Breaking Through Key Bottlenecks in PROTAC Development

A recent collaboration involved the rapid production of a proteolysis-targeting chimera (PROTAC) candidate, with the goal of submitting an Investigational New Drug (IND) application and delivering clinical trial material for first-in-human (FIH) studies within just 14 months. By leveraging an integrated CMC platform and advanced enabling technologies in both API process development and formulation, WuXi STA’s team successfully delivered the FIH material in just 12 months — two months ahead of schedule.

PROTACs: A Unique Modality with Unique Challenges

Targeted protein degraders (TPDs) eliminate disease-causing proteins by inducing their degradation within cells. Among them, PROTACs are bifunctional molecules that recruit an E3 ubiquitin ligase to a target protein, tagging it with ubiquitin for destruction by the proteasome. This mechanism allows PROTACs to act without requiring high-affinity binding to an active site, offering a compelling strategy to tackle “undruggable” targets.

However, the promise of PROTACs comes with unique development challenges, particularly in enhancing oral bioavailability. Due to their large molecular weight and structural complexity, PROTACs often suffer from poor solubility and suboptimal pharmacokinetics. Recognizing these development hurdles, the partner opted to collaborate with WuXi STA, part of WuXi AppTec, to address the challenges effectively.

In this project, the PROTAC compound presented multiple development challenges. With a molecular weight nearing 800 and poor water solubility that translated to an oral bioavailability of just 0.9%, formulation posed a major hurdle. In addition, the initial synthetic route involved 24 steps and yielded only 0.3%. Three of these steps required palladium (Pd) catalysis, complicating purification due to residual Pd removal and elevating cost. The specific molecular structure of the PROTAC further hindered crystallization and purification. The initial production costs exceeded $1 million for just 1 kilogram of API—an unsustainable cost for clinical development.

Navigating Synthesis and Formulation Hurdles

To address these challenges, WuXi STA’s process development team, biocatalysis team, and crystallization technology team worked collaboratively. Drawing on extensive experience in the PROTAC field, the chemistry and biocatalysis experts redesigned the synthesis route — introducing biocatalytic transformations in place of Pd-catalyzed steps, thereby improving both efficiency and cost-effectiveness.

Crystallization was similarly optimized. The team employed high-throughput crystallization screening to pinpoint processes that met both purity and yield requirements. Based on data from crystal form stability and solubility tests, two solvent systems were selected for further optimization, yielding a robust crystallization process.

In parallel, WuXi STA’s formulation development team systematically evaluated multiple bioavailability enhancement technologies, including spray-dried dispersions (SDD), hot-melt extrusion, nanomilling, and liquid formulations. SDD emerged as the optimal choice, offering the ability to disperse poorly soluble drugs in an amorphous state within a polymer matrix, significantly increasing the surface area-to-volume ratio and improving dissolution.

Delivering Results: A More Efficient Path to First-in-Human Trial

By leveraging its integrated CMC platform and advanced enabling technologies in both API process development and formulation, WuXi STA developed a more scalable, efficient, and cost-effective manufacturing process. Key achievements included:

• Reducing synthesis steps from 24 to 16, while replacing Pd catalysts with biocatalysts in two steps.
• Improving the oral bioavailability of the tablet form by approximately 30-fold through SDD optimization, laying a solid foundation for future clinical application.

These advancements, enabled by parallel workflows and close cross-functional collaboration, allowed the team to complete IND-enabling production and formulation ahead of schedule and successfully supply the drug for the first-in-human study within 12 months.

As the field of targeted protein degradation continues to evolve, WuXi STA remains committed to leveraging its integrated CRDMO platform to empower the development of targeted protein degraders (including PROTACs), helping partners translate scientific innovation into life-changing medicines for patients around the world.

Reference:

[1] Advancing targeted protein degraders: leveraging CMC strategies for rapid IND submission and bioavailability solutions. Retrieved June 2, 2025, from https://sta.wuxiapptec.com/wp-content/uploads/2024/10/Advancing-targeted-protein-degraders.pdf

[2] PROTAC protein degraders to drug the undruggable enter phase 3 trials. Retrieved June 2, 2025, from https://www.nature.com/articles/d41591-024-00072-8