Objective Flavans are a set of naturally occurring flavonoids possessing a 2-phenylchroman nucleus,which are widely distributed in the plant kingdom.A number of flavan compounds exhibit antitumor activities.In our previous report,a straightforward synthetic procedure for 2(±)-7,8,3’,4’,5’-pentamethoxyflavan(PMF)was developed.To be more important,PMF showed growth inhibitory effect on various human tumor cell lines,especially against HL60 cells.In the present study,we aim to investigate the molecular mechanisms of action of PMF in HL60 cells.This is the first report of the molecular mechanisms on anti-tumor effect of flavan compounds.Methods Trypan blue exclusion experiment was used for cell growth inhibition assay.Cell apoptosis,cell cycle distribution and the mitochondrial membrane potential(MMP)were assessed by flowcytometric analysis after AO/EB,PI and Rh123 flurescence staining,respectively.Cell cycle-and apoptosis-related proteins were detected using western blotting analysis.Results PMF(1-30 μM)inhibited the growth of HL60 cells in a time-and concentration-dependent manner.Antiproliferative effect of PMF on HL60 cells was associated with G2/M cell cycle arrest,which was mediated by regulating the expression of p21,Cdc25C and cyclin A proteins and inhibiting the phosphorylation of Cdc2 at Thr161.The prolonged PMF treatment also induced apoptosis of HL60 cells,which was characterized by DNA fragmentation,cleavage of poly(ADP-ribose)polymerase,caspase-3,caspase-8 and caspase-9,changes of Bcl-2 and Bax expression and a decrease in the mitochondrial membrane potential(MMP).Furthermore,caspase-3 inhibitor,not caspase-8 inhibitor and caspase-9 inhibitor,completely blocked PMF-caused apoptosis.Conclusions PMF inhibited the growth of HL60 cells via induction of G2/M arrest and apoptosis.Blockade of cell cycle was associated with the downregulation of Cdc2 complex activity.Both death receptor and mitochondrial apoptotic pathways explained PMF-caused apoptosis. Objective Flavans are a set of naturally occurring flavonoids possessing a 2-phenylchroman nucleus, which are widely distributed in the plant kingdom. A number of flavan compounds exhibit antitumor activities. In our previous report, a straightforward synthetic procedure for 2 (±) -7 , 8,3 ’, 4’, 5’-pentamethoxyflavan (PMF) was developed. To be more important, PMF showed growth inhibitory effect on various human tumor cell lines, especially against HL60 cells. In the present study, we aim to investigate the molecular mechanisms of action of PMF in HL60 cells. This is the first report of the molecular mechanisms on anti-tumor effect of flavan compounds. Methods Trypan blue exclusion experiment was used for cell growth inhibition assay. Cell apoptosis, cell cycle distribution and the mitochondrial membrane potential (MMP) were assessed by flowcytometric analysis after AO / EB, PI and Rh123 flurescence staining, respectively. Cell cycle-and apoptosis-related proteins were detected using western blotting analysis. Res Inhibition of growth of HL60 cells in a time-and-concentration dependent manner. Antiproliferative effect of PMF on HL60 cells was associated with G2 / M cell cycle arrest, which was mediated by regulating the expression of p21 , Cdc25C and cyclin A proteins and inhibiting the phosphorylation of Cdc2 at Thr161. The prolonged PMF treatment also induced apoptosis of HL60 cells, which was characterized by DNA fragmentation, cleavage of poly (ADP-ribose) polymerase, caspase-3, caspase- 8 and caspase-9, changes of Bcl-2 and Bax expression and a decrease in the mitochondrial membrane potential (MMP) .Furthermore, caspase-3 inhibitor, not caspase-8 inhibitor and caspase-9 inhibitor, completely blocked PMF-caused apoptosis. Conclusions PMF inhibited the growth of HL60 cells via induction of G2 / M arrest and apoptosis. Blockade of cell cycle was associated with the downregulation of Cdc2 complex activity. Both death receptor and mitochondrial apoptotic pathways explained PMF-caused apoptosis.