PC-766B is a macrolide antibiotic produced by N. brasiliensis that is active against Gram-positive bacteria and some fungi, yet inactive against Gram-negative bacteria. It also demonstrates antitumor activity against mouse P388 leukemia and B16 melanoma cells in vitro (IC50s = 0.1 and 0.4 ng/ml, respectively) and in vivo, but weakly inhibits the Na+,K+-ATPase compared to structurally related antibiotics.
