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.

Utilizing structure-based design, we have discovered a family of cell-permeable macrocyclic Cyclin A/B RxL inhibitors that show potent and selective activity against RB1/E2F-dysregulated cancer cell lines. Lead compound 34 demonstrated proof-of-concept efficacy via intraperiotoneal (IP) administration in mouse cell line-derived xenograft (CDX) tumor models.

The present disclosure provides efficient and reliable methods for preparing cyclized peptidic compounds. Advantageously, the currently described methods allow for on-resin cyclization using a limited number of processing steps, while increasing the chemical diversity available for the cyclized peptidic compounds produced.

A summary of structure-permeability lessons and a survey of the diverse structures observed in bioactive cyclic peptide natural products

Lipophilicity and flexibility play important roles in determining the passive permeability of a cyclic peptide natural product

Cyclic peptide natural products adopt solvent-dependent conformations that permit passive permeability.

Dual inhibitors of cyclin A and cyclin B RxL motifs (cyclin A/Bi) selectively kill SCLC cells and other cancer cells with high E2F activity. Genetic screens revealed that cyclin A/Bi induces apoptosis through cyclin B- and CDK2-dependent spindle assembly checkpoint activation. Mechanistically, cyclin A/Bi hyperactivates E2F and cyclin B by blocking cyclin A–E2F and cyclin B–MYT1 RxL interactions. Notably, cyclin A/Bi promoted the formation of neomorphic cyclin B–CDK2 complexes, which drive spindle assembly checkpoint activation and mitotic cell death. Finally, orally administered cyclin A/Bi showed robust anti-tumour activity in chemotherapy-resistant SCLC patient-derived xenografts. These findings reveal gain-of-function mechanisms through which cyclin A/Bi triggers apoptosis and support their development for E2F-driven cancers.

Semi-automated synthesis of macrocyclic peptides on the solid phase enables robust sampling of chemical space for early stage drug discovery. Here we highlight several methods we have used to approach resin loading, site-specific N-alkylation, challenging couplings, and cyclization. 

Cyclic peptides are potentially the future of intracellular protein-protein interaction inhibition. We review intrinsically permeable cyclic peptide therapeutics and model systems. 

Natural product permeability is rationalized via computational modeling

Non-proteinogenic backbone elements permit passive permeability and oral bioavailability

PhD dissertation