A new platform using genome editing and magnetic cell sorting, discovered by researchers at the University of Toronto, could help reveal new drug targets for cancer and regenerative medicine.
Shana Kelley, a University Professor in the Leslie Dan Faculty of Pharmacy at U of T, had been developing a portable, chip-like device that uses tiny magnets to sort large populations of mixed cell types as part of her Medicine by Design team project.
She speculated that the device could be used with a CRISPR-based gene-editing technology developed by fellow Medicine by Design leader Jason Moffat, a professor in the Donnelly Centre for Cellular and Biomolecular Research.
The professors reasoned that the two methods could make it faster to come through the human genome for potential drug targets.
The result of their joint effort, also in collaboration with Stephane Angers, a professor at Pharmacy, and Edward Sargent, University Professor at the Department of Electrical and Computer Engineering, is called MICS, for microfluidic cell sorting.
MICS will enable researchers to scour the human genome faster when searching for genes, and their protein products, that can be targeted by drugs.
In one hour, MICS can collect precious rare cells, in which CRISPR revealed promising drug targets, from a large and mixed cell population. The same experiment would take 20 to 30 hours using the gold standard method of fluorescence-based sorting.
Researchers use CRISPR to switch off in cells each of around 20,000 human genes and see how this affects levels of a disease-related protein which, say, helps cancer spread. This can reveal other gene candidates, and the proteins they encode, that work in the same pathway and which could be targeted with drugs to remove the target protein and halt cancer.
The caveat is that genetic screens result in mixed cell populations, with the desired effect present in a vanishingly small proportion of cells which have to be scooped out for further study. Most cell-sorting instruments use laser beams to separate fluorescently labeled cells, but this takes time.
MICS works faster thanks to tiny magnets engineered to bind to the target protein, which leaves the cells sprinkled with magnetic particles. About half the size of a credit card, its surface is streaked with strips of magnetic material that ferry the cells from one end of the device to another. Once at the far end, the cells fall into distinct collection channels based on how many particles they carry as a proxy for the amount of the target protein.
To test if MICS can reveal new drug targets, the researchers focused on cancer immunotherapy, in which the immune system is engineered to destroy tumor cells. They looked for a way to reduce the levels of the CD47 protein which sends a “don’t eat me” signal to the immune system and is often hijacked by cancer cells as a way of escaping immune detection. Others have found that blocking CD47 directly has harmful side effects, prompting the Medicine by Design team to look for the genes that regulate CD47 protein levels.
A genome-wide CRISPR screen revealed a gene called QPCTL which codes for an enzyme that helps camouflage CD47 from the immune system and that could be blocked with an off-the-shelf drug.
On the regenerative medicine front, MICS will help reveal the genes that activate stem cells to turn into specialized cell types, which will make easier harvesting of desired cell types for therapy.
Although Kelley’s team initially developed magnetic cell sorting for isolating tumor cells from the blood, its repurposing for drug target discovery could have a wider impact.