Inactivation of DNA repair triggers neoantigen generation and impairs tumour growth.

Molecular alterations in genes involved in DNA mismatch repair (MMR) promote cancer initiation and foster tumour progression. Cancers deficient in MMR frequently show favourable prognosis and indolent progression. The functional basis of the clinical outcome of patients with tumours that are deficient in MMR is not clear. Here we genetically inactivate MutL homologue 1 (MLH1) in colorectal, breast and pancreatic mouse cancer cells. The growth of MMR-deficient cells was comparable to their proficient counterparts in vitro and on transplantation in immunocompromised mice. By contrast, MMR-deficient cancer cells grew poorly when transplanted in syngeneic mice. The inactivation of MMR increased the mutational burden and led to dynamic mutational profiles, which resulted in the persistent renewal of neoantigens in vitro and in vivo, whereas MMR-proficient cells exhibited stable mutational load and neoantigen profiles over time. Immune surveillance improved when cancer cells, in which MLH1 had been inactivated, accumulated neoantigens for several generations. When restricted to a clonal population, the dynamic generation of neoantigens driven by MMR further increased immune surveillance. Inactivation of MMR, driven by acquired resistance to the clinical agent temozolomide, increased mutational load, promoted continuous renewal of neoantigens in human colorectal cancers and triggered immune surveillance in mouse models. These results suggest that targeting DNA repair processes can increase the burden of neoantigens in tumour cells; this has the potential to be exploited in therapeutic approaches.

Discovery of methylated circulating DNA biomarkers for comprehensive non-invasive monitoring of treatment response in metastatic colorectal cancer.

OBJECTIVE: Mutations in cell-free circulating DNA (cfDNA) have been studied for tracking disease relapse in colorectal cancer (CRC). This approach requires personalised assay design due to the lack of universally mutated genes. In contrast, early methylation alterations are restricted to defined genomic loci allowing comprehensive assay design for population studies. Our objective was to identify cancer-specific methylated biomarkers which could be measured longitudinally in cfDNA (liquid biopsy) to monitor therapeutic outcome in patients with metastatic CRC (mCRC). DESIGN: Genome-wide methylation microarrays of CRC cell lines (n=149) identified five cancer-specific methylated loci (EYA4, GRIA4, ITGA4, MAP3K14-AS1, MSC). Digital PCR assays were employed to measure methylation of these genes in tumour tissue DNA (n=82) and cfDNA from patients with mCRC (n=182). Plasma longitudinal assessment was performed in a patient subset treated with chemotherapy or targeted therapy. RESULTS: Methylation in at least one marker was detected in all tumour tissue samples and in 156 mCRC patient cfDNA samples (85.7%). Plasma marker prevalence was 71.4% for EYA4, 68.5% for GRIA4, 69.7% for ITGA4, 69.1% for MAP3K14-AS1% and 65.1% for MSC. Dynamics of methylation markers was not affected by treatment type and correlated with objective tumour response and progression-free survival. CONCLUSION: This five-gene methylation panel can be used to circumvent the absence of patient-specific mutations for monitoring tumour burden dynamics in liquid biopsy under different therapeutic regimens. This method might be proposed for assessing pharmacodynamics in clinical trials or when conventional imaging has limitations.

Colorectal cancer early methylation alterations affect the crosstalk between cell and surrounding environment, tracing a biomarker signature specific for this tumor.

Colorectal cancer (CRC) develops through the accumulation of both genetic and epigenetic alterations. However, while the former are already used as prognostic and predictive biomarkers, the latter are less well characterized. Here, performing global methylation analysis on both CRCs and adenomas by Illumina Infinium HumanMethylation450 Bead Chips, we identified a panel of 74 altered CpG islands, demonstrating that the earliest methylation alterations affect genes coding for proteins involved in the crosstalk between cell and surrounding environment. The panel discriminates CRCs and adenomas from peritumoral and normal mucosa with very high specificity (100%) and sensitivity (99.9%). Interestingly, over 70% of the hypermethylated islands resulted in downregulation of gene expression. To establish the possible usefulness of these non-invasive markers for detection of colon cancer, we selected three biomarkers and identified the presence of altered methylation in stool DNA and plasma cell-free circulating DNA from CRC patients.

Aberrant methylation of imprinted genes is associated with negative hormone receptor status in invasive breast cancer.

Epigenetic regulation of imprinted genes enables monoallelic expression according to parental origin, and its disruption is implicated in many cancers and developmental disorders. The expression of hormone receptors is significant in breast cancer because they are indicators of cancer cell growth rate and determine response to endocrine therapies. We investigated the frequency of aberrant events and variation in DNA methylation at nine imprinted sites in invasive breast cancer and examined the association with estrogen and progesterone receptor status. Breast tissue and blood from patients with invasive breast cancer (n = 38) and benign breast disease (n = 30) were compared with those from healthy individuals (n = 36), matched with the cancer patients by age at diagnosis, ethnicity, body mass index, menopausal status and familial history of cancer. DNA methylation and allele-specific expression were analyzed by pyrosequencing. Tumor-specific methylation changes at IGF2 DMR2 were observed in 59% of cancer patients, IGF2 DMR0 in 38%, DIRAS3 DMR in 36%, GRB10 ICR in 23%, PEG3 DMR in 21%, MEST ICR in 19%, H19 ICR in 18%, KvDMR in 8% and SNRPN/SNURF ICR in 4%. Variation in methylation was significantly greater in breast tissue from cancer patients compared with that in healthy individuals and benign breast disease. Aberrant methylation of three or more sites was significantly associated with negative estrogen-alpha (Fisher's exact test, p = 0.02) and progesterone-A (p = 0.02) receptor status. Aberrant events and increased variation in imprinted gene DNA methylation, therefore, seem to be frequent in invasive breast cancer and are associated with negative estrogen and progesterone receptor status, without loss of monoallelic expression.

The prevalence of loss of imprinting of H19 and IGF2 at birth.

Imprinted genes are monoallelically expressed according to the parent of origin and are critical for proper placental and embryonic development. Disruption of methylation patterns at imprinted loci resulting in loss of imprinting (LOI) may lead to serious imprinting disorders (e.g., Beckwith-Wiedemann syndrome) and is described in some cancers (e.g., Wilms' tumor). As most research has focused on children with cancer or other abnormal phenotypes, the imprinting status in healthy infants at birth has not been characterized. We examined the prevalence of H19 and IGF2 LOI at birth by allele-specific expression assays analysis on 114 human individuals. Overall expression and methylation analyses were performed on a subset of samples. We found that LOI of H19 was observed for 4% of individuals in cord blood and 3.3% in placenta, and for IGF2 of 22% of individuals in the cord blood and 0% in placenta. Interestingly, LOI status did not correspond to aberrant methylation levels of the imprinted DMRs or with changes in overall gene expression for the majority of individuals. Our observations suggest that LOI is present in phenotypically healthy infants. Determining a "normal" human epigenotype range is important for discovering factors required to maintain a healthy pregnancy and embryonic development.

Preclinical efficacy of carfilzomib in BRAF-mutant colorectal cancer models.

Serine/threonine-protein kinase B-raf (BRAF) mutations are found in 8-15% of colorectal cancer patients and identify a subset of tumors with poor outcome in the metastatic setting. We have previously reported that BRAF-mutant human cells display a high rate of protein production, causing proteotoxic stress, and are selectively sensitive to the proteasome inhibitors bortezomib and carfilzomib. In this work, we tested whether carfilzomib could restrain the growth of BRAF-mutant colorectal tumors not only by targeting cancer cells directly, but also by promoting an immune-mediated antitumor response. In human and mouse colorectal cancer cells, carfilzomib triggered robust endoplasmic reticulum stress and autophagy, followed by the emission of immunogenic-damage-associated molecules. Intravenous administration of carfilzomib delayed the growth of BRAF-mutant murine tumors and mobilized the danger-signal proteins calreticulin and high mobility group box 1 (HMGB1). Analyses of drug-treated samples revealed increased intratumor recruitment of activated cytotoxic T cells and natural killers, concomitant with the downregulation of forkhead box protein P3 (Foxp3)+ T-cell surface glycoprotein CD4 (CD4)+ T cells, indicating that carfilzomib promotes reshaping of the immune microenvironment of BRAF-mutant murine colorectal tumors. These results will inform the design of clinical trials in BRAF-mutant colorectal cancer patients.

Transcriptome-wide gene expression outlier analysis pinpoints therapeutic vulnerabilities in colorectal cancer.

Multiple strategies are continuously being explored to expand the drug target repertoire in solid tumors. We devised a novel computational workflow for transcriptome-wide gene expression outlier analysis that allows the systematic identification of both overexpression and underexpression events in cancer cells. Here, it was applied to expression values obtained through RNA sequencing in 226 colorectal cancer (CRC) cell lines that were also characterized by whole-exome sequencing and microarray-based DNA methylation profiling. We found cell models displaying an abnormally high or low expression level for 3533 and 965 genes, respectively. Gene expression abnormalities that have been previously associated with clinically relevant features of CRC cell lines were confirmed. Moreover, by integrating multi-omics data, we identified both genetic and epigenetic alternations underlying outlier expression values. Importantly, our atlas of CRC gene expression outliers can guide the discovery of novel drug targets and biomarkers. As a proof of concept, we found that CRC cell lines lacking expression of the MTAP gene are sensitive to treatment with a PRMT5-MTA inhibitor (MRTX1719). Finally, other tumor types may also benefit from this approach.

DNA demethylation triggers cell free DNA release in colorectal cancer cells.

BACKGROUND: Liquid biopsy based on cell-free DNA (cfDNA) analysis holds significant promise as a minimally invasive approach for the diagnosis, genotyping, and monitoring of solid malignancies. Human tumors release cfDNA in the bloodstream through a combination of events, including cell death, active and passive release. However, the precise mechanisms leading to cfDNA shedding remain to be characterized. Addressing this question in patients is confounded by several factors, such as tumor burden extent, anatomical and vasculature barriers, and release of nucleic acids from normal cells. In this work, we exploited cancer models to dissect basic mechanisms of DNA release. METHODS: We measured cell loss ratio, doubling time, and cfDNA release in the supernatant of a colorectal cancer (CRC) cell line collection (N = 76) representative of the molecular subtypes previously identified in cancer patients. Association analyses between quantitative parameters of cfDNA release, cell proliferation, and molecular features were evaluated. Functional experiments were performed to test the impact of modulating DNA methylation on cfDNA release. RESULTS: Higher levels of supernatant cfDNA were significantly associated with slower cell cycling and increased cell death. In addition, a higher cfDNA shedding was found in non-CpG Island Methylator Phenotype (CIMP) models. These results indicate a positive correlation between lower methylation and increased cfDNA levels. To explore this further, we exploited methylation microarrays to identify a subset of probes significantly associated with cfDNA shedding and derive a methylation signature capable of discriminating high from low cfDNA releasers. We applied this signature to an independent set of 176 CRC cell lines and patient derived organoids to select 14 models predicted to be low or high releasers. The methylation profile successfully predicted the amount of cfDNA released in the supernatant. At the functional level, genetic ablation of DNA methyl-transferases increased chromatin accessibility and DNA fragmentation, leading to increased cfDNA release in isogenic CRC cell lines. Furthermore, in vitro treatment of five low releaser CRC cells with a demethylating agent was able to induce a significant increase in cfDNA shedding. CONCLUSIONS: Methylation status of cancer cell lines contributes to the variability of cfDNA shedding in vitro. Changes in methylation pattern are associated with cfDNA release levels and might be exploited to increase sensitivity of liquid biopsy assays.

Liquid Biopsy of Cerebrospinal Fluid Enables Selective Profiling of Glioma Molecular Subtypes at First Clinical Presentation.

PURPOSE: Current glioma diagnostic guidelines call for molecular profiling to stratify patients into prognostic and treatment subgroups. In case the tumor tissue is inaccessible, cerebrospinal fluid (CSF) has been proposed as a reliable tumor DNA source for liquid biopsy. We prospectively investigated the use of CSF for molecular characterization of newly diagnosed gliomas. EXPERIMENTAL DESIGN: We recruited two cohorts of newly diagnosed patients with glioma, one (n = 45) providing CSF collected in proximity of the tumor, the other (n = 39) CSF collected by lumbar puncture (LP). Both cohorts provided tumor tissues by surgery concomitant with CSF sampling. DNA samples retrieved from CSF and matched tumors were systematically characterized and compared by comprehensive (NGS, next-generation sequencing) or targeted (ddPCR, droplet digital PCR) methodologies. Conventional and molecular diagnosis outcomes were compared. RESULTS: We report that tumor DNA is abundant in CSF close to the tumor, but scanty and mostly below NGS sensitivity threshold in CSF from LP. Indeed, tumor DNA is mostly released by cells invading liquoral spaces, generating a gradient that attenuates by departing from the tumor. Nevertheless, in >60% of LP CSF samples, tumor DNA is sufficient to assess a selected panel of genetic alterations (IDH and TERT promoter mutations, EGFR amplification, CDKN2A/B deletion: ITEC protocol) and MGMT methylation that, combined with imaging, enable tissue-agnostic identification of main glioma molecular subtypes. CONCLUSIONS: This study shows potentialities and limitations of CSF liquid biopsy in achieving molecular characterization of gliomas at first clinical presentation and proposes a protocol to maximize diagnostic information retrievable from CSF DNA.

Temozolomide Treatment Alters Mismatch Repair and Boosts Mutational Burden in Tumor and Blood of Colorectal Cancer Patients.

The majority of metastatic colorectal cancers (mCRC) are mismatch repair (MMR) proficient and unresponsive to immunotherapy, whereas MMR-deficient (MMRd) tumors often respond to immune-checkpoint blockade. We previously reported that the treatment of colorectal cancer preclinical models with temozolomide (TMZ) leads to MMR deficiency, increased tumor mutational burden (TMB), and sensitization to immunotherapy. To clinically translate these findings, we designed the ARETHUSA clinical trial whereby O6-methylguanine-DNA-methyltransferase (MGMT)-deficient, MMR-proficient, RAS-mutant mCRC patients received priming therapy with TMZ. Analysis of tissue biopsies and circulating tumor DNA (ctDNA) revealed the emergence of a distinct mutational signature and increased TMB after TMZ treatment. Multiple alterations in the nucleotide context favored by the TMZ signature emerged in MMR genes, and the p.T1219I MSH6 variant was detected in ctDNA and tissue of 94% (16/17) of the cases. A subset of patients whose tumors displayed the MSH6 mutation, the TMZ mutational signature, and increased TMB achieved disease stabilization upon pembrolizumab treatment. SIGNIFICANCE: MMR-proficient mCRCs are unresponsive to immunotherapy. We provide the proof of concept that inactivation of MMR genes can be achieved pharmacologically with TMZ and molecularly monitored in the tissue and blood of patients with mCRC. This strategy deserves additional evaluation in mCRC patients whose tumors are no longer responsive to standard-of-care treatments. See related commentary by Willis and Overman, p. 1612. This article is highlighted in the In This Issue feature, p. 1599.

True conversions from RAS mutant to RAS wild-type in circulating tumor DNA from metastatic colorectal cancer patients as assessed by methylation and mutational signature.

The paucity of targeted treatments available in patients with RAS mutant colorectal cancers contributes to the poor prognosis of this patient group compared to those with RAS wild-type disease. Recent liquid biopsy-driven studies have demonstrated that RAS mutant clones might disappear in plasma during the clonal evolution of the disease, opening new unforeseen perspectives for EGFR blockade in these patients. Nevertheless, the lack of detection of RAS mutations in plasma might depend on the low amount of released circulating tumor DNA (ctDNA), making it necessary a more accurate selection of patients with true RAS mutation conversions. In this liquid biopsy-based study, we assessed RAS mutational status in initially RAS-mutant patients at the time of progressive disease from any line of therapy and investigated the incidence of true conversions to plasma RAS wild-type, comparing a colon cancer specific methylation profile with a mutational signature of ctDNA. Globally, considering either mutational panel or methylation profile as reliable tests to confirm or exclude the presence of ctDNA, the percentage of "true RAS converters" was 37.5%. In our series we observed a trend toward a better PFS in patients who received anti-EGFR as second or subsequent treatment lines compared to those who did not.

ERBB3 overexpression due to miR-205 inactivation confers sensitivity to FGF, metabolic activation, and liability to ERBB3 targeting in glioblastoma.

In glioblastoma (GBM), the most frequent and lethal brain tumor, therapies suppressing recurrently altered signaling pathways failed to extend survival. However, in patient subsets, specific genetic lesions can confer sensitivity to targeted agents. By exploiting an integrated model based on patient-derived stem-like cells, faithfully recapitulating the original GBMs in vitro and in vivo, here, we identify a human GBM subset (∼9% of all GBMs) characterized by ERBB3 overexpression and nuclear accumulation. ERBB3 overexpression is driven by inheritable promoter methylation or post-transcriptional silencing of the oncosuppressor miR-205 and sustains the malignant phenotype. Overexpressed ERBB3 behaves as a specific signaling platform for fibroblast growth factor receptor (FGFR), driving PI3K/AKT/mTOR pathway hyperactivation, and overall metabolic upregulation. As a result, ERBB3 inhibition by specific antibodies is lethal for GBM stem-like cells and xenotransplants. These findings highlight a subset of patients eligible for ERBB3-targeted therapy.

Circulating Methylated DNA to Monitor the Dynamics of RAS Mutation Clearance in Plasma from Metastatic Colorectal Cancer Patients.

The clearance of RAS mutations in plasma circulating tumor DNA (ctDNA) from originally RAS-mutant metastatic colorectal cancer (mCRC) has been recently demonstrated. Clinical trials investigating whether RAS mutant mCRC who "convert" to wild-type in plasma might benefit from EGFR blockade are ongoing. Detection of tumor-specific DNA methylation alterations in ctDNA has been suggested as a specific tool to confirm the tumoral origin of cell-free DNA. We monitored RAS clearance in plasma from patients with RAS-mutant mCRC at baseline (pre-treatment) (T0); after 4 months of first-line therapy (T1); at the time of first (T2) and second (T3) progression. A five-gene methylation panel was used to confirm the presence of ctDNA in samples in which RAS mutation clearance was detected. At T1, ctDNA analysis revealed wild-type RAS status in 83% of samples, all not methylated, suggesting at this time point the lack of ctDNA shedding. At T2, ctDNA analysis revealed wild-type RAS status in 83% of samples, of which 62.5% were found methylated. At T3, 50% of wild-type RAS samples were found methylated. Non-methylated samples were found in patients with lung or brain metastases. This five-gene methylation test might be useful to confirm the presence of ctDNA in RAS wild-type plasma samples.

Capecitabine and Temozolomide versus FOLFIRI in RAS-Mutated, MGMT-Methylated Metastatic Colorectal Cancer.

PURPOSE: To determine whether second-line therapy with capecitabine and temozolomide was superior to irinotecan, leucovorin, and fluorouracil (FOLFIRI) in patients with RAS-mutated, methyl-guanine methyltransferase (MGMT)-methylated metastatic colorectal cancer (mCRC). PATIENTS AND METHODS: In this randomized, phase II trial, we enrolled patients with RAS-mutated, MGMT-methylated mCRC after failure of oxaliplatin-based regimen. Patients with centrally confirmed MGMT methylation were stratified by first-line progression-free survival (PFS) and prior bevacizumab and randomized to either capecitabine plus temozolomide (arm A, CAPTEM) or FOLFIRI (arm B). The primary endpoint was PFS analyzed on intention-to-treat basis, with 90% power and one-sided significance level of 0.05 to detect an increase of median time from 2 months in arm B to 4 months in arm A. RESULTS: Between November 2014 and May 2019, 86 patients were randomly assigned to arm A (n = 43) or arm B (n = 43). After a median follow-up of 30.5 months (interquartile range, 12.2-36.3), 79 disease progression or death events occurred. Superiority of arm A was not demonstrated (one-sided P = 0.223). Progression-free survival and overall survival were 3.5 (2.0-5.0) and 9.5 (8.2-25.8) in arm A versus 3.5 (2.3-6.1) and 10.6 (8.5-20.8) in arm B [HR = 1.19 (0.82-1.72) and HR = 0.97 (0.58-1.61)], respectively. Grade ≥3 treatment-related adverse events had higher incidence in arm B versus A (47.6% vs 16.3%), and quality of life was significantly worse in arm B. Patients with positive MGMT expression by IHC did not benefit from CAPTEM. CONCLUSIONS: Temozolomide-based therapy warrants further investigation in molecularly hyperselected subgroups.

Whole exome sequencing analysis of urine trans-renal tumour DNA in metastatic colorectal cancer patients.

BACKGROUND: The analysis of circulating free tumour DNA (ctDNA) in blood, commonly referred as liquid biopsy, is being used to characterise patients with solid cancers. Tumour-specific genetic variants can also be present in DNA isolated from other body fluids, such as urine. Unlike blood, urine sampling is non-invasive, can be self-performed, and allows recurrent longitudinal monitoring. The features of tumour DNA that clears from the glomerular filtration barrier, named trans-renal tumour DNA (trtDNA), are largely unexplored. PATIENTS AND METHODS: Specimens were collected from 24 patients with KRAS or BRAF mutant metastatic colorectal cancer (mCRC). Driver mutations were assessed by droplet digital PCR (ddPCR) in ctDNA from plasma and trtDNA from urine. Whole exome sequencing (WES) was performed in DNA isolated from tissue, plasma and urine. RESULTS: Out of the 24 CRC cases, only four had sufficient DNA to allow WES analyses in urine and plasma. We found that tumour alterations primarily reside in low molecular weight fragments (less than 112 bp). In patients whose trtDNA was more than 2.69% of the urine derived DNA, cancer-specific molecular alterations, mutational signatures and copy number profiles identified in urine DNA are comparable with those detected in plasma ctDNA. CONCLUSIONS: With current technologies, WES analysis of trtDNA is feasible in a small fraction of mCRC patients. Tumour-related genetic information is mainly present in low molecular weight DNA fragments. Although the limited amounts of trtDNA poses analytical challenges, enrichment of low molecular weight DNAs and optimised computational tools can improve the detection of tumour-specific genetic information in urine.

Evolving neoantigen profiles in colorectal cancers with DNA repair defects.

BACKGROUND: Neoantigens that arise as a consequence of tumor-specific mutations can be recognized by T lymphocytes leading to effective immune surveillance. In colorectal cancer (CRC) and other tumor types, a high number of neoantigens is associated with patient response to immune therapies. The molecular processes governing the generation of neoantigens and their turnover in cancer cells are poorly understood. We exploited CRC as a model system to understand how alterations in DNA repair pathways modulate neoantigen profiles over time. METHODS: We performed whole exome sequencing (WES) and RNA sequencing (RNAseq) in CRC cell lines, in vitro and in vivo, and in CRC patient-derived xenografts (PDXs) to track longitudinally genomic profiles, clonal evolution, mutational signatures, and predicted neoantigens. RESULTS: The majority of CRC models showed remarkably stable mutational and neoantigen profiles; however, those carrying defects in DNA repair genes continuously diversified. Rapidly evolving and evolutionary stable CRCs displayed characteristic genomic signatures and transcriptional profiles. Downregulation of molecules implicated in antigen presentation occurred selectively in highly mutated and rapidly evolving CRC. CONCLUSIONS: These results indicate that CRCs carrying alterations in DNA repair pathways display dynamic neoantigen patterns that fluctuate over time. We define CRC subsets characterized by slow and fast evolvability and link this phenotype to downregulation of antigen-presenting cellular mechanisms. Longitudinal monitoring of the neoantigen landscape could be relevant in the context of precision medicine.

A Genomic Analysis Workflow for Colorectal Cancer Precision Oncology.

BACKGROUND: The diagnosis of colorectal cancer (CRC) is routinely accomplished through histopathologic examination. Prognostic information and treatment decisions are mainly determined by TNM classification, first defined in 1968. In the last decade, patient-specific CRC genomic landscapes were shown to provide important prognostic and predictive information. Therefore, there is a need for developing next generation sequencing (NGS) and bioinformatic workflows that can be routinely used for the assessment of prognostic and predictive biomarkers. MATERIALS AND METHODS: To foster the application of genomics in the clinical management of CRCs, the IDEA workflow has been built to easily adapt to the availability of patient specimens and the clinical question that is being asked. Initially, IDEA deploys ad-hoc NGS assays to interrogate predefined genomic target sequences (from 600 kb to 30 Mb) with optimal detection sensitivity. Next, sequencing data are processed through an integrated bioinformatic pipeline to assess single nucleotide variants, insertions and deletions, gene copy-number alterations, and chromosomal rearrangements. The overall results are gathered into a user-friendly report. RESULTS: We provide evidence that IDEA is capable of identifying clinically relevant molecular alterations. When optimized to analyze circulating tumor DNA, IDEA can be used to monitor response and relapse in the blood of patients with metastatic CRC receiving targeted agents. IDEA detected primary and secondary resistance mechanisms to ERBB2 blockade including sub-clonal RAS and BRAF mutations. CONCLUSIONS: The IDEA workflow provides a flexible platform to integrate NGS and bioinformatic tools for refined diagnosis and management of patients with advanced CRC.

High Circulating Methylated DNA Is a Negative Predictive and Prognostic Marker in Metastatic Colorectal Cancer Patients Treated With Regorafenib.

Background: Regorafenib improves progression free survival (PFS) in a subset of metastatic colorectal cancer (mCRC) patients, although no biomarkers of efficacy are available. Circulating methylated DNA (cmDNA) assessed by a five-gene panel was previously associated with outcome in chemotherapy treated mCRC patients. We hypothesized that cmDNA could be used to identify cases most likely to benefit from regorafenib (i.e., patients with PFS longer than 4 months). Methods: Plasma samples from mCRC patients were collected prior to (baseline samples N = 60) and/or during regorafenib treatment (N = 62) for the assessment of cmDNA and total amount of cell free DNA (cfDNA). Results: In almost all patients, treatment with regorafenib increased the total cfDNA, but decreased cmDNA warranting the normalization of cmDNA to the total amount of circulating DNA (i.e., cmDNA/ml). We report that cmDNA/ml dynamics reflects clinical response with an increase in cmDNA/ml associated with higher risk of progression (HR for progression = 1.78 [95%CI: 1.01-3.13], p = 0.028). Taken individually, high baseline cmDNA/ml (above median) was associated with worst prognosis (HR for death = 3.471 [95%CI: 1.83-6.57], p < 0.0001) and also predicted shorter PFS (<16 weeks with PPV 86%). In addition, high cmDNA/ml values during regorafenib treatment predicted with higher accuracy shorter PFS (<16 weeks with a PPV of 96%), therefore associated with increased risk of progression (HR for progression = 2.985; [95%CI: 1.63-5.46; p < 0.0001). Conclusions: Our data highlight the predictive and prognostic value of cmDNA/ml in mCRC patients treated with regorafenib.

Refining the selection of patients with metastatic colorectal cancer for treatment with temozolomide using proteomic analysis of O6-methylguanine-DNA-methyltransferase.

BACKGROUND: The repair enzyme O6-methylguanine-DNA-methyltransferase (MGMT) is a validated predictor of benefit from temozolomide (TMZ) in glioblastoma. However, only 10% of patients with MGMT-methylated metastatic colorectal cancer (mCRC) respond to TMZ. METHODS: Archived tumour samples (N = 41) from three phase II TMZ trials carried out in MGMT-methylated mCRC (assessed by methylation-specific polymerase chain reaction [PCR]) were stratified by MGMT status as assessed by three different methods: mass spectrometry, PCR/methyl-BEAMing and RNA-seq. The performance of each method was assessed in relation to overall response rate, progression-free survival (PFS) and overall survival (OS). RESULTS: Overall, 9 of 41 patients responded to TMZ. Overall response rates were 50% (9/18), 50% (6/12) and 35% (8/23) among patients determined likely to respond to TMZ by mass spectrometry, methyl-BEAMing and RNA-seq, respectively. Low/negative MGMT protein expressors by mass spectrometry had longer PFS than high MGMT expressors (3.7 vs 1.8 months; HR = 0.50, P = 0.014). Results for OS were similar but statistically non-significant (8.7 vs. 7.4 months; HR = 0.55, P = 0.077). No significant association between survival and MGMT status by methyl-BEAMing or RNA-seq could be demonstrated as comparable subgroups survival could not be confirmed/excluded. Specifically, the association of high versus low methyl-BEAMing MGMT hypermethylation with survival was HR = 0.783, P = 0.46 for PFS and 0.591, P = 0.126 for OS, while association of low versus high RNA-seq MGMT level with survival was HR = 0.697, P = 0.159 for PFS and HR = 0.697, P = 0.266 for OS. CONCLUSIONS: Quantitative proteomic analysis of MGMT may be useful for refining the selection of patients eligible for salvage treatment with single-agent TMZ.

Mutations in the RAS-MAPK, PI(3)K (phosphatidylinositol-3-OH kinase) signaling network correlate with poor survival in a population-based series of colon cancers.

The RAS-MAPK, PI (3)K signaling pathways form a network that play a central role in tumorigenesis. The BRAF, KRAS and PI3KCA genes code 3 partners of this network and have been found to be activated by mutation in colorectal cancer; these mutations lead to unrestricted cell growth. We evaluated the clinicopathological features and the prognosis of patients with activated-network colon cancers in a population-based study. A total of 586 colon adenocarcinomas were evaluated using sequencing for mutations of KRAS and PI3KCA, and allelic discrimination for mutation of BRAF. Clinicopathological characteristics were correlated to the risk of bearing a mutation of the network using logistic regression. Three-year survival rates were compared with the Log rank test. A multivariate survival analysis using the Cox model was performed. After adjustment for age and microsatellite instability, activation of the network by mutation of at least 1 of the 3 genes was significantly associated with female sex (p = 0.02) and proximal location (p < 0.001). Lower levels of 3-year survival were associated with activation of the network by mutation of at least 1 of the 3 genes (59.4 and 69.4%, respectively; p = 0.009). These results remained significant in a multivariate analysis adjusted for sex, age, location, stage and microsatellite instability (HR = 1.48; CI CI(95%) = [1.07-2.04]). Our study is the first report to underline the potential role of RAS-MAPK, PI (3)K network mutations on survival in colon cancers. Because of the role of this signaling network on anticancer agents, the evaluation of its mutations could have clinical implications.