Synthesis and evaluation of the cancer cell growth inhibitory activity of the ionic derivatives of oleanolic acid and ursolic acid with improved solubility

Abstract

Formation of ionic derivatives from drugs provided a simple tool to tune physical properties including water solubility and biological activity of the drugs. Oleanolic acid (OA) and ursolic acid (UA) are two ubiquitous isomeric triterpene phytochemicals with many pharmacological effects. But the poor water solubility greatly limits their clinical application. In order to improve the solubility of OA and UA, this research exploited a non-covalent synthetic approach to prepare a series of novel ionic derivatives of OA and UA by a simple acid-base neutralization method for converting them into simple organic salts. The OA/UA based ionic derivatives were characterized by HRMS, FTIR, NMR, XRPD, and TGA-DSC, their solubilities and apparent 1-octanol/water partition coefficients were measured under different conditions. The solubility of the ionic derivatives turned out to be higher than that of OA/UA under most of experiment conditions, which indicated our aim to improve the solubility was attained. The apparent 1-octanol/water partition coefficients indicated that the ionic derivatives of OA/UA had higher hydrophilicity than OA/UA under most of the experiment conditions. Moreover, the human hepatoma cell lines (HepG2) growth inhibitory activity of the derivatives was also evaluated by MTT assay. The results suggested that UA based ionic derivatives exhibited significantly lower IC50 values than OA based ionic derivatives under the same conditions, indicating stronger inhibitory effect on the growth of HepG2 cells.