Pharmacokinetics of bestatin and oral activity for treatment of experimental metastases

Bestatin is a low molecular weight aminopeptidase inhibitor originally isolated from culture filtrates of Streptomyces olivoreticuli. The serum pharmacokinetics in mice are dependent on route of administration, with a short t1/2 (1.69 min t1/2 alpha and 12.8 min t1/2 beta), but a high initial serum level following i.v. administration. When administered via the i.p., s.c., i.m., or p.o. routes of administration, bestatin had serum t1/2 beta s of 8.56, 16.91, 19.25, or 15.4 min, respectively. The maximum area under the curve (concentration X time) occurred following i.v. and i.m. administration, with a lower level following p.o. or i.p. administration. Bestatin had therapeutic activity for experimental metastases, not only following i.v., i.p., and i.m. routes of administration but also following oral administration. Because of its brief serum t1/2, bestatin's therapeutic activity depends on aggressive (either daily or twice daily injection, especially following p.o. administration) and high-dose administration. Thus, the rate-limiting aspect of bestatin's therapeutic activity appears to be associated with its pharmacokinetics.