Potential use of cholecalciferol polyethylene glycol succinate as a novel pharmaceutical additive.

D-alpha-tocopheryl polyethylene glycol succinate (TPGS) has been utilized in numerous drug delivery formulations in recent years. Because of its amphiphilic structure, it can be used as emulsifier and vehicle for lipid-based drug delivery formulations. It is also an effective P-glycoprotein (P-gp) inhibitor. However, TPGS represents only one of the surfactants in the class of "Vitamin-PEG" conjugated surfactants. To design a new adjuvant or additive, a conjugate made of vitamin D (cholecalciferol) and PEG-cholecalciferol polyethylene glycol succinate (CPGS) was synthesized via a two-step reaction. We hypothesized that CPGS may exhibit similar characteristics to TPGS, and thus the physicochemical properties as well as the anticancer properties of CPGS were studied. The results demonstrated that CPGS reduced the particle size and increased the encapsulation efficiency of the PLGA nanoparticles, indicating that CPGS may also have the emulsifier function similar to TPGS. The drug release profiles showed that the nanoparticles with CPGS additive had a lower initial burst and more sustained release pattern. In vitro testing with Caco-2 cells showed that CPGS could increase the cytotoxicity of DOX-loaded PLGA nanoparticles. Based on the rhodamine accumulation study, the increased cytotoxicity is possibly due to the P-gp inhibition by CPGS. From current results, the use of CPGS as an adjuvant is promising and may enhance the efficacy of the overall drug delivery system.