The anticancer potential of flavonoids isolated from the stem bark of Erythrina suberosa through induction of apoptosis and inhibition of STAT signaling pathway in human leukemia HL-60 cells

Abstract

Erythrina suberosa is an ornamental tall tree found in India, Pakistan, Nepal, Bhutan, Burma, Thailand and Vietnam. We have isolated four known distinct metabolites designated as α-Hydroxyerysotrine, 4'-Methoxy licoflavanone (MLF), Alpinumisoflavone (AIF) and Wighteone. Among the four isolated metabolites the two flavonoids, MLF and AIF were found to be the most potent cytotoxic agent with IC50 of ∼20μM in human leukemia HL-60 cells. We are reporting first time the anticancer and apoptotic potential of MLF and AIF in HL-60 cells. Both MLF and AIF inhibited HL-60 cell proliferation and induce apoptosis as measured by several biological endpoints. MLF and AIF induce apoptosis bodies formation, enhanced annexinV-FITC binding of the cells, increased sub-G0 cell fraction, loss of mitochondrial membrane potential (Δψm), release of cytochrome c, Bax, activation of caspase-9, caspase-3 and PARP (poly ADP Ribose polymers) cleavage in HL-60 cells. MLF and AIF also increase the expression of apical death receptor, Fas, with inhibition of anti-apoptotic protein Bid. All the above parameters revealed that these two flavonoids induce apoptosis through both extrinsic and intrinsic apoptotic pathways in HL-60 cells. In spite of apoptosis, these two flavonoids significantly inhibit nuclear transcription factor NF-κB and STAT (Signal Transducer and Activator of Transcription) signaling pathway, which are highly expressed in leukemia. The present study provide an insight of molecular mechanism of cell death induced by MLF and AIF in HL-60 cells which may be useful in managing and treating leukemia.

Keywords: 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide; 4′-Methoxy licoflavanone; AIF; Alpinumisoflavone; Apoptosis; Erythrina suberosa; Flavonoids; IKK; IκB kinase; MLF; MTT; NF-κB; PI; PS; PTP; Rh-123; Rhodamine-123; STAT; Ser; Signal Transducer and Activator of Transcription; Tyr; mitochondrial membrane potential; mitochondrial permeability transition pore; nuclear transcription factor–κB; phosphatidyl serine; propidium iodide; serine; tyrosine; Δψ(m).