Charge converting nanostructured lipid carriers containing a cell-penetrating peptide for enhanced cellular uptake

The aim of this study was the development of nanostructured lipid carriers (NLCs) decorated with a polycationic cell-penetrating peptide (CPP). A coating with polyphosphates (PP) enables charge conversion at target cells being triggered by the membrane bound enzyme intestinal alkaline phosphatase (IAP).

The CPP, stearyl-nona-L-arginine (R9SA) was obtained by solid phase synthesis. Formed nanocarriers were characterized regarding size, polydispersity index, zeta potential and charge conversion in the presence of IAP and on Caco-2 cells. The BCS class IV drug saquinavir (SQV) was loaded into NLCs in different concentrations. Mucus diffusion ability of the NLCs was evaluated by the rotating tube method. Furthermore, cellular uptake was evaluated on Caco-2 cells and endosomal escape properties were investigated using erythrocytes.

All NLCs were obtained in a size range between 146 nm and 152 nm and a polydispersity index of 0.2. Incubation of PP coated PP-R9SA-NLCs with IAP led to a charge conversion from -41.8 mV to 6.4 mV (Δ48.2 mV). After four hours of incubation with IAP, phosphate release reached a plateau, indicating a faster polyphosphate cleavage than on Caco-2. Drug load and encapsulation efficiency of SQV was obtained up to 80.6% and 46.5 µg/mg. Mucus diffusion was increasing in the following rank order: R9SA-NLCs < blank NLCs < PP-R9SA-NLCs. R9SA-NLCs and PP-R9SA-NLCs increased the cellular uptake 15.6- and 13.2-fold, respectively, compared to the control NLCs. Erythrocytes interaction study revealed enhanced endosomal escape properties for R9SA-NLCs and PP-R9SA-NLCs when incubated with IAP.