In addition, TIR@siRNA with US irradiation treatment showed a higher ROS level than TIR treatment after US irradiation, proving that the gene silencing effect of Nrf2-siRNA could inhibit the ROS depletion initiated by Nrf2. cell death (ICD) of cancer. However, the SDT efficacy is extremely limited by Nrf2-based natural redox balance regulation pathway in cancer cells in response to the increased contents of reactive oxygen species (ROS). Nuclear-targeting strategy has shown unique advantages in tumor therapy by directly destroying the DNA. Thus it can be ABT-639 hydrochloride seen that Nrf2-siRNA augmented nuclear-targeting SDT could boost ICB therapy against colorectal cancer. Results The nuclear-targeting delivery system TIR@siRNA (TIR was the abbreviation of assembled TAT-IR780) with great gene carrier capacity and smaller diameter ( 60 nm) was designed to achieve the gene augmented nuclear-targeting SDT facilitating the anti-PD-L1 (programmed cell death-ligand-1) therapy against colorectal cancer. In CT26 cells, TIR@siRNA successfully delivered IR780 (the fluorescent dye used as sonosensitizer) into cell nucleus and Nrf2-siRNA into cytoplasm. Under US (utrasound) irradiation, TIR@siRNA notably increased the cytotoxicity and apoptosis-inducing activity of SDT through down-regulating the Nrf2, directly damaging the DNA, activating mitochondrial apoptotic pathway while remarkably inducing ICD of CT26 cells. In CT26 tumor-bearing mice, ABT-639 hydrochloride TIR@siRNA mediated gene enhanced ABT-639 hydrochloride nuclear-targeting SDT greatly inhibited tumor growth, noticeably increased the T cell infiltration and boosted DPPA-1 peptide-based anti-PD-L1 therapy to ablate the primary CT26 tumors and suppress the intestinal metastases. Conclusions All results demonstrate that TIR@siRNA under US irradiation can efficiently inhibit the tumor progression toward colorectal CT26 cancer in vitro and in vivo by its mediated gene augmented nuclear-targeting sonodynamic therapy. Through fully relieving the immunosuppressive microenvironment of colorectal cancer by this treatment, this nanoplatform provides a new synergistic strategy for enhancing the anti-PD-L1 therapy to ablate colorectal cancer and inhibit its metastasis. Graphical Abstract Supplementary Information The online version contains supplementary material available at 10.1186/s12951-021-01094-x. 0.05 were considered statistically significant. Results and discussion Synthesis, preparation and characterization of the TIR@siRNA nanoparticles The dye IR780, with excellent NIR fluorescence Ki67 antibody properties, has been promisingly applied as a sonosensitizer in SDT in previous studies [34, 35]. Due to its strong lipophilicity and lack of modifiable groups, the biomedical applications of IR780 are limited to a great extent. ABT-639 hydrochloride Numerous studies have improved the hydrophilicity of IR780 by using nanomaterials (e.g., micelles, mesoporous silica and liposomes) through physical encapsulation. Here, we used a chemically coupled approach to improve the hydrophilicity of IR780 for application in SDT against cancer. The TAT peptide with better water solubility reacted with IR780 through a substitution reaction, and the chemical structure of the product TAT-IR780 is shown in Scheme ?Scheme1A.1A. Thin-layer chromatography was used to confirm the formation of the new substances. The chromatographic behaviors of the product, IR780 and TAT peptide mixed with IR780 were completely different, as observed from Additional file 1:?Fig. S1A. Furthermore, the molecular weight of TAT-IR780 was characterized by using mass spectrometry and calculated to be 2165 from the peaks of the tetravalent, trivalent and bivalent ions observed at m/z 541.8, 722.6 and 1083.7, respectively (Additional file 1:?Fig. S1B). The calculated molecular weight of TAT-IR780 was consistent with the value given by ChemDraw software, demonstrating the successful synthesis of TAT-IR780. Next, we assessed the gene loading capacity of TAT-IR780 to load Nrf2-siRNA through a gel retardation assay due to the high ABT-639 hydrochloride positive charge of the TAT peptide. As shown in Fig.?1A, the migration of Nrf2-siRNA was completely inhibited when the N/P ratio was increased to 32/1. Thus, the zeta potentials of TIR and the nanocomplexes with N/P ratios of 32/1 and 64/1 were +?34.2 mV, +?11.9 mV and +?22.5 mV, respectively. Considering the zeta potential, in an effort to make the prepared particles more compact and smaller to meet the need for nuclear targeting and safeguard the full loading of siRNA, the high N/P ratio of 64/1 was chosen to prepare the nuclear-targeting system. The TEM images showed that TIR was around 200 nm with low contrast while the hydration diameter of TIR was 76.01 nm with a PDI of 0.519 (Fig.?1B, C), which might due to the weak assembly.
In addition, TIR@siRNA with US irradiation treatment showed a higher ROS level than TIR treatment after US irradiation, proving that the gene silencing effect of Nrf2-siRNA could inhibit the ROS depletion initiated by Nrf2
