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NIH Awards Three Grants Supporting RNAi, microRNA Rx Development

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By Doug Macron

The National Institutes of Health last month earmarked nearly $650,000 to fund three research projects focused on developing RNAi- and microRNA-based therapeutics for cancer and Huntington's disease.

The first grant was awarded to Mirna Therapeutics to support the company's work on creating therapeutic miRNA mimics as cancer treatments.

The company has "identified approximately ten tumor suppressor miRNAs and is in the process of developing mimetics for two of these that will be subjected to efficacy and safety studies using advanced rodent and primate studies," Mirna said in the grant's abstract.

With the NIH's grant funding, which is worth $287,270 and is set to run from July 1 until the end of March 2011, Mirna plans to develop "nucleotide analogs to improve the stabilities and activities of mimetics of two miRNAs that have proven to have therapeutic activities in mouse models of several different cancers."

Mirna did not specify in the abstract the two miRNAs that are the focus of the NIH-funded effort. The company has, however, disclosed that it is working on mimics for miR-34a as a therapy for prostate and other solid tumors and an undisclosed miRNA for solid tumors including non-small cell lung cancer. Mirna has said that it expects to file investigational new drug applications for the two agents by 2011 (GSN 6/24/2010).

This month, Mirna announced the publication of data in Cancer Research showing that a miR-34a mimic, formulated with proprietary lipid-based nanoparticles, reduced the expression of "multiple" targets of the miRNA when systemically delivered to two different mouse models of non-small cell lung cancer.

Further, treatment induced apoptosis and inhibited the growth of established tumors, but did not trigger changes in serum levels of cytokines or liver and kidney enzymes, Mirna said.

In the grant's abstract, the company said it hopes to develop mimics that are up to ten times more effective than the molecules it has used in efficacy studies to date. These mimics will be "coupled with delivery agents" developed in parallel, and the combinations will be tested in mouse models.

The second grant was awarded to Sirnaomics to support development of a multi-targeted siRNA-based treatment for glioblastoma multiforme.

"Despite decades of intensive surgical treatment, chemotherapy, radiotherapy, and tremendous basic science and clinical research focused on combating this disease, the prognosis [for the disease] remains virtually unchanged, with survival rates still measured in months," the company said in the grant's abstract. Yet research has identified a number of intracellular molecules and their associated signaling pathways as potential therapeutic targets for the disease.

In line with its strategy of developing therapies containing multiple siRNAs, Sirnaomics said in the abstract that it will create three cocktails: one containing siRNAs against epidermal growth factor receptor, vascular endothelial growth factor, and O6-methylguanine-DNA-methlytransferase; one with siRNAs against EGFR, VEGF, and matrix metalloproteinase 9; and one with siRNAs for EGFR, VEGF, and transforming growth factor.

Each will be packaged in polymer and liposomal nanoparticles, and their efficacy will be tested in human and mouse glioma cell line tumor models, and the delivery systems will be evaluated and optimized for the most effective siRNA cocktail, Sirnaomics said.

The company added that it will examine the cocktails in combination with the chemotherapeutics temozolomide and bevacizumab.

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Sirnaomics grant, which has a six-month term, began on June 2 and is worth $269,298.

The last grant went to Oregon Health and Science University researcher Jodi McBride to fund the evaluation of an RNAi-based treatment for Huntington's disease in non-human primates.

Huntington's disease, the grant's abstract states, is caused by an expanded tri-nucleotide repeat — CAG — in exon 1 of the huntingtin gene. "The glutamine expansion in the encoded protein … confers a toxic gain of function, causing degeneration of neurons in many brain regions, particularly in the striatum."

Although normal expression of the huntingtin protein plays an important role in various cellular processs, McBride and colleagues have previously shown that partial non-allele specific silencing of the gene was well tolerated and therapeutically beneficial in a mouse model of Huntington's disease.

With funding from the NIH, McBride aims to follow up on these findings by testing the approach in rhesus macaques, which will be treated with unilateral, stereotaxic injections into the striatum of a recombinant viral vector that expresses mi2.4, an artificial miRNA that targets exon 2 of mouse and human huntingtin transcripts, according to the abstract.

"The opposite hemisphere [of the animals' brains] will be injected with a control miRNA that does not reduce [huntingtin] expression," it adds, and the macaques will undergo behavioral evaluation to determine the efficacy and tolerability of treatment. Three months following the injections, the macaques will be sacrificed and their brains examined for silencing efficiency and several different safety profiles, the abstract notes.

As part of the grant project, McBride and colleagues aim to establish a non-human primate model of Huntington's disease that includes motor dysfunction, cognitive deficits, and emotional manifestations.

To do so, rhesus monkeys will receive injections into the striatum of either a virus expressing a fragment of mutant huntingtin with 82 CAG repeats or a control fragment with only 18 repeats.

"This strategy has been previously utilized to create a successful rodent model" of the disease, the abstract states. "Animals will evaluated monthly on a variety of motor, cognitive, and psychological assays. Six months post-injection, animals will be euthanized and their brains will be analyzed."

The last part of the grant involves further testing the therapeutic efficacy of the mi2.4 vector in non-human primates, which will receive co-injections of the vector, as well as a control, into the striatum. The animals will also receive the fragment of mutant huntingtin with 82 CAG repeats.

The primates will be evaluated for six month, then sacrificed, the abstract states. Their brains will be examined for the prevention of Huntington's disease pathology.

McBride's grant began on June 15 and runs until the end of May 2011, and is worth $89,942.

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