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March 28, 2022

Canadian Nuclear Laboratories sets its sights on the ‘rarest drug on Earth’

On a nuclear research campus in the Ottawa Valley, Canadian researchers spent decades quietly transforming the way we fight cancer. With Actinium-225, they are about to do it again.

If you haven’t heard of an isotope called Actinium-225, it’s for good reason. Even with an army of nuclear scientists at your disposal, you’d be hard pressed to find more than just a trace of Actinium-225 on the planet. An alpha-emitting isotope with a short half-life, Actinium-225 is so rare that the annual global production is less than a grain of sand. Given this scarcity, it should come as no surprise that the isotope has been dubbed ‘the rarest drug on Earth.’

Today, the unique properties of Actinium-225 have also made it one of the most sought-after isotopes in the world by the medical community. The material made headlines in 2016 when a German patient suffering from terminal cancer was treated with a novel new therapy enabled by this rare isotope. Eight months later, the tumours had largely disappeared, the patient was still alive, and international researchers were clamouring for more Actinium-225 in order to explore the potential of this radioisotope.

“Given the extraordinary results, it is clear why this case captured the world’s attention, and further studies have shown just as much promise,” explains Joe McBrearty, President and Chief Executive Officer at CNL. “Unfortunately, the limited supply of the isotope has really hampered the world’s ability to advance research on targeted alpha therapy, which is the treatment that uses Actinium-225. There is not a lot of the material to make use of, and it is also quite difficult to produce.”

Enter Canadian Nuclear Laboratories (CNL). CNL operates the Chalk River Laboratories north of Ottawa, which is owned by the federal government’s nuclear crown corporation, Atomic Energy of Canada Limited (AECL). Chalk River once produced more than half the world’s supply of molybdenum-99, a key isotope used for cancer diagnostic procedures, among others. CNL estimates that isotopes produced in Chalk River have been used in over one billion medical procedures.

With the closure of the National Research Universal reactor in 2018, CNL ceased producing molybdenum-99, but the company still fulfills a vital role as a national research laboratory, with considerable strengths in health sciences and the development and testing of medical isotopes and radiopharmaceuticals.  With the growing interest in Actinium-225, CNL quickly recognized that it was one of a handful of companies in the world that could not only produce research quantities of the rare material, but study it as well.

“CNL has all of the health science laboratories, equipment and expertise to conduct research programs based on Actinium-225, but we also have the nuclear materials needed to produce more of this rare isotope,” explains Dr. Jeff Griffin, Vice-President of Science and Technology at CNL. “Over the past three years, we have developed a small scale generator which produces enough Actinium-225 for our own research, but also meaningful quantities that we can share with strategic partners in industry and academia to advance treatment safety and efficacy.”

How do those treatments work, exactly? Actinium-225 is attached to what is known as a targeting molecule, such as an antibody, that is designed to seek out and bind with cancer cells. As the isotope decays, it emits high-energy alpha particles that effectively kill cancer cells, leaving nearby healthy cells virtually unharmed in the process. With a favourable half-life of 10 days, Actinium-225 lasts long enough to do its job in fighting cancer and does not harmfully linger in the body. Due to its many unique attributes it is seen as a ‘goldilocks’ isotope in nuclear medicine.

This treatment is collectively known as targeted alpha therapy (TAT), and CNL is positioning itself to be an international hub for this type of research into the future. In addition to radioisotope production, CNL also maintains capabilities to conduct biological research at its Biological Research Facility, a unique facility that holds the necessary capabilities to perform TAT-related research and development for universities and innovative companies, and which is on its way to obtain Good Laboratory Practice (GLP) recognition.

But even bigger plans are in the works. CNL sees a clear opportunity to build on its legacy in isotope production and processing, and is exploring the construction of new facilities on its main campus that would establish a stable, commercial supply chain for Actinium-225. In pursuit of that goal, CNL recently signed a Memorandum of Understanding with ITM Isotope Technologies Munich, a leading radiopharmaceutical biotech company based out of Germany.

It’s all very exciting for the many researchers who are quietly advancing nuclear science and technology at the Chalk River Laboratories, a Canadian science institution that once transformed the way the world fights cancer and diagnose many life threatening diseases, and which gave hope to millions of people all over the world. With Actinium-225, they’re about do it again.

*Article originally appeared in the Toronto Star “Advancements in Cancer Care” insert (2021 March 20).

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