Rational Design of a Potent, Selective, and Metabolically Stable CDK9 Inhibitor to Counteract Osimertinib Resistance through Mcl-1 Suppression and Enhanced BRD4 Co-Targeting

Overcoming osimertinib resistance in NSCLC treatment remains a significant clinical challenge. CDK9 has emerged as a promising target due to its critical role in sustaining oncogenic transcriptional programs, particularly via Mcl-1 regulation. Herein, we report the structure-guided optimization of a previously identified CDK9 inhibitor (<b>Z11</b>), resulting in the discovery of <b>T7</b>, a potent, selective, and metabolically stable candidate (IC₅₀ = 1.2 nM). <b>T7</b> effectively suppressed cell proliferation, reduced colony formation, and induced apoptosis in Osimertinib-resistant NSCLC cells by downregulating Mcl-1. Furthermore, <b>T7</b> significantly inhibited the growth of resistant organoids and demonstrated marked antitumor efficacy in a xenograft model. Notably, combining <b>T7</b> with the BRD4 inhibitor <b>JQ1</b> further enhanced antitumor activity both in vitro and in vivo, revealing a complementary therapeutic strategy. These findings identify <b>T7</b> as a promising next-generation CDK9 inhibitor for addressing Osimertinib resistance in NSCLC and underscore the potential of transcriptional cotargeting approaches to improve clinical outcomes.