Researchers put cancer into deep freeze
Inserting icy cold metallic probes into a tumour can freeze it to the brink of death, the study suggests, allowing doctors to finish off the diseased cells with a potent anti-cancer drug.
Monitoring the treatment - called cryochemotherapy -with high-tech imaging techniques should also ensure that healthy tissue is left unharmed, potentially giving fewer side-effects than conventional treatments.
Techniques involving freezing have been around for some time, but have had limited success, since it has been difficult to ensure that all the cancer cells have been destroyed. It only takes a handful of cells to survive for a tumour to regrow.
But when cells are frozen, their outer barriers - called membranes - become leaky, allowing large molecules such as drugs to enter them more easily. Scientists decided to exploit this fact by combining freezing with chemotherapy.
Dr Lluis M Mir from the CNRS and the Institut Gustave-Roussy near Paris and Dr Boris Rubinsky from the University of California at Berkeley treated frozen cancer cells with a drug called Bleomycin, which is potentially highly toxic to cells, but is usually unable to pass through their membranes. They compared the effectiveness of the combined treatment with freezing on its own.
Treatment with freezing alone left around 250 surviving cells - easily enough to form a new tumour. But when cancer cells were given Bleomycin as well, hardly any survived - an average of less than one with the higher concentrations of drug.
Researchers believe that as well as being highly potent, cryochemotherapy should also be more selective than conventional treatments, since the frozen probes can be precisely targeted to the tumour.
Dr Mir explains: "Frozen tissues show up very clearly on scanning images, so it is a simple matter to ensure that you are giving the cold probes to the tumour and avoiding the healthy tissue.
"Although the drug we are using is extremely toxic, it can only enter cells that have been frozen, which means that unfrozen healthy tissue will be left unaffected.
"We are due to enter preclinical trials shortly and are excited by the prospects of our technique, although there's lots of work to do to develop it for patients."
Sir Paul Nurse, Interim Chief Executive of Cancer Research UK, says: "Designing selective treatments, which attack tumours while leaving healthy tissue unharmed, is one of the most important goals in anti-cancer drug development. This will mean we can develop more effective treatments with far fewer side-effects. This study represents an early step towards that goal."
- British Journal of Cancer86 (10)
Note to editors:
After each treatment, dead cells were washed away and any remaining cells were grown into clusters called clones, which can easily be counted.
Treatment with freezing alone left around 250 clones. But when freezing was combined with Bleomycin, virtually no cancer cells survived. Even at extremely low concentrations of drug (10 nM) there were only around 13 clones, while for higher concentrations the average was between 0 and 1.