Reducing The Liver Toxicity Of Chemotherapy Via PH-sensitive Polymeric Conjugate Micelles

Nanocarriers have been widely applied to enhance the anticancer efficacy of chemotherapy,but the removal of associated hepatotoxicity is still a major challenge.This is due to the biodistribution of the system that causes cytotoxic drug loaded nanoparticles be accumulated heavily in liver.This effect is even more pronounced when the drugs that are contained in the nanoparticles can cause severe hepatotoxicity,such as several anticancer drugs.To solve this problem,we reported a novel type of nanocarrier that was made of hepatoprotective compound(oleanolic acid/OA)with a model drug(methotrexate/MTX)being physically encapsulated.The OA-loaded prodrug(OA-NCs)was synthesized by conjugating modified OA with methoxy poly(ethylene glycol)(mPEG)through hydrazone bond,then MTX was encapsulated within it using a dialysis method to obtain drug-loaded micelle(OA-NCs/MTX).The MTX loading was determined to be ca.5.1%(w/w)by HPLC.The pH-sensitive micelles were stable at pH 7.4 with a critical micelle concentration of 10.5 ?M.Dynamic light scattering(DLS)and transmission electron microscope(TEM)characterization demonstrated two micelles were spherical shape with an appropriate size distribution.In vitro drugs release experiment indicated OA-NCs/MTX possessed pH responsive activity.Under acidic condition(pH = 5.0),the broken of hydrazone bond leads to the decomposition of micelles and the rapid release of OA and MTX.The adjuvant antitumor effect of OA was also proved in 4T1 cells.In the animal model of 4T1 tumor bearing mice,biodistribution study showed the Cy5 labeled OA-NCs/MTX can selectively target in mice tumor,which accorded with the EPR effect.Moreover,according to the in vivo antitumor study,OA-NCs/MTX exhibited excellent antitumor efficacy because of the passive tumor targeting of nanoparticles.From the in vivo hepatoprotection assays,unsurprisingly,we can know MTX caused severe liver injury,which was manifested by increased liver mass,increased levels of alanine transaminase(ALT),aspartate transaminase(AST)and lactate dehydrogenase(LDH)both in serum and liver homogenate.In addition,the increase of MDA level and the concentration decrease of glutamine peroxidase(GSH-Px)and superoxide dismutase(SOD)proved that the hepatotoxicity induced by MTX was associated with increased oxidative stress.When treated by OA-NCs/MTX,the activities of ALT,AST and LDH in serum were greatly reduced compared with free MTX.In addition,the oxidative stress parameters and ROS production MDA in liver returned to normal level when treated by OA-loaded micelles.These results suggested OA can against OS caused by MTX.Histopathological analysis also verified that designed OA prodrug can effectively alleviate the liver damage induced by MTX.All results showed that the new pH-responsive micelle can greatly improve anticancer efficacy and significantly reduce the hepatotoxicity caused by MTX due to the hepatoprotective function of OA.Therefore,the current work would offer a new strategy for achieving favorable anticancer effect and low hepatotoxicity simultaneously,which can be applied to numerous anticancer drugs and hepatoprotective materials.