0.977, Fisher parameter (F) = 259.016 and root mean square error (RMSE) = 0.095, respectively, which indicated that the LS-SVM model had a good potential to predict the pIC₅₀ (9 - log(IC₅₀ nM)) values compared with other modeling methods. Also, molecular docking evaluated interactions between ligands and enzyme and their free energy of binding were calculated and used as descriptors. Molecular docking and the QSAR study completed each other. The results represented that the final model can be useful to design some new inhibitors. So, the knowledge of the QSAR modeling and molecular docking was used in pIC₅₀ prediction and 51 new compounds were developed as PARP-1 inhibitors that 9 compounds had the best-proposed values for pIC₅₀. The maximum enhancement of the inhibitory activity of compounds was 33.394%.

Toxic effects of the Emamectin Benzoate exposure on cultured human bronchial epithelial (16HBE) cells

Pesticides pollution has caused serious environmental problems in recent years, and mounting evidence has shown that more and more insecticides have serious risk in human health. Emamectin Benzoate formally regarded as a highly safety insecticide based on its exclusive targets, but the cytotoxicity to human lung was ignored for a long time. In the present study, bioassay experiments were used to assess the toxicity of the Emamectin Benzoatein on human non-target cells including cell viability assay, DNA damage assay, flow cytometer assay and western blotting assay. The results indicated that Emamectin Benzoatecan cause the inhibition of the proliferation, cytochrome c release, activation of caspase-3/9 and increase Bax/Bcl-2 ratio, which means it induced the cytotoxicity on 16HBE cells associated with the mitochondrial apoptosis. Besides, the DNA damge caused by the Emamectin Benzoate suggest it has a potential genotoxic effect on human lung cells.

Novel Therapeutics for Recurrent Cervical Cancer: Moving Towards Personalized Therapy

While screening programs and HPV vaccination have decreased the incidence of cervical cancer, still over 13,000 cases occur in the USA annually. Early-stage cervical cancer has an excellent long-term prognosis, with 5-year survival for localized disease being > 90%. Survival decreases markedly for both locally advanced and metastatic disease, and both are associated with a higher risk of recurrence. Few effective treatment options exist for persistent, recurrent, or metastatic cervical cancer. In 2014, the anti-VEGF antibody bevacizumab was approved in combination with chemotherapy based on the results of the Phase III GOG-240 study. As the majority of cervical cancers have a viral etiology, which impairs the immune system, immunotherapy using checkpoint inhibitors and other agents, appears to be a promising approach. In June 2018, the US FDA approved the anti-PD1 antibody pembrolizumab for recurrent or metastatic cervical cancer with PD-L1 expression that progressed after one or more lines of chemotherapy. Another anti-PD1 antibody, cemiplimab also shows potential in this setting, either as monotherapy or combined with radiotherapy, and it is currently being evaluated in a Phase III trial. Additional checkpoint inhibitors including nivolumab, durvalumab, atezolizumab, and camrelizumab are in different stages of clinical development for the disease. Finally, an additional targeted approach being pursued involves PARP inhibitors (rucaparib and olaparib are both in Phase II) based on earlier study results.

Modulators of Redox Metabolism in Head and Neck Cancer

SIGNIFICANCE

Head and neck squamous cell cancer (HNSCC) is a complex disease characterized by high genetic and metabolic heterogeneity. Radiation therapy (RT) alone or combined with systemic chemotherapy is widely used for treatment of HNSCC as definitive treatment or as adjuvant treatment after surgery. Antibodies against epidermal growth factor receptor are used in definitive or palliative treatment. Recent Advances: Emerging targeted therapies against other proteins of interest as well as programmed cell death protein 1 and programmed death-ligand 1 immunotherapies are being explored in clinical trials.

CRITICAL ISSUES

The disease heterogeneity, invasiveness, and resistance to standard of care RT or chemoradiation therapy continue to constitute significant roadblocks for treatment and patients' quality of life (QOL) despite improvements in treatment modality and the emergence of new therapies over the past two decades.

FUTURE DIRECTIONS

As reviewed here, alterations in redox metabolism occur at all stages of HNSCC management, providing opportunities for improved prevention, early detection, response to therapies, and QOL. Bioinformatics and computational systems biology approaches are key to integrate redox effects with multiomics data from cells and clinical specimens and to identify redox modifiers or modifiable target proteins to achieve improved clinical outcomes. Antioxid. Redox Signal.

PARP inhibitors as potential therapeutic agents for various cancers: focus on niraparib and its first global approval for maintenance therapy of gynecologic cancers

Poly (ADP-ribose) polymerases (PARPs) are an important family of nucleoproteins highly implicated in DNA damage repair. Among the PARP families, the most studied are PARP1, PARP2 and PARP 3. PARP1 is found to be the most abundant nuclear enzyme under the PARP series. These enzymes are primarily involved in base excision repair as one of the major single strand break (SSB) repair mechanisms. Being double stranded, DNA engages itself in reparation of a sub-lethal SSB with the aid of PARP. Moreover, by having a sister chromatid, DNA can also repair double strand breaks with either error-free homologous recombination or error-prone non-homologous end-joining. For effective homologous recombination repair, DNA requires functional heterozygous breast cancer genes (BRCA) which encode BRCA1/2. Currently, the development of PARP inhibitors has been one of the promising breakthroughs for cancer chemotherapy. In March 2017, the United States Food and Drug Administration (FDA) approved niraparib for maintenance therapy of recurrent gynecologic cancers (epithelial ovarian, primary peritoneal and fallopian tube carcinomas) which are sensitive to previous platinum based chemotherapy irrespective of BRCA mutation and homologous recombination deficiency status. It is the third drug in this class to receive FDA approval, following olaparib and rucaparib and is the first global approval for maintenance therapy of the aforementioned cancers. Niraparib preferentially blocks both PARP1 and PARP2 enzymes. The daily tolerated dose of niraparib is 300 mg, above which dose limiting grade 3 and 4 toxicities were observed. In combination with humanized antibody, pembrolizumab, it is also under investigation for those patients who have triple negative breast cancer. By and large, there are several clinical trials that are underway investigating clinical efficacy and safety, as well as other pharmacokinetic and pharmacodynamic profiles of this drug for various malignancies.

[Impairment of DNA damage response and cancer]

Maintaining the genetic integrity is a key process in cell viability and is enabled by a wide network of repair pathways. When this system is defective, it generates genomic instability and results in an accumulation of chromosomal aberrations and mutations that may be responsible for various clinical phenotypes, including susceptibility to develop cancer. Indeed, these defects can promote not only the initiation of cancer, but also allow the tumor cells to rapidly acquire mutations during their evolution. Several genes are involved in these damage repair systems and particular polymorphisms are predictive of the onset of cancer, the best described of them being BRCA. In addition to its impact on carcinogenesis, the DNA damage repair system is now considered as a therapeutic target of choice for cancer treatment, as monotherapy or in combination with other cytotoxic therapies, such as chemotherapies or radiotherapy. PARP inhibitors are nowadays the best known, but other agents are emerging in the field of clinical research. The enthusiasm in this area is coupled with promising results and a successful collaboration between clinicians and biologists would allow to optimize treatment plans in order to take full advantage of the DNA repair system modulation.

MC37, a new mono-carbonyl curcumin analog, induces G2/M cell cycle arrest and mitochondria-mediated apoptosis in human colorectal cancer cells

(E)-1-(3'-fluoro-[1,1'-biphenyl-3-yl)-3-(3-hydroxy-4-methoxyphenyl)prop-2-en-1-one) (MC37), a novel mono-carbonyl curcumin analog, was previously synthesized in our laboratory as a nuclear factor kappa B (NF-κB) inhibitor with excellent cytotoxicity against several cancer cell lines. In this study, our further investigations showed that the potent growth inhibitory activity of MC37 in human colorectal cancer cells was associated with the arrest of cell cycle progression and the induction of apoptosis. As a multi-targeted agent, MC37 inhibited the intracellular microtubule assembly, altered the expression of cyclin-dependent kinase 1 (CDK1), and ultimately induced G2/M cell cycle arrest. Moreover, MC37 collapsed the mitochondrial membrane potential (MMP), increased the Bax/Bcl-2 ratio, activated the caspase-9/3 cascade, and finally led to cancer cells apoptosis, suggesting that the mitochondrial-mediated apoptotic pathway was involved in MC37-induced apoptosis. In conclusion, these observations demonstrated that mono-carbonyl curcumin analogs would serve as multi-targeted lead for promising anti-colorectal cancer agent development.