INJECTING flesh-eating bugs into cancers sounds like a crazy idea. But early
signs suggest the only danger is that the bacteria consume tumour cells so fast
our bodies would struggle to cope.
The trick is to pick anaerobic bacteria that thrive in the oxygen-poor
interior of fast-growing tumours, but die as they reach the oxygen-rich edges.
鈥淭he exciting thing is we can combine this approach with chemo-therapy and
hit the tumour from both the inside and the outside,鈥� says Bert Vogelstein of
Johns Hopkins School of Medicine in Baltimore, Maryland.
Tumours supply themselves with food and oxygen by growing their own blood
vessels. But some tumours grow so rapidly their interiors become starved of
blood and oxygen, and turn into 鈥渘ecrotic鈥� regions full of dead and dying
cells.
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Surprisingly, this makes them harder to destroy. Drugs can鈥檛 reach the tissue
at lethal doses because the blood supply is so poor, while radiation treatments
need oxygen to trigger cell death. After treatment stops, surviving cancer cells
from the necrotic region can start dividing again.
Cancer researchers have long realised that anaerobic bacteria could be used
to attack the necrotic region without harming healthy tissue. But the microbes
tested so far have left parts of tumours untouched. So Vogelstein鈥檚 team widened
the search, testing 26 strains of anaerobic bacteria.
When they injected the soil bacterium Clostridium novyi into the
bloodstream of mice with tumours, it spread throughout the necrotic region,
consuming living tumour cells as well as dead tissue. 鈥淭hat was completely
unexpected,鈥� says Vogelstein. 鈥淲e thought we鈥檇 have to genetically engineer it
to do that.鈥� But the microbes died near the edges of the tumour, leaving the job
half done.
So the researchers tried combining the bugs with chemotherapy. 鈥淭he tumour
died so quickly, you could almost watch it,鈥� says Vogelstein. Out of eight
animals given the combination treatment, the tumours shrank dramatically or
disappeared completely in seven, and regrew in only one, the team will report in
a future issue of Proceedings of the National Academy of Sciences.
鈥淐ombining these different approaches is a very clever move,鈥� says Rakesh
Jain, a cancer researcher at Harvard Medical School in Boston. 鈥淚t鈥檚 wonderful
飞辞谤办.鈥�
The catch is that three of the eight mice died. But the researchers think
this could be because the tumours were destroyed so quickly that the waste
products flooded the animals鈥� circulation. 鈥淲e鈥檒l need to go to larger animals
to test that theory out,鈥� says Vogelstein. In small animals these toxins spread
too quickly to combat, but in humans they shouldn鈥檛 be lethal.
Vogelstein says it will probably be years before the therapy is ready for its
clinical debut. But when the time comes, it won鈥檛 be hard to stock up on the
prolific microbe. 鈥淲e can grow a world supply of it in my lab in a day,鈥� he
says.