Selective extracellular arginine deprivation by a single injection of cellular non-uptake arginine deiminase nanocapsules for sustained tumor inhibition

The metabolic enzyme-based arginine deprivation represents a tremendous opportunity to treat argininosuccinate synthetase (ASS1)-deficient tumors. Arginine deiminase (ADI), a typical representative, has aroused great interest. To date, the functional modification of ADI, such as PEGylation, has been applied to improve its weakness significantly, reducing its immunogenicity and extending its blood circulation time. However, the advantages of ADI, such as the cellular non-uptake property, are often deprived by current modification methods. The cellular non-uptake property of ADI only renders extracellular arginine degradation that negligibly influences normal cells. However, current-functionalized ADIs can be readily phagocytized by cells, causing the imbalance of intracellular amino acids and the consequent damage to normal cells. Therefore, it is necessary to exploit a new method that can simultaneously improve the weakness of ADI and maintain its advantage of cellular non-uptake. Here, we utilized a kind of phosphorylcholine (PC)-rich nanocapsule to load ADI. These nanocapsules possessed extremely weak cellular interaction and could avoid uptake by endothelial cells (HUVEC), immune cells (RAW 264.7), and tumor cells (H22), selectively depriving extracellular arginine. Besides, these nanocapsules increased the blood half-life time of ADI from the initial 2 h to 90 h and efficiently avoided its immune or inflammatory responses. After a single injection of ADI nanocapsules into H22 tumor-bearing mice, tumors were stably suppressed for 25 d without any detectable side effects. This new strategy first realizes the selective extracellular arginine deprivation for the treatment of ASS1-deficient tumors, potentially promoting the clinical translation of metabolic enzyme-based amino acid deprivation therapy. Furthermore, the research reminds us that the functionalization of drugs can not only improve its weakness but also maintain its advantages.