Selective induction of apoptosis by the pyrrolo-1,5-benzoxazepine 7-[[dimethylcarbamoyl]oxy]-6-(2-naphthyl)pyrrolo-[2,1-d] (1,5)-benzoxazepine (PBOX-6) in Leukemia cells occurs via the c-Jun NH2-terminal kinase-dependent phosphorylation and inactivation of Bcl-2 and Bcl-XL

Effects of partial dietary supplementation of fish meal with soymeal on the stress and apoptosis response in the digestive system of common dentex (Dentex dentex)

Background

Soybean is a common alternative protein source of plant origin in aquafeeds as it has a reasonably balanced amino acid profile and is widely available. This study aimed to investigate the influence of partial substitution of fish meal with soy meal on cytoprotective pathways and apoptosis in the digestive system of common dentex (Dentex dentex), using the activation of Hsp70, p38 MAPK, Bcl-2 and caspase-3. The experimental approach involved feeding of common dentex with three isoprotein and isoenergetic diets that contained fish meal as a protein source (FM), partial replacement of fish meal by soy meal 25% (SM25) and 40% (SM40) for 3 months.

Results

The SM40 diet induced Hsp70 activation only in the middle part of intestine. On the other hand, both SM25 and SM40 diets diminished the phosphorylation of p38 MAPK in the anterior and the middle part of intestine, whereas only SM25 induced p38 MAPK phosphorylation in the stomach. Moreover, a decrease in the levels of caspase-3 activity was observed in the middle and posterior intestine, as well as in the stomach after feeding with SM25 diets. Furthermore, Bcl-2 levels were increased by SM40 in the anterior and by SM25 in the middle part of intestine.

Conclusions

SM25 and SM40 diets elicited a tissue and soy concentration specific cellular and cell protective response in the different parts of the digestive tract in common dentex.

Pre-clinical evaluation of a novel class of anti-cancer agents, the Pyrrolo-1, 5-benzoxazepines

Microtubules are currently ranked one of the most validated targets for chemotherapy; with clinical use of microtubule targeting agents (MTAs) extending beyond half a century. Recent research has focused on the development of novel MTAs to combat drug resistance and drug associated toxicities. Of particular interest are compounds structurally different to those currently used within the clinic. The pyrrolo-1, 5-benzoxazepines (PBOXs) are a structurally distinct novel group of anti-cancer agents, some of which target tubulin. Herein, we review the chemistry, mechanism of action, preclinical development of the PBOXs and comparisons with clinically relevant chemotherapeutics. The PBOXs induce a range of cellular responses including; cell cycle arrest, apoptosis, autophagy, anti-vascular and anti-angiogenic effects. The apoptotic potential of the PBOXs extends across a wide spectrum of cancer-derived cell lines, by targeting tubulin and multiple molecular pathways frequently deregulated in human cancers. Extensive experimental data suggest that combining the PBOXs with established chemotherapeutics or radiation is therapeutically advantageous. Pre-clinical highlights of the PBOXs include; cancer specificity and improved therapeutic efficacy as compared to some current first line therapeutics.

The pyrrolo-1,5-benzoxazepine, PBOX-15, enhances TRAIL‑induced apoptosis by upregulation of DR5 and downregulation of core cell survival proteins in acute lymphoblastic leukaemia cells

Apoptotic defects are frequently associated with poor outcome in pediatric acute lymphoblastic leukaemia (ALL) hence there is an ongoing demand for novel strategies that counteract apoptotic resistance. The death ligand TRAIL (tumour necrosis factor-related apoptosis-inducing ligand) and its selective tumour receptor system has attracted exceptional clinical interest. However, many malignancies including ALL are resistant to TRAIL monotherapy. Tumour resistance can be overcome by drug combination therapy. TRAIL and its agonist antibodies are currently undergoing phase II clinical trials with established chemotherapeutics. Herein, we present promising therapeutic benefits in combining TRAIL with the selective anti-leukaemic agents, the pyrrolo-1,5-benzoxazepines (PBOXs) for the treatment of ALL. PBOX-15 synergistically enhanced apoptosis induced by TRAIL and a DR5-selective TRAIL variant in ALL-derived cells. PBOX-15 enhanced TRAIL-induced apoptosis by dual activation of extrinsic and intrinsic apoptotic pathways. The specific caspase-8 inhibitor, Z-IETD-FMK, identified the extrinsic pathway as the principal mode of apoptosis. We demonstrate that PBOX-15 can enhance TRAIL-induced apoptosis by upregulation of DR5, reduction of cellular mitochondrial potential, activation of the caspase cascade and downregulation of PI3K/Akt, c-FLIP, Mcl-1 and IAP survival pathways. Of note, the PI3K pathway inhibitor LY-294002 significantly enhanced the apoptotic potential of TRAIL and PBOX-15 validating the importance of Akt downregulation in the TRAIL/PBOX-15 synergistic combination. Considering the lack of cytotoxicity to normal cells and ability to downregulate several survival pathways, PBOX-15 may represent an effective agent for use in combination with TRAIL for the treatment of ALL.

The novel pyrrolo-1,5-benzoxazepine, PBOX-6, synergistically enhances the apoptotic effects of carboplatin in drug sensitive and multidrug resistant neuroblastoma cells

Neuroblastoma, a malignancy of neuroectoderrmal origin, accounts for 15% of childhood cancer deaths. Despite advances in understanding the biology, it remains one of the most difficult paediatric cancers to treat. A major obstacle in the effective treatment of neuroblastoma is the development of multidrug resistance (MDR). There is thus a compelling demand for new treatment strategies for this cancer that can bypass such resistance mechanisms. The pyrrolo-1,5-benzoxazepine (PBOX) compounds are a series of novel microtubule-targeting agents that potently induce apoptosis in various cancer cell lines, ex vivo patient samples and in vivo cancer models. In this study we examined the ability of two members, PBOX-6 and -15, to exhibit anti-cancer effects in a panel of drug sensitive and MDR neuroblastoma cell lines. The PBOX compounds potently reduced the viability of all neuroblastoma cells examined and exhibited a lower fold resistance in MDR cells when compared to standard chemotherapeutics. In addition, the PBOX compounds synergistically enhanced apoptosis induced by etoposide, carboplatin and doxorubicin. Exposure of drug sensitive and resistant cell lines to PBOX-6/carboplatin induced cleavage of Bcl-2, a downregulation of Mcl-1 and a concomitant increase in Bak. Furthermore, activation of caspase-3, -8 and -9 was demonstrated. Finally, gene silencing of Mcl-1 by siRNA was shown to sensitise both drug sensitive and multidrug resistant cells to carboplatin-induced apoptosis demonstrating the importance of Mcl-1 downregulation in the apoptotic pathway mediated by the PBOX compounds in neuroblastoma. In conclusion, our findings indicate the potential of the PBOX compounds in enhancing chemosensitivity in neuroblastoma.

Inhibition of late-stage autophagy synergistically enhances pyrrolo-1,5-benzoxazepine-6-induced apoptotic cell death in human colon cancer cells

The pyrrolo-1,5-benzoxazepines (PBOXs) are a novel group of selective apoptotic agents displaying promising therapeutic potential in both ex vivo chemotherapy-refractory patient samples and in vivo murine carcinoma models. In this report, we present novel data concerning the induction of autophagy by the PBOXs in adenocarcinoma-derived colon cancer cells. Autophagy is a lysosome-dependent degradative pathway recently associated with chemotherapy. However, whether autophagy facilitates cell survival in response to chemotherapy or contributes to chemotherapy-induced cell death is highly controversial. Autophagy was identified by enhanced expression of LC3B-II, an autophagosome marker, an increase in the formation of acridine orange-stained cells, indicative of increased vesicle formation and electron microscopic confirmation of autophagic structures. The vacuolar H+ ATPase inhibitor bafilomycin-A1 (BAF-A1) inhibited vesicle formation and enhanced the apoptotic potential of PBOX-6. These findings suggest a cytoprotective role of autophagy in these cells following prolonged exposure to PBOX-6. Furthermore, BAF-A1 and PBOX-6 interactions were determined to be synergistic and caspase-dependent. Potentiation of PBOX-6-induced apoptosis by BAF-A1 was associated with a decrease in the levels of the anti-apoptotic protein, Mcl-1. The data provide evidence that autophagy functions as a survival mechanism in colon cancer cells to PBOX-6-induced apoptosis and a rationale for the use of autophagy inhibitors to further enhance PBOX‑6‑induced apoptosis in colon cancer.

PBOX-15, a novel microtubule targeting agent, induces apoptosis, upregulates death receptors, and potentiates TRAIL-mediated apoptosis in multiple myeloma cells

Background:

In recent years, much progress has been made in the treatment of multiple myeloma. However, a major limitation of existing chemotherapeutic drugs is the eventual emergence of resistance; hence, the development of novel agents with new mechanisms of action is pertinent. Here, we describe the activity and mechanism of action of pyrrolo-1,5-benzoxazepine-15 (PBOX-15), a novel microtubule-targeting agent, in multiple myeloma cells.

Methods:

The anti-myeloma activity of PBOX-15 was assessed using NCI-H929, KMS11, RPMI8226, and U266 cell lines, and primary myeloma cells. Cell cycle distribution, apoptosis, cytochrome c release, and mitochondrial inner membrane depolarisation were analysed by flow cytometry; gene expression analysis was carried out using TaqMan Low Density Arrays; and expression of caspase-8 and Bcl-2 family of proteins was assessed by western blot analysis.

Results:

Pyrrolo-1,5-benzoxazepine-15 induced apoptosis in ex vivo myeloma cells and in myeloma cell lines. Death receptor genes were upregulated in both NCI-H929 and U266 cell lines, which displayed the highest and lowest apoptotic responses, respectively, following treatment with PBOX-15. The largest increase was detected for the death receptor 5 (DR5) gene, and cotreatment of both cell lines with tumour necrosis factor-related apoptosis-inducing ligand (TRAIL), the DR5 ligand, potentiated the apoptotic response. In NCI-H929 cells, PBOX-15-induced apoptosis was shown to be caspase-8 dependent, with independent activation of extrinsic and intrinsic apoptotic pathways. A caspase-8-dependent decrease in expression of Bim_EL preceded downregulation of other Bcl-2 proteins (Bid, Bcl-2, Mcl-1) in PBOX-15-treated NCI-H929 cells.

Conclusion:

PBOX-15 induces apoptosis and potentiates TRAIL-induced cell death in multiple myeloma cells. Thus, PBOX-15 represents a promising agent, with a distinct mechanism of action, for the treatment of this malignancy.

Novel pyrrolo-1,5-benzoxazepine compounds display significant activity against resistant chronic myeloid leukaemia cells in vitro, in ex vivo patient samples and in vivo

BACKGROUND

Imatinib is a direct and potent inhibitor of the constitutively active tyrosine kinase, breakpoint cluster region-Abelson (Bcr-Abl), which is central to the pathogenesis of chronic myeloid leukaemia (CML) patients. As such, imatinib has become the front-line treatment for CML patients. However, the recent emergence of imatinib resistance, commonly associated with point mutations within the kinase domain, has led to the search for alternative drug treatments and combination therapies for CML.

METHODS

In this report, we analyse the effects of representative members of the novel pro-apoptotic microtubule depolymerising pyrrolo-1,5-benzoxazepines or PBOX compounds on chemotherapy-refractory CML cells using a series of Bcr-Abl mutant cell lines, clinical ex vivo patient samples and an in vivo mouse model.

RESULTS

The PBOX compounds potently reduce cell viability in cells expressing the E225K and H396P mutants as well as the highly resistant T315I mutant. The PBOX compounds also induce apoptosis in primary CML samples including those resistant to imatinib. We also show for the first time, the in vivo efficacy of the pro-apoptotic PBOX compound, PBOX-6, in a CML mouse model of the T315I Bcr-Abl mutant.

CONCLUSION

Results from this study highlight the potential of these novel series of PBOX compounds as an effective therapy against CML.

Sequential treatment with flavopiridol synergistically enhances pyrrolo-1,5-benzoxazepine-induced apoptosis in human chronic myeloid leukaemia cells including those resistant to imatinib treatment

The Bcr-Abl kinase inhibitor, imatinib mesylate, is the front line treatment for chronic myeloid leukaemia (CML), but the emergence of imatinib resistance has led to the search for alternative drug treatments and the examination of combination therapies to overcome imatinib resistance. The pro-apoptotic PBOX compounds are a recently developed novel series of microtubule targeting agents (MTAs) that depolymerise tubulin. Recent data demonstrating enhanced MTA-induced tumour cell apoptosis upon combination with the cyclin dependent kinase (CDK)-1 inhibitor flavopiridol prompted us to examine whether this compound could similarly enhance the effect of the PBOX compounds. We thus characterised the apoptotic and cell cycle events associated with combination therapy of the PBOX compounds and flavopiridol and results showed a sequence dependent, synergistic enhancement of apoptosis in CML cells including those expressing the imatinib-resistant T315I mutant. Flavopiridol reduced the number of polyploid cells formed in response to PBOX treatment but only to a small extent, suggesting that inhibition of endoreplication was unlikely to play a major role in the mechanism by which flavopiridol synergistically enhanced PBOX-induced apoptosis. The addition of flavopiridol following PBOX-6 treatment did however result in an accelerated exit from the G2/M transition accompanied by an enhanced downregulation and deactivation of the CDK1/cyclin B1 complex and an enhanced degradation of the inhibitor of apoptosis protein (IAP) survivin. In conclusion, results from this study highlight the potential of these novel series of PBOX compounds, alone or in sequential combination with flavopiridol, as an effective therapy against CML.

Ursolic acid overcomes Bcl-2-mediated resistance to apoptosis in prostate cancer cells involving activation of JNK-induced Bcl-2 phosphorylation and degradation

Androgen-independent prostate cancers express high levels of Bcl-2, and this over-expression of Bcl-2 protects prostate cancer cells from undergoing apoptosis. Ursolic acid (UA) has demonstrated an anti-proliferative effect in various tumor types. The aim of this study is to evaluate the difference between UA-induced apoptosis in androgen-dependent prostate cancer cell line LNCaP cells and androgen-independent prostate cancer cell line LNCaP-AI cells and to reveal the molecular mechanisms underlying the apoptosis. We found that UA treatment in vitro can effectively induce apoptosis in LNCaP and LNCaP-AI cells. UA can overcome Bcl-2-mediated resistance to apoptosis in LNCaP-AI cells. Intrinsic apoptotic pathways can be triggered by UA treatment because c-Jun N-terminal kinase (JNK) is activated and subsequently provokes Bcl-2 phosphorylation and degradation, inducing activation of caspase-9. Although further evaluation is clearly needed, the present results suggest the potential utility of UA as a novel therapeutic agent in advanced prostate cancer.

Novel microtubule-targeting agents, pyrrolo-1,5-benzoxazepines, induce apoptosis in multi-drug-resistant cancer cells

PURPOSE

The development of multi-drug resistance (MDR) due to the expression of members of the ATP binding cassette (ABC) transporter family is a major obstacle in cancer treatment. The broad range of substrate specificities associated with these transporters leads to the efflux of many anti-cancer drugs from tumour cells. Therefore, the development of new chemotherapeutic agents that are not substrates of these transporters is important. We have recently demonstrated that some members of a novel series of pyrrolo-1,5-benzoxazepine (PBOX) compounds are microtubule-depolymerising agents that potently induce apoptosis in several cancer cell lines and impair growth of mouse breast tumours. The aim of this current study was to establish whether PBOXs were capable of inducing apoptosis in cancer cells expressing either P-glycoprotein or breast cancer resistance protein (BCRP), two of the main ABC transporters associated with MDR.

METHODS

We performed in vitro studies to assess the effects of PBOXs on cell proliferation, cell cycle and apoptosis in human cancer cell lines and their drug-resistant substrains expressing either P-glycoprotein or BCRP. In addition, we performed a preliminary molecular docking study to examine interactions between PBOXs and P-glycoprotein.

RESULTS

We established that three representative PBOXs, PBOX-6, -15 and -16 were capable of inducing apoptosis in drug-resistant HL60-MDR1 cells (expressing P-glycoprotein) and HL60-ABCG2 cells (expressing BCRP) with similar potencies as in parental human promyelocytic leukaemia HL60 cells. Likewise, resistance to PBOX-6 and -16 was not evident in P-glycoprotein-expressing A2780-ADR cells in comparison with parent human ovarian carcinoma A2780 cells. Finally, we deduced by molecular docking that PBOX-6 is not likely to form favourable interactions with the substrate binding site of P-glycoprotein.

CONCLUSION

Our results suggest that pro-apoptotic PBOX compounds may be potential candidates for the treatment of P-glycoprotein- or BCRP-associated MDR cancers.

The novel tubulin-targeting agent pyrrolo-1,5-benzoxazepine-15 induces apoptosis in poor prognostic subgroups of chronic lymphocytic leukemia

Pyrrolo-1,5-benzoxazepine-15 (PBOX-15) is a novel microtubule depolymerization agent that induces cell cycle arrest and subsequent apoptosis in a number of cancer cell lines. Chronic lymphocytic leukemia (CLL) is characterized by clonal expansion of predominately nonproliferating mature B cells. Here, we present data suggesting PBOX-15 is a potential therapeutic agent for CLL. We show activity of PBOX-15 in samples taken from a cohort of CLL patients (n = 55) representing both high-risk and low-risk disease. PBOX-15 exhibited cytotoxicity in CLL cells (n = 19) in a dose-dependent manner, with mean IC(50) of 0.55 micromol/L. PBOX-15 significantly induced apoptosis in CLL cells (n = 46) including cells with poor prognostic markers: unmutated IgV(H) genes, CD38 and zeta-associated protein 70 (ZAP-70) expression, and fludarabine-resistant cells with chromosomal deletions in 17p. In addition, PBOX-15 was more potent than fludarabine in inducing apoptosis in fludarabine-sensitive cells. Pharmacologic inhibition and small interfering RNA knockdown of caspase-8 significantly inhibited PBOX-15-induced apoptosis. Pharmacologic inhibition of c-jun NH(2)-terminal kinase inhibited PBOX-15-induced apoptosis in mutated IgV(H) and ZAP-70(-) CLL cells but not in unmutated IgV(H) and ZAP-70(+) cells. PBOX-15 exhibited selective cytotoxicity in CLL cells compared with normal hematopoietic cells. Our data suggest that PBOX-15 represents a novel class of agents that are toxic toward both high-risk and low-risk CLL cells. The need for novel treatments is acute in CLL, especially for the subgroup of patients with poor clinical outcome and drug-resistant disease. This study identifies a novel agent with significant clinical potential.

Regulation of Bcl-2 phosphorylation in response to oxidative stress in cardiac myocytes

Oxidative stress promotes cardiac myocyte death and has been implicated in the pathogenesis of many cardiovascular diseases. Bcl-2 family proteins are key regulators of the apoptotic response, while their functions can be regulated by post-transcriptional modifications including phosphorylation, dimerization or proteolytic cleavage. This study used adult cardiac myocytes to test the hypothesis that activation of specific kinase signalling pathways by oxidative stress may modulate either the expression or the phosphorylation of Bcl-2, with the resulting effect of a decrease or increase in its anti-apoptotic function. Stimulation of cardiac myocytes with 0.2 mM H(2)O(2), which induces apoptosis, resulted in a marked down-regulation of Bcl-2 protein simultaneously with an increase in its phosphorylation. Inhibition of p38-MAPK resulted in attenuation of Bcl-2 phosphorylation, whereas inhibition of ERK1/2, JNKs or PI-3-K had no effect. These data suggest that activation of p38 MAPK by oxidative stress results in the phosphorylation and degradation of Bcl-2 and the inactivation of its anti-apoptotic activity.

Transcriptional down-regulation of Bcl-2 by vinorelbine: identification of a novel binding site of p53 on Bcl-2 promoter

The Bcl-2 family contains a panel of proteins which are conserved regulators of apoptosis in mammalian cells, like the anti-apoptotic protein Bcl-2. According to its significant role in altering susceptibility to apoptosis, the deciphering of the mechanism of Bcl-2 expression modulation may be crucial for identifying therapeutics strategies for cancer. Treatment with microtubule-targeting agents, including taxanes and Vinca alkaloids, generally leads to a decrease in Bcl-2 intracellular amounts. Whereas the interest for these chemotherapeutics is accompanied by advances in the fundamental understanding of their anticancer properties, the molecular mechanism underlying changes in Bcl2 expression remains poorly understood. We report here that p53 contributes to vinorelbine-induced Bcl-2 down-regulation. Indeed, the decrease in Bcl-2 protein levels observed during vinorelbine-induced apoptosis was correlated to the decrease in mRNA levels, as a result of the inhibition of Bcl-2 transcription and promoter activity. In this context, we evaluated p53 contribution in the Bcl-2 transcriptional down-regulation. We identified, by chromatin immunoprecipitation, a novel p53 binding site in the Bcl-2 promoter, within a region upstream P(1) promoter. We showed that vinorelbine treatment increased this interaction in A549 cells. This work strengthens the links between p53 and Bcl-2 at a transcriptional level, upon microtubule-targeting agent treatment. Our study also provides answers that will be useful to assess microtubule-targeting agents' mechanism of action and that may help to better understand and increase their effectiveness.

ZD6474 inhibits Src kinase leading to apoptosis of imatinib-resistant K562 cells

ZD6474 is an orally available, small-molecule tyrosine kinase inhibitor. This study explores the effect of ZD6474 on imatinib-resistant K562 cell lines, which show markedly increased SRC family kinases (SFKs) activity. ZD6474 induces growth arrest and apoptosis of imatinib-resistant and parental K562 cells, as well as inhibition of Src activity and its downstream effectors, the anti-apoptotic Bcl-2 family. ZD6474 treatment also inhibits the activity of STAT3 and reactivation of its activity results in suppression of the anti-tumor effects of SFKs inhibitors. A single oral administration of ZD6474 produced dose-dependent inhibition of imatinib-resistant K562 cells xenograft tumors. These results suggest that clinical assessment of ZD6474 against imatinib-resistant CML is warranted.

BubR1 is required for a sustained mitotic spindle checkpoint arrest in human cancer cells treated with tubulin-targeting pyrrolo-1,5-benzoxazepines

Intrinsic or acquired resistance to chemotherapy is a major clinical problem that has evoked the need to develop innovative approaches to predict and ultimately reverse drug resistance. A prolonged G(2)M arrest has been associated with apoptotic resistance to various microtubule-targeting agents (MTAs). In this study, we describe the functional significance of the mitotic spindle checkpoint proteins, BubR1 and Bub3, in maintaining a mitotic arrest after microtubule disruption by nocodazole and a novel series of MTAs, the pyrrolo-1,5-benzoxazepines (PBOXs), in human cancer cells. Cells expressing high levels of BubR1 and Bub3 (K562, MDA-MB-231, and HeLa) display a prolonged G(2)M arrest after exposure to MTAs. On the other hand, cells with low endogenous levels of mitotic spindle checkpoint proteins (SK-BR-3 and HL-60) transiently arrest in mitosis and undergo increased apoptosis. The phosphorylation of BubR1 correlated with PBOX-induced G(2)M arrest in four cell lines tested, indicating an active mitotic spindle checkpoint. Gene silencing of BubR1 by small interfering RNA interference reduced PBOX-induced G(2)M arrest without enhancing apoptotic efficacy. Further analysis demonstrated that PBOX-treated BubR1-depleted cells were both mononucleated and multinucleated with a polyploid DNA content, suggesting a requirement for BubR1 in cytokinesis. Taken together, these results suggest that BubR1 contributes to the mitotic checkpoint induced by the PBOXs.

STI-571 (imatinib mesylate) enhances the apoptotic efficacy of pyrrolo-1,5-benzoxazepine-6, a novel microtubule-targeting agent, in both STI-571-sensitive and -resistant Bcr-Abl-positive human chronic myeloid leukemia cells

Interactions between the Bcr-Abl kinase inhibitor STI-571 (imatinib mesylate) and a novel microtubule-targeting agent (MTA), pyrrolo-1,5-benzoxazepine (PBOX)-6, were investigated in STI-571-sensitive and -resistant human chronic myeloid leukemia (CML) cells. Cotreatment of PBOX-6 with STI-571 induced significantly more apoptosis in Bcr-Abl-positive CML cell lines (K562 and LAMA-84) than either drug alone (P < 0.01). Cell cycle analysis of propidium iodide-stained cells showed that STI-571 significantly reduced PBOX-6-induced G2M arrest and polyploid formation with a concomitant increase in apoptosis. Similar results were obtained in K562 CML cells using lead MTAs (paclitaxel and nocodazole) in combination with STI-571. Potentiation of PBOX-6-induced apoptosis by STI-571 was specific to Bcr-Abl-positive leukemia cells with no cytoxic effects observed on normal peripheral blood cells. The combined treatment of STI-571 and PBOX-6 was associated with the down-regulation of Bcr-Abl and repression of proteins involved in Bcr-Abl transformation, namely the antiapoptotic proteins Bcl-x(L) and Mcl-1. Importantly, PBOX-6/STI-571 combinations were also effective in STI-571-resistant cells. Together, these findings highlight the potential clinical benefits in simultaneously targeting the microtubules and the Bcr-Abl oncoprotein in STI-571-sensitive and -resistant CML cells.

Caspase-activated DNase (CAD)-independent oligonucleosomal DNA fragmentation in chronic myeloid leukaemia cells; a requirement for serine protease and Mn2+-dependent acidic endonuclease activity

We have previously reported that the pro-apoptotic pyrrolobenzoxazepine, PBOX-6, induces apoptosis in chronic myelogenous leukaemia (CML) cells which is accompanied by oligonucleosomal DNA fragmentation. In this study we show that PBOX-6-induced oligonucleosomal DNA fragmentation occurs in the absence of caspase and CAD activation in CML cells. Dissection of the signalling pathway has revealed that induction of apoptosis requires the upstream activation of a trypsin-like serine protease that promotes the phosphorylation and inactivation of anti-apoptotic Bcl-2. In addition, in this system chymotrypsin-like serine proteases are dispensable for high molecular weight DNA fragmentation, however are required for the activation of a relatively small manganese-dependent acidic endonuclease that is responsible for oligonucleosomal fragmentation of DNA. Furthermore, we demonstrate mitochondrial involvement during PBOX-6-induced apoptosis and suggest the existence of unidentified mitochondrial effectors of apoptosis.

Thymosin alpha1 suppresses proliferation and induces apoptosis in human leukemia cell lines

Thymosin alpha1 (Talpha1), a 28-amino acid peptide, is a well-known immune system enhancer for the treatment of various diseases. In the present investigation, the effects of Talpha1 on the proliferation and apoptosis of human leukemia cell lines (HL-60, K562 and K562/ADM) were studied. The proliferation was significantly depressed after 96 h of treatment with Talpha1, and obvious signs of apoptosis, i.e., cell morphology, nuclei condensation and Annexin V binding, were observed thereafter. Moreover, the up-regulation of Fas/Apol (CD95) and decrease in bcl-2 anti-apoptotic gene expression were observed in apoptotic cells. The expression and the function of P-glycoprotein (P-gp) can be slightly inhibited by Talpha1. It is noteworthy that K562 and K562/ADM were more sensitive than HL-60 cells when subjected to Talpha1. Furthermore, HepG-2, the human hepatoma cell line, displayed significant less sensitivity to Talpha1 than all the human leukemia cell lines. D-Tubocurarine (TUB), a nicotinic acetylcholine receptors (nAChRs) antagonist, significantly antagonized the inhibition effects induced by Talpha1, whereas atropine, a muscarinic acetylcholine receptor antagonist, did not exhibit such effects. All the results indicate that Talpha1 was able to significantly suppress proliferation and induce apoptosis in human leukemia cell lines.

Identification of tubulin as the molecular target of proapoptotic pyrrolo-1,5-benzoxazepines

We have demonstrated previously that certain members of a series of novel pyrrolo-1,5-benzoxazepine (PBOX) compounds potently induce apoptosis in a variety of human chemotherapy-resistant cancer cell lines and in primary ex vivo material derived from cancer patients. A better understanding of the molecular mechanisms underlying the apoptotic effects of these PBOX compounds is essential to their development as antineoplastic therapeutic agents. This study sought to test the hypothesis that proapoptotic PBOX compounds target the microtubules. We show that a representative proapoptotic PBOX compound, PBOX-6, induces apoptosis in both the MCF-7 and K562 cell lines. An accumulation of cells in G2/M precedes apoptosis in response to PBOX-6. PBOX-6 induces prometaphase arrest and causes an accumulation of cyclin B1 levels and activation of cyclin B1/CDK1 kinase in a manner similar to that of two representative antimicrotubule agents, nocodazole and paclitaxel. Indirect immunofluorescence demonstrates that both PBOX-6 and another pro-apoptotic PBOX compound, PBOX-15, cause microtubule depolymerization in MCF-7 cells. They also inhibit the assembly of purified tubulin in vitro, whereas a nonapoptotic PBOX compound (PBOX-21) has no effect on either the cellular microtubule network or on the assembly of purified tubulin. This suggests that the molecular target of the pro-apoptotic PBOX compounds is tubulin. PBOX-6 does not bind to either the vinblastine or the colchicine binding site on tubulin, suggesting that it binds to an as-yet-uncharacterised novel site on tubulin. The ability of PBOX-6 to bind tubulin and cause microtubule depolymerization confirms it as a novel candidate for antineoplastic therapy.