Diethyl ether as a drug-loading and sizereducing cosolvent to produce monodisperse, nanoscale perfluorocarbon agents

Perfluorocarbon nanodroplets (PFC NDs) have been proposed as in situ microbubble precursors for cancer imaging and therapy. Unlike microbubbles that are purely intravascular agents, PFC NDs can accumulate in solid tumours from leaky tumour vasculature before their conversion to echogenic microbubbles by externally applied ultrasound. If anti-cancer drugs can be effectively incorporated into the PFC NDs, it may be possible to expand the use of PFC NDs towards the controlled in vivo delivery of high concentrations of toxic cancer drugs with high temporal and spatial precision to tumours. However, due to the hydrophobic and lipophobic characters of PFCs, the formation of both high quality nanoscale droplets and the efficient loading of drugs into PFC NDs remain a challenge. In this study, a lipophilic solvent that is co-miscible in both PFC and water is explored as a means to load lipophilic drug molecules into PFCs and as a way to produce high quality, monodisperse PFC agents on the nanometer size regime. Diethyl ether (DEE) was selected as the drug-loading and size-reducing solvent, and a fluorescent molecule, DiI, was selected as the lipophilic drug surrogate. Monodisperse, micron-scale precursor droplets were produced using standard microfluidics. After the removal of DEE, this method resulted in a ~5 fold reduction in size from the precursor droplets to monodisperse DiI-loaded PFC droplets. The successful loading of DiI into monodisperse PFC NDs suggests that this cosolvent method can be used to produce lipophilic anti-cancer drug-loaded PFC NDs for evaluation in US-mediated cancer therapy.