Heparin-folate-retinoic acid bioconjugates for targeted delivery of hydrophobic photosensitizers

Amphiphilic heparin-retinoic acid (HR) and heparin-folate-retinoic acid bioconjugates (HFR) were synthesized by chemical conjugation of a hydrophobic anticancer agent all-trans-retinoic acid (RA) and a targeting ligand, folic acid (FA), to the high molecular weight heparin backbone. The HR and HFR bioconjugates had a high RA content (22%, w/w) and could self-assemble into nanoparticles with efficient encapsulation of a hydrophobic photosensitizer, pheophorbide a (PhA). The HFR bioconjugate demonstrated higher PhA loading content and loading efficiency compared to HR bioconjugate. The PhA-loaded HR and HFR nanoparticles had an average diameter of about 70 nm, a negatively charged surface, a sustained release pattern and self-quenching effect in a buffered solution. Furthermore, the cellular uptake of PhA-loaded HFR nanoparticles in folate receptor-positive HeLa cells was higher than that of PhA-loaded HR nanoparticles. Upon irradiation, HFR nanoparticles selectively enhanced the phototoxicity of PhA in HeLa cells while the dark-toxicity of the nanoparticles was minimal without light treatment. HFR nanoparticles also demonstrated targeted anti-cancer effect, improving the cytotoxicity of RA in HeLa cells compared to HR nanoparticles at RA concentration ≥50 μg/mL. The targeting effect of HFR and PhA-loaded HFR nanoparticles was not observed in folate receptor-negative HT-29 cells. The results indicated that HFR nanoparticles may be useful for targeted delivery of hydrophobic PDT agents and as a potential nanocarrier for dual chemo-and photodynamic therapies.