Purification and identification of an actinomycin D analogue from actinomycetes associated with Ganoderma applanatum via magnetic molecularly imprinted polymers and tandem mass spectrometry

Actinomycetes are main producers of antibiotics and targeted screening could improve the efficiency of discovering new drugs. This study describes, for the first time, the isolation of endophytic actinomycetes from the macrofungus Ganoderma applanatum. To increase the efficiency of screening, novel actinomycin D (Act D) molecularly-imprinted polymers were adsorbed to the surface of Fe3O4@SiO2 magnetic microspheres (MMIPs) and using in the isolation. A monolithic column prepared with magnetic molecularly imprinted polymers was employed to adsorb actinomycin D and its analogues for selective analysis and identification via MS/MS spectroscopy. The MMIP-monolithic column was selective for the structural features of Act D and its analogue, and the maximum loading of the MMIPs for Act D was ∼23.5 μg/g. The recognition time of the Act D was 20-30 min and had good discriminative ability. A new analogue was identified from endophytic actinomycetes KLBMP 2541, and it was purified using MMIPs comparison with MMIPs-solid phase extraction. Structural identification analysis confirmed that the new analogue was 2-methyl-actinomycin D, which has better anti-tumor activity than Act D. The presented method combines the advantages of MMIPs and MS with popular solutions to enable high affinity and selectivity screening of specific antibiotics from endophytic actinomycetes.