PUTTING NATURE TO WORK
There’s more than one way to skin a cat. Or make medicine, for that matter. It all depends on the kind— tabby or calico? A small molecule or biologic?
One key feature distinguishing biologic drugs such as monoclonal antibodies from small molecule drugs such as aspirin is their production. This highly complex process, biomanufacturing, requires much more time and expense than needed for small molecules.
In this article, we’ll revisit key components of biomanufacturing by examining cell bank production and the different types of cells used in biomanufacturing.
IMPORTANT TERM: BIOMANUFACTURING
Biomanufacturing is the production of biological products from living cells. Companies use the process to make biologic drugs such as antibodies and enzyme replacement therapies. Small molecule drugs can be synthesized chemically. As their name suggests, biologics require living cells.
Biomanufacturing isn’t just about medicine, though. For instance, companies use the process to make enzymes for bioremediation—cleaning up toxic stuff in the environment. The food processing industry also uses biomanufactured products.
STEP NUMBER ONE: ESTABLISHING THE CELL BANK
First things first. Biomanufacturing involves engineering a cell to produce a specific protein. Scientists use well-established techniques to transfer a gene encoding the desired protein into a “production cell.” The two most commonly used production cells are E. coli bacterial cells and Chinese hamster ovary cells, or CHO cells. Once a manufacturer successfully manipulates a cell to produce said protein, the cells multiply. Scientists call these genetically identical cells the production cell line.
STEP TWO: THE MASTER CELL BANK
Step two is for the manufacturer to establish a master cell bank that supplies genetically identical cells for future products. Companies create cell banks by transferring the production cell line to a bioreactor. Though they may sound scary, bioreactors are simply vessels filled with a growth medium — a “broth” with the required nutrients brewing in optimal temperature, pH, and oxygen concentration conditions for cell growth.
The cells are left to simmer or multiply for a few generations, creating hundreds of millions of identical copies. The manufacturer collects this slough and portions them into small vials. Each of the several hundred receptacles contains about a million (million!) cells. The vials are then frozen with liquid nitrogen, cooling them to -196 degrees Celsius. The deep freeze stops cell growth; In other words, if some future scientist thawed one of the vials in twenty years, they would find the cells inside exactly as they were at storage— barring an apocalypse or someone tripping over the power strip. This stable longevity is key, as product consistency over the lifetime of the product is critical to drug safety.
Manufacturers typically divide the master cell bank for storage into three separate locations so a disaster in one place doesn’t wipe out this vital resource.
In each location where a product is manufactured, a manufacturer creates a working cell bank by thawing one vial from the master cell bank and “expanding it,” or allowing it to multiply for a few generations — and then freezing several hundred vials for storage. Each new biomanufacturing campaign starts by thawing a vial of cells from the working cell bank.
MAMMALIAN VS. BACTERIAL
The first biologic drug, insulin, was produced using E. coli cells. Researchers soon realized, however, that they couldn’t produce every therapeutic in bacterial cells. Highly complex proteins, such as monoclonal antibodies and certain enzymes, present two main obstacles. Bacterial cells cannot correctly fold these complex proteins, nor can they confer required posttranslational modifications – chemical and physical changes made to a protein by cellular enzymes after the protein is produced.
NO, NOT THAT E. COLI
Life-saving drugs grown in E. coli bacteria seems a bit sketchy, does it not? The same bug that causes food poisoning? Not exactly. While it sounds unsavory, it’s important to remember that there are many different strains of E. coli, most of which are benign. In fact, E. coli bacteria make up a big chunk of healthy gut microbiota.
HAMSTER OVARIES? WHAT???
Why Chinese Hamster Ovary cells? Well, since you had to ask… When scientists first realized they needed some cell type other than E. coli to produce complex biologic drugs, CHO cells were handy. Scientists worldwide have already used them in many experiments and made a convenient platform for biologics. More than thirty years of data have made it clear that producing drugs in these cells is safe. As a result, the FDA has granted them “generally regarded as safe” (GRAS) status for therapeutic protein production. That is, drug companies can use them to manufacture a product without first demonstrating their safety.
Of course, it’s important to remember that no matter what type of cells are used to produce the therapeutic protein, the “nursery” cells don’t make it into the final product. After manufacturers grow therapeutic protein-producing cells for several days or weeks, the next step is to purify the therapeutic protein away from other cellular proteins and the cells themselves.