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Celecoxib, a selective cyclooxygenase-2 (COX-2) inhibitor, has been demonstrated to exert antitumor activity in a variety of cancer cells. The underlying mechanism involves inhibition of cell cycle progression and induction of apoptosis. Besides, celecoxib has also been found to induce autophagy in some solid tumor cells. The aim of this study was to investigate the effect of celecoxib on cell proliferation in HL-60 human acute leukemia cells and to explore the potential mechanism. HL-60 cells were exposed to various concentrations of celecoxib and cell viability was evaluated by the MTT assay. Apoptosis was analyzed with flow cytometry and the amount of autophagosome was evaluated by LysoTracker probe labelling. The expression of apoptosis- and autophagy-related proteins was assayed by Western blot and LysoSensor probe labelling was used to detect the effect of celecoxib on the lysosomal functions. The results of this study indicated that celecoxib inhibited cell proliferation in a time- and dose-dependent fashion. The flow cytometry analysis showed that celecoxib induced apoptosis at low concentrations and mainly cell necrosis at high concentrations. The Western blot test confirmed the induction of apoptosis by the upregulation of apoptosis-related proteins cleaved caspase-3 and cleaved PARP. Furthermore, this study demonstrated that celecoxib prevented the autophagic flux by inhibiting lysosome function; the fluorescence intensity of the LysoTracker probe and the level of autophagy-related proteins LC3-II and p62 were increased, but the fluorescence intensity of the LysoSensor probe was weakened. These findings show that celecoxib is an autophagy suppresser and has antitumor effects in HL-60 cells by inducing cell apoptosis and necrosis.

Background/Aims: Resistance of leukemia stem cells (LSCs) to chemotherapy in patients with acute myeloid leukemia (AML) causes relapse of disease. Hedgehog (Hh) signaling plays a critical role in the maintenance and differentiation of cancer stem cells. Yet its role in AML remains controversial. The purpose of the present study is to investigate the role of GLI1, the transcriptional activator of Hh signaling, in AML progenitor cells and to explore the anti-AML effects of GLI small-molecule inhibitor GANT61. Methods: The expression of GLI1 mRNA and protein were examined in AML progenitor cells and normal cells. The proliferation, colony formation, apoptosis and differentiation of AML progenitor cells were also analyzed in the presence of GANT61. Results: Kasumi-1 and KG1a cells, containing more CD34+ cells, expressed higher level of GLI1 compared to U937 and NB4 cells with fewer CD34+ cells. Consistently, a positive correlation between the protein levels of GLI1 and CD34 was validated in the bone marrow mononuclear cells (BMMC) of AML patients tested. GANT61 inhibited the proliferation and colony formation in AML cell lines. Importantly, GANT61 induced apoptosis in CD34+ enriched Kasumi-1 and KG1a cells, whereas it induced differentiation in U937 and NB4 cells. Furthermore, GANT61 enhanced the cytotoxicity of cytarabine (Ara-c) in primary CD34+ AML cells, indicating that inhibition of GLI1 could be a promising strategy to enhance chemosensitivity. Conclusions: The present findings suggested that Hh signaling was activated in AML progenitor cells. GLI1 acted as a potential target for AML therapy.

Doxycycline, a tetracycline-based antibiotic, has been reported to attenuate melanoma cell migration through inhibiting the focal adhesion kinase (FAK) signaling pathway. However, it remains to be elucidated whether doxycycline exerts this effect on leukemia cell migration. The present study aimed to examine the role of doxycycline in leukemia cell migration. The invasion capacities of the human leukemia cell lines KG1a (acute myelogenous leukemia) and K562 (chronic myelogenous leukemia) were evaluated using Matrigel® matrix-coated Transwell® chamber assays; leukemic cell lines treated with doxycycline (1 µg/ml) or anti-β1-integrin antibodies were added to the upper chamber, while untreated cells were included as controls. Reverse transcription quantitative polymerase chain reaction was performed in order to further understand the influence of doxycycline treatment on the expression of FAK and gelatinases in the KG1a and K562 leukemic cell lines. In addition, FAK protein expression and phosphorylation were determined using western blot analysis in order to investigate the mechanism by which doxycycline inhibited leukemic cell migration. The results revealed that doxycycline treatment significantly attenuated the migration of KG1a and K562 cells, which was demonstrated to be associated with inhibition of the expression and phosphorylation of FAK. In addition, doxycycline treatment inhibited matrix metalloproteinase (MMP)-2 and MMP-9 expression. Furthermore, incubation with blocking anti-β1-integrin antibodies had an analogous inhibitory effect on leukemic cell migration to that of doxycycline. In conclusion, the results of the present study suggested that doxycycline attenuated leukemic cell migration through inhibiting the FAK signaling pathway. Therefore, doxycycline may have potential for use as a novel strategy for the treatment of leukemia.

To date, acute myeloid leukemia (AML) shows very poor outcome for conventional chemotherapy. Leukemia stem cells (LSCs) are insensitive to conventional chemotherapeutic drugs and play a central role in the pathogenesis of AML. Failure to effectively ablate these cells may lead to AML relapse following chemotherapy. Phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling pathway is constructively activated in LSCs. This pathway can be inhibited by PI-103, a novel synthesized molecule of the pyridofuropyrimidine class, resulting in the apoptosis of LSCs. Therefore, we investigate the influences of PI-103 in combination with daunorubicin (DNR) on the LSCs. Our data indicate that PI-103 synergistically sensitizes LSCs to DNR-induced cytotoxicity. In addition, the PI-103/DNR co-treatment can induce significant apoptosis in LSCs, but sparing hematopoietic stem cells. The synergistic effect and the LSCs-specific apoptosis mechanism may be associated with the inhibition of PI3K/Akt/mTOR signaling pathway. Our results suggest that PI-103 in combination with DNR may be a potent and less toxic therapy for targeting LSCs and deserve further preclinical and clinical studies in the treatment of AML.

To explore the mechanism underlying antileukaemia effect of sodium valproate, the growth and survival of the K562 cell line were investigated. Global profiles of gene expression in K562 cells exposed to sodium valproate were assessed and validated. The differentially expressed genes identified were further used to query the connectivity map database to retrieve a ranked list of compounds that act on the same intracellular targets as sodium valproate. A significant increase in cell apoptosis and a change in gene expression profile were observed in valproate-exposed K562 cells. The significant enrichment analysis of gene ontology terms for the differentially expressed genes showed that these genes were involved in many important biological processes. Eight differentially expressed genes involved in apoptosis were verified by quantitative real-time PCR. The connectivity map analysis showed gene expression profile in K562 cells exposed to sodium valproate was most similar to that of HDACi and PI3K inhibitors, suggesting that sodium valproate might exert antileukaemic action by inhibiting HDAC as well as inhibiting PI3K pathway. In conclusion, our data might provide clues to elucidate the molecular and therapeutic potential of VPA in leukaemia treatment, and the connectivity map is a useful tool for exploring the molecular mechanism of drug action.