Metabolites are molecular fingerprints of what your cells are up to and Dr. Arun Sreekumar wants to know the impression made by cancer.
You've likely heard about metabolites; your physician probably screens for some known ones such as triglycerides or cholesterol at your annual physical. Scientists suspect we have about 3,000 metabolites that come from our food or are synthesized from different compounds in our bodies.
Dr. Sreekumar, a cancer researcher at the Medical College of Georgia Cancer Center, wants those screens of the blood or urine to also detect early signs of cancers such as leukemia, bladder, kidney and breast when the chance for cure is best.
He's already begun to identify metabolites that indicate not only the presence of prostate cancer, but its aggressiveness, a tool that could help tailor optimal treatment. The search began in men at risk: those with elevated prostate specific antigen, or PSA, levels. A PSA test along with a digital rectal exam is today's standard for prostate screening so physicians typically do both in men age 50 and older. But PSA levels are actually better at helping determine if prostate cancer has returned, Dr. Sreekumar says.
Elevated levels of PSA, a protein, are not always predictive of cancer, which means a lot of men get unnecessary biopsies. PSA measurements also can't distinguish between tumors that have a good outcome versus those with a poor one.
"The physician does not really have the tools in hand to really say that this tumor will spread to other organs or not." says the Georgia Cancer Coalition Distinguished Cancer Scholar. "We want to find clinical markers that supplement PSA."
Aggressiveness is a major factor in prostate cancer treatment. In fact some men with slow growing disease likely won't even need treatment. So he wants to provide a complement of biomarkers that accurately diagnose and categorize the disease then help monitor success of treatment. These early studies indicate a urine test may one day be possible to do just that.
He and colleagues at the University of Michigan reported in the Feb. 12 issue of Nature what appears to be one of the first metabolites implicated in cancer invasion. They looked at 1,126 metabolites in 262 samples taken from men with high PSA levels. They consistently found elevated levels of the amino acid sarcosine in the prostate tissues of men with cancer; levels were highest in what appeared to be the most aggressive tumors.
Sarcosine, a modified form of the amino acid glycine, was a known entity but its function was unclear. Scientists thought it might be a dumping ground for excess methyl groups needed to enable chemical changes of genes, proteins and other body components that can affect what and how much they do.
This process called methylation can be a good thing – like when it's helping an embryo develop – but when it goes badly, it can cause disease such as cancer. While sarcosine's dumping role seemed to protect from cancer, the Michigan scientists found its action actually helps induce tumors. In fact, when they added it to prostate cancer cells, the cells became more aggressive. Exactly how that process works is still under study but the findings were pretty consistent.
"When we looked at patients with metastatic disease, sarcosine levels were sky high compared to patients with localized tumors," says Dr. Sreekumar. "It's enabling invasion."
Because cancer and people are both very heterogenous, measures need to be taken in larger population samples, he says. Also, they found a small group of patients with negative biopsies and high sarcosine levels. "We don't know how many of them have missed cancer," says Dr. Sreekumar who joined the MCG faculty in February.