AIM: JS-38(mitothiolore), a synthetic version of a metabolite isolated from Xenorhabdus sp., was evaluated for its anti-tumor and white blood cell(WBC) elevating activities. METHOD: These anti-proliferative activities were assessed in vitro using a panel of ten cell lines. The anti-tumor activities were tested in vivo using B16 allograft mouse models and xenograft models of A549 human lung carcinoma and QGY human hepatoma in nude mice. The anti-tumor interactions of JS-38 and cyclophosphamide(CTX) or 5-fluorouracil(5-Fu) were studied in a S180 sarcoma model in ICR mice. Specific stimulatory effects were determined on peripheral neutrophils in normal and CTX- and 5-Fu-induced neutropenic mice. RESULTS: The IC50 values ranged from 0.1 to 2.0 μmol·L-1. JS-38(1 μmol·L-1) caused an increase in A549 tumor cell apoptosis. Multi-daily gavage of JS-38(15, 30, and 60 mg?kg-1?d-1) inhibited in vivo tumor progression without a significant effect on body weight. JS-38 additively enhanced the in vivo anti-tumor effects of CTX or 5-Fu. JS-38 increased peripheral neutrophil counts and neutrophil rates in normal BALB/c mice almost as effectively as granulocyte colony-stimulating factor(G-CSF). In mice with neutropenia induced by CTX or 5-Fu, JS-38 rapidly restored neutrophil counts. CONCLUSION: These results suggest that JS-38 has anti-tumor activity, and also has the ability to increase peripheral blood neutrophils. AIM: JS-38 (mitothiolore), a synthetic version of a metabolite isolated from Xenorhabdus sp., Was evaluated for its anti-tumor and white blood cell (WBC) elevating activities. METHODS: These anti-proliferative activities were assessed in vitro using a panel of ten cell lines. The anti-tumor activities were tested in vivo using B16 allograft mouse models and xenograft models of A549 human lung carcinoma and QGY human hepatoma in nude mice. The anti-tumor interactions of JS-38 and cyclophosphamide (CTX ) or 5-fluorouracil (5-Fu) were studied in a S180 sarcoma model in ICR mice. Specific stimulatory effects were determined on peripheral neutrophils in normal and CTX- and 5-Fu-induced neutropenic mice. RESULTS: The IC50 values ​​ranged from 0.1 to 2.0 μmol·L-1. JS-38 (1 μmol·L-1) caused an increase in A549 tumor cell apoptosis. Multi-daily gavage of JS- d-1) inhibited in vivo tumor progression without a significant effect on body weight. JS-38 additively enhanced the in vivo anti-tumor effects of CTX or 5-Fu. JS-38 increased peripheral neutrophil counts and neutrophil rates in normal BALB / c mice almost as effectively as granulocyte colony-stimulating factor (G-CSF) CONCLUSION: These results suggest that JS-38 has anti-tumor activity, and also the ability to increase peripheral blood neutrophils.