The efficacy of nanoparticle (NP)-based drug delivery technology is hampered by aberrant tumor stromal microenvironments (TSMs) that hinder NP transportation. Therefore, the promotion of NP permeation into deep tumor sites via the regulation of tumor microenvironments is of critical importance. Herein, we propose a potential solution using a dihydrazidine (HDZ)-loaded nanoparticle drug delivery system containing a pH-responsive, cyclic RGD peptide-modified prodrug based on doxorubicin (cRGD-Dex-DOX). With a combined experimental and theoretical approach, we find that the designed NP system can recognize the acid tumor environments and precisely release the encapsulated HDZ into tumor tissues. HDZ can notably downregulate the expression levels of hypoxia-inducible factor 1α (HIF1α), α-smooth muscle actin, and fibronectin through the dilation of tumor blood vessels. These changes in the TSMs enhance the enrichment and penetration of NPs and also unexpectedly promote the infiltration of activated T cells into tumors, suggesting that such a system may offer an effective “multifunctional therapy” through both improving the chemotherapeutic effect and enhancing the immune response to tumors. In vivo experiments on 4T1 breast cancer bearing mice indeed validate that this therapy has the most outstanding antitumor effects over all the other tested control regimens, with the lowest side effects as well.

The co-assembly of charged nanoparticles with oppositely charged molecular ions has emerged as a promising technique in the fabrication of nanoparticle superstructures. However, the underlying mechanism behind these molecular ions in mediating the repulsion between these charged nanoparticles remains elusive. Herein, coarse-grained molecular dynamics simulations are used to elucidate the effects of valency, shape and size of molecular anions on their co-assembly with gold nanoparticles coated with positively charged ligands. The findings suggest that the valency, shape and size of molecular anions significantly influence the repulsion and aggregating dynamics among these positively charged nanoparticles. Moreover, the free energy calculations reveal that ring-shaped molecular anions with higher valencies and larger sizes are more effective at reducing the repulsion between these gold nanoparticles and thus enhance the stability of the aggregate. This study contributes to a better understanding of the critical roles of valence, shape and size of ions in mediating the electrostatic co-assembly of nanoparticles with oppositely charged ions and it also guides the future design of DNA templates and DNA origami in co-assembly with oppositely charged nanoparticles.