Synthesis and characterization of the redox-responsive amphiphilic fluorescent alginate derivatives as the multi-functional hydrophobic anticancer drug delivery system with visualization and sustained release

To develop the multi-functional hydrophobic anticancer drug carriers with visualization and sustained release, a novel amphiphilic alginate derivative (LSA-SS-DEAC) containing chromophobe groups was designed and synthesized by grafting hydrophobic fluorescent molecule, 7-(diethylamino-coumarin-3-carboxylic acid (DEAC-COOH) onto hydrophilic low molecular alginate backbone through cystamine by water-soluble carbodiimide chemical method. The molecular structure and self-assembly properties of the synthesized LSA-SS-DEAC were characterized. Furthermore, the encapsulation of anti-cancer drugs, doxorubicin hydrochloride (DOX) in LSA-SS-DEAC self-assembled micelles was realized by ultrasonic dialysis method. Subsequently, the in vitro drug release behavior and in vitro cytotoxicity of LSA-SS-DEAC micelles in simulated tumor microenvironment were also studied. The resultant LSA-SS-DEAC with the critical micelle concentration (CMC) of 0.26 mg/mL exhibited the ability to spontaneously form spherical micelles with the particle size of 250.2 ± 4.3 nm (PDI = 0.23) and zeta potential of −49.1 ± 0.4 mV, which presented good stability in pH 7.4 PBS and excellent fluorescence properties and redox responsiveness. The drug-loaded LSA-SS-DEAC micelles had the optimal EE value of about 42.2% when the DOX/LSA-SS-DEAC mass ratio was 3:10. Meanwhile, The drug-loaded LSA-SS-DEAC micelles exhibited sustained release in GSH-free environment, and the cumulative drug release rates were 40.3% and 46.6% in pH 7.4 and 5.0 PBS for 48 h, respectively. However, in the simulated tumor cell microenvironment (pH 5.0 PBS + 10 mM GSH), the disulfide bond between the core-shell was broken under the GSH trigger, and the LSA-SS-DEAC micelles collapsed, resulting in a cumulative drug release rate of about 64% at 12 h. In vitro cytotoxicity results showed that LSA-SS-DEAC had low cytotoxicity, and revealed obvious inhibitory effect on HeLa cells after DOX loading. Fluorescence imaging results indicated that LSA-SS-DEAC micelles could emit green light after ingested by cells, and their fluorescence properties were not affected after encapsulation of DOX. Accordingly, LSA-SS-DEAC micelles had the potential for drug localization tracking and rapid drug release at focal sites, which could be expected to be an ideal drug carriers for hydrophobic anticancer drug delivery.