Abstract
It is hypothesized that L-arginine (ARG) can improve etoposide (VP-16) water solubility while preserving its anticancer activity. Factorial design is used to identify conditions for optimum drug aqueous solubility after freeze-drying. The physicochemical properties of the optimized formulation is further analyzed by X-ray powder diffraction, scanning electron microscopy, proton nuclear magnetic resonance, and fourier transform infrared spectroscopy. Drug stability in formulation is analyzed using mass spectrometry based fragmentation analysis. Liquid chromatography tandem mass spectrometry and cell viability assay on Michigan Cancer Foundation-7 ( MCF-7) cell line are performed to assess the drug cellular uptake and the anticancer activity, respectively. At the VP-16: ARG ratio of 4:10 (w/w), the drug apparent solubility increased significantly (similar to 65-folds) with a 3.5-fold improvement in the drug dissolution rate. The interaction between VP-16 and ARG transforms the drug from crystalline to amorphous solid state. VP-16-ARG complex in lower native drug concentration range (50-300 mu M) has lower anticancer activity compared with native VP-16, due to reduced intracellular transport of the more hydrophilic complex as indicated by the cell viability assay and confirmed by cell uptake study. However, at higher drug concentrations (500 mu M) the complex's higher anticancer activity is ascribed to the synergistic effect between ARG and VP-16. These data suggest that an optimal ARG concentration can have positive effects with potential benefits for chemotherapy.