RALEIGH, NC—North Carolina State University professor Stefan Franzen first learned about a distinctive plant virus when he met his colleague Steven Lommel over a beer in Poland several years ago. He did not immediately realize that the meeting would lead to a new approach to nanoparticle drug delivery.
“We got a little bit lucky there,” says Franzen, who holds a PhD in biophysical and biological chemistry. “Serendipity is part of science too.”
“I had known Steve for a long time,” he says. “When I first learned of the properties of the plant virus he was studying, I didn’t get it. I was staring at it for a year without seeing why it is so advantageous. Then, it began to sink in.”
Franzen and his company, NanoVector, had been “playing with nanoparticles for a while,” in particular gold nanoparticles, for use as a targeted drug delivery mechanism. They presented difficult problems that did not show signs of being solved.
Problems with metal nanoparticles
At first Franzen thought Lommel’s plant virus might work with his gold nanoparticles, and even published some work related to the possibility. But eventually, he decided the gold nanoparticles just had too many disadvantages that “All these people who want to promote metal nanoparticles have to solve,” he says.
Lommel, a Ph.D., is a professor of plant pathology, professor of genetics, and Associate Vice-Chancellor for Research at NCSU. His primary research program is in the areas of plant virology, plant viral pathogenesis and plant genomics. He has been working with plant viruses since 1978.
The Eureka! Moment
Recalling that initial meeting in Poland six or seven years ago, Lommel says, “Stefan and I knew each other from NCSU, but didn’t know each other’s research. We shared a hotel and talked a lot. I told him we had just learned to open and close my virus and that it has a hollow cavity in it.”
That is what eventually led to the “Eureka!” moment, he says. Together, Franzen, Lommel, and Bruce Oberhardt, who had been with the company from its inception, revived the inert NanoVector.
“Since then, we have been developing it,” says Lommel of the "plant nanoparticle."
“Its natural properties give it a real advantage," he says. "It can open and close without falling apart. It has a lot of flexibility and potential.”
He points out that NanoVector is not making a drug, but rather a “drug formulation.” It will allow the company to package many current cancer drugs that are not targeted to cancer cells. Targeting drugs is the whole basic idea behind nanoparticle delivery.
Untargeted drugs that affect your healthy cells as well as cancer cells are why your hair falls out during chemotherapy.
To target, “You want to sequester the drug,” says Franzen. “You want it to go into something. You can do some clever things with polymers, but this is more elegant. It’s easier to control and has the advantage of thousands of years of evolution.”
Franzen and Lommel have had several “epiphanies” over the years since sharing beers in Poland. Recently, they realized the plant virus has a natural loading and unloading mechanism built into it. “It’s an exquisite calcium sensor,” Franzen says.
It has a lot of “up potential
Although it may take additional months of research, that finding means they can control the loading and unloading of the medicine in the virus via calcium.
NanoVector is initially targeting cancer therapies, but Franzen says that once the company overcomes regulatory issues, the system could be used to administer pain drugs or any other targeted medicines. “It has a lot of up potential,” he says.
Lommel notes that the company has received grant money and funding from private sources. “We’re doing a dance with some angel investors now,” he says.
The company brought in serial entrepreneur Albert Bender, also a PhD, who was founder and CEO of four venture-backed startups, as CEO.
“We have a division of labor here,” says Lommel. “I’m not doing the business side after spending the last 30 years studying plant viruses.”
MONDAY: Part Two: The business side of NanoVector.
J Am Chem Soc. 2007 Aug 18; : 17705477 (P,S,E,B,D)
Encapsidation of Nanoparticles by Red Clover Necrotic Mosaic Virus.
Lina Loo, Richard Guenther, Steven Lommel, Stefan Franzen
Icosahedral virus capsids demonstrate a high degree of selectivity in packaging cognate nucleic acid genome components during virion assembly. The 36 nm icosahedral plant virus Red clover necrotic mosaic virus (RCNMV) packages its two genomic ssRNAs via a specific capsid protein (CP) genomic RNA interaction. A 20-nucleotide hairpin structure within the genomic RNA-2 hybridizes with RNA-1 to form a bimolecular complex, which is the origin of assembly (OAS) in RCNMV that selectively recruits and orients CP subunits initiating virion assembly. In this Article, an oligonucleotide mimic of the OAS sequence was attached to Au, CoFe2O4, and CdSe nanoparticles ranging from 3 to 15 nm, followed by addition of RNA-1 to form a synthetic OAS to direct the virion-like assembly by RCNMV CP. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements were consistent with the formation of virus-like particles (VLPs) comparable in size to native RCNMV. Attempts to encapsidate nanoparticles with diameters larger than 17 nm did not result in well-formed viral capsids. These results are consistent with the presence of a 17 nm cavity in native RCNMV. Covalent linkage of the OAS to nanoparticles directs RNA-dependent encapsidation and demonstrates that foreign cargo can be packaged into RCNMV virions. The flexibility of the RCNMV CP to encapsidate different materials, as long as it is within encapsidation constraint, is a critical factor to be considered as a drug delivery and diagnostic vehicle in biomedical applications.
Viral cargo delivery14 January 2008
US chemists have used a virus capsule to package and release molecules, which could lead to targeted delivery of therapeutic compounds.
Stefan Franzen and his colleagues at North Carolina State University in Raleigh used the red clover necrotic mosaic virus as a vehicle for dye molecules that can be loaded and unloaded on demand.
To explore its versatility for nano-packaging and delivery, Franzen first worked on capturing dye molecules into the capsid. As divalent ions are integral to the virus structure, Ca2+ and Mg2+ depletion in the solution induces significant conformational changes. This leads to surface pores forming, allowing dye molecules to infuse into the interior cavity. Restoring the ion balance closes the pores, trapping the dye inside the virus. When Franzen lowered the ion concentration, the pores reopened and the dye molecules were released.
Franzen's final aim is to use the capsids for intracellular drug delivery - the next stage is to study their ability to package and deliver cargo into a target cell, he explained. The idea is that loaded viruses should be triggered to open their surface pores and release their package inside a cell where the divalent ion concentrations are low. This concept is 'advantageous because the virus capsid will be able to act as container to protect a cargo until it reaches the targeted cell to be released', explained Franzen.
Xiao Xiao, a professor of gene therapy at the University of North Carolina School of Pharmacy, says NanoVector's technology is promising because plant viruses will not infect humans and because human cells do not have a defense mechanism against a plant virus.
The drawback, Xiao says, is that once the plant virus enters a cell, the body will remember and develop a defense system within several weeks. If extended treatment is needed, he says, the body would start to block the virus.
"There's no easy way around that problem," Xiao says.Bender, CEO of NanoVector, admits that resistance could be a problem. He says the company will research the body's immune response to plant viruses in the coming months.