Immunomodulatory and therapeutic properties of FK-565 in mice.

The heptanoyl tripeptide, FK-565 is a biological response modifier with potent therapeutic properties for the treatment of experimental and spontaneous metastases. Doses of FK-565 greater than 5 mg/kg are required for in vivo augmentation of natural killer cells, macrophages, and for therapeutic activity, presumably because FK-565 is a peptide small molecular mass which is rapidly degraded and excreted. Optimal therapeutic activity is observed at approximately 25-50 mg/kg FK-565, administered i.v. three times per week for 4 weeks. In addition to its therapeutic properties, which were consistently greater than the positive control at optimal doses, FK-565 had significant immunoaugmentary properties for natural killer cells, macrophages, and T cells both in vitro and in vivo, suggesting that its therapeutic activity is due to immune augmentation.