Bacteria that can cause deadly infections in humans and animals have shown promise in treating cancer by “eating” tumors from the inside out.

Two new studies at the Johns Hopkins Kimmel Cancer Center have demonstrated that, combined with specially-packaged anti-cancer drugs, the bacterial therapy’s prospects for cancer eradication has dramatically improved.

Boffins conducting the studies, which were carried out on mouse models, found that genetically-modified bacteria called Clostridium novyi-NT (C.novy-NT) have a special taste for oxygen-starved environments much like those found in the core of cancer cell clusters.

“It is not difficult to kill cancer cells. The challenge is killing them while sparing normal cells,” said Bert Vogelstein, M.D., professor and co-director of the Ludwig Center and Howard Hughes Medical Institute at the Johns Hopkins Kimmel Cancer Center.

The Hopkins team had discovered in 2001 that though the bacteria was able to grow and spread in the oxygen-poor core of mouse tumors and the blackened scars signaling that most of the cancer cells had been destroyed, it could not destroy cancer cells at the still oxygen-rich edge of the tumors.

When the Hopkins team added specially-packaged chemotherapy to the bacterial attack, the combination temporarily wiped out both large and small tumors in almost 100 mice and permanently cured more than two-thirds of them.

The likely explanation is that combination treatment works because the bacteria expose the tumors to six times the amount of chemotherapy than is usually the case by improving the breakdown and dispersal of the chemotherapy’s fatty package at the tumor site.

The investigators repeated experiments using two packaged chemotherapy drugs — doxorubicin and irinotecan — and observed similar tumor-killing effects of both when used in combination with the bacteria.

“Drugs contained in these ‘Trojan horse’ compartments are specifically released at the tumor site by the C-novyi-NT bacteria which may improve the effectiveness and safety of the therapy,” said Ian Cheong, Ph.D., the lead author of the study.

The study is published in the November 24 issue of Science.

In a companion study published in the November 19 online issue of Nature Biotechnology, the Hopkins team decoded the entire C.novyi-NT genome which Shibin Zhou, M.D., Ph.D., assistant professor of oncology at the Johns Hopkins Kimmel Cancer Center, says “was instrumental in identifying liposomase and will help improve our bacterial-based therapies.”