An affinity for pure drugs

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Science Translational Medicine  19 Aug 2020:
Vol. 12, Issue 557, eabd4936
DOI: 10.1126/scitranslmed.abd4936


High-affinity supramolecular interactions improve the purification of recombinant therapeutic proteins, simplifying their production.

Antibodies, cytokines, and other bioactive proteins are precious laboratory reagents and critical therapeutic drugs that have transformed the landscape of the pharmaceutical industry in recent years. Unlike small-molecule drugs that can be made synthetically by chemical reactions, the manufacture of protein therapeutics requires multistep processes that include protein production by cells and extensive subsequent purification. These purification processes are often laborious and costly, limiting drug availability to patients.

Typically, therapeutic proteins are produced by cells in culture and then recovered in a complex mixture of other unwanted proteins and biomolecules. Conventional purification techniques use biomolecule-conjugated agarose beads that specifically interact with the target protein to pull it from solution, allowing unwanted components to be washed away. However, these methods require optimization for each new target protein, include extensive secondary purification steps, and use materials (biomolecule-conjugated beads) with a limited capacity for sterilization and re-use. In contrast, An et al. developed an approach to protein purification that is simple, cost-effective, and generalizable to new protein therapeutics. To accomplish this, the team leveraged the guest-host interaction between cucurbit[7]uril and adamantylammonium (CB[7] and AdA, respectively), which have an affinity orders of magnitude stronger than that of biomolecules typically used for purification. The target protein (trastuzumab, or Herceptin, used as a model protein drug) was covalently bound to AdA via an enzyme-specific reaction, enabling selective modification in the presence of other biomolecules. When introduced to CB[7]-conjugated agarose beads, AdA-Herceptin bound to the beads and unwanted proteins were washed away. AdA-Herceptin was recoverable from the beads by addition of a competitive guest molecule, displacing AdA-Herceptin into solution. In direct comparison with biomolecule-conjugated agarose beads, the new method produced a near three-fold increase in product yield and purity. Notably, the CB[7] beads could be reused after removal of the competitive guest, autoclaved for sterilization, and scaled up to larger batch sizes without notable losses in product yield or purity.

Some case-specific limitations may remain in this process, such as the potential for AdA modification to hinder protein bioactivity. However, it is encouraging that bioactivity of Herceptin was unaffected here and that the approach was generalizable to smaller proteins, including recombinant human interferon-ɑ and granulocyte-colony stimulating factor. As the demand for biomolecular therapeutics continues to grow for immunooncology and immunomodulatory therapies, improved processing techniques will be essential to meet clinical demands. The development of versatile purification methods such as these is an important investment in the future of these key therapeutics.

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