Programmed Cell Death Induced by (−)-8,9-Dehydroneopeltolide in Human Promyelocytic Leukemia HL-60 Cells under Energy Stress Conditions

Abstract

(+)-Neopeltolide is a marine macrolide natural product that exhibits potent antiproliferative activity against several human cancer cell lines. Previous study has established that this natural product primarily targets the complex III of the mitochondrial electron transport chain. However, the biochemical mode-of-actions of neopeltolide have not been investigated in detail. Here we report that (−)-8,9-dehydroneopeltolide (8,9-DNP), a more accessible synthetic analogue, shows potent cytotoxicity against human promyelocytic leukemia HL-60 cells preferentially under energy stress conditions. Nuclear morphology analysis, as well as DNA ladder assay, indicated that 8,9-DNP induced significant nuclear condensation/fragmentation and DNA fragmentation, and these events could be suppressed by preincubating the cells with a pan-caspase inhibitor, N-benzyloxycarbonyl-Val-Ala-Asp(OMe)-fluoromethylketone (zVAD). Immunoblot analysis demonstrated the release of cytochrome c from the mitochondria and the cleavage of full-length caspase-3 and poly(ADP-ribose) polymerase (PARP). These results indicated that 8,9-DNP induced caspase-dependent apoptotic programmed cell death under energy stress conditions. It was also found that 8,9-DNP induced non-apoptotic cell death in the presence/absence of zVAD under energy stress conditions. Immunoblot analysis showed the intracytosolic release of apoptosis-inducing factor (AIF), although it did not further translocate to the nucleus. It appears most likely that, in the presence of zVAD, 8,9-DNP triggered necrotic cell death as a result of severe intracellular ATP depletion.

A Synthetic Analogue of Neopeltolide, 8,9-Dehydroneopeltolide, Is a Potent Anti-Austerity Agent against Starved Tumor Cells

“…Meanwhile, it is also known that execution of apoptosis or autophagy requires a certain level of intracellular ATP concentration [ 42 ]. It is speculated that the apoptosis-inducing ability of 8,9-DNP in human promyelocytic leukemia HL-60 cells under glucose-deprived conditions, described in our previous work [ 22 ], would be ascribable to the availability of nutrients other than glucose, which provide cells with sufficient amounts of ATP to activate the apoptosis machinery. Anti-austerity agents that target mETC likely cause immediate shortage of cellular energy and, eventually, necrotic cell death in tumor cells under extreme starvation conditions.…”

“…Subsequently, Kozmin and co-workers determined that neopeltolide is a potent and specific inhibitor of complex III of the mitochondrial electron transport chain (mETC), on the basis of their finding that the growth inhibitory activity of neopeltolide in yeast cells was substantially enhanced by replacing glucose with galactose or glycerol [ 16 ]. Our group has been working on the synthesis and structure–activity relationship studies on neopeltolide and its analogues [ 17 , 18 , 19 , 20 , 21 ] and has previously reported that 8,9-dehydroneopeltolide ( 2 : 8,9-DNP), a synthetic equipotent analogue of neopeltolide, induced apoptosis in human promyelocytic leukemia HL-60 cells in glucose-deprived medium [ 22 ]. However, the biological mode-of-action(s) by which neopeltolide exerts its anti-proliferative activity in human cancer cells remains largely unclear.…”

Muscarine, imidazole, oxazole and thiazole alkaloids

“…Since it shows potent in vitro anti-proliferative activities against the growth of several cancer cell lines including A549 human lung adenocarcinoma, NCI/ADR-RES ovarian sarcoma, and P388 murine leukemia at nanomolar levels, a variety of strategies have been developed for the synthesis of neopeltolide and its analogues aiming to explore the structure-activity relationship and identify its molecular targets. [134][135][136][137][138][139] A synthetic analogue of (+)-neopeltolide, (+)-8,9dehydroneopeltolide 211, was shown to induce caspasedependent apoptotic programmed cell death under energy stress conditions. 138 Phorboxazoles A 212 and B 213, isolated from the Indian sponge of the genus Phorbas sp., possess an unprecedented molecular architecture consisting of a 21-membered macrolactone ring core and a terminus brominated side-chain moiety.…”

Marine Compounds and Cancer: Where Do We Stand?

“…Fuwa and colleagues from Japan report the induction of both apoptotic and non-apoptotic cell death by (−)-8,9-dehydroneopeltolide —a synthetic analog of the marine macrolide (+)-neopeltolide—under cellular stress conditions. The induction of non-apoptotic cell death was explained by an intracellular ATP depletion induced by the compound [ 32 ]. Akl and colleagues from USA, Jordan and Kuwait describe the ability of araguspongine C (a macrocyclic oxaquinolizidine alkaloid isolated from the marine sponge Xestospongia sp.)…”