The cationic RVA self-assemblies were then sequentially co-incubated with anionic siRNA and
γ-PGA to form binary (RVA/siRNA) and ternary (
γ-PGA/RVA/siRNA) gene complexes. Optimal N/P ratios were screened by the dynamic light scattering (DLS) investigation on particle size and zeta potential (
Fig. 2A). Results showed that by N/P ratio increasing from 10 to 40, size of the complexes fluctuated between 186 nm to 220 nm, and zeta potential was in the range of 38 mV to 44 mV. While at lower N/P of 5, size of complexes was very large (~807 nm), which was probably caused by the poor compressing capacity of RVA self-assemblies. After some preliminary experiments, RVA/siRNA binary complexes with N/P of 30 were selected for the following incubation with the targeting motif of
γ-PGA (Fig. S1) [
24]. The modification of negatively charged
γ-PGA decreased zeta potential in a dosage-dependent mode, showing -36 mV at weight ratio of 5 (
γ-PGA: siRNA) (
Fig. 2B). The
γ-PGA/RVA/siRNA complexes was dispersed in the medium containing 10% fetal bovine serum to study its stability under physiological conditions (
Fig. 2C). The results showed that the particle size of
γ-PGA/RVA/siRNA complexes is around 200 nm and remain unchanged within 5 d, while the zeta potential is also maintaining stability during the test. It indicates that the complexes of
γ-PGA/RVA/siRNA has good stability under physiological conditions. Morphology of RVA assemblies and
γ-PGA/RVA/siRNA complexes exhibited globular grain by transmission electron microscopy (TEM) observation with an average diameter ~75 and 125 nm, respectively (
Figs. 2D and
E). From the agarose gel electrophoresis evaluation, RVA assemblies were able to completely compress siRNA at N/P ratios higher than 6 (
Fig. 2F). Adding of negatively charged
γ-PGA did not disturb the condensation capacity (
Fig. 2G) [
34]. In the tumor mimicking microenvironment (5 mmol/L glutathione solution, GSH), migration bands of siRNA could be observed in RVA/siRNA complexes (
Fig. 2F). This GSH responsiveness indicated a redox sensitive release instinct of RVA gene complexes [
35]. In addition, the release of ATRA at different concentrations was measured by an ultraviolet spectrophotometer at 365 nm and a standard curve for ATRA release was plotted (
Fig. 2H), as well as the release of ATRA in the RVA assembly in PBS and GSH (5 mmol/L) conditions. When PBS was used alone, the release of ATRA was markedly slow, with a 48 h cumulative release rate of only 20.76% (
Fig. 2I). In contrast, the release of ATRA under GSH condition was significantly accelerated, indicating a supersensitive reaction of the disulfide bonds with cumulative release of 67.15% after 48 h.