An international team of researchers led by the University of California San Diego has developed a new strategy to enhance pharmaceutical production in Chinese hamster ovary (CHO) cells, which are commonly used to manufacture protein-based drugs for treating cancer, autoimmune diseases and much more. By knocking out a gene circuit responsible for producing lactic acid—a metabolite that makes the cells' environment toxic—researchers eliminate a primary hurdle in developing cells that can produce higher amounts of pharmaceuticals like Herceptin and Rituximab, without compromising their growth or energy production.
The research, published on Jan. 14 in Nature Metabolism, also challenges long-held assumptions about the necessity of lactic acid metabolism in cell survival.
CHO cells have become essential tools in modern medicine, serving as the "living factories" that produce more than half of today's top-selling protein-based drugs, including therapies for cancer, autoimmune diseases and more. But despite their success, they have one main flaw: low protein yield. CHO cells don't always produce enough of the desired drugs to meet demand, which makes these pharmaceuticals more costly.
Now, researchers have developed an approach that promises to improve the yields of CHO cells in drug production. The approach targets a key metabolic process: the secretion of lactic acid.
During protein production, CHO cells release lactic acid as a byproduct of their metabolism. The more active they are, the more lactic acid they produce. "As we grow cells to produce more drugs, lactic acid builds up and kills the cells, thus reducing the yields of life-saving drugs while driving up manufacturing costs," said study senior author Nathan Lewis, who led the study while serving as a professor in the Shu Chien-Gene Lay Department of Bioengineering and Department of Pediatrics at UC San Diego (now at the University of Georgia).
Efforts to stop lactic acid production have so far focused on inhibiting the enzyme responsible for this process, lactate dehydrogenase. But these efforts have been unsuccessful, as lactate dehydrogenase is essential for cell survival. "If you try to remove it or block it, the cells die," said Lewis. "This has been demonstrated in multiple studies."
In the new study, Lewis and colleagues, co-led by UC San Diego bioengineering Ph.D. alumnus Hooman Hefzi (now a professor at Technical University of Denmark), took a different approach. Instead of focusing on lactate dehydrogenase itself, they mapped out a network of genes—five in CHO cells and six in human cells—that work together to control lactic acid production. The researchers hypothesized that this gene circuit was responsible for the cells' overproduction of lactate.
When the researchers knocked out this gene circuit, the CHO cells stopped producing lactic acid. Moreover, the cells demonstrated improved growth and, compared to similarly treated controls, produced significantly higher yields of protein-based drugs such as Herceptin and Rituximab, which are used to treat breast cancer and lymphoma, respectively. The modified CHO cells also successfully produced a variety of other therapeutic proteins, including Enbrel, a treatment for rheumatoid arthritis and psoriasis, and erythropoietin, which stimulates red blood cell production.
Challenging the Warburg effect
This work also sheds light on a key biological process known as the Warburg effect. First observed in cancer cells by German scientist Otto Warburg 100 years ago, the Warburg effect refers to a metabolic shift that causes cells to overproduce lactic acid. This process has long been thought to be critical for cell proliferation and energy production.
Yet, the new research challenges that notion. By eliminating the Warburg effect in CHO cells, researchers found that the cells maintained normal growth rates and energy output. This suggests that the Warburg effect may not be as essential as previously hypothesized.
The researchers note that these newly engineered "Warburg-null" CHO cells are also compatible with industrial cell line development processes. That means these cells could easily be integrated into real-world drug production, which could be a game-changer for biomanufacturing.
The team has discovered additional tweaks that further boost the CHO cells' productivity, and are continuing to study their implications on the entire drug manufacturing process.
"Our work has the potential to make drug production far more efficient, which could significantly lower manufacturing costs," said Lewis. "By improving the productivity of these cells, we're taking an important step toward making life-saving therapies, like cancer treatments and gene therapies, more affordable and accessible to patients worldwide."
Paper: "Multiplex genome editing eliminates the Warburg Effect without impacting growth rate in mammalian cells."
This work was supported by the Novo Nordisk Foundation through the Technical University of Denmark, the National Institute of General Medical Sciences, and the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Actions.
Disclosures: A patent based on this work has been issued with Hooman Hefzi and Nathan E. Lewis as inventors (US Patent 11,242,510, WO2017192437).
