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Gastric cancer is one of the most common malignant solid tumors in the world, especially in Asia with high mortality due to a lack of effective treatment. The potential usage of the newly constructed arginine-depleting enzyme—mono-PEGylated Bacillus caldovelox arginase mutant (BCA-M-PEG20), an effective drug against multiple cancer cell lines such as cervical and lung cancers, for the treatment of gastric cancer was demonstrated. Our results indicated that BCA-M-PEG20 significantly inhibited argininosuccinate synthetase (ASS)-positive gastric cancer cells, MKN-45 and BGC-823, while another arginine-depleting enzyme, arginine deiminase (ADI, currently under Phase III clinical trial), failed to suppress the growth of gastric cancer cells. In vitro studies demonstrated that BCA-M-PEG20 inhibited MKN-45 cells by inducing autophagy and cell cycle arrest at the S phase under 0.58 U/mL (IC50 values). Significant caspase-dependent apoptosis was induced in MKN-45 after the treatment with 2.32 U/mL of BCA-M-PEG20. In vivo studies showed that administrations of BCA-M-PEG20 at 250 U/mouse twice per week significantly suppressed about 50% of tumor growth in the MKN-45 gastric cancer xenograft model. Taken together, BCA-M-PEG20 demonstrated a superior potential to be an anti-gastric cancer drug.

The reaction of a series of electron‐deficient isoindolium‐based allenes with sulfhydryl compounds has been studied, leading to the formation of isoindolium‐based vinyl sulfides. The vinyl sulfides generated could be readily converted into the corresponding indanones and amines upon heating at 30–70 °C with good yields up to 61 %. The thermal cleavage reaction of vinyl sulfides was further studied for developing temperature‐sensitive systems. Notably, a novel FRET‐based fluorescent temperature sensor was designed and synthesized for temperature sensing at 50 °C, giving a 6.5‐fold blue fluorescence enhancement. Moreover, chemoselective bioconjugation of cysteine‐containing peptides with the isoindolium‐based allenes for the construction of multifunctional peptide bioconjugates was investigated. Thermal cleavage of isoindoliums on the modified peptides at 35–70 °C gave indanone bioconjugates with up to >99 % conversion. These results indicated the biocompatibility of this novel temperature‐sensitive reaction.