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Apr 15, 2011 (Vol. 31, No. 8)

New Strategies Tackle siRNA Therapeutic Delivery Issues

Researchers Take Aim at the Four Separate Hurdles that Stand Between Success and Failure

  • Targeting Lung Cancer

    Click Image To Enlarge +
    siRNA-mediated transcript knockdown in lungs: Persistent target gene knock-down in mouse lung following a single IV injection of siRNA (2.0 mg/kg) formulated with EGEN’s TheraSilence™ lipopolyamine. RNA was isolated from whole lung homogenates and analyzed by qRT-PCR. Transcript levels of animal injected with the active siRNA are compared to animals that were injected with a nonsilencing siRNA control seqence.

    EGEN is focusing on synthesizing biocompatible delivery vehicles to deliver genes as well as siRNAs. “We are utilizing a variety of different delivery approaches in our TheraSilence™ platform that are designed specifically for in vivo RNAi applications including lipids, polymers and lipopolyamines,” according to Jason Fewell, Ph.D., vp of preclinical R&D. “In our lipopolyamine nanoparticle systems we use a single lipid-based core structure with a flexible head group that allows for modification by covalent attachment of functional groups such as polyethylene glycol and targeting ligands. We can then dial in various ratios of the core structure with the modified structures to optimize delivery for different applications.

    “This approach provides for controlled formulation conditions and is distinct from other technologies that use multiple different lipid types in a single formulation. The advantages we find with our system are that it creates a more uniform structure, simplifies the manufacturing process, and provides consistent advantages in uptake.”

    The company describes new results that employed a murine model of lung cancer. “Our preliminary studies indicated preferential uptake and retention of siRNA in the lung endothelium following intravenous administration of our lipopolyamine system. As proof of principal we subsequently targeted STAT3, which is involved in the cellular processes of apoptosis and proliferation and is implicated in a variety of cancers, especially the lung. We found that the administration of STAT3 siRNA provided sustained knockdown of STAT3 transcript and resulted in decreased tumor growth. When delivered intravenously, the toxicity was low and well tolerated. We monitored liver transaminases, liver toxicity, lung histopathology, and various cytokine markers of inflammation.”

    Dr. Fewell reports they will next pursue increasing dosing regimens to get a more robust knockdown. They also want to optimize treatment regimens as well as evaluate this delivery system as a potential therapy for additional diseases of the lung with the goal of rapidly moving the technology into preclinical development.

    “We have already learned much about nucleic acid based drug development utilizing our TheraPlas™ plasmid DNA delivery platform. The latter provides for the local delivery of IL-12 gene for treatment of tumors in the peritoneal cavity.” The company’s lead product, EGEN-001, is currently in Phase II trials for ovarian cancer.

  • Targeting Leukocytes

    Leukocytes are implicated in inflammatory diseases, blood cancers, and leukocyte-tropic viral infections. However, systemic delivery to leukocytes is complicated by their resistance to conventional transfection methods and to their dispersal throughout the body. Dan Peer, Ph.D., head, laboratory of nanomedicine, Tel Aviv University, and colleagues created a novel approach that exclusively targets integrins of leukocytes using nanoparticles armed with specific monoclonal antibodies and entrap siRNAs.

    “Often cationic-based nanoparticles have been utilized for delivery of siRNAs. But these can also produce a set of adverse effects such as cytokine storm that causes serious flu-like symptoms. It’s not just about delivery, it’s also about safety. We, instead, developed neutral lipid-based nanoparticles (~80 nanometers) surface functionalized with a polysugar called hyaluronan, a naturally occurring glycosaminoglycan. These biopolymers are safer and stealth-like to the immune system. They also create a scaffold for the attachment of antibodies or antibody fragments. Because this is a platform technology, one can change the targeting antigen, much like a GPS system, by changing the homing antibody.”

    Dr. Peer cites the example of inflammatory bowel disease (IBD). In this case, particles are loaded with a monoclonal antibody against a gut-specific integrin called β7 integrin. “Using our I-tsNP (integrin-targeted stabilized nanoparticles) we identified cyclin D1 (CD1) as a potential novel target for IBD. CD1, a cell-cycle regulator, becomes upregulated during IBD in both epithelial and inflammatory cells. We utilized a mouse model and found that leukocyte-directed CD1 siRNA inhibits the intestinal inflammatory response.”

    According to Dr. Peer, other applications include viral diseases that affect lymphocytes such as HIV. “In this case I-tsNP surface modified with LFA-1 integrin monoclonal antibodies were employed to deliver CCR5-siRNAs to human lymphocytes and monocytes. This system was shown to protect mice from HIV infection and did not induce an interferon response or secretion of TNF-alpha (an inflammatory cytokine).”

    For the future, Dr. Peer plans to study gene-expression patterns to help identify novel targets. “We want to better understand the mechanisms and gene-expression patterns between patient and normal samples. We are already learning a lot from such studies.”

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