Targeting tumor stroma via ultrasound-activated nanodroplets: Disrupting exosome-driven microenvironment crosstalk for enhanced antitumor efficacy.

The tumor microenvironment (TME) plays a crucial role in the initiation and progression of tumors. Therefore, targeting the TME has emerged as an important strategy in antitumor therapy. Two critical stromal cell types in the TME-tumor-associated macrophages (TAMs) and cancer-associated fibroblasts (CAFs)-secrete exosomes that promote tumor growth, invasion, metastasis, drug resistance, and immune evasion. Inhibiting the secretion of exosomes by these cells may represent an effective strategy for antitumor therapy targeting the TME. In this study, we constructed Man/HTTIPKV-imipramine-nanodroplets (M/H-I-NDs) with a size of 258.93 nm, which were surface-modified with two specific ligands (Man and HTTIPKV) and loaded with the exosome inhibitor imipramine, using an ultrasonic emulsification and oscillation method. We systematically evaluated the characteristics, properties, biosafety, ultrasound imaging capability, and targeting efficiency of M/H-I-NDs. We validated the ability of M/H-I-NDs combined with ultrasound-targeted microbubble destruction (UTMD) to inhibit exosomes derived from TAMs and CAFs. We investigated the in vitro and in vivo antitumor and antimetastatic effects of M/H-I-NDs combined with UTMD using murine 4 T1 breast cancer cells and tumor models. M/H-I-NDs exhibited excellent targeting ability, drug delivery, and penetration efficiency and favorable biosafety. M/H-I-NDs showed 3.4-fold higher accumulation in mice tumor tissue than in non-targeted NDs. The study showed that the drug release of M/H-I-NDs combined with UTMD is about 50 % higher than that of non-stimulated M/H-I-NDs within 64 h. The M/H-I-NDs and UTMD combination significantly inhibited the generation of exosomes by 87.5 % derived from TAMs and 54 % derived from CAFs. The activity of tumor cells in vitro decreased by about 80 %, and the tumor volume in mice in vivo decreased by about 85 % (Day 14), demonstrating strong antitumor effects in vitro and in vivo. The combined application of M/H-I-NDs and UTMD, as a stroma-targeted therapeutic strategy integrating dual-ligand precision and ultrasound-enhanced drug delivery to simultaneously disrupt TAMs and CAFs exosome signaling, may represent a potential clinical antitumor treatment.