New Screening Technique Identifies Genes Behind Heart Cell Damage from Chemotherapy

By LabMedica International staff writers
Posted on 03 Dec 2024

Image: A sarcomere, or part of a cardiomyocyte that helps heart cells beat, retains its structure after treatment with indisulam and doxorubicin (Photo courtesy of Joseph Wu lab/Stanford Medicine)

Doxorubicin is a potent chemotherapy drug that effectively targets cancer cells, but it also disrupts heart cells, causing them to beat irregularly, organize incorrectly, or even die. When used in high doses or over extended periods, doxorubicin can lead to heart failure, which limits its use despite its cancer-fighting effectiveness. Now, researchers may have uncovered why doxorubicin harms heart cells and identified a drug that could keep them beating.

A team of researchers at Stanford Medicine (Stanford, CA, USA) has developed a genetic screening tool using CRISPR, a powerful gene-editing technology, to identify genes involved in doxorubicin-induced heart damage. Through this method, they identified a gene that seemed to play a key role in the drug's harmful effects on the heart. Although it was known that doxorubicin damages heart cells, the specific genes responsible for this damage were unclear. The researchers focused their search on 2,300 genes that are already targeted by existing drugs. They utilized a novel genetic screening technique to observe the effects of doxorubicin on heart cells derived from induced pluripotent stem cells, which can differentiate into any cell type. By using CRISPR to turn on or off individual genes within these heart cells, the researchers exposed the cells to doxorubicin and noted which ones survived. The next step was to understand why these cells survived. To uncover this, the researchers sequenced the DNA of each cell, searching for genetic markers associated with survival.

Their findings revealed that the heart cells that survived after doxorubicin treatment lacked a gene called CA12. This gene is responsible for catalyzing reactions involving carbon dioxide, which helps regulate essential body functions such as respiration and saliva production. Further genetic tests confirmed their hypothesis: when CA12 was deleted from heart cells, they became resistant to doxorubicin-induced damage. While the exact role of CA12 during doxorubicin treatment is still not fully understood, the researchers are working to figure out its function. Once CA12 was identified as a critical factor in doxorubicin toxicity, the team sought a way to prevent the CA12 protein from causing harm to heart cells. They selected 40 drugs known to inhibit carbonic anhydrase proteins like CA12 and tested them alongside doxorubicin on heart cells. By comparing the survival rates of these cells, they identified which drugs helped the cells survive the treatment.

Their research, published in Cell Stem, found that a drug called indisulam, currently being studied as a potential cancer treatment, helped heart cells survive doxorubicin toxicity. Indisulam protected the heart cells’ ability to contract and relax, maintaining essential cellular functions. The next phase of the research involved testing indisulam in living organisms. Mice were treated with doxorubicin and then given either indisulam or a control. The mice that received indisulam along with doxorubicin showed improved heart function, less heart atrophy, and better-maintained heart cell structure. The researchers are now focused on understanding how indisulam blocks CA12 activity and plan further testing to reduce doxorubicin’s toxicity. Additionally, they aim to explore how multiple genes work together in causing heart cell damage, rather than focusing on one gene at a time. The team has ambitious plans for their CRISPR-based screening tool and intends to apply it beyond heart cell toxicity in future studies.

“This CRISPR screen is a valid tool for drug discovery. That, to me, is the key take-home message of the study,” said Joseph Wu, MD, PhD, a professor of cardiovascular medicine and the director of the Stanford Cardiovascular Institute. “It’s a proof of principle. In the future you could use it for other types of toxicity or diseases. We think it’s a very powerful tool.”