The National Institutes of Health last month awarded one-year grants to Calando Pharmaceuticals and SomaGenics to support development of improved delivery methods for RNAi molecules.
Calando Pharmaceuticals' grant, issued by the NIH's National Institute of General Medical Sciences, is worth $100,000 and will fund research into a novel, systemic delivery system for modified siRNA duplexes.
Unlike Calando's core delivery technology, which is based on a linear cyclodextrin-containing polymer that can deliver nucleic acids such as siRNAs, the technology being developed under the grant "requires no synthetic delivery system … for in vivo delivery," Calando states in the grant's abstract.
Further, the technology may prove effective for transporting siRNAs across the blood-brain barrier, which has long been a roadblock for drug delivery in general.
SomaGenics' grant — also awarded by the NIGMS and worth $297,420 — is for the evaluation of various chemical modifications designed to boost shRNA delivery and uptake in the liver.
While SomaGenics' interest in therapeutics has been mostly focused on a novel antisense-related technology called RNA lassos (see RNAi News, 4/30/2004), the grant reveals an expansion into RNAi — specifically RNAi for hepatitis C.
Calando is "looking to work on the grant as an internal pilot/proof of concept study to more fully understand and test out the technology … Then we can think of moving it along further if results warrant."
According to Calando, it has formulated siRNA duplexes with phosphorothioate sense strands and phosphodiester antisense strands using proteins designed to target cell-surface receptors associated with endocytosis.
"Thus, the [phosphorothioate] sense strand is employed to carry the antisense strand, impart stability to the duplex, and to bind to proteins that can provide for cellular targeting and/or cellular uptake," eliminating the need for an artificial delivery technology, the company stated.
To test the duplexes, Calando said it will incorporate the phosphorothioate and phosphodiester modifications into siRNAs designed to inhibit luciferase, FAS, and EWS-FL11, and "investigate their behavior and their binding to proteins that can be ligands for cell-surface receptors." These include asialofetuin for the asialoglycoprotein receptor on hepatocytes and transferrin for transferrin receptor on cancer cells and the blood-brain barrier.
The company said it plans to "measure the in vivo biocompatibility of the siRNA duplexes in mice by monitoring for toxicities and changes in blood chemistries."
Calando added that it intends to examine multiple dosing regimens in two mouse models: a transgenic model with liver luciferase expression and a metastatic tumor model that creates brain metastases, which will help determine whether the duplexes have crossed the blood-brain barrier.
These experiments, the company said, will help "define how to best target the …siRNA duplexes to liver and metastatic tumors," and whether they can be delivered to the brain. Based on the results of the work, "disease targets in the locations successfully reached will be explored," with the goal of developing a clinical drug candidate.
John Petrovich, president and CEO of Calando, said in an e-mail this week that the delivery approach was developed at the California Institute of Technology laboratory of Mark Davis, one of Calando's co-founders.
He told RNAi News that "it's a delivery technology that we are not emphasizing right now" as the company focuses on its cyclodextrin polymer technology, but that "it still is a viable method for some forms of delivery."
"We are looking to work on the grant as an internal pilot/proof of concept study to more fully understand and test out the technology … Then we can think of moving it along further if results warrant," he added in his e-mail.
Since shRNAs must be processed by Dicer, "any chemical modifications must not block [their] ability to act as a substrate for Dicer."
Both siRNAs and shRNAs "have been used successfully in cell culture … however, so far their application has been limited by the low stability of RNA and poor efficiency of delivery," SomaGenics said in its grant's abstract.
"The attachment of cholesterol groups to antisense oligonucleotides has been shown to improve their delivery, and it was recently demonstrated that cholesterol attached to the 5' termini of the sense strand of siRNAs improves uptake both in cultured cells and in livers of living mice," the company added.
Unlike siRNAs, however, shRNAs must be processed by Dicer. "Hence, any chemical modifications must not block [their] ability to act as a substrate for Dicer," the company noted.
Since certain modifications used to enhance delivery of siRNAs may not be applicable to shRNAs, SomaGenics intends to test various ones on an shRNA-based hepatitis C inhibitor for improved ability to inhibit virus-mediated reporter expression in a human hepatocyte cell line and in a mouse liver model.
The modifications "will also be tested on a more realistic cell-based model of HCV, the HCV replicon," in collaboration with the NIH's National Institute of Allergy and Infectious Diseases, the company said.
Officials from SomaGenics were not available for additional comment on the research.