Multi-Water Bridges Enable Design of BET BD1-Selective Inhibitors for Pancreatic Cancer Therapy

Rational design of bromodomain (BD)-selective inhibitors could mitigate on-target toxicities associated with pan-BET inhibition but is challenging despite the availability of high-resolution structures. By simultaneously forming water bridges with BD1-specific residues in both the BC ring and the ZA channel, we identified a potent and orally bioavailable BET BD1-selective inhibitor <b>DDO-8958</b>, which exhibited a <i>K</i>_D of 5.6 nM for BRD4 BD1 and a 214-fold selectivity for BRD4 BD1 over BD2. The cocrystal structure demonstrated a unique multi-water bridge mechanism involving BD1-specific residues K91- and D145-driven BD1 selectivity. <b>DDO-8958</b> extensively influenced the oncogene expression and metabolic pathway, including oxidative phosphorylation in MIA PaCa-2. <i>In vivo</i>, <b>DDO-8958</b> inhibited tumor growth and markedly augmented the therapeutic efficacy of the glycolysis inhibitor 2-DG. These findings illuminate that multi-water bridges enable design of BD1-selective inhibitors and a therapeutic strategy involving combined targeting of BD1-induced epigenetic reprogramming and glycolysis pathways for the management of pancreatic cancer.