Raspberry-like poly(γ-glutamic acid) hydrogel particles for pH-dependent cell membrane passage and controlled cytosolic delivery of antitumor drugs

Abstract

In this research, we synthesized bioderived poly(amino acid) hydrogel particles that showed pH-dependent membrane-disrupting properties and controlled cytosolic delivery of antitumor drugs. Poly(γ-glutamic acid) (γ-PGA) that has been produced extensively using bacteria, especially those of Bacillus subtilis species, was modified with cholesterol (γ-PGA/Chol), and the γ-PGA/Chol conjugates were used to form polymeric nanoparticles the size of 21.0±1.1 nm in aqueous solution. When the polymeric nanoparticles were mixed with doxorubicin (Dox), raspberry-like hydrogel particles (RBHPs) were formed by the electrostatic interaction between the cationically charged Dox and the anionically charged nanoparticles. The average size and surface charge of the RBHPs in aqueous solution were 444.9±122.5 nm and −56.44 mV, respectively. The loaded amount of Dox was approximately 63.9 μg/mg of RBHPs. The RBHPs showed controlled drug release behavior in both in vitro and ex vivo cell-based experiments. Through fluorescence microscopy and fluorescence-activated cell sorting, the cellular uptake of RBHPs into human cervical cancer cells (HeLa) was analyzed. The cytotoxic effect, evaluated by the methyl tetrazolium salt assay, was dependent on both the concentration of RBHPs and the treatment time. The pH-dependent membrane-disrupting properties of the RBHPs and the subsequent cytosolic delivery of Dox were evaluated using a standard hemolysis assay. Upon an increase in hydrophobicity at the lysosomal acidic pH, RBHPs could easily interact, penetrate cell membranes, and destabilize them. Taken together, the data suggested that RBHPs could be used as drug delivery carriers after loading with other therapeutic drugs, such as proteins or small interfering RNA for cancer therapy.

Keywords:

• hydrogel particles
• controlled release
• endosomal escape
• antitumor

Supplementary material

Figure S1 Results of hemolysis with γ-PGA/Chol nanoparticles.

Notes: 1, PBS; 2, 0.2% Triton X; 3, γ-PGA; 4, γ-PGA/Chol nanoparticles.

Abbreviations: γ-PGA, poly(γ-glutamic acid); Chol, cholesterol; PBS, phosphate-buffered saline.

Acknowledgments

This work was supported by financial support from the National Research Foundation of Korea (NRF) funded by the Korean government (MEST) (numbers 2014R1A2A1A10049960 and 2015R1A2A1A15051980); a grant from the Korea Health Technology R&D Project, provided through the Korea Health Industry Development Institute, funded by the Ministry of Health and Welfare (grant number HI14C2680); and the National Research Council of Science and Technology grant by the Korea government (MSIP) (number CAP-15-09-KIMS).

Disclosure

The authors report no conflicts of interest in this work.