S-nitrosothiols loaded mini-sized Au@silica nanorod elicits collagen depletion and mitochondrial damage in solid tumor treatment

To a large extent, the dense extracellular matrix (ECM), which tightly connects tumor cells to arm the tumor into an intractable fortress, significantly decreases the nanoparticles delivery efficacy and overall performance in cancer treatments. Therefore, it is necessary to transform the dense stroma of solid tumors to loose state, which could realize deep penetration of nanomedicine and enhance cancer treatment effects. Here, we fabricated a protein-free collagen nanosweeper, triphenylphosphonium bromide (TPP) coated and S-nitrosothiols loaded mini-sized Au@silica nanorod (Au@SiO₂-SNO/PEG/TPP, GSNP-TPP), to clear the transport barriers of nanoparticles as well as elevate enhanced permeability and retention (EPR) effect, thus alleviating the diffusion resistance and realizing further penetration of nanoparticles. Methods: By modifying the Au@silica with thermo-sensitive S-nitrosothiols, the carrier could release the nitric oxide (NO) due to the surface overheat as well as perform photothermal therapy (PTT) under near-infrared (NIR) laser irradiation. The level of collagen depletion was observed via western blotting and immunofluorescent staining. In addition, the dual-imaging and antitumor efficiency of GSNP-TPPs were evaluated with the HeLa tumor-bearing mouse model. Results: On one hand, the released NO could deplete collagen by activating matrix metalloproteinases (MMPs) to break collagen fibers, thus loosening the dense ECM to enhance the cellular internalization. On the other hand, with the mitochondrial-targeted effect of TPP, the diffusible NO in tumor might rapidly interact with superoxide anion (O₂Ÿ^-) to produce highly toxic and powerful reactive nitrogen species (RNS) -- peroxynitrite (ONOO^-), which resulted in mitochondrial damage to induce cell apoptosis. With the unique properties of mini-sized gold nanorods, the formulated nanoparticles exhibited good computed tomography (CT) and multi-spectral optoacoustic tomography (MSOT) imaging effects in precisely locating and monitoring tumor. Moreover, the antitumor efficacy of GSNP-TPPs + laser group was further confirmed by ex-vivo histological analysis of tumor tissue. Conclusion: This work points out a strategy to overcome the obstacle standing in nanoparticles penetration, and opens the door of further exploitation of NO-related theranostic systems.

Keywords: Nitric oxide; RNS; collagen depletion; mitochondrial-targeted; nanosweeper; thermal-sensitive.