Engineered Nanobody-Bearing Extracellular Vesicles Enable Precision Trop2 Knockdown in Resistant Breast Cancer

<b>Background/Objectives</b>: Trophoblast cell surface antigen 2 (Trop2), a transmembrane glycoprotein overexpressed in a broad spectrum of epithelial malignancies but minimally expressed in normal tissues, has emerged as a clinically relevant prognostic biomarker and therapeutic target, particularly in breast cancer. This study aims to develop an enhanced way of targeting Trop2 expression in tumors and blocking it using extracellular vesicles (EVs) bioengineered to express a nanobody sequence against Trop2 (NB60 E). <b>Methods</b>: Here, a plasmid construct was designed to express the Trop2 sequence, NB60, flanked with HA tag and myc epitope and a PDGFR transmembrane domain in the C-terminal region, and was transfected into HEK293T cells for EVs isolation. The potency of NB60 E to knock down Trop2 in letrozole-resistant breast cancer cells (LTLT-Ca and MDA-MB-468 cells) was initially investigated. Thereafter, the effects of NB60 E on the cell viability and downstream signaling pathway of Trop2 via MTT assay and Western blotting were determined. Lastly, we also examined whether NB60 E treatment in Jurkat T cells affects IL-6, TNF-α, and IL-2 cytokine production by enzyme-linked immunosorbent assay (ELISA). <b>Results</b>: Results revealed treatment with NB60 E significantly reduced surface Trop2 expression across both cell lines by 23.5 ± 1.5% in MDA-MB-468, and 61.5 ± 1.5% in LTLT-Ca, relative to the HEK293T-derived control EVs (HEK293T E). NB60 E treatment resulted in a marked reduction in LTLT-Ca cell viability by 52.8 ± 0.9% at 48 h post-treatment. This was accompanied by downregulation of key oncogenic signaling molecules: phosphorylated ERK1/2 (p-ERK 1/2) decreased by 30 ± 4%, cyclin D1 by 67 ± 11%, phosphorylated STAT3 (p-STAT3) by 71.8 ± 1.6%, and vimentin by 40.8 ± 1.4%. ELISA analysis revealed significant decreases in IL-6 (-57.5 ± 1.5%, 7.4 ± 0.35 pg/mL) and TNF-α (-32.1 ± 0.3%, 6.1 ± 1.2 pg/mL) levels, coordinated by an increase in IL-2 secretion (22.1 ± 2.7%, 49.2 ± 1.1 pg/mL). Quantitative analysis showed marked reductions in the number of nodes (-45 ± 4.4%), junctions (-55 ± 3.5%), and branch points (-38 ± 1.2%), indicating suppression of angiogenic capacity. In vivo experiment using near-infrared Cy7 imaging demonstrated rapid and tumor-selective accumulation of NB60 E within 4 h post-administration, followed by efficient systemic clearance by 24 h. The in vivo results demonstrate the effectiveness of NB60 E in targeting Trop2-enriched tumors while being efficiently cleared from the system, thus minimizing off-target interactions with normal cells. Lastly, Trop2 expression in LTLT-Ca tumor xenografts revealed a significant reduction of 41.0 ± 4% following NB60 E treatment, confirming efficient targeted delivery. <b>Conclusions</b>: We present a first-in-field NB60 E-grafted EV therapy that precisely homes to Trop2-enriched breast cancers, silences multiple growth-and-invasion pathways, blocks angiogenesis, and rewires cytokine crosstalk, achieving potent antitumor effects with self-clearing, biomimetic carriers. Our results here show promising potential for the use of NB60 E as anti-cancer agents, not only for letrozole-resistant breast cancer but also for other Trop2-expressing cancers.