Associate professor Department of Mechanical and Materials Engineering, Tatung University Taipei, Taiwan (Republic of China)
Introduction: Microenvironment-sensitive polymeric nanovehicles have been intensively explored for the selective release of chemotherapeutic drugs in tumors. In particular, the slight difference in pH change in tumor tissue (pH 6.5-6.8), endosome (pH 5.5-6.5), lysosome (pH 4.5-5.5), and that of blood and normal tissue (pH 7.4) has been extensively utilized to trigger the disassembly of pH-responsive nanodelivery system and cargo drugs into the cytosol via endolysosomal acidification and escape. Furthermore, the redox-responsive property also shows great potential owing to the redox environment in the intracellular space (approximately 2-10 mM) compared to that in extracellular space (approximately 2-20 μM). Herein, the design of stimuli-responsive carriers can promote physiological specificity and the on-demand therapeutic efficacy delivery of therapeutic agents in response to specific stimuli for precision cancer drug delivery. In this study, redox and pH dual-responsive controlled drug delivery nanocarriers based on ionically assembled nanoparticles (PICs) have been developed for targeted delivery and controlled drug release.
Materials and Methods: N, O-carboxymethyl chitosan (NOCC) was prepared according to Chen et al. with slight modifications. Chitosan powder was suspended in isopropyl alcohol and stirred at room temperature. Next, sodium hydroxide solution was added to the stirred slurry. Monochloroacetic acid was batch-added to the reaction mixture for a few hours at 60 °C. Next, the pH value of the reaction solution was adjusted to 7. The solid was filtered and rinsed in 75% ethyl alcohol to desalt and dewater. Thiolated hyaluronic acid (HA-SH) was synthesized according to previous studies. EDC and NHS were added to HA in PBS buffer and then were reacted for 2 h. Cysteamine was added to the previous mixture and stirred for 24 hours. After the reaction, the product solution was purified by dialysis. The products were dried using the freeze-drying method and preserved at −20 °C before use. PICs are prepared via electrostatic interaction between NOCC and HA-SH. To prepare NOCC/ doxorubicin hydrochloride (Dox)/HA-SH NPs, 80 μL of NOCC solution was added to the Dox solution, followed by mixing with HA-SH solution. The mixed solutions were incubated at room temperature for 10 min to achieve equilibrium.
Results, Discussions, and Conclusions: The model drug Dox was successfully encapsulated through physical adsorption and electrostatic interactions to form a PICs nanocarrier. HA-SH was used as a polyanion to act as an ionic crosslinker through polyelectrolyte complexation with NOCC polycations and the formation of interfacial PICs complexes. The results show that the Dox loading efficiency in PICs is above 73 % with high stability. The PICs also show no apparent toxicity to Hela cells, indicating that the carriers have good biocompatibility under the tested concentration. The accumulated amount of Dox from the PICs drug carrier was approximately 56.7%, 52.4%, and 34.3% at pH 5.0, 6.5, and 7.4 in 24 hours, respectively. The intracellular acidic environment (endo/lysosome, pH 5.0) can trigger carboxymethyl protonation to promote the electrostatic repulsion of Dox. The reducing microenvironment (10 mM GSH) in tumor cells can hydrolyze disulfide bonds, leading to the disintegration of the carrier structure. The cumulative release ratio was high over 95%, almost twice as high at pH 5.0 in the absence of GSH. Additionally, no obvious change (less than 5%) was observed when the PICs carrier was incubated with or without 10 μM GSH at pH 7.4 (the typical pH of physiological environments). In vitro, release studies reveal that the stimuli-responsive system can release Dox in a redox and pH dual-sensitive manner. When coculture with cells, it also demonstrates that PICs effectively deliver the therapeutic cargo to cancer cells through HA receptor-mediated endocytosis. PICs can enhance drug accumulation in tumor cells and improve antitumor efficacy. In summary, the redox-responsive with crosslinked disulfide bonds and pH-responsive with protonation/deprotonation properties can provide better stability for encapsulated anticancer drugs in the blood circulation and extracellular milieu before reaching the targeted site. Taken together, PICs are promising nanocarriers with good biocompatibility, tumor targetability, and controlled drug release capability for the delivery of chemodrugs in cancer therapy.
Acknowledgements (Optional): This research was funded by the National Science and Technology Council, Taiwan (MOST 111-2221-E-036-002 -) and Tatung University (B112-M07-024).
