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San Diego synthetic biology company Synthorx is entering the drug discovery game with a couple extra base pairs up its sleeve: It’s developing new biologic drugs with an expanded DNA alphabet, adding synthetic nucleotides X and Y to the standard lineup of A, C, G, and T.

The company just raised $10 million, on top of $6 million in investment it collected back in 2014.

CEO Court Turner spoke with STAT about the company’s technology — and its plans for developing drugs for diabetes and other conditions with that loaded-up DNA.


How does your technology work?

If you go back to the beginning of time, all nature around you is coded based around four nucleotides: A, G, C, and T. After 16 years of research, we’ve added X and Y. So instead of having two base pairs, we’ve got three — which basically translates to having a larger hard drive on a computer. These unnatural base pairs are replicated and transcribed exactly the same as A, C, G, and T.

What can you do with that expanded genetic alphabet?

The four natural nucleotides combine to make 64 codons, and 20 natural amino acids. With six nucleotides, we now have access to 216 codons, which theoretically incorporate into well over 100 amino acids.


We’re using whole cells to work as a natural factory for producing our compounds. We feed the synthetic DNA into a bacterial cell line normally used to produce protein therapeutics — except the resulting protein now has one or more synthetic amino acids.

We want to impart some characteristics in these new protein therapeutics — whether it means extending the half-life, or improving the pharmacokinetics, attaching more things onto a protein to give it a better drug property.

What’s the rationale behind developing these synthetic amino acids?

The idea of putting a synthetic amino acid into a protein has been thought about for a while, but it’s been hard to do it at scale.

So we’re going after targets that have been in the eye of pharma companies for many years, but haven’t been addressable by traditional methods — mostly because they could only make these compounds in small amounts, and couldn’t scale them for drug development.

We’ll do partnered deals, but also internally develop drugs. We’re looking at metabolic disease — for example, diabetes — and infectious disease. We’re looking to build antibiotics.

An expanded genetic code sounds promising and futuristic, but $10 million doesn’t seem like a lot in the biotech world. What gives?

It’s a little cheaper to run a biotech company in San Diego, when compared to Boston. We’re going to double the size of the company with this raise — go up to 16 people —and get a CSO [chief scientific officer] and a CBO [chief business officer]. It’ll give us years of runway to go after a number of these programs.