Neutron scattering reveals drug mechanism
14 Dec 2012 by Evoluted New Media
New insights into the origin of the side effects of an antifungal drug have been provided by neutron scattering experiments undertaken by researchers at Kings College London.
Amphotericin (AmB) has been used since the 1950s to treat fungal infections in immunocompromised individuals such as those with HIV or severe burn victims. However, in recent years, antibiotic resistance in fungi has increased dramatically and has resulted in the prescription of increased doses of AmB which have in many cases produced severe side effects. It has been shown that at these doses, almost 50% of patients experience some form of kidney poisoning.
“In the 1950s, when amphotericin was discovered, the fact that it worked was all that was really deemed necessary, but now we know that the drug has a very low therapeutic index, with worrying side effects at the high doses needed for these times,” Dr David Barlow, who lead the study, told Laboratory News
Barlow and his colleagues undertook neutron diffraction experiments at the Institut Laue-Langevin to reveal how AmB reacts with fungal and animal cell membranes.
The team modelled the two different membranes with layers of lipids (fatty molecules found in all cells) which were combined with cholesterol (for animal membranes) and ergosterol (for fungal membranes).
When neutrons encounter obstacles whose size is comparable with their wavelength, they scatter along well-defined angles. It is this property which allows scientists to analyse the scattering patterns and infer the structure of the material the neutrons have passed through.
The results revealed the first experimental evidence for AmB causing pores to form in the fungal membranes, resulting in eventual cell death. The pores were found to penetrate more deeply into the fungal membranes than the human membranes at relatively low doses. However, at higher (clinically relevant) doses, AmB caused holes to form in both types of membrane and hence cause damage to the healthy tissue.
These findings could have implications for the design of new, safer antifungal agents.
“Until now, no one has been able to experimentally determine how AmB works. Knowledge of amphotericin’s mechanism of action could lead to designing an analogue of the drug that works in a similar way but without the side effects. We intend to carry out more detailed experiments, improving the resolution of the analysis so we can identify which parts of the drug’s chemical structure are interacting with fungal and human membranes,” Barlow told Laboratory News.
