Anti-cancer Fungi

Mycology, the study of fungi, is an often-overlooked member of the microbiology family. Having said that there are plenty of dedicated mycologists out there doing all sorts of cool stuff and plenty more fungal species doing all sorts of weird and wonderful things.

I have written about fungi before but only in the recent zombie posts and I feel I may have been a bit negative on fungi. Particularly when they seem to be capable of much good.

In recent years researchers have made some potentially amazing discoveries that could result in significant cancer treatments based on the observations of polysaccharopeptides recovered from some species of fungi.

Polysaccharopeptides are commonly recovered from Coriolus versicolor commonly called Turkey tail fungus or Yun-zhi (credit, credit and credit)

What’s a polysaccharopeptide? It’s a contraction of the full description polysaccharide peptide. Essentially it is a long repeating unit sugar chain connected to a small protein sequence. Sounds innocuous but these molecules (or more accurately the fungi harbouring these polysaccharopeptides) have been used in traditional Asian medicine for a long time.

Beginning in the 1980’s these compounds began to attract more attention due to their apparent anti-tumour activity. The interest in polysaccharopeptides started to build when it was identified that the anti-tumour activity was not due to direct killing of tumour cells, but instead was due to an upregulation of the host immune system assisting the host to take care of its own cancer.

It appears now that polysaccharopeptides have 3 major activities; the activation of phagocytes, the activation of natural killer T-cells and the activation of helper (or CD4⁺) T cells. Without getting into the nitty gritty immunology of it all phagocytes ‘eat’ foreign material, tissue debris and misbehaving cells, natural killer T cells respond to misbehaving cells by ordering them to die and CD4⁺ T cells produce lots of chemicals which assist the immune system in many different ways. Essentially these polysaccharopeptides are acting as a turbo boost button for the immune system.

The real power in a compound that stimulates an immune response to handle a tumour, rather than a compound that directly kills cells, is that the body has in-built defences to make sure it doesn’t destroy its own healthy cells. When you give polysaccharopeptides to healthy individuals their immune systems are activated but with nothing to attack they scale back down again without doing any damage compared to current approaches to cancer therapy including chemo and radiotherapy which cannot target a tumour cell directly which can result in nasty wound as well as side effects like hair loss and infertility.

Clinical trials of polysaccharopeptides are starting to become very exciting as synergistic combinations of traditional treatments are used alongside these compounds often to great effect.

A study in 1995 of 227 Japanese breast cancer sufferers saw that when split into two groups, one receiving standard chemotherapy treatment and the other receiving the chemotherapy and a supplement of polysaccharopeptide saw the 10 year survival rates jump from 64% to 81% in the chemo + polysaccharopeptide group. Similar results were observed in a 1994 study on gastric and oesophageal cancer patients where the 5 year survival rate jumped from 60% to 73% when chemotherapy was supplemented with polysaccharopeptide.

Other trials on colorectal, liver and lung cancers as well as disseminated cancers like leukaemia have also indicated favourable results for the supplementation of current therapies with polysaccharopeptides.

More recently we can add prostate cancer to the list of cancers that may benefit from the addition of polysaccharopeptide to therapeutic protocols. While not human trials, a recent study has found polysaccharopeptides can be used to prevent the development of cancers indicating there may be more to discover about these interesting molecules.

When fed a diet including polysaccharopeptides mice that are genetically engineered to develop prostate cancer simply didn’t. When I say didn’t I mean the mice that received only water got prostate cancer and at the end of 20 weeks the not a single water + polysaccharopeptide mice had a single prostate tumour.

As amazing as this result is the researchers went further and looked at why there were no cancers developing and found that the recently identified cancer stem cells of the prostate (a long lived, self renewing, cancer cell progenitor in the prostate) were being heavily inhibited in the polysaccharopeptide supplemented mice.

While only a small study, it suggests there may be a very important future role to be played by polysaccharopeptides in cancer therapy and, importantly, might lift the reputation of fungi in the eyes of people who ruthlessly destroy all the fungi and mould they can find.

ARGH!!! KILL IT!!! (credit)

References

King-Fai Cheng & Ping-Chung Leung (2008). General review of polysaccharopeptides (PSP) from C. versicolor: Pharmacological and clinical studies Cancer Therapy, 6
Luk SU, Lee TK, Liu J, Lee DT, Chiu YT, Ma S, Ng IO, Wong YC, Chan FL & Ling MT (2011). Correction: Chemopreventive Effect of PSP Through Targeting of Prostate Cancer Stem Cell-Like Population. PloS one, 6 (6) PMID: 21674070