Perfluoropentane Phase-Change Nanodroplets for Focused Ultrasound-Enhanced Drug Penetration and Immune Response

Background/Objectives: Solid tumors are characterized by a dense stromal structure and heterogeneous microenvironments that limit intratumoral drug penetration and contribute to immune exclusion. We developed perfluoropentane (PFP)-based phase-change nanodroplets (IMP700) and aimed to identify focused ultrasound (FUS) parameters that enhance cavitation and sonoporation to improve drug delivery and immune engagement in tumor models. Methods: IMP700 was prepared as lipid-shelled PFP nanodroplets and physicochemically characterized. Acoustic droplet vaporization (ADV), echogenicity, and cavitation were evaluated in vitro and in vivo using ultrasound imaging and cavitation analysis under varying FUS parameters, including acoustic intensity, duty cycle, and pulse repetition frequency (PRF), in PANC-1 xenograft tumors. Sonoporation was assessed by co-administering an ultrasound-responsive doxorubicin liposome (IMP301), and intratumoral drug distribution was analyzed by confocal imaging. Immune responses were evaluated in a syngeneic 4T1 tumor model by quantifying CD8⁺ T-cell infiltration after repeated treatments. Results: IMP700 exhibited nanoscale size and high PFP encapsulation efficiency and underwent ADV with increased echogenicity and intensity-dependent cavitation. In vivo, a 2% duty cycle and 10 Hz PRF produced strong and reproducible cavitation. Under these conditions, IMP700 markedly increased inertial cavitation and enhanced intratumoral drug penetration compared to FUS alone. Combined IMP700 and FUS treatment also increased intratumoral CD8⁺ T-cell infiltration. Conclusions: IMP700 amplifies FUS-induced cavitation, improves sonoporation-mediated drug delivery, and promotes CD8⁺ T-cell infiltration, which supports the use of FUS-activated nanodroplets as a strategy to overcome stromal and immunological barriers in solid tumors.