Tuesday August 11 2009
Melittin is a component in honeybee venom
The Daily Mail today reported how “tiny 'nanobee' particles full of venom target diseased cells”. It said that scientists have developed microscopic “bees” carrying melittin (the poison that causes the pain of stings) that can target cancer cells. The nanobees, which were tested in mice, slowed the growth of breast tumours and shrank skin cancer tumours.
This research into the potential anti-cancer effects of the melittin-containing nanoparticles is still at a very early stage. The effects have only been tested over a short period of time and on a limited number of cancerous cell types in the laboratory and in mice. Much more research will be needed to investigate the safety and effectiveness of this treatment in animals before it could be considered for testing in humans.
Where did the story come from?
The research was carried out by Neelesh R Soman and colleagues from the Washington University School of Medicine, St Louis, Missouri, USA. The study was funded by the National Institutes of Health and the American Heart Association. It was published in The Journal of Clinical Investigation, a peer-reviewed journal.
What kind of scientific study was this?
This was an animal study looking at the effect of melittin-containing nanoparticles on tumours in mice.
The chemical melittin is a component in honeybee venom. It kills cells in mammals by making holes in the membranes surrounding cells and the important structures within the cells, resulting in cell death. The researchers wanted to develop a method to incorporate this chemical into tiny particles (nanoparticles) and to target these particles so that they only attack cancer cells. They had already succeeded in making melittin-containing nanoparticles, and in this paper they describe some of the chemical and laboratory tests they carried out on these particles.
The researchers began by investigating how cells are affected by melittin-containing nanoparticles and melittin in the laboratory. They then looked at how mice’s bodies dealt with intravenous injections of these chemicals. They looked at the effects of melittin-containing nanoparticles on three types of tumour in live mice: mouse melanoma skin cancers, pre-cancerous skin lesions and human breast cancer cells transplanted into immunocompromised mice.
The researchers also investigated the effects of melittin-containing nanoparticles that had been adapted to help target newly forming cancers by targeting the new blood vessels that feed the tumours. The targeted and non-targeted melittin-containing nanoparticles were injected (seven injections over an 18-day period) into genetically engineered mice that are prone to developing squamous cell carcinoma (a type of skin cancer) and compared to the effects of salt water injections.
What were the results of the study?
In laboratory tests melittin was found to be less toxic to cells when incorporated into nanoparticles than it was when added to cells by itself. The concentration of melittin-containing nanoparticles needed to cause 50% of melanoma cancer cells to break open and die in the laboratory was lower than the concentration that caused 50% of red blood cells to break open.
Intravenous injections of free melittin into mice led to rupture of red blood cells as expected. However, mice injected with melittin-containing nanoparticles over 18 days (one injection every three days) showed no evidence of rupture of red blood cells, no physiological signs of adverse effects and no evidence of damage to the liver, lungs, kidney and heart on microscopic examination.
The researchers found that injecting the nanoparticles into immunocompromised mice that had been transplanted with human breast cancer cells reduced growth of the tumour by about 25% compared with control injections (salt water). The nanoparticles also reduced the size of mouse melanoma tumours transplanted into non-immunocompromised mice by about 88% compared with control injections (salt water). The injections did not affect normal organ weight or normal levels of various chemicals in the blood. The injections did increase the levels of haemoglobin (the oxygen-carrying pigment from red blood cells) and reduced levels of one liver enzyme in the blood.
Laboratory tests showed that melittin-containing nanoparticles that targeted new blood vessels could kill mouse blood-vessel-lining cells and human melanoma cells. These targeted nanoparticles also reduced the formation of pre-cancerous lesions on the ears of mice that were prone to developing skin cancer, while non-targeted nanoparticle injections did not. The nanoparticle injections did not seem to have a toxic effect on the mice’s organs.
What interpretations did the researchers draw from these results?
The researchers conclude that they have demonstrated that synthetic nanoparticles can be used to deliver melittin, and these particles can kill both established tumours and pre-cancerous lesions.
What does the NHS Knowledge Service make of this study?
This research into the potential anti-cancer effects of melittin-containing nanoparticles is still at a very early stage. The effects have only been tested over a short period of time and on a limited number of cancerous cell types in the laboratory and in mice. Much more research will be needed to investigate the safety and effectiveness of this treatment in animals before it could be considered for testing in humans.