Wednesday, March 21, 2012

How is a painkiller curing cancer?

Cancer has been one area of science that the Indian media is willing to spend space on. Sadly, I couldn’t come across too many reports -- forget Indian reports -- that would lure a lay-reader to go beyond the ‘Aspirin a Cancer killer’ headline and bother to find out what was actually done here.

What is Aspirin?

Aspirin belongs to a class of drugs called nonsteroidal anti-inflammatory drugs or NSAIDs which is usally called ‘Dispirin’ in India. The main use of Aspirin is as a pain-killer, though more recently it has shown to prevent cardiovascular (heart) problems and now cancer.
How does it work?

Aspirin blocks the activity of an enzyme in our body called cyclo-oxygenase. Cyclo-oxygenase is needed to produce various chemicals in our body like prostaglandins, prostacyclins and thromboxane.

Pain: Prostaglandins are chemicals produced during injuries because of which we get swellings, inflammation and thereby pain. A high dose of aspirin (300mg and over) prevents the enzyme cyclo-oxygenase from producing these prostaglandins. And Voila! No pain.

Cardiovascular diseases: A lower dose of aspirin blocks cyclo-oxygenase too, but not enough to prevent prostaglandin production. At lower doses, aspirin prevents cyclo-oxygenase’s role in the production of another chemical called thromboxane. Thromboxane is usually produced by blood cells called platelets (with the help of cyclo-oxygenage) to help clot our blood and prevent too much bleeding, when you hurt your knee for example. But clotting of blood within your blood stream can obstruct free flow of blood and result in a stroke or a heart attack. So by preventing the production of thromboxane, blood is less likely to clump together in your blood vessels and cause complications.

Cancer: While the above two uses of Aspirin are relatively well established, it’s role in cancer prevention/cure has been debated since the 70’s by Bennett and Del Tacca. But three recent studies on the topic conducted by Peter Rothwell of the Oxford University however have silenced some skeptics. They conducted a randomized, controlled trials and concluded that a daily low dose of Aspirin for just 3 to 5 years is enough to lower risk of certain cancers, particularly bowel cancer in people who are at risk.

However, it must be noted that all these studies have been epidemiological studies. Though statistics have been proved to be immensely useful to establish correlation between two factors, is it enough? From what I have explored, not many biological reasons for this phenomenon have emerged. If they have then, nobody seems to be talking about them enough.

How is Aspirin doing this?
The biological processes involved in this correlation have still not been established. However there have been some explanations proposed.

As mentioned, Aspirins thins blood, makes it less likely to clot by its effect on blood clotting platelets. Now platelets, save us from bleeding to death no doubt, but they have been show to play a sinister role as well. They prime cancer cells for metastasis ie. They help cancer cells spread from its site of origin. How it does this is detailed in this easy-to-understand article .
So since Aspirin is anti-platelet, and platelets are pro-cancer, this could be one of the mechanisms by which Aspirin cures cancer.
Last month Australian scientists made another explanation.
Co-lead author Tara Karnezis said tumors secret proteins and compounds called growth factors, attracting blood and lymphatic vessels to their vicinity and allowing the cancer to flourish and spread. These growth factors also encourage lymphatic vessels -- or "supply lines" -- to widen, which enables the spread of cancer, she added. "But a group of drugs reverse the widening of the supply line and make it hard for the tumor to spread -- at the end of the day that's what kills people," Karnezis said. "This discovery unlocks a range of potentially powerful new therapies to target this pathway in lymphatic vessels, effectively tightening a tumor's supply lines and restricting the transport of cancer cells to the rest of the body."

Reality checks
So whatever the reason, this doesn’t mean we can simply start gobbling up pills and expect to be Cancer free. There are several concerns that haven’t been addressed.

Aspirin has been known to have side-effects, one of the more serious though rare one is stomach bleeding.

Some critics have noted that some of the doses given in the study were much higher than the 75mg dose typically given in the UK, said a BBC report (Since the article is Lancet, read Elsevier, stuck up folks aren’t letting me read it for free and verify this myself).

The benefit of Aspirin for healthy people is yet to be quantified. The lead author Prof Rothwell himself has said that for most fit and healthy people, the most important things they can do to reduce their lifetime cancer risk is to give up smoking, take exercise and have a healthy diet. Aspirin does seem to reduce the risk further – but only by a small amount if there is no risk factor.


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