RNA interference (RNAi) is a biological process found in nearly all human cells in which small double -stranded RNA molecules inhibit the expression of specific genes by targeting mRNA transcripts for degradation(1). Since it’s discovery in 1998, researchers have been able to readily exploit the cellular machinery of this pathway by designing synthetic RNA molecules, known as small interfering RNA(siRNA), for targeted suppression of specific genes(2). The ‘programmable’ nature of siRNA technology allows for therapeutic application where RNAi-based therapies present a novel approach to treatment of several illnesses that can not be improved by conventional small molecule drugs(2).
RNAi-based therapies are especially desirable for the treatment of rare genetic diseases. Rare genetic diseases are typically single gene mutations that may result in the production of abnormal protein products or aberrations in gene expression levels resulting in overproduction of proteins(3). Therefore, siRNA -mediated suppression of target mRNA transcripts encoding these proteins would have an immediate impact on ameliorating the symptoms. Similar to other drug molecules, the appropriate concentration or dosage of siRNA delivered to patients is essential for therapeutic efficacy and limiting side effects. Determining the appropriate dose for an individual depends on the extend to which protein expression levels are mis-regulated which is primarily influenced by translation efficiency. A patient with significantly high levels of aberrant protein expression would require a different dose or frequency of dosing compared to another patient with lower expression levels.
In order to tackle this issue, our team is able to apply the knowledge that we gained from our RNAi wet lab studies alongside calculations from our software tools to assist in providing estimates for siRNA dosing. As mentioned previously, the extend to which protein expression levels are mis-regulated is influenced by translation efficiency of the mRNA transcripts. Therefore, by using calculations derived from our CapsidBuilder software tool, readjustments to baseline translation efficiencies, which is proportional to protein expression levels, may be used to determine a new and reduced expression level that is comparable to healthy individuals. The translation efficiency is a value that represents the percentage of transcribed mRNA sequences that are occupied by the ribosomes. When adjusting this value to lower efficiency levels(since the patient has abnormally high levels), we are therefore reducing expression by decreasing the probability of ribosomal occupying the mRNA transcript. As a result, the number of remaining unbound transcripts may then be assumed to be available for siRNA targeting. In this way, a siRNA molecule concentration may be estimated from these calculations and can be used as an initial resource to inform researchers or clinicians of a projected dosing range for a specific patient. All in all, through our project we hope to encourage the use of multidisciplinary approaches to navigate the progression of gene therapy technology for the betterment of patient care.
References
Setten, R. L. et al. (2019) The current state and future directions of RNAi-based therapeutics.
Soutschek, J. et al. (2004) Therapeutic silencing of an endogenous gene by systemic administration of modified siRNAs.
Chial, H. (2008) Rare Genetic Disorders: Learning About Genetic Disease Through Gene Mapping, SNPs, and Microarray Data.
