title: Covalent EGFR inhibitor analysis reveals importance of reversible interactions to potency and mechanisms of drug resistance.
abstract: Covalent inhibition is a reemerging paradigm in kinase drug design, but the roles of inhibitor binding affinity and chemical reactivity in overall potency are not well-understood. To characterize the underlying molecular processes at a microscopic level and determine the appropriate kinetic constants, specialized experimental design and advanced numerical integration of differential equations are developed. Previously uncharacterized investigational covalent drugs reported here are shown to be extremely effective epidermal growth factor receptor (EGFR) inhibitors (kinact/Ki in the range 10(5)-10(7) M(-1)s(-1)), despite their low specific reactivity (kinact ≤ 2.1 × 10(-3) s(-1)), which is compensated for by high binding affinities (Ki < 1 nM). For inhibitors relying on reactivity to achieve potency, noncovalent enzyme-inhibitor complex partitioning between inhibitor dissociation and bond formation is central. Interestingly, reversible binding affinity of EGFR covalent inhibitors is highly correlated with antitumor cell potency. Furthermore, cellular potency for a subset of covalent inhibitors can be accounted for solely through reversible interactions. One reversible interaction is between EGFR-Cys797 nucleophile and the inhibitor's reactive group, which may also contribute to drug resistance. Because covalent inhibitors target a cysteine residue, the effects of its oxidation on enzyme catalysis and inhibitor pharmacology are characterized. Oxidation of the EGFR cysteine nucleophile does not alter catalysis but has widely varied effects on inhibitor potency depending on the EGFR context (e.g., oncogenic mutations), type of oxidation (sulfinylation or glutathiolation), and inhibitor architecture. These methods, parameters, and insights provide a rational framework for assessing and designing effective covalent inhibitors.
authors.affiliation: Oncology Research Unit, Worldwide Medicinal Chemistry, and Pharmacokinetics and Drug Metabolism, Pfizer Worldwide Research and Development, La Jolla, Pfizer Inc., San Diego, CA 92121.
authors.forename: Phillip A
authors.initials: PA
authors.lastname: Schwartz
authors.forename: Petr
authors.initials: P
authors.lastname: Kuzmic
authors.forename: James
authors.initials: J
authors.lastname: Solowiej
authors.forename: Simon
authors.initials: S
authors.lastname: Bergqvist
authors.forename: Ben
authors.initials: B
authors.lastname: Bolanos
authors.forename: Chau
authors.initials: C
authors.lastname: Almaden
authors.forename: Asako
authors.initials: A
authors.lastname: Nagata
authors.forename: Kevin
authors.initials: K
authors.lastname: Ryan
authors.forename: Junli
authors.initials: J
authors.lastname: Feng
authors.forename: Deepak
authors.initials: D
authors.lastname: Dalvie
authors.forename: John C
authors.initials: JC
authors.lastname: Kath
authors.forename: Meirong
authors.initials: M
authors.lastname: Xu
authors.forename: Revati
authors.initials: R
authors.lastname: Wani
authors.forename: Brion William
authors.initials: BW
authors.lastname: Murray
mesh_terms: D000970:Antineoplastic Agents / Q000138:chemical synthesis / Q000494:pharmacology; D002384:Catalysis; D045744:Cell Line, Tumor; D002626:Chemistry, Pharmaceutical; D003545:Cysteine / Q000737:chemistry; D015195:Drug Design; D004351:Drug Resistance; D004791:Enzyme Inhibitors / Q000138:chemical synthesis* / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D066246:ErbB Receptors / Q000037:antagonists & inhibitors* / Q000737:chemistry; D006801:Humans; D020128:Inhibitory Concentration 50; D013058:Mass Spectrometry; D010100:Oxygen / Q000737:chemistry; D010766:Phosphorylation; D011485:Protein Binding; D011487:Protein Conformation; D011799:Quinazolines / Q000737:chemistry; D015398:Signal Transduction
chemical_list: D000970:Antineoplastic Agents; D004791:Enzyme Inhibitors; D011799:Quinazolines; D066246:ErbB Receptors; D003545:Cysteine; D010100:Oxygen
keywords: capture period; cysteine oxidation; protein kinase; signaling; warhead interactions