Image courtesy of PNAS
DNA origami nanostructures may be used to overcome drug resistance in acute myeloid leukemia (AML), according to preclinical research published in the journal Small.
Researchers found they could create these nanostructures in 10 minutes and load them with the anthracycline daunorubicin.
When the team introduced the structures to daunorubicin-resistant AML cells, the drug delivery vehicles entered the cells via endocytosis.
This allowed the drug to bypass defenses in the cell membrane that are effective against the free drug.
Once the nanostructures broke down, daunorubicin flooded the cells and killed them off.
Other research groups have used this delivery technique to overcome drug resistance in solid tumors, but this is the first time researchers have shown the same technique works on drug-resistant leukemia cells.
To create the DNA origami nanostructures, the researchers used the genome of a common bacteriophage and synthetic strands that were designed to fold up the bacteriophage DNA.
Although the folded-up shape performs a function, the DNA itself does not, explained Patrick Halley, a graduate student at The Ohio State University in Columbus.
“[T]he DNA capsule doesn’t do anything except hold a shape,” Halley said. “It’s just a static, rigid structure that carries things. It doesn’t encode any proteins or do anything else that we normally think of DNA as doing.”
The researchers tested the DNA origami nanostructures in AML cell lines that had developed resistance to daunorubicin. When molecules of daunorubicin enter these cells, the cells recognize the drug molecules and eject them through openings in the cell wall.
“Cancer cells have novel ways of resisting drugs, like these ‘pumps,’ and the exciting part of packaging the drug this way is that we can circumvent those defenses so that the drug accumulates in the cancer cell and causes it to die,” said John Byrd, MD, of The Ohio State University.
“Potentially, we can also tailor these structures to make them deliver drugs selectively to cancer cells and not to other parts of the body where they can cause side effects.”
In tests, the resistant AML cells effectively absorbed molecules of daunorubicin when they were hidden inside the rod-shaped nanostructures.
The researchers tracked the nanostructures inside the cells using fluorescent tags. Each structure measures about 15 nanometers wide and 100 nanometers long, and each has 4 hollow, open-ended interior compartments.
Study author Christopher Lucas, PhD, of The Ohio State University, said the design of the nanostructures maximizes the surface area available to carry the drug.
“The way daunorubicin works is it tucks into the cancer cell’s DNA and prevents it from replicating,” Dr Lucas said. “So we designed a capsule structure that would have lots of accessible DNA base-pairs for it to tuck into. When the capsule breaks down, the drug molecules are freed to flood the cell.”
The researchers said they designed the nanostructures to be strong and stable so they wouldn’t fully disintegrate and release the bulk of the drug until it was too late for the cells to eject them.
And that’s what the team observed with a fluorescence microscope. The cells drew the nanostructures into the organelles that would normally digest them (if they were food).
When the nanostructures broke down, the drug flooded the cells and caused them to disintegrate. Most cells died within the first 15 hours after consuming the nanostructures.
“DNA origami nanostructures have a lot of potential for drug delivery, not just for making effective drug delivery vehicles, but enabling new ways to study drug delivery,” said Carlos Castro, PhD, of The Ohio State University.
“For instance, we can vary the shape or mechanical stiffness of a structure very precisely and see how that affects entry into cells.”
Dr Castro said he hopes to create a streamlined and economically viable process for building DNA origami nanostructures as part of a modular drug delivery system.
Dr Byrd said the technique should work on most any form of drug-resistant cancer if further research shows it can be translated to animal models.
