Using bacteria to detect cancer in urine
Few of us are ever eager to pee into a cup, but there may soon be good reason to be: Researchers at the Massachusetts Institute of Technology have developed a test that accurately detects liver cancer in urine.
The test, described last week in the journal Nature Translational Medicine, has so far only been evaluated in mice. If it were to work similarly in humans, it could enable the detection of liver cancer, among the deadliest of cancers, far earlier than current techniques and for a fraction of the price.
The test relies on an unlikely hero: the bacterium E. coli. “Bacteria have immense potential,” says Neil Forbes, a bioengineer at the University of Massachusetts Amherst, who was not involved in the study.
Bacteria naturally flourish in tumors, taking advantage of abundant nutrients and a weakened immune system. “You could tune them for different cancer sites, different stages, use them for detection, use them for therapy,” says Forbes.
In the past, bacteria were almost always injected directly into the bloodstream at high concentrations. Bioengineer Tal Danino and colleagues at MIT and the University of California, San Diego, wanted to see whether bacteria could instead be consumed at low concentrations and still reach liver tumors.
The team began with a probiotic strain of E. coli, previously used to treat inflammatory bowel disease. They engineered the bacteria to produce many copies of an enzyme called lacZ. They then fed the bacteria to mice — some with liver cancer, some without.
Finally, the scientists injected the mice with a molecule that, when chopped in half by lacZ, releases a chemical that changes the color of urine from yellow to red. In mice with cancer, the bacteria grew furiously, produced lacZ and the urine changed color. In mice without cancer, the urine remained normal.
Bacteria can grow in tumors as small as 1 millimeter, so the urine test has the potential to detect liver tumors — which tend to be small and dispersed — very early on, which would improve survival rates for patients. Current imaging techniques, such as CT scans, are lucky to flag tumors at 1 centimeter.
The engineered bacteria had no negative health effects on the mice, but much more work will need to be done to see whether the same is true for humans.
The researchers also hope the test can be used to detect other types of cancer in the gastrointestinal tract, says Danino.