Genetic and hypoxic alterations of the microRNA-210-ISCU1/2 axis promote iron-sulfur deficiency and pulmonary hypertension

Iron-sulfur (Fe-S) clusters are essential for mitochondrial metabolism, but their regulation in pulmonary hypertension (PH) remains enigmatic. We demonstrate that alterations of the miR-210-ISCU1/2 axis cause Fe-S deficiencies in vivo and promote PH. In pulmonary vascular cells and particularly endothelium, hypoxic induction of miR-210 and repression of the miR-210 targets ISCU1/2 down-regulated Fe-S levels. In mouse and human vascular and endothelial tissue affected by PH, miR-210 was elevated accompanied by decreased ISCU1/2 and Fe-S integrity. In mice, miR-210 repressed ISCU1/2 and promoted PH. Mice deficient in miR-210, via genetic/pharmacologic means or via an endothelial-specific manner, displayed increased ISCU1/2 and were resistant to Fe-S-dependent pathophenotypes and PH. Similar to hypoxia or miR-210 overexpression, ISCU1/2 knockdown also promoted PH. Finally, cardiopulmonary exercise testing of a woman with homozygous ISCU mutations revealed exercise-induced pulmonary vascular dysfunction. Thus, driven by acquired (hypoxia) or genetic causes, the miR-210-ISCU1/2 regulatory axis is a pathogenic lynchpin causing Fe-S deficiency and PH. These findings carry broad translational implications for defining the metabolic origins of PH and potentially other metabolic diseases sharing similar underpinnings.

Abstract B17: Inhibition of lung tumor progression in a metastatic mouse model following intravenous delivery of siRNA nanocomplexes

Exploiting the RNAi pathway offers the potential to advance the treatment of many diseases through highly specific and efficient silencing of gene products. Unfortunately, the requisite safe and efficient delivery of nucleic acids to target cells remains a fundamental problem for the development of RNA and DNA based therapeutics. We have developed a versatile lipopolyamine based delivery system that has been optimized for in vivo delivery by incorporating functional groups onto the core cationic lipopolyamine structure. The direct modification of the core structure (named Staramine) allows for the generation of nanoparticle formulations with a wide range of physicochemical properties and does not require the co-formulation of commercial helper or pegylated lipids. We have previously reported safe, efficient and persistent siRNA mediated transcript knockdown specifically in the lung endothelium using the Starmaine delivery system. Here we extend those observations by administering a siRNA that targets vascular endothelial growth factor receptor 2 (VEGFR-2; KDR/Flk-1) in an animal model of metastatic lung cancer. VEGFR-2, a receptor tyrosine kinase, has been shown to be mainly expressed on endothelial cells and plays a critical role in cell proliferation and differentiation and consequently is also important in angiogenesis associated tumor growth and metastasis. Repeated intravenous administration of nanocomplexes comprised of Staramine formulated VEGFR-2 siRNA (~2 mg/kg/dose) resulted in a significant (40%) reduction of VEGFR-2 transcript levels in isolated tumors from the lungs of mice compared to control injected animals. Similar levels of transcript knockdown were not achieved in tumors when using siRNAs against targets not having the high level of endothelial cell restriction that is seen with VEGFR-2. Immunohistopathology of the lungs of tumor bearing mice administered VEGFR-2 siRNA indicated a significant decrease in vascular density in lung tumors and was consistent with an overall reduction in tumor burden in the mouse lungs. These results support the continued evaluation of using Staramine to deliver siRNAs and other similar molecules as potential therapies for diseases of the lung where the vascular endothelium may be involved.

Citation Format: Jason G. Fewell, Khursheed Anwer, Kevin Polach, Majed Matar, Jennifer Rice, Angela Rea-Ramsey, Jeff Sparks, Diane McClure, Casey Pence, Elaine Brunhoeber, Leslie Wilkinson. Inhibition of lung tumor progression in a metastatic mouse model following intravenous delivery of siRNA nanocomplexes [abstract]. In: Proceedings of the AACR Special Conference on Noncoding RNAs and Cancer; 2012 Jan 8-11; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(2 Suppl):Abstract nr B17.

Abstract 4995: Lung specific target gene inhibition following intravenous delivery of siRNA nanocomplexes

RNA interference offers the promise of a new class of therapeutics that can specifically target many diseases that have aberrant gene expression as the root cause. This is potentially true even for diseases that are currently considered non-druggable by small molecules or other conventional therapies. The means to efficiently deliver RNAi based therapeutics into target cells still poses arguably the most significant barrier to overcome for this platform technology. Cationic systems (lipids and polymers) have been extensively used for siRNA delivery and a wide range of experimental approaches have indicated that siRNA specific knockdown in vivo can be achieved using these systems. However, there is considerable concern that the dose levels required to achieve therapeutically relevant knockdown will result in unacceptable toxicity. This is particularly relevant when applied to systemic delivery. To address this issue we have developed a novel core cationic lipopolyamine structure that is chemically flexible allowing for incorporation of active moieties that improve safety, stability, and efficiency, creating a family of functionalized RNAi delivery systems. Here we show that systemic (intravenous) administration of siRNA nanocomplexes formulated with one of these functionalized systems produces significant target gene knockdown specifically in the lung with duration of at least 7 days following a single injection. Administration was well tolerated with no indications of acute or long term toxicities. Detailed biodistribution analysis reveals that siRNA is initially distributed primarily to lungs, liver and spleen, with the majority of the siRNA accumulating in the liver. Lung specific knockdown is explained through the observed rates of siRNA clearance, which are considerably faster for the liver and spleen than those observed in the lung. This results in higher lung siRNA concentrations on the timescale of RNAi mediated transcript knockdown. In a model of metastatic lung cancer administration of siRNA targeting STAT3 resulted in significant transcript depletion in the lungs and a significant reduction in tumor burden. These results support the continued evaluation of this delivery system as a potential siRNA based therapeutic approach for a variety of diseases of the lung.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4995. doi:10.1158/1538-7445.AM2011-4995