Mini-Proteins Combine Best of Monoclonals and Small-Molecule Drugs

The field of mini-proteins is so new that only a handful of research papers have been published about them, but they appear to have the potential to transform drug development—and thus biomanufacturing—by combining the best features of small molecules and antibodies and minimizing their limitations.

“Mini-proteins are in the range of about 50 to 150 amino acids. That puts them in the 10 kD range, compared to the 150 kD range of monoclonal antibodies (mAbs),” says David Longo, co-founder and CEO of Ordaos Bio. Consequently, these relatively svelte mini-proteins can go where antibodies can’t, penetrating the blood-brain barrier and the tumor microenvironment, and binding to targets that small molecules can’t reach, including flat surfaces.

As to why they haven’t yet been widely embraced, Longo notes, “The biopharma industry has a lot of structure around antibodies, so changing that is difficult.” There also are concerns about potential—though mitigatable—therapeutic risks. For example, mini-proteins can be constructed to minimize immunogenicity, and longer half-lives can be engineered naturally, PEGylated, or conjugated with albumin into the mini-proteins.

Because mini-proteins can be made of simpler structures like helices, they are easy to manufacture using standard processes. “They don’t necessarily require any cysteines,” Longo explains, “so there is no risk of disulfide bonds forming bridges or binding to other proteins and aggregating. Therefore, you can use synthesis techniques—cell-free technologies or bacterial synthesis, for example—that are easier to work with, less expensive, and faster than using Chinese hamster ovary (CHO) cells or other mammalian cell lines.”

The real advantage is in removing serendipity from drug discovery and design, continues Longo, thus creating optimal proteins for manufacturing.

“Traditional proteins, antibodies, and even nanobodies go through an arduous process,” he says, before the best development candidates can be selected. “We flip that process entirely,” with an in silico, de novo design system that builds proteins into small, configurable systems one amino acid at a time, which thus increases confidence in the mini-protein’s targeting ability.

By optimizing protein design, Longo says clients have seen about a 60% improvement in output efficiency. Consequently, “by increasing the yield, the cost of the drug will be reduced, and manufacturing will be much easier.”