Dirt bugs may have the grit to beat disease

Common soil bacteria injected into solid cancers in pet dogs and one human patient shrank tumours, scientists reported this week.

The findings offered hope that the treatment could turn out to be more effective than existing cancer therapies for inoperable tumours that often fail to respond to radiation and chemotherapy.

Radiation requires oxygen to kill cells, but the deep interior of tumours is nearly oxygen-free. Chemotherapy requires blood vessels to carry drugs into tumours, the interiors of which generally lack such plumbing.

"These conditions make the tumours perfect for bacteria that thrive in low-oxygen environments," said oncologist Shibin Zhou of the Johns Hopkins Sidney Kimmel Comprehensive Cancer Centre in Baltimore, Maryland, a senior author of the study.

Doctors first tried using streptococcus bacteria to attack tumours 100 years ago, but that proved to be toxic, ineffective, or both.

The idea nevertheless made sense and a decade ago Hopkins scientists resurrected the approach using clostridium novyi soil bacteria. They modified the bug by removing DNA that makes a toxic protein and injected only spores, which are less likely to cause infection. Sixteen dogs received injections of 100million clostridium spores. Tumours shrank in three of the 16 dogs and disappeared in three more, reported the Science Translational Medicine.

At MD Anderson Cancer Centre in Houston, a patient with an aggressive cancer received an injection of 10000 spores into a tumour in her arm. She ran a fever - a sign her immune system was attacking the cancer - but the tumour shrank.

Zhou said the spores release enzymes that destroy nearby tumour cells. Also, the immune system senses the bacteria and dispatches tumour-killing cells.