Proteolysis Targeting Chimera Loaded Extracellular Vesicles for Developing Triple Negative Breast Cancer Treatment.

Proteolysis targeting chimeras (PROTACs) represent an emerging targeted cancer therapy approach. However, their poor cell penetration and instability in vivo pose daunting challenges for wide-spread clinical usage. To enhance the in vivo therapeutic efficacy of PROTACs, we introduced extracellular vesicles (EVs) for in vivo PROTAC delivery, which is leveraged by a novel microfluidic droplet-based EV electro-transfection system (μDES). We previously developed YX968 PROTAC, which can selectively degrade both HDAC3 and HDAC8 in triple negative breast cancer (TNBC) cells and effectively suppress the tumour cell growth without provoking global hyperacetylation. In this manuscript, we demonstrated that YX968 loaded EVs via the μDES system can retain the optimal integrity of drug loaded EVs with improved loading efficiency compared to other transfection approaches, which, in turn, significantly enhances the therapeutic function of PROTAC in vivo in TNBC mouse models. Intraperitoneal injections of YX968 loaded EVs led to significantly enhanced intratumoral degradation of HDAC3 and HDAC8 than YX986 alone, which resulted in advanced TNBC tumour inhibition without noticeable tissue toxicity. Such EV-based delivery strategy, with a scalable EV loading approach, enhanced the in vivo PROTAC drug stability and bioavailability and improved tissue penetration and targeting, filling an important gap in the clinical translation of PROTAC-based cancer therapy.