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GIST: Assessment of Tumor Mutations and TKI Plasma Exposure

ABSTRACT: Gastrointestinal stromal tumors (GISTs) belong to the sarcoma group and are characterized by oncogenic mutations in the c-KIT, PDGFRA, BRAF and NF-1 genes that drive tumor growth. Since tyrosine kinase inhibitors (TKIs) have become available, the median survival of GIST patients increased from 9 months to over 5 years. Consequently, this rare disease has become a role model for other targeted therapies. However, response to TKIs is extremely heterogeneous: ~15% of the patients experience no benefit from imatinib, whereas ~17% of the patients enjoy stable disease for over 9 years. Treatment failure due to primary and secondary resistance is caused in part by mutations in oncogenic genes that cause change in drug sensitivity. A new technique, using circulating tumor DNA, has enabled us to assess mutations in a simple blood sample obtained from patients on treatment, and thus detect new mutations early in the course of the disease. Also, differences in pharmacokinetic drug behavior add to the observed heterogeneity, and may cause resistance due to drug underexposure and thereby proliferation of the least sensitive tumor cells. This offers the opportunity to optimize and personalize targeted treatment for individual GIST patients by timely treatment adaptation based on early detection of secondary TKIs resistance mutations. Achieving this urgently requires data on daily clinical practice, including prospective serial mutation analysis and serial drug plasma concentration measurement. At a fundamental level this will also help to unravel the driving factors behind primary and secondary TKIs resistance in this model disease.

DISEASE(S): Gastro-intestinal Stromal Tumor,Gastrointestinal Stromal Tumors

PROVIDER: 2181421 | ecrin-mdr-crc |

REPOSITORIES: ECRIN MDR

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Project description:GISTs are the most common mesenchymal tumors and they display neuromuscular features. Gain-of-function mutations in KIT or PDGFRA are the initiating event in most of the cases and KIT oncogenic signaling is essential throughout all the disease. Interestingly, KIT oncogenic signaling is driven by PI3K/mTOR and RAS/MAPK pathways regardless of KIT primary or secondary mutations. Hence, dissection of KIT-downstream pathways may result in the identification of novel KIT critical effectors and a new opportunity to overcome disease heterogeneity of resistance mechanisms in GIST. Using human clinically representative GIST cell models, we undertook pharmacological and functional screenings such as Cell titer glo, kinase activation, apoptosis induction and proliferation to identify key signaling nodes within PI3K/mTOR and RAS/MAPK pathways. In vitro and in vivo validations were undertaken to model novel therapeutic strategies. Transcriptomic analysis (RNAseq) found essential genes co-regulated by both pathways. Functional studies, such as immunofluorescence, kinase activation, flow cytometry and proliferation were performed on a viral gene overexpression and knock-down models to elucidate their regulation and potential role in GIST biology. PI3K/mTOR and MEK1/2 are the most essential KIT-downstream mediators. Single node inhibition did not yield sustained antiproliferative and apoptotic effect, but simultaneous intermittent ablation was synergistic in vitro and in vivo, supporting the critical role of these two pathways.Transcriptomic analyses underscored FBXO32 (a SCF E3 ubiquitin-ligase and the main effector of muscular atrophy) as the most differentially expressed gene co-regulated by PI3K/mTOR and RAS/MAPK pathways. Functional studies demonstrated that FBXO32 is transcriptionally activated by FOXO3a which, in turn, is regulated by PI3K/mTOR and RAS/MAPK pathways. Notoriously, FBXO32 proved to have a pro-survival role in GIST cells. Microarray studies hinted a participation of FBXO32 in cell cycle arrest, which has been previously described as an adaptive pro-survival mechanism in GIST cells. This mechanism was further confirmed by functional studies. Remarkably, FBXO32 was expressed upon KIT inhibition in a panel of GIST cell lines, regardless the mutational status of KIT, and in a gene set database from GIST patients treated with first-line treatment, imatinib. PI3K/mTOR and MEK1/2 are the critical mediators of KIT oncogenic signaling in GIST, and their intermittent co-inhibition is an effective and well-tolerated therapeutic strategy to treat GIST tumors, independently of their KIT mutational status. FBXO32 emerges as a common mediator of KIT-downstream PI3K/mTOR and RAS/MAPK pathways with a critical pro-survival role in GIST participating in cell cycle arrest as pro-survival mechanism.

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GIST: Assessment of Tumor Mutations and TKI Plasma Exposure

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