Structural Optimization and Structure–Activity Relationship Studies of 6,6-Dimethyl-4-(phenylamino)-6<i>H</i>-pyrimido[5,4-<i>b</i>][1,4]oxazin-7(8<i>H</i>)-one Derivatives as A New Class of Potent Inhibitors of Pan-Trk and Their Drug-Resistant Mutants

Abstract

Tropomyosin receptor kinases (TrkA, TrkB, and TrkC) are attractive therapeutic targets for multiple cancers. Two first-generation small-molecule Trks inhibitors, larotrectinib and entrectinib, have just been approved to use clinically. However, the drug-resistance mutations of Trks have already emerged, which calls for new-generation Trks inhibitors. Herein, we report the structural optimization and structure-activity relationship studies of 6,6-dimethyl-4-(phenylamino)-6<i>H</i>-pyrimido[5,4-<i>b</i>][1,4]oxazin-7(8<i>H</i>)-one derivatives as a new class of pan-Trk inhibitors. The prioritized compound <b>11g</b> exhibited low nanomolar IC₅₀ values against TrkA, TrkB, and TrkC and various drug-resistant mutants. It also showed good kinase selectivity. <b>11g</b> displayed excellent <i>in vitro</i> antitumor activity and strongly suppressed Trk-mediated signaling pathways in intact cells. In <i>in vivo</i> studies, compound <b>11g</b> exhibited good antitumor activity in BaF3-TEL-TrkA and BaF3-TEL-TrkC^G623R allograft mouse models without exhibiting apparent toxicity. Collectively, <b>11g</b> could be a promising lead compound for drug discovery targeting Trks and deserves further investigation.