SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Gastrointestinal stromal tumor

176

Imatinib mesylate (Gleevec) inhibits Abl1, c-Kit, and related protein tyrosine kinases (PTKs) and serves as a therapeutic for chronic myelogenous leukemia and gastrointestinal stromal tumors. Imatinib also has efficacy against various pathogens, including pathogenic mycobacteria, where it decreases bacterial load in mice, albeit at doses below those used for treating cancer. We report that imatinib at such low doses unexpectedly induces differentiation of hematopoietic stem cells and progenitors in the bone marrow, augments myelopoiesis but not lymphopoiesis, and increases numbers of myeloid cells in blood and spleen. Whereas progenitor differentiation relies on partial inhibition of c-Kit by imatinib, lineage commitment depends upon inhibition of other PTKs. Thus, imatinib mimics “emergency hematopoiesis,” a physiological innate immune response to infection. Increasing neutrophil numbers by adoptive transfer sufficed to reduce mycobacterial load, and imatinib reduced bacterial load of Franciscella spp., which do not utilize imatinib-sensitive PTKs for pathogenesis. Thus, potentiation of the immune response by imatinib at low doses may facilitate clearance of diverse microbial pathogens.

Concepts: Immune system, Cancer, Bacteria, Bone marrow, Innate immune system, Tyrosine kinase, Imatinib, Gastrointestinal stromal tumor

173

Gastrointestinal stromal tumor (GIST) is the most common sarcoma of the gastrointestinal tract and arises from the interstitial cells of Cajal. It is characterized by expression of the receptor tyrosine kinase CD117 (KIT). In 70-80% of GIST cases, oncogenic mutations in KIT are present, leading to constitutive activation of the receptor, which drives the proliferation of these tumors. Treatment of GIST with imatinib, a small-molecule tyrosine kinase inhibitor, inhibits KIT-mediated signaling and initially results in disease control in 70-85% of patients with KIT-positive GIST. However, the vast majority of patients eventually develop resistance to imatinib treatment, leading to disease progression and posing a significant challenge in the clinical management of these tumors. Here, we show that an anti-KIT monoclonal antibody (mAb), SR1, is able to slow the growth of three human GIST cell lines in vitro. Importantly, these reductions in cell growth were equivalent between imatinib-resistant and imatinib-sensitive GIST cell lines. Treatment of GIST cell lines with SR1 reduces cell-surface KIT expression, suggesting that mAb-induced KIT down-regulation may be a mechanism by which SR1 inhibits GIST growth. Furthermore, we also show that SR1 treatment enhances phagocytosis of GIST cells by macrophages, indicating that treatment with SR1 may enhance immune cell-mediated tumor clearance. Finally, using two xenotransplantation models of imatinib-sensitive and imatinib-resistant GIST, we demonstrate that SR1 is able to strongly inhibit tumor growth in vivo. These results suggest that treatment with mAbs targeting KIT may represent an alternative, or complementary, approach for treating GIST.

Concepts: Immune system, Protein, Cancer, Bacteria, Signal transduction, Monoclonal antibodies, Enzyme inhibitor, Gastrointestinal stromal tumor

166

Gastrointestinal stromal tumors (GIST) arise within the interstitial cell of Cajal (ICC) lineage due to activating KIT/PDGFRA mutations. Both ICC and GIST possess primary cilia (PC), which coordinate PDGFRA and Hedgehog signaling, regulators of gastrointestinal mesenchymal development. Therefore, we hypothesized that Hedgehog signaling may be altered in human GIST and controls KIT expression. Quantitative RT-PCR, microarrays, and next generation sequencing were used to describe Hedgehog/PC-related genes in purified human ICC and GIST. Genetic and pharmacologic approaches were employed to investigate the effects of GLI manipulation on KIT expression and GIST cell viability. We report that Hedgehog pathway and PC components are expressed in ICC and GIST and subject to dysregulation during GIST oncogenesis, irrespective of KIT/PDGFRA mutation status. Using genomic profiling, 10.2% of 186 GIST studied had potentially deleterious genomic alterations in 5 Hedgehog-related genes analyzed, including in the PTCH1 tumor suppressor (1.6%). Expression of the predominantly repressive GLI isoform, GLI3, was inversely correlated with KIT mRNA levels in GIST cells and non-KIT/non-PDGFRA mutant GIST. Overexpression of the 83-kDa repressive form of GLI3 or small interfering RNA-mediated knockdown of the activating isoforms GLI1/2 reduced KIT mRNA. Treatment with GLI1/2 inhibitors, including arsenic trioxide, significantly increased GLI3 binding to the KIT promoter, decreased KIT expression, and reduced viability in imatinib-sensitive and imatinib-resistant GIST cells. These data offer new evidence that genes necessary for Hedgehog signaling and PC function in ICC are dysregulated in GIST. Hedgehog signaling activates KIT expression irrespective of mutation status, offering a novel approach to treat imatinib-resistant GIST.

Concepts: DNA, Gene, Genetics, Cell nucleus, Gene expression, Cell, Cancer, Gastrointestinal stromal tumor

165

BACKGROUND: Pigmented villonodular synovitis (PVNS) is a rare locally aggressive tumors. PVNS is characterized in most cases by a specific t(1;2) translocation, which fuses the colony stimulating factor-1 (CSF1) gene to the collagen type VIa3 (COL6A3) promoter thus leading through a paracrine effect to the attraction of non-neoplastic inflammatory cells expressing CSF1-receptor. Imatinib is a tirosin-kinase inhibitors (TKI) active against CSF1-receptor whose activity in naive PVNS was already described. We report on two PVNS patients who responded to imatinib after failure to nilotinib, another CSF1-receptor inhibitor. METHODS: Since August 2012, 2 patients with progressive, locally advanced PVNS resistant to nilotinib (Patient1: man, 34 years; Patient2: woman, 24 years) have been treated with second-line imatinib 400 mg/day. Both patients are evaluable for response. RESULTS: Both pts are still on treatment (7 and 4 months). Patient1 had a dimensional response by MRI after 2 months from starting imatinib, together with symptomatic improvement. In Patient2 a metabolic response was detected by [18F]fluorodeoxyglucose–positron emission tomography (PET) at 6 weeks coupled with tumor shrinkage by MRI, and symptomatic improvement CONCLUSIONS: Imatinib showed antitumor activity in 2 patients with nilotinib-resistant PVNS. This observation strengthen the idea that targeted agent with similar profile can give a different clinical result, as already described for gastrointestinal stromal tumor (GIST) patients treated with the same agents. Molecular studies are needed to clarify the biologic mechanism(s) underlying the response.

Concepts: Cancer, Oncology, Brain tumor, Radiation therapy, Enzyme inhibitor, Chronic myelogenous leukemia, Gastrointestinal stromal tumor, Pigmented villonodular synovitis

162

The use of potential surrogate endpoints for overall survival, such as disease-free-survival (DFS) or time-to-treatment failure (TTF) is increasingly common in randomized controlled trials (RCT) in cancer. However, the definition of time-to-event (TTE) endpoints is rarely precise and lacks uniformity across trials. Endpoint definition can impact trial results by affecting estimation of treatment effect and statistical power. The DATECAN initiative (Definition for the Assessment of Time-to-event Endpoints in CANcer trials) aims to provide recommendations for definitions of TTE endpoints. We report guidelines for RCT in sarcomas and gastro-intestinal-stromal tumors (GIST).

Concepts: Epidemiology, Cancer, Medical statistics, Randomized controlled trial, Statistical significance, Effect size, Gastrointestinal stromal tumor

26

Introduction: Gastrointestinal stromal tumors (GISTs) are abdominal sarcomas which are extremely refractory to chemotherapy treatment. The treatment of GISTs has been revolutionized by use of KIT/platelet-derived growth factor receptor-α (PDGFRA) kinase inhibitors. Unfortunately, most tumors develop resistance to front-line (imatinib) or second-line (sunitinib) therapy. Regorafenib, a KIT/PDGFRA/vascular endothelial growth factor receptor (VEGFR) oral kinase inhibitor, has been shown to improve progression-free survival in the third- or fourth-line setting. Areas covered: This review covers the preclinical and clinical studies of regorafenib for treatment of GIST. A literature search on regorafenib was carried out using the PubMed database up to October 2013. Expert opinion: Currently, imatinib and sunitinib represent the only proven first- and second-line therapies, respectively, for advanced GISTs. Based on the results of a Phase III study, regorafenib is now established as the only proven third-line therapy. Regorafenib activity in this setting is believed to be due to its activity against oncogenic forms of KIT/PDGFRA. Although side effects are common with this agent, they can be effectively managed with a combination of supportive care, dose interruptions/reductions. The toxicity profile is similar to other oral kinase inhibitors with anti-VEGFR activity. Regorafenib is mainly metabolized by CYP3A4, and concomitant use of strong inducers/inhibitors of this enzyme should be avoided.

Concepts: Immune system, Clinical trial, Cancer, Oncology, Signal transduction, Enzyme inhibitor, Gastrointestinal stromal tumor, Growth factor receptor

25

After identification of activating mutations of the KIT gene in gastrointestinal stromal tumor (GIST)-the most common sarcomaof the gastrointestinal tract-a phase 2 study demonstrated efficacy of imatinib mesylate in patients with metastatic GIST harboring a KIT exon 11 mutation. Initial results of long-term follow-up have found a survival benefit in this subgroup of patients.

Concepts: DNA, Cancer, Oncology, Evolution, DNA repair, Imatinib, Gastrointestinal stromal tumor, Mesylate

12

About 10-15% of adult, and most pediatric, gastrointestinal stromal tumors (GIST) lack mutations in KIT, PDGFRA, SDHx, or RAS pathway components (KRAS, BRAF, NF1). The identification of additional mutated genes in this rare subset of tumors can have important clinical benefit to identify altered biological pathways and select targeted therapies.

Concepts: DNA, Medicine, Gene, Genetics, Mutation, Natural selection, Evolution, Gastrointestinal stromal tumor

8

Gastrointestinal stromal tumors (GISTs) are composed of various molecular subtypes, with differing prognostic and predictive relevance. Previously, tumors lacking mutations in the KIT and PDGFRA genes have been designated as ‘wild-type’ GISTs; however, they represent a heterogeneous group currently undergoing further subclassification. Primary and secondary resistance to imatinib poses a significant clinical challenge, therefore ongoing research is trying to evaluate mechanisms to overcome resistance. Thorough understanding of the prognostic and predictive relevance of different genetic subtypes of GIST can guide clinical decision-making both in the adjuvant and the metastatic setting. Further work is required to identify tailored therapies for specific subgroups of GISTs wild-type for KIT and PDGFRA mutations and to identify predictive factors of resistance to currently approved systemic therapies.

Concepts: DNA, Medicine, Gene, Genetics, Cancer, Therapy, Gastrointestinal stromal tumor, Systemic therapy

6

Gastrointestinal stromal tumors (GISTs) have significant variability in size and malignant behavior. Our current understanding is limited to pathological analyses, autopsy studies, and small case series. The aim of the current study is to define the risk factors, incidence, and mortality rates of GIST <2 cm in the National Cancer Institute's Surveillance, Epidemiology, and End Results database.

Concepts: Epidemiology, Cancer, Oncology, Pathology, Medical statistics, United States, National Cancer Institute, Gastrointestinal stromal tumor