A novel PDGFRA mutation in gastrointestinal stromal tumours, L839P, is sensitive to imatinib in vitro

Evidence suggests that different types of mutation in gastrointestinal stromal tumours (GISTs) correlate with different response rates to imatinib (Glivec, STI571). The purpose of this study was to explore the sensitivity of the PDGFRA(L839P) mutant, a novel gain-of-function mutation isoform related to GISTs, to imatinib in vitro. The eukaryotic expression vectors pcDNA3.1-PDGFRA(Wild), pcDNA3.1-PDGFRA(D842V) and pcDNA3.1-PDGFRA(L839P) were constructed and transfected into Chinese hamster ovary (CHO) cells by liposome methods. The responses of cells with PDGFRA(Wild), PDGFRA(L839P) and PDGFRA(D842V) mutants to imatinib were determined by methyl thiazolyl tetrazolium (MTT) assay, western blotting and apoptosis assays. Reults of the MTT assay revealed that the growth rate of CHO(PDGFRA(L839P)) cells decreased to approximately 60% when exposed to 1 mu M imatinib and to approximately 50% with 5 mu M imatinib. However, the growth rate of CHO(PDGFRA(D842V)) cells did not significantly change with 5 mu M imatinib. Western blot analysis indicated that 1 mu M imatinib completely blocked the phosphorylation of PDGFRA(L839P), but did not affect PDGFRA(D842V) phosphorylation. Apoptosis analysis suggested that the percentage of apoptotic CHO(PDGFRA(L839P)) cells increased approximately 4-fold (from 5.90 to 25.2%) with 1 mu M imatinib. Although the treatment of CHO(PDGFRA(D842V)) and CHO(PDGFRA(Wild)) cells with 5 mu M imatinib resulted in a slight increase in the number of apoptotic cells, the percentage of apoptotic cells remained approximately 10% of the total population. Our findings showed that the PDGFRA gene mutation isoform L839P is sensitive to inhibition by imatinib. Screening for PDGFRA mutations in GISTs is essential to identify the response to treatment with imatinib.