Xinglu Zhou

Abrogation of Akt signaling by Isobavachalcone contributes to its anti-proliferative effects towards human cancer cells

Akt signaling pathway has attracted much attention as a promising target for cancer therapeutics. Herein, we report that Isobavachalcone (IBC), a natural chalcone, potently abrogates Akt signaling and exerts anti-proliferative effects on several human cancer cell lines. Modeling results from the Sybyl/FlexiDock program suggest that IBC potentially binds to the ATP-binding pocket of Akt, which is confirmed by the observations that IBC inhibits Akt1 kinase in vitro. Further studies reveal that IBC significantly abates Akt phosphorylation at Ser-473 and Akt kinase activity in cells, which subsequently leads to inhibition of Akt downstream substrates and evokes significant levels of apoptosis associated with mitochondria pathway.

Bortezomib Sensitizes Human Acute Myeloid Leukemia Cells to All-Trans-Retinoic Acid-induced Differentiation by modifying the RARα/STAT1 axis

All-trans-retinoic acid (ATRA) has held great promise for differentiation-based therapy but reportedly downregulates retinoic acid receptor-α (RARα) in a proteasome-dependent manner, which leads to decreased acute myeloid leukemia (AML) cell differentiation efficiency. Therefore, research strategies that seek to further sensitize cells to retinoids and extend the range of retinoid-affected myeloid malignancies beyond acute promyelocytic leukemia (APL) are key investigative avenues. Here, we show that bortezomib, the first proteasome inhibitor approved for newly diagnosed and relapsed multiple myeloma, exhibited strong synergism with ATRA to promote HL60 and NB4 AML cell differentiation. We observed that bortezomib sensitized AML cells to ATRA-induced morphologic, biochemical, and functional changes, indicative of myeloid differentiation without cell death. In addition, treatment of human leukemia HL60 xenografts with bortezomib and ATRA together did not increase bortezomib-induced progressive weight loss but resulted in significant tumor growth inhibition in addition to increased differentiation (P < 0.05). These enhanced differentiation effects were accompanied by RARα stabilization and STAT1 activation. Taken together, our study was the first to evaluate bortezomib and ATRA synergy in AML cell differentiation and to assess new opportunities for bortezomib and ATRA combination as a promising approach for future differentiation therapy. Mol Cancer Ther; 12(2); 195–206. ©2012 AACR.

MEK/ERK dependent activation of STAT1 mediates dasatinib-induced differentiation of acute myeloid leukemia.

Dasatinib (BMS-354825) is a FDA-approved multitargeted kinase inhibitor of BCR/ABL and Src kinases. It is now used in the treatment of chronic myelogenous leukemia (CML) with resistance or intolerance to prior therapies, including imatinib. Here we report a novel effect of dasatinib on inducing the differentiation of acute myeloid leukemia (AML) cells through MEK/ERK-dependent activation of signal transducer and activator of transcription 1 (STAT1). We found that dasatinib could induce the differentiation of AML cells as demonstrated by the expression of differentiation marker CD11b, G0/G1 phase arrest and decreased ratio of nucleus to cytoplasm. Of note, dasatinib induced robust phosphorylation of STAT1 both at Tyr701 and Ser727 as well as the redistribution of STAT1 from the cytoplasm to the nucleus, thus leading to the transcription of STAT1-targeted genes. Knocking down STAT1 expression by shRNA significantly attenuated dasatinib-induced differentiation, indicating an important role of STAT1 in myeloid maturation. We further found that dasatinib-induced activation of STAT1 was regulated by the MEK/ERK kinases. The phosporylation of MEK and ERK occurred rapidly upon dasatinib treatment and increased progressively as differentiation was induced. MEK inhibitors PD98059 and U0216 not only inhibited the phosphorylation of STAT1, but also abrogated dasatinib-induced myeloid differentiation, suggesting that MEK/ERK dependent phosphorylation of STAT1 might be indispensable for the differentiating effect of dasatinib in AML cells. Taken together, our study suggests that STAT1 is an important mediator in dasatinib-induced differentiation of AML cells, whose activation requires the activation of MEK/ERK cascades.

Inhibition of all‐Trans‐retinoic acid‐induced proteasome activation potentiates the differentiating effect of retinoid in acute myeloid leukemia cells

All‐trans retinoic acid (ATRA) is nowadays considered to be the sole efficient agent for differentiation‐based therapy in leukemia; however, the mechanisms of ATRAs biological effects remain largely unknown. Here we first reported that ATRA‐induced myeloid leukemia differentiation was accompanied with the increased level of ubiquitin–protein conjugates and the upregulation of proteasome activity. To explore the functional role of the activated proteasome in retinoic acid (RA) signaling, the effects of proteasome inhibitors on RA‐induced cell differentiation were determined. Our results demonstrated that inhibition of ATRA‐elevated proteasome activity obviously promoted the myeloid maturation program triggered by ATRA, suggesting that the overactivated proteasome is not beneficial for ATRAs effects. Further studies demonstrated that the synergistic differentiating effects of ATRA and proteasome inhibitors might be associated with the protection of retinoic acid receptor alpha (RARα) from degradation by the ubiquitin–proteasome pathway (UPP). Moreover, the accumulated RARα was able to enhance the transcription of its target gene, which might also contribute to the enhanced differentiation of leukemia cells. Together, by linking the UPP to ATRA‐dependent signaling, our data provide a novel insight into studying the mechanisms of ATRA‐elicited cellular effects and imply the possibility of combination of ATRA and proteasome inhibitors in leukemia therapy. Mol. Carcinog.

Pharmacophore identification, virtual screening and biological evaluation of prenylated flavonoids derivatives as PKB/Akt1 inhibitors.

A total of 24 well-defined PKB/Akt1 inhibitors were used to generate pharmacophore models applying Catalyst/HypoGen program. The best ranked model (Hypo_1) was then validated by cost analysis, prediction capability, Cat-Scramble and receiver operating characteristic (ROC) studies. Then, pharmacophore-based virtual screening combined with docking study was performed to search an in-house compound database. Nine preferable hits 75-80, HTS-02143, BTB-14740 and HTS-08006 were prepared and biologically evaluated. Several compounds were identified as good PKB/Akt1 inhibitors, suggesting that Hypo_1 would be reliable and useful in virtual screening. Flow cytometric and western blotting analysis on compounds 79 and 80 further demonstrated that the inhibition of phosphorylation of PKB/Akt1 and its substrates (such as GSK3β) was responsible for their cytotoxic activities.

The ubiquitin-proteasome pathway plays essential roles in ATRA-induced leukemia cells G0/G1 phase arrest and transition into granulocytic differentiation

All-trans retinoic acid (ATRA) has been successfully used in differentiation therapy for acute promyelocytic leukemia (APL) in the clinic. ATRA-induced differentiation of leukemia cells is accompanied by a G0/G1 arrest, yet how ATRA couples cell cycle arrest to differentiation remains largely unknown. Here we observed that the ubiquitin-proteasome pathway (UPP) was activated upon ATRA treatment in the human acute myeloid leukemia cell lines, NB4 and HL-60, as represented by the accumulation of ubiquitinated proteins, the up-regulation of ubiquitin mRNA and increased 20S proteasome activity. Interestingly, we found that complete inhibition of proteasome activity suppressed ATRA-induced proliferation/differentiation (P/D) transition in both cell lines. Furthermore, we demonstrate that the exact protein contributing to this phenomenon is different in these two cell lines. Cyclin-dependent kinase 2 (CDK2) and Cyclin E were degraded by the UPP; they accumulated significantly after complete inhibition of the proteasome in ATRA-treated NB4 and HL-60 cells, respectively. These findings suggested that the UPP might be indispensable in the ATRA-induced G0/G1 arrest and differentiation of leukemia cells. The exact protein degraded by the UPP to promote the myeloid maturation program set in motion by the retinoid may be cell type dependent.

Synthesis and evaluation of novel 7-azaindazolyl-indolyl-maleimide derivatives as antitumor agents and protein kinase C inhibitors

A series of novel 7-azaindazolyl-indolyl-maleimides were synthesized and evaluated for their antiproliferative activity in vitro against various human cancer cell lines and protein kinase C inhibitory activity. Compounds 8a-c, 8e and 14a were the most promising compounds against K562, A549, ECA-109, KB and SMMC-7721 cell lines in vitro. Compounds 9a-j showed moderate PKC inhibition. Further mechanism of action studies revealed that the antiproliferative activity of compound 8b in KB cells might involve the mitochondria-mediated apoptosis pathway.

Efficient activation of p53 pathway in A549 cells exposed to L2, a novel compound targeting p53-MDM2 interaction.

The tumor suppressor p53 plays a key role in the regulation of cell cycle, apoptosis, DNA repair, and senescence. It acts as a transcriptional factor, and is able to activate various genes to exert specific functions. MDM2, the main regulator of p53, inhibits the function of p53 through direct interaction. On the basis of this finding, inhibiting the MDM2–p53 interaction can be a potentially important target for cancer therapy. We showed here that L2, an analog of small-molecule MDM2 antagonist nutlins, stabilized p53 and selectively activated the p53 pathway in p53 wild-type A549 cells, resulting in a pronounced antiproliferation effect through inducing cell cycle arrest and apoptosis. Meanwhile, we confirmed by immunoprecipitation analysis that L2 could also inhibit MDM2–p53 interaction, similar to nutlin-1. Real-time PCR results revealed that L2 had no effect on the p53 gene transcriptional level, but it could induce the upregulation of p21 at the transcriptional level, which was the downstream of p53. Therefore, we concluded that the accumulation of p53 caused by L2 was mainly because of the decrease of the protein degradation rather than the elevation of p53 gene expression. Furthermore, no phosphor-p53 formed after L2 treatments, indicating that a genetoxic mechanism was unlikely to contribute to the activation of p53 by L2. In conclusion, the data acquired from A549 cells indicated that L2 exhibited high antiproliferation activity by disrupting MDM2–p53 interaction, and that the mechanism was derived from the activation of p53 and the p53 pathway. It was also surprising that L2 showed high antiproliferation effect against p53 null HL60 cells, which was quite different from nutlin-1. G2/M phase arrest might have contributed to the high antiproliferation activity of L2 on HL60 cells. The changes of p53 and MDM2 protein levels in L2-treated HL60 cells indicated that the mechanisms involved in the cell cycle arrest in A549 and HL60 cells were probably different, to which our future research would be devoted.

Involvement of mitogen‐activated protein kinase in signal transducer and activator of transcription‐1 mediated differentiation induced by bortezomib in acute myeloid leukemia cells

In this paper we report a new myeloid differentiation effect of bortezomib (BTZ) in acute myeloid leukemia (AML) cell lines and primary patient‐derived AML cells; this effect was assayed by investigating growth‐inhibition, cell morphology, differentiation markers, and nitro‐blue tetrazolium reduction. We show that BTZ induces the phosphorylation of several mitogen‐activated protein (MAP) kinases, including MEK/ERK, c‐Jun N‐terminal kinase (JNK), and p38 MAPK. BTZ‐induced cell differentiation is almost completely reversed by PD98059, an inhibitor of MEK, which also attenuates the increase in phospho‐JNK p46. However, p38 activation does not appear to be required for the differentiation induced by BTZ. Furthermore, the differentiation effect of BTZ is associated with increased protein level of signal transducer and activator of transcription‐1 (STAT1), a molecular determinant of myeloid differentiation, due to effects on both its synthesis and degradation. In short, this study reveals that BTZ activates the MEK/ERK cascade, which further up‐regulates the expression and activity of the key myeloid transcription factor STAT1, thus promoting myeloid differentiation. These findings contribute to an unexpected potential mechanism for the antitumor activity of BTZ in AML.

XQ2, a Novel TPZ Derivative, Induced G2/M Phase Arrest and Apoptosis under Hypoxia in Non-Small Cell Lung Cancer Cells

Hypoxia is one of the inevitable circumstances of various tumors. It controls various levels of regulation in tumor progression and results in tumor resistance to radiotherapy and chemotherapy. Here we investigated a synthetic TPZ derivative, N-ethoxymethyl-3-amino-1,2,4-benzotriazine-1,4-dioxide (XQ2), a novel compound that induced anti-cancer effects both in normoxia and in hypoxia, cell proliferation assay found that XQ2 exhibited a potent inhibitory effect on the tested cancer cell lines both in normoxia and in hypoxia. Flow cytometry and western blot studies indicated that XQ2 induces G2/M arrest and a caspase-dependent apoptosis in A549 cells. Additionally, intracellular reactive oxygen species (ROS) appear to play a key role in the anticancer effect of XQ2 in hypoxia. Taken together, our data suggest that XQ2 exerted anticancer action by suppressing the ROS level and triggering cell-cycle arrest and the caspase-dependent pathway, which is associated with apoptosis.