Vitamin C shown to inhibit tumour growth in mice
A team of US researchers has shown that vitamin C can inhibit the growth of some tumours in mice.
Many scientists have previously argued that vitamin C may help to prevent cancer growth as a result of its antioxidant action, mopping up free radical molecules and preventing the damage they can cause to DNA.
However, the team at Johns Hopkins found that antioxidants may actually work by hampering a tumour's ability to grow under oxygen-starved conditions.
The researchers were investigating mice which had been implanted with either human lymphoma or human liver cancer cells, both of which produce high levels of free radicals, which could potentially damage DNA.
These free radicals can be mopped up by giving the mice antioxidants such as vitamin C.
However, the researchers unexpectedly noticed that cancer-implanted mice didn't show significant DNA damage, regardless of whether they were fed antioxidants or not.
Lead author Dr Chi Dang, Johns Hopkins Family Professor in Oncology Research, commented: "Clearly, if DNA damage was not in play as a cause of the cancer, then whatever the antioxidants were doing to help was also not related to DNA damage."
The researchers realised that some other mechanism must be involved and decided to investigate a protein called hypoxia-induced factor (HIF-1), which is switched on when cells run low on oxygen.
They found that HIF-1 disappeared in cancer cells which had been treated with vitamin C, despite being abundant in the untreated cells.
Dr Dang explained: "When a cell lacks oxygen, HIF-1 helps it compensate. HIF-1 helps an oxygen-starved cell convert sugar to energy without using oxygen and also initiates the construction of new blood vessels to bring in a fresh oxygen supply."
HIF-1 is therefore critical for the survival of certain rapidly-growing tumours, which require large amounts of oxygen. However, HIF-1 cannot function without free radicals, meaning that removal of free radicals by antioxidants - such as vitamin C - can prevent these tumours from growing. Publishing the findings in the journal Cancer Cell, Dr Dang said: "The potential anti-cancer benefits of antioxidants have been the driving force for many clinical and preclinical studies.
"By uncovering the mechanism behind antioxidants, we are now better suited to maximise their therapeutic use."
However, the researchers noted that the findings are still at an early stage and we don't yet know how they translate to humans. They advised people not to rush out and buy bulk supplies of vitamin C supplements as a means of cancer prevention.