Macbecin I (MacI)

Macbecin belongs to the ansamycin family of antibiotics and was first isolated from actinomycete bacteria. Macbecin possesses potent antitumor properties. Macbecin has an unusual macrocyclic lactam structure. There are two variants Macbecin I and II which correspond to the oxidized 1,4-benzoquinone and reduced hydroquinone respectively. Macbecins mechanism of action is in part due to heat shock protein Hsp90 protein inhibition. Macbecin I showed marked antitumor activity against intraperitoneally (ip) inoculated leukemia P388, melanoma B16, and Ehrlich carcinoma in mice on ip administration. The maximum effect measured in terms of ILS% (increase of life span) was 97 at a daily dose level of 10 mg/kg for leukemia P388, 103 at 5 mg/kg for melanoma B16, and 206 at 10 mg/kg for Ehrlich carcinoma.