In the same way freezer burn can make ice cream unpalatable, it can also damage human cells, tissues, and organs necessary for life-saving procedures.
Figuring out how to safely deep freeze, thaw and transplant biological samples – especially entire organs – has been a Holy Grail of regenerative medicine for decades. While it’s now possible to freeze single cells, as well as eggs and sperm, the process for preventing ice recrystallization isn’t perfect, and larger tissues and organs are usually damaged beyond repair.
But if cryopreserved human organs could be safely stored and then used, hearts, lungs, kidneys and more could be banked for transplant at any time, and patients dying while on waiting lists would be a thing of the past.
While that’s still a dream, University of Ottawa organic chemist Robert Ben and University of Alberta cryobiologist Jason Acker have developed a molecule designed to more effectively inhibit ice recrystallization in single cells.
Recrystallization happens as biological samples are flash frozen with frozen nitrogen to -200C, as temperatures bounce around during storage and shipping, and especially as samples are warmed.
“Basically, the ice changes structure so that large crystals grow larger at the expense of smaller crystals,” says Ben. “These crystals then damage cell membranes and also inside the cell.”
Traditional peptide-based ice recrystallization inhibitors (IRIs) are toxic and can damage the cells they are meant to preserve. “Using current techniques, we lose a certain percentage of cells off the top,” says Ben. “Even the viable ones are not always doing what they’re supposed to do when they are thawed.”
While cryopreserved stem cells are still used with very sick patients and it can work out, it depends on the number of quality cells left over after thawing. Sometimes patients must endure repeated stem cell transplants, and sometimes it just isn’t effective and the patient dies.
“Any improvement we can make is significant,” says Ben.
That’s why Ben and Acker’s company, PanTHERA CryoSolutions, which emerged from their long-time research collaboration, is aiming to release its first ice recrystallization inhibitor (IRI) by the end of this year.
Their IRI is based on a naturally occurring antifreeze glycoprotein isolated from Antarctic fish. Not only is it smaller than traditional IRIs, which means it can more effectively enter cells, its carbohydrate-base makes it less toxic to human tissue.
Coming up with this glycoprotein involved evaluating more than 2,000 molecules – all slightly different, paired down versions of the fish glycoprotein. Their breakthrough came in 2015 when one of the resulting molecules allowed them to successfully freeze and quickly thaw human red blood cells.
Jay Kizhakkedathu, a polymer chemist at the University of British Columbia who was not involved in Ben and Acker’s research, says the toxicity of preservation agents has been one of the most significant barriers to cryopreservation.
“Their molecule has favourable toxicology profile, which makes it unique and attractive for use in cell preservation,” says Kizhakkedathu.
PanTHERA’s potential customers are cryopreservation companies serving the gene and cell therapy markets. Seattle’s BioLife Solutions — the largest in the industry, with 70 per cent of the global market — has not only licensed the product, it invested US$1 million in the company in 2020.
“We’re the only corporation globally using this small molecule approach to directly address the negative outcomes of ice recrystallization,” says Ben.