Publication Shows Potential of Therapeutic Gene Silencing

Calando Pharmaceuticals Inc., subsidiary of Arrowhead Research Corporation has announced that collaborators using Calando's proprietary siRNA delivery technology have published the first clear in vivo demonstration of sequence-specific gene inhibition in tumors from the systemic administration of targeted formulations of siRNA.

The research, published in Cancer Research, represents a significant advance in the development of systemic RNAi therapeutics.

Systemic delivery through the bloodstream enables RNAi therapeutics to target metastatic cancer located throughout the body, and raises the prospect for broad application of RNAi therapeutics to treat a wide range of cancers and other systemic diseases.

In the published research, Caltech and Children's Hospital Los Angeles investigators created a mouse model of Ewing's sarcoma that mimics the tumor localizations in humans and also provides for simultaneous, real-time bioluminescence imaging of the disseminated tumors by using human Ewing's sarcoma cells engineered to express luciferase.

Two groups of 10 mice each received sham injections and naked anti-EWS-FLI1 siRNA, respectively, and three additional groups of 10 mice each received various siRNA sequences formulated with Calando's proprietary cyclodextrin-containing polymer siRNA delivery system: siRNA with an unrelated sequence to EWS-FLI1, anti-EWS-FLI1 siRNA and anti-EWS-FLI1 siRNA that did not contain the tumor targeting ligand.

All injections were at 2.5mg/kg via the tail vein at normal venous pressure. The data show that only the targeted anti-EWS-FLI1 formulation provided any anti-tumor efficacy - control sequences and removal of the targeting ligand eliminated the anti-tumor effects.

Additionally, no abnormalities in IL-12 and interferon-alpha, liver and kidney function tests, complete blood counts or pathology of major organs were observed.

Of major significance is that the cyclodextrin-containing delivery system does not produce an interferon response like those obtained from lipid delivery of siRNA even when published immunostimulatory motifs are included in the siRNA.

“The results from the Caltech-CHLA collaboration conclusively show sequence-specific anti-tumor effects and the molecular targeting to and within tumor cells by the delivered siRNAs,” said Dr. Mark Davis, professor of Chemical Engineering at Caltech and founder of Calando.

“This study shows that the polymer system can deliver siRNA therapeutics by a route of administration and at a dose amenable to use in humans.”

“It is important to recognize that these results were achieved with the delivery of natural RNA sequences,” said John Petrovich, Chief Executive Officer of Calando Pharmaceuticals.

“No chemical modifications are necessary for siRNAs delivered with Calando's polymeric system.”

“We believe this will give us an easier regulatory path, and possibly result in reduced off-target effects.”

He noted that the delivery system is currently very well-characterized, and that considerable progress had been made in advancing the cGMP scale-up and preclinical development of the polymer.