The Potential Anti-Cancer Power of “Parasites”

I have read the vast majority of papers ever written on the subject of therapeutic helminths, and cannot, for the life of me, remember reading one that specifically addresses their potential anti-cancer effects.  I knew that helminths’ inflammation-modulating effect should theoretically be highly beneficial in terms of lowering cancer risk, but today, for the first time, I read a whole paper[i] devoted to all the mechanisms by which “parasites” may be effective.

A few caveats:

Let me start by saying that unfortunately, none of the organisms currently used for helminthic therapy were mentioned in this paper.  Currently, then, there is only research on several organisms that are very unappealing, in that they are both unavailable commercially and have (often terrible) negative side effects.  Still, the paper provides amazing insight into the potential of such organisms to both prevent and treat cancers.

Secondly, some parasitic organisms may actually be carcinogenic. For example, Schistosoma (which has so many negative effects on people that it will never be used in helminthic therapy) is associated with bladder cancer, and certain blood-borne flukes (again, these are really dangerous), are associated with liver cancer.  Likewise, there are bacteria – for example, H.pylori, which are associated with gastric cancers.  To sum up:  there are good and bad of every kind of organism.

Third caveat:  this research is definitely in its infancy.  But what we do know so far is so promising that it’s worth reading and writing about even at this early stage.

Now a short summary of some of the paper’s highlights:

1. Immune surveillance means that your immune system is constantly on the lookout for abnormal cells, which it then (ideally) destroys.  When things go wrong, for example, the immune system is compromised, cancer cells may avoid detection.  One example:  Trypanosoma cruzi (cruzi), a protozoa (single-celled organism) associated with disease in humans, has antitumor effects.  Epidemiological studies show that infection with this is associated with lower incidence of colon cancer, but more than that, in experimental models of breast and colon cancers, the organism is preventative.  Antibodies to T.cruzi “…were able to specifically recognize human breast and colon cancer cell lines. Interestingly these antibodies also recognized 68% of tumor biopsies from breast and colon cancer patients.”  That is, antibodies that target certain pathogenic protozoa can also target tumor cells and can help the immune system recognize them before they become problematic.
2. Since the beginning of the 19^th century, we have known that inflammation is associated with the development of cancer. For example, it’s accepted fact that chronic inflammation plays a major role in the development of colon cancer.  Thus, patients with ulcerative colitis have a greatly increased risk of developing this.  The current experimental model used for colitis involves exposing rodents to chemicals that induce inflammation.  The larval stage of an organism called Taenia crassiceps, which is closely related the beef tapeworm, dramatically down-regulates inflammation in such a model, and was “…able to inhibit the development of carcinogenesis in colon associated with inflammation.”  It reduced 60% of the total number of tumors, and more than that, 50% of the mice infected with this tapeworm did not develop tumors at all.
3. A chemical derived from the above mentioned T.cruzi seems to prevent the formation of blood (and thus, nutrient) supply to breast tumors in both in vitro and in vivo experiments. T.cruzi also seems to induce tumor cell death (apoptosis).

This is the opening sentence of the paper’s conclusion:  “In this review we have gathered information about the different antitumor mechanisms triggered by some helminth and protozoan parasites, together they may target around 50% of the hallmarks of cancer….parasites can interfere in the growth and proliferation of a variety of transformed cell lines in vitro, but also, and more importantly, parasites and their products can modulate cancer development in vivo from melanoma to colon cancer.”

So once again, we are faced with a situation where currently available science hints at amazingly exciting potential treatments, but far too much is still unknown.  One encouraging final bit of news for you though: the commercially available organisms used for helminthic therapy all have proven anti-inflammatory effect.  Just last month, in fact, when this cancer paper was published, so was one entitled, “The Benign Helminth Hymenolepis diminuta Ameliorates Chemically Induced Colitis in a Rat Model System.”[ii]  Rats that are colonized with H.diminuta, and then exposed to a chemical that ordinarily induces colitis, have lower inflammation and less severe colitis symptoms – perhaps lowering colon cancer risk???

We can only hope that in the near future, the  helminths currently used therapeutically are looked at for their anti-cancer potential.

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[i] Callejas, BE, Martinez-Saucedo, D, Terrazas, LI. Parasites as negative regulators of cancer.  Bioscience Reports. 2018. DOI: 10.1042/BSR20180935

[ii] Jirku Pomajbikova, K, Jirku, M, Leva, J, Sobotkova, K, Morien, E, Parfrey, LW. The benign helminth Hymenolepis diminuta ameliorates chemically induced colitis in a rat model system.  Parasitology. 2018;145(10):1324-1335.