Establishment and characterization of novel cell lines and xenografts from patients with gastrointestinal stromal tumors

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.

The role of novel fusion genes in human GIST cell lines derived from imatinib-resistant GIST patients: A therapeutic potential of fusion gene

Gastrointestinal stromal tumor (GIST) is the most common sarcoma in the gastrointestinal (GI) tract. Approximately 85% of the GIST is associated with a c-KIT mutation. A few GISTs show mutations in the gene encoding platelet-derived growth factor receptor alpha (PDGFR α or PDGFRA) without c-KIT gene mutation. GIST without c-KIT or PDGFRA mutations, which called wild type GIST, is about 5-10% of the total GIST. Fusion genes were also reported as one of the factors associated with carcinogenesis and drug resistance. With five cell lines derived from imatinib-resistant patients, novel fusion genes were identified from RNA sequencing and both physiological role and therapeutic potential were elucidated. Next-generation sequencing (NGS) analysis and lentiviral transduction were used to effect of fusion gene on GISTs. All the GIST cell lines carried c-KIT-positivity. Three different fusion gene analysis methods were used to find candidate fusion genes, including EIF3K-ACTN4, SYNCRIP-SNX14 and EXOC2-AK7. A novel interchromosomal fusion gene of the candidates, especially EXOC2-AK7, was confirmed in both tissue and cell line. The transduction of fusion gene increased the proliferation compared with the control group. Additionally, the fusion gene increased wound coverage capability. The fusion gene-transduced cell lines were more sensitive than the control group in the treatment of imatinib. In conclusion, five different imatinib-resistant GIST cell lines including the EXOC2-AK7 fusion gene derived from GIST-R5 represent important research tools for the investigation of cancer cell mechanisms underlying drug resistance and genetic variation. Furthermore, our study may facilitate pre-clinical studies of new therapeutic strategies.

Current status of publicly available sarcoma cell lines for use in proteomic studies

Cell lines are valuable resources for proteomic studies and can be used as tools to verify the significance of proteomic findings. Here, the authors overview the current status of the publicly available sarcoma cell lines. The authors surveyed seven major cell banks and found that the diversity observed in the sarcoma cell banks was largely insufficient; sarcoma cell lines are available for only a limited histological subtype. They also observed a number of issues with the pathological diagnosis of the cell lines, limitations in their behavioral diversity, and various unmet needs. Well characterized cell lines with accurate diagnosis based on modern diagnosis criteria should be available from public cell banks. The authors conclude that additional cell lines, along with detailed genetic and pathological analyses, should be prepared and deposited in order to promote sarcoma-specific proteomic research. The authors focused on sarcoma cell lines, but their discussion can be applied to the other cancers.

Antitumor effect of the tyrosine kinase inhibitor nilotinib on gastrointestinal stromal tumor (GIST) and imatinib-resistant GIST cells

Despite the benefits of imatinib for treating gastrointestinal stromal tumors (GIST), the prognosis for high risk GIST and imatinib-resistant (IR) GIST remains poor. The mechanisms of imatinib resistance have not yet been fully clarified. The aim of the study was to establish imatinib-resistant cell lines and investigate nilotinib, a second generation tyrosine kinase inhibitor (TKI), in preclinical models of GIST and imatinib-resistant GIST. For a model of imatinib-resistant GIST, we generated resistant cells from GK1C and GK3C cell lines by exposing them to imatinib for 6 months. The parent cell lines GK1C and GK3C showed imatinib sensitivity with IC₅₀ of 4.59±0.97 µM and 11.15±1.48 µM, respectively. The imatinib-resistant cell lines GK1C-IR and GK3C-IR showed imatinib resistance with IC₅₀ values of 11.74±0.17 µM (P<0.001) and 41.37±1.07 µM (P<0.001), respectively. The phosphorylation status of key cell signaling pathways, receptor tyrosine kinase KIT (CD117), platelet-derived growth factor receptor alpha (PDGFRA) and downstream signaling kinases: serine-threonine kinase Akt (AKT) and extracellular signal-regulated kinase 1/2 (ERK1/2) or the non-receptor tyrosine kinase: proto-oncogene tyrosine-protein kinase Src (SRC), was analyzed in established cell lines and ERK1/2 phosphorylation was found to be increased compared to the parental cells. Nilotinib demonstrated significant antitumor efficacy against GIST xenograft lines and imatinib-resistant GIST cell lines. Thus, nilotinib may have clinical potential for patients with GIST or imatinib-resistant GIST.