By Doug Macron
The University of Massachusetts Medical School announced this week that one of its researchers, Michael Czech, has been awarded a five-year, $6 million grant from the National Institutes of Health to develop an oral RNAi delivery technology.
The grant was issued under the NIH's Transformative R01 program, which is designed to support high-risk but innovative research projects that "have the potential to create or overturn fundamental paradigms," according to the agency. It runs from Sept. 21, 2009, until Aug. 31, 2014, and is worth roughly $1.17 million this year.
While the funding will directly benefit Czech's lab, it is also expected to be a boon for RXi Pharmaceuticals, which Czech co-founded, since the company holds an exclusive license to the delivery approach for therapeutic RNAi applications (see RNAi News, 10/16/2008).
Called glucan-encapsulated siRNA particles, or GERPs, the technology comprises hollow, porous beta-1,3-D-glucan shells containing transfer RNA and polyethylenimine, which are loaded with an siRNA payload. When delivered orally, the GERPs are designed to be taken up by M cells, which are specialized cells in the small intestine that ferry antigens through the intestinal wall so they can be phagocytosed by macrophages.
In light of these and other data, as well as the market potential of an oral RNAi drug, RXi has made GERPs the centerpiece of its technology portfolio. The company has also indicated that it could potentially be the delivery approach used with its first RNAi drug candidate, which is to be named later this year (see RNAi News, 6/25/2009).
But according to Czech, much work remains to be done before GERPs are ready for testing in humans.
"Science is science, and the most important thing is to focus on a rigorous analysis of each step" of the GERPs' development," he told RNAi News this week. "It's really impossible to tell how long that will take."
Still, the funding from the NIH is likely to expedite the process, which Czech described as "an exercise in simplifying and refining the technology, [which will be] really important … in terms of getting this to the clinic."
According to the grant's abstract, the project will evaluate the ability of GERPs to deliver siRNAs to macrophages in various tissues in vitro, as well as their ability to trigger RNAi-mediated gene silencing in inflammatory macrophages in mouse models of insulin resistance and type II diabetes.
But in order to do so, Czech and colleagues will need to optimize the GERPs — a multi-faceted effort that includes verifying the purity of the delivery vehicle's glucan shell, which is "prepared from a very complex mixture of oligosaccharides and other components," he explained.
[ pagebreak ]
"It actually may be that small amounts of other components — we know, for example, there is chitin in the shell even as it's purified by our methodology — could be important in the overall bio-distribution," he noted. "We'd like to have that outside shell as pure as possible, and we'd like to have it most optimized in terms of its interaction with the receptors that are involved in transcytosis and phagocytosis."
Additionally, Czech is aiming to refine the GERP core, which is currently comprised of anionic and cationic materials in tRNA and PEI, respectively, he said. "Obviously, there are some toxicities involved with PEI at high concentrations … [and] tRNA is not likely to be the best or final anionic anchor for the core."
As such, there is "lots of work to be done," not only optimizing the components of the GERP core, but also potentially winnowing those down to possibly a single, low-toxic compound capable of absorbing siRNAs at low concentrations, he added.
Czech said he is also weighing the possibilities of the various chemical modifications that can be applied to the siRNAs, to not only stabilize them but also bind them better to the GERPs, while considering improvements that could be made to boost the number of siRNAs that are released from the delivery vehicles.
"If we're only getting five percent or 10 percent of the siRNA out, we want to be able to increase that to, hopefully, 100 percent," he said.
Yet another issue is the component of the GERPs used to help the siRNA cross biological membranes, Czech said. Thus far, GERPs have been incubated with Endo-Porter, a peptide "thought to be able to make membranes more permeable to oligonucleotides and large molecules," he said. But "do we need that component? Is it going to be realistic to have a peptide within a vehicle like this? Can we find something that is going to be more appropriate for a therapeutic?
"As you can see, we are really in the trenches at every step in the pathway and every aspect of the vehicle, trying to refine, optimize, and simplify the chemistry and formulations," Czech noted.
And while developing the GERPs as an oral delivery technology is the main focus of the NIH-funded project, Czech is also working on optimizing them for intraperitoneal and, to a lesser degree, intravenous delivery.
IP delivery is being explored primarily because it offers the chance to examine the in vivo effects of GERPs in a different context, he said. And while there may be "interesting indications" that can be addressed by IP delivery, "at this point, it's mostly an effort to understand the analyses that we do in a more detailed way and to have a rapid way to test different chemistries and formulations."
As for IV delivery, Czech said that it is "an approach we're just beginning to look at."
Since there are a number of different companies and academic researchers investigating IV administration of siRNAs, it is "potentially less interesting," he said. Still, because GERPs can be used to selectively target macrophages, monocytes, and dendritic cells, "IV delivery may [prove] very interesting and potentially very useful."
Currently, RXi's interest in GERPs for oral delivery is well known, but the company has yet to publicly discuss the technology's potential through other routes of administration. Company officials did not return a request for comment.