Paclitaxel-loaded SCK nanoparticles: an investigation of loading capacity and cell killing abilities in vitro

Block copolymer nanoparticles having two different hydrodynamic diameters (120 nm vs 50 nm) and core diameters (60 nm vs 20 nm) with variable paclitaxel loading (5 to 20 wt % with respect to polymer weight, 4.4 μg/mL to 21.7 μg/mL paclitaxel concentrations in ultrapure water) were prepared for their in vitro cytotoxicity evaluation. Empty nanoparticles did not show any inherent cytotoxicity even at their highest concentration, whereas paclitaxel-loaded nanoparticles resulted in IC50 values that were better than free paclitaxel at 2 h (0.021 μM vs 0.046 μM) incubation periods, and approximately equal to free paclitaxel at 72 h (0.004 μM vs 0.003 μM) continuous incubation. Confocal fluorescence microscopy images demonstrated that the drug-loaded nanoparticles internalized into KB cells within 2 h and released their payload, resulting in cytotoxicity as evident from the fragmented nuclei present. Functionalization of the nanoparticle surfaces with poly(ethylene oxide) (2 kDa PEO, 5 PEO per block copolymer chain) did not affect the loading of paclitaxel or cell kill ability. No free paclitaxel was found in these nanoparticle formulations indicated by analytical assays.