New bacteria target cancers in mice

Scientists from Johns Hopkins University, US, have created bacteria that selectively target large advanced tumours in mice.

The scientists found a way to exploit a special germ's taste for oxygen-starved environments and direct them to target pockets of dead and dying cells within large tumours. These advanced tumours generally have areas of poor blood circulation and thus little oxygen. The lack of oxygen renders them relatively resistant to conventional chemotherapy and radiation but open to bacteria that can grow without oxygen.

"The idea is to selectively attack these tumours from inside with the bacteria and from the outside with chemotherapy," says Bert Vogelstein, Howard Hughes Medical Institute.

The scientists systematically screened numerous bacterial species to find one that would thrive in an oxygen poor environment and, at the same time, destroy surrounding tumour cells. They settled on one spore-forming bacterial species, called Clostridium novyi.

Clostridium novyi is normally found in soil and dust and contains a toxin that can cause lethal side effects in animals. They genetically modified the bacteria to remove the toxin gene to make them harmless to normal animals. Then, they injected spores of these bacteria and conventional chemotherapeutic agents into mice with large tumours composed of transplanted human colon cancer cells.

More than half of the tumours treated, including very large tumours, were completely destroyed within 24 hours. The tumours decomposed and turned into blackened scars, while the surrounding healthy tissues remained intact. The tumour scars then gradually disappeared over the next two weeks, leaving healthy tissue behind.

Clinical trials are not planned at this time as it will take several years to determine which chemotherapy agents make the best combinations and to develop strategies to avoid the toxicity associated with rapid destruction of large tumour masses.