This “nanocage” turns out to be an excellent mailman for medications
RNA medications, which allow proteins to be produced by one’s own body, are on the rise. But how exactly can they be delivered into the body? Minuscule, spherical molecules - called nanocages - can bind, transport, and deliver RNA into the cell, UvA chemists and Leiden biologists discovered. To their surprise, even to a very specific address.
Sometimes it happens in chemical research that a molecule used for chemical applications suddenly turns out to be suitable for something completely different. That happened to chemist Eduard Bobylev. In the chemistry lab of catalysis professors Joost Reek and Bas de Bruin, he was working on nanocages, spherical molecules a few nanometers in size widely used in chemistry to accelerate reactions, purify water, or separate reaction mixtures.
Bobylev’s PhD project aimed to test the nanocages in biology. To do so, the cages first had to be stable enough to withstand degradation in the human cell or human body. This is because nanocages consist of metal atoms and organic connecting pieces that “self-assemble” into a cage-shaped structure, but can also break down just as easily. Using metals such as platinum and palladium, Bobylev succeeded in synthesizing stable nanocages for use in human cells.
“These nanocages turned out to be very similar in shape and positive charge to histones, the proteins in the cell around which the DNA is wound like a spool of yarn,” Bobylev says. “That gave us the idea that if histones can bind genetic material, perhaps nanocages can, too.”
RNA medications
The nanocages could act as messengers for promising RNA drugs if genetic material binds. But what exactly is RNA?
Since the mRNA vaccine in the Covid-19 pandemic rocketed to market, RNA - a copy of DNA - has gained tremendous name recognition. RNA translates genetic material (DNA) into proteins, which in turn play an important role in a variety of cellular processes. In the case of certain genetic diseases, there are faults in the DNA, causing certain proteins either not to be produced or to be produced incorrectly. The cell can still produce the correct proteins by introducing the missing pieces of RNA into the body. Thus, RNA drugs can stimulate the production of proteins.
Nanocages. In nature, catalysis, the acceleration of a chemical reaction, takes place on an assembly line. This is what enzymes do, which consist of a hollow - a kind of lock - into which the molecules they convert fit like a key.
Because of the complex structure of the hollow, under mild conditions enzymes can perform very selective reactions. “Truly a chemist’s dream,” says Bobylev. That principle is not entirely coincidentally similar to a nanocage. Nanocages are an attempt to recreate these enzymes in nature, in a research program of the Van ‘t Hoff Institute for Molecular Sciences (HIMS).
Messenger
This could theoretically treat many genetic diseases, but this is not yet possible. The main hurdle, in fact, is to deliver the RNA into the cells. This requires a messenger, called a vector in biology, to bring the RNA into the cell. Viruses or nanofat spheres are often used, although these are still not always selective enough for different cell types. They deliver their “package” to all cells, not just the specific cells that need the RNA.
But nanocages have that selectivity, as published by researchers in late April in the journal Chem. For that research, the UvA chemists enlisted the help of Professor of Supramolecular Chemistry Alexander Kros at Leiden University. There, Bobylev’s two types of nanocages were added to two different human cell lines.
Then something extraordinary happened. Bobylev says: “The surprising thing was that the nanocages reacted differently. The nanocage with platinum delivered a lot of RNA to one cell type, and little to the other. For the nanocage with palladium, it was vice versa. This was even though a commercially available vector showed no differences in release between the two cell types. That’s not always helpful, because the RNA should be delivered only to where it’s needed.”
Thus the researchers concluded that the nanocages are selective for human cells. “That’s rare for RNA vectors. For small molecules, to my knowledge, that has not yet been reported.” The selectivity has now been demonstrated in human cells in the laboratory. The next step is to demonstrate the mechanism in laboratory animals and then in humans.
Double toxicity
But there’s still a way to go because the positive charge of the nanocages also has a downside. Namely, the nanocages not only bind well to RNA but also to other parts of the cell. This can disrupt cellular processes and ultimately result in cell death. “In the case of cancer cells, this is advantageous,” says Bobylev, “We call that double toxicity: first the RNA harms the cancer cell and then the nanocage does it again.” But for any other use, the toxicity needs to be lowered for cells that should be attacked. “We can do that by adding fewer binding sites for RNA to the cage.”
