Enhancement of host resistance to opportunistic infections by ubenimex (bestatin).

Ubenimex is a low molecular biological response modifier (BRM) which has been demonstrated to have antitumor and immunomodulatory activities. In this study, the effect of ubenimex on infection with Candida albicans was investigated in normal and immunosuppressed mice, and it showed a prophylactic effect. In normal mice, ubenimex prolonged survival time in a dose-dependent manner. In immunosuppressed mice treated with cyclophosphamide 4 days before infection, ubenimex at 5 mg/kg for 5 days significantly increased the number of survivors. Significant improvement in peritoneal leukocyte counts and in function of neutrophils including phagocytosis and release of activated oxygen was observed in ubenimex-treated mice. These results indicate that ubenimex is a potent BRM for prevention against opportunistic infections.