Pretargeted Mitochondrial Delivery of Organoarsenicals for Cancer Immunotherapy

Mitochondrial targeting of organoarsenic compounds shows potential for cancer therapy, but current delivery approaches face significant challenges such as poor tumor selectivity and systemic toxicity, leading to dose-limiting side effects and reduced therapeutic efficacy. In this study, we present a subcellular pretargeted delivery strategy designed to selectively and efficiently accumulate organoarsenic therapeutics within tumor cell mitochondria. This approach leverages P-TCO-TPP, an alkaline phosphatase (ALP)-responsive small-molecule probe containing a phosphate-caged near-infrared merocyanine fluorophore, trans-cyclooctene (TCO), and triphenylphosphonium (TPP) groups. This enables the <i>in situ</i> self-assembly of mitochondria-targeting nanoparticles upon ALP-mediated dephosphorylation. These mitochondria-localized nanoparticles then rapidly capture tetrazine-arsenic conjugates (Tz-As) via bioorthogonal inverse electron demand Diels-Alder (IEDDA) reaction, resulting in a >5-fold increase in mitochondrial arsenic accumulation. This, in turn, leads to mitochondrial proteins labeling, thioredoxin reductase inhibition, severe mitochondrial dysfunction, and immunogenic cell death in tumor cells. Notably, this strategy achieves strong antitumor efficacy with minimal toxicity in both subcutaneous cervical HeLa and orthotopic breast 4T1 tumor models. Furthermore, combining this strategy with anti-PD-L1 immunotherapy induces complete 4T1 tumor regression in 40% of mice, extended survival, and nearly prevents pulmonary metastasis. This subcellular pretargeted strategy offers a robust platform for precision mitochondrial drug delivery, enhancing therapeutic potential of various cytotoxic agents in cancer immunotherapy.