Probing inhibitory effects of destruxins from Metarhizium anisopliae using insect cell based impedance spectroscopy: inhibition vs chemical structure

A noninvasive technique based on electric cell-substrate impedance sensing (ECIS) was demonstrated for on-line probing inhibitory effects of five destruxins on Spodoptera frugiperda Sf9 insect cells. Such chemically structurally similar cyclic hexadepsipeptides, were isolated and purified from the fungus Metarhizium anisopliae. Based on a response function, the inhibitory effect of the destruxins was established from determining the half-inhibition concentration (ECIS50), i.e., the level at which 50% inhibition of the cell response was obtained. Probing by cell based impedance spectroscopy indicated that only a slight change in their chemical structures provoked a significant effect on inhibition. Destruxin B was most inhibitory but replacement of a single methyl group with hydrogen (destruxin B2) or addition of a hydroxyl group (destruxin C) significantly reduced the inhibition. The removal of one methyl group and one hydrogen (destruxin A) lowered the inhibitory effect even more whereas the formation of an epoxy ring (destruxin E) in the structure nullified the inhibitory effect.