Adaptive Plasticity Tumor Cells Modulate MAPK-Targeting Therapy Response in Colorectal Cancer.

MAPK pathway inhibitors (MAPKi) are increasingly used in the treatment of advanced colorectal cancer, but often produce short-lived responses in patients. Although acquired resistance by mutations in tumors have been found to reduce response in some patients, additional mechanisms underlying the limited response durability of MAPK targeting therapy remain unknown. Here, we denote new contributory tumor biology and provide insight on the impact of tumor plasticity on therapy response.

Epigenome Reprogramming Through H3K27 and H3K4 Trimethylation as a Resistance Mechanism to DNA Methylation Inhibition in BRAFV600E-Mutated Colorectal Cancer.

Purpose: BRAFV600E-mutated colorectal cancer exhibits a strong correlation with DNA hypermethylation, suggesting that this subgroup of tumors presents unique epigenomic phenotypes. Nonetheless, 5-azacitidine, which inhibits DNA methyltransferase activity, is not efficacious in BRAFV600E colorectal cancer in vivo.

Experimental Design: We randomized and treated mice implanted with patient-derived tumor xenografts harboring BRAFV600E mutation with control, 5-azacitidine, vemurafenib (BRAF inhibitor), or the combination.

Defining the KRAS- and ERK-dependent transcriptome in KRAS-mutant cancers.

How the oncogene drives cancer growth remains poorly understood. Therefore, we established a systemwide portrait of KRAS- and extracellular signal-regulated kinase (ERK)-dependent gene transcription in KRAS-mutant cancer to delineate the molecular mechanisms of growth and of inhibitor resistance. Unexpectedly, our KRAS-dependent gene signature diverges substantially from the frequently cited Hallmark KRAS signaling gene signature, is driven predominantly through the ERK mitogen-activated protein kinase (MAPK) cascade, and accurately reflects KRAS- and ERK-regulated gene transcription in KRAS-mutant cancer patients.

Antitumor Efficacy of Dual Blockade with Encorafenib + Cetuximab in Combination with Chemotherapy in Human BRAFV600E-Mutant Colorectal Cancer.

Purpose: Encorafenib + cetuximab (E+C) is an effective therapeutic option in chemorefractory BRAFV600E metastatic colorectal cancer (mCRC). However, there is a need to improve the efficacy of this molecular-targeted therapy and evaluate regimens suitable for untreated BRAFV600E in patients with mCRC.

Experimental Design: We performed a series of in vivo studies using BRAFV600E mCRC tumor xenografts.

Resistance Mechanisms to Anti-Epidermal Growth Factor Receptor Therapy in Wild-Type Colorectal Cancer Vary by Regimen and Line of Therapy.

Purpose: Acquired resistance to anti-epidermal growth factor receptor (EGFR) inhibitor (EGFRi) therapy in colorectal cancer (CRC) has previously been explained by the model of acquiring new mutations in , among other MAPK-pathway members. However, this was primarily on the basis of single-agent EGFRi trials and little is known about the resistance mechanisms of EGFRi combined with effective cytotoxic chemotherapy in previously untreated patients.

Methods: We analyzed paired plasma samples from patients with wild-type metastatic CRC enrolled in three large randomized trials evaluating EGFRi in the first line in combination with chemotherapy and as a single agent in third line.

Chromatin state dynamics confers specific therapeutic strategies in enhancer subtypes of colorectal cancer.

Objective: Enhancer aberrations are beginning to emerge as a key epigenetic feature of colorectal cancers (CRC), however, a comprehensive knowledge of chromatin state patterns in tumour progression, heterogeneity of these patterns and imparted therapeutic opportunities remain poorly described.

Design: We performed comprehensive epigenomic characterisation by mapping 222 chromatin profiles from 69 samples (33 colorectal adenocarcinomas, 4 adenomas, 21 matched normal tissues and 11 colon cancer cell lines) for six histone modification marks: H3K4me3 for Pol II-bound and CpG-rich promoters, H3K4me1 for poised enhancers, H3K27ac for enhancers and transcriptionally active promoters, H3K79me2 for transcribed regions, H3K27me3 for polycomb repressed regions and H3K9me3 for heterochromatin.

Results: We demonstrate that H3K27ac-marked active enhancer state could distinguish between different stages of CRC progression.

ARID1A Mutation May Define an Immunologically Active Subgroup in Patients with Microsatellite Stable Colorectal Cancer.

Purpose: AT-rich interactive domain 1A () is commonly mutated in colorectal cancer, frequently resulting in truncation and loss of protein expression. ARID1A recruits MSH2 for mismatch repair during DNA replication. ARID1A deficiency promotes hypermutability and immune activation in preclinical models, but its role in patients with colorectal cancer is being explored.

Evolving Strategies for the Management of BRAF-Mutant Metastatic Colorectal Cancer.

Detection of the BRAF V600E mutation has important genetic, prognostic, and therapeutic implications for patients with metastatic colorectal cancer (mCRC), as it aids in the identification of a subgroup of patients who derive little benefit from standard treatments and have an extremely poor prognosis. Secondary analyses of BRAF V600E-mutated subsets from multiple randomized clinical trials have demonstrated a lack of therapeutic benefit and poor prognosis with conventional cytotoxic chemotherapy doublets, highlighting the need for novel effective treatments for this subpopulation. In contrast to patients with BRAF V600E-mutated metastatic melanoma, only 5% of patients with BRAF V600E-mutated mCRC responded to BRAF inhibitor monotherapy in an early-phase trial.