Leucinostatins from Ophiocordyceps spp. and Purpureocillium spp. Demonstrate Selective Antiproliferative Effects in Cells Representing the Luminal Androgen Receptor Subtype of Triple Negative Breast Cancer

The structures of four leucinostatin analogues (1-4) from Ophiocordyceps spp. and Purpureocillium spp. were determined together with six known leucinostatins [leucinostatins B (5), A (6), B2 (7), A2 (8), F (9), and D (10)]. The structures of the metabolites were established using a combination of analytical methods including HRESIMS and MS/MS experiments, 1D and 2D NMR spectroscopy, chiral HPLC, and advanced Marfey's analysis of the acid hydrolysate, as well as additional empirical and chemical methods. Compounds 1-10 were evaluated for their biological effects on triple negative breast cancer (TNBC) cells. Leucinostatins 1-10 showed selective cytostatic activities in MDA-MB-453 and SUM185PE cells representing the luminal androgen receptor subtype of TNBC. This selective activity motivated further investigation into the mechanism of action of leucinostatin B (5). The results demonstrate that this peptidic fungal metabolite rapidly inhibits mTORC1 signaling in leucinostatin-sensitive TNBC cell lines, but not in leucinostatin-resistant cells. Leucinostatins have been shown to repress mitochondrial respiration through inhibition of the ATP synthase, and we demonstrated that both the mTORC1 signaling and LAR-selective activities of 5 were recapitulated by oligomycin. Thus, inhibition of the ATP synthase with either leucinostatin B or oligomycin is sufficient to selectively impede mTORC1 signaling and inhibit the growth of LAR-subtype cells.