Multiwavelength videomicrofluorometric study of cytotoxic properties of a marine peptide, didemnin B, using adriamycin as reference compound

Didemnin B (DB), a marine natural product, has very encouraging biological activity in vitro (Antineoplastic, immunosuppressive, antiviral). To learn more about its intracellular effects and targets, videomicrofluorometry on single living cells ann a protocol of multiple labeling. Hoechst 342 for nu clear DNA, Rhodamine 123 for mitochondria and Nile Red for plasma membrane, have been used DB behaves differently from Adriamycin, inducing at its IC5 0 close of (20 nM) an accumulation of the CEM-WT lymphoblasts in the S phas e of the cell cycle while we observed a 50% decrease of the mitochondrial l abeling by R123, showing a decrease of the mitochondrial energetic state. C ytostatic dose of DB (250 nM) confirms these observations. However the trea tment with a dose reported as apoptotic (1000 nM) induces a much faster eff ect (corresponding to that of 72 hours at the IC50 dose), 24 hours incubati on induced a drastic decrease of nuclear DNA content as well as of the mito chondria energetic state. The evolution of NAD(P)H cellular content exhibit ed an increase that seems to indicate that the decrease of mitochondrial en ergetic state was dependent on inhibition of the mitochondrial activity due to an effect of DB at the mitochondrial level, either direct or mediated F urthermore, the decrease of mitochondrial labeling appears as a very early even in the mechanisms leading to apoptosis.