Cancer solutions
tumours are a form of uncontrolled tissue growth. One of the main reasons why a malignant tumour can lead to death is that the tumour secretes factors that induce the growth of blood vessels in its neighbourhood. Thus, by increasingly monopolising the supply of nutrients, the tumour succeeds in starving the healthy tissues of the body. Anything that can control the formation of new blood vessels is potentially an agent to control tumour growth.
Some years ago, scientists decided to follow up the observation made by many cancer surgeons that the removal of certain localised tumours leads to the rapid appearance of secondary tumours in other places, and leads to metastases. They reasoned that the primary tumour could be secreting an inhibitory factor or a factor that prevented secondary foci of cancer cells from growing to any appreciable extent.
Once the primary focus was excised, the secondaries, unimpeded by any further secretion of the factor, could proceed in the direction of uncontrolled growth. This hunch proved to be correct and led to the isolation of two factors, angiostatin, discovered in 1994, and endostatin, discovered in 1997. The discoveries have led to furiously competitive research aimed at using these inhibitors for human cancer therapy. Repeated injections can be a risky course to take, and field workers have wondered whether a genetic means of providing angiostatin or endostatin might be found.
F Griscelli and colleagues at the National Centre for Scientific Research in Villejuif, France, have now made a beginning in this direction ( Proceedings of the us National Academy of Sciences , Vol 95, No 11). The method used was to infect the tumour cells with a virus (adenovirus) that had been engineered genetically to contain a dna sequence capable of making the region of angiostatin implicated in inhibiting the proliferation of endothelial cells. The results were striking.
There was a significant reduction in the growth of tumour cells in culture. Besides, when the genetically manipulated virus was injected into mice that had tumours of foreign origin in them, the tumours regressed significantly.
Exciting as these findings are, it will still be some time before scientists know how well the technique works with humans. Apart from issues of safety and practicability, investigators in the field are looking into other issues too. One benefit of this technique would be to direct the genetically-engineered virus to its appropriate target.
Further, is angiostatin of guaranteed efficacy against all tumours, or a large variety of tumours, or against just a few? Regardless of the answers and the test results, it is clear that attempts to fight cancer by preventing the growth of new blood vessels is the most promising one.
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