Although previous studies showed that coumestrol induced cycle arrest in breast cancer cells at the G1/S phase (Zafar et al., 2017), current study showed that coumestrol induced cycle arrest on G2/M phase of the K562 and Jurkat cells. is highly expressed in cancer cells and maintains the integrity of the mitochondria. Coumestrol, daidzein and genistein previously have been shown to down-regulate Bcl-2 expression in human hepatoma, hepatic and breast cancer cells (Jin et al., 2010, Li et al., 2012, Park et EPZ-5676 (Pinometostat) al., 2013). Down-regulation of Bcl-2 led to loss of mitochondrial integrity and released of cytochrome into the cytosol. This initiated the caspase cascade apoptosis induction (Skommer et al., 2010). Previous studies also showed that treatment of human hepatoma, prostate and hepatic cancer cells with coumestrol, daidzein and genistein up-regulate the caspase-3, ?9 and ?7 which marks the intrinsic apoptosis pathways (Lee EPZ-5676 (Pinometostat) et al., 2013, Li et al., 2010, Park et al., 2013). Like genistein, estradiol also caused significant apoptosis in K562, Jurkat and U937 cells. Previous study stated that estradiol at pharmacological dose inhibited proliferation of murine leukemia cells. Sex steroid such as estrogens and progesterone has been shown to exert cytostatic/cytotoxic EPZ-5676 (Pinometostat) effects on leukemia cells. Mossuz et al. (1998) exhibited that U937 cells proliferation was inhibited by treatment with estradiol and testosterone (Mossuz et al., 1998). Apart from mediating its effect by binding to estrogens receptors, leukemia cell also expressed lower affinity receptors called type-2 estrogens binding sites (type-2 EBS), where estrogens have been shown to exert reversible cell proliferation inhibitions by binding to the type-2 EBS (Mossuz et al., 1998, Blagosklonny and Neckers, 1994). Do et al. (2002) stated that this estrogens apoptotic induction properties were attributed mainly by the Fas/FasL death receptor pathway (Do et al., 2002). Ligation of the Fas receptors induce cleavage of pro-caspase 8 into caspase 8 and brought on apoptosis (Do et al., 2002). This results showed that this Jurkat cell was the only cell line which could be induced necrosis by coumestrol, daidzein and estradiol, this obtaining was in line with study of Azmi et al. (2018) that showed the Jurkat cells was the most sensitive EPZ-5676 (Pinometostat) to natural compounds in Camellia sinensis extract with the necrosis value (18.93??0.96%, p?EPZ-5676 (Pinometostat) was significantly higher than negative control (Azmi et al., 2018). Cell cycle progression is tightly regulated by positive and negative cell cycle regulating factors such as the cyclin and cyclin-dependent kinase (CDKs), also cyclin-dependent kinase inhibitor (CKIs) (Lim et al., 2017, Zheng et al., 2017, Casagrande and Darbon, 2001). Assembling of CDK4 and CDK 6 with cyclin D1 and CDK2 with cyclin E allow the progression of the G1 phase, while CDK2-cyclin A controls the S phase and CDK1 assemble with cyclin A and B regulates G2/M phase progression (Casagrande and Darbon, 2001, Choi and Kim, 2008). In the current study, cycle arrest at G2/M phase was observed in coumestrol treated K562 and Jurkat cells, and estradiol treated K562, Jurkat and U937 cells, and daidzein treated Jurkat cells. The effect of estradiol arresting the cycle at the G2/M is in concurrent with study Rabbit polyclonal to DGCR8 by Mossus et al 1998 that stated estradiol arrest U937 cells at the G2/M phase. Although previous studies showed that coumestrol induced cycle arrest in breast cancer cells at the G1/S phase (Zafar et al., 2017), current study showed that coumestrol induced cycle arrest on G2/M phase of the K562 and Jurkat cells. The mechanism of which coumestrol induces this effect on these cells has yet to be elucidated. However, cycle arrest at G2/M phase is suggested to be caused by down-regulation of CDK 1 and cyclin B expressions which controls the G2/M phase (Pietenpol and Stewart, 2002, Shapiro and Harper, 1999). Estrogens and flavonoids that ligate to type-2 EBS were able inhibit CDK1 which mediated the G2/M progression (Mossuz et al., 1998). p53 also played roles in G2/M arrest by inducing.