Response to treatment with chemical and biological inhibitors of c-met mutated form

c-MET is a receptor tyrosine kinase that, after binding with its ligand, hepatocyte growth factor (HGF), activates many signaling pathways, driving proliferation, motility, migration and invasion. Although c-MET is important in the control of tissue homeostasis under normal physiological conditions, it has also been found to be aberrantly activated in human cancers via mutation, amplification or protein overexpression. Activating point mutations were identified in the kinase domain of MET, either in the germline of patients affected by hereditary papillary renal carcinoma (HPRC) or in spontaneously occurring tumors; in particular, nine missense mutations (defined METPRC mutations), leading to constitutive activation of MET protein, have been identified in HPRC families. Given the importance of MET as a target for cancer therapies, clinical trials aimed at inhibiting it through the use of tyrosine kinase inhibitors (TKIs) have recently been started. The aim of project was: (i) to evaluate if METPRC mutants are sensitive to PHA-665752 (a small kinase inhibitor of MET), (ii) if some mutants are insensitive to the inhibitor, to investigate the mechanisms responsible for resistance, (iii) to check if the resistant mutants are still sensitive to other chemicals inhibitors or monoclonal antibodies against MET, (iv) to identify activating point mutations in human surgically resected lung cancers. We have found that some METPRC mutants cannot be inhibited by PHA-665752. Treatment with this TKI does not alter either receptor phosphorylation or MET mutants-induced biological activities (migration, invasion, anchorage-independent growth). We showed that these mutants are insensitive also to JNJ-38877605, a multitargeted tyrosine kinase inhibitor.. When we performed the mutational analysis on lung cancer samples, in one tumor we found the presence of one of the identified“resistant” mutations. To determine whether the mutants resistant to PHA-665752 could be inhibited with other strategies, we treated the mutant-expressing cells with the monoclonal antibody DN30, directed against the extracellular portion of the receptor. Our results showed that DN30 was indeed able to inhibit all the METPRC mutants. In conclusion, we have identified some METPRC mutants which do not respond to the ATP competitive kinase inhibitors. Since the identified METPRC mutations are located in the kinase domain and alter its conformation; it is likely that the competitive inhibitors are unable to interact with the ATP binding site in the context of the mutated receptors; this would render these mutants "resistant" to the action of tyrosine kinase inhibitors. However, these mutated forms still remain responsive to treatment antibodies directed against the MET extracellular portion: This observation is important since the use of monoclonal antibodies represent a therapeutic alternative for patients with tumors carrying MET mutants resistant to TKIs.