Tuesday, March 27, 2012

Cornell ChemE Prof Makes Glycoproteins Without CHO Cell Culture

Just out yesterday:

Cornell Chemical Engineering Professor Produces Glycoproteins with E.Colicornell article

The thrust of the story is that a Cornell professor, Matthew DeLisa, has figured out how to make glycoproteins using E.Coli. Readers of my blog know that the reason we humans use Chinese Hamster Ovary (CHO) cells to make human glycoproteins is because only mammalian cells can do post-translational glycosylation while the simpler bacteria cannot.

This is where Dr. DeLisa says, "Not anymore."

You'll have to read the paper from his Nature paper (included at the bottom) if you want to get wonkish, but described in lay terms, the Cornell research team added:

  • Four enzymes from yeast cells:

    1. Yeast uridine diphosphate-N-acetylglucosamine transferases Alg13
    2. and Alg14
    3. Mannosyltransferases Alg1
    4. and Alg2
  • One enzyme bacterial from from Campylobacter jejuni
    oligosaccharyltransferase PglB

to E.coli cultures to get the desired glycan structures. All this, I presume, involves more than cleverness and advanced pipetting skills.

Sounds quite promising as the tech is being commercialized through a startup called Glycobia. As science is skeptical, so is this fermentation engineer (of the commercial value of this venture).

The process economics of CHO vs. E.Coli does not clearly point in the direction of bacterial cultures. If you look at two nearly identical drugs, Lucentis (made with E.coli) vs. Avastin (made with CHO), you have drastically higher cost for the E.coli product. Lucentis is the Fab region of the antibody while Avastin is the whole antibody (Fab + Fc) and the costs are $2,000 vs $150 (assuming the same concentration of API gets the job done). The markup has little to do with Genentech being greedy.

A quick Google search of "cho vs e coli process economics" will get you to a book by Ajit Sadana (1998) on Bioseparation of proteins. Starting on page 66, he goes through an example of Activase (tPA) made in CHO vs. E.coli.

CHO had 5 steps while E.coli had 16. CHO had a 47% yield while E.coli had a 2.8% yield... primarily due to the extra recovery steps to remove the endotoxin that E.coli creates that CHO does not. Sure, this example is 1998 technology talking about (likely small scale) purification, but I have yet to see the process economics work in favor of E.coli for biologics.

If contamination concerns (like the Genzyme Allston plant cited) are the main cost avoidance, I'm going to come out and say that this research will remain academic: bioreactor contaminations are easy to prevent when management is committed to contamination reduction.

If replacing the known quantity that is CHO with an unknown quantity that is E.coli + Bottom-Up Glycoengineering (BUG) technology is all we get (i.e. without orders of magnitude increase in culture titers or reduction in variability), then my money with CHO.

More reading:

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