Veritas Bio, a biotechnology holding company established by two co-founders of expressed RNAi firm Nucleonics, said this week that the US Patent and Trademark Office has issued a notice of allowance on a patent application covering a novel liver-directed RNAi delivery technology.
Poised to receive a patent on the technology, Veritas is now on the lookout for companies interested in licensing the delivery approach for use within their own RNAi research and development programs.
The patent application, No. 20100323001, is entitled “In Vivo Delivery of Double-Stranded RNA to a Target Cell,” and claims methods of delivering nucleic acids to mammalian cells via intracellular transfer “wherein the dsRNA is delivered to or expressed in a first cell different from the target cell,” according to its abstract.
It was filed on Nov. 6, 2007, and lists Catherine Pachuk as the sole inventor.
According to Pachuk, who co-founded both Nucleonics and Veritas with Satish Chandran, the intellectual property specifically relates to the use of muscle- or skin-derived exosomes as liver delivery vehicles.
Also known as exovesicles or nanovesicles, exosomes have long been known to shuttle material between cells, including ones distant from each other. Pachuk’s interest in them began when she noticed that “molecules that were administered locally to one site [in muscle or skin] appeared to be having effects in other tissues and other cells that were pretty far from [the site of] the local administration,” she told Gene Silencing News.
This observation held up when siRNAs or siRNA-expression vectors were administered into muscle, which triggered target gene downregulation in the livers of mice, she said.
“For example, if we add siRNA against hepatitis B [to] a model in which the animal was expressing HBV genes in the liver, we would see downregulation of HBV” in that organ, Pachuk explained. “We’ve had similar observations in T cells, as well.”
A review of the literature showed that nanovesicles had already been described as associated with skeletal muscle cells, but their function remained unclear, she said.
What was known was that they are derived from muscle cells, are about 80 nanometers in diameter, and comprise cytosol and membrane components from the cells that extrude them, either into circulation or the lymphatic system.
Pachuk and colleagues eventually concluded that exovesicles are capable of loading cytosolic molecules — including siRNAs, expressed shRNAs, and other RNAi compounds that had been added in the lab — and carrying them to other cell types in the body where they are taken up in a functional way.
Speculating as to their natural role, she said that she and others believe that they serve to carry signals between cells.
“We know that naturally these exovesicles contain messenger RNAs and proteins, and they are delivering these molecules to other cells where they are functioning,” she said. “So, it seems pretty clear that these are used in signaling much in the way hormones are used.”
Pachuk said that she also believes they may serve a detoxification purpose, carrying unwanted molecules out of cells and into the liver.
Importantly, the exovesicles protect their payload, and Pachuk found in in vivo testing that unmodified siRNAs remain active when carried into liver cells or T cells after intramuscular injection compared with siRNAs that are systemically injected and quickly degrade in the bloodstream.
While the delivery approach thus far seems best suited for liver and T cell delivery, Pachuk said that Veritas’ patent application also covers the inclusion of a plasmid vector encoding a targeting ligand, which would theoretically be incorporated onto the surface of the exovesicles to enable their delivery to specific cell types.
Further, research from other groups published after the IP was filed indicates that exovesicles travel to a variety of tissues and organs including the brain, she noted. And last month, a paper appearing in Neuron presented data showing that exovesicles could travel from neurons to muscle.
“I don’t think [the technology] is limited to liver and T cells,” Pachuk said, adding that Veritas has filed additional patent applications on using exosomes to deliver RNAi molecules against various targets in different cells types.
She said that Vertias has also considered generating exovesicles in vitro so that they can be harvested and used in vivo, but this work is very preliminary.
As CSO of Somahlution, a life sciences firm focused on organ and surgical conduit transplantation technologies and led by Chandran, Pachuk said she has no plans to transition Veritas into a drug-development firm, and that the goal is to find parties interested in licensing the RNAi delivery IP for further development.
But Pachuk and Chandran haven’t entirely stepped away from the RNAi therapeutics field, and are thinking about incorporating the gene-silencing technology into certain of Somahlution’s programs, she said.
Citing the recent rabies-related death of a kidney transplant recipient who received the organ from an infected individual who had died of encephalitis but was only diagnosed with rabies post-mortem, Pachuk said that the company is interested in using RNAi to down-regulate potential pathogens in donated organs.
“That’s not where we are now, but it’s an idea we’ve kicked around,” she said.