Bcr-Abl-mediated resistance to apoptosis is independent of constant tyrosine-kinase activity

Apoptotic and Cell Cycle Effects of Triterpenes Isolated from Phoradendron wattii on Leukemia Cell Lines

Current antineoplastic agents present multiple disadvantages, driving an ongoing search for new and better compounds. Four lupane-type triterpenes, 3α,24-dihydroxylup-20(29)-en-28-oic acid (1), 3α,23-dihydroxy-30-oxo-lup-20(29)-en-28-oic acid (2), 3α,23-O-isopropylidenyl-3α,23-dihydroxylup-20(29)-en-28-oic acid (3), and 3α,23-dihydroxylup-20(29)-en-28-oic acid (4), previously isolated from Phoradendron wattii, were evaluated on two cell lines of chronic (K562) and acute (HL60) myeloid leukemia. Compounds 1, 2, and 4 decreased cell viability and inhibit proliferation, mainly in K562, and exhibited an apoptotic effect from 24 h of treatment. Of particular interest is compound 2, which caused arrest in active phases (G2/M) of the cell cycle, as shown by in silico study of the CDK1/Cyclin B/Csk2 complex by molecular docking. This compound [3α,23-dihydroxy-30-oxo-lup-20(29)-en-28-oic acid] s a promising candidate for incorporation into cancer treatments and deserves further study.

BCR-ABL1 Tyrosine Kinase Complex Signaling Transduction: Challenges to Overcome Resistance in Chronic Myeloid Leukemia

The constitutively active BCR-ABL1 tyrosine kinase, found in t(9;22)(q34;q11) chromosomal translocation-derived leukemia, initiates an extremely complex signaling transduction cascade that induces a strong state of resistance to chemotherapy. Targeted therapies based on tyrosine kinase inhibitors (TKIs), such as imatinib, dasatinib, nilotinib, bosutinib, and ponatinib, have revolutionized the treatment of BCR-ABL1-driven leukemia, particularly chronic myeloid leukemia (CML). However, TKIs do not cure CML patients, as some develop TKI resistance and the majority relapse upon withdrawal from treatment. Importantly, although BCR-ABL1 tyrosine kinase is necessary to initiate and establish the malignant phenotype of Ph-related leukemia, in the later advanced phase of the disease, BCR-ABL1-independent mechanisms are also in place. Here, we present an overview of the signaling pathways initiated by BCR-ABL1 and discuss the major challenges regarding immunologic/pharmacologic combined therapies.

Design, synthesis and investigation of the mechanism of action underlying anti-leukemic effects of the quinolinequinones as LY83583 analogs

Literature conclusively shows that one of the quinolinequinone analogs (6-anilino-5,8-quinolinequinone), referred to as LY83583 hereafter, an inhibitor of guanylyl cyclase, was used as the inhibitor of the cell proliferation in cancer cells. In the present work, a series of analogs of the LY83583 containing alkoxy group(s) in aminophenyl ring (AQQ1-15) were designed and synthesized via a two-step route and evaluated for their in vitro cytotoxic activity against four different cancer cell lines (K562, Jurkat, MT-2, and HeLa) and human peripheral blood mononuclear cells (PBMCs) by MTT assay. The analog (AQQ13) was identified to possess the most potent cytotoxic activity against K562 human chronic myelogenous (CML) cell line (IC₅₀ = 0.59 ± 0.07 μM) with significant selectivity (SI = 4.51) compared to imatinib (IC₅₀ = 5.46 ± 0.85 μM; SI = 4.60). Based on its superior cytotoxic activity, the analog AQQ13 was selected for further mechanistic studies including determination of its apoptotic effects on K562 cell line via annexin V/ethidium homodimer III staining potency, ABL1 kinase inhibitory activity, and DNA cleaving capacity. Results ascertained that the analog AQQ13 induced apoptosis in K562 cell line with notable DNA-cleaving activity. However, AQQ13 demonstrated weak ABL1 inhibition indicating the correlation between anti-K562 and anti-ABL1 activities. In continuance, respectively conducted in silico molecular docking and Absorption, Distribution, Metabolism, and Excretion (ADME) studies drew attention to enhanced binding interactions of AQQ13 towards DNA and its high compatibility with the potential limits of specified pharmacokinetic parameters making it as a potential anti-leukemic drug candidate. Our findings may provide a new insight for further development of novel quinolinequinone-based anticancer analogs against CML.

Bothrops moojeni L-amino acid oxidase induces apoptosis and epigenetic modulation on Bcr-Abl+ cells

Background:

Resistance to apoptosis in chronic myeloid leukemia (CML) is associated with constitutive tyrosine kinase activity of the Bcr-Abl oncoprotein. The deregulated expression of apoptosis-related genes and alteration in epigenetic machinery may also contribute to apoptosis resistance in CML. Tyrosine kinase inhibitors target the Bcr-Abl oncoprotein and are used in CML treatment. The resistance of CML patients to tyrosine kinase inhibitors has guided the search for new compounds that may induce apoptosis in Bcr-Abl⁺ leukemic cells and improve the disease treatment.

Methods:

In the present study, we investigated whether the L-amino acid oxidase isolated from Bothrops moojeni snake venom (BmooLAAO-I) (i) was cytotoxic to Bcr-Abl⁺ cell lines (HL-60.Bcr-Abl, K562-S, and K562-R), HL-60 (acute promyelocytic leukemia) cells, the non-tumor cell line HEK-293, and peripheral blood mononuclear cells (PBMC); and (ii) affected epigenetic mechanisms, including DNA methylation and microRNAs expression in vitro.

Results:

BmooLAAO-I induced ROS production, apoptosis, and differential DNA methylation pattern of regulatory apoptosis genes. The toxin upregulated expression of the pro-apoptotic genes BID and FADD and downregulated DFFA expression in leukemic cell lines, as well as increased miR-16 expression - whose major predicted target is the anti-apoptotic gene BCL2 - in Bcr-Abl⁺ cells.

Conclusion:

BmooLAAO-I exerts selective antitumor action mediated by H₂O₂ release and induces apoptosis, and alterations in epigenetic mechanisms. These results support future investigations on the effect of BmooLAAO-I on in vivo models to determine its potential in CML therapy.

Cytotoxic and pro-apoptotic action of MjTX-I, a phospholipase A2 isolated from Bothrops moojeni snake venom, towards leukemic cells

Background

Chronic myeloid leukemia (CML) is a BCR-ABL1⁺ myeloproliferative neoplasm marked by increased myeloproliferation and presence of leukemic cells resistant to apoptosis. The current first-line therapy for CML is administration of the tyrosine kinase inhibitors imatinib mesylate, dasatinib or nilotinib. Although effective to treat CML, some patients have become resistant to this therapy, leading to disease progression and death. Thus, the discovery of new compounds to improve CML therapy is still challenging. Here we addressed whether MjTX-I, a phospholipase A₂ isolated from Bothrops moojeni snake venom, affects the viability of imatinib mesylate-resistant Bcr-Abl⁺ cell lines.

Methods

We examined the cytotoxic and pro-apoptotic effect of MjTX-I in K562-S and K562-R Bcr-Abl⁺ cells and in the non-tumor HEK-293 cell line and peripheral blood mononuclear cells, using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and the hypotonic fluorescent solution methods, associated with detection of caspases 3, 8, and 9 activation and poly (ADP-ribose) polymerase (PARP) cleavage. We also analyzed the MjTX-I potential to modulate the expression of apoptosis-related genes in K562-S and K562-R cells.

Results

MjTX-I decreased the viability of K562-S and K562-R cells by 60 to 65%, without affecting the viability of the non-tumor cells, i.e. it exerted selective cytotoxicity towards Bcr-Abl⁺ cell lines. In leukemic cell lines, the toxin induced apoptosis, activated caspases 3, 8, and 9, cleaved PARP, downregulated expression of the anti-apoptotic gene BCL-2, and upregulated expression of the pro-apoptotic gene BAD.

Conclusion

The antitumor effect of MjTX-I is associated with its potential to induce apoptosis and cytotoxicity in Bcr-Abl positive cell lines sensitive and resistant to imatinib mesylate, indicating that MjTX-I is a promising candidate drug to upgrade the CML therapy.

BCR-ABL1-induced downregulation of WASP in chronic myeloid leukemia involves epigenetic modification and contributes to malignancy

Chronic myeloid leukemia (CML) is a myeloproliferative disease caused by the BCR–ABL1 tyrosine kinase (TK). The development of TK inhibitors (TKIs) revolutionized the treatment of CML patients. However, TKIs are not effective to those at advanced phases when amplified BCR–ABL1 levels and increased genomic instability lead to secondary oncogenic modifications. Wiskott–Aldrich syndrome protein (WASP) is an important regulator of signaling transduction in hematopoietic cells and was shown to be an endogenous inhibitor of the c-ABL TK. Here, we show that the expression of WASP decreases with the progression of CML, inversely correlates with the expression of BCR–ABL1 and is particularly low in blast crisis. Enforced expression of BCR–ABL1 negatively regulates the expression of WASP. Decreased expression of WASP is partially due to DNA methylation of the proximal WASP promoter. Importantly, lower levels of WASP in CML advanced phase patients correlate with poorer overall survival (OS) and is associated with TKI response. Interestingly, enforced expression of WASP in BCR–ABL1-positive K562 cells increases the susceptibility to apoptosis induced by TRAIL or chemotherapeutic drugs and negatively modulates BCR–ABL1-induced tumorigenesis in vitro and in vivo. Taken together, our data reveal a novel molecular mechanism that operates in BCR–ABL1-induced tumorigenesis that can be used to develop new strategies to help TKI-resistant, CML patients in blast crisis (BC).

Nickel pyrithione induces apoptosis in chronic myeloid leukemia cells resistant to imatinib via both Bcr/Abl-dependent and Bcr/Abl-independent mechanisms

BACKGROUND

Acquired imatinib (IM) resistance is frequently characterized by Bcr-Abl mutations that affect IM binding and kinase inhibition in patients with chronic myelogenous leukemia (CML). Bcr-Abl-T315I mutation is the predominant mechanism of the acquired resistance to IM. Therefore, it is urgent to search for additional approaches and targeting strategies to overcome IM resistance. We recently reported that nickel pyrithione (NiPT) potently inhibits the ubiquitin proteasome system via targeting the 19S proteasome-associated deubiquitinases (UCHL5 and USP14), without effecting on the 20S proteasome. In this present study, we investigated the effect of NiPT, a novel proteasomal deubiquitinase inhibitor, on cell survival or apoptosis in CML cells bearing Bcr-Abl-T315I or wild-type Bcr-Abl.

METHODS

Cell viability was examined by MTS assay and trypan blue exclusion staining assay in KBM5, KBM5R, K562, BaF3-p210-WT, BaF3-p210-T315I cells, and CML patients' bone marrow samples treated with NiPT. Cell apoptosis in CML cells was detected with Annexin V-FITC/PI and rhodamine-123 staining followed by fluorescence microscopy and flow cytometry and with western blot analyses for apoptosis-associated proteins. Expression levels of Bcr-Abl in CML cells were analyzed by using western blotting and real-time PCR. The 20S proteasome peptidase activity was measured using specific fluorogenic substrate. Active-site-directed labeling of proteasomal DUBs, as well as the phosphorylation of USP14 was used for evaluating the inhibition of the DUBs activity by NiPT. Mouse xenograft models of KBM5 and KBM5R cells were analyzed, and Bcr-Abl-related proteins and protein biomarkers related to proliferation, differentiation, and adhesion in tumor tissues were detected by western blots and/or immunohistological analyses.

RESULTS

NiPT induced apoptosis in CML cells and inhibited the growth of IM-resistant Bcr-Abl-T315I xenografts in nude mice. Mechanistically, NiPT induced decreases in Bcr-Abl proteins, which were associated with downregulation of Bcr-Abl transcription and with the cleavage of Bcr-Abl protein by activated caspases. NiPT-induced ubiquitin proteasome system inhibition induced caspase activation in both IM-resistant and IM-sensitive CML cells, and the caspase activation was required for NiPT-induced Bcr-Abl downregulation and apoptotic cell death.

CONCLUSIONS

These findings support that NiPT can overcome IM resistance through both Bcr-Abl-dependent and Bcr-Abl-independent mechanisms, providing potentially a new option for CML treatment.

Thymoquinone inhibits growth of human medulloblastoma cells by inducing oxidative stress and caspase-dependent apoptosis while suppressing NF-κB signaling and IL-8 expression

Medulloblastoma (MB) is the most common malignant brain tumor of childhood. The transcription factor NF-κB is overexpressed in human MB and is a critical factor for MB tumor growth. NF-κB is known to regulate the expression of interleukin-8 (IL-8), the chemokine that enhances cancer cell growth and resistance to chemotherapy. We have recently shown that thymoquinone (TQ) suppresses growth of hepatocellular carcinoma cells in part by inhibiting NF-κB signaling. Here we sought to extend these studies in MB cells and show that TQ suppresses growth of MB cells in a dose- and time-dependent manner, causes G2M cell cycle arrest, and induces apoptosis. TQ significantly increased generation of reactive oxygen species (ROS), while pretreatment of MB cells with the ROS scavenger N-acetylcysteine (NAC) abrogated TQ-induced cell death and apoptosis, suggesting that TQ-induced cell death and apoptosis are oxidative stress-mediated. TQ inhibitory effects were associated with inhibition of NF-κB and altered expression of its downstream effectors IL-8 and its receptors, the anti-apoptotic Bcl-2, Bcl-xL, X-IAP, and FLIP, as well as the pro-apoptotic TRAIL-R1, caspase-8, caspase-9, Bcl-xS, and cytochrome c. TQ-triggered apoptosis was substantiated by up-regulation of the executioner caspase-3 and caspase-7, as well as cleavage of the death substrate poly(ADP-ribose)polymerase. Interestingly, pretreatment of MB cells with NAC or the pan-caspase inhibitor zVAD-fmk abrogated TQ-induced apoptosis, loss of cyclin B1 and NF-κB activity, suggesting that these TQ-mediated effects are oxidative stress- and caspase-dependent. These findings reveal that TQ induces both extrinsic and intrinsic pathways of apoptosis in MB cells, and suggest its potential usefulness in the treatment of MB.

In Vitro Antileukemia Activity of ZSTK474 on K562 and Multidrug Resistant K562/A02 Cells

Chronic myelogenous leukemia (CML) is a malignant hematological disorder mainly caused by the Bcr-Abl tyrosine kinase. While Bcr-Abl inhibitors including Imatinib showed antitumor efficacy on many CML patients, resistance was frequently reported in recent years. Therefore, novel drugs for CML are still expected. ZSTK474 is a specific phosphatidylinositol 3-kinase (PI3K) inhibitor that we identified. In the present study, the efficacy of ZSTK474, alone or in combination with Imatinib, on K562 CML cells as well as on its multidrug resistance counterpart K562/A02 cells, was investigated. ZSTK474 inhibited the cell proliferation with an IC₅₀ of 4.69 μM for K562 and 7.57 μM for K562/A02 cells, respectively. Treatment by ZSTK474 resulted in cell cycle arrest in G1 phase, which might be associated with upregulation of p27, and downregulation of cyclin D1. ZSTK474 also inhibited phosphorylation of Akt and GSK-3β, which might be involved in the effect on the above cell cycle-related proteins. Moreover, combination of ZSTK474 and Imatinib indicated synergistic effect on both cell lines. In conclusion, ZSTK474 exhibited antileukemia activity alone, and showed synergistic effect when combined with Imatinib, on CML K562 cells as well as the multidrug resistant ones, providing a potential therapeutic approach for CML patients.

CR-LAAO antileukemic effect against Bcr-Abl(+) cells is mediated by apoptosis and hydrogen peroxide

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm characterized by the presence of the Bcr-Abl tyrosine kinase protein, which confers resistance to apoptosis in leukemic cells. Tyrosine kinase inhibitors (TKIs) are effectively used to treat CML; however, CML patients in the advanced (CML-AP) and chronic (CML-CP) phases of the disease are usually resistant to TKI therapy. Thus, it is necessary to seek for novel agents to treat CML, such as the enzyme l-amino acid oxidase from Calloselasma rhodostoma (CR-LAAO) snake venom. We examined the antitumor effect of CR-LAAO in Bcr-Abl(+) cell lines and peripheral blood mononuclear cells (PBMC) from healthy subjects and CML patients. CR-LAAO was more cytotoxic towards Bcr-Abl(+) cell lines than towards healthy subjects' PBMC. The H2O2 produced during the enzymatic action of CR-LAAO mediated its cytotoxic effect. The CR-LAAO induced apoptosis in Bcr-Abl(+) cells, as detected by caspases 3, 8, and 9 activation, loss of mitochondrial membrane potential, and DNA damage. CR-LAAO elicited apoptosis in PBMC from CML-CP patients without TKI treatment more strongly than in PBMC from healthy subjects and TKI-treated CML-CP and CML-AP patients. The antitumor effect of CR-LAAO against Bcr-Abl(+) cells makes this toxin a promising candidate to CML therapy.

HS-543 induces apoptosis of Imatinib-resistant chronic myelogenous leukemia with T315I mutation

Chronic myeloid leukemia (CML) is characterized by a constitutive activation of Bcr-Abl tyrosine kinase. Bcr-Abl/T315I is the predominant mutation that causes resistance to Imatinib. In the present study, we synthesized a novel Bcr-Abl inhibitor, HS-543, and investigated its effect on cell survival or apoptosis in CML cells bearing Bcr-Abl/T315I (BaF3/T315I) or wild-type Bcr-Abl (BaF3/WT). HS-543 showed anti-proliferative effects in the BaF3/WT cells as well as the BaF3/T315I cells with resistance to Imatinib and strongly inhibited the Bcr-Abl signaling pathway in a dose-dependent manner. Furthermore, it significantly increased the sub G₁ phase associated with early apoptosis, with increased levels of cleaved PARP and cleaved caspase-3, as well as the TUNEL-positive apoptotic cells. In addition, we found that HS-543 induced apoptosis with the loss of mitochondrial membrane potential by decreasing the expression of Mcl-1 and survivin, together with increasing that of Bax. In BaF3/T315I xenograft models, HS-543 significantly delayed tumor growth, unlike Imatinib. Our results demonstrate that HS-543 exhibits the induction of apoptosis and anti-proliferative effect by blocking the Bcr-Abl signaling pathway in the T315I-mutated Bcr-Abl cells with resistance to Imatinib. We suggest that HS-543 may be a novel promising agent to target Bcr-Abl and overcome Imatinib resistance in CML patients.

Anti-rheumatic agent auranofin induced apoptosis in chronic myeloid leukemia cells resistant to imatinib through both Bcr/Abl-dependent and -independent mechanisms

Resistance to Imatinib mesylate (IM) is an emerging problem for patients with chronic myelogenous leukemia (CML). T315I mutation in the Bcr-Abl is the predominant mechanism of the acquired resistance to IM and second generation tyrosine kinase inhibitors (TKI). Therefore it is urgent to search for new measures to overcome TKI-resistance. Auranofin (AF), clinically used to treat rheumatic arthritis, was recently approved by US Food and Drug Administration for Phase II clinical trial to treat cancer. In contrast to the reports that AF induces apoptosis by increasing intracellular reactive oxygen species (ROS) levels via inhibiting thioredoxin reductase, our recent study revealed that AF-induced apoptosis depends on inhibition of proteasomal deubiquitinases (UCHL5 and USP14). Here we report that (i) AF induces apoptosis in both Bcr-Abl wild-type cells and Bcr-Abl-T315I mutation cells and inhibits the growth of IM-resistant Bcr-Abl-T315I xenografts in vivo; (ii) AF inhibits Bcr-Abl through both downregulation of Bcr-Abl gene expression and Bcr-Abl cleavage mediated by proteasome inhibition-induced caspase activation; (iii) proteasome inhibition but not ROS is required for AF-induced caspase activation and apoptosis. These findings support that AF overcomes IM resistance through both Bcr/Abl-dependent and -independent mechanisms, providing great clinical significance for cancer treatment.

Apoptosis-related gene expression profile in chronic myeloid leukemia patients after imatinib mesylate and dasatinib therapy

BACKGROUND/AIMS

We investigated the effects of tyrosine kinase inhibitors (TKIs) on the expression of apoptosis-related genes (BCL-2 and death receptor family members) in chronic myeloid leukemia (CML) patients.

METHODS

Peripheral blood mononuclear cells from 32 healthy subjects and 26 CML patients were evaluated before and after treatment with imatinib mesylate (IM) and dasatinib (DAS) by quantitative PCR.

RESULTS

Anti-apoptotic genes (c-FLIP and MCL-1) were overexpressed and the pro-apoptotic BIK was reduced in CML patients. Expression of BMF, A1, c-FLIP, MCL-1, CIAP-2 and CIAP-1 was modulated by DAS. In IM-resistant patients, expression of A1, c-FLIP, CIAP-1 and MCL-1 was upregulated, and BCL-2, CIAP-2, BAK, BAX, BIK and FASL expression was downregulated.

CONCLUSION

Taken together, our results point out that, in CML, DAS interferes with the apoptotic machinery regulation. In addition, the data suggest that apoptosis-related gene expression profiles are associated with primary resistance to IM.

ApoptomiRs expression modulated by BCR-ABL is linked to CML progression and imatinib resistance

BACKGROUND

Chronic myeloid leukemia (CML) is a myeloproliferative disease characterized by the presence of Philadelphia chromosome (Ph) leading to expression of a BCR-ABL1 fusion oncogene. The BCR-ABL protein has a constitutive tyrosine kinase activity which is responsible for CML pathogenesis by promoting cell apoptosis resistance; however, the cellular and molecular mechanisms associated with BCR-ABL expression and apoptosis impairment in CML leukemic cells have not been fully elucidated.

METHODS

This study evaluated apoptomiRs and their predicted apoptotic genes in BCR-ABL(+) cells from patients in different phases of CML treated with tyrosine kinase inhibitor (TKI) according to their imatinib (IM) response by qPCR. Phosphotyrosine and c-ABL expressions in HL-60.BCR-ABL cells treated with TKI were done by Western blot.

RESULTS

We found that dasatinib (DAS) modulated miR-let-7d, miR-let-7e, miR-15a, miR-16, miR-21, miR-130a and miR-142-3p expressions while IM modulated miR-15a and miR-130a levels. miR-16, miR-130a and miR-145 expressions were modulated by nilotinib (NIL). We observed higher miR-15a, miR-130b and miR-145; and lower miR-16, miR-26a and miR-146a expressions in CML-CP in comparison with controls. CML-AP patients showed low miR-let-7d, miR-15a, miR-16, miR-29c, miR-142-3p, miR-145, and miR-146a levels in comparison with CML-CP. We noted that the miR-26a, miR-29c, miR-130b and miR-146a expressions were downregulated in IM resistant patients in comparison with IM responsive patients.

CONCLUSIONS

This study showed the modulation of apoptomiRs by BCR-ABL kinase activity and the deregulation of apoptomiRs and their predicted apoptotic target genes in different CML phases and after treatment with TK inhibitors. ApoptomiRs may be involved in the BCR-ABL(+) cell apoptosis regulation.

Thymoquinone suppression of the human hepatocellular carcinoma cell growth involves inhibition of IL-8 expression, elevated levels of TRAIL receptors, oxidative stress and apoptosis

Hepatocellular carcinoma (HCC) is the fourth most common solid tumor worldwide. The chemokine interleukin-8 (IL-8) is overexpressed in HCC and is a potential target for therapy. Although the transcription factor NF-κB regulates IL-8 expression, and while thymoquinone (TQ; the most bioactive constituent of black seed oil) inhibits NF-κB activity, the precise mechanisms by which TQ regulates IL-8 and cancer cell growth remain to be clarified. Here, we report that TQ inhibited growth of HCC cells in a dose- and time-dependent manner, caused G2M cell cycle arrest, and stimulated apoptosis. Apoptosis was substantiated by activation of caspase-3 and -9, as well as cleavage of poly(ADP-ribose)polymerase. TQ treatments inhibited expression of NF-κB and suppressed IL-8 and its receptors. TQ treatments caused increased levels of reactive oxygen species (ROS) and mRNAs of oxidative stress-related genes, NQO1 and HO-1. Pretreatment of HepG2 cells with N-acetylcysteine, a scavenger of ROS, prevented TQ-induced cell death. TQ treatment stimulated mRNA expression of pro-apoptotic Bcl-xS and TRAIL death receptors, and inhibited expression of the anti-apoptotic gene Bcl-2. TQ enhanced TRAIL-induced death of HepG2 cells, in part by up-regulating TRAIL death receptors, inhibiting NF-κB and IL-8 and stimulating apoptosis. Altogether, these findings provide insights into the pleiotropic molecular mechanisms of TQ-dependent suppression of HCC cell growth and underscore potential of this compound as anti-HCC drug.

Gambogic acid induces apoptosis in imatinib-resistant chronic myeloid leukemia cells via inducing proteasome inhibition and caspase-dependent Bcr-Abl downregulation

PURPOSE

Chronic myelogenous leukemia (CML) is characterized by the constitutive activation of Bcr-Abl tyrosine kinase. Bcr-Abl-T315I is the predominant mutation that causes resistance to imatinib, cytotoxic drugs, and the second-generation tyrosine kinase inhibitors. The emergence of imatinib resistance in patients with CML leads to searching for novel approaches to the treatment of CML. Gambogic acid, a small molecule derived from Chinese herb gamboges, has been approved for phase II clinical trial for cancer therapy by the Chinese Food and Drug Administration (FDA). In this study, we investigated the effect of gambogic acid on cell survival or apoptosis in CML cells bearing Bcr-Abl-T315I or wild-type Bcr-Abl.

EXPERIMENTAL DESIGN

CML cell lines (KBM5, KBM5-T315I, and K562), primary cells from patients with CML with clinical resistance to imatinib, and normal monocytes from healthy volunteers were treated with gambogic acid, imatinib, or their combination, followed by measuring the effects on cell growth, apoptosis, and signal pathways. The in vivo antitumor activity of gambogic acid and its combination with imatinib was also assessed with nude xenografts.

RESULTS

Gambogic acid induced apoptosis and cell proliferation inhibition in CML cells and inhibited the growth of imatinib-resistant Bcr-Abl-T315I xenografts in nude mice. Our data suggest that GA-induced proteasome inhibition is required for caspase activation in both imatinib-resistant and -sensitive CML cells, and caspase activation is required for gambogic acid-induced Bcr-Abl downregulation and apoptotic cell death.

CONCLUSIONS

These findings suggest an alternative strategy to overcome imatinib resistance by enhancing Bcr-Abl downregulation with the medicinal compound gambogic acid, which may have great clinical significance in imatinib-resistant cancer therapy.

Olean-12-eno[2,3-c] [1,2,5]oxadiazol-28-oic acid (OEOA) induces G1 cell cycle arrest and differentiation in human leukemia cell lines

Oleanolic acid (3β-hydroxy-olea-12-en-28-oic acid) is a natural pentacyclic triterpenoic acid found in many fruits, herbs and medicinal plants. In the past decade, increasing evidence has suggested that oleanolic acid exhibits inhibitory activities against different types of cancer including skin cancer and colon cancer, but not leukemia. We report here that a derivative of oleanolic acid, olean-12-eno[2,3-c] [1], [2], [5]oxadiazol-28-oic acid (designated OEOA) effectively blocks the proliferation of human leukemia cells. OEOA significantly reduces cell proliferation without inducing cell death in three types of leukemia cell lines, including K562, HEL and Jurket. Moreover, exposure of K562 cells to OEOA results in G1 cell cycle arrest, with a concomitant induction of cyclin-dependent kinase inhibitor p27 and downregulation of cyclins and Cdks that are essential for cell cycle progression. Interestingly, OEOA also enhances erythroid differentiation in K562 cells through suppressing the expression of Bcr-Abl and phosphorylation of Erk1/2. These findings identify a novel chemical entity for further development as therapeutics against leukemia.

Gene expression signatures associated with the in vitro resistance to two tyrosine kinase inhibitors, nilotinib and imatinib

The use of selective inhibitors targeting Bcr-Abl kinase is now established as a standard protocol in the treatment of chronic myelogenous leukemia; however, the acquisition of drug resistance is a major obstacle limiting the treatment efficacy. To elucidate the molecular mechanism of drug resistance, we established K562 cell line models resistant to nilotinib and imatinib. Microarray-based transcriptome profiling of resistant cells revealed that nilotinib- and imatinib-resistant cells showed the upregulation of kinase-encoding genes (AURKC, FYN, SYK, BTK and YES1). Among them, the upregulation of AURKC and FYN was observed both in nilotinib- and imatinib-resistant cells irrespective of exposure doses, while SYK, BTK and YES1 showed dose-dependent upregulation of expression. Upregulation of EGF and JAG1 oncogenes as well as genes encoding ATP-dependent drug efflux pump proteins such as ABCB1 was also observed in the resistant cells, which may confer alternative survival benefits. Functional gene set analysis revealed that molecular categories of ‘ATPase activity', ‘cell adhesion' or ‘tyrosine kinase activity' were commonly activated in the resistant clones. Taken together, the transcriptome analysis of tyrosine kinase inhibitors (TKI)-resistant clones provides the insights into the mechanism of drug resistance, which can facilitate the development of an effective screening method as well as therapeutic intervention to deal with TKI resistance.

BCR-ABL-mediated upregulation of PRAME is responsible for knocking down TRAIL in CML patients

Tumor necrosis factor-related apoptosis-inducing ligand-TNFSF10 (TRAIL), a member of the TNF-α family and a death receptor ligand, was shown to selectively kill tumor cells. Not surprisingly, TRAIL is downregulated in a variety of tumor cells, including BCR-ABL-positive leukemia. Although we know much about the molecular basis of TRAIL-mediated cell killing, the mechanism responsible for TRAIL inhibition in tumors remains elusive because (a) TRAIL can be regulated by retinoic acid (RA); (b) the tumor antigen preferentially expressed antigen of melanoma (PRAME) was shown to inhibit transcription of RA receptor target genes through the polycomb protein, enhancer of zeste homolog 2 (EZH2); and (c) we have found that TRAIL is inversely correlated with BCR-ABL in chronic myeloid leukemia (CML) patients. Thus, we decided to investigate the association of PRAME, EZH2 and TRAIL in BCR-ABL-positive leukemia. Here, we demonstrate that PRAME, but not EZH2, is upregulated in BCR-ABL cells and is associated with the progression of disease in CML patients. There is a positive correlation between PRAME and BCR-ABL and an inverse correlation between PRAME and TRAIL in these patients. Importantly, knocking down PRAME or EZH2 by RNA interference in a BCR-ABL-positive cell line restores TRAIL expression. Moreover, there is an enrichment of EZH2 binding on the promoter region of TRAIL in a CML cell line. This binding is lost after PRAME knockdown. Finally, knocking down PRAME or EZH2, and consequently induction of TRAIL expression, enhances Imatinib sensibility. Taken together, our data reveal a novel regulatory mechanism responsible for lowering TRAIL expression and provide the basis of alternative targets for combined therapeutic strategies for CML.

TLR4/MYD88-dependent, LPS-induced synthesis of PGE2 by macrophages or dendritic cells prevents anti-CD3-mediated CD95L upregulation in T cells

Antigen-presenting cells (APCs) control T-cell responses by multiple mechanisms, including the expression of co-stimulatory molecules and the production of cytokines and other mediators that control T-cell proliferation, survival and differentiation. Here, we demonstrate that soluble factor(s) produced by Toll-like receptor (TLR)-activated APCs suppress activation-induced cell death (AICD). This effect was observed in non-stimulated APCs, but it was significantly increased after lipopolysaccharide (LPS) treatment. Using different KO mice, we found that the LPS-induced protective factor is dependent on TLR4/MyD88. We identified the protective factor as prostaglandin E(2) (PGE(2)) and showed that both APC-derived supernatants and PGE(2) prevented CD95L upregulation in T cells in response to TCR/CD3 stimulation, thereby avoiding both AICD and activated T cell killing of target macrophages. The PGE(2) receptors, EP2 and EP4, appear to be involved since pharmacological stimulation of these receptors mimics the protective effect on T cells and their respective antagonists interfere with the protection induced by either APCs derived or synthetic PGE(2). Finally, the engagement of EP2 and EP4 synergistically activates protein kinase A (PKA) and exchange protein directly activated by cAMP pathways to prevent AICD. Taken together, these results indicate that APCs can regulate T-cell levels of CD95L by releasing PGE(2) in response to LPS through a TLR4/MyD88-dependent pathway, with consequences for both T cell and their own survival.

Synergistic interactions between vorinostat and sorafenib in chronic myelogenous leukemia cells involve Mcl-1 and p21CIP1 down-regulation

PURPOSE

Interactions between the multikinase inhibitor sorafenib (Bay 43-9006) and the histone deacetylase inhibitor vorinostat were examined in chronic myelogenous leukemia (CML) cells sensitive and resistant to imatinib mesylate.

EXPERIMENTAL DESIGN

K562, LAMA 84, and primary CML patient-derived CD34(+) mononuclear cells were exposed to vorinostat followed by sorafenib, after which effects on cell viability and various survival signaling pathways were monitored by flow cytometry, clonogenic assays, and Western blotting. Real-time reverse transcription-PCR was used to monitor gene expression, and the functional contribution of p21(CIP1) and Mcl-1 down-regulation were determined in cells transfected with corresponding constructs.

RESULTS

Pretreatment (24 h) with vorinostat followed by sorafenib optimally induced mitochondrial injury and cell death in Bcr/Abl(+) cells (e.g., K562 and LAMA 84). Similar results were obtained in imatinib mesylate-resistant cells expressing activated Lyn as well as in primary CD34(+) bone marrow cells obtained from CML patients. This regimen also markedly inhibited CML cell colony formation. Combined but not individual treatment of CML cells with vorinostat and sorafenib triggered pronounced mitochondrial dysfunction (i.e., cytochrome c, Smac, and AIF release), caspase activation, poly(ADP-ribose) polymerase cleavage, and down-regulation of Mcl-1. Sorafenib also blocked vorinostat-mediated induction of p21(CIP1). Down-regulation of Mcl-1 was caspase and transcription independent, whereas p21(CIP1) down-regulation was partially caspase and transcription dependent. Enforced expression of p21(CIP1) and particularly Mcl-1 significantly attenuated vorinostat/sorafenib-mediated lethality.

CONCLUSIONS

These findings suggest that combined treatment with vorinostat and sorafenib synergistically induces apoptosis in CML cells through a process that involves Mcl-1 down-regulation and inhibition of p21(CIP1) induction.

The challenges of targeting chronic myeloid leukemia stem cells

Chronic myeloid leukemia (CML) is sustained by a clonally amplified population of Bcr Abl-positive pluripotent stem cells. Persistence of a large, functionally intact yet suppressed residual normal hematopoietic stem cell population in most patients with CML has made it possible to aim at the development of curative therapies. However, achieving this goal requires the identification of agents that will eradicate the leukemic stem cell population. Several potent Bcr-Abl-targeted drugs have now been introduced into clinical practice with remarkable effects. Nevertheless, accumulating data indicate that the leukemic CML stem cells in patients with chronic phase CML are less responsive to these agents than the bulk of the neoplastic cells. In this article, we review emerging evidence that CML stem cells have a number of unusual properties that underlie their relative insensitivity to treatment, including those that specifically target the Bcr-Abl oncoprotein. The biology of the neoplastic stem cells in patients with CML is clearly important to the future attainment of cures and might also prove a paradigm relevant to other types of malignancies that are sustained by transformed stem cell populations.

Pomolic acid may overcome multidrug resistance mediated by overexpression of anti-apoptotic Bcl-2 proteins

Multidrug resistance (MDR) is multifactorial and may be mediated by overexpression of anti-apoptotic proteins. This paper investigated whether pomolic acid (PA) was able to overcome resistance mediated by overexpression of Bcl-2 or BcL-xL. The results obtained showed that overexpression of these proteins partially inhibited the PA-induced apoptosis, loss of mitochondrial membrane potential and caspase -3 and -9 activation observed in HL-60/neo. Since Bcl-2 transfected cell lines were shown to be quite resistant to a series of chemotherapeutic agents, the data presented call attention to the possible clinical significance of PA as an anti-MDR drug.

Transient or long-term silencing of BCR-ABL alone induces cell cycle and proliferation arrest, apoptosis and differentiation

BCR-ABL fusion protein, a t(9;22) translocation product is indispensable for generation, maintenance and progression of chronic myeloid leukemia. RNA interference is an approach to silence gene at post-transcriptional level. We show that dsRNA targeted against the translocation region leads to more than 90% inhibition of BCR-ABL mRNA and protein expression levels using K562 as a model. Lack of BCR-ABL leads to cell cycle arrest in G1 phase as observed by decrease in cyclin D1 and increase in p21 and p27 cdk inhibitors mRNA. Apoptosis resistance imparted by BCR-ABL is lost in these cells in caspase-dependent or independent manner. Decrease in Bcl-XL is observed along with decrease in mitochondrial membrane integrity. Transient removal of BCR-ABL expression has a profound effect on proliferation and clonogenic capacity also confirmed by long-term silencing using lentiviral vectors. Interestingly, low level of BCR-ABL message leads to enhanced erythroid differentiation and reduced expression of megakaryocytic markers. Importantly, in six CML patient samples studied, silencing BCR-ABL in the lineage depleted enriched stem cell population leads to a decrease in colony-forming capacity. Thus, long-term silencing of BCR-ABL might prove to be a promising alternative approach in CML patients especially for those who do not respond to any other drug treatment.

Nanomolar concentration of NSC606985, a camptothecin analog, induces leukemic-cell apoptosis through protein kinase Cδ–dependent mechanisms

As a promising new class of anticancer drugs, camptothecins have advanced to the forefront of several areas of therapeutic and developmental chemotherapy. In the present study, we report that NSC606985, a rarely studied camptothecin analog, induces apoptosis in acute myeloid leukemia (AML) cells NB4 and U937 and inhibits the proliferation without cell death in breakpoint cluster region–Abelson murine leukemia (bcr-abl) kinase-carrying leukemic K562 cells. For apoptosis induction or growth arrest, nanomolar concentrations of NSC606985 are sufficient. At such low concentrations, this agent also significantly inhibits the clonogenic activity of hematopoietic progenitors from patients with AML. For apoptosis induction, NSC606985 rapidly induces the proteolytic activation of protein kinase Cδ (PKCδ) with loss of mitochondrial transmembrane potential (ΔΨm) and caspase-3 activation. Cotreatment with rottlerin, a PKCδ-specific inhibitor, completely blocks NSC606985-induced mitochondrial ΔΨm loss and caspase-3 activation, while the inhibition of caspase-3 by z-DEVD-fluoromethyl ketone (Z-DEVD-fmk) only partially attenuates PKCδ activation and apoptosis. These data indicate that NSC606985-induced PKCδ activation is an early event upstream to mitochondrial ΔΨm loss and caspase-3 activation, while activated caspase-3 has an amplifying effect on PKCδ proteolysis. In addition, NSC606985-induced apoptosis by PKCδ also involves caspase-3–independent mechanisms. Taken together, our results suggest that NSC606985 is a potential agent for the treatment of AML.

The development of imatinib as a therapeutic agent for chronic myeloid leukemia

Imatinib has revolutionized drug therapy of chronic myeloid leukemia (CML). Preclinical studies were promising but the results of clinical trials by far exceeded expectations. Responses in chronic phase are unprecedented, with rates of complete cytogenetic response (CCR) of more than 40% in patients after failure of interferon-α (IFN) and more than 80% in newly diagnosed patients, a level of efficacy that led to regulatory approval in record time. While most of these responses are stable, resistance to treatment after an initial response is common in more advanced phases of the disease. Mutations in the kinase domain (KD) of BCR-ABL that impair imatinib binding have been identified as the leading cause of resistance. Patients with CCR who achieve a profound reduction of BCR-ABL mRNA have a very low risk of disease progression. However, residual disease usually remains detectable with reverse transcription–polymerase chain reaction (RT-PCR), indicating that disease eradication may pose a significant challenge. The mechanisms underlying the persistence of minimal residual disease are unknown. In this manuscript, we review the preclinical and clinical development of imatinib for the therapy of CML, resistance and strategies that may help to eliminate resistant or residual leukemia.

Pathobiology of lymphoid and myeloid blast crisis and management issues

Despite recent improvements in the treatment of early-stage disease, the blastic phase of chronic myeloid leukemia (CML) remains a therapeutic challenge. For imatinib-naïve patients, imatinib provided encouraging hematologic and cytogenetic benefits; however, the vast majority of CML blast crisis cases today arise in patients already on imatinib-based therapy. Clonal evolution and duplication of the Philadelphia chromosome continue to be associated with blastic phase transformation, but recent studies have identified BCR/ABL kinase domain mutations in 30%-40% of blast crisis patients. This implies that BCR-ABL-targeted therapy might have influenced the molecular road map to blastic transformation. In this review, we will examine the effect of imatinib on primitive CML progenitors and how this might influence the pathophysiology of blast crisis. A rational framework for deciding how best to integrate stem cell transplantation, traditional chemotherapy, imatinib, and other BCR-ABL kinase inhibitors in the care of blast crisis patients will also be discussed.

Biology of chronic myelogenous leukemia--signaling pathways of initiation and transformation

Chronic myeloid leukemia (CML) is caused by the Bcr-Abl oncoprotein,the product of the t(9;22) chromosomal translocation that generates the Philadelphia chromosome. Different disease phenotypes are associated with each of the three Bcr-Abl isoforms: p190Bcr-Abl, p210Bcr-Abl, and p230Bcr-Abl all of which have a constitutively activated tyrosine kinase. Mechanisms associated with malignant transformation include altered cellular adhesion, activation of mitogenic signaling pathways, inhibition of apoptosis, and proteasomal degradation of physiologically important cellular proteins.CML is subject to an inexorable progression from an "indolent" chronic phase to a terminal blast crisis. Disease progression is presumed to be associated with the phenomenon of genomic instability.

Bortezomib and flavopiridol interact synergistically to induce apoptosis in chronic myeloid leukemia cells resistant to imatinib mesylate through both Bcr/Abl-dependent and -independent mechanisms

Interactions between the cyclin-dependent kinase (CDK) inhibitor flavopiridol and the proteasome inhibitor bortezomib were examined in Bcr/Abl(+) human leukemia cells. Coexposure of K562 or LAMA84 cells to subtoxic concentration of flavopiridol (150-200 nM) and bortezomib (5-8 nM) resulted in a synergistic increase in mitochondrial dysfunction and apoptosis. These events were associated with a marked diminution in nuclear factor kappaB (NF-kappaB)/DNA binding activity; enhanced phosphorylation of SEK1/MKK4 (stress-activated protein kinase/extracellular signal-related kinase 1/mitogen-activated protein kinase kinase 4), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAPK); down-regulation of Bcr/Abl; and a marked reduction in signal transducer and activator of transcription 3 (STAT3) and STAT5 activity. In imatinib mesylate-resistant K562 cells displaying increased Bcr/Abl expression, bortezomib/flavopiridol treatment markedly increased apoptosis in association with down-regulation of Bcr/Abl and BclxL, and diminished phosphorylation of Lyn, Hck, CrkL, and Akt. Parallel studies were performed in imatinib mesylate-resistant LAMA84 cells exhibiting reduced expression of Bcr/Abl but a marked increase in expression/activation of Lyn and Hck. Flavopiridol/bortezomib effectively induced apoptosis in these cells in association with Lyn and Hck inactivation. The capacity of flavopiridol to promote bortezomib-mediated Bcr/Abl down-regulation and apoptosis was mimicked by the positive transcription elongation factor-b (P-TEFb) inhibitor DRB (5,6-dichloro 1-beta-d-ribofuranosylbenzinida-sole). Finally, the bortezomib/flavopiridol regimen also potently induced apoptosis in Bcr/Abl(-) human leukemia cells. Collectively, these findings suggest that a strategy combining flavopiridol and bortezomib warrants further examination in chronic myelogenous leukemia and related hematologic malignancies.