Gut Bacteria Influence Asparagine Metabolism, Impacting Cancer Growth and Immune Response
Researchers at Weill Cornell Medicine have identified that gut bacteria can influence the metabolism of the amino acid asparagine, which in turn affects whether it promotes tumor growth or activates immune cells against cancer. Published on January 2 in Cell Microbe and Host, the study suggests the gut microbiome plays a role in the body's response to cancer and could lead to new treatment strategies involving targeted dietary or microbial interventions.
The study suggests the gut microbiome plays a role in the body's response to cancer and could lead to new treatment strategies involving targeted dietary or microbial interventions.
Research Focus and Findings
The research, co-led by Dr. Chunjun (CJ) Guo, Dr. David Artis, and Dr. Nicholas Collins, established in mouse models that certain bacteria within the gut can deplete amino acids, influencing tumor progression. The study focused on asparagine, an amino acid recognized as essential for both cancer cell survival and the activity of cytotoxic CD8+ T cells, which are immune cells responsible for targeting and destroying tumor cells.
Bacterial Regulation of Asparagine Metabolism
The team investigated Bacteroides ovatus, a common gut bacterium, which contains the bo-ansB gene. This gene codes for an enzyme that breaks down asparagine. Through experiments using mouse models:
- When the bo-ansB gene was present, B. ovatus consumed more asparagine in the gut. This resulted in a reduced amount of asparagine entering the bloodstream and reaching tumors.
- Conversely, when the bo-ansB gene was inactivated or removed, the bacteria were unable to deplete asparagine in the intestine. This led to higher levels of the amino acid in the blood circulation and within tumors.
These findings indicate that gut bacteria regulate the amount of asparagine absorbed from the gut, thereby affecting its availability to both tumors and immune cells throughout the body.
Impact on Tumor Growth and Immune Response
Further experiments involved mouse models of colorectal cancer, where diets were supplemented with asparagine:
- In mice with bo-ansB-containing bacteria, tumors exhibited increased growth when fed extra dietary asparagine. This was attributed to the bacteria consuming the amino acid, thereby limiting its availability for immune activation.
- In mice where the bo-ansB gene was deleted, the same asparagine-rich diet resulted in more asparagine reaching the tumor. This asparagine was absorbed by CD8+ T cells, which triggered them into a "stem-like" state. This state is associated with sustained and effective anti-tumor responses.
- In contrast, insufficient asparagine levels reduced the effectiveness of CD8+ T cells in suppressing tumor growth.
The study also identified that higher asparagine levels in the tumor microenvironment, which occurred in the absence of bo-ansB, promoted CD8+ T cells to express an increased amount of the SLC1A5 protein transporter on their surface. This transporter was found to be critical for the cancer-fighting capabilities of these immune cells. Blocking SLC1A5 reversed these observed positive effects. The stem-like CD8+ T cells were described as acting as a renewable source, capable of maturing into cancer-killing T cells that produce immune factors to attack tumors.
Future Implications for Cancer Therapy
The researchers suggest that these findings could lead to novel cancer treatment and monitoring strategies. Future clinical approaches might involve reshaping the gut microbiome or dietary intake to either restrict tumor growth or enhance immune cell activity.
Specific areas of future exploration include:
- Biomarkers: Enzymes and metabolites produced by the microbiota are considered potential biomarkers for cancer progression.
- Personalized Therapies: Future cancer care could integrate immunotherapy with customized diets and microbiome-targeted approaches. These might include specific probiotics, engineered gut bacteria, or personalized dietary plans designed to fine-tune amino acid availability.
- Continued Research: Researchers emphasize the importance of continuing to study the interactions among diet, microbiota, and the immune system to develop personalized therapies that can enhance the immune system's fight against cancer based on an individual's unique microbiota.