Environmental-responsive Targeted Nano-delivery System For Tumor Therapy

Traditional chemotherapy has defects such as poor selectivity,uncontrolled release and large dosage,resulting in limited bioavailability of drug and therapeutic effect.Hyaluronic acid(HA)with tumor-targeting ability as a nano-drug carrier can selectively accumulate in tumor site to reduce the damage to normal tissues.Based on the special microenvironment of tumor tissue,environmental-responsive bonds are introduced to the targeted nano-delivery system to control drug release,thereby improving the effective concentration of drug in tumor cells.On the basis of chemotherapy,polydopamine(PDA)nanoparticles with high photothermal conversion efficiency are introduced to realize chemotherapy-photothermal combined therapy,reducing the drug dosage.Therefore,in this work,environment-responsive targeted HA nanodelivery carriers were constructed to deliver an antitumor drug podophyllotoxin(PPT),combining with photothermal therapy,for achieving good tumor treatment effect.The present work mainly includes the following parts:(1)HA which has tumor-targeting ability was used to conjugate to antitumor drug PPT to construct p H-sensitive prodrugs named HA-CO-O-PPT via esterification reaction.HA-CO-OPPT spontaneously assembled into nanoparticles in aqueous medium.HA-CO-O-PPT nanoparticles had a uniformly ellipsoid or spherical morphology with size of about 130 nm,and their drug loading(DL)was 10.05%.Nanoparticles could maintain the structural integrity under normal physiological environment,while exhibiting a p H-responsive drug release mode with cumulative release reaching 65.2% due to hydrolysis of ester bonds in acidic environment of tumor.Moreover,the nanoparticles could accumulate the tumor site via HA-mediated targeting,and their cellular uptake efficiency exceeded 97%.The nanoparticles could more effectively inhibit the growth of tumor cells than free PPT,and showed low toxicity to normal cells.Furthermore,it was found that the tumor inhibition ratio of the nanoparticles reached 85%,indicating good antitumor activities in vivo,and the nanoparticles exhibited negligible toxicity to main organs.(2)To further improve drug release efficiency and enhance tumor treatment effect,p H/reduction dual-sensitive targeted prodrug(HA-S-S-PPT)nanoparticles were prepared.HA was first reacted with cystamine dihydrochloride to introduce disulfide bonds,and then coupled with carboxylated PPT to synthesize p H/reduction dual-sensitive prodrugs named HA-CO-OPPT.Similarly,p H-sensitive prodrugs(HA-NH-CO-PPT)were synthesized as the control.HAS-S-PPT spontaneously assembled into nanoparticles in aqueous medium.HA-S-S-PPT nanoparticles had a uniformly ellipsoid or spherical morphology with size of about 100 nm,and their DL was 13.01%.The nanoparticles showed good serum stability,long-term stability and blood compatibility.In vitro drug release behavior showed the cumulative release of PPT was low under normal physiological environment.Whereas,the nanoparticles could effectively release PPT due to the cleavage of ester and disulfide bonds triggered by low p H and high GSH concentration in tumor site.The nanoparticles exhibited 27.1% and 22.5% higher cumulative release than HA-NH-CO-PPT and HA-CO-O-PPT nanoparticles,indicating that the p H and reduction dual-sensitive nanoparticles could more effectively promote drug release than p Hsensitive nanoparticles.In addition,HA-S-S-PPT nanoparticles could actively target to the tumor site,and their cellular uptake efficiency was more than 97%.HA-S-S-PPT nanoparticles could more effectively inhibit the growth of tumor cells than HA-NH-CO-PPT and HA-CO-OPPT nanoparticles.Furthermore,in vivo tumor inhibition results showed that the tumor inhibition ratio of HA-S-S-PPT nanoparticles reached 92%,which was 27% and 7% higher than that of HA-NH-CO-PPT and HA-CO-O-PPT nanoparticles,indicating that HA-S-S-PPT nanoparticles had better anticancer effect than HA-NH-CO-PPT and HA-CO-O-PPT nanoparticles.The body weight of the mice scarcely decreased,the blood indexes were normal,and no obvious toxicity to main organs was observed,indicating HA-S-S-PPT micelles had high in vivo safety.(3)To further reduce PPT dosage,ablate tumors and improve the antitumor efficiency in the prognosis period,HA-S-S-PPT was combined with PDA nanoparticles to construct HA-SS-PPT/PDA composite nanoparticles for combined chemotherapy and photothermal therapy.HA-S-S-PPT/PDA had a uniformly spherical morphology with size of about 140 nm.Under the irradiation of 808 nm laser,the photothermal conversion efficiency of HA-S-S-PPT/PDA was 41.12%,showing high photothermal conversion efficiency.No significant decrease in photothermal activity of HA-S-S-PPT/PDA was observed after 4 cycles laser irrdation,indicating HA-S-S-PPT/PDA had excellent photothermal stability.HA-S-S-PPT/PDA showed low hemolysis ratio(less than 5%)and high cell viability to normal cells(beyond 80%),demonstrating excellent blood compatibility and low cytotoxicity.In addition,HA-S-SPPT/PDA could selectively accumulate tumor site,and their cellular uptake efficiency exceeded 98%.CCK-8 and Calcein-AM/PI co-staining method confirmed that chemophotothermal combined therapy had more significant inhibition effect on tumor cells than single-mode treatment.Furthermore,the results of in vivo tumor inhibition showed that the tumor inhibition ratio of HA-S-S-PPT/PDA was 95%,which was better than 88% of PDA.When the PPT dosage was three times lower than the normal dosage,HA-S-S-PPT/PDA still exhibited a better therapeutic effect than HA-S-S-PPT(92% of inhibition ratio),confirming that chemotherapy combined with photothermal therapy could significantly improve the antitumor effect and reduce PPT dosage.No obvious toxicity to main organs in mice was observed,indicating HA-S-S-PPT/PDA had high in vivo safety.