ETV1-Positive Cells Give Rise to BRAFV600E -Mutant Gastrointestinal Stromal Tumors

Modeling human gastric cancers in immunocompetent mice

Gastric cancer (GC) is a major cause of cancer-related mortality worldwide. GC is determined by multiple (epi)genetic and environmental factors; can occur at distinct anatomic positions of the stomach; and displays high heterogeneity, with different cellular origins and diverse histological and molecular features. This heterogeneity has hindered efforts to fully understand the pathology of GC and develop efficient therapeutics. In the past decade, great progress has been made in the study of GC, particularly in molecular subtyping, investigation of the immune microenvironment, and defining the evolutionary path and dynamics. Preclinical mouse models, particularly immunocompetent models that mimic the cellular and molecular features of human GC, in combination with organoid culture and clinical studies, have provided powerful tools for elucidating the molecular and cellular mechanisms underlying GC pathology and immune evasion, and the development of novel therapeutic strategies. Herein, we first briefly introduce current progress and challenges in GC study and subsequently summarize immunocompetent GC mouse models, emphasizing the potential application of genetically engineered mouse models in antitumor immunity and immunotherapy studies.

Treatment of BRAF V600E mutant gastrointestinal stromal tumor with dabrafenib: a case report

Background

Gastrointestinal stromal tumor (GIST) is a rare mesenchymal tumor arising in the gut, most commonly stomach or small bowel. The most common driver mutations are KIT and PDGFRA which can be treated with imatinib or avapritinib (for PDGFRA D842V-mutant GIST), respectively. BRAF V600E mutant GISTs are rare and these do not respond to imatinib. Multiple clinical trials have shown antitumor effects with dabrafenib in BRAF-mutant melanoma and a few case reports have demonstrated treatment of BRAF V600E mutant GIST with a BRAF kinase inhibitor.

Case Description

We present a case of a 67-year-old woman diagnosed with high-risk GIST following initial resection. She was initially treated with adjuvant imatinib which was discontinued after 7 months because molecular analysis of her tumor showed the absence of KIT and PDGFRA mutations and a BRAF V600E mutation. When her disease progressed, she was started on sunitinib and subsequently regorafenib. Both agents were discontinued due to severe palmar-plantar erythrodysesthesia and clinical progression. She was subsequently started on dabrafenib based on the presence of a BRAF V600E mutation; this therapy led to a partial response. Her disease remained stable on this medication for 19 months before progression and addition of trametinib to her treatment. Her disease continued to progress and she was switched to everolimus with mixed response before re-challenging with dabrafenib and trametinib. Her imaging showed a mixed response to the re-challenge before progressing after 5 months and transitioning to hospice.

Conclusions

We describe an uncommon molecular subtype of GIST with a BRAF V600E mutation. As expected, her disease was resistant to standard GIST therapy, however there was notable tumor regression following treatment with dabrafenib. This case shows the importance of molecular testing in GIST and adds to the current body of literature on the treatment of BRAF-mutant GIST.

Advances in immunology and immunotherapy for mesenchymal gastrointestinal cancers

Mesenchymal gastrointestinal cancers are represented by the gastrointestinal stromal tumors (GISTs) which occur throughout the whole gastrointestinal tract, and affect human health and economy globally. Curative surgical resections and tyrosine kinase inhibitors (TKIs) are the main managements for localized GISTs and recurrent/metastatic GISTs, respectively. Despite multi-lines of TKIs treatments prolonged the survival time of recurrent/metastatic GISTs by delaying the relapse and metastasis of the tumor, drug resistance developed quickly and inevitably, and became the huge obstacle for stopping disease progression. Immunotherapy, which is typically represented by immune checkpoint inhibitors (ICIs), has achieved great success in several solid tumors by reactivating the host immune system, and been proposed as an alternative choice for GIST treatment. Substantial efforts have been devoted to the research of immunology and immunotherapy for GIST, and great achievements have been made. Generally, the intratumoral immune cell level and the immune-related gene expressions are influenced by metastasis status, anatomical locations, driver gene mutations of the tumor, and modulated by imatinib therapy. Systemic inflammatory biomarkers are regarded as prognostic indicators of GIST and closely associated with its clinicopathological features. The efficacy of immunotherapy strategies for GIST has been widely explored in pre-clinical cell and mouse models and clinical experiments in human, and some patients did benefit from ICIs. This review comprehensively summarizes the up-to-date advancements of immunology, immunotherapy and research models for GIST, and provides new insights and perspectives for future studies.

Small Gastric Stromal Tumors: An Underestimated Risk

BACKGROUND AND OBJECTIVES

Small gastrointestinal stromal tumors (GISTs) are defined as tumors less than 2 cm in diameter, which are often found incidentally during gastroscopy. There is controversy regarding the management of small GISTs, and a certain percentage of small GISTs become malignant during follow-up. Previous studies which used Sanger targeted sequencing have shown that the mutation rate of small GISTs is significantly lower than that of large tumors. The aim of this study was to investigate the overall mutational profile of small GISTs, including those of wild-type tumors, using whole-exome sequencing (WES) and Sanger sequencing.

METHODS

Thirty-six paired small GIST specimens, which were resected by endoscopy, were analyzed by WES. Somatic mutations identified by WES were confirmed by Sanger sequencing. Sanger sequencing was performed in an additional 38 small gastric stromal tumor samples for examining hotspot mutations in KIT, PDGFRA, and BRAF.

RESULTS

Somatic C-KIT/PDGFRA mutations accounted for 81% of the mutations, including three novel mutation sites in C-KIT at exon 11, across the entire small gastric stromal tumor cohort (n = 74). In addition, 15% of small GISTs harbored previously undescribed BRAF-V600E hotspot mutations. No significant correlation was observed among the genotype, pathological features, and clinical classification.

CONCLUSIONS

Our data revealed a high overall mutation rate (~96%) in small GISTs, indicating that genetic alterations are common events in early GIST generation. We also identified a high frequency of oncogenic BRAF-V600E mutations (15%) in small GISTs, which has not been previously reported.

MIR31HG Expression Predicts Poor Prognosis and Promotes Colorectal Cancer Progression

Purpose

Long noncoding RNAs (lncRNAs) are correlated with cancer pathogenesis and prognosis. Many studies have shown that aberrant expression of MIR31HG is implicated in the cancer progression and patient prognosis. However, the biological function and predictive value of MIR31HG in colorectal cancer is unclear.

Methods

The correlation between MIR31HG expression and clinicopathological characteristics of colorectal cancer patients was analyzed by collating the information from The Cancer Genome Atlas (TCGA) database. Kaplan–Meier analysis, univariable and multivariable Cox regression analysis were performed to evaluate the prognostic value of MIR31HG. Gene set enrichment analysis (GSEA) was conducted to identify the potential carcinogenic mechanisms implicated in MIR31HG. Moreover, MIR31HG was knocked down using siRNA in colorectal cancer cells, and cell migration, invasion, growth and colony formation assays were performed. The expression of MIR31HG influenced gene markers was quantified by qRT-PCR in MIR31HG-silenced colorectal cancer cells.

Results

In TCGA database, we found that MIR31HG was elevated in colorectal cancer patients. The patients with high MIR31HG expression had poor overall survival and disease-specific survival. Univariable and multivariable analyses showed that MIR31HG expression was an independent prognostic predictor in colorectal cancer patients. GSEA revealed that MIR31HG mainly modulated focal adhesion, extracellular matrix organization, integrin cell surface interactions and focal adhesion-PI3K-Akt-mTOR-signaling pathway. Besides, MIR31HG knockdown significantly impaired colorectal cancer cell migration, invasion, growth and colony formation. Further qRT-PCR data confirmed that alteration of MIR31HG expression notably affected the tumorigenesis-related key gene expression in the cells.

Conclusion

Our findings provide evidence that MIR31HG is a key factor in maintaining the malignant phenotype of colorectal cancer and may act as an independent predictor for patients with colorectal cancer.

New treatment strategies for advanced-stage gastrointestinal stromal tumours

When gastrointestinal stromal tumour (GIST), the most common form of sarcoma, was first recognized as a distinct pathological entity in the 1990s, patients with advanced-stage disease had a very poor prognosis owing to a lack of effective medical therapies. The discovery of KIT mutations as the first and most prevalent drivers of GIST and the subsequent development of the first KIT tyrosine kinase inhibitor (TKI), imatinib, revolutionized the treatment of patients with this disease. We can now identify the driver mutation in 99% of patients with GIST via molecular diagnostic testing, and therapies have been developed to treat many, but not all, molecular subtypes of the disease. At present, seven drugs are approved by the FDA for the treatment of advanced-stage GIST (imatinib, sunitinib, regorafenib, ripretinib, avapritinib, larotrectinib and entrectinib), all of which are TKIs. Although these agents can be very effective for treating certain GIST subtypes, challenges remain and new therapeutic approaches are needed. In this Review, we discuss the molecular subtypes of GIST and the evolution of current treatments, as well as their therapeutic limitations. We also highlight emerging therapeutic approaches that might overcome clinical challenges through novel strategies predicated on the biological features of the distinct GIST molecular subtypes.

Phase II Trial of Imatinib Plus Binimetinib in Patients With Treatment-Naive Advanced Gastrointestinal Stromal Tumor

PURPOSE

Dual targeting of the gastrointestinal stromal tumor (GIST) lineage-specific master regulators, ETV1 and KIT, by MEK and KIT inhibitors were synergistic preclinically and may enhance clinical efficacy. This trial was designed to test the efficacy and safety of imatinib plus binimetinib in first-line treatment of GIST.

METHODS

In this trial (NCT01991379), treatment-naive adult patients with confirmed advanced GISTs received imatinib (400 mg once daily) plus binimetinib (30 mg twice daily), 28-day cycles. The primary end point was RECIST1.1 best objective response rate (ORR; complete response plus partial response [PR]). The study was designed to detect a 20% improvement in the ORR over imatinib alone (unacceptable rate of 45%; acceptable rate of 65%), using an exact binomial test, one-sided type I error of 0.08 and type II error of 0.1, and a planned sample size of 44 patients. Confirmed PR or complete response in > 24 patients are considered positive. Secondary end points included Choi and European Organisation for Research and Treatment of Cancer Response Rate, progression-free survival (PFS), overall survival (OS), pathologic responses, and toxicity.

RESULTS

Between September 15, 2014, and November 15, 2020, 29 of 42 evaluable patients with advanced GIST had confirmed RECIST1.1 PR. The best ORR was 69.0% (two-sided 95% CI, 52.9 to 82.4). Thirty-nine of 41 (95.1%) had Choi PR approximately 8 weeks. Median PFS was 29.9 months (95% CI, 24.2 to not estimable); median OS was not reached (95% CI, 50.4 to not estimable). Five of eight patients with locally advanced disease underwent surgery after treatment and achieved significant pathologic response (≥ 90% treatment effect). There were no unexpected toxicities. Grade 3 and 4 toxicity included asymptomatic creatinine phosphokinase elevation (79.1%), hypophosphatemia (14.0%), neutrophil decrease (9.3%), maculopapular rash (7.0%), and anemia (7.0%).

CONCLUSION

The study met the primary end point. The combination of imatinib and binimetinib is effective with manageable toxicity and warrants further evaluation in direct comparison with imatinib in frontline treatment of GIST.

A smooth muscle-derived, Braf-driven mouse model of gastrointestinal stromal tumor (GIST): evidence for an alternative GIST cell-of-origin

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumor of the gut. GISTs are thought to arise solely from interstitial cells of Cajal (ICC), a KIT-positive population that controls gut motility. Activating gain-of-function mutations in KIT and PDGFRA are the most frequent driver events, and most of these tumors are responsive to the tyrosine kinase inhibitor imatinib. Less common drivers include mutant BRAFV600E and these tumors are resistant to imatinib. A mouse model of GIST was recently reported using Etv1, the master transcriptional regulator of ICC-intramuscular (IM) and ICC-myenteric (MY), to induce mutant Braf expression. ICC hyperplasia was observed in Etv1CreERT2 ;BrafLSL-V600E/+ mice but loss of Trp53 was required for development of GIST. We identified previously expression of the pan-ErbB negative regulator, LRIG1, in two distinct subclasses of ICC [ICC-deep muscular plexus (DMP) in small intestine and ICC-submucosal plexus (SMP) in colon] and that LRIG1 regulated their development from smooth muscle cell progenitors. Using Lrig1CreERT2 to induce BrafV600E , we observed ICC hyperplasia beyond the confines of ICC-DMP and ICC-SMP expression, suggesting smooth muscle cells as the cell-of-origin. To examine this possibility, we selectively activated BrafV600E in smooth muscle cells. Myh11CreERT2 ;BrafLSL-V600E/+ mice developed not only ICC hyperplasia but also GIST and in the absence of Trp53 disruption. In addition to providing a simpler model for mutant Braf GIST, these results provide conclusive evidence for smooth muscle cells as an alternative cell-of-origin for GIST. © 2020 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Genomic Study of Chinese Quadruple-negative GISTs Using Next-generation Sequencing Technology

PURPOSE

Approximately 10% of gastrointestinal stromal tumors (GISTs) are devoid of KIT, PDGFRA (platelet-derived growth factor-alpha), BRAF, and SDH alterations. The aim of this study was to characterize molecular drivers in Chinese patients with quadruple-negative GISTs.

PATIENTS AND METHODS

In 1022 Chinese patients with GIST, mutations of KIT and PDGFRA were analyzed by direct sequencing. Of these mutations, 142 KIT/PDGFRA wild-type (WT) GISTs were detected, and succinate dehydrogenase (SDH) deficiency was determined using immunohistochemistry analysis of succinate dehydrogenase B. In 78 KIT/PDGFRA/SDH cases, we performed targeted 425 cancer-related gene analysis using next-generation sequencing. The correlation between molecular findings and clinicopathologic features was also analyzed.

RESULTS

We defined 72 quadruple-negative GISTs from enrollments. They featured nongastric localization with histologic characteristics of spindle cells and male predilection. An overall 27.78% (20/72) of quadruple-negative tumors carried TP53, and 25.00% (18/72) carried RB1 mutations, which were frequently associated with high mitotic index and large size. TP53 analyses demonstrated coexistence with mutational activation of other oncogenes in 12 of 20 cases. A total of 18 RB1-mutated cases were independent of TP53. Further, no tumors carried NF1 and BRAF mutations.

CONCLUSIONS

We report the genomic analysis of Chinese quadruple-negative patients. These databases may help advance our understanding of quadruple-negative GISTs' progression. Next-generation sequencing from GISTs is feasible to provide relevant data for guiding individualized therapy.

ETS variant 5 promotes colorectal cancer angiogenesis by targeting platelet-derived growth factor BB

ETS transcription factors play important roles in tumor cell invasion, differentiation and angiogenesis. In this study, we initially demonstrated that ETS translocation variant 5 (ETV5) is abnormally upregulated in colorectal cancer (CRC), is positively correlated with CRC tumor size, lymphatic metastasis and tumor node metastasis (TNM) stage and indicates shorter survival and disease-free survival in CRC patients. In vitro and in vivo experiments revealed that the downregulation of ETV5 could significantly suppress CRC cell proliferation. Moreover, overexpression of ETV5 could stimulate CRC angiogenesis in vitro and in vivo, which is consistent with RNA-seq results. Then, we identified platelet-derived growth factor BB (PDGF-BB) as a direct target of ETV5 that plays an important role in ETV5-mediated CRC angiogenesis through an angiogenesis antibody microarray. Additionally, PDGF-BB could activate VEGFA expression via the PDGFR-β/Src/STAT3 pathway in CRC cells and appeared to be positively correlated with ETV5 in CRC tissues. Finally, we revealed that ETV5 could bind directly to the promoter region of PDGF-BB and regulate its expression through ChIP and luciferase assays. Overall, our study suggested that the transcription factor ETV5 could stimulate CRC malignancy and promote CRC angiogenesis by directly targeting PDGF-BB. These findings suggest that EVT5 may be a potential new diagnostic and prognostic marker in CRC and that targeting ETV5 might be a potential therapeutic option for inhibiting CRC angiogenesis.

COP1/DET1/ETS axis regulates ERK transcriptome and sensitivity to MAPK inhibitors

Aberrant activation of MAPK signaling leads to the activation of oncogenic transcriptomes. How MAPK signaling is coupled with the transcriptional response in cancer is not fully understood. In 2 MAPK-activated tumor types, gastrointestinal stromal tumor and melanoma, we found that ETV1 and other Pea3-ETS transcription factors are critical nuclear effectors of MAPK signaling that are regulated through protein stability. Expression of stabilized Pea3-ETS factors can partially rescue the MAPK transcriptome and cell viability after MAPK inhibition. To identify the players involved in this process, we performed a pooled genome-wide RNAi screen using a fluorescence-based ETV1 protein stability sensor and identified COP1, DET1, DDB1, UBE3C, PSMD4, and COP9 signalosome members. COP1 or DET1 loss led to decoupling between MAPK signaling and the downstream transcriptional response, where MAPK inhibition failed to destabilize Pea3 factors and fully inhibit the MAPK transcriptome, thus resulting in decreased sensitivity to MAPK pathway inhibitors. We identified multiple COP1 and DET1 mutations in human tumors that were defective in the degradation of Pea3-ETS factors. Two melanoma patients had de novo DET1 mutations arising after vemurafenib treatment. These observations indicate that MAPK signaling-dependent regulation of Pea3-ETS protein stability is a key signaling node in oncogenesis and therapeutic resistance to MAPK pathway inhibition.