Cationic lipids percentage and processing temperature are critical in designing siRNA lipid nanoparticles.

To design a clinically viable small interfering RNA (siRNA) formulation, it is essential to understand the in vivo siRNA delivery mechanism during the product development. However, majority of reported siRNA delivery studies are based on testing only isolated factors, with ambiguous interpretation of often in vitro transfection results. Correlating physicochemical properties with in vivo transfection efficiency thus represents an important step towards rational design of siRNA delivery systems. In this study, design of experiments studies were applied to probe formulation attributes and process parameters, with in vivo activities evaluated as a primary response along with physicochemical properties. Statistical analysis was performed to identify the significance of each input factor towards the in vivo transfection efficiency using a Positive Readout System. The interactions between these factors were also analyzed. Our results indicated that among the formulation factors evaluated, the percentage of cationic lipid is of most significant effect. During the process, temperature stands out as the most significant factor impacting the in vivo activities. These results shed light on our design of siRNA lipid nanoparticle formulations in the early development stage.