Orally Bioavailable Cyclin A/B RxL Inhibitors: Optimization of a Novel Class of Macrocyclic Peptides That Target E2F-High and G1-S-Checkpoint-Compromised Cancers

Cyclins A and B bind and activate their cognate cyclin-dependent kinase (CDK) to regulate progression through the S and G2/M phases of the cell cycle, respectively. Cyclins recruit substrates and regulators through the binding of an RxL motif with a Hydrophobic Patch (HP) on the cyclin surface. We recently disclosed the first class of passively permeable macrocyclic peptides that bind to the HP of both Cyclin A and Cyclin B and selectively kill cancer cells with high E2F activity. We used a lead example to demonstrate in vivo tumor regression in cell-line-derived xenograft models of small-cell lung cancer (SCLC) via intraperitoneal dosing. Here we describe the optimization of this series for drug-like properties and oral bioavailability, resulting in the discovery of a lead compound, which demonstrates tumor regression in CDX models of SCLC via oral dosing. We are currently evaluating Cyclin A/B inhibition in a Phase 1 clinical trial.