Bestatin of formula (I) and its acidic salts are new. Bestatin is produced by cultivation of a bestatin-producing Streptomyces in a C- and N-contg. nutrient medium under aerobic conditions. Bestatin has substantially no antibacterial activity, but it shows weak inhibition of cell (including tumour cell) growth in mammals and strong inhibition of aminopeptidase B, leucine aminopeptidase and bleomycin hydrolase. On account of its inhibition of bleomycin hydrolase, bestatin strongly synergizes the antitumour effect of bleomycin. It can therefore be used in combination with bleomycin for the treatment of squamous cell carcinoma, and in the analysis of biological functions and disease processes.
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