Modelling the response surface to predict the hydrodynamic diameters of theranostic magnetic siRNA nanovectors.

Short interfering RNAs (siRNAs) appear to be a promising tool to treat various human diseases, such as cancer via the RNA interference (RNAi) mechanism. Since the systemic administration of siRNAs is limited by their capacity to attain the site of action, novel delivery systems are needed. Previously, we reported the formulation of magnetic siRNA nanovectors (MSN) using electrostatic assembly of the following components: (1) functionalized superparamagnetic iron oxide nanoparticles (SPIONs) able to act as agents for magnetic resonance imaging (MRI) and/or thermal therapy, (2) siRNAs as active molecules and (3) chitosan to protect siRNAs and to enhance their transfection efficacy. In this work, experimental design was used to further improve the formulation protocol and to optimize the component quantities. The aim was to obtain response surface plots that will help to optimize and predict the component quantities of the MSNs regarding their hydrodynamic diameter (DH). The influent parameters of the formulation process were determined using a Plackett-Burman design. The results show that the order of incorporation of the components is the most influent parameter on the DH of MSNs. A Box-Behnken design was used to optimize the component quantities. The model equations provided the parameters to obtain MSNs with DH smaller than 100 nm to allow their systemic administration.