Among all the different types of cancer treatment, photodynamic therapy – where light is used to destroy malignant cells – could have one of the strangest side effects: Patients are often better able to see in the dark.
Last year, researchers finally figured out why this is happening: Rhodopsin, a light-sensitive protein in the retinas of our eyes, interacts with a photosensitive compound called chlorine e6, a crucial part of this type of cancer treatment.
The work builds on what scientists already knew about the organic compound retinal, which is in the eye and is usually not sensitive to infrared light.
Visible light triggers the separation of the retina from rhodopsin – it is converted into an electrical signal that our brains interpret to see. While we don’t get much visible light at night, it turns out that this mechanism can also be triggered by another combination of light and chemistry.
Under infrared light and with an injection of chlorine, the retina changes the same way it does under visible light.
“This explains the increase in visual acuity at night,” chemist Antonio Monari, from the University of Lorraine in France, told Laure Cailloce. CNRS back in January 2020.
“However, we did not know precisely how rhodopsin and its active retinal group interacted with chlorine. It is this mechanism that we have now succeeded in elucidating via molecular simulation.”
In addition to some high-level chemical calculations, the team used molecular simulation to model the movements of individual atoms (in terms of respective attraction or repulsion), as well as the breaking or creation of chemical bonds.
The simulation took several months – and went through millions of calculations – before it could accurately model the chemical reaction caused by infrared radiation. In real life, the reaction would take place in nanoseconds.
“For our simulation, we placed a virtual rhodopsin protein inserted into its lipid membrane in contact with several e6 chlorine molecules and water, or several tens of thousands of atoms,” Monari said. CNRS.
As chlorine e6 absorbs infrared radiation, it interacts with oxygen in the eye tissue, turning it into highly reactive singlet oxygen – in addition to destroying cancer cells, singlet oxygen can also react with the retina and provide improvement. night vision, shown in the simulation.
Now that scientists know the chemistry behind this bizarre side effect, they may be able to limit the risk of this happening in patients undergoing photodynamic therapy, who have reported seeing silhouettes and contours in the body. darkness.
Later, this chemical reaction could even be exploited to help treat certain types of blindness or hypersensitivity to light – although trying to use e6 chlorine to give you night vision is absolutely not recommended. superhuman.
This is another example of the information we can also get from molecular simulations and how the most powerful computers on the planet are able to give us a deeper understanding of science than we would otherwise have.
“Molecular simulation is already being used to shed light on fundamental mechanisms – for example, why some DNA lesions are better repaired than others – and allow the selection of potential therapeutic molecules by mimicking their interaction with a chosen target. “said Monari. CNRS.
The research was published in the Journal of Physical Chemistry Letters.
A version of this article was first published in February 2020.