and Leu858Arg/Thr790Met Calcium Channel review EGFR was performed . Interestingly, the Leu858Arg mutant has a 30 fold higher Km for ATP than wild type EGFR. However, the Thr790Met gatekeeper mutation restores the Km of Leu858Arg to 8.4 M. Thus, it is the lower Km for ATP that causes the drug resistance conferred by the double mutant of EGFR. Notably, the gatekeeper mutation alone does not alter the Km of the kinase for ATP, the structural bases for how these mutations affect EGFR,s Km for ATP are not understood. Thus, the Leu858Arg mutation contributes to EGFR,s sensitivity to erlotinib, gefitinib and AEE788 by altering its Km for ATP, which allows these inhibitors to effectively outcompete the high intra cellular concentrations of ATP.
Conversion of the gatekeeper residue of the Leu858Arg mutant from a threonine to a methionine restores this enzyme,s low micromolar Km for ATP and reduces the effectiveness of these inhibitors in cells. The Thr790Met Bafetinib gatekeeper represents a generic resistance mutation that will affect any ATP competitive inhibitor, independent of which interactions they make with the ATP binding cleft. Pre clinical cellular studies have shown that irreversible inhibitors such as neratinib and EKB 569 are able to effectively inhibit the Thr790Met mutant of EGFR kinase. These inhibitors are able to achieve greater ATP binding site occupancy in this kinase by forming a covalent bond with an active site cysteine. For example, neratinib proved to be considerably more effective than gefitinib in suppressing EGFR auto phosphorylation and phosphorylation of downstream effectors AKT and MAPK in a NCI H1975 bronchoalveolar cancer cell line harboring the Leu858Arg/Thr790Met mutant.
However, in clinical settings involving patients with the Thr790Met resistance mutation, irreversible inhibitors have demonstrated only limited success and dose limiting toxicity has been observed. A series of irreversible inhibitors that were specifically developed to target the Thr790Met mutant of EGFR were recently reported. These inhibitors, which are based on an anilinopyrimidine based core rather than a 4 anilinoquinazoline scaffold, are significantly more potent against gefitinib resistant cell lines than previously described irreversible inhibitors. Furthermore, these covalent inhibitors are selective for the Thr790Met EGFR mutant over the wild type kinase.
A crystal structure of an analog from this series bound to the Thr790Met EGFR kinase catalytic domain provides an explanation for the increased potency of the anilinopyrimidine based inhibitors against the gatekeeper mutant. While gefitinib and other 4 anilinoquinazoline based inhibitors are able to avoid a steric clash with the methionine gatekeeper residue, a substituent from the anilinopyrimidine based core forms a favorable interaction with this residue. This interaction most likely contributes to the increased potencies observed for these inhibitors and helps explain their selectivity for the gatekeeper mutant over wild type EGFR. Importantly, the most selective compound in this series was found to cause significant tumor regression in Thr790Met containing murine models with a minimal amount of observed toxicity. While extensive testing is needed to determine if any of these inhibitors will be of clinical utility, the development of mutant selective kinase inhibitors appears