Paracelsus' poison

Spider venom to treat cancer?

I was intrigued by an all-too-short, short news item reporting that a Queensland research group has won funding to study the use of spider venoms as treatments for cancer. Venoms for cancer? This might surprise people, as the point of venoms is to kill or injure things. How can they be used as medicine?

The reason is of course the dictum of my blog patron “it is the dose that makes the poison”. To kill or harm you the venom has to interfere with the body’s processes, often in interesting ways that humans hadn’t discovered until we studied the venom. By using a controlled dose we can use that effect to treat disease.

One of our most successful treatments for high blood pressure is a modified version of a South American Pit Viper venom. A large dose of the venom causes your blood pressure to plummet, a small dose lowers it. Hundred of thousands of people are living better lives by taking a little bit of (highly) modified venom each day.

I’m sure the Queensland team will find something in spider venom to kill cancer cells (like this study here), but that’s the easy part. Killing cancer cells is quite easy, cyanide will effectively do the trick. But killing cancer cells without killing the rest of you is hard. After all, cancer cells are your cells, driven to grow uncontrollably by mutations in the cells growth machinery.

So far, with a few exceptions, most of our treatments exploit the fact that cancer cells grow much faster than ordinary cells, so are directed at the mechanisms of growth. Unfortunately, bone marrow cells, the cells that line your gut and the cells in your hair follicles also grow rather fast, and tend to be hit by our treatments. Which is why many cancer therapies cause horrible gastrointestinal problems and cause your hair to fall out.

Most likely, a spider venom would work in this way, hitting fast growing cells. If we are really lucky, a venom component might target something unique to the cancer. All cancers are caused by mutations in the cells growth pathways, our newest anti-cancer drugs target these mutant pathways. In some cancers like chronic myeloid leukaemia, there is a key mutation present in most of these cancers. Drugs targeting this mutated enzyme produce an 80-90% remission rate with none of the horrible side effects of drugs based on growth alone.

Sadly, because of the diversity and complexity of the cells growth mechanisms, in general not all cancer cells have the same suite of mutations. Thus most cancer drugs aimed at the mutant pathways have much more modest effects. But even these modest effects can be very worthwhile, especially in cancers that have currently few treatments, like Glioma.

A scorpion venom is currently under trial for Glioma. It doesn’t attack growth pathways per se, but accessory pathways. A peptide derived from a different scorpion venom binds almost exclusively to tumour tissue, and is being trialed to deliver anti-cancer treatments direct to the tumour.

So discovering a spider venom for cancer is quite realistic. Even if it’s a more general “kill all rapidly dividing cells” type, it’s possible to make delivery systems that will take the venom directly to the cancer. Cancers have very few features that distinguish them from normal cells, and making this kind of delivery system is not easy, but it remains a possibility. I will follow the Queensland groups work with great interest.

So next time you see a spider, give it some respect, its venoms could one day help cancer victims.