By Thomas K. Pendergast
As scientists around the world scramble to make a vaccine to fight COVID-19, a local team of about 60 people – co-led by a Sunset District resident – is working on a unique potential solution that is roughly analogous to a molecular prophylactic.
UCSF’s Peter Walter, PhD, is leading this effort with his collaborator, Dr. Aashish Manglik, to test and produce AeroNabs, a nasal spray or nebulizing inhaler that would act as a first line of defense against infection in the nose, throat and lungs, where the virus enters the body.
The spray is not an anti-viral vaccine, but instead uses nanobodies, tiny molecular proteins that “sheath” parts of the virus attempting to penetrate the cell, thus preventing replication.
“It was selected to have the property that it just latches onto the virus. Once it’s found it doesn’t let go. And it latches in such a way on a particular protein that is required for the virus to enter cells,” Walter said.
Once it adheres to the virus, it renders it inactive. In that respect, the proteins act as a prophylactic.
“But if you already have viruses that are proliferating, every time the virus takes over the cell it makes more of itself. It replicates inside the cell, and every time it does that, it has to exit the cell to invade the next cell, to do more damage. And every time it comes back out and there are AeroNabs around, they will catch it at that stage. So, it would be an early-stage therapeutic as long as the virus is still in the airways and hasn’t invaded deeper into the body,” he said.
Walter went a little deeper explaining the details:
“Proteins are linear sequences of building blocks; the building blocks are the amino acids. Our genome specifies which kind of amino acid is linked to which one in this long chain. And we can basically engineer any sequence that we would like to have by synthesizing the DNA and then the DNA will be translated into that amino acid sequence, building a protein that is now of a predicted sequence,” he said.
Walter and his team started with nanobodies naturally created by llamas, then basically went from there and made adjustments. He said the synthesized DNA sequence then has to fold up and assemble itself. He said it is like origami.
“It has to assume a three-dimensional structure, which is dictated by the sequence itself,” Walter continued. “That’s where we engineer nanobodies that have the same ‘scaffolding,’ the same matrix as the llama antibodies, but then have three random ‘loops’ hanging out. And it’s these loops that are of great variety.”
Walter said they create a massive number of DNA sequences to find what amounts to a needle in a haystack.
“We made two billion versions of it, just random sequences,” he said. “And out of those we selected, a few now bind themselves to the virus and then activate the virus-block protein. In two billion you can find something that binds to anything.”
Walter compared the process to panning for gold, filtering out a lot of sand and dirt until what is left is the valuable nugget.
“You keep on enriching them until you end up with the nugget that behaves just like you want it to,” he said. “Nanobodies are so particularly powerful here because they are tiny, tiny little protein molecules, with incredible stability, so they are far more stable than the common antibodies, which all need to be injected. And the nanobodies offer the opportunity to inhale them and therefore kill the virus before it ever causes and infection.
“Many of the receptor molecules with which the cell senses what’s going on the outside … they are the kind of receptors which bind to various hormones, to small molecules in the circulation and affect the cells’ behavior, including brain cells, including heart cells, so many of the signal-sensing molecules with which cells communicate with one another are of this protein family. This is what Aashish’s lab was already studying,” Walter said.
So, in choosing nanobodies, they already had an advantage because of Dr. Manglik’s research into them.
“We have been working together using these nanobodies for an entirely different purpose, and then the virus took over the work. We decided it can be applied as a wonderful tool to attack the beast. It’s a repurposing of the toolkit that we have in the laboratory. In that respect it was both a natural progression on the technology but also an entire reinvention regarding the targets.”
Walter said they are now looking for commercial partners to begin clinical testing of AeroNabs.
“We are in active discussions,” he said. “There are many companies that are quite interested right now. So that’s ongoing.”
Walter said he hopes to have selected a partner within weeks to help with the manufacturing and to navigate the appropriate approval processes and clinical testing, including making sure that it is safe with no side effects.
“It’s an agent that only interacts with the virus,” he said. “It just latches onto the virus and prevents it from entering the cell but cannot replicate; it cannot do harm. In that respect it’s not interfering with human physiology. So we don’t anticipate any side effects.”
Walter acknowledged the possibility of never finding a successful vaccine, but he is doubtful of that.
“We all hope for a vaccine. There are so many groups working on it that the chances are pretty good,” he said. “But even once we have a vaccine, we don’t know currently how long the immunity will last once you have received the vaccine. We also don’t know how quickly the manufacturing process could ramp up, so how available it is, who will get it first. So there are many complications: What’s happening in the Third World? How expensive will it be? There are many questions associated with it.
“Right now we think we have a very viable stop-gap solution that can bridge until the vaccine is available. And even then, let’s say we have a perfect vaccine. There are still going to be people who are contraindicated for that, so (nanobodies) will remain a viable protection. Elderly people and immunocompromised people may not be suitable for receiving a strong vaccination.”
Instead of getting an injection, a nose spray or nebulizer would also be more convenient than getting a vaccination shot.
“We’re thinking of two modes of applications: one would be a nasal spray which would catch the virus before it ever gets to the lungs. That would be a very simple little bottle that you can just spritz it up your nose a couple of times a day,” he said. “The other one is a nebulizer, such as is being used for asthma treatment for example, which forms these much finer droplets that would be inhaled deep into the lungs. No matter whether you go through the nose or the mouth, it will end up in the same place – in the lung spaces.”
Walter emphasized that AeroNabs is the result of a team effort.
“It really was only possible because of (the team’s) enthusiasm and their generosity, their dedication to go after the virus,” he said. “They all worked on their own projects before and they put their own projects aside and worked for a couple of months on this particular viral project instead.”