The endo-lysosomal escape of drug carriers is crucial to enhancing the efficacy of their macromolecular payload, especially the payloads that are susceptible to lysosomal degradation. Current vectors that enable the endo-lysosomal escape of macromolecules such as DNA are limited by their toxicity and by their ability to carry only limited classes of therapeutic agents. In this paper, we report the rapid (<10 min) endo-lysosomal escape of biodegradable nanoparticles (NPs) formulated from the copolymers of poly(DL-lactide-co-glycolide) (PLGA). The mechanism of rapid escape is by selective reversal of the surface charge of NPs (from anionic to cationic) in the acidic endo-lysosomal compartment, which causes the NPs to interact with the endo-lysosomal membrane and escape into the cytosol. PLGA NPs are able to deliver a variety of therapeutic agents, including macromolecules such as DNA and low molecular weight drugs such as dexamethasone, intracellularly at a slow rate, which results in a sustained therapeutic effect. PLGA has a number of advantages over other polymers used in drug and gene delivery including biodegradability, biocompatibility, and approval for human use granted by the U.S. Food and Drug Administration. Hence PLGA is well suited for sustained intracellular delivery of macromolecules.

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Summary From an shRNA screen, we identified ClpP as a member of the mitochondrial proteome whose knockdown reduced the viability of K562 leukemic cells. Expression of this mitochondrial protease that has structural similarity to the cytoplasmic proteosome is increased in the leukemic cells from approximately half of patients with AML. Genetic or chemical inhibition of ClpP killed cells from both human AML cell lines and primary samples in which the cells showed elevated ClpP expression, but did not affect their normal counterparts. Importantly, Clpp knockout mice were viable with normal hematopoiesis. Mechanistically, we found ClpP interacts with mitochondrial respiratory chain proteins and metabolic enzymes, and knockdown of ClpP in leukemic cells inhibited oxidative phosphorylation and mitochondrial metabolism.

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