In its natural form, Clostridium novyi is at best benign (it lives in the soil) and at worst harmful (it can cause infections). But a slightly modified version of the bacterium could be a completely new treatment for cancer. Injecting thousands of spores of a modified C. novyi into rats, dogs, and one human patient shrank or even eradicated their tumors.
The intriguing study published this week in Science Translational Medicine describes how to harness the bacteria's natural ability to attack cells for good. C. novyi likes to oxygen-poor environments — like the soil or, in this case, deep inside dense tumors where chemotherapy and radiation can't penetrate. To make it safer as a cancer treatment, the C. novyi was modified to take out a gene for toxins.
The team, led by researchers at the Johns Hopkins Sidney Kimmel Comprehensive Cancer Center, first tested C. novyi in rats where they had induced tumors. The bacteria make enzymes that broke through cell wells, then gobble up the proteins spilled by the cancerous cells. The rat studies showed promise, so the researchers then injected the bacterium into the naturally occurring tumors of 16 dogs whose owners had given permission. After the injection, the tumors disappeared in three of the dogs and shrank by at least 30 per cent in three others. The dogs showed signs of bacterial infection — fever, inflammation, abscesses — but the side effects were no worse than what we already tolerate in cancer treatments.
Then the researchers tested the treatment in a human patient. A 53-year-old woman whose retroperitoneal leiomyosarcoma — a rare smooth muscle tumour — had spread to her liver, lungs, abdomen, upper arm, and shoulder had 10,000 spores of C. novyi injected only into the tumour in her shoulder. That tumour shrank; the others did not. More human trials are currently underway.
It's just one study so far, but this study is promising evidence that bacteria therapy for cancer could work. There idea has been studied for decades now, but other bacteria such as Streptococcus pyogenes used to treat cancer were too dangerous and inconsistent in their effectiveness. C. novyi seems to be an improvement. Doctors have also experimented with using viruses like measles to attack tumours.
Bacteria and viruses that make us sick, after all, are already exquisitely engineered to attack our cells — we just need to prompt them to attack the right ones. [Science Translational Medicine]
Picture: Rod-shaped C. novyi (dark purple) germinating in a dog tumour. David L. Huso and Baktiar Karim of the Johns Hopkins Department of Pathology