ERCC1 isoform expression and DNA repair in non-small-cell lung cancer.

BACKGROUND: The excision repair cross-complementation group 1 (ERCC1) protein is a potential prognostic biomarker of the efficacy of cisplatin-based chemotherapy in non-small-cell lung cancer (NSCLC). Although several ongoing trials are evaluating the level of expression of ERCC1, no consensus has been reached regarding a method for evaluation. METHODS: We used the 8F1 antibody to measure the level of expression of ERCC1 protein by means of immunohistochemical analysis in a validation set of samples obtained from 494 patients in two independent phase 3 trials (the National Cancer Institute of Canada Clinical Trials Group JBR.10 and the Cancer and Leukemia Group B 9633 trial from the Lung Adjuvant Cisplatin Evaluation Biology project). We compared the results of repeated staining of the entire original set of samples obtained from 589 patients in the International Adjuvant Lung Cancer Trial Biology study, which had led to the initial correlation between the absence of ERCC1 expression and platinum response, with our previous results in the same tumors. We mapped the epitope recognized by 16 commercially available ERCC1 antibodies and investigated the capacity of the different ERCC1 isoforms to repair platinum-induced DNA damage. RESULTS: We were unable to validate the predictive effect of immunostaining for ERCC1 protein. The discordance in the results of staining for ERCC1 suggested a change in the performance of the 8F1 antibody since 2006. We found that none of the 16 antibodies could distinguish among the four ERCC1 protein isoforms, whereas only one isoform produced a protein that had full capacities for nucleotide excision repair and cisplatin resistance. CONCLUSIONS: Immunohistochemical analysis with the use of currently available ERCC1 antibodies did not specifically detect the unique functional ERCC1 isoform. As a result, its usefulness in guiding therapeutic decision making is limited. (Funded by Eli Lilly and others.).

Single-cell multiomics profiling reveals heterogeneous transcriptional programs and microenvironment in DSRCTs.

Desmoplastic small round cell tumor (DSRCT) is a rare, aggressive sarcoma driven by the EWSR1::WT1 chimeric transcription factor. Despite this unique oncogenic driver, DSRCT displays a polyphenotypic differentiation of unknown causality. Using single-cell multi-omics on 12 samples from five patients, we find that DSRCT tumor cells cluster into consistent subpopulations with partially overlapping lineage- and metabolism-related transcriptional programs. In vitro modeling shows that high EWSR1::WT1 DNA-binding activity associates with most lineage-related states, in contrast to glycolytic and profibrotic states. Single-cell chromatin accessibility analysis suggests that EWSR1::WT1 binding site variability may drive distinct lineage-related transcriptional programs, supporting some level of cell-intrinsic plasticity. Spatial transcriptomics reveals that glycolytic and profibrotic states specifically localize within hypoxic niches at the periphery of tumor cell islets, suggesting an additional role of tumor cell-extrinsic microenvironmental cues. We finally identify a single-cell transcriptomics-derived epithelial signature associated with improved patient survival, highlighting the clinical relevance of our findings.

Replication Stress is an Actionable Genetic Vulnerability in Desmoplastic Small Round Cell Tumors.

Desmoplastic small round cell tumor (DSRCT) is an aggressive sarcoma subtype that is driven by the EWS-WT1 chimeric transcription factor. The prognosis for DSRCT is poor, and major advances in treating DSCRT have not occurred for over two decades. To identify effective therapeutic approaches to target DSRCT, we conducted a high-throughput drug sensitivity screen in a DSRCT cell line assessing chemosensitivity profiles for 79 small-molecule inhibitors. DSRCT cells were sensitive to PARP and ATR inhibitors (PARPi, ATRi), as monotherapies and in combination. These effects were recapitulated using multiple clinical PARPi and ATRi in three biologically distinct, clinically-relevant models of DSRCT, including cell lines, a patient-derived xenograft (PDX)-derived organoid model, and a cell line-derived xenograft mouse model. Mechanistically, exposure to a combination of PARPi and ATRi caused increased DNA damage, G2/M checkpoint activation, micronuclei accumulation, replication stress, and R-loop formation. EWS-WT1 silencing abrogated these phenotypes and was epistatic with exogenous expression of the R-loop resolution enzyme RNase H1 in reversing the sensitivity to PARPi and ATRi monotherapies. The combination of PARPi and ATRi also induced EWS-WT1-dependent cell-autonomous activation of the cGAS/STING innate immune pathway and cell surface expression of PD-L1. Taken together, these findings point towards a role for EWS-WT1 in generating R-loop-dependent replication stress that leads to a targetable vulnerability, providing a rationale for the clinical assessment of PARPi and ATRi in DSRCT.

p38 Mitogen-activated protein kinase signaling, ERCC1 expression, and viability of lung cancer cells from never or light smoker patients.

BACKGROUND: Expression of DNA-repair proteins and activated mitogen-activated protein kinases (MAPKs) may differ according to smoking status. The authors investigated whether p38 MAPK activity contributed to the viability of cisplatin in lung cancer cell lines from never or light smokers and to ERCC1 mRNA expression. METHODS: Activated p38 MAPK was tested as a predictor for ERCC1 levels in 117 lung adenocarcinomas. Cell viabilities of NCI-H1975, NCI-H1793, NCI-H1650, and NCI-H1651 cell lines, derived from never or light smokers, were measured after treatment with the p38 MAPK inhibitor SB202190 and cisplatin. The role of p38α (MAPK14) and p38ß (MAPK11) isoforms and ERCC1 was evaluated using RNA interference. RESULTS: ERCC1 protein-level expression was predicted by activated p38 MAPK in lung adenocarcinoma tissues. The p38-specific inhibitor SB202190 strongly decreased cell viability (43%-63%). SB202190 plus cisplatin significantly decreased cell viability in every cell line, including cisplatin-resistant NCI-H1793. Genetic inhibition, targeting both MAPK11 and MAPK14, reduced the viability of the different cell lines: down-regulation of p38ß accounted for most of this effect. Cisplatin's effect was greater after MAPK11 down-regulation for NCI-H1651, and MAPK14 down-regulation for NCI-H1650. In addition, both SB202190 and MAPK11 inhibition reduced excision repair cross-complementing 1 mRNA levels. CONCLUSIONS: Lung cancer cells from never or light smokers rely on p38 MAPK signaling for survival. MAPK11 is involved in that pathway and might contribute to ERCC1 expression. Sensitization to cisplatin can be achieved by pharmacological inhibition of p38 MAPK signaling.

PBRM1 Deficiency Confers Synthetic Lethality to DNA Repair Inhibitors in Cancer.

Inactivation of Polybromo 1 (PBRM1), a specific subunit of the PBAF chromatin remodeling complex, occurs frequently in cancer, including 40% of clear cell renal cell carcinomas (ccRCC). To identify novel therapeutic approaches to targeting PBRM1-defective cancers, we used a series of orthogonal functional genomic screens that identified PARP and ATR inhibitors as being synthetic lethal with PBRM1 deficiency. The PBRM1/PARP inhibitor synthetic lethality was recapitulated using several clinical PARP inhibitors in a series of in vitro model systems and in vivo in a xenograft model of ccRCC. In the absence of exogenous DNA damage, PBRM1-defective cells exhibited elevated levels of replication stress, micronuclei, and R-loops. PARP inhibitor exposure exacerbated these phenotypes. Quantitative mass spectrometry revealed that multiple R-loop processing factors were downregulated in PBRM1-defective tumor cells. Exogenous expression of the R-loop resolution enzyme RNase H1 reversed the sensitivity of PBRM1-deficient cells to PARP inhibitors, suggesting that excessive levels of R-loops could be a cause of this synthetic lethality. PARP and ATR inhibitors also induced cyclic GMP-AMP synthase/stimulator of interferon genes (cGAS/STING) innate immune signaling in PBRM1-defective tumor cells. Overall, these findings provide the preclinical basis for using PARP inhibitors in PBRM1-defective cancers. SIGNIFICANCE: This study demonstrates that PARP and ATR inhibitors are synthetic lethal with the loss of PBRM1, a PBAF-specific subunit, thus providing the rationale for assessing these inhibitors in patients with PBRM1-defective cancer. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/81/11/2888/F1.large.jpg.

PARP inhibition enhances tumor cell-intrinsic immunity in ERCC1-deficient non-small cell lung cancer.

The cyclic GMP-AMP synthase/stimulator of IFN genes (cGAS/STING) pathway detects cytosolic DNA to activate innate immune responses. Poly(ADP-ribose) polymerase inhibitors (PARPi) selectively target cancer cells with DNA repair deficiencies such as those caused by BRCA1 mutations or ERCC1 defects. Using isogenic cell lines and patient-derived samples, we showed that ERCC1-defective non-small cell lung cancer (NSCLC) cells exhibit an enhanced type I IFN transcriptomic signature and that low ERCC1 expression correlates with increased lymphocytic infiltration. We demonstrated that clinical PARPi, including olaparib and rucaparib, have cell-autonomous immunomodulatory properties in ERCC1-defective NSCLC and BRCA1-defective triple-negative breast cancer (TNBC) cells. Mechanistically, PARPi generated cytoplasmic chromatin fragments with characteristics of micronuclei; these were found to activate cGAS/STING, downstream type I IFN signaling, and CCL5 secretion. Importantly, these effects were suppressed in PARP1-null TNBC cells, suggesting that this phenotype resulted from an on-target effect of PARPi on PARP1. PARPi also potentiated IFN-γ-induced PD-L1 expression in NSCLC cell lines and in fresh patient tumor cells; this effect was enhanced in ERCC1-deficient contexts. Our data provide a preclinical rationale for using PARPi as immunomodulatory agents in appropriately molecularly selected populations.

A novel antibody-based approach to detect the functional ERCC1-202 isoform.

ERCC1/XPF endonuclease plays an important role in multiple DNA repair pathways and stands as a potential prognostic and predictive biomarker for cisplatin-based chemotherapy. Four distinct ERCC1 isoforms arising from alternative splicing have been described (201, 202, 203 and 204) but only the 202 isoform is functional in DNA excision repair, when interacting with its obligate partner XPF. Currently, there is no tool to assess specifically the expression of ERCC1-202 due to high sequence homology between the four isoforms. Here, we generated monoclonal antibodies directed against the heterodimer of ERCC1 and its obligate interacting partner XPF by genetic immunization. We obtained three monoclonal antibodies (2C11, 7C3 and 10D10) recognizing specifically the heterodimer ERCC1-202/XPF as well as the ERCC1-204/XPF with no affinity to ERCC1 or XPF monomers. By combining one of these three heterodimer-specific antibodies with a commercial anti-ERCC1 antibody (clone 4F9) unable to recognize the 204 isoform in a proximity ligation assay (PLA), we managed to specifically detect the functional ERCC1-202 isoform. This methodological breakthrough can constitute a basis for the development of clinical tests to evaluate ERCC1 functional proficiency.

TPF induction chemotherapy increases PD-L1 expression in tumour cells and immune cells in head and neck squamous cell carcinoma.

BACKGROUND: Antiprogrammed cell death-1/programmed cell death-ligand 1 (PD-1/PD-L1) therapies have demonstrated promising activity in advanced head and neck squamous cell carcinoma (HNSCC), with overall response rates of approximately 20% in unselected populations and survival benefit. Whether induction docetaxel, platinum and fluorouracil (TPF) modifies PD-L1 expression or tumour immune infiltrates is unknown. PATIENTS AND METHODS: Patients with locally advanced HNSCC treated at Gustave Roussy (Villejuif, France) between 2006 and 2013 by induction TPF followed by surgery were retrospectively considered. Patients with paired samples (pre-TPF and post-TPF) were kept for further analysis. PD-L1 expression was quantified by immunohistochemistry according to a validated protocol. The objective of the study was to compare PD-L1 expression on tumour cells (TC) and immune cells (IC) (positivity threshold of ≥5%) before and after TPF. CD8+ and Foxp3+ lymphocytes densities before and after TPF were also quantified. RESULTS: Out of 313 patients receiving induction TPF, 86 underwent surgery; paired samples were available for 21 of them. Baseline PD-L1 expression was ≥5% in two and five samples for TC and IC, respectively. A significant increase of PD-L1 expression was observed after TPF, with 15 samples (71%) presenting a positive staining in IC after induction chemotherapy (P=0.003; Wilcoxon rank-sum test) and eight samples (38%) in TC (P=0.005; Wilcoxon rank-sum test). Tumour-infiltrating CD8+ mean densities also significantly increased post-TPF (P=0.01). There was no significant difference in Foxp3+ expression, CD8/Foxp3 ratio or correlation with outcome. CONCLUSION: TPF induction chemotherapy in advanced HNSCC increases PD-L1 positivity on tumour-infiltrating ICs, as well as CD8+ lymphocytes density. These results warrant independent validation on larger datasets and might help therapeutic strategy in advanced HNSCC.

DNA repair deficiency sensitizes lung cancer cells to NAD+ biosynthesis blockade.

Synthetic lethality is an efficient mechanism-based approach to selectively target DNA repair defects. Excision repair cross-complementation group 1 (ERCC1) deficiency is frequently found in non-small-cell lung cancer (NSCLC), making this DNA repair protein an attractive target for exploiting synthetic lethal approaches in the disease. Using unbiased proteomic and metabolic high-throughput profiling on a unique in-house-generated isogenic model of ERCC1 deficiency, we found marked metabolic rewiring of ERCC1-deficient populations, including decreased levels of the metabolite NAD+ and reduced expression of the rate-limiting NAD+ biosynthetic enzyme nicotinamide phosphoribosyltransferase (NAMPT). We also found reduced NAMPT expression in NSCLC samples with low levels of ERCC1. These metabolic alterations were a primary effect of ERCC1 deficiency, and caused selective exquisite sensitivity to small-molecule NAMPT inhibitors, both in vitro - ERCC1-deficient cells being approximately 1,000 times more sensitive than ERCC1-WT cells - and in vivo. Using transmission electronic microscopy and functional metabolic studies, we found that ERCC1-deficient cells harbor mitochondrial defects. We propose a model where NAD+ acts as a regulator of ERCC1-deficient NSCLC cell fitness. These findings open therapeutic opportunities that exploit a yet-undescribed nuclear-mitochondrial synthetic lethal relationship in NSCLC models, and highlight the potential for targeting DNA repair/metabolic crosstalks for cancer therapy.

No evidence for viral sequences in five lepidic adenocarcinomas (former "BAC") by a high-throughput sequencing approach.

BACKGROUND: The hypothesis of an infectious etiology of the formerly named bronchiolo-alveolar carcinoma (BAC) has raised controversy. We investigated tumor lung tissues from five patients with former BAC histology using high-throughput sequencing technologies to discover potential viruses present in this type of lung cancer. Around 180 million single reads of 100 bases were generated for each BAC sample. RESULTS: None of the reads showed a significant similarity for Jaagsiekte sheep retrovirus (JSRV) and no other viruses were found except for endogenous retroviruses. CONCLUSIONS: In conclusion, we have demonstrated the absence of JSRV and other known human viruses in five samples of well-characterized lepidic adenocarcinoma.

ERCC1 function in nuclear excision and interstrand crosslink repair pathways is mediated exclusively by the ERCC1-202 isoform.

ERCC1 (excision repair cross-complementation group 1) plays essential roles in the removal of DNA intrastrand crosslinks by nucleotide excision repair, and that of DNA interstrand crosslinks by the Fanconi anemia (FA) pathway and homology-directed repair processes (HDR). The function of ERCC1 thus impacts on the DNA damage response (DDR), particularly in anticancer therapy when DNA damaging agents are employed. ERCC1 expression has been proposed as a predictive biomarker of the response to platinum-based therapy. However, the assessment of ERCC1 expression in clinical samples is complicated by the existence of 4 functionally distinct protein isoforms, which differently impact on DDR. Here, we explored the functional competence of each ERCC1 protein isoform and obtained evidence that the 202 isoform is the sole one endowed with ERCC1 activity in DNA repair pathways. The ERCC1 isoform 202 interacts with RPA, XPA, and XPF, and XPF stability requires expression of the ERCC1 202 isoform (but none of the 3 others). ERCC1-deficient non-small cell lung cancer cells show abnormal mitosis, a phenotype reminiscent of the FA phenotype that can be rescued by isoform 202 only. Finally, we could not observe any dominant-negative interaction between ERCC1 isoforms. These data suggest that the selective assessment of the ERCC1 isoform 202 in clinical samples should accurately reflect the DDR-related activity of the gene and hence constitute a useful biomarker for customizing anticancer therapies.

Prognostic value of LIPC in non-small cell lung carcinoma.

Non-small cell lung carcinoma (NSCLC) is the most common form of lung cancer and is associated with a high mortality rate worldwide. The majority of individuals bearing NSCLC are treated with surgery plus adjuvant cisplatin, an initially effective therapeutic regimen that, however, is unable to prevent relapse within 5 years after tumor resection in an elevated proportion of patients. The factors that predict the clinical course of NSCLC and its sensitivity to therapy remain largely obscure. One notable exception is provided by pyridoxal kinase (PDXK), the enzyme that generates the bioactive form of vitamin B6. PDXK has recently been shown to be required for optimal cisplatin responses in vitro and in vivo and to constitute a bona fide prognostic marker in the NSCLC setting. Together with PDXK, 84 additional factors were identified that influence the response of NSCLC cells to cisplatin, in vitro including the hepatic lipase LIPC. Here, we report that the intratumoral levels of LIPC, as assessed by immunohistochemistry in two independent cohorts of NSCLC patients, positively correlate with disease outcome. In one out of two cohorts studied, the overall survival of NSCLC patients bearing LIPChigh lesions was unaffected, if not slightly worsened, by cisplatin-based adjuvant therapy. Conversely, the overall survival of patients with LIPClow lesions was prolonged by post-operative cisplatin. Pending validation in appropriate clinical series, these results suggest that LIPClow NSCLC patients would be those who mainly benefit from adjuvant cisplatin therapy. Thus, the expression levels of LIPC appear to have an independent prognostic value (and perhaps a predictive potential) in the setting of NSCLC. If these findings were confirmed by additional studies, LIPC expression levels might allow not only for NSCLC patient stratification, but also for the implementation of personalized therapeutic approaches.

Prognostic impact of vitamin B6 metabolism in lung cancer.

Patients with non-small cell lung cancer (NSCLC) are routinely treated with cytotoxic agents such as cisplatin. Through a genome-wide siRNA-based screen, we identified vitamin B6 metabolism as a central regulator of cisplatin responses in vitro and in vivo. By aggravating a bioenergetic catastrophe that involves the depletion of intracellular glutathione, vitamin B6 exacerbates cisplatin-mediated DNA damage, thus sensitizing a large panel of cancer cell lines to apoptosis. Moreover, vitamin B6 sensitizes cancer cells to apoptosis induction by distinct types of physical and chemical stress, including multiple chemotherapeutics. This effect requires pyridoxal kinase (PDXK), the enzyme that generates the bioactive form of vitamin B6. In line with a general role of vitamin B6 in stress responses, low PDXK expression levels were found to be associated with poor disease outcome in two independent cohorts of patients with NSCLC. These results indicate that PDXK expression levels constitute a biomarker for risk stratification among patients with NSCLC.

Molecular Characteristics of ERCC1-Negative versus ERCC1-Positive Tumors in Resected NSCLC.

PURPOSE: Excision repair cross-complementation group 1 (ERCC1) is a protein involved in repair of DNA platinum adducts and stalled DNA replication forks. We and others have previously shown the influence of ERCC1 expression upon survival rates and benefit of cisplatin-based chemotherapy in patients with resected non-small-cell lung cancer (NSCLC). However, little is known about the molecular characteristics of ERCC1-positive and ERCC1-negative tumors. EXPERIMENTAL DESIGN: We took advantage of a cohort of 91 patients with resected NSCLC, for which we had matched frozen and paraffin-embedded samples to explore the comparative molecular portraits of ERCC1-positive and ERCC1-negative tumors of NSCLC. We carried out a global molecular analysis including assessment of ERCC1 expression levels by using both immunohistochemistry (IHC) and quantitative reverse transcriptase PCR (qRT-PCR), genomic instability, global gene and miRNA expression, and sequencing of selected key genes involved in lung carcinogenesis. RESULTS: ERCC1 protein and mRNA expression were significantly correlated. However, we observed several cases with clear discrepancies. We noted that ERCC1-negative tumors had a higher rate of genomic abnormalities versus ERCC1-positive tumors. ERCC1-positive tumors seemed to share a common DNA damage response (DDR) phenotype with the overexpression of seven genes linked to DDR. The miRNA expression analysis identified miR-375 as significantly underexpressed in ERCC1-positive tumors. CONCLUSIONS: Our data show inconsistencies in ERCC1 expression between IHC and qRT-PCR readouts. Furthermore, ERCC1 status is not linked to specific mutational patterns or frequencies. Finally, ERCC1-negative tumors have a high rate of genomic aberrations that could consequently influence prognosis in patients with resected NSCLC.