Macrocyclic peptides are large enough to disrupt difficult protein-protein interactions (like biologics) but small enough to be orally bioavailable (like small molecules). This new modality can tackle targets previously undruggable by conventional small molecules, creating a best-of-both-worlds therapeutic.
Despite promising preclinical data, most at Merck were skeptical the complex molecule would be orally bioavailable. The pivotal "aha" moment wasn't in the lab but when Phase 1 clinical data showed oral absorption and profound cholesterol reduction in humans, instantly validating the decade-long effort.
Merck's biocatalysis platform starts with enzymes from nature and uses directed evolution—iterative lab-based mutation and selection—to create novel manufacturing tools. This process rapidly builds unnatural functions, enabling the scalable synthesis of complex drugs that would otherwise be impractical.
The success of enlicitide wasn't a single discovery but was built on a generation's worth of investment in biocatalysis at Merck, starting in the 90s. This demonstrates that world-changing innovation is a slow, consistent build-up of incremental learnings from prior projects, not a sudden eureka moment.
The discovery team's triumph in designing a highly potent molecule created an enormous challenge for the development organization. They were handed a structurally complex compound that was nearly impossible to produce, turning their focus to inventing a manufacturing process as innovative as the drug itself.
In selecting targets for its macrocyclic peptide platform, Merck strategically prioritizes two factors: 1) extracellular targets that don't require difficult cell penetration, and 2) disease areas where existing options are only injectable. This creates a clear path to differentiation and addresses high unmet patient needs.
While current biocatalysis excels at modifying molecules that resemble natural compounds (like nucleosides), the future lies in pushing directed evolution further. The goal is to engineer enzymes that perform chemistry on intermediates that look nothing like what's found in nature, vastly expanding the druggable universe.