Granuloma‐Forming Activity and Antitumor Activity of Newly Isolated Mycoloyl Glycolipid from Rhodococcus terrae 70012 (Rt. GM‐2)

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Abstract
A newly isolated mycoloyl glycolipid (Rt. GM‐2) from Rhodococcus terrae 70012 was identified and the granulomagenic and antitumor activities were studied as compared with trehalose‐6,6′‐dimycolate (cord factor) also from R. terrae (Rt. TDM). The alkaline hydrolysis products of Rt. GM‐2 contained trehalose, methyl‐α‐mycolate and a less‐polar ester than the usual methyl‐α‐mycolate, possibly β‐keto mycolate (1: 1: 1, by mol. ratios). On the other hand, analysis of alditol acetate obtained after the mild permethylation, NaBH4 reduction, and acetylation showed the occurrence of 2,3,4‐tri‐O‐methyl‐6‐O‐acetylglucitol. Therefore, the original glycolipid (Rt. GM‐2) was identified tentatively as 6‐O‐α‐mycoloyl 6′‐O‐β‐ketomy‐coloyl trehalose. Intravenous injection of Rt. GM‐2 in the form of water‐in‐oil‐in‐water emulsion caused prominent granulomas in lungs and spleen of ICR and BALB/c mice. The granulomagenic effects were as strong as those caused by Rt. TDM. The lung and spleen weights reached peaks one week after an injection of Rt. GM‐2 in mice and then gradually decreased. Multiple intravenous injections of Rt. GM‐2 and Rt. TDM showed antitumor activity against subcutaneously implanted Sarcoma‐180, and caused prominent granulomatous changes and growth suppression of mice.