Generally speaking, we go to great lengths to rid our bodies of foreign bacteria, whether its by brushing our teeth, washing our hands or taking antibiotics. But new research suggests that when it comes to treating tumors, we may one day invite the bugs in. According to a study published yesterday in the early online edition of the Proceedings of the National Academy of Sciences, a bacterium that normally resides in soil, dust and dead flesh quickly destroys large tumors in mice when injected along with chemotherapy drugs.

Current cancer treatments are limited in part by their inability to destroy poorly vascularized areas of tumors: radiation requires oxygen to kill cells and chemotherapy drugs demand a blood system to reach their target. Anaerobic bacteria, on the other hand, actually prefer oxygen-free, or hypoxic, environments. Researchers have thus wondered for some time whether such bacteria might prove useful in combating tumors. Now Bert Vogelstein of Johns Hopkins University and his colleagues have shown that they can be. "The idea is to selectively attack these tumors from inside with the bacteria and from the outside with chemotherapy," Vogelstein explains. The team genetically engineered the bacterium Clostridium novyi, producing a toxin-free strain that, when administered with conventional drugs, eliminated nearly half of the advanced tumors in their lab mice within 24 hours. The healthy tissues surrounding the tumors, in contrast, remained intact.

The teams so-called combination bacteriolytic therapy (COBALT) did have some negative outcomes, however. As many as 45 percent of the mice with the largest tumors died after treatment, presumably because of toxins released by the deteriorating tumor cells. "Any therapy which dramatically shrinks tumors may be subject to this side effect," the authors note. Yet although such tumor lysis is difficult to control in mice, it may be more easily controlled in humans. Still, whether or not COBALT will even work against human tumors at all remains to be seen. Says team member Kenneth Kinzler: "We hope that this research will add a new dimension to cancer treatment but realize that the way tumors respond to treatment in mice can be different than in humans."