Small interfering RNA-induced suppression of ERCC1 enhances sensitivity of human cancer cells to cisplatin

ERCC1 abundance is an indicator of DNA repair-apoptosis decision upon DNA damage

DNA repair is essential for successful propagation of genetic material and fidelity of transcription. Nucleotide excision repair (NER) is one of the earliest DNA repair mechanisms, functionally conserved from bacteria to human. The fact that number of NER genes vary significantly between prokaryotes and metazoans gives the insight that NER proteins have evolved to acquire additional functions to combat challenges associated with a diploid genome, including being involved in the decision between DNA repair and apoptosis. However, no direct association between apoptosis and NER proteins has been shown to date. In this study, we induced apoptosis with a variety of agents, including oxaliplatin, doxorubicin and TRAIL, and observed changes in the abundance and molecular weight of NER complex proteins. Our results showed that XPA, XPC and ERCC1 protein levels change during DNA damage-induced apoptosis. Among these, ERCC1 decrease was observed as a pre-mitochondria depolarisation event which marks the "point of no return" in apoptosis signalling. ERCC1 decrease was due to proteasomal degradation upon lethal doses of oxaliplatin exposure. When ERCC1 protein was stabilised using proteasome inhibitors, the pro-apoptotic activity of oxaliplatin was attenuated. These results explain why clinical trials using proteasome inhibitors and platinum derivatives showed limited efficacy in carcinoma treatment and also the importance of how deep understanding of DNA repair mechanisms can improve cancer therapy.

Forkhead box proteins as the critical regulators of cisplatin response in tumor cells

Cisplatin (CDDP) is one of the most common chemotherapy drugs used in a wide range of cancer patients; however, there is a high rate of CDDP resistance among cancer patients. Considering the side effects of cisplatin in normal tissues, it is necessary to predict the CDDP response in cancer patients. Therefore, identifying the molecular mechanisms involved in CDDP resistance can help to introduce the prognostic markers. Several molecular mechanisms such as apoptosis inhibition, drug efflux, drug detoxification, and increased DNA repair are involved in CDDP resistance. Regarding the key role of transcription factors in regulation of many cellular processes related to drug resistance, in the present review, we discussed the role of Forkhead box (FOX) protein family in CDDP response. It has been reported that FOX proteins mainly promote CDDP resistance through the regulation of DNA repair, autophagy, epithelial-mesenchymal transition (EMT), and signaling pathways. Therefore, FOX proteins can be introduced as the prognostic markers to predict CDDP response in cancer patients. In addition, considering that oncogenic role of FOX proteins, the CDDP treatment along with FOX inhibition can be used as a therapeutic strategy in cancer patients.

Cisplatin Resistance: Genetic and Epigenetic Factors Involved

Cisplatin (CDDP) is the drug of choice against different types of cancer. However, tumor cells can acquire resistance to the damage caused by cisplatin, generating genetic and epigenetic changes that lead to the generation of resistance and the activation of intrinsic resistance mechanisms in cancer cells. Among them, we can find mutations, alternative splicing, epigenetic-driven expression changes, and even post-translational modifications of proteins. However, the molecular mechanisms by which CDDP resistance develops are not clear but are believed to be multi-factorial. This article highlights a description of cisplatin, which includes action mechanism, resistance, and epigenetic factors involved in cisplatin resistance.

The ZEB2-dependent EMT transcriptional programme drives therapy resistance by activating nucleotide excision repair genes ERCC1 and ERCC4 in colorectal cancer

Resistance to adjuvant chemotherapy is a major clinical problem in the treatment of colorectal cancer (CRC). The aim of this study was to elucidate the role of an epithelial to mesenchymal transition (EMT)‐inducing protein, ZEB2, in chemoresistance of CRC, and to uncover the underlying mechanism. We performed IHC for ZEB2 and association analyses with clinical outcomes on primary CRC and matched CRC liver metastases in compliance with observational biomarker study guidelines. ZEB2 expression in primary tumours was an independent prognostic marker of reduced overall survival and disease‐free survival in patients who received adjuvant FOLFOX chemotherapy. ZEB2 expression was retained in 96% of liver metastases. The ZEB2‐dependent EMT transcriptional programme activated nucleotide excision repair (NER) pathway largely via upregulation of the ERCC1 gene and other components in NER pathway, leading to enhanced viability of CRC cells upon oxaliplatin treatment. ERCC1‐overexpressing CRC cells did not respond to oxaliplatin in vivo, as assessed using a murine orthotopic model in a randomised and blinded preclinical study. Our findings show that ZEB2 is a biomarker of tumour response to chemotherapy and risk of recurrence in CRC patients. We propose that the ZEB2‐ERCC1 axis is a key determinant of chemoresistance in CRC.

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.

Hypermethylation of lncRNA MEG3 impairs chemosensitivity of breast cancer cells

Background

Chemoresistance posed a barrier to successful treatment of breast cancer (BC), and lncRNA MEG3 has been documented to implicate in BC development. However, whether MEG3 methylation, which led to low MEG3 expression, was relevant to BC progression and chemoresistance remained uncertain.

Methods

In the aggregate, 374 pairs of tumor tissues and adjacent normal tissues were collected from pathologically confirmed BC patients, and four BC cell lines, including MDA‐MB‐231, Bcap‐37, MCF‐7, and SK‐BR‐3, were purchased. Moreover, methylation‐specific polymerase chain reaction (PCR) was adopted to evaluate the methylation status of BC tissues and cell lines, and chemo‐tolerance of BC cell lines was assessed by performing MTT assay. Concurrently, transwell assay and scratch assay were carried out to estimate the migratory and invasive capability of BC cell lines.

Results

Methylated MEG3, lowly expressed MEG3, large tumor size (≥2 cm), advanced TNM grade and lymphatic metastasis were potentially symbolic of poor prognosis among BC patients (P < .05). Besides, MDA‐MB‐231 cell line exhibited the strongest resistance against paclitaxel, adriamycin, and vinorelbine (P < .05), while MCF‐7 cell line seemed more sensitive against these drugs than any other BC cell line (P < .05). Furthermore, pcDNA3.1‐MEG3 and 5‐Aza‐dC markedly sensitized MDA‐MB‐231 and MCF‐7 cell lines against the drug treatments (P < .05). Simultaneously, proliferation and metastasis of the BC cell lines were slowed down under the force of pcDNA3.1‐MEG3 and 5‐Aza‐dC (P < .05).

Conclusion

Preventing methylation of MEG3 might matter in lessening BC chemoresistance, owing to its hindering proliferation and metastasis of BC cells.

ERCC1 Is a Predictor of Anthracycline Resistance and Taxane Sensitivity in Early Stage or Locally Advanced Breast Cancers

Genomic instability could be a beneficial predictor for anthracycline or taxane chemotherapy. We interrogated 188 DNA repair genes in the METABRIC cohort (n = 1980) to identify genes that influence overall survival (OS). We then evaluated the clinicopathological significance of ERCC1 in early stage breast cancer (BC) (mRNA expression (n = 4640) and protein level, n = 1650 (test set), and n = 252 (validation)) and in locally advanced BC (LABC) (mRNA expression, test set (n = 2340) and validation (TOP clinical trial cohort, n = 120); and protein level (n = 120)). In the multivariate model, ERCC1 was independently associated with OS in the METABRIC cohort. In ER+ tumours, low ERCC1 transcript or protein level was associated with increased distant relapse risk (DRR). In ER−tumours, low ERCC1 transcript or protein level was linked to decreased DRR, especially in patients who received anthracycline chemotherapy. In LABC patients who received neoadjuvant anthracycline, low ERCC1 transcript was associated with higher pCR (pathological complete response) and decreased DRR. However, in patients with ER−tumours who received additional neoadjuvant taxane, high ERCC1 transcript was associated with a higher pCR and decreased DRR. High ERCC1 transcript was also linked to decreased DRR in ER+ LABC that received additional neoadjuvant taxane. ERCC1 based stratification is an attractive strategy for breast cancers.

ERCC1-XPF deficiency is a predictor of olaparib induced synthetic lethality and platinum sensitivity in epithelial ovarian cancers

PURPOSE

PARP inhibitor maintenance therapy in platinum sensitive sporadic ovarian cancers improves progression free survival. However, biomarker for synthetic lethality in platinum sensitive sporadic disease is yet to be defined. ERCC1-XPF heterodimer is a key player in nucleotide excision repair (NER) involved in the repair of platinum induced DNA damage. In the current study, we tested whether ERCC1-XPF deficiency would predict synthetic lethality to the PARP inhibitor Olaparib and platinum sensitivity in ovarian cancers.

METHODS

ERCC1, XPF and PARP1 protein expression was evaluated in tumors from a cohort of 331 patients treated at Nottingham University Hospitals and correlated to clinicopathological features and survival. Pre-clinically, ERCC1 and XPF was depleted in A2780 (platinum sensitive) and A2780cis (platinum resistant) ovarian cancer cell lines and tested for platinum sensitivity as well as for Olaparib induced synthetic lethality.

RESULTS

Low ERCC1 was significantly associated with improved progression free survival (PFS) in patients with ovarian cancers in univariate (p = 0.001) and multivariate (p = 0.002) analysis. In addition, low ERCC1/low XPF (p = 0.003) or low ERCC1/low PARP1 (p = 0.0001) tumors was also linked to better PFS compared to high ERCC1/high XPF or high ERCC1/high PARP1 tumors. Pre-clinically, ERCC1 or XPF depletion not only increased platinum sensitivity but also increased toxicity to Olaparib therapy. Increased sensitivity was associated with DNA double strand breaks (DSBs) accumulation, cell cycle arrest and increased apoptosis.

CONCLUSION

The data provide evidence that low ERCC1 is not only a predictor of platinum sensitivity but is also a promising biomarker for Olaparib induced synthetic lethality in ovarian cancers.

Prognostic Value of Excision Repair Cross-Complementing mRNA Expression in Gastric Cancer

Except for excision repair cross-complementing 1 (ERCC1), mRNA expression of the remaining ERCC genes has not been investigated in the prognosis of gastric cancer (GC). The present study aimed to explore the mRNA expression and prognostic values of each member of the ERCC family in GC patients by using the Kaplan–Meier (KM) plotter tool. The details of each ERCC family member were entered into a database and GC patients were separated into high and low expression to draw survival plots using the KM plotter. In the present study, we observed that high expression of ERCC1 mRNA was significantly associated with longer overall survival (OS) for all GC patients (hazard ratio [HR]=0.77, 95% confidence intervals [CI]=0.63–0.95, P=0.016) compared with low expression. High expression of ERCC4 and ERCC6 mRNA indicated a worse OS for all GC patients (HR=1.28, 95% CI=1.02–1.6, P=0.035 and HR=1.25, 95% CI=1.02–1.54, P=0.029, respectively) and especially for patients with intestinal-type GC (HR=1.87, 95% CI=1.26–2.79, P=0.0018 and HR=1.62, 95% CI=1.04–2.54, P=0.033, respectively). High ERCC8 mRNA expression indicated a worse OS for all GC patients (HR=1.34, 95% CI=1.02–1.76, P=0.034) and especially for patients with diffuse-type GC (HR=2.25, 95% CI=1.36–3.75, P=0.0013). In conclusion, our findings indicate that ERCC4, ERCC6, and ERCC8 may be potential biomarkers for GC prognosis and may serve as potential therapeutic targets for GC. However, these findings still need further verification.

Nucleotide excision repair protein ERCC1 and tumour-infiltrating lymphocytes are potential biomarkers of neoadjuvant platinum resistance in high grade serous ovarian cancer

OBJECTIVE

ERCC1 is a nucleotide excision repair protein that may have a role in drug resistance in high grade serous ovarian cancer (HGSOC). We hypothesized that ERCC1 expression and tumour infiltrating lymphocytes (TILS) are induced by chemotherapy in HGSOC, which may be prognostically useful.

METHODS

115 HGSOC patients were used for this study. 92 (80%) of the tissue analysed had not been exposed to platinum chemotherapy. The remaining 20% (n = 23) of cases received combination or monotherapy with carboplatin before tissue was collected. Immunohistochemistry was used to score for ERCC1 expression and morphology to score for TILs. Correlation analysis of all clinical parameters, TILs and ERCC1 and Kaplan-Meier survival analysis was performed using the ERCC1 and TILs scoring parameters (0, 1, 2 or 3).

RESULTS

ERCC1 expression was 2-fold higher in the neoadjuvant chemotherapy group compared to the primary cytoreductive surgery group (p < 0.0001). The mean overall survival for the neoadjuvant group with high ERCC1 was 141.6 ± 20.2 months which was significantly longer than absent ERCC1 survival of 61 + 22.6 months (p = 0.028). ERCC1 score strongly correlated with TILs score across the whole cohort (0.349, p = 1.3 × 10^-4) suggesting there is a relationship between ERCC1 expression and TILs, but this requires further investigation.

CONCLUSION

In conclusion, ERCC1 was identified as a potential biomarker of platinum response overall survival in HGSOC undergoing neoadjuvant HGSOC treatment.

ERCC1 assessment in upfront treatment with and without cisplatin-based chemotherapy in stage IIIB/IV non-squamous non-small cell lung cancer

Prior studies have demonstrated an association between excision repair cross-complementation group 1 (ERCC1) expression level and outcomes in patients with advanced non-small cell lung cancer (NSCLC) treated with platinum-based chemotherapy. The aim of this study was to assess the impact of ERCC1 on survival for patients with stage IIIB/IV non-squamous NSCLC (NS-NSCLC) enrolled in the INNOVATIONS trial, thus receiving as treatment either erlotinib/bevacizumab (EB) or cisplatin/gemcitabine/bevacizumab (PGB). We retrospectively analyzed tumor tissue of 72 patients using immunohistochemistry to assess the expression of ERCC1. The distribution between treatment arms was equal (36 patients each). Two different H scores were calculated and correlated with survival. In ERCC1-positive patients, no significant difference in terms of progression-free survival (PFS) between treatment arms has been detected. ERCC1-negative patients benefited from PGB compared to EB arm (H score: HR = 0.377, 95% CI [0.167-0.849], p = 0.0151; modified H score: HR = 0.484, 95% CI [0.234-1.004], p = 0.0468). With respect to the scoring system, in the EB-arm, a significant superior PFS turned out in ERCC1-positive patients when employing the H-score (HR = 0.430, 95% CI [0.188-0.981], p = 0.0397; median 4.9 vs. 3.9 months), but not with the modified H-score. Our findings support the hypothesis that NS-NSCLC displaying a low ERCC1 expression might benefit from cisplatin-based chemotherapy. High expression indicated better PFS in the EB arm supporting the prognostic impact. However, as impact of ERCC1-assessment even might depend on scoring systems differences, the need in standardization of assessment methodology is emphasized.

Systematic immunohistochemical screening for mismatch repair and ERCC1 gene expression from colorectal cancers in China: Clinicopathological characteristics and effects on survival

BACKGROUND

We performed a systematic screening of colorectal cancer (CRC) tissues to investigate whether mismatch repair (MMR) status and ERCC1 protein expression could be predictive of clinical outcomes for these patients following the recommendation of The Evaluation of Genomic Applications in Practice of Prevention (EGAPP).

METHODS

The expression of four MMR genes and ERCC1 were assessed by immunohistochemistry (IHC) from cancer tissue samples of 2233 consecutive CRC patients.

RESULTS

We observed that most CRC patients with a proficient MMR (pMMR) status tended to have simultaneous ERCC1 protein expression (P< 0.001). Stage III CRC patients with deficient MMR (dMMR) had higher prognoses than the same stage patients with pMMR (DFS: 74% vs 65%, P = 0.04; OS: 79% vs 69%, P = 0.04). Here, dMMR is also associated with poorer survival for stage II patients after chemotherapy (DFS: 66% vs 78%, P = 0.04). Stage II and III patients that were shown to express ERCC1 protein had higher DFS and OS than those that were deficient in expression (stage II, DFS: 83% vs 70%, P = 0.006; OS 85% vs 73%, P = 0.02. Stage III, DFS: 67% vs56%, P = 0.03; OS: 71% vs 57%, P = 0.04).

CONCLUSIONS

Our results indicate that dMMR appeared to predictive of a survival benefit for stage III CRC patients. We also found the determination of ERCC1 expression to be useful for predicting DFS or OS for stage II and III CRC patients. In addition, the expression of MMR genes and ERCC1 showed a significant relationship.

Excision Repair Cross-complementation Group 1 is a Prognostic Biomarker in Patients with Colorectal Cancer Receiving Chemotherapy

Background:

Conflicting results about the association between expression level of excision repair cross-complementation group 1 (ERCC1) and clinical outcome in patients with colorectal cancer (CRC) receiving chemotherapy have been reported. Thus, we searched the available articles and performed the meta-analysis to elucidate the prognostic role of ERCC1 expression in patients with CRC.

Methods:

A thorough literature search using PubMed (Medline), Embase, Cochrane Library, Web of Science databases, and Chinese Science Citation Database was conducted to obtain the relevant studies. Pooled hazard ratios (HRs) or odds ratios (ORs) with 95% confidence intervals (CIs) were calculated to estimate the results.

Results:

A total of 11 studies were finally enrolled in this meta-analysis. Compared with patients with lower ERCC1 expression, patients with higher ERCC1 expression tended to have unfavorable overall survival (OS) (HR = 2.325, 95% CI: 1.720–3.143, P < 0.001), progression-free survival (PFS) (HR = 1.917, 95% CI: 1.366–2.691, P < 0.001) and poor response to chemotherapy (OR = 0.491, 95% CI: 0.243–0.990, P = 0.047). Subgroup analyses by treatment setting, ethnicity, HR extraction, detection methods, survival analysis, and study design demonstrated that our results were robust.

Conclusions:

ERCC1 expression may be taken as an effective prognostic factor predicting the response to chemotherapy, OS, and PFS. Further studies with better study design and longer follow-up are warranted in order to gain a deeper understanding of ERCC1's prognostic value.

Chemoresistance and targeted therapies in ovarian and endometrial cancers

Gynecological cancers are known for being very aggressive at their advanced stages. Indeed, the survival rate of both ovarian and endometrial cancers is very low when diagnosed lately and the success rate of current chemotherapy regimens is not very efficient. One of the main reasons for this low success rate is the acquired chemoresistance of these cancers during their progression. The mechanisms responsible for this acquired chemoresistance are numerous, including efflux pumps, repair mechanisms, survival pathways (PI3K/AKT, MAPK, EGFR, mTOR, estrogen signaling) and tumor suppressors (P53 and Par-4). To overcome these resistances, a new type of therapy has emerged named targeted therapy. The principle of targeted therapy is simple, taking advantage of changes acquired in malignant cancer cells (receptors, proteins, mechanisms) by using compounds specifically targeting these, thus limiting their action on healthy cells. Targeted therapies are emerging and many clinical trials targeting these pathways, frequently involved in chemoresistance, have been tested on gynecological cancers. Despite some targets being less efficient than expected as mono-therapies, the combination of compounds seems to be the promising avenue. For instance, we demonstrate using ChIP-seq analysis that estrogen downregulate tumor suppressor Par-4 in hormone-dependent cells by directly binding to its DNA regulatory elements and inhibiting estrogen signaling could reinstate Par-4 apoptosis-inducing abilities. This review will focus on the chemoresistance mechanisms and the clinical trials of targeted therapies associated with these, specifically for endometrial and ovarian cancers.

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.

Inhibition of DNA-repair genes Ercc1 and Mgmt enhances temozolomide efficacy in gliomas treatment: a pre-clinical study

Gliomas are the most common primary brain tumors. To date, therapies do not allow curing patients, and glioblastomas (GBMs) are associated with remarkably poor prognosis. This situation is at least partly due to intrinsic or acquired resistance to treatment, especially to chemotherapy. In 2005, temozolomide (TMZ) has become the first chemotherapeutic drug validated for GBM. Nevertheless TMZ efficacy depends on Mgmt status. While the methylation of Mgmt promoter was considered so far as a prognostic marker, its targeting is becoming an effective therapeutic opportunity. Thus, arrival of both TMZ and Mgmt illustrated that considerable progress can still be realized by optimizing adjuvant chemotherapy. A part of this progress could be accomplished in the future by overcoming residual resistance. The aim of the present study was to investigate the involvement of a set of other DNA-repair genes in glioma resistance to temozolomide. We focused on DNA-repair genes located in the commonly deleted chromosomal region in oligodendroglioma (1p/19q) highly correlated with patient response to chemotherapy. We measured effects of inhibition of ten DNA-repair genes expression using siRNAs on astrocytoma cell response to cisplatin (CDDP) and TMZ. SiRNAs targeting ercc1, ercc2, mutyh, and pnkp significantly sensitized cells to chemotherapy, increasing cell death by up to 25%. In vivo we observed a decrease of subcutaneous glioma tumor growth after injection of siRNA in conjunction with absorption of TMZ. We demonstrated in this pre-clinical study that targeting of DNA-repair genes such as Ercc1 could be used as an adjuvant chemosensitization treatment, similarly to Mgmt inhibition.

Influence on radiosensitivity of lung glandular cancer cells when ERCC1 gene silenced by targeted siRNA

OBJECTIVE

To identify the influence on radiosensitivity of lung glandular cancer cells when excisions repair cross-complementing group1 (ERCC1) gene was silenced by targeted siRNA.

METHODS

siRNA which targeting to ERCC1 and control siRNA was designed and synthesized. The human lung glandular cancer SPC-A-1 cells was transfected. A total of 56 nude mice were divided into two groups, and two kinds of SPC-A-1 cells were transplanted to armpit of right forelimb, to establish the nude mice subcutaneous xenotransplanted tumor model of human lung glandular cancer cells. After the tumor was developed, the nude mice were randomly divided into four groups and accepted different doses of X-Ray radiation, then the change of tumor volume, survival time of mice in every group were recorded and the average lifetime was calculated. Twenty-one days later of X-ray experiment, two mice were taken and killed in each group and the tumors organizations were stripped. The cell apoptosis rate and cell cycle distributions were obtained by FCM (flow cytometry).

RESULTS

The volume of tumor which ERCC1 gene was silenced was less than single irradiation group after X-ray irradiation, and the growth speed was slower and the lifetime of mice was lengthened as well (P < 0.05). The cells apoptosis rate and the rate of G2/M cells which ERCC1 gene was silenced were higher than the same dose control group and the rate of G1 cells were lower, which indicated that the cells could be stopped at G2/M point, the cell proliferation was inhibited, the cell apoptosis was promoted and the radiation sensitivity was improved after the ERCC1 was silenced.

CONCLUSIONS

The radiation sensitivity of lung glandular tumor could be improved after the ERCC1 gene was silenced by siRNA.

The predictive value of ERCC1 and p53 for the effect of panobinostat and cisplatin combination treatment in NSCLC

Cisplatin is one of the most common chemotherapeutic drugs for non-small cell lung cancer (NSCLC). However, the response rate is limited because of drug resistance. Histone deacetylase inhibitors (HDACis), which can alter DNA accessibility by regulating chromatin structure and inducing apoptosis, exhibit a synergistic action with cisplatin. However, no biomarkers that can predict the efficacy of the combination of HDACis and cisplatin have been reported. Our study found that panobinostat, an HDAC inhibitor, increased the cisplatin sensitivity of several NSCLC cell lines with low ERCC1 expression but not those with high ERCC1 expression or gain-of-function (GOF) p53 mutation despite of ERCC1 expression level. ERCC1 knockdown increased the cisplatin sensitivity of NSCLC cell lines with high ERCC1 expression without GOF p53 mutations. In addition, in low ERCC1 expression NSCLC cell lines, knockdown of GOF mutant p53 enhanced cisplatin sensitivity. Further double knockdown of ERCC1 and GOF mutant p53 but not ERCC1 knockdown alone increased the cisplatin sensitivity of cells with both high ERCC1 expression and GOF p53 mutations. Therefore, this study demonstrated that ERCC1 expression combined with p53 mutation status may determine the efficacy of cisplatin and HDACi combined therapy and guide the development of future NSCLC therapies.

Cancer chemoresistance; biochemical and molecular aspects: a brief overview

The effectiveness of chemotherapy is one of the main challenges in cancer treatment and resistance to classic drugs and traditional treatment processes is an obstacle to this goal. Drug resistance that may be inherent or adventitious can cause poor treatment outcome and tumor relapse. In most cases, resistance to a drug can lead to resistance to many other drugs structure and function of which is not necessarily similar to the first drug. This phenomenon is the main mechanism behind failure of many of metastatic cancers. There are various molecular mechanisms involved in multidrug resistance, including change in the activity of membrane transporters (such as ABC transporters), increase of drug metabolism, change of the target enzyme (such as mutations that change thymidylate synthase and topoisomerases), promotion of DNA damage repair, and escape from drug induced apoptosis. Clinical and laboratory investigations on biomarkers involved in the response to chemotherapy have characterized the key factors behind the failure of treatments. Knowing the molecular factors involved in drug resistance may help us to develop new strategies for more promising chemotherapy and reduce the rate of relapse. In this brief review, molecular mechanisms and tumor microenvironment leading to decreased drug sensitivity, and strategies of reversing drug resistance are described.

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

ERCC1-XPF is a structure-specific endonuclease that is required for the repair of DNA lesions, generated by the widely used platinum-containing cancer chemotherapeutics such as cisplatin, through the Nucleotide Excision Repair and Interstrand Crosslink Repair pathways. Based on mouse xenograft experiments, where ERCC1-deficient melanomas were cured by cisplatin therapy, we proposed that inhibition of ERCC1-XPF could enhance the effectiveness of platinum-based chemotherapy. Here we report the identification and properties of inhibitors against two key targets on ERCC1-XPF. By targeting the ERCC1-XPF interaction domain we proposed that inhibition would disrupt the ERCC1-XPF heterodimer resulting in destabilisation of both proteins. Using in silico screening, we identified an inhibitor that bound to ERCC1-XPF in a biophysical assay, reduced the level of ERCC1-XPF complexes in ovarian cancer cells, inhibited Nucleotide Excision Repair and sensitised melanoma cells to cisplatin. We also utilised high throughput and in silico screening to identify the first reported inhibitors of the other key target, the XPF endonuclease domain. We demonstrate that two of these compounds display specificity in vitro for ERCC1-XPF over two other endonucleases, bind to ERCC1-XPF, inhibit Nucleotide Excision Repair in two independent assays and specifically sensitise Nucleotide Excision Repair-proficient, but not Nucleotide Excision Repair-deficient human and mouse cells to cisplatin.

[Advances in the relationship between microRNA and cisplatin resistance of lung cancer]

微小RNA（microRNA, miRNA）是一类长约22 nt的非编码小分子RNA，在转录后水平上负性调节靶基因的活性。微小RNA在肿瘤的发生、发展中发挥着广泛的作用，包括肿瘤的进展、分化、转移和耐药等。化疗药物的耐药是临床肿瘤治疗的难题，如何克服肿瘤细胞的顺铂耐药性引起人们的广泛兴趣。越来越多的研究证明微小RNA在影响肿瘤耐药中发挥着重要的作用。本文将对微小RNA与肿瘤治疗尤其是顺铂治疗的研究进展作一综述。

Excision repair cross complementation group 1 is a chemotherapy-tolerating gene in cisplatin-based treatment for non-small cell lung cancer

This study aimed to evaluate the biological functions of excision repair cross complementation goup 1 (ERCC1) in cell proliferation, cell cycle, invasion and cisplatin response of non-small cell lung cancer (NSCLC) cells. Firstly, ERCC1 gene was successfully transfected into H1299 cells by gene cloning and transfection techniques. Then, cell proliferation was determined with the cell growth curve and colony-forming assays. Flow cytometry (FCM) was employed to investigate the cell cycle distribution. The ability of cell invasion was estimated by means of Matrigel invasion assays. Response of NSCLC cells to cisplatin was detected utilizing MTT assays, and the intracellular drug concentrations were determined by the high performance liquid chromatography (HPLC) analysis. Expression of the two cell membrane proteins, P-glycoprotein (P-gp) and multidrug resistance-associated protein (MRP), was also evaluated utilizing FCM technique. By contrast, ERCC1 expression in the NSCLC A549 cells was silenced by small interfering RNA (siRNA) through RNAi technique. In addition, the cytotoxic effect of cisplatin on A549 cells was detected by MTT assays. In the present study, the results demonstrated that ERCC1 had no effect on cell proliferation, cell cycle and the ability of invasion, but showed significant impact on cisplatin response of the NSCLC H1299 cells. Furthermore, siRNA-induced suppression of ERCC1 evidently enhanced sensitivity to cisplatin of NSCLC A549 cells. Therefore, it is confirmed that ERCC1 is a chemotherapy-tolerating gene and a promising predictor in tailoring chemotherapy of NSCLC.

FOXM1 modulates cisplatin sensitivity by regulating EXO1 in ovarian cancer

Cisplatin is commonly used in ovarian cancer chemotherapy, however, chemoresistance to cisplatin remains a great clinical challenge. Oncogenic transcriptional factor FOXM1 has been reported to be overexpressed in ovarian cancer. In this study, we aimed to investigate the potential role of FOXM1 in ovarian cancers with chemoresistance to cisplatin. Our results indicate that FOXM1 is upregulated in chemoresistant ovarian cancer samples, and defends ovarian cancer cells against cytotoxicity of cisplatin. FOXM1 facilitates DNA repair through regulating direct transcriptional target EXO1 to protect ovarian cancer cells from cisplatin-mediated apoptosis. Attenuating FOXM1 and EXO1 expression by small interfering RNA, augments the chemotherapy efficacy against ovarian cancer. Our findings indicate that targeting FOXM1 and its target gene EXO1 could improve cisplatin effect in ovarian cancer, confirming their role in modulating cisplatin sensitivity.

Nucleotide excision repair: why is it not used to predict response to platinum-based chemotherapy?

Platinum based therapy is one of the most effectively used chemotherapeutic treatments for cancer. The mechanism of action of platinum compounds is to damage DNA and drive cells into apoptosis. The most commonly used platinum containing agents are cis-diammine-dichloroplatinum (II)], more commonly known as cisplatin, its analogue carboplatin, and oxaliplatin. Cisplatin is used to treat a wide variety of tumours such as ovarian, testicular, head and neck and non-small cell lung cancers (NSCLCs). In addition, it forms the basis of most combined treatment regimes. Despite this, cisplatin and its analogues are extremely toxic and although some patients benefit substantially from treatment, a large proportion suffer the toxic side effects without any therapeutic benefit. Nucleotide excision repair (NER) is a versatile DNA repair system that recognises DNA damage induced by platinum based therapy. For many years the components of the NER pathway have been studied to determine mRNA and protein expression levels in response or resistance to cisplatin in many forms of cancer; particularly testicular, ovarian and NSCLCs. Despite the consistent finding that over or under expression of subsets of NER proteins and mRNA highly correlate with response to cisplatin, the translation of these findings into the clinical setting has not been forthcoming. This review summarises the results of previous investigations into NER in cisplatin response and clinical trials where the expression of NER proteins were compared to the response to platinum therapies in treatment.

Conformational determinants for the recruitment of ERCC1 by XPA in the nucleotide excision repair (NER) Pathway: structure and dynamics of the XPA binding motif

XPA is an essential protein in the nucleotide excision repair (NER) pathway, in charge of recruiting the ERCC1-XPF endonuclease complex to the DNA damage site. The only currently available structural insight into the binding of XPA to ERCC1 derives from the solution NMR structure of a complex between the ERCC1 central fragment and a 14-residue peptide, corresponding to the highly conserved binding motif of the XPA N-terminus, XPA₆₇₋₈₀. The extensive all-atom molecular-dynamics simulation study of the XPA₆₇₋₈₀ peptide both bound to the ERCC1 central fragment and free in solution presented here completes the profile of the structural determinants responsible for the ERCC1/XPA₆₇₋₈₀ complex stability. In addition to the wild-type, this study also looks at specific XPA₆₇₋₈₀ mutants in complex with the ERCC1 central domain and thus contributes to defining the conformational determinants for binding, as well as all of the essential structural elements necessary for the rational design of an XPA-based, ERCC1-specific inhibitor.

Predictive value of ERCC1, ERCC2, and XRCC1 overexpression for stage III colorectal cancer patients receiving FOLFOX-4 adjuvant chemotherapy

OBJECTIVES

To determine the correlation between expression of three DNA repair genes and early failure/clinical outcome of stage III colorectal cancer (CRC) patients administrated with FOLFOX-4, including the excision repair cross-complementation group 1 (ERCC1), the excision repair cross-complementing 2 (ERCC2), and X-ray repair cross-complementing protein 1 (XRCC1).

MATERIALS AND METHODS

We retrospectively analyzed clinicopathological features and ERCC1, ERCC2, XRCC1 expressions by immunohistochemical staining in 180 stage III CRC patients undergoing curative resection and treated with FOLFOX-4 chemotherapy to identify predictors of postoperative early failure.

RESULTS

Among 180 CRC patients, 44 patients were classified into early failure group, and 136 patients were categorized into non-early failure group. A multivariate logistic regression analysis showed that ERCC1 overexpression (P = 0.005), and high postoperative carcinoembryonic antigen (CEA) levels (P = 0.001) were independent predictors of early failure. Additionally, ERCC1 overexpression was not only a predictor of early failure but also for disease-free survival (P < 0.001) and overall survival (P < 0.001). However, no predictive roles of ERCC2 and XRCC1 expression among these analyzed patients.

CONCLUSIONS

ERCC1 overexpression is an important predictor of early failure in patients with stage III CRC administrating FOLFOX-4 adjuvant chemotherapy and this marker may help identify patients who would benefit from intensive follow-up and enhance therapeutic programs.

Different strategies to overcome multidrug resistance in cancer

The risk of acquisition of resistance to chemotherapy remains a major hurdle in the management of various types of cancer patients. Several cellular and noncellular mechanisms are involved in developing both intrinsic and acquired resistance in cancer cells toward chemotherapy. This review covers the various multidrug resistance (MDR) mechanisms observed in cancer cells as well as the various strategies developed to overcome these MDR mechanisms. Extensive studies have been conducted during the last several decades to enhance the efficacy of chemotherapy by suppressing or evading these MDR mechanisms including the use of new anticancer drugs that could escape from the efflux reaction, MDR modulators or chemosensitizers, multifunctional nanocarriers, and RNA interference (RNAi) therapy.

The effects of ERCC1 expression levels on the chemosensitivity of gastric cancer cells to platinum agents and survival in gastric cancer patients treated with oxaliplatin-based adjuvant chemotherapy

Excision repair cross-complementing 1 (ERCC1) is reported to be involved in the sensitivity of cancer cells to platinum-based chemotherapy. The present study was designed to evaluate the effects of ERCC1 expression on the chemosensitivity of platinum agents in gastric cancer cell lines, and on survival in gastric cancer patients treated with surgery followed by oxaliplatin-based adjuvant chemotherapy. ERCC1 expression levels were measured by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and western blot analysis, respectively. The chemosensitivity of a series of gastric cancer cell lines to platinum agents in vitro was evaluated using CellTiter 96 Aqueous One Solution Cell Proliferation Assay kit. The apoptotic effect of the drugs was evaluated by double staining with Annexin-V-fluorescein isothiocyanate (FITC) and propidium iodide (PI). The results demonstrated that the expression levels of ERCC1 mRNA were correlated with the chemosensitivity of platinum agents, and depletion of ERCC1 sensitized the relatively resistant MKN45 cells to cisplatin and oxaliplatin. Univariate analyses revealed that patients with low ERCC1 levels had longer relapse-free survival (RFS) and overall survival (OS) than those with high ERCC1 levels (median RFS, 18 vs. 7 months, P=0.001; median OS, 27 vs. 11 months, P=0.001). Multivariate analyses suggested that high ERCC1 expression is an independent prognostic marker of poor RFS [hazard ratio (HR), 2.16; 95% confidence interval (CI), 1.09–4.25; P= 0.026] and OS (HR, 2.21; 95% CI, 1.07–4.55; P=0.031). These results suggest that overexpression of ERCC1 is correlated with platinum drug resistance in gastric cancer cells, and that depletion of ERCC1 sensitizes gastric cancer cell lines to cisplatin and oxaliplatin. Gastric cancer patients with low levels of ERCC1 expression demonstrate a benefit from oxaliplatin-based adjuvant chemotherapy.

PARP inhibition selectively increases sensitivity to cisplatin in ERCC1-low non-small cell lung cancer cells

Platinum compounds are the foundation of chemotherapy regimens for non-small cell lung cancer (NSCLC) despite poor response rates and limited response duration. It has been reported that tumor expression of excision repair cross-complementation group 1 (ERCC1), a key component in nucleotide excision repair, may correlate with clinical response to platinum agents. We found that most primary lung tumor specimens demonstrated a stronger protein expression of poly (adenosine diphosphate ribose) polymerases 1 (PARP1) than their normal counterparts. Therefore, we hypothesized that combining PARP inhibition with platinum compounds may be an approach to improve platinum-based therapy for NSCLC. Drug combination experiments revealed that two distinct PARP inhibitors, olaparib and veliparib, not only potentiated the cell killing by cisplatin but also conferred cytotoxicity as a single agent specifically in ERCC1-low HCC827 and PC9 but not in ERCC1-high A549 and H157 lung cancer cells. Moreover, small interfering RNA knockdown of ERCC1 in A549 and H157 cells increased their sensitivities to both cisplatin and olaparib in a synergistic manner in our model. Furthermore, mechanistic studies indicated that combined PARP inhibitor and cisplatin could lead to sustained DNA double-strand breaks, prolonged G2/M cell cycle arrest with distinct activation of checkpoint kinase 1 signaling and more pronounced apoptosis preferentially in lung cancer cells with low ERCC1 expression. Collectively, these data suggest that there is a synergistic relationship between PARP inhibition and low ERCC1 expression in NSCLC that could be exploited for novel therapeutic approaches in lung cancer therapy based on tumor ERCC1 expression.

DSIR: assessing the design of highly potent siRNA by testing a set of cancer-relevant target genes

Chemically synthesized small interfering RNA (siRNA) is a widespread molecular tool used to knock down genes in mammalian cells. However, designing potent siRNA remains challenging. Among tools predicting siRNA efficacy, very few have been validated on endogenous targets in realistic experimental conditions. We previously described a tool to assist efficient siRNA design (DSIR, Designer of siRNA), which focuses on intrinsic features of the siRNA sequence. Here, we evaluated DSIR’s performance by systematically investigating the potency of the siRNA it designs to target ten cancer-related genes. mRNA knockdown was measured by quantitative RT-PCR in cell-based assays, revealing that over 60% of siRNA sequences designed by DSIR silenced their target genes by at least 70%. Silencing efficacy was sustained even when low siRNA concentrations were used. This systematic analysis revealed in particular that, for a subset of genes, the efficiency of siRNA constructs significantly increases when the sequence is located closer to the 5′-end of the target gene coding sequence, suggesting the distance to the 5′-end as a new feature for siRNA potency prediction. A new version of DSIR incorporating these new findings, as well as the list of validated siRNA against the tested cancer genes, has been made available on the web (http://biodev.extra.cea.fr/DSIR).

Transcriptional Gene Silencing (TGS) via the RNAi Machinery in HIV-1 Infections

Gene silencing via non-coding RNA, such as siRNA and miRNA, can occur at the transcriptional, post-transcriptional, and translational stages of expression. Transcriptional gene silencing (TGS) involving the RNAi machinery generally occurs through DNA methylation, as well as histone post-translational modifications, and corresponding remodeling of chromatin around the target gene into a heterochromatic state. The mechanism by which mammalian TGS occurs includes the recruitment of RNA-induced initiation of transcriptional gene silencing (RITS) complexes, DNA methyltransferases (DNMTs), and other chromatin remodelers. Additionally, virally infected cells encoding miRNAs have also been shown to manipulate the host cell RNAi machinery to induce TGS at the viral genome, thereby establishing latency. Furthermore, the introduction of exogenous siRNA and shRNA into infected cells that target integrated viral promoters can greatly suppress viral transcription via TGS. Here we examine the latest findings regarding mammalian TGS, specifically focusing on HIV-1 infected cells, and discuss future avenues of exploration in this field.

Exploring biomarkers in head and neck cancer

Personalized medicine based on predictive markers linked to drug response, it is hoped, will lead to improvements in outcomes and avoidance of unnecessary treatment in squamous cell carcinoma of the head and neck (SCCHN). Recent research has shown that expression of ERCC1 may predict resistance to treatment with platinum agents. Future testing for this marker may help select the optimal type of chemotherapy. Infection with human papillomavirus (HPV) is associated with less aggressive disease and better prognosis in locally advanced SCCHN treated with chemoradiation or radiation alone; HPV-positive patients may ultimately benefit from less intensive, less toxic therapy. K-RAS mutations, occurring in about 40% of colorectal cancers and associated with lack of benefit from epidermal growth factor receptor (EGFR) antibodies in this disease, are found in <5% of SCCHN patients, making routine testing for K-RAS mutations unwarranted at this time. Virtually all head and neck tumors overexpress EGFR, which limits the usefulness of EGFR expression as a marker for treatment selection. Although the incidence of EGFR tyrosine kinase domain mutations is very rare, a better understanding of the role of EGFR mutations, expression, amplification, and downstream effects in SCCHN may help define the role of EGFR in this setting. These observations caution against extrapolating results obtained with biomarkers in other types of cancer to SCCHN. Validation of each biomarker in the context of SCCHN clinical trials will be required before a specific marker can be incorporated into daily practice.

DNA repair capacity in peripheral lymphocytes predicts survival of patients with non-small-cell lung cancer treated with first-line platinum-based chemotherapy

PURPOSE

Platinum-based regimens are the standard chemotherapy for patients with advanced non-small-cell lung cancer (NSCLC). DNA repair capacity (DRC) in tumor cells plays an important role in resistance to platinum-based drugs. We have previously reported that efficient DRC, as assessed by an in vitro lymphocyte-based assay, was a determinant of poor survival in patients with NSCLC in a relatively small data set. In this larger independent study of 591 patients with NSCLC, we further evaluated whether DRC in peripheral lymphocytes predicts survival of patients with NSCLC who receive platinum-based chemotherapy.

PATIENTS AND METHODS

All patients were recruited at The University of Texas MD Anderson Cancer Center and donated blood samples before the start of any chemotherapy. We measured DRC in cultured T lymphocytes by using the host-cell reactivation assay, and we assessed associations between DRC in peripheral lymphocytes and survival of patients with NSCLC who were treated with first-line platinum-based chemotherapy.

RESULTS

We found an inverse association between DRC in peripheral lymphocytes and patient survival. Compared with patients in the low tertile of DRC, patients with NSCLC in the high tertile of DRC had significantly worse overall and 3-year survival (adjusted hazard ratio [HR], 1.33; 95% CI, 1.04 to 1.71; P = .023; and HR, 1.35; 95% CI, 1.04 to 1.76; P = .025, respectively). This trend was more pronounced in patients with early-stage tumors, adenocarcinoma, or squamous cell carcinoma.

CONCLUSION

We confirmed that DRC in peripheral lymphocytes is an independent predictor of survival for patients with NSCLC treated with platinum-based chemotherapy.

DNA repair gene polymorphism associated with sensitivity of lung cancer to therapy

This study aimed to investigate association between single-nucleotide polymorphisms (SNPs) of excision repair cross-complementing gene 1 (ERCC1), excision repair cross-complementing gene 2 (ERCC2), and X-ray repair cross-complementing group 1 (XRCC1) with sensitivity of advanced non-small cell lung cancer (NSCLC) patients to platinum-based chemotherapy. A total of 89 NSCLC patients were recruited and treated with two cycles of platinum-based chemotherapy. DNA was extracted from peripheral lymphocytes for detection of SNPs of ERCC1 Asn118Asn, ERCC2 Lys751Gln, and XRCC1 Arg399Gln. The overall response rate of these patients was 29.2%. There was no statistically significant difference of treatment response between the wild genotypes and the variant genotypes for the ERCC1 Asn118Asn and ERCC2 Lys751Gln gene. The distributions of genotypes XRCC1 Arg399Gln differed significantly between the response and non-response groups (76.9 vs. 23.1%, P = 0.001). The XRCC1 399Arg/Arg genotype carriers had a higher response rate than that of the Gln genotype carriers (OR = 4.81, 95%CI = 1.778-13.013, P = 0.002). The combination of the favorable genotypes of ERCC1, ERCC2, and XRCC1 had a higher response rate compared to that of patients with other genotypes. The combined polymorphisms of ERCC1, ERCC2, and XRCC1 may be associated with sensitivity of NSCLC to platinum-based chemotherapy. Further studies will verify these SNPs as biomarkers for prediction of platinum-based chemotherapy responses of NSCLC patients.

Expression of ERCC1 and its clinicopathological correlations in non-small cell lung cancer

Excision Repair Cross-Complementing Group 1 (ERCC1) is an important DNA repair gene, playing critical role in nucleotide excision repair pathway and having a significant influence on genomic instability. Some studies support that ERCC1 might be a potential predictive and prognostic marker in non-small cell lung cancer (NSCLC). ERCC1 has also been shown to be a promising biomarker in NSCLC treated with a cisplatin-based regimen. Therefore, the determination of ERCC1 expression at DNA, mRNA and protein level in different stages of NSCLC is still an important topic in the cancer. Ninety-one formalin-fixed paraffin-embedded tumor samples histopathologically diagnosed as NSCLC were examined in this study. ERCC1 expression at protein level were scored by immunohistochemistry. The gene amplification and mRNA expression levels for ERCC1 were determined by real-time quantitative PCR. There was complete concordance among the three methods in 39 tumor samples (42.9%). A strong correlation was found between DNA amplification and mRNA expression (r=0.662) while there was no correlation between mRNA and protein assessment for ERCC1 expression (r=-0.013). ERCC1 expression at mRNA and DNA level (63.1 and 84.2%, respectively) in tumors at stage III was higher than at the other stages. In contrast, the protein expression at stage II and III (56.6 and 52.6%, respectively) of NSCLC was lower than that of tumors with stage I NSCLC. These results show that the mechanism by which ERCC1 expression might play a role in tumor behavior. This study was also confirmed that the appropriate validation and qualification in methods used for ERCC1 status were needed before its clinical application and implementation.

Downregulation of XPF-ERCC1 enhances cisplatin efficacy in cancer cells

Bulky cisplatin lesions are repaired primarily by nucleotide excision repair (NER), in which the structure specific endonuclease XPF-ERCC1 is a critical component. It is now known that the XPF-ERCC1 complex has repair functions beyond NER and plays a role in homologous recombination (HR). It has been suggested that expression of ERCC1 correlates with cisplatin drug resistance in non-small cell lung cancer (NSCLC). In our study, using NSCLC, ovarian, and breast cancer cells, we show that the XPF-ERCC1 complex is a valid target to increase cisplatin cytotoxicity and efficacy. We targeted XPF-ERCC1 complex by RNA interference and assessed the repair capacity of cisplatin intrastrand and interstrand crosslinks by ELISA and alkaline comet assay, respectively. We also assessed the repair of cisplatin-ICL-induced double-strand breaks (DSBs) by monitoring gamma-H2AX focus formation. Interestingly, XPF protein levels were significantly reduced following ERCC1 downregulation, but the converse was not observed. The transcript levels were unaffected suggesting that XPF protein stability is likely affected. The repair of both types of cisplatin-DNA lesions was decreased with downregulation of XPF, ERCC1 or both XPF-ERCC1. The ICL-induced DSBs persist in the absence of XPF-ERCC1. The suppression of the XPF-ERCC1 complex significantly decreases the cellular viability which correlates well with the decrease in DNA repair capacity. A double knockdown of XPF-ERCC1 displays the greatest level of cellular cytotoxicity when compared with XPF or ERCC1 alone. The difference in cytotoxicity observed is likely due to the level of total protein complex remaining. These data demonstrate that XPF-ERCC1 is a valid target to enhance cisplatin efficacy in cancer cells by affecting cisplatin-DNA repair pathways.

Up-regulation of Fas reverses cisplatin resistance of human small cell lung cancer cells

Background/Aim

Fas/FasL system is a major regulator of apoptosis. The mechanisms by which Fas mediates cisplatin resistance remain unclear. The aim of this study is to explore the effect of Fas over-expression on cisplatin resistance of small cell lung cancer cells and its possible mechanisms.

Materials and methods

Fas was over-expressed in H446/CDDP cells by infection with the adenoviruses containing Fas. Sensitivity of Fas-overexpressed H446/CDDP cells to cisplatin was evaluated using MTT assay. Expressions of Fas, GST-π and ERCC1 were detected by RT-PCR and Western blot analysis. Apoptosis rate was examined by FACS.

Results

Over-expression of Fas in H446/CDDP cells significantly decreased the expressions of GST-π and ERCC1 at mRNA and protein levels, and increased the cell apoptosis. Furthermore, up-regulation of Fas significantly decreased the tolerance of H446/CDDP cells to cisplatin.

Conclusion

Over-expression of Fas reverses drug resistance of H446/CDDP cells, possibly due to the increased cell sensitivity to apoptosis and the decreased expressions of GST-π and ERCC1.

FOXM1 confers acquired cisplatin resistance in breast cancer cells

The transcription factor Forkhead box M1 (FOXM1) is a key regulator of cell proliferation and is overexpressed in many forms of primary cancers, leading to uncontrolled cell division and genomic instability. To address the role of FOXM1 in chemoresistance, we generated a cisplatin-resistant breast cancer cell line (MCF-7-CIS(R)), which had an elevated level of FOXM1 protein and mRNA expression relative to the parental MCF-7 cells. A close correlation was observed between FOXM1 and the expression of its proposed downstream targets that are involved in DNA repair; breast cancer-associated gene 2 (BRCA2) and X-ray cross-complementing group 1 (XRCC1) were expressed at higher levels in the resistant cell lines compared with the sensitive MCF-7 cells. Moreover, cisplatin treatment induced DNA damage repair in MCF-7-CIS(R) and not in MCF-7 cells. Furthermore, the expression of a constitutively active FOXM1 (DeltaN-FOXM1) in MCF-7 cells alone was sufficient to confer cisplatin resistance. Crucially, the impairment of DNA damage repair pathways through the small interfering RNA knockdown inhibition of either FOXM1 or BRCA2/XRCC1 showed that only the silencing of FOXM1 could significantly reduce the rate of proliferation in response to cisplatin treatment in the resistant cells. This suggests that the targeting of FOXM1 is a viable strategy in circumventing acquired cisplatin resistance. Consistently, the FOXM1 inhibitor thiostrepton also showed efficacy in causing cell death and proliferative arrest in the cisplatin-resistant cells through the downregulation of FOXM1 expression. Taken together, we have identified a novel mechanism of acquired cisplatin resistance in breast cancer cells through the induction of FOXM1.

Cellular and molecular mechanisms for the synergistic cytotoxicity elicited by oxaliplatin and pemetrexed in colon cancer cell lines

Purpose

Oxaliplatin effect in the treatment of colorectal cancer is improved upon combination with thymidylate synthase (TS) inhibitors. Pemetrexed is polyglutamated by the folylpolyglutamate synthase (FPGS) and blocks folate metabolism and DNA synthesis by inhibiting TS, dihydrofolate reductase (DHFR) and glycinamide ribonucleotide formyltransferase (GARFT). The present study evaluates the pharmacological interaction between oxaliplatin and pemetrexed in colorectal cancer cells.

Methods

Human HT29, WiDr, SW620 and LS174T cells were treated with oxaliplatin and pemetrexed. Drug interaction was studied using the combination index method, while cell cycle was investigated with flow cytometry. The effects of drugs on Akt phosphorylation and apoptosis were studied with ELISA and fluorescence microscopy, respectively. RT-PCR analysis was performed to assess whether drugs modulated the expression of pemetrexed targets and of genes involved in DNA repair (ERCC1 and ERCC2). Finally, platinum–DNA adduct levels were detected by ultra-sensitive multi-collector inductively coupled plasma mass spectrometry (ICP-MS).

Results

A dose-dependent inhibition of cell growth was observed after drug exposure, while a synergistic interaction was detected preferentially with sequential combinations. Oxaliplatin enhanced cellular population in the S-phase. Drug combinations increased apoptotic indices with respect to single agents, and both drugs inhibited Akt phosphorylation. RT-PCR analysis showed a correlation between the FPGS/(TS × DHFR × GARFT) ratio and pemetrexed sensitivity, as well as a downregulation of ERCC1, ERCC2, TS, DHFR and GARFT after drug exposure. In addition, pretreatment with pemetrexed resulted in an increase of oxaliplatin–DNA adducts.

Conclusion

These data demonstrate that oxaliplatin and pemetrexed synergistically interact against colon cancer cells, through modulation of cell cycle, inhibition of Akt phosphorylation, induction of apoptosis and modulation of gene expression.

Oxaliplatin: pre-clinical perspectives on the mechanisms of action, response and resistance

Oxaliplatin is a third-generation platinum compound that has shown a wide range of anti-tumour activity in metastatic cancer and in multiple cell lines. It contains a diaminocyclohexane carrier ligand and is one of the least toxic platinum agents. In the past decade, the use of oxaliplatin for the treatment of colorectal cancer has become increasingly popular because neither cisplatin nor carboplatin demonstrate significant activity. Similar to cisplatin, oxaliplatin binds to DNA, leading to GG intra-strand crosslinks. Oxaliplatin differs from its parent compounds in its mechanisms of action, cellular response and development of resistance, which are not fully understood. Like most chemotherapeutic agents, efficacy of oxaliplatin is limited by the development of cellular resistance. ERCC1 (excision repair cross-complementation group 1) mediated nucleotide excision repair pathway appears to be the major pathway involved in processing oxaliplatin, because the loss of mismatch repair does not lead to oxaliplatin resistance. Recent findings support the involvement of many genes and different pathways in developing oxaliplatin resistance. This mini-review focuses on the effects of oxaliplatin treatment on cell lines with special emphasis on colorectal cell lines.

HIV-1 TAR miRNA protects against apoptosis by altering cellular gene expression

Background

RNA interference is a gene regulatory mechanism that employs small RNA molecules such as microRNA. Previous work has shown that HIV-1 produces TAR viral microRNA. Here we describe the effects of the HIV-1 TAR derived microRNA on cellular gene expression.

Results

Using a variation of standard techniques we have cloned and sequenced both the 5' and 3' arms of the TAR miRNA. We show that expression of the TAR microRNA protects infected cells from apoptosis and acts by down-regulating cellular genes involved in apoptosis. Specifically, the microRNA down-regulates ERCC1 and IER3, protecting the cell from apoptosis. Comparison to our cloned sequence reveals possible target sites for the TAR miRNA as well.

Conclusion

The TAR microRNA is expressed in all stages of the viral life cycle, can be detected in latently infected cells, and represents a mechanism wherein the virus extends the life of the infected cell for the purpose of increasing viral replication.

ERCC1 expression and RAD51B activity correlate with cell cycle response to platinum drug treatment not DNA repair

BACKGROUND

The H69CIS200 and H69OX400 cell lines are novel models of low-level platinum-drug resistance. Resistance was not associated with increased cellular glutathione or decreased accumulation of platinum, rather the resistant cell lines have a cell cycle alteration allowing them to rapidly proliferate post drug treatment.

RESULTS

A decrease in ERCC1 protein expression and an increase in RAD51B foci activity was observed in association with the platinum induced cell cycle arrest but these changes did not correlate with resistance or altered DNA repair capacity. The H69 cells and resistant cell lines have a p53 mutation and consequently decrease expression of p21 in response to platinum drug treatment, promoting progression of the cell cycle instead of increasing p21 to maintain the arrest.

CONCLUSION

Decreased ERCC1 protein and increased RAD51B foci may in part be mediating the maintenance of the cell cycle arrest in the sensitive cells. Resistance in the H69CIS200 and H69OX400 cells may therefore involve the regulation of ERCC1 and RAD51B independent of their roles in DNA repair. The novel mechanism of platinum resistance in the H69CIS200 and H69OX400 cells demonstrates the multifactorial nature of platinum resistance which can occur independently of alterations in DNA repair capacity and changes in ERCC1.

ZNRD1 might mediate UV irradiation related DNA damage and repair in human esophageal cancer cells by regulation of ERCC1

The downregulation of zinc ribbon domain-containing 1 (ZNRD1) protein was recently found to partially reverse the resistance of human leukemia cells toward chemical therapeutic drugs. Therefore, the ZNRD1 protein might be involved in the process of DNA damage and repair. To explore the possible protective effects of ZNRD1 on DNA damage induced by ultraviolet (UV)-C irradiation in human esophageal squamous cancer cell line EC109, we designed and transfected a expression vector into EC109 cells, and established an overexpression cell line. The single-cell gel electrophoresis (comet assay) was used to investigate the DNA damage and repair in UV-C-irradiated control and transfected cells. It was found that the ZNRD1-expressing cells exhibited a significant enhanced DNA repair capacity. Moreover, the overexpression of ZNRD1 could upregulate the expression of excision repair cross-complementing 1 (ERCC1) gene. Collectively, these findings suggested that ZNRD1 might play an important role in the process of DNA damage and repair by regulating the expression of ERCC1.