About microRNAs

microRNAs represent a new approach for the treatment of human disease. Most RNAs, such as messenger RNAs, are transcribed from genes and are used to make proteins through the process of translation. Recently, an entirely new category of RNAs was discovered: microRNAs or miRNAs. Like messenger RNAs, microRNAs are also transcribed from genes. However, these small microRNAs do not encode proteins but have been found to regulate the expression of other genes. There are approximately 500 microRNAs that have been identified in the human genome, and these are believed to regulate the expression of up to 30 percent of all human genes by preventing translation of messenger RNAs into proteins.

microRNAs have been found to be extremely important for human development, normal physiology, and disease. For example, research has shown that:

Animals cannot live without certain microRNAs
microRNAs are often conserved across species
Most microRNAs are highly abundant and dynamically regulated during development
Many microRNAs exhibit tissue-specific expression
microRNA expression or function is significantly altered in many disease states

microRNAs thus act as master regulators for physiological pathways or genetic networks to achieve integrated biological functions. This ability to affect the expression of multiple genes in the pathway of disease makes microRNAs an exciting new platform for drug discovery and development. When inappropriately expressed or mutated, microRNAs represent disease targets whose selective antagonism can result in broad modulation of points on a disease pathway in a manner that is not easily achievable by today’s medicines. The in vivo work on microRNAs pioneered by Alnylam and Isis has demonstrated effective down-regulation of microRNAs and consequent effects on therapeutically relevant processes. To date, microRNAs have been implicated in several disease areas, such as cancer, viral infection, and metabolic disorders.

Therapeutic programs

Regulus’ most advanced program is a microRNA (miRNA) therapeutic that targets miR-122 for the treatment of hepatitis C virus (HCV) infection, a significant disease worldwide where emerging therapies target viral genes and are therefore prone to viral resistance. We are targeting miR-122, an endogenous host gene required for viral infection by HCV.

Early research from the laboratory of Dr. Peter Sarnow at Stanford University identified that miR-122 interacts directly with a specific sequence in the 5' non-coding sequence region of the HCV genome leading to increased abundance of thefacilitating viral mRNA, replication; thereby suggesting that antagonism of miR-122 can define a strategy for developing an anti-viral drug that targets a required host factor.

In addition to our miR-122 program, we are actively exploring additional areas for development of microRNA therapeutics, including cancer, other viral disease, metabolic disorders, and inflammatory diseases.

Intellectual Property

The combination of Isis and Alnylam IP estates for microRNA therapeutics creates what we believe is an unparalleled patent position for pharmaceutical products that target microRNAs.

Regulus has been granted exclusive licenses to both Isis' and Alnylam's intellectual property for microRNA applications. This includes a portfolio of over 900 patents and patent applications, of which over 600 are issued, owned by Isis pertaining to chemical modification of oligonucleotides for therapeutic applications. In addition, Regulus has acquired rights to a large estate of patents and patent applications accumulated by both Alnylam and Isis in the field of microRNA therapeutics, including early fundamental patents in the field of microRNAs, such as the Tuschl III patent.

During his research efforts at the Max Planck Institute, Dr. Tuschl discovered more than 120 naturally occurring microRNAs that are present in mammalian cells. These microRNAs have the potential to be new drug targets or therapeutic products and are the subjects of the licensed patent applications. The Tuschl III patent series, which Alnylam and Isis both co-exclusively licensed for all therapeutic applications, are now combined to form Regulus’ exclusive patent position in this space.

Useful Publications

Isis and Alnylam scientists and collaborators were the first to discover microRNA antagonist strategies that work in vitro and in vivo in animal studies. These and other useful publications are:

Gottwein et al. (2007) Nature, 450, 1096-1099

The study shows that a virally derived microRNA mimics the gene expression control by an endogenous host microRNA that has previously been implicated in human cancer. Evidence from the study suggests that the viral microRNA, which is encoded by the Kaposi's Sarcoma Associated Herpesvirus, or KSHV, may represent the first example of a viral microRNA oncogene, termed an "oncomir."
Dolken et al. (2007) J Virol., 24, 13771-13782

Characterizes the contribution of viral microRNAs to viral infection in mice infected with murine cytomegalovirus (CMV) and establishes this system as a model to study viral microRNAs in virus infections in vivo. Viral microRNAs are highly expressed during infection, some are more abundant than most cellular microRNAs and may thus compete with the function of cellular microRNAs.
Esau et al. (2004) J Biol Chem., 279, 52361-52365

Functional experiments with microRNA antagonising oligonulceotides identifyed one microRNA, miR-143, thatplays a significant role in adipocyte differentiation by possible regulating the ERK pathway.
Krutzfeldt et al. (2005) Nature 438, 685-689

This study describes the exciting finding that cholesterol-modified RNA oligonucleotides, termed “antagomirs”, can be used to functionally inactivate microRNAs in various tissues in a mouse. Specifically, it was shown that an abundant liver-specific microRNA can be inactivated for a long time, resulting in changes in abundance of distinct mRNAs. This finding demonstrates that microRNAs can function as a sensor to fine-tune gene expression, and suggests that antagomirs can be applied as therapeutics for disease.
Esau et al. (2006) Cell Metab., 3, 87-98

Extension the results confirming the interesting therpaeutic potential due to pharmacological intervention with miR-122 by another type microRNA inhibitors (ASOs) and a longer treatment protocol. After 4 weeks, ASO-122-treated mice exhibited decreased cholesterol and triglyceride levels without changes in plasma glucose concentrations. Isolated hepatocytes of treated mice exhibited decreased hepatic fatty-acid synthesis and sterol synthesis as well as increased fatty-acid oxidation.
Davis et al. (2006) Nucleic Acids Res., 34, 2294-304

This study defines important factors for designing improved microRNA targeting ASOs, enabling more effective microRNA functionalization and therapeutic targeting.
Krutzfeldt et al. (2007) Nucleic Acids Res., 35, 2885-92

This study further validates the effectiveness of cholesterol conjugated microRNA antagonists in vivo by defining specificity, mechanistic effects and subcellular localization due to oligonucleotide administration. This facilitated new studies to silence microRNAs for functional analysis and in clinically relevant settings
Li et al. (2007) Cell 129,147-61

The article provides strong evidence in support of specific developmental and disease relevant roles of single microRNAs in mammals. The work develops a compelling analysis to show that one micro-RNA, miR-181a, modulates the steady-state levels of multiple negative regulators of T-cell receptor (TCR) signaling and develops evidence that it is the integration of effects from the entire array of these multiple phosphatases, rather than one particular target, which is crucial for the effect of miR-181a.
Esau, Monia. (2007) Adv Drug Deliv. Rev., 59, 101-14

Recent review outlining the therapeutic potential of microRNAs as targets, the possible therapeutic approaches as well as useful indications due to deeper knowledge of the link of microRNA biology with disease.