The poor penetration of nanoparticles in solid tumors has been a critical factor limiting the clinical benefits of nanomedicine. Therefore, we depleted the dense extracellular matrix (ECM) and normalized tumor vessels to enhance drug delivery and therapeutic efficacy. We used candesartan as an angiotensin system inhibitor, which reduced ECM content and facilitated "vascular normalization" by targeting the angiotensin-signaling axis, resulting in improved anti-cancer therapeutic effects. We also combined candesartan with PEGylated liposome-encapsulated zoledronic acid (ZOL) (PEG-ZOL-LPs) to assess how this affected anti-tumor therapy. Our findings indicated that the migration of 4T1 mouse breast cancer cells was inhibited by candesartan. Moreover, the ECM depletion (including collagen I and hyaluronan) by candesartan was achieved through the downregulation of TGF-β1 in vitro, consistent with in vivo results. Furthermore, treatment groups that received candesartan also had significantly decreased tumor vessel permeability and proportions of circulating endothelial progenitor cells (CEPCs) in the serum, which resulted in normalization of tumor vasculature and improved delivery of PEG-ZOL-LPs. Finally, the positive effect candesartan in terms of tumor growth was found not to have an impact of the efficacy of the PEG-ZOL-LPs treatment. This unexpected lack of effect of candesartan on the performance of PEG-ZOL-LPs would be due to dynamics of the effect of both treatments. It might be possible that a different protocol of administration could lead to a synergistic effect. Graphical abstract The schematic illustration showed that candesartan favored depletion of tumor stroma and tumor vascular normalization to improve the anti-cancer efficacy of PEG-ZOL-LPs.
Keywords: Anti-tumor effect; Extracellular matrix; Liposome; Vascular normalization.