Recent studies on antibiotics and small molecular immunomodulators with potential usefulness in treating lung cancer: Part II - Small molecular weight immunomodulators produced by microorganisms.

A screening method to identify microbial products that bind to surfaces of cells involved in immunity has been established. By means of this method, several small molecular weight compounds, bestatin, amastatin, forphenicine, and esterastin, inhibiting enzymes located on the cell surface, aminopeptidase B and leucine aminopeptidase, aminopeptidase A, alkaline phosphatase, and esterase, were discovered. These small molecular weight microbial products showed immunity-modifying activity. Among these, bestatin, which has an extremely low toxicity, was studied in detail. The clinical study indicated that bestatin enhances the cellular immunity in cancer patients. The use of small molecular weight immunomodifiers to annihilate minimal residual tumors in the lung is discussed.