Imatinib response in two GIST patients carrying two hitherto functionally uncharacterized PDGFRA mutations: an imaging, biochemical and molecular modeling study

Beside the well known in vivo and in vitro Imatinib resistant D842V mutation in PDGFRA receptor, very few are the information concerning the in vivo Imatinib activity with respect to the other PDGFRA mutations for which only in vitro data are available. Two patients carrying PDGFRA mutations in exons 18 (involving residues DIMH842-845) and 12 (V561D), respectively, were treated with Imatinib at a dose of 400 mg/day. According to Response Evaluation Criteria in Solid Tumors criteria, after a median treatment of 7 months both patients showed clinical partial response, and underwent surgery of the minimal residual disease. Tumor response was confirmed pathologically. In both patients, analyses of PDGFRA performed on pre- and/or post-treatment material were compared to affinity data of the mutated receptor towards the inhibitor. Molecular modeling evidence was found to be consistent with sensitivity of mutated PDGFRA receptors to Imatinib. Thus, the in vivo evidence that these two mutations of PDGFRA are sensitive to Imatinib was confirmed by a multidimensional approach comprising in silico experiments that, in association to molecular and biochemical analyses, constitutes a powerful tool to predict Imatinib sensitivity, clinically beneficial in the treatment of these tumors with molecularly targeted therapies.