Abstract LB002: Extracellular vesicle loading of proteolysis targeting chimeras for targeted therapeutic delivery
Authors: Erwin Nina , Pan Xiaoshu , Awasthee Nikee , Xiao Yufeng , Zheng Guangrong , Liao Daiqing , He Mei 
Published: April 2023

Abstract
Breast cancer is a significant public health issue that remains the second leading cause of cancer death among women. Current treatment strategies for breast cancer can contribute to severe side effects and insufficient efficacy. For example, chemotherapy, radiotherapy, and hormone receptor and HER2 targeted therapies can lead to healthy cell damage, a partial, delayed effect, and cardiac toxicity and acquired immune resistance, respectively. An emerging alternative targeted therapy approach is proteolysis targeting chimeras (PROTAC), which triggers proteasomal degradation of target proteins implicated in cancer. PROTAC provides precision targeting of low-affinity targets for robust, selective efficacy. However, wide-spread clinical use is limited due to instability and poor cell penetration in vivo. In order to enhance the efficacy of PROTAC, we introduce a novel extracellular vesicle (EV) transfection platform for highly efficient loading of PROTAC. This approach can enhance cellular delivery by utilizing EV’s in vivo properties, like high biocompatibility, long circulation times, and specific targeting. Microfluidic droplet-based electroporation (μDES) was developed and optimized for high- efficient EV transfection, which offers continuous flow transfection suited for scaling up and GMP manufacturing. We compared the drug loading efficiency to conventional transfection methods, including simple incubation, chemical transfection through lipofection, and conventional physical transfection through the Neon electrotransfection system (ThermoFisher). The resulting EVs were characterized by nanoparticle tracking analysis for size, concentration, and zeta potential, and by TEM for morphological determinations. PROTAC transfection efficiency was also measured through absorbance spectrometry. The resulting μDES PROTAC-loaded EVs showed little, or no, changes compared to the native EVs and Neon control group, while offering higher recovery and transfection rates. We also tested the in vitro therapeutic functionality of PROTAC loaded EVs for histone deacetylase 3 and 8 degradation in the breast cancer cell line MDA-MB-231 with western blot analysis. We demonstrated high degradation ability of µDES loaded EVs and, thus, significantly higher therapeutic function. We also plan to investigate biodistribution behavior of the therapeutic EVs in vivo. PROTAC delivery by EVs could enhance stability, biocompatibility, transportability, and targeting ability of the drug. This serves as a novel PROTAC drug delivery, formulation, and administrative strategy that fills an important gap in current PROTAC use.
Citation Format: Nina Erwin, Xiaoshu Pan, Nikee Awasthee, Yufeng Xiao, Guangrong Zheng, Daiqing Liao, Mei He. Extracellular vesicle loading of proteolysis targeting chimeras for targeted therapeutic delivery [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB002.