The Study On The Mechanism Of The Gastrointestinal Stromal Tumor Patients With Acquired Resistance To Imatinib Therapy

【Objective】1.To assess the efficacy and safety of imatinib mesylate in patients with unresectable and/or metastatic GIST or in adjuvant treatment.2.To explore the mechanisms responsible for the acquired resistance to imatinib.3.To characterize oncogenic KIT signaling mechanisms in GISTs,and to determine which signaling pathways might be of potential relevance to therapeutic interventions.【Methods】1.32 patients with GIST were analyzed for efficacy and safety retrospectively.Front-line imatinib treatment consisted of 400 mg once daily.Dose escalation to 600mg or 800 mg a day was allowed if the tumor progressed and the patients tolerated the initial dose.2.With the bidirectional DNA sequencing and the analysis of an ABI PRISM 310 capillary electrophoresis system,we sequenced the KIT and PDGFRA gene in the 32 GIST patients before or after imatinib treatment.3.Detected by Western blottying,ctivation of signaling intermediates was evaluated in GISTs with different KIT mutational mechanisms to evaluate the relevance of the type of KIT mutation for differential activation of signaling pathways.【Results】1.Of 32 patients with GIST,CD117-positive was confirmed in 28 cases(87.5%),and 23 patients(71.9%) were judged to be positive in expressing CD34.1 patient had CR(3.1%),10 patients(31.3%) achieved PR,9 patients(28.1%)had SD,and 4 patients(12.5%)had PD.8 patients(25%) who obtained neoadjuvant therapy after radical resection were alive without disease.9(28.1%) out of 32 patients had no adverse effects related to the drug.23 cases (71.9%)appeared mild adverse effects which were of gradeⅠorⅡ, including 17 patients had two or more side effects.3 patients(9.4%) displayed gradeⅢadverse reaction,and all cases had no adverse effects of gradeⅣ.2.In 22 of 32 cases carried activating mutations in KIT,17 cases were found mutations in exon 11 encoding the juxtamembrane domain,2 patients were found in exon 9,1 case was found mutation in exon 13. Two cases were found mutation in PDGFRA gene exon 18,and 8 patients were found no mutation in KIT and PDGFRA gene(Wild type).In 13 patients,including 9 patients who were secondary resistance to imatinib and 4 cases who were primary resistance to imatinib,secondary mutation were only identified in patients with acquired resistance to imatinib.Secondary KIT mutations were identified in 4 out of 9 imatinib-resistant patients.In 3 patients,we found an identical novel exon-17 missense mutation,T2467G, resulting in a substitution of Tyr by Asp at codon 823(Y823 D)in tyrosine kinase domain of KIT.We found a novel exon 13 missense mutation,A1924G,in the other one patient.3.KIT expressed strongly in all GIST patients.The level of p-KIT expression decreased dramatically in patients with GIST after imatinib therapy,especially in patients who obtained CR during the treatment,nonetheless,p-KIT expression increased when the GIST patients acquired resistance.The level of MAPK,p-MAPK,and p-MTOR expression in all GIST patients were strong,and the deference were no significace.P-AKT expressed strongly in untreated GIST patients and in GIST patients who showed secondary resistance to imatinib,by contrast,the level of p-AKT expression in GIST patients who responsed to imatinib were lower.Of all GIST patients,the level of PCNA and BCL2 expression were similar. PAKT expression in untreated GIST patients and in GIST patients who showed secondary resistance to imatinib were stronger than other GIST patients who responsed to imatinib.【Conclusion】1.Imatinib is generally safe and has significant activity in the treatment of GIST patients.Most of the adverse effects were mild and manageable.2.The exon-17 missense mutation,T2467G,and exon 13 missense mutation,A1924G,in tyrosine kinase domain of KIT are correlated with imatinib resistance.3.Signal transduction pathways such as RAS/RAF/MAPK and PI3-K/AKT/MTOR pathways are constitutively activated in a KIT-dependent manner.They are essential to GIST pathogenesis,and the PI3-K/AKT/MTOR pathway is particularly relevant for therapeutic targeting in imatinib-resistant GIST.