Recombinant proteins are a mainstay in today’s pharmacopeia, but manufacturing them at scale remains technically and logistically challenging. Cell-based systems—whether they be bacterial, plant or mammalian—are inherently cumbersome to manipulate and maintain. Present-day capacity can’t always meet the demand, as the early days of the pandemic demonstrated when supplies of monoclonal antibodies for COVID-19 were limited to the rich and famous. And the ability to modify proteins at specific sites is not always straightforward, taking months or sometimes years to accomplish.
Now Jeff Bode’s group at ETH in Zurich has come up with a way to construct proteins from scratch using a solid-phase peptide synthesis platform that allows fine-tuning of “biological activity by making small, but important, changes in amino acid side chains,” says Bode. Putting unnatural amino acids into a recombinant protein produced in cells is possible but complicated (requiring expanding the genetic code) and expensive. With a totally synthetic process, Bode says that many non-canonical amino acids can be added into a peptide chain, wherever they want.
In addition, with their particular ligation process, which pairs an α-ketoacid with a hydroxylamine—a so-called KAHA reaction, which Bode’s group first described in 2006—they can make proteins of several hundred amino acids by making 30- to 40-mer peptides and then stitching them together. Technologies for ligating small peptides together to make larger peptides or small proteins have been around for decades, but serial purification steps can reduce yields, making this process unfit for protein manufacturing at the scale needed for biologic production. However, after a decade of trying different combinations of N- and C-terminal end groups, Bode’s group found that this KAHA pairing, unlike most organic reactions, works well in the presence of other organic functional groups found on amino acid side chains. “We sometimes call it the ‘teenager in love reaction’, as the ketoacid and hydroxylamine just stick to each other and completely ignore everything else around them,” jokes Bode.
Vijaya Pattabiraman (known as Vijay), Bright Peak’s senior vice president and head of technology, notes that the hydroxylamine functional group opened doors for them, allowing them to move beyond 100 amino acids to chain lengths that are at least the size of some small globular proteins. Key was the choice of hydroxylamine. What they found, quite by accident, was that when oxaproline is used as the hydroxylamine of the pair, ester (rather than amide) bonds are created, which are stable to all standard reactions, reagents and purification schemes. Then, under conditions for protein folding, the ester bond spontaneously converts to an amide. “We got lucky in that oxaproline behaves in this unexpected way, which proved crucial for making some really difficult proteins,” Bode remarks.
With this combination, the group set its sights first on a class of proteins that is both potent and relevant in therapeutic settings: cytokines. Alex Mayweg, who sits on Bright Peak’s board and whose venture capital firm Versant Ventures put in the whole $35 million series A round in September 2020, says, “Cytokines are a wonderful playground; they are very potent molecules. We know the efficacy is there, but the field needs to learn how to tame them to make really good drugs.” In June Versant and a group of new investors, among them RA Capital, funded Bright Peak’s B round of $107 million.
To use interleukin (IL)-2 as a cancer therapeutic, for example, requires eliminating its effects on immune modulating cells by blocking the interaction with the α-subunit of the IL-2 receptor. Most of the other groups trying to create an IL-2 cancer therapy (and there are many) achieve this by attaching polyethylene glycol (PEG) groups at the α-subunit receptor binding site. Bright Peak’s approach, instead, is to create a permanent ‘dead alpha’. (PEG molecules notoriously fall off the molecule over time, which can lead to unwanted effects.) Bright Peak still employs PEG, which enhances stability in vivo, but its use is independent of the blocking of α-receptor binding.
In addition to introducing n
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