21-hydroxy Oligomycin A is an antibiotic which was first isolated from S. cyaneogriseus ssp.noncyanogenus [1]. 21-hydroxy Oligomycin A functions as μM inhibitor of the multidrug efflux pump P-gp, and low nM inhibitors of K-Ras PM localization [1].

Cancer cell viability screening confirmed that 21-hydroxy Oligomycin A was cytotoxic to human colorectal carcinoma cells (IC50 > 3 μM), and was inhibitor of the ABC transporter efflux pump P-glyco-protein (P-gp). Significantly, 21-hydroxy Oligomycin A was exceptionally potent inhibitor of K-Ras PM localisation with Emax of 0.67–0.75 and an IC50 of 1.5–14 nM [1]. 21-hydroxy Oligomycin A was inhibitor of K-Ras PM localisation in MDCK cell with an IC50 of 4.82 ± 0.70 nM. 21-hydroxy Oligomycin A was moderately cytotoxic towards both SW620 and SW620 Ad300 cells with the IC50 of 14.4 ± 0.6 and 11.8 ± 3.1 μM, respectively. In the flow cytometry assay, 21-hydroxy Oligomycin A (20 μM) increased intracellular calcein fluorescence significantly when compared with the negative control [1].

Reference:
[1] Salim A A, Tan L, Huang X C, et al.? Oligomycins as inhibitors of K-Ras plasma membrane localisation[J]. Organic & biomolecular chemistry, 2016, 14(2): 711-715.