Preparation of intravenous injection nanoformulation of VESylated gemcitabine by co-assembly with TPGS and its anti-tumor activity in pancreatic tumor-bearing mice

Our recent publication showed that VES-dFdC nanocapsules in pure water could be obtained via the self-assembling of VES-dFdC prodrug synthesized by coupling gemcitabine (dFdC) with vitamin E succinate (VES). To prepare the intravenous injection nanoformulation, we present here a novel strategy to improve the stability and drug concentration of VES-dFdC nanoformulation in PBS or isotonic solution . Particularly, d -α-tocopheryl polyethylene glycol succinate (TPGS), usually used as drug solubilizer and coincidentally contains the same VES moiety as VES-dFdC prodrug and PEG chain, is selected to co-assemble with VES-dFdC prodrug. The zeta potentials of all the TPGS/VES-dFdC co-assemblies were close to 0   mV, and their particle size measured by dynamic light scattering (DLS) decreased from 113 to 36   nm with increasing TPGS/VES-dFdC molar ratios from 0.15 to 1.5. Stable colloidal suspensions were obtained without aggregates in PBS at 4   °C in one month or isotonic solution at 37   °C in one week, and the weight concentration of VES-dFdC prodrug increased from 7 to 17   mg/mL when the molar ratios of TPGS/VES-dFdC ranged from 0.5/1 to 1.5/1. The concentration of VES-dFdC prodrug was high enough to be used as intravenous injection nanoformulation in nude mice . Interestingly, along with the increase of TPGS/VES-dFdC molar ratios from 0.3/1 to 1.5/1, the morphology of TPGS/VES-dFdC co-assemblies changed from loose nanocapsule to compact micelle revealed by transmission electron microscope (TEM). Finally, the co-assembly of TPGS/VES-dFdC (TPGS/VES-dFdC: 1/1) was selected as intravenous injection nanoformulation to evaluate the antitumor activity . Compared with native dFdC, TPGS/VES-dFdC nanoformulation with 0.2   mmol/kg of dosage showed similar low toxicity in vivo , but 4.7 times high of tumor inhibition rate in nude mice with pre-established BxPC-3 tumors.