Shining a Light on Drug Development: Revolutionizing Radiolabeling
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Researchers have developed a revolutionary method for making radioactive molecules. Until now, tracing the exact pathway a potential drug candidate takes within the body has been a challenging and time-consuming task. This new technique means that new medicines may reach patients much faster than ever before.
Radiolabeled Compounds
Radiolabeling solves the challenge of tracing a compound's journey through the body, and has been a key element within the drug discovery and development pipeline for many years. Radiolabeling involves substituting one or more atoms belonging to your investigational drug compound, with a radioisotope. This allows you to monitor the in vivo behavior of a drug, tracing its distribution within the body. Meaning scientists can confirm that the drug is affecting the part of the body it is intended for.
"Is it going to the right place? The wrong place? The right place and the wrong place?" These were the questions asked by Prof. David MacMillan, University Professor of Chemistry, Princeton University. It was these exact questions that lead David’s Laboratory at Princeton to pioneer the novel approach that enables the creation of these radioactive substitutes.
A drug’s journey from conceptualization, to its approval and launch, can take many years. When you consider the amount of people who could potentially benefit from a drug, this is a long time to wait. MacMillan commented: “…everything that we can do to take that 14- or 12-year time frame and compress it is going to advantage society, because it gets medicines to people — to society — so much faster."
Getting Medicines to Patients Faster
Until now, it has been a very time-consuming process to integrate radioactive isotopes into the compound of interest. “Getting these radioactive atoms into the drug is not a trivial thing to do," MacMillan explained. "People have developed long, sometimes month-long, two-month, three-month long sequences just to get a tiny amount of a substance with a few radioactive atoms."
Is there a way to accelerate this process?
MacMillan and colleagues were able to ‘shed light’ on the situation — literally. Using blue LED light and photocatalysts they were able to fuel the substitution more efficiently. “It was a wacky idea! Fortunately, it worked,” MacMillan said. This research was published online November 9 in Science.
The novel technique involved replacing the hydrogen atom in H2O with tritium. Tritium, also known as hydrogen-3, is a radioactive version of hydrogen. Tritium’s nucleus contains one proton and two neutrons. Their “heavy water” technique, involved submerging a potential drug candidate in radioactive water, a light is then shined on to the compound, in the presence of a photocatalyst. The non-radioactive atom (hydrogen) is removed by the catalyst and replaced with tritium. 
Gleevec® (imatinib mesylate), an anti-cancer drug, is submerged in heavy water (T2O) and bathed in blue LED light to replace hydrogen atoms with tritium atoms (green circles) in a one-step direct hydrogen isotope exchange (HIE). Clinicians can trace radioactive compounds in the body using sophisticated imaging technologies for research and diagnostic purposes. Credit: Yong Yao Loh, Kazunori Nagao, and David MacMillan/Princeton University.
This new process takes hours, as opposed to months. Eighteen commercially available drugs have been tested, in addition to several potential drug compounds. The technique isn’t exclusive to tritium, hydrogen can also be substituted for deuterium (hydrogen-2) which is not radioactive, these substitutions have potential in both academic and industry applications.
MacMillan emphasizes: "No one's patenting any of this, because we want it to be available for everyone to use."
The simplicity of this technique means that it can be used earlier on in the drug development process. Allowing scientists to take a more comprehensive look at the safety, efficacy, and overall suitability of drug candidates a lot earlier on, helping identify the most promising compounds to take forward.
