Repurposing the PDMA-approved drugs in Japan using an insect model of staphylococcal infection

A total of 1253 compounds approved as therapeutic drugs in Japan (Pharmaceuticals and Medical Devices Agency (PMDA)-approved compounds) were screened for their therapeutic effects against Staphylococcus aureus infection using the silkworm infection model. In the first stage of screening with an index of prolonged survival, 80 compounds were identified as hits. Of these, 64 compounds were clinically used as antimicrobial agents, and the remaining 16 compounds were not. The 16 compounds were examined for their dose-dependent therapeutic effects on the silkworm model as a second screening step, and we obtained five compounds as a result. One of the compounds (capecitabine) had no documented in vitro minimum inhibitory concentration (MIC) value against S. aureus. The MIC value of capecitabine against S. aureus strains ranged from 125 to 250 µg/ml, and capecitabine was therapeutically effective at a dose of 200 mg/kg in a murine model of S. aureus infection. These results suggest that silkworm-based drug repositioning studies are of potential value. Furthermore, the therapeutic effects of capecitabine demonstrated in this study provide an important scientific rationale for clinical observational studies examining the association between staphylococcal infection events and capecitabine administration in cancer chemotherapy patients.