ABSTRACT
First generation EGFR TKIs (gefitinib, erlotinib) provide significant clinical benefit for NSCLC cancer patients with oncogenic EGFR mutations. Ultimately, these patients' disease progresses, often driven by a second-site mutation in the EGFR kinase domain (T790M). Another liability of the first generation drugs is severe adverse events driven by inhibition of WT EGFR. As such, our goal was to develop a highly potent irreversible inhibitor with the largest selectivity ratio between the drug-resistant double mutants (L858R/T790M, Del/T790M) and WT EGFR. A unique approach to develop covalent inhibitors, optimization of reversible binding affinity, served as a cornerstone of this effort. PF-06459988 was discovered as a novel, third generation irreversible inhibitor, which demonstrates (i) high potency and specificity to the T790M-containing double mutant EGFRs, (ii) minimal intrinsic chemical reactivity of the electrophilic warhead, (iii) greatly reduced proteome reactivity relative to earlier irreversible EGFR inhibitors, and (iv) minimal activity against WT EGFR.
Subject(s)
Drug Discovery , ErbB Receptors/antagonists & inhibitors , ErbB Receptors/genetics , Mutant Proteins/antagonists & inhibitors , Protein Kinase Inhibitors/pharmacology , Pyrimidines/pharmacology , Pyrroles/pharmacology , Carcinoma, Non-Small-Cell Lung/drug therapy , Carcinoma, Non-Small-Cell Lung/genetics , Dose-Response Relationship, Drug , Humans , Lung Neoplasms/drug therapy , Lung Neoplasms/genetics , Models, Molecular , Molecular Structure , Mutation , Protein Kinase Inhibitors/chemical synthesis , Protein Kinase Inhibitors/chemistry , Pyrimidines/chemical synthesis , Pyrimidines/chemistry , Pyrroles/chemical synthesis , Pyrroles/chemistry , Structure-Activity Relationship , Tumor Cells, CulturedABSTRACT
Rapid mutations of proteins that are targeted in cancer therapy often lead to drug resistance. Often, the mutation directly affects a drug's binding site, effectively blocking binding of the drug, but these mutations can have other effects such as changing the protein turnover half-life. Utilizing SILAC MS, we measured the cellular turnover rates of an important non-small cell lung cancer target, epidermal growth factor receptor (EGFR). Wild-type (WT) EGFR, EGFR with a single activating mutant (Del 746-750 or L858R), and the drug-resistant double mutant (L858R/T790M) EGFR were analyzed. In non-small cell lung cancer cell lines, EGFR turnover rates ranged from 28 hours in A431 cells (WT) to 7.5 hours in the PC-9 cells (Del 746-750 mutant). The measurement of EGFR turnover rate in PC-9 cells dosed with irreversible inhibitors has additional complexity due to inhibitor effects on cell viability and results were reported as a range. Finally, essential amino acid recycling (K and R) was measured in different cell lines. The recycling was different in each cell line, but the overall inclusion of the effect of amino acid recycling on calculating EGFR turnover rates resulted in a 10-20% reduction in rates.
ABSTRACT
Pteridinones were designed based on a non-selective kinase template. Because of the uniqueness of the PI3K and mTOR binding pockets, a methyl group was introduced to C-4 position of the peteridinone core to give compounds with excellent selectivity for PI3K and mTOR. This series of compounds were further optimized to improve their potency against PI3Kα and mTOR. Finally, orally active compounds with improved solubility and robust in vivo efficacy in tumor growth inhibition were identified as well.
Subject(s)
Antineoplastic Agents/chemistry , Antineoplastic Agents/therapeutic use , Phosphoinositide-3 Kinase Inhibitors , Protein Kinase Inhibitors/chemistry , Protein Kinase Inhibitors/therapeutic use , Pteridines/chemistry , Pteridines/therapeutic use , TOR Serine-Threonine Kinases/antagonists & inhibitors , Administration, Oral , Animals , Antineoplastic Agents/administration & dosage , Antineoplastic Agents/pharmacology , Cell Line, Tumor , Glioma/drug therapy , Humans , Mice , Models, Molecular , Neoplasms/drug therapy , Phosphatidylinositol 3-Kinases/chemistry , Phosphatidylinositol 3-Kinases/metabolism , Protein Kinase Inhibitors/administration & dosage , Protein Kinase Inhibitors/pharmacology , Pteridines/administration & dosage , Pteridines/pharmacology , Solubility , Structure-Activity Relationship , TOR Serine-Threonine Kinases/chemistry , TOR Serine-Threonine Kinases/metabolismABSTRACT
Checkpoint kinase 1 (CHK1) is a key element in the DNA damage response pathway and plays a crucial role in the S-G(2)-phase checkpoint. Inhibiting CHK1 is a therapeutic strategy involving abrogation of the G2/M mitotic checkpoint defense of tumor cells toward lethal damage induced by DNA-directed chemotherapeutic agents. To date, most CHK1 inhibition approaches have involved targeting the ATP site of this kinase. In this study, we provide crystallographic and kinetic characterization of two small molecule inhibitors that bind to an allosteric site in the proximity of the CHK1 substrate site. Analysis of kinetic and biophysical data has led to the conclusion that these small molecule allosteric site inhibitors of CHK1 are reversible and are neither ATP- nor peptide substrate-competitive. K(i) values of 1.89 and 0.15 microM, respectively, have been determined for these compounds using a mixed inhibitor kinetic analysis. Cocrystal structures of the inhibitors bound to CHK1 reveal an allosteric site, unique to CHK1, located in the C-terminal domain and consisting of a shallow groove linked to a small hydrophobic pocket. The pocket displays induced fit characteristics in the presence of the two inhibitors. These findings establish the potential for the development of highly selective CHK1 inhibitors.
