In 2001 Elbashir and Tuschl (1) published they had managed to silence gene expression in mammalian cells using small interfering RNA (siRNA). This was the catalyst for an explosion of research using siRNA to demonstrate the effect of knocking out targets without the need to identify compounds capable of doing this job. Potentially highly specific, the opportunity to use these as therapeutics was rapidly explored. Ten years later the first clinical trials are coming through; impressively fast.
Probably the largest obstacle to therapeutic siRNA has been delivery, which often is either toxic, or not very effective – as any of us who have tried to transfect siRNA into primary cells will be able to appreciate. Advances in materials science are seemingly solving this problem encapsulating siRNA in nanoparticles, resulting in safe and effective delivery. CALAA-01 (Calando Pharmaceuticals) lead the way being the first to deliver siRNA therapeutically demonstrating phase I efficacy and safety, as well as localisation to melanoma metastases.
One particular advantage of siRNA is that once delivery has been optimised, it is possible for several different siRNAs for different targets to be contained within on package. This could enable simultaneous delivery of different targets simultaneously effecting different aspects of the same disease, i.e. metastasis and well as tumour growth. By also hitting a known resistance pathway this duel delivery could enable the chemotherapy to be more effective.
A recently published article (2) has done just this, delivering two siRNAs in lipid nanoparticles (known as ALN-VSP) for both VEGF-A (vascular endothelial growth factor-A) and kinesin spindle protein (KSP) for the treatment of advanced solid tumours with liver metastases. KSP is involved in cancer proliferation and VEGF-A in the growth of new blood vessels.
The study was phase I, dose escalation, on patients who had already been heavily pre-treated with chemotherapy and/or anti VEGF/VEGFR agents with the ALN-VSP administered as 15 minute IV every 2 weeks for 1 month.
The safety profile was very encouraging with ALN-VSP being generally well-tolerated with mainly low-grade fatigue, nausea and fever noted in 15-24% of patients. The lipid nanoparticle of ALN-VSP distributes primarily to the liver and spleen and the delivery was also excellent. Liver biopsies were performed on 12 patients before the first dose and then at 2 and 7 days post dose. qPCR identified VEGF siRNA present in all 12 patients and KSP siRNA present in 11 of the 12.
Of the patients treated, 7 had no disease progression (measured by computerized tomography [CT] scan) after the treatment cycles and continued onto an extension study. One patient in particular with endometrial cancer achieved a complete response after 20 months of treatment
This is clearly fantastic progress for ALN-VSP, and specifically for the handful of patients who were positively affected from participation in the trial. The results from this study also demonstrate the ability for safe delivery of multiple siRNA to specific sites tumour and this extends the promising start for these methods of siRNA delivery which may open up previously un-druggable targets.
1. Elbashir SM, Harborth J, Lendeckel W, Yalcin a, Weber K, Tuschl T. Duplexes of 21-nucleotide RNAs mediate RNA interference in cultured mammalian cells. Nature 411: 494–8, 2001.
2. Tabernero J, Shapiro GI, Lorusso PM, Cervantes A, Schwartz GK, Weiss GJ, Paz-Ares L, Cho DC, Infante JR, Alsina M, Gounder MM, Falzone R, Harrop J, Seila White AC, Toudjarska I, Bumcrot D, Meyers RE, Hinkle G, Svrzikapa N, Hutabarat RM, Clausen V a, Cehelsky J, Nochur S V, Gamba-Vitalo C, Vaishnaw AK, Sah DWY, Gollob J a, Burris H a. First-in-Man Trial of an RNA Interference Therapeutic Targeting VEGF and KSP in Cancer Patients with Liver Involvement. Cancer discovery (January 28, 2013). doi: 10.1158/2159-8290.CD-12-0429.