Chemoresistance of cisplatin therapy is related to extensive repair of cisplatin-modified DNA in the nucleus by the nucleotide excision repair (NER). Delivering cisplatin to the mitochondria to attack mitochondrial genome lacking NER machinery can lead to a rationally designed therapy for metastatic, chemoresistant cancers and might overcome the problems associated with conventional cisplatin treatment. An engineered hydrophobic mitochondria-targeted cisplatin prodrug, Platin-M, was constructed using a strainpromoted alkyne–azide cycloaddition chemistry. Efficient delivery of Platin-M using a biocompatible polymeric nanoparticle (NP) based on biodegradable poly(lactic-co-glycolic acid)-block-polyethyleneglycol functionalized with a terminal triphenylphosphonium cation, which has remarkable activity to target mitochondria of cells, resulted in controlled release of cisplatin from Platin-M locally inside the mitochondrial matrix to attack mtDNA and exhibited otherwise-resistant advanced cancer sensitive to cisplatin-based chemotherapy. Identification of an optimized targeted-NP formulation with brain-penetrating properties allowed for delivery of Platin-M inside the mitochondria of neuroblastoma cells resulting in ～17 times more activity than cisplatin. The remarkable activity of Platin-M and its targeted-NP in cisplatin-resistant cells was correlated with the hyperpolarization of mitochondria in these cells and mitochondrial bioenergetics studies in the resistance cells further supported this hypothesis. This unique dual-targeting approach to controlled mitochondrial delivery of cisplatin in the form of a prodrug to attack the mitochondrial genome lacking NER machinery and in vivo distribution of the delivery vehicle in the brain suggested previously undescribed routes for cisplatinbased therapy.
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