How biotech drugs are produced

I’m a researcher in a pharmaceutical biotechnology company, and I’m concerned by the lack of public understanding about what it is we do. In this article I’ll explain some of the process of pharmaceutical manufacture at a biotechnology company, and how you go from a cell stored in liquid nitrogen to a vial of drug for injection. This is intended to be a readable, layman’s explanation of the process. My perspective is fermentation-centric, so apologies to the areas I can’t fully represent. In a later article I’ll discuss more of the research process, where I am involved. I’m also going to sprinkle the article with links to references that have more detail and explanations of technology or equipment.

The master cell bank

The basic concept in biotech is that you identify a molecule that you want, and the sequence of DNA that could be used to produce that molecule. Then you genetically engineer a cell line (CHO or E. coli) to produce it and come up with the correct bioreactor conditions so that they can grow and produce it. Once you have settled on this combination of cell and DNA you place that “master” cell line in liquid nitrogen for permanent storage. This is your gold standard copy from which all drug production starts. You probably have more than one master cell bank to protect you from things like fire and earthquake, since if you lose the master cell line you will have no FDA certified source of cells to produce your product! That would be bad.

The first step in production is to take some of your master cell bank and carefully grow it up in a bioreactor. The goal here is not to make any product, but just to make some more cells, which can then be frozen as a “working cell bank.” Because the master cell bank is so important you try to avoid accessing it as much as possible. Every now and then you take some master cells and create a new working stock.

The working cell bank

The working cell bank is where you go for starting material any time you want to actually make some product. Like the master cell bank, the working bank is also stored in liquid nitrogen, but they are less carefully protected than the master cell bank. If these catch fire you can always make some more from the master. When you are ready to start a production run you revive some of your cells and start to culture them.

Fermentation

The fermentation process is fundamentally similar to the production of beer or wine. You provide a healthy, nutritious environment for your cells where they grow and produce their metabolic products. In the case of biotech those products are molecules that we’ve engineered them to produce. The process varies depending on what kind of cells you are using, but generally you need to go from your frozen starting material of a few mL, and end up with a few thousand liters in a big, production-scale bioreactor.

You might put 1 mL into, say, a 2-liter glass flask, and grow your cells up in that volume. Once you have a good population in there you transfer them to a 10 liter reactor, then from there you transfer them to a 500 liter reactor, then from there you transfer them to a 10,000 liter reactor. During that entire process you are keeping the cells alive and growing, but you are not producing any drug molecule, you are only having the cells reproduce themselves. This is because the cells only have a certain amount that they can do, and they can either grow, or they can divide their efforts between growing and making your product. Up until you reach production scale you don’t want them to do anything but hurry up and grow. Once you reach the production scale reactor you let them grow up to a nice big population and then tell them to start producing your drug molecule. We have many ways of telling the cells what to do, so one way we might tell them “hey, start producing my molecule!” is to tie that gene to a specific controller sequence, called a promoter.

Promoters are a way that genes regulate whether they are turned on or off. You might imagine a case where a cell wouldn’t produce much of the protein for digesting chocolate if there is no chocolate around, so the gene for chocolate is tied to a chocolate promoter. Only when there is chocolate around does the chocolate promoter activate the chocolatase gene. What we can do is take the chocolate promoter and tie it to our gene for the drug molecule. Now if we want them to make our drug we just give them chocolate and they’ll start making it. There are many different promoters out there (none are for chocolate) so we can choose what we want to use to turn gene expression off and on. Once the reactor has enough cells in it, you give them the chocolate and they start producing your drug molecule. After you’ve made enough, that completes the batch and you harvest the contents of the reactor.

Harvesting just means taking out the stuff you want from the reactor. If the drug is in the liquid then you might centrifuge it (spin it really really fast so dense stuff settles to the bottom) and keep the liquid. If the drug is in the cell bodies, you might centrifuge and keep the pellet at the bottom. Or you might just harvest everything and send it all to recovery for them to sort out.

Recovery / Purification

This is where the drug molecule is separated from everything else that was in the bioreactor, like cell bodies, growth media, dead cell parts, etc. It’s critically important that this separation is done perfectly. Biological drugs can’t survive going through your stomach, so they have to be injected. Any impurity, especially a once-living impurity, can cause a massive immune response. This is extremely rare due to the huge number of quality checks that take place throughout this process. There are many different kinds of purification technologies, from various fancy filters to huge chromatography columns.

A chromatography column is a way to separate the components of a solution by time based on how well they stick to the material packed into the column. You can imagine that if you have your column packed with something that your drug molecule finds “sticky,” then it will take your drug molecule longer to make its way through than all of the other stuff which doesn’t find that column sticky. This is a complex subject, and I’m not really able to do it justice here, but there’s a lot of development work that goes into taking a mess of bacterial or mammalian cells and growth media and then ending up with something pure enough to inject into a patient.

Formulation

Formulation is the step where you take your drug molecule and you actually turn that into a drug. This means putting the drug molecule in ultrapure water, the right buffer liquid, at the right pH, at the right concentrations, so that you end up with something that is safe to inject into a person.

Filling

This is the stage where you actually take the active drug created in Formulation and put it in vials or pre-filled syringes or whatever. This is the final preparation step before the product gets boxed up and goes out to doctors and pharmacies.

I hope this has been informative as far as what the process actually looks like to get biotechnology drugs to your pharmacy. I didn’t even touch on the massive quality organization that exists and operates in parallel to the manufacturing process. Extensive tests for purity and quality are performed at every step of the process to make sure that what leaves the door is safe for injection.

Of course, what’s most interesting to me is how you develop that process, and that technology, but that will wait for another time.

If you have any questions for me please feel free to post a comment and I’ll try to answer them.