Inhibition of the ERCC1-XPF structure-specific endonuclease to overcome cancer chemoresistance

Small Molecule Antagonists of the DNA Repair ERCC1/XPA Protein-Protein Interaction

The DNA excision repair protein ERCC1 and the DNA damage sensor protein, XPA are highly overexpressed in patient samples of cisplatin-resistant solid tumors including lung, bladder, ovarian, and testicular cancer. The repair of cisplatin-DNA crosslinks is dependent upon nucleotide excision repair (NER) that is modulated by protein-protein binding interactions of ERCC1, the endonuclease, XPF, and XPA. Thus, inhibition of their function is a potential therapeutic strategy for the selective sensitization of tumors to DNA-damaging platinum-based cancer therapy. Here, we report on new small-molecule antagonists of the ERCC1/XPA protein-protein interaction (PPI) discovered using a high-throughput competitive fluorescence polarization binding assay. We discovered a unique structural class of thiopyridine-3-carbonitrile PPI antagonists that block a truncated XPA polypeptide from binding to ERCC1. Preliminary hit-to-lead studies from compound 1 reveal structure-activity relationships (SAR) and identify lead compound 27 o with an EC50 of 4.7 μM. Furthermore, chemical shift perturbation mapping by NMR confirms that 1 binds within the same site as the truncated XPA67-80 peptide. These novel ERCC1 antagonists are useful chemical biology tools for investigating DNA damage repair pathways and provide a good starting point for medicinal chemistry optimization as therapeutics for sensitizing tumors to DNA damaging agents and overcoming resistance to platinum-based chemotherapy.

Unveiling Novel ERCC1-XPF Complex Inhibitors: Bridging the Gap from In Silico Exploration to Experimental Design

Modifications in DNA repair pathways are recognized as prognostic markers and potential therapeutic targets in various cancers, including non-small cell lung cancer (NSCLC). Overexpression of ERCC1 correlates with poorer prognosis and response to platinum-based chemotherapy. As a result, there is a pressing need to discover new inhibitors of the ERCC1-XPF complex that can potentiate the efficacy of cisplatin in NSCLC. In this study, we developed a structure-based virtual screening strategy targeting the inhibition of ERCC1 and XPF interaction. Analysis of crystal structures and a library of small molecules known to act against the complex highlighted the pivotal role of Phe293 (ERCC1) in maintaining complex stability. This residue was chosen as the primary binding site for virtual screening. Using an optimized docking protocol, we screened compounds from various databases, ultimately identifying more than one hundred potential inhibitors. Their capability to amplify cisplatin-induced cytotoxicity was assessed in NSCLC H1299 cells, which exhibited the highest ERCC1 expression of all the cell lines tested. Of these, 22 compounds emerged as promising enhancers of cisplatin efficacy. Our results underscore the value of pinpointing crucial molecular characteristics in the pursuit of novel modulators of the ERCC1-XPF interaction, which could be combined with cisplatin to treat NSCLC more effectively.

Targeting the DNA Damage Response for Cancer Therapy

Over the course of long-term evolution, cells have developed intricate defense mechanisms in response to DNA damage; these mechanisms play a pivotal role in maintaining genomic stability. Defects in the DNA damage response pathways can give rise to various diseases, including cancer. The DNA damage response (DDR) system is instrumental in safeguarding genomic stability. The accumulation of DNA damage and the weakening of DDR function both promote the initiation and progression of tumors. Simultaneously, they offer opportunities and targets for cancer therapeutics. This article primarily elucidates the DNA damage repair pathways and the progress made in targeting key proteins within these pathways for cancer treatment. Among them, poly (ADP-ribose) polymerase 1 (PARP1) plays a crucial role in DDR, and inhibitors targeting PARP1 have garnered extensive attention in anticancer research. By delving into the realms of DNA damage and repair, we aspire to explore more precise and effective strategies for cancer therapy and to seek novel avenues for intervention.

XPF-ERCC1 Blocker Improves the Therapeutic Efficacy of 5-FU- and Oxaliplatin-Based Chemoradiotherapy in Colorectal Cancer

5-FU-based chemoradiotherapy (CRT) and oxaliplatin-based CRT are commonly used therapies for advanced colorectal cancer (CRC). However, patients with a high expression of ERCC1 have a worse prognosis than those with a low expression. In this study, we investigated the effect of XPF-ERCC1 blockers on chemotherapy and 5-FU-based CRT and oxaliplatin (OXA)-based CRT in colorectal cancer cell lines. We investigated the half-maximal inhibitory concentration (IC50) of 5-FU, OXA, XPF-ERCC1 blocker, and XPF-ERCC1 blocker, and 5-FU or OXA combined and analyzed the effect of XPF-ERCC1 blocker on 5-FU-based CRT and oxaliplatin-based CRT. Furthermore, the expression of XPF and γ-H2AX in colorectal cells was analyzed. In animal models, we combined the XPF-ERCC1 blocker with 5-FU and OXA to investigate the effects of RC and finally combined the XPF-ERCC1 blocker with 5-FU- and oxaliplatin-based CRT. In the IC50 analysis of each compound, the cytotoxicity of the XPF-ERCC1 blocker was lower than that of 5-FU and OXA. In addition, the XPF-ERCC1 blocker combined with 5-FU or OXA enhanced the cytotoxicity of the chemotherapy drugs in colorectal cells. Furthermore, the XPF-ERCC1 blocker also increased the cytotoxicity of 5-FU-based CRT and OXA -based CRT by inhibiting the XPF product DNA locus. In vivo, the XPF-ERCC1 blocker was confirmed to enhance the therapeutic efficacy of 5-FU, OXA, 5-FU-based CRT, and OXA CRT. These findings show that XPF-ERCC1 blockers not only increase the toxicity of chemotherapy drugs but also increase the efficacy of combined chemoradiotherapy. In the future, the XPF-ERCC1 blocker may be used to improve the efficacy of 5-FU- and oxaliplatin-based CRT.

Repurposing Antimalarial Pyronaridine as a DNA Repair Inhibitor to Exploit the Full Potential of Gold-Nanoparticle-Mediated Radiation Response

Radiation therapy (RT) is frequently used to locally treat tumors. One of the major issues in RT is normal tissue toxicity; thus, it is necessary to limit dose escalation for enhanced local control in patients that have locally advanced tumors. Integrating radiosensitizing agents such as gold nanoparticles (GNPs) into RT has been shown to greatly increase the cure rate of solid tumors. The objective of this study was to explore the repurposing of an antimalarial drug, pyronaridine (PYD), as a DNA repair inhibitor to further enhance RT/GNP-induced DNA damage in cancerous cell lines. We were able to achieve inhibitory effects of DNA repair due to PYD at 500 nM concentration. Our results show a significant enhancement in DNA double-strand breaks of 42% in HeLa cells treated with PYD/GNP/RT in comparison to GNP/RT alone when irradiated with a dose of 2 Gy. Furthermore, there was a significant reduction in cellular proliferation for both HeLa and HCT-116 irradiated cells with the combined treatment of PYD/GNP/RT. Therefore, the emergence of promising novel concepts introduced in this study could lay the foundation for the transition of this treatment modality into clinical environments.

HMG20A was identified as a key enhancer driver associated with DNA damage repair in oral squamous cell carcinomas

Background

Oral squamous cell carcinoma (OSCC) is the main type of oral cancer. Disturbing DNA repair is an invaluable way to improve the effectiveness of tumor treatment. Here, we aimed to explore the key enhancer drivers associated with DNA damage repair in OSCC cells.

Methods

Gene Set Enrichment Analysis (GSEA), Gene Set Variation Analysis (GSVA) and Kaplan-Meier analysis were applied to explore the relationship among DNA repair-related genes expression and clinical phenotypes based on The Cancer Genome Atlas (TCGA) database. HOMER software and Integrative Genomics Viewer were applied to identify and visualize enhancers using GSE120634. Toolkit for Cistrome Data Browser was applied to predict transcription factors. Human Protein Atlas Database was used to analyze the protein levels of transcription factors in OSCC and control tissues. Seventy-two OSCC patients were included in this study. qRT-PCR was used to detect transcription factor expression in OSCC and adjacent control tissues collected in this study. qRT-PCR and ChIP-qPCR were used to verify the binding of transcription factors to enhancers, and regulation of target genes transcription. Transcription factor knockdown and control cells were treated with cisplatin. CCK8 was used to detect cell viability and proliferation. Western blotting was implemented to detect the levels of DNA repair-related proteins. Transwell assay was used to detect cell invasion.

Results

DNA repair was positively associated with the OSCC metastatic phenotype. Patients in the cluster with high expression of DNA repair-related genes had a worse prognosis and a higher proportion of advanced stage, low-differentiation, alcohol consumption and smoking compared to the cluster with low DNA repair-related gene expression. Seventeen metastasis-specific enhancer-controlled upregulated DNA repair-related genes, with the top two upregulated genes being ADRM1 26 S proteasome ubiquitin receptor (ADRM1) and solute carrier family 12 member 7 (SLC12A7) were screened. High mobility group 20 A (HMG20A) was the key prognostic enhancer driver regulating metastasis-specific DNA repair-related genes, with higher expression in OSCC tissues than normal control tissues, and higher expression in metastatic OSCC tissues than non-metastatic OSCC tissues. HMG20A bound to the metastasis-specific enhancers of ADRM1 and SLC12A7, thereby promoting ADRM1 and SLC12A7 expression. Knockdown of HMG20A enhanced cisplatin sensitivity of cells, and inhibited OSCC cells from repairing DNA damage caused by cisplatin, as well as proliferation and invasion of OSCC cells.

Conclusion

HMG20A was identified as the key prognostic enhancer driver regulating DNA repair in OSCC cells, providing a new therapeutic target for OSCC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-022-02500-y.

Recent Advances in the Development of Non-PIKKs Targeting Small Molecule Inhibitors of DNA Double-Strand Break Repair

The vast majority of cancer patients receive DNA-damaging drugs or ionizing radiation (IR) during their course of treatment, yet the efficacy of these therapies is tempered by DNA repair and DNA damage response (DDR) pathways. Aberrations in DNA repair and the DDR are observed in many cancer subtypes and can promote de novo carcinogenesis, genomic instability, and ensuing resistance to current cancer therapy. Additionally, stalled or collapsed DNA replication forks present a unique challenge to the double-strand DNA break (DSB) repair system. Of the various inducible DNA lesions, DSBs are the most lethal and thus desirable in the setting of cancer treatment. In mammalian cells, DSBs are typically repaired by the error prone non-homologous end joining pathway (NHEJ) or the high-fidelity homology directed repair (HDR) pathway. Targeting DSB repair pathways using small molecular inhibitors offers a promising mechanism to synergize DNA-damaging drugs and IR while selective inhibition of the NHEJ pathway can induce synthetic lethality in HDR-deficient cancer subtypes. Selective inhibitors of the NHEJ pathway and alternative DSB-repair pathways may also see future use in precision genome editing to direct repair of resulting DSBs created by the HDR pathway. In this review, we highlight the recent advances in the development of inhibitors of the non-phosphatidylinositol 3-kinase-related kinases (non-PIKKs) members of the NHEJ, HDR and minor backup SSA and alt-NHEJ DSB-repair pathways. The inhibitors described within this review target the non-PIKKs mediators of DSB repair including Ku70/80, Artemis, DNA Ligase IV, XRCC4, MRN complex, RPA, RAD51, RAD52, ERCC1-XPF, helicases, and DNA polymerase θ. While the DDR PIKKs remain intensely pursued as therapeutic targets, small molecule inhibition of non-PIKKs represents an emerging opportunity in drug discovery that offers considerable potential to impact cancer treatment.

Modulation of ERCC1-XPF Heterodimerization Inhibition via Structural Modification of Small Molecule Inhibitor Side-Chains

Inhibition of DNA repair enzymes is an attractive target for increasing the efficacy of DNA damaging chemotherapies. The ERCC1-XPF heterodimer is a key endonuclease in numerous single and double strand break repair processes, and inhibition of the heterodimerization has previously been shown to sensitize cancer cells to DNA damage. In this work, the previously reported ERCC1-XPF inhibitor 4 was used as the starting point for an in silico study of further modifications of the piperazine side-chain. A selection of the best scoring hits from the in silico screen were synthesized using a late stage functionalization strategy which should allow for further iterations of this class of inhibitors to be readily synthesized. Of the synthesized compounds, compound 6 performed the best in the in vitro fluorescence based endonuclease assay. The success of compound 6 in inhibiting ERCC1-XPF endonuclease activity in vitro translated well to cell-based assays investigating the inhibition of nucleotide excision repair and disruption of heterodimerization. Subsequently compound 6 was shown to sensitize HCT-116 cancer cells to treatment with UVC, cyclophosphamide, and ionizing radiation. This work serves as an important step towards the synergistic use of DNA repair inhibitors with chemotherapeutic drugs.

Nucleases and Co-Factors in DNA Replication Stress Responses

DNA replication stress is a constant threat that cells must manage to proliferate and maintain genome integrity. DNA replication stress responses, a subset of the broader DNA damage response (DDR), operate when the DNA replication machinery (replisome) is blocked or replication forks collapse during S phase. There are many sources of replication stress, such as DNA lesions caused by endogenous and exogenous agents including commonly used cancer therapeutics, and difficult-to-replicate DNA sequences comprising fragile sites, G-quadraplex DNA, hairpins at trinucleotide repeats, and telomeres. Replication stress is also a consequence of conflicts between opposing transcription and replication, and oncogenic stress which dysregulates replication origin firing and fork progression. Cells initially respond to replication stress by protecting blocked replisomes, but if the offending problem (e.g., DNA damage) is not bypassed or resolved in a timely manner, forks may be cleaved by nucleases, inducing a DNA double-strand break (DSB) and providing a means to accurately restart stalled forks via homologous recombination. However, DSBs pose their own risks to genome stability if left unrepaired or misrepaired. Here we focus on replication stress response systems, comprising DDR signaling, fork protection, and fork processing by nucleases that promote fork repair and restart. Replication stress nucleases include MUS81, EEPD1, Metnase, CtIP, MRE11, EXO1, DNA2-BLM, SLX1-SLX4, XPF-ERCC1-SLX4, Artemis, XPG, and FEN1. Replication stress factors are important in cancer etiology as suppressors of genome instability associated with oncogenic mutations, and as potential cancer therapy targets to enhance the efficacy of chemo- and radiotherapeutics.

Every protagonist has a sidekick: Structural aspects of human xeroderma pigmentosum-binding proteins in nucleotide excision repair

The seven xeroderma pigmentosum proteins (XPps), XPA-XPG, coordinate the nucleotide excision repair (NER) pathway, promoting the excision of DNA lesions caused by exposition to ionizing radiation, majorly from ultraviolet light. Significant efforts are made to investigate NER since mutations in any of the seven XPps may cause the xeroderma pigmentosum and trichothiodystrophy diseases. However, these proteins collaborate with other pivotal players in all known NER steps to accurately exert their purposes. Therefore, in the old and ever-evolving field of DNA repair, it is imperative to reexamine and describe their structures to understand NER properly. This work provides an up-to-date review of the protein structural aspects of the closest partners that directly interact and influence XPps: RAD23B, CETN2, DDB1, RPA (RPA70, 32, and 14), p8 (GTF2H5), and ERCC1. Structurally and functionally vital domains, regions, and critical residues are reexamined, providing structural lessons and perspectives about these indispensable proteins in the NER and other DNA repair pathways. By gathering all data related to the major human xeroderma pigmentosum-interacting proteins, this review will aid newcomers on the subject and guide structural and functional future studies.

Targeting protein-protein interactions in the DNA damage response pathways for cancer chemotherapy

Cellular DNA damage response (DDR) is an extensive signaling network that orchestrates DNA damage recognition, repair and avoidance, cell cycle progression and cell death. DDR alteration is a hallmark of cancer, with the deficiency in one DDR capability often compensated by a dependency on alternative pathways endowing cancer cells with survival and growth advantage. Targeting these DDR pathways has provided multiple opportunities for the development of cancer therapies. Traditional drug discovery has mainly focused on catalytic inhibitors that block enzyme active sites, which limits the number of potential drug targets within the DDR pathways. This review article describes the emerging approach to the development of cancer therapeutics targeting essential protein-protein interactions (PPIs) in the DDR network. The overall strategy for the structure-based design of small molecule PPI inhibitors is discussed, followed by an overview of the major DNA damage sensing, DNA repair, and DNA damage tolerance pathways with a specific focus on PPI targets for anti-cancer drug design. The existing small molecule inhibitors of DDR PPIs are summarized that selectively kill cancer cells and/or sensitize cancers to front-line genotoxic therapies, and a range of new PPI targets are proposed that may lead to the development of novel chemotherapeutics.

Recent Advances in Therapeutic Application of DNA Damage Response Inhibitors against Cancer

DNA integrity is continuously challenged by intrinsic cellular processes and environmental agents. To overcome this genomic damage, cells have developed multiple signaling pathways collectively named as DNA damage response (DDR) and composed of three components: (i) sensor proteins, which detect DNA damage, (ii) mediators that relay the signal downstream and recruit the repair machinery, and (iii) the repair proteins, which restore the damaged DNA. A flawed DDR and failure to repair the damage lead to the accumulation of genetic lesions and increased genomic instability, which is recognized as a hallmark of cancer. Cancer cells tend to harbor increased mutations in DDR genes and often have fewer DDR pathways than normal cells. This makes cancer cells more dependent on particular DDR pathways and thus become more susceptible to compounds inhibiting those pathways compared to normal cells, which have all the DDR pathways intact. Understanding the roles of different DDR proteins in the DNA damage response and repair pathways and identification of their structures have paved the way for the development of their inhibitors as targeted cancer therapy. In this review, we describe the major participants of various DDR pathways, their significance in carcinogenesis, and focus on the inhibitors developed against several key DDR proteins.

Molecular Mechanisms of Chemotherapy Resistance in Head and Neck Cancers

Chemotherapy resistance is a huge barrier for head and neck cancer (HNC) patients and therefore requires close attention to understand its underlay mechanisms for effective strategies. In this review, we first summarize the molecular mechanisms of chemotherapy resistance that occur during the treatment with cisplatin, 5-fluorouracil, and docetaxel/paclitaxel, including DNA/RNA damage repair, drug efflux, apoptosis inhibition, and epidermal growth factor receptor/focal adhesion kinase/nuclear factor-κB activation. Next, we describe the potential approaches to combining conventional therapies with previous cancer treatments such as immunotherapy, which may improve the treatment outcomes and prolong the survival of HNC patients. Overall, by parsing the reported molecular mechanisms of chemotherapy resistance within HNC patient’s tumors, we can improve the prediction of chemotherapeutic responsiveness, and reveal new therapeutic targets for the future.

Identification of Bioactive SNM1A Inhibitors

SNM1A is a nuclease required to repair DNA interstrand cross-links (ICLs) caused by some anticancer compounds, including cisplatin. Unlike other nucleases involved in ICL repair, SNM1A is not needed to restore other forms of DNA damage. As such, SNM1A is an attractive target for selectively increasing the efficacy of ICL-based chemotherapy. Using a fluorescence-based exonuclease assay, we screened a bioactive library of compounds for inhibition of SNM1A. Of the 52 compounds initially identified as hits, 22 compounds showed dose-response inhibition of SNM1A. An orthogonal gel-based assay further confirmed nine small molecules as SNM1A nuclease activity inhibitors with IC₅₀ values in the mid-nanomolar to low micromolar range. Finally, three compounds showed no toxicity at concentrations able to significantly potentiate the cytotoxicity of cisplatin. These compounds represent potential leads for further optimization to sensitize cells toward chemotherapeutic agents inducing ICL damage.

The role of DNA damage response in chemo- and radio-resistance of cancer cells: Can DDR inhibitors sole the problem?

Up to now, many improvements have been made in providing more therapeutic strategies for cancer patients. The lack of susceptibility to common therapies like chemo- and radio-therapy is one of the reasons why we need more methods in the field of cancer therapy. DNA damage response (DDR) is a set of mechanisms which identifies DNA lesions and triggers the repair process for restoring DNA after causing an arrest in the cell cycle. The ability of DDR in maintaining the genome stability and integrity can be favorable to cancerous cells which are exposed to radiation therapy or are treated with chemotherapeutic agents. When DDR mechanisms are error-free in cancer cells, they can escape the expected cellular death and display resistance to treatment. In this regard, targeting different components of DDR can help to increase the susceptibility of advanced tumors to chemo- and radio-therapy.

Chimeric antigen receptor T-cell therapy for melanoma

INTRODUCTION

In recent years, chimeric antigen receptor (CAR) T cell therapy has emerged as a cancer treatment. After initial therapeutic success for hematologic malignancies, this approach has been extended for the treatment of solid tumors including melanoma.

AREAS COVERED

T cells need to be reprogramed to recognize specific antigens expressed only in tumor cells, a difficult problem since cancer cells are simply transformed normal cells. Tumor antigens, namely, CSPG4, CD70, and GD2 have been targeted by CAR-T cells for melanoma. Moreover, different co-stimulatory signaling domains need to be selected to direct T cell fate. In this review, various approaches for the treatment of melanoma and their effectiveness are comprehensively reviewed and the current status, challenges, and future perspective of CAR-T cell therapy for melanoma are discussed. Literature search was accomplished in three databases (PubMed, Google scholar, and Clinicaltrials.gov). Published papers and clinical trials were screened and relevant documents were included by checking pre-defined eligibility criteria.

EXPERT OPINION

Despite obstacles and the risk of adverse events, CAR T cell therapy could be used for patients with treatment-resistant cancer. Clinical trials are underway to determine the efficacy of this approach for the treatment of melanoma.

Enhancing the activity of platinum-based drugs by improved inhibitors of ERCC1-XPF-mediated DNA repair

PURPOSE

The ERCC1-XPF 5'-3' DNA endonuclease complex is involved in the nucleotide excision repair pathway and in the DNA inter-strand crosslink repair pathway, two key mechanisms modulating the activity of chemotherapeutic alkylating agents in cancer cells. Inhibitors of the interaction between ERCC1 and XPF can be used to sensitize cancer cells to such drugs.

METHODS

We tested recently synthesized new generation inhibitors of this interaction and evaluated their capacity to sensitize cancer cells to the genotoxic activity of agents in synergy studies, as well as their capacity to inhibit the protein-protein interaction in cancer cells using proximity ligation assay.

RESULTS

Compound B9 showed the best activity being synergistic with cisplatin and mitomycin C in both colon and lung cancer cells. Also, B9 abolished the interaction between ERCC1 and XPF in cancer cells as shown by proximity ligation assay. Results of different compounds correlated with values from our previously obtained in silico predictions.

CONCLUSION

Our results confirm the feasibility of the approach of targeting the protein-protein interaction between ERCC1 and XPF to sensitize cancer cells to alkylating agents, thanks to the improved binding affinity of the newly synthesized compounds.

Antitumor Drugs and Their Targets

Through novel methodologies, including both basic and clinical research, progress has been made in the therapy of solid cancer. Recent innovations in anticancer therapies, including immune checkpoint inhibitor biologics, therapeutic vaccines, small drugs, and CAR-T cell injections, mark a new epoch in cancer research, already known for faster (epi-)genomics, transcriptomics, and proteomics. As the long-sought after personalization of cancer therapies comes to fruition, the need to evaluate all current therapeutic possibilities and select the best for each patient is of paramount importance. This is a novel task for medical care that deserves prominence in therapeutic considerations in the future. This is because cancer is a complex genetic disease. In its deadly form, metastatic cancer, it includes altered genes (and their regulators) that encode ten hallmarks of cancer-independent growth, dodging apoptosis, immortalization, multidrug resistance, neovascularization, invasiveness, genome instability, inflammation, deregulation of metabolism, and avoidance of destruction by the immune system. These factors have been known targets for many anticancer drugs and treatments, and their modulation is a therapeutic goal, with the hope of rendering solid cancer a chronic rather than deadly disease. In this article, the current therapeutic arsenal against cancers is reviewed with a focus on immunotherapies.

Inhibition of DNA Repair in Cancer Therapy: Toward a Multi-Target Approach

Alterations in DNA repair pathways are one of the main drivers of cancer insurgence. Nevertheless, cancer cells are more susceptible to DNA damage than normal cells and they rely on specific functional repair pathways to survive. Thanks to advances in genome sequencing, we now have a better idea of which genes are mutated in specific cancers and this prompted the development of inhibitors targeting DNA repair players involved in pathways essential for cancer cells survival. Currently, the pivotal concept is that combining the inhibition of mechanisms on which cancer cells viability depends is the most promising way to treat tumorigenesis. Numerous inhibitors have been developed and for many of them, efficacy has been demonstrated either alone or in combination with chemo or radiotherapy. In this review, we will analyze the principal pathways involved in cell cycle checkpoint and DNA repair focusing on how their alterations could predispose to cancer, then we will explore the inhibitors developed or in development specifically targeting different proteins involved in each pathway, underscoring the rationale behind their usage and how their combination and/or exploitation as adjuvants to classic therapies could help in patients clinical outcome.

Design, synthesis and in vitro cell-free/cell-based biological evaluations of novel ERCC1-XPF inhibitors targeting DNA repair pathway

The structure-specific ERCC1-XPF endonuclease is essential for repairing bulky DNA lesions and helix distortions induced by UV radiation, which forms cyclobutane pyrimidine dimers (CPDs), or chemicals that crosslink DNA strands such as cyclophosphamide and platinum-based chemotherapeutic agents. Inhibition of the ERCC1-XPF endonuclease activity has been shown to sensitize cancer cells to these chemotherapeutic agents. In this study, we have conducted a structure activity relationship analysis based around the previously identified hit compound, 4-((6-chloro-2-methoxyacridin-9-yl)amino)-2-((4-methylpiperazin1-yl)methyl)phenol (F06), as a reference compound. Three different series of compounds have been rationally designed and successfully synthesized through various modifications on three different sites of F06 based on the corresponding suggestions of the previous pharmacophore model. The in vitro screening results revealed that 2-chloro-9-((3-((4-(2-(dimethylamino)ethyl)piperazin-1-yl)methyl)-4-hydroxyphenyl)amino)acridin-2-ol (B9) has a potent inhibitory effect on the ERCC1-XPF activity (IC₅₀ = 0.49 μM), showing 3-fold improvement in inhibition activity compared to F06. In addition, B9 not only displayed better binding affinity to the ERCC1-XPF complex but also had the capacity to potentiate the cytotoxicity effect of UV radiation and inhibiting the nucleotide excision repair, by the inhibition of removal of CPDs, and cyclophosphamide toxicity to colorectal cancer cells.

Mechanisms of Multidrug Resistance in Cancer Chemotherapy

Cancer is one of the main causes of death worldwide. Despite the significant development of methods of cancer healing during the past decades, chemotherapy still remains the main method for cancer treatment. Depending on the mechanism of action, commonly used chemotherapeutic agents can be divided into several classes (antimetabolites, alkylating agents, mitotic spindle inhibitors, topoisomerase inhibitors, and others). Multidrug resistance (MDR) is responsible for over 90% of deaths in cancer patients receiving traditional chemotherapeutics or novel targeted drugs. The mechanisms of MDR include elevated metabolism of xenobiotics, enhanced efflux of drugs, growth factors, increased DNA repair capacity, and genetic factors (gene mutations, amplifications, and epigenetic alterations). Rapidly increasing numbers of biomedical studies are focused on designing chemotherapeutics that are able to evade or reverse MDR. The aim of this review is not only to demonstrate the latest data on the mechanisms of cellular resistance to anticancer agents currently used in clinical treatment but also to present the mechanisms of action of novel potential antitumor drugs which have been designed to overcome these resistance mechanisms. Better understanding of the mechanisms of MDR and targets of novel chemotherapy agents should provide guidance for future research concerning new effective strategies in cancer treatment.

Nanoparticle-Mediated Gene Silencing for Sensitization of Lung Cancer to Cisplatin Therapy

Platinum-based chemotherapy remains a mainstay treatment for the management of advanced non-small cell lung cancer. A key cellular factor that contributes to sensitivity to platinums is the 5'-3' structure-specific endonuclease excision repair cross-complementation group 1 (ERCC1)/ xeroderma pigmentosum group F (XPF). ERCC1/XPF is critical for the repair of platinum-induced DNA damage and has been the subject of intense research efforts to identify small molecule inhibitors of its nuclease activity for the purpose of enhancing patient response to platinum-based chemotherapy. As an alternative to small molecule inhibitors, small interfering RNA (siRNA) has often been described to be more efficient in interrupting protein-protein interactions. The goal of this study was therefore to determine whether biocompatible nanoparticles consisting of an amphiphilic triblock copolymer (polyethylenimine-polycaprolactone-polyethylene glycol (PEI-PCL-PEG)) and carrying siRNA targeted to ERCC1 and XPF made by microfluidic assembly are capable of efficient gene silencing and able to sensitize lung cancer cells to cisplatin. First, we show that our PEI-PCL-PEG micelleplexes carrying ERCC1 and XPF siRNA efficiently knocked down ERCC1/XPF protein expression to the same extent as the standard siRNA transfection reagent, Lipofectamine. Second, we show that our siRNA-carrying nanoparticles enhanced platinum sensitivity in a p53 wildtype model of non-small cell lung cancer in vitro. Our results suggest that nanoparticle-mediated targeting of ERCC1/XPF is feasible and could represent a novel therapeutic strategy for targeting ERCC1/XPF in vivo.

Inhibitors of the Fanconi anaemia pathway as potential antitumour agents for ovarian cancer

The Fanconi anaemia (FA) pathway is an important mechanism for cellular DNA damage repair, which functions to remove toxic DNA interstrand crosslinks. This is particularly relevant in the context of ovarian and other cancers which rely extensively on interstrand cross-link generating platinum chemotherapy as standard of care treatment. These cancers often respond well to initial treatment, but reoccur with resistant disease and upregulation of DNA damage repair pathways. The FA pathway is therefore of great interest as a target for therapies that aim to improve the efficacy of platinum chemotherapies, and reverse tumour resistance to these. In this review, we discuss recent advances in understanding the mechanism of interstrand cross-link repair by the FA pathway, and the potential of the component parts as targets for therapeutic agents. We then focus on the current state of play of inhibitor development, covering both the characterisation of broad spectrum inhibitors and high throughput screening approaches to identify novel small molecule inhibitors. We also consider synthetic lethality between the FA pathway and other DNA damage repair pathways as a therapeutic approach.

Computer-aided drug design of small molecule inhibitors of the ERCC1-XPF protein-protein interaction

The heterodimer of DNA excision repair protein ERCC-1 and DNA repair endonuclease XPF (ERCC1-XPF) is a 5'-3' structure-specific endonuclease essential for the nucleotide excision repair (NER) pathway, and it is also involved in other DNA repair pathways. In cancer cells, ERCC1-XPF plays a central role in repairing DNA damage induced by chemotherapeutics including platinum-based and cross-linking agents; thus, its inhibition is a promising strategy to enhance the effect of these therapies. In this study, we rationally modified the structure of F06, a small molecule inhibitor of the ERCC1-XPF interaction (Molecular Pharmacology, 84, 2013 and 12), to improve its binding to the target. We followed a multi-step computational approach to investigate potential modification sites of F06, rationally design and rank a library of analogues, and identify candidates for chemical synthesis and in vitro testing. Our top compound, B5, showed an improved half-maximum inhibitory concentration (IC₅₀ ) value of 0.49 µM for the inhibition of ERCC1-XPF endonuclease activit, and lays the foundation for further testing and optimization. Also, the computational approach reported here can be used to develop DNA repair inhibitors targeting the ERCC1-XPF complex.

Optimised oligonucleotide substrates to assay XPF-ERCC1 nuclease activity for the discovery of DNA repair inhibitors

We report the design and optimisation of novel oligonucleotide substrates for a sensitive fluorescence assay for high-throughput screening and functional studies of the DNA repair enzyme, XPF-ERCC1, with a view to accelerating inhibitor and drug discovery.

Targeting DNA Repair in Tumor Cells via Inhibition of ERCC1-XPF

The ERCC1-XPF heterodimer is a 5'-3' structure-specific endonuclease, which plays an essential role in several DNA repair pathways in mammalian cells. ERCC1-XPF is primarily involved in the repair of chemically induced helix-distorting and bulky DNA lesions, such as cyclobutane pyrimidine dimers (CPDs), and DNA interstrand cross-links. Inhibition of ERCC1-XPF has been shown to potentiate cytotoxicity of platinum-based drugs and cyclophosphamide in cancer cells. In this study, the previously described ERCC1-XPF inhibitor 4-((6-chloro-2-methoxyacridin-9-yl)amino)-2-((4-methylpiperazin-1-yl)methyl)phenol (compound 1) was used as a reference compound. Following the outcome of docking-based virtual screening (VS), we synthesized seven novel derivatives of 1 that were identified in silico as being likely to have high binding affinity for the ERCC1-XPF heterodimerization interface by interacting with the XPF double helix-hairpin-helix (HhH2) domain. Two of the new compounds, 4-((6-chloro-2-methoxyacridin-9-yl)amino)-2-((4-cyclohexylpiperazin-1-yl)methyl)phenol (compound 3) and 4-((6-chloro-2-methoxyacridin-9-yl)amino)-2-((4-(2-(dimethylamino)ethyl) piperazin-1-yl) methyl) phenol (compound 4), were shown to be potent inhibitors of ERCC1-XPF activity in vitro. Compound 4 showed significant inhibition of the removal of CPDs in UV-irradiated cells and the capacity to sensitize colorectal cancer cells to UV radiation and cyclophosphamide.

Platinum Resistance in Ovarian Cancer: Role of DNA Repair

Epithelial ovarian cancer (EOC) is the most lethal gynecological cancer. It is initially responsive to cisplatin and carboplatin, two DNA damaging agents used in first line therapy. However, almost invariably, patients relapse with a tumor resistant to subsequent treatment with platinum containing drugs. Several mechanisms associated with the development of acquired drug resistance have been reported. Here we focused our attention on DNA repair mechanisms, which are fundamental for recognition and removal of platinum adducts and hence for the ability of these drugs to exert their activity. We analyzed the major DNA repair pathways potentially involved in drug resistance, detailing gene mutation, duplication or deletion as well as polymorphisms as potential biomarkers for drug resistance development. We dissected potential ways to overcome DNA repair-associated drug resistance thanks to the development of new combinations and/or drugs directly targeting DNA repair proteins or taking advantage of the vulnerability arising from DNA repair defects in EOCs.

Platinum Resistance in Ovarian Cancer: Role of DNA Repair

Epithelial ovarian cancer (EOC) is the most lethal gynecological cancer. It is initially responsive to cisplatin and carboplatin, two DNA damaging agents used in first line therapy. However, almost invariably, patients relapse with a tumor resistant to subsequent treatment with platinum containing drugs. Several mechanisms associated with the development of acquired drug resistance have been reported. Here we focused our attention on DNA repair mechanisms, which are fundamental for recognition and removal of platinum adducts and hence for the ability of these drugs to exert their activity. We analyzed the major DNA repair pathways potentially involved in drug resistance, detailing gene mutation, duplication or deletion as well as polymorphisms as potential biomarkers for drug resistance development. We dissected potential ways to overcome DNA repair-associated drug resistance thanks to the development of new combinations and/or drugs directly targeting DNA repair proteins or taking advantage of the vulnerability arising from DNA repair defects in EOCs.

Platinum Resistance in Ovarian Cancer: Role of DNA Repair

Epithelial ovarian cancer (EOC) is the most lethal gynecological cancer. It is initially responsive to cisplatin and carboplatin, two DNA damaging agents used in first line therapy. However, almost invariably, patients relapse with a tumor resistant to subsequent treatment with platinum containing drugs. Several mechanisms associated with the development of acquired drug resistance have been reported. Here we focused our attention on DNA repair mechanisms, which are fundamental for recognition and removal of platinum adducts and hence for the ability of these drugs to exert their activity. We analyzed the major DNA repair pathways potentially involved in drug resistance, detailing gene mutation, duplication or deletion as well as polymorphisms as potential biomarkers for drug resistance development. We dissected potential ways to overcome DNA repair-associated drug resistance thanks to the development of new combinations and/or drugs directly targeting DNA repair proteins or taking advantage of the vulnerability arising from DNA repair defects in EOCs.

Identification and Characterization of Synthetic Viability with ERCC1 Deficiency in Response to Interstrand Crosslinks in Lung Cancer

PURPOSE

ERCC1/XPF is a DNA endonuclease with variable expression in primary tumor specimens, and has been investigated as a predictive biomarker for efficacy of platinum-based chemotherapy. The failure of clinical trials utilizing ERCC1 expression to predict response to platinum-based chemotherapy suggests additional mechanisms underlying the basic biology of ERCC1 in the response to interstrand crosslinks (ICLs) remain unknown. We aimed to characterize a panel of ERCC1 knockout (Δ) cell lines, where we identified a synthetic viable phenotype in response to ICLs with ERCC1 deficiency.

EXPERIMENTAL DESIGN

We utilized the CRISPR-Cas9 system to create a panel of ERCC1Δ lung cancer cell lines which we characterized.

RESULTS

We observe that loss of ERCC1 hypersensitizes cells to cisplatin when wild-type (WT) p53 is retained, whereas there is only modest sensitivity in cell lines that are p53^mutant/null. In addition, when p53 is disrupted by CRISPR-Cas9 (p53*) in ERCC1Δ/p53^WT cells, there is reduced apoptosis and increased viability after platinum treatment. These results were recapitulated in 2 patient data sets utilizing p53 mutation analysis and ERCC1 expression to assess overall survival. We also show that kinetics of ICL-repair (ICL-R) differ between ERCC1Δ/p53^WT and ERCC1Δ/p53* cells. Finally, we provide evidence that cisplatin tolerance in the context of ERCC1 deficiency relies on DNA-PKcs and BRCA1 function.

CONCLUSIONS

Our findings implicate p53 as a potential confounding variable in clinical assessments of ERCC1 as a platinum biomarker via promoting an environment in which error-prone mechanisms of ICL-R may be able to partially compensate for loss of ERCC1.See related commentary by Friboulet et al., p. 2369.

Targeting the DNA Repair Endonuclease ERCC1-XPF with Green Tea Polyphenol Epigallocatechin-3-Gallate (EGCG) and Its Prodrug to Enhance Cisplatin Efficacy in Human Cancer Cells

The 5′-3′ structure-specific endonuclease ERCC1/XPF (Excision Repair Cross-Complementation Group 1/Xeroderma Pigmentosum group F) plays critical roles in the repair of cisplatin-induced DNA damage. As such, it has been identified as a potential pharmacological target for enhancing clinical response to platinum-based chemotherapy. The goal of this study was to follow up on our previous identification of the compound NSC143099 as a potent inhibitor of ERCC1/XPF activity by performing an in silico screen to identify structural analogues that could inhibit ERCC1/XPF activity in vitro and in vivo. Using a fluorescence-based DNA-endonuclease incision assay, we identified the green tea polyphenol (-)-epigallocatechin-3-gallate (EGCG) as a potent inhibitor of ERCC1/XPF activity with an IC₅₀ (half maximal inhibitory concentration) in the nanomolar range in biochemical assays. Using DNA repair assays and clonogenic survival assays, we show that EGCG can inhibit DNA repair and enhance cisplatin sensitivity in human cancer cells. Finally, we show that a prodrug of EGCG, Pro-EGCG (EGCG octaacetate), can enhance response to platinum-based chemotherapy in vivo. Together these data support a novel target of EGCG in cancer cells, namely ERCC1/XPF. Our studies also corroborate previous observations that EGCG enhances sensitivity to cisplatin in multiple cancer types. Thus, EGCG or its prodrug makes an ideal candidate for further pharmacological development with the goal of enhancing cisplatin response in human tumors.

Melanoma cells resistant towards MAPK inhibitors exhibit reduced TAp73 expression mediating enhanced sensitivity to platinum-based drugs

The efficacy of targeted MAPK signalling pathway inhibitors (MAPKi) in metastatic melanoma therapy is limited by the development of resistance mechanisms that results in disease relapse. This situation still requires treatment alternatives for melanoma patients with acquired resistance to targeted therapy. We found that melanoma cells, which developed resistance towards MAPKi show an enhanced susceptibility to platinum-based drugs, such as cisplatin and carboplatin. We found that this enhanced susceptibility inversely correlates with the expression level of the p53 family member TAp73. We show that the lower expression of the TAp73 isoform in MAPKi-resistant melanoma cells enhances accumulation of DNA double-strand breaks upon cisplatin and carboplatin treatment by reducing the efficiency of nucleotide excision repair. These data suggest that a subgroup of melanoma patients with acquired resistance to MAPKi treatment and low TAp73 expression can benefit from chemotherapy with platinum-based drugs as a second-line therapy.

Melatonin Sensitizes Hepatocellular Carcinoma Cells to Chemotherapy Through Long Non-Coding RNA RAD51-AS1-Mediated Suppression of DNA Repair

DNA repair systems are abnormally active in most hepatocellular carcinoma (HCC) cells due to accumulated mutations, resulting in elevated DNA repair capacity and resistance to chemotherapy and radiotherapy. Thus, targeting DNA repair mechanisms is a common treatment approach in HCC to sensitize cancer cells to DNA damage. In this study, we examined the anti-HCC effects of melatonin and elucidated the regulatory mechanisms. The results of functional assays showed that in addition to inhibiting the proliferation, migration, and invasion abilities of HCC cells, melatonin suppressed their DNA repair capacity, thereby promoting the cytotoxicity of chemotherapy and radiotherapy. Whole-transcriptome and gain- and loss-of-function analyses revealed that melatonin induces expression of the long noncoding RNA RAD51-AS1, which binds to RAD51 mRNA to inhibit its translation, effectively decreasing the DNA repair capacity of HCC cells and increasing their sensitivity to chemotherapy and radiotherapy. Animal models further demonstrated that a combination of melatonin and the chemotherapeutic agent etoposide (VP16) can significantly enhance tumor growth inhibition compared with monotherapy. Our results show that melatonin is a potential adjuvant treatment for chemotherapy and radiotherapy in HCC.

DNA repair pathways and cisplatin resistance: an intimate relationship

The main goal of chemotherapeutic drugs is to induce massive cell death in tumors. Cisplatin is an antitumor drug widely used to treat several types of cancer. Despite its remarkable efficiency, most tumors show intrinsic or acquired drug resistance. The primary biological target of cisplatin is genomic DNA, and it causes a plethora of DNA lesions that block transcription and replication. These cisplatin-induced DNA lesions strongly induce cell death if they are not properly repaired or processed. To counteract cisplatin-induced DNA damage, cells use an intricate network of mechanisms, including DNA damage repair and translesion synthesis. In this review, we describe how cisplatin-induced DNA lesions are repaired or tolerated by cells and focus on the pivotal role of DNA repair and tolerance mechanisms in tumor resistance to cisplatin. In fact, several recent clinical findings have correlated the tumor cell status of DNA repair/translesion synthesis with patient response to cisplatin treatment. Furthermore, these mechanisms provide interesting targets for pharmacological modulation that can increase the efficiency of cisplatin chemotherapy.

Association between common polymorphisms in ERCC gene and prognosis of osteosarcoma in patients treated with chemotherapy: a meta-analysis

Purpose

Some previous studies have sought to investigate the roles of excision repair cross complementation group 1 (ERCC1), ERCC2, ERCC4, and ERCC5 gene polymorphisms in the prognosis of osteosarcoma patients. However, their results were inconclusive. Here, we performed a meta-analysis to determine the strength of the association between eight polymorphisms in the ERCC genes (rs11615, rs3212986, rs2298881, rs13181, rs1799793, rs1800067, rs2296147, and rs1047768) and prognosis of osteosarcoma patients treated with chemotherapy.

Materials and methods

We retrieved the relevant studies from PubMed, Embase, and Web of Science in human osteosarcoma published prior to July 2017. Primary outcomes included overall survival (OS) and event-free survival, expressed by hazard ratios (HRs) with their corresponding 95% CIs. STATA software (version 12.0) was utilized to perform data synthesis.

Results

A total of 13 eligible follow-up studies involving 2,303 patients met all the inclusion criteria, conducted in two populations of ethnic descent: 11 Asians and two Caucasians. In the present meta-analysis, we demonstrated that the homozygous variant genotypes in ERCC2 rs1799793 and ERCC5 rs2296147 were significantly associated with OS in osteosarcoma (TT vs GG for rs1799793: HR = 0.62, 95% CI = 0.41-0.93, P_{heterogeneity} = 0.310, I² = 15.3%, P = 0.020; TT vs CC for rs2296147: HR = 0.42, 95% CI = 0.23-0.78, P_{heterogeneity} = 0.708, I² = 0.0%, P = 0.006). In addition, no evidence of association was observed between prognosis in osteosarcoma and ERCC1 rs11615, ERCC1 rs3212986, ERCC1 rs2298881, ERCC2 rs13181, ERCC4 rs1800067, and ERCC5 rs1047768 polymorphisms.

Conclusion

Our meta-analysis indicated that TT genotype in the ERCC2 rs1799793 and ERCC5 rs2296147 might prolong the survival time of patients with osteosarcoma, suggesting that the rs1799793 and rs2296147 polymorphisms can be used as predictors for prognosis of osteosarcoma patients treated with chemotherapy.

Clinically Applicable Inhibitors Impacting Genome Stability

Advances in technology have facilitated the molecular profiling (genomic and transcriptomic) of tumours, and has led to improved stratification of patients and the individualisation of treatment regimes. To fully realize the potential of truly personalised treatment options, we need targeted therapies that precisely disrupt the compensatory pathways identified by profiling which allow tumours to survive or gain resistance to treatments. Here, we discuss recent advances in novel therapies that impact the genome (chromosomes and chromatin), pathways targeted and the stage of the pathways targeted. The current state of research will be discussed, with a focus on compounds that have advanced into trials (clinical and pre-clinical). We will discuss inhibitors of specific DNA damage responses and other genome stability pathways, including those in development, which are likely to synergistically combine with current therapeutic options. Tumour profiling data, combined with the knowledge of new treatments that affect the regulation of essential tumour signalling pathways, is revealing fundamental insights into cancer progression and resistance mechanisms. This is the forefront of the next evolution of advanced oncology medicine that will ultimately lead to improved survival and may, one day, result in many cancers becoming chronic conditions, rather than fatal diseases.

Computational Characterization of Small Molecules Binding to the Human XPF Active Site and Virtual Screening to Identify Potential New DNA Repair Inhibitors Targeting the ERCC1-XPF Endonuclease

The DNA excision repair protein ERCC-1-DNA repair endonuclease XPF (ERCC1-XPF) is a heterodimeric endonuclease essential for the nucleotide excision repair (NER) DNA repair pathway. Although its activity is required to maintain genome integrity in healthy cells, ERCC1-XPF can counteract the effect of DNA-damaging therapies such as platinum-based chemotherapy in cancer cells. Therefore, a promising approach to enhance the effect of these therapies is to combine their use with small molecules, which can inhibit the repair mechanisms in cancer cells. Currently, there are no structures available for the catalytic site of the human ERCC1-XPF, which performs the metal-mediated cleavage of a DNA damaged strand at 5′. We adopted a homology modeling strategy to build a structural model of the human XPF nuclease domain which contained the active site and to extract dominant conformations of the domain using molecular dynamics simulations followed by clustering of the trajectory. We investigated the binding modes of known small molecule inhibitors targeting the active site to build a pharmacophore model. We then performed a virtual screening of the ZINC Is Not Commercial 15 (ZINC15) database to identify new ERCC1-XPF endonuclease inhibitors. Our work provides structural insights regarding the binding mode of small molecules targeting the ERCC1-XPF active site that can be used to rationally optimize such compounds. We also propose a set of new potential DNA repair inhibitors to be considered for combination cancer therapy strategies.

Identification of small molecule inhibitors of ERCC1-XPF that inhibit DNA repair and potentiate cisplatin efficacy in cancer cells

ERCC1-XPF heterodimer is a 5′-3′ structure-specific endonuclease which is essential in multiple DNA repair pathways in mammalian cells. ERCC1-XPF (ERCC1-ERCC4) repairs cisplatin-DNA intrastrand adducts and interstrand crosslinks and its specific inhibition has been shown to enhance cisplatin cytotoxicity in cancer cells. In this study, we describe a high throughput screen (HTS) used to identify small molecules that inhibit the endonuclease activity of ERCC1-XPF. Primary screens identified two compounds that inhibit ERCC1-XPF activity in the nanomolar range. These compounds were validated in secondary screens against two other non-related endonucleases to ensure specificity. Results from these screens were validated using an in vitro gel-based nuclease assay. Electrophoretic mobility shift assays (EMSAs) further show that these compounds do not inhibit the binding of purified ERCC1-XPF to DNA. Next, in lung cancer cells these compounds potentiated cisplatin cytotoxicity and inhibited DNA repair. Structure activity relationship (SAR) studies identified related compounds for one of the original Hits, which also potentiated cisplatin cytotoxicity in cancer cells. Excitingly, dosing with NSC16168 compound potentiated cisplatin antitumor activity in a lung cancer xenograft model. Further development of ERCC1-XPF DNA repair inhibitors is expected to sensitize cancer cells to DNA damage-based chemotherapy.

Sequential decitabine and carboplatin treatment increases the DNA repair protein XPC, increases apoptosis and decreases proliferation in melanoma

BACKGROUND

Melanoma has two key features, an over-representation of UV-induced mutations and resistance to DNA damaging chemotherapy agents. Both of these features may result from dysfunction of the nucleotide excision repair pathway, in particular the DNA damage detection branch, global genome repair (GGR). The key GGR component XPC does not respond to DNA damage in melanoma, the cause of this lack of response has not been investigated. In this study, we investigated the role of methylation in reduced XPC in melanoma.

METHODS

To reduce methylation and induce DNA-damage, melanoma cell lines were treated with decitabine and carboplatin, individually and sequentially. Global DNA methylation levels, XPC mRNA and protein expression and methylation of the XPC promoter were examined. Apoptosis, cell proliferation and senescence were also quantified. XPC siRNA was used to determine that the responses seen were reliant on XPC induction.

RESULTS

Treatment with high-dose decitabine resulted in global demethylation, including the the shores of the XPC CpG island and significantly increased XPC mRNA expression. Lower, clinically relevant dose of decitabine also resulted in global demethylation including the CpG island shores and induced XPC in 50% of cell lines. Decitabine followed by DNA-damaging carboplatin treatment led to significantly higher XPC expression in 75% of melanoma cell lines tested. Combined sequential treatment also resulted in a greater apoptotic response in 75% of cell lines compared to carboplatin alone, and significantly slowed cell proliferation, with some melanoma cell lines going into senescence. Inhibiting the increased XPC using siRNA had a small but significant negative effect, indicating that XPC plays a partial role in the response to sequential decitabine and carboplatin.

CONCLUSIONS

Demethylation using decitabine increased XPC and apoptosis after sequential carboplatin. These results confirm that sequential decitabine and carboplatin requires further investigation as a combination treatment for melanoma.

Melanoma cells replicate through chemotherapy by reducing levels of key homologous recombination protein RAD51 and increasing expression of translesion synthesis DNA polymerase ζ

BACKGROUND

The global incidence of melanoma has been increasing faster than any other form of cancer. New therapies offer exciting prospects for improved survival, but the development of resistance is a major problem and there remains a need for additional effective melanoma therapy. Platinum compounds, such as cisplatin, are the most effective chemotherapeutics for a number of major cancers, but are ineffective on metastatic melanoma. They cause monofunctional adducts and intrastrand crosslinks that are repaired by nucleotide excision repair, as well as the more toxic interstrand crosslinks that are repaired by a combination of nuclease activity and homologous recombination.

METHODS

We investigated the mechanism of melanoma resistance to cisplatin using a panel of melanoma and control cell lines. Cisplatin-induced changes in levels of the key homologous recombination protein RAD51 and compensatory changes in translesion synthesis DNA polymerases were identified by western blotting and qRT-PCR. Flow cytometry, immunofluorescence and western blotting were used to compare the cell cycle and DNA damage response and the induction of apoptosis in cisplatin-treated melanoma and control cells. Ectopic expression of a tagged form of RAD51 and siRNA knockdown of translesion synthesis DNA polymerase zeta were used to investigate the mechanism that allowed cisplatin-treated melanoma cells to continue to replicate.

RESULTS

We have identified and characterised a novel DNA damage response mechanism in melanoma. Instead of increasing levels of RAD51 on encountering cisplatin-induced interstrand crosslinks during replication, melanoma cells shut down RAD51 synthesis and instead boost levels of translesion synthesis DNA polymerase zeta to allow replication to proceed. This response also resulted in synthetic lethality to the PARP inhibitor olaparib.

CONCLUSIONS

This unusual DNA damage response may be a more appropriate strategy for an aggressive and rapidly growing tumour like melanoma that enables it to better survive chemotherapy, but also results in increased sensitivity of cultured melanoma cells to the PARP inhibitor olaparib.

Fanconi Anemia Signaling and Cancer

The extremely high cancer incidence associated with patients suffering from a rare human genetic disease, Fanconi anemia (FA), demonstrates the importance of FA genes. Over the course of human tumor development, FA genes perform critical tumor-suppression roles. In doing so, FA provides researchers with a unique genetic model system to study cancer etiology. Here, we review how aberrant function of the 22 FA genes and their signaling network contributes to malignancy. From this perspective, we will also discuss how the knowledge discovered from FA research serves basic and translational cancer research.

Drugging the Cancers Addicted to DNA Repair

Defects in DNA repair can result in oncogenic genomic instability. Cancers occurring from DNA repair defects were once thought to be limited to rare inherited mutations (such as BRCA1 or 2). It now appears that a clinically significant fraction of cancers have acquired DNA repair defects. DNA repair pathways operate in related networks, and cancers arising from loss of one DNA repair component typically become addicted to other repair pathways to survive and proliferate. Drug inhibition of the rescue repair pathway prevents the repair-deficient cancer cell from replicating, causing apoptosis (termed synthetic lethality). However, the selective pressure of inhibiting the rescue repair pathway can generate further mutations that confer resistance to the synthetic lethal drugs. Many such drugs currently in clinical use inhibit PARP1, a repair component to which cancers arising from inherited BRCA1 or 2 mutations become addicted. It is now clear that drugs inducing synthetic lethality may also be therapeutic in cancers with acquired DNA repair defects, which would markedly broaden their applicability beyond treatment of cancers with inherited DNA repair defects. Here we review how each DNA repair pathway can be attacked therapeutically and evaluate DNA repair components as potential drug targets to induce synthetic lethality. Clinical use of drugs targeting DNA repair will markedly increase when functional and genetic loss of repair components are consistently identified. In addition, future therapies will exploit artificial synthetic lethality, where complementary DNA repair pathways are targeted simultaneously in cancers without DNA repair defects.

Disruption of DNA repair in cancer cells by ubiquitination of a destabilising dimerization domain of nucleotide excision repair protein ERCC1

DNA repair pathways present in all cells serve to preserve genome stability, but in cancer cells they also act reduce the efficacy of chemotherapy. The endonuclease ERCC1-XPF has an important role in the repair of DNA damage caused by a variety of chemotherapeutic agents and there has been intense interest in the use of ERCC1 as a predictive marker of therapeutic response in non-small cell lung carcinoma, squamous cell carcinoma and ovarian cancer. We have previously validated ERCC1 as a therapeutic target in melanoma, but all small molecule ERCC1-XPF inhibitors reported to date have lacked sufficient potency and specificity for clinical use. In an alternative approach to prevent the repair activity of ERCC1-XPF, we investigated the mechanism of ERCC1 ubiquitination and found that the key region was the C-terminal (HhH)₂ domain which heterodimerizes with XPF. This ERCC1 region was modified by non-conventional lysine-independent, but proteasome-dependent polyubiquitination, involving Lys33 of ubiquitin and a linear ubiquitin chain. XPF was not polyubiquitinated and its expression was dependent on presence of ERCC1, but not vice versa. To our surprise we found that ERCC1 can also homodimerize through its C-terminal (HhH)₂ domain. We exploited the ability of a peptide containing this C-terminal domain to destabilise both endogenous ERCC1 and XPF in human melanoma cells and fibroblasts, resulting in reductions of up to 85% in nucleotide excision repair and near two-fold increased sensitivity to DNA damaging agents. We suggest that the ERCC1 (HhH)₂ domain could be used in an alternative strategy to treat cancer.

Potential Strategies to Target Protein-Protein Interactions in the DNA Damage Response and Repair Pathways

This review article discusses some insights about generating novel mechanistic inhibitors of the DNA damage response and repair (DDR) pathways by focusing on protein-protein interactions (PPIs) of the key DDR components. General requirements for PPI strategies, such as selecting the target PPI site on the basis of its functionality, are discussed first. Next, on the basis of functional rationale and biochemical feasibility to identify a PPI inhibitor, 26 PPIs in DDR pathways (BER, MMR, NER, NHEJ, HR, TLS, and ICL repair) are specifically discussed for inhibitor discovery to benefit cancer therapies using a DNA-damaging agent.

18F-fludrodeoxyglucose maximal standardized uptake value and metabolic tumor burden are associated with major chemotherapy-related tumor markers in NSCLC patients

Objective

Metabolic activity and tumor burden are significant for prognosis and metastasis of non-small cell lung cancer (NSCLC), including maximum standardized uptake value (SUV_max), metabolic tumor volume (MTV), and total lesion glycolysis (TLG). Chemotherapy resistance is a great challenge for treating NSCLC patients and is also closely related with several biomarkers such as epidermal growth factor receptor (EGFR), p53, and excision repair cross-complementing group 1 protein (ERCC1). Our purpose was to determine the correlation between positron emission tomography/computed tomography (PET/CT) parameters and tumor markers-related chemotherapy resistance in NSCLC.

Methods

Forty-six NSCLC chemotherapy-naïve patients were enrolled. The SUV_max, MTV, and TLG were calculated by PET/CT imaging, and expression of EGFR, p53, and ERCC1 were analyzed by immunohistochemistry on tissues. SUV_max, MTV, and TLG compared for their performance in predicting the expression of EGFR, p53, and ERCC1 were illustrated with statistical analysis.

Results

SUV_max was significantly correlated with p53 expression (P=0.001), and MTV and TLG were significantly associated with ERCC1 (P=0.000; P=0.000). Furthermore, multiple stepwise regression analysis revealed that SUV_max was the primary predictor for p53, MTV and TLG was the primary predictor for ERCC1. SUV_max had a sensitivity of 91% and specificity of 50% for the detection of p53 positive. The sensitivities of MTV and TLG were 83% and 80%, and specificities were 69% and 75% for the detection of ERCC1 positive, respectively. When we suggested p53 or ERCC1 positive, the cutoff value of SUV_max, MTV, and TLG were 7.68, 23.62, and 129.65 cm³, respectively.

Conclusion

SUV_max, MTV, and TLG were closely associated with p53 and ERCC1’ expressions. Therefore, ¹⁸F-fludrodeoxyglucose PET/CT could be a new way of predicting p53 or ERCC1-related chemotherapy effect in NSCLC patients with more convenience.

A Platinum(IV) Anticancer Prodrug Targeting Nucleotide Excision Repair To Overcome Cisplatin Resistance

DNA damage response plays a key role not only in maintaining genome integrity but also in mediating the antitumor efficacy of DNA-damaging antineoplastic drugs. Herein, we report the rational design and evaluation of a Pt^IV anticancer prodrug inhibiting nucleotide excision repair (NER), one of the most pivotal processes after the formation of cisplatin-induced DNA damage that deactivates the drug and leads to drug resistance in the clinic. This dual-action prodrug enters cells efficiently and causes DNA damage while simultaneously inhibiting NER to promote apoptotic response. The prodrug is strongly active against the proliferation of cisplatin-resistant human cancer cells with an up to 88-fold increase in growth inhibition compared with cisplatin, and the prodrug is much more active than a mixture of cisplatin and an NER inhibitor. Our study highlights the importance of targeting downstream pathways after the formation of Pt-induced DNA damage as a novel strategy to conquer cisplatin resistance.

DNA repair targeted therapy: The past or future of cancer treatment?

The repair of DNA damage is a complex process that relies on particular pathways to remedy specific types of damage to DNA. The range of insults to DNA includes small, modest changes in structure including mismatched bases and simple methylation events to oxidized bases, intra- and interstrand DNA crosslinks, DNA double strand breaks and protein-DNA adducts. Pathways required for the repair of these lesions include mismatch repair, base excision repair, nucleotide excision repair, and the homology directed repair/Fanconi anemia pathway. Each of these pathways contributes to genetic stability, and mutations in genes encoding proteins involved in these pathways have been demonstrated to promote genetic instability and cancer. In fact, it has been suggested that all cancers display defects in DNA repair. It has also been demonstrated that the ability of cancer cells to repair therapeutically induced DNA damage impacts therapeutic efficacy. This has led to targeting DNA repair pathways and proteins to develop anti-cancer agents that will increase sensitivity to traditional chemotherapeutics. While initial studies languished and were plagued by a lack of specificity and a defined mechanism of action, more recent approaches to exploit synthetic lethal interaction and develop high affinity chemical inhibitors have proven considerably more effective. In this review we will highlight recent advances and discuss previous failures in targeting DNA repair to pave the way for future DNA repair targeted agents and their use in cancer therapy.

Xeroderma Pigmentosum Group A Promotes Autophagy to Facilitate Cisplatin Resistance in Melanoma Cells through the Activation of PARP1

Xeroderma pigmentosum group A (XPA), a key protein in the nucleotide excision repair pathway, has been shown to promote the resistance of tumor cells to chemotherapeutic drugs by facilitating the DNA repair process. However, the role of XPA in the resistance of melanoma to platinum-based drugs like cisplatin is largely unknown. In this study, we initially found that XPA was expressed at higher levels in cisplatin-resistant melanoma cells than in cisplatin-sensitive ones. Furthermore, the knockdown of XPA not only increased cellular apoptosis but also inhibited cisplatin-induced autophagy, which rendered the melanoma cells more sensitive to cisplatin. Moreover, we discovered that the increased XPA in resistant melanoma cells promoted poly(adenosine diphosphate-ribose) polymerase 1 (PARP1) activation and that the inhibition of PARP1 could attenuate the cisplatin-induced autophagy. Finally, we proved that the inhibition of PARP1 and the autophagy process made resistant melanoma cells more susceptible to cisplatin treatment. Our study shows that XPA can promote cell-protective autophagy in a DNA repair-independent manner by enhancing the activation of PARP1 in melanoma cells resistant to cisplatin and that the XPA-PARP1-mediated autophagy process can be targeted to overcome cisplatin resistance in melanoma chemotherapy.