Apoptotic response to homoharringtonine in human wt p53 leukemic cells is independent of reactive oxygen species generation and implicates Bax translocation, mitochondrial cytochrome c release and caspase activation

Bortezomib exerts its anti-cancer activity through the regulation of Skp2/p53 axis in non-melanoma skin cancer cells and C. elegans

Non-melanoma skin cancer (NMSC), encompassing basal and squamous cell carcinoma, is the most prevalent cancer in the United States. While surgical removal remains the conventional therapy with a 95% 5-year cure rate, there is a growing interest in exploring alternative treatment strategies. In this study, we investigated the role of Bortezomib (BTZ), a proteasome inhibitor, in NMSC. Using two NMSC cell lines (A431 and A388), we examined the effects of BTZ treatment. Our results demonstrated that 48 h of BTZ treatment led to downregulating Skp2 expression in both A431 and A388 cells while upregulating p53 expression, specifically in A388 cells. These alterations resulted in impaired cellular growth and caspase-dependent cell death. Silencing Skp2 in A388 cells with siRNA confirmed the upregulation of p53 as a direct target. Furthermore, BTZ treatment increased the Bax to Bcl-2 ratio, promoting mitochondrial permeability and the subsequent release of cytochrome C, thereby activating caspases. We also found that BTZ exerted its antitumor effects by generating reactive oxygen species (ROS), as blocking ROS production significantly reduced BTZ-induced apoptotic cell death. Interestingly, BTZ treatment induced autophagy, which is evident from the increased expression of microtubule-associated proteins nucleoporin p62 and LC-3A/B. In addition to cell lines, we assessed the impact of BTZ in an in vivo setting using Caenorhabditis elegans (C. elegans). Our findings demonstrated that BTZ induced germline apoptosis in worms even at low concentrations. Notably, this increased apoptosis was mediated through the activity of CEP-1, the worm's counterpart to mammalian p53. In summary, our study elucidated the molecular mechanism underlying BTZ-induced apoptosis in NMSC cell lines and C. elegans. By targeting the skp2/p53 axis, inducing mitochondrial permeability, generating ROS, and promoting autophagy, BTZ demonstrates promising anti-cancer activity in NMSC. These findings provide novel insights into potential therapeutic strategies for controlling the unregulated growth of NMSC.

Deleterious effect of bone marrow-resident macrophages on hematopoietic stem cells in response to total body irradiation

Bone marrow resident macrophages interact with a population of long-term hematopoietic stem cell (LT-HSC) but their role on LT-HSC properties after stress is not well defined. Here, we show that a 2 Gy total body irradiation (TBI)-mediated death of LT-HSC is associated with increased percentages of LT-HSC with reactive oxygen species (ROS) and of bone marrow resident macrophages producing nitric oxide (NO), resulting in an increased percentage of LT-HSC with endogenous cytotoxic peroxynitrites. Pharmacological or genetic depletion of bone marrow resident macrophages impairs the radio-induced increases in the percentage of both ROS+ LT-HSC and peroxynitrite+ LT-HSC and results in a complete recovery of a functional pool of LT-HSC. Finally, we show that after a 2 Gy-TBI, a specific decrease of NO production by bone marrow resident macrophages improves the LT-HSC recovery, whereas an exogenous NO delivery decreases the LT-HSC compartment. Altogether, these results show that bone marrow resident macrophages are involved in the response of LT-HSC to a 2 Gy-TBI and suggest that regulation of NO production can be used to modulate some deleterious effects of a TBI on LT-HSC.

Sanguinarine mediated apoptosis in Non-Small Cell Lung Cancer via generation of reactive oxygen species and suppression of JAK/STAT pathway

Effective treatment of lung cancer remains a significant clinical challenge due to its multidrug resistance and side effects of the current treatment options. The high mortality associated with this malignancy indicates the need for new therapeutic interventions with fewer side effects. Natural compounds offer various benefits such as easy access, minimal side effects, and multi-molecular targets and thus, can prove useful in treating lung cancer. Sanguinarine (SNG), a natural compound, possesses favorable therapeutic potential against a variety of cancers. Here, we examined the underlying molecular mechanisms of SNG in Non-Small Cell Lung Cancer (NSCLC) cells. SNG suppressed cell growth and induced apoptosis via downregulation of the constitutively active JAK/STAT pathway in all the NSCLC cell lines. siRNA silencing of STAT3 in NSCLC cells further confirmed the involvement of the JAK/STAT signaling cascade. SNG treatment increased Bax/Bcl-2 ratio, which contributed to a leaky mitochondrial membrane leading to cytochrome c release accompanied by caspase activation. In addition, we established the antitumor effects of SNG through reactive oxygen species (ROS) production, as inhibiting ROS production prevented the apoptosis-inducing potential of SNG. In vivo xenograft tumor model further validated our in vitro findings. Overall, our study investigated the molecular mechanisms by which SNG induces apoptosis in NSCLC, providing avenues for developing novel natural compound-based cancer therapies.

CPEB3 regulates the proliferation and apoptosis of bovine cumulus cells

Cytoplasmic polyadenylation element-binding protein 3 (CPEB3) is a member of the Cytoplasmic polyadenylation element-binding family, which has been found to regulate the translation of dormant and masked mRNA in Xenopus oocytes and plays potential roles in regulating biological functions in cells and tissues. However, its role in cumulus cells is not clear. In this study, the mRNA expression of CPEB3 in bovine cumulus cells was inhibited with small interfering RNA. Cell cycle progression, proliferation, and apoptosis were measured after inhibition of CPEB3. Subsequently, changes in intracellular Reactive oxygen species content, mitochondrial membrane potential and expansion-related gene expression were examined. The results showed that after CPEB3 inhibition, cumulus cells had an abnormal cell cycle, the numbers of cells in the S and G2/M phases were significantly increased, cell proliferation was increased and apoptosis rates were decreased. These effects were likely due CPEB3 inhibition-induced decreases in intracellular Reactive oxygen species levels; increases in mitochondrial membrane potential; decreases in apoptosis; downregulation of CCNA, CCND, CCNE, CDK2, CDK4, CDK6, p21, and p27 mRNA expression; and upregulation of CCNB, CDK1, HAS2, PTGS2, PTX3, and CEBPB mRNA expression. Therefore, CPEB3 plays potential roles in regulating the biological and physiological functions of bovine cumulus cell.

Apoptotic and cell cycle response to homoharringtonine and harringtonine in wild and mutant p53 hepatocarcinoma cells

This study aimed to evaluate the modes of action of harringtonine (HT) and homoharringtonine (HHT) alkaloids in cell with wild (HepG2/C3A) and mutant p53 (HuH-7.5). We performed assays for cytotoxicity, genotoxicity, induction of apoptosis, cell cycle phase, and membrane integrity. Obtained data were compared with the relative expression of mRNA of genes related to proliferation, apoptosis, cell cycle control, metabolism of xenobiotics, and reticulum endoplasmic stress. The relative expression of the genes showed an increase in apoptosis-inducing mRNAs, such as TNF and BBC3, as well as a reduction in BCL2 and BAK. The mRNAs of CYP2E1 and CYP2C19 xenobiotic metabolism genes increased in both lineages, while CYP3A4 increased only in the HuH-7.5 lineage. The mRNA expression of endoplasmic reticulum (ER) stress genes (ERN1 and EIF2AK3) was shown to increase in HHT and HT treatments. A similar increase was recorded in the mRNA expression of the TRAF2 gene. The changes observed in this study support the hypothesis that ER stress was more strongly associated with TNF induction, causing cell death by apoptosis in p53 mutant cells. This result with wild and mutant p53 cells may have clinical implications in the use of these compounds.

Greensporone A, a Fungal Secondary Metabolite Suppressed Constitutively Activated AKT via ROS Generation and Induced Apoptosis in Leukemic Cell Lines

Greensporone A is a fungal secondary metabolite that has exhibited potential in vitro for anti-proliferative activity in vitro. We studied the anticancer activity of greensporone A in a panel of leukemic cell lines. Greensporone A-mediated inhibition of proliferation is found to be associated with the induction of apoptotic cell death. Greensporone A treatment of leukemic cells causes inactivation of constitutively activated AKT and its downstream targets, including members GSK3 and FOXO1, and causes downregulation of antiapoptotic genes such as Inhibitor of Apoptosis (IAPs) and Bcl-2. Furthermore, Bax, a proapoptotic member of the Bcl-2 family, was found to be upregulated in leukemic cell lines treated with greensporone A. Interestingly, gene silencing of AKT using AKT specific siRNA suppressed the expression of Bcl-2 with enhanced expression of Bax. Greensporone A-mediated increase in Bax/Bcl-2 ratio causes permeabilization of the mitochondrial membrane leading to the accumulation of cytochrome c in the cytoplasm. Greensporone A-induced cytochrome c accumulation causes the activation of caspase cascade and cleavage of its effector, poly(ADP-ribose) polymerase (PARP), leading to apoptosis. Greensporone A-mediated apoptosis in leukemic cells occurs through the generation of reactive oxygen species (ROS) due to depletion of glutathione (GSH) levels. Finally, greensporone A potentiated the anticancer activity of imatinib in leukemic cells. In summary, our study showed that greensporone A suppressed the growth of leukemic cells via induction of apoptotic cell death. The apoptotic cell death occurs by inhibition of AKT signaling and activation of the intrinsic apoptotic/caspase pathways. These results raise the possibility that greensporone A could be developed as a therapeutic agent for the treatment of leukemia and other hematological malignancies.

Complexation with C60 Fullerene Increases Doxorubicin Efficiency against Leukemic Cells In Vitro

Conventional anticancer chemotherapy is limited because of severe side effects as well as a quickly evolving multidrug resistance of the tumor cells. To address this problem, we have explored a C₆₀ fullerene-based nanosized system as a carrier for anticancer drugs for an optimized drug delivery to leukemic cells.Here, we studied the physicochemical properties and anticancer activity of C₆₀ fullerene noncovalent complexes with the commonly used anticancer drug doxorubicin. C₆₀-Doxorubicin complexes in a ratio 1:1 and 2:1 were characterized with UV/Vis spectrometry, dynamic light scattering, and high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The obtained analytical data indicated that the 140-nm complexes were stable and could be used for biological applications. In leukemic cell lines (CCRF-CEM, Jurkat, THP1 and Molt-16), the nanocomplexes revealed ≤ 3.5 higher cytotoxic potential in comparison with the free drug in a range of nanomolar concentrations. Also, the intracellular drug's level evidenced C₆₀ fullerene considerable nanocarrier function.The results of this study indicated that C₆₀ fullerene-based delivery nanocomplexes had a potential value for optimization of doxorubicin efficiency against leukemic cells.

Synergistic cytotoxicity of homoharringtonine and etoposide in acute myeloid leukemia cells involves disrupted antioxidant defense

Background/Aims

Cytotoxicity induced by reactive oxygen species (ROS) is critical for the effectiveness of chemotherapeutic drugs used in the treatment of acute myeloid leukemia (AML). This study aimed to investigate whether ROS contributes to cytotoxicity in AML cells when treated with homoharringtonine (HHT) and etoposide (ETP) in combination.

Methods

AML cell lines THP1 and HL60 and primary AML cells from patients were treated with HHT and ETP alone or in combination, and cell viability was determined by trypan blue exclusion test, and apoptosis was analyzed by annexin-V/propidium iodide double staining as well as Western blot for measuring expression of cleaved caspase-9 and cleaved caspase-3. Intracellular ROS level was detected by DCFH-DA fluorescence assay, and N-Acetyl-L-cysteine (NAC) was used to scavenge intracellular ROS. Retroviral infection was applied to mediate stable overexpression in AML cells.

Results

We show that HHT and ETP exhibit synergistic cytotoxicity in AML cell lines and primary AML cells in vitro, and meanwhile, HHT causes elevated ROS generation in ETP-treated AML cells. We next reveal that the elevated ROS is a critical factor for the synergistic cytotoxicity, since ROS scavenge by NAC remarkably diminishes this effect. Mechanistically, we demonstrate that HHT causes elevated ROS generation by disabling thioredoxin-mediated antioxidant defense. Finally, similar to HHT treatment, depletion of thioredoxin sensitizes AML to ETP treatment.

Conclusion

These results provide the foundation for augmenting the efficacy of ETP in treating AML with HHT, and also highlight the importance of targeting ROS in improving treatment outcome in AML.

Greensporone C, a Freshwater Fungal Secondary Metabolite Induces Mitochondrial-Mediated Apoptotic Cell Death in Leukemic Cell Lines

Therapeutic agents used in the treatment of cancer are known to develop resistance against cancer cells. Hence, there is a continuing need to investigate novel agents for the treatment and management of cancer. Antitumor activity of greensporone C (GC), a new resorcylic acid lactone isolated from an organic extract of a culture of a Halenospora sp. freshwater fungus, was subjected for screening against a panel of leukemic cell lines (K562, U937, and AR320). In all the three cell lines, cell proliferation was inhibited in dose-dependent fashion. GC further arrested the cells in SubG0 phase in dose-dependent manner. Annexin V/PI dual staining data confirmed apoptotic death of treated K562 and U937 leukemic cells. Treatment with GC suppressed constitutively phosphorylated AKT and downregulated expression of inhibitor of apoptotic proteins XIAP, cIAP-1, and cIAP-2. In summation to this, GC-treated leukemic cells upregulated protein expression of pro-apoptotic proteins, Bax with concomitant decrease in expression of anti-apoptotic proteins including Bcl-2 and Bcl-xL. Upregulation of Bax was associated with cytochrome c release which was confirmed from the collapse of mitochondrial membrane. Released cytochrome c further activated caspase cascade which in turn initiated apoptosis process. Anticancer activity of this isolated fungal compound GC was potentiated via stimulating production of reactive oxygen species (ROS) along with depletion of reduced glutathione (GSH) levels in K562 and U937 leukemic cells. Pretreatment of these cells with N-acetyl cysteine prevented GC-induced depletion of reduced GSH level and mitochondrial-caspase-induced apoptosis. Altogether, our data show that GC modulates the apoptotic response of human leukemic cells and raises the possibility of its use as a novel therapeutic strategy for hematological malignancies.

Inhibition of Proliferation in U937 Cells Treated by Blue Light Irradiation and Combined Blue Light Irradiation/Drug

The cell viability and apoptosis of tumor U937 cells treated by blue light (BL) irradiation have been examined. BL irradiation can specially inhibit the proliferation and promote the apoptosis of U937 cells, relating to the production of reactive oxygen species (ROS) and the decline of mitochondrial membrane potential (ΔΨm). The apoptosis is further associated with varying downregulated B-cell lymphoma-extra large (Bcl-X_L) and B-cell lymphoma 2 (Bcl-2) genes, upregulated Bcl-2-associated X (Bax) gene, the activation of caspase-3 and caspase-9, and the cleavage of poly (ADP-ribose) polymerase (PARP) by the BL irradiation process. Moreover, BL irradiation induced proliferation inhibition is higher than that treated by a common chemotherapeutic drug of homoharringtonine (HHT). When we synergize BL irradiation with HHT (BL-HHT), a higher proliferation inhibition is obtained than that treated by BL irradiation or HHT alone. These results are helpful for establishing a low toxicity and high efficiency strategy of BL irradiation for clinical treatment of acute myeloid leukemia, not limited to U937 cells.

Effects of 1,3,5-triphenyl-4,5-dihydro-1H-pyrazole derivatives on cell-cycle and apoptosis in human acute leukemia cell lines

Pyrazoline is an important 5-membered nitrogen heterocycle that has been extensively researched. Ten derivatives were synthesized and tested for antileukemic effects on 2 human acute leukemia cell lines, K562 and Jurkat. The most cytotoxic of these derivatives, compound 21, was chosen for investigation of cytotoxicity mechanisms. The results obtained with selectivity calculations revealed that compound 21 is more selective for acute leukemia (K562 and Jurkat cell lines) than for other tumor cell lines. Moreover, compound 21 was not cytotoxic to normal cell lines, indicating a potential use in clinical tests. Compound 21 caused a significant cell cycle arrest in the S-phase in Jurkat cells and increased the proportion of cells in the sub G0/G1 phase in both cell lines. Cells treated with compound 21 demonstrated morphological changes characteristic of apoptosis in the EB/AO assay, confirmed by externalization of phosphatidylserine by the annexin V – fluorescein isothiocyanate method and by DNA fragmentation. An investigation of cytotoxicity mechanisms suggests the involvement of an intrinsic apoptosis pathway due to mitochondrial damage and an increase in the ratio of mitochondrial Bax/Bcl2. Pyrazoline 21 obeyed Lipinski’s “rule of five” for drug-likeness. Based on these preliminary results, the antileukemic activity of compound 21 makes it a potential anticancer agent.

Pharmacokinetics and excretion of (14)C-omacetaxine in patients with advanced solid tumors

Background Omacetaxine mepesuccinate is indicated in adults with chronic myeloid leukemia resistant and/or intolerant to ≥ 2 tyrosine kinase inhibitor treatments. This phase I study assessed the disposition, elimination, and safety of (14)C-omacetaxine in patients with solid tumors. Methods The study comprised a 7-days pharmacokinetic assessment followed by a treatment period of ≤ six 28-days cycles. A single subcutaneous dose of 1.25 mg/m(2) (14)C-omacetaxine was administered to six patients. Blood, urine, and feces were collected through 168 h or until radioactivity excreted within 24 h was <1 % of the dose. Total radioactivity (TRA) was measured in all matrices and concentrations of omacetaxine, 4'-desmethylhomoharringtonine (4'-DMHHT), and cephalotaxine were measured in plasma and urine. For each treatment cycle, patients received 1.25 mg/m(2) omacetaxine twice daily for 7 days. Results Mean TRA recovered was approximately 81 % of the dose, with approximately half of the radioactivity recovered in feces and half in urine. Approximately 20 % of the dose was excreted unchanged in urine; cephalotaxine (0.4 % of dose) and 4' DMHHT (9 %) were also present. Plasma concentrations of TRA were higher than the sum of omacetaxine and known metabolites, suggesting the presence of other (14)C-omacetaxine-derived compounds. Fatigue and anemia were common, consistent with the known toxicity profile of omacetaxine. Conclusion Renal and hepatic processes contribute to the elimination of (14)C-omacetaxine-derived radioactivity in cancer patients. In addition to omacetaxine and its known metabolites, other (14)C-omacetaxine-derived materials appear to be present in plasma and urine. Omacetaxine was adequately tolerated, with no new safety signals.

Evidence for microRNA-31 dependent Bim-Bax interaction preceding mitochondrial Bax translocation during radiation-induced apoptosis

Downregulation of microRNA-31 has been linked with enhanced stress resistance, while its overexpression leads to cell death. In this study, we found mediatory role of microRNA-31 in γ-radiation-induced apoptosis in a model insect cell line Sf9 carrying well-conserved apoptotic machinery. Mature microRNA-31 is perfectly conserved amongst insects; hence we used biotinylated probes designed from Bombyx mori sequence for its successful detection in Sf9 cells. Target identification using Bombyx mori 3′UTRs predicted miR-31′s potential role in Lepidopteran apoptosis, which prompted us to investigate alterations in its expression during radiation-induced cell death. We found significant overexpression of Sf-miR-31 following lethal dose (1,000Gy–3,000Gy) irradiation. Its mediatory role was finally confirmed as antisense-microRNA-31 could successfully inhibit radiation-induced cytochrome-c release, caspase-3 activation and apoptosis. While Bax/Bcl-2 expression remained unchanged, lethal radiation doses induced Bim overexpression and direct Bim-Bax interaction (co-immunoprecipitation) which is not yet unequivocally demonstrated during apoptosis. Quite important, these events were found to be dependent on radiation-induced miR-31 overexpression, as antisense-miR-31 inhibited both the responses and resulted in significant inhibition of cell death. Pro-apoptotic role of miR-31 was further confirmed when miR-31 mimic induced apoptosis involving similar Bim/Bax alterations. Therefore, our study reveals an important mediatory role of miR-31 in radiation-induced cell death.

Sulfonoquinovosyl diacylglyceride selectively targets acute lymphoblastic leukemia cells and exerts potent anti-leukemic effects in vivo

DNA topoisomerase II inhibitors e.g. doxorubicin and etoposide are currently used in the chemotherapy for acute lymphoblastic leukemia (ALL). These inhibitors have serious side effects during the chemotherapy e.g. cardiotoxicity and secondary malignancies. In this study we show that sulfonoquinovosyl diacylglyceride (SQDG) isolated from Azadirachta indica exerts potent anti-ALL activity both in vitro and in vivo in nude mice and it synergizes with doxorubicin and etoposide. SQDG selectively targets ALL MOLT-4 cells by inhibiting catalytic activity of topoisomerase I enzyme and inducing p53 dependent apoptotic pathway. SQDG treatment induces recruitment of ATR at chromatin and arrests the cells in S-phase. Down-regulation of topoisomerase I or p53 renders the cells less sensitive for SQDG, while ectopic expression of wild type p53 protein in p53 deficient K562 cells results in chemosensitization of the cells for SQDG. We also show that constant ratio combinations of SQDG and etoposide or SDQG and doxorubicin exert synergistic effects on MOLT-4 cell killing. This study suggests that doses of etoposide/doxorubicin can be substantially reduced by combining SQDG with these agents during ALL chemotherapy and side effects caused can be minimized. Thus dual targeting of topoisomerase I and II enzymes is a promising strategy for improving ALL chemotherapy.

Differential effects of polyphenols on proliferation and apoptosis in human myeloid and lymphoid leukemia cell lines

BACKGROUND

Mortality rates for leukemia are high despite considerable improvements in treatment. Since polyphenols exert pro-apoptotic effects in solid tumors, our study investigated the effects of polyphenols in haematological malignancies. The effect of eight polyphenols (quercetin, chrysin, apigenin, emodin, aloe-emodin, rhein, cis-stilbene and trans-stilbene) were studied on cell proliferation, cell cycle and apoptosis in four lymphoid and four myeloid leukemic cells lines, together with normal haematopoietic control cells.

METHODS

Cellular proliferation was measured by CellTiter-Glo(®) luminescent assay; and cell cycle arrest was assessed using flow cytometry of propidium iodide stained cells. Apoptosis was investigated by caspase-3 activity assay using flow cytometry and apoptotic morphology was confirmed by Hoescht 33342 staining.

RESULTS

Emodin, quercetin, and cis-stilbene were the most effective polyphenols at decreasing cell viability (IC50 values of 5-22 μM, 8-33 μM, and 25-85 μM respectively) and inducing apoptosis (AP50 values (the concentration which 50% of cells undergo apoptosis) of 2-27 μM, 19-50 μM, and 8-50 μM respectively). Generally, lymphoid cell lines were more sensitive to polyphenol treatment compared to myeloid cell lines, however the most resistant myeloid (KG-1a and K562) cell lines were still found to respond to emodin and quercetin treatment at low micromolar levels. Non-tumor cells were less sensitive to all polyphenols compared to the leukemia cells.

CONCLUSIONS

These findings suggest that polyphenols have anti-tumor activity against leukemia cells with differential effects. Importantly, the differential sensitivity of emodin, quercetin, and cis-stilbene between leukemia and normal cells suggests that polyphenols are potential therapeutic agents for leukemia.

Pharmacokinetic study of omacetaxine mepesuccinate administered subcutaneously to patients with advanced solid and hematologic tumors

PURPOSE

Omacetaxine mepesuccinate is a first-in-class cephalotaxine demonstrating clinical activity in chronic myeloid leukemia. A subcutaneous (SC) formulation demonstrated efficacy and safety in phase 1/2 trials in patients previously treated with ≥1 tyrosine kinase inhibitor. This study assessed pharmacokinetics and safety of SC omacetaxine in patients with advanced cancers.

METHODS

Omacetaxine 1.25 mg/m(2) SC was administered BID, days 1-14 every 28 days for 2 cycles, until disease progression or unacceptable toxicity. Blood and urine were collected to measure omacetaxine concentrations and inactive metabolites. Adverse events, including QT interval prolongation, were recorded. Tumor response was assessed at cycle 2 completion.

RESULTS

Pharmacokinetic parameters were estimated from cycle 1, day 1 data in 21 patients with solid tumors or hematologic malignancies and cycle 1, day 11 data in 10 patients. Omacetaxine was rapidly absorbed, with mean peak plasma concentrations observed within 1 h, and widely distributed, as evidenced by an apparent volume of distribution of 126.8 L/m(2). Plasma concentration versus time data demonstrated biexponential decay; mean steady-state terminal half-life was 7 h. Concentrations of inactive metabolites 4'-DMHHT and cephalotaxine were approximately 10 % of omacetaxine and undetectable in most patients, respectively. Urinary excretion of unchanged omacetaxine accounted for <15 % of the dose. Grade 3/4 drug-related adverse events included thrombocytopenia (48 %) and neutropenia (33 %). Two grade 2 increases in QTc interval (>470 ms) were observed and were not correlated with omacetaxine plasma concentration. No objective responses were observed.

CONCLUSIONS

Omacetaxine is well absorbed after SC administration. Therapeutic plasma concentrations were achieved with 1.25 mg/m(2) BID, supporting clinical development of this dose and schedule.

Homoharringtonine-Induced Apoptosis of Human Leukemia HL-60 Cells is Associated with Down-Regulation of Telomerase

Homoharringtonine (HHT), first isolated from the Chinese evergreen Cephalotaxus Harringtonia, has been shown inhibiting activity in leukemia in initial studies in China and in later studies in the US, but the detailed mechanism of action is still unclear. The goal of the experiments shown here is to explore the effect of HHT on the telomerase activity and apoptosis of human leukemia HL-60 cells. The telomerase activity of HL-60 cells was examined by the telomeric repeat amplification protocol (TRAP) — an enzyme-linked immunosorbent assay (ELISA). Apoptosis was analyzed by morphological observation, DNA agarose gel electrophoresis, flow cytometry (FCM), and TdT-mediated dUTP-biotin nick end labeling (TUNEL). After treatment with HHT at 5–500 μg/l for 48 hours, the level of telomerase activity in HL-60 cells decreased in a dose-and time-dependent manner. Simultaneously, HL-60 cells underwent apoptosis. In conclusion, our data suggest that HHT can inhibit the telomerase content of HL-60 cells effectively and induce apoptosis.

The antitumor activity of homoharringtonine against human mast cells harboring the KIT D816V mutation

Gain-of-function mutations of the receptor tyrosine kinase KIT play a critical role in the pathogenesis of systemic mastocytosis (SM) and gastrointestinal stromal tumors. The various juxtamembrane type of KIT mutations, including V560G, are found in 60% to 70% of patients with gastrointestinal stromal tumors; loop mutant D816V, which exists in approximately 80% of SM patients, is completely resistant to imatinib. In the present study, we hypothesized that homoharringtonine (HHT), a protein synthesis inhibitor, would decrease the level of KIT protein by inhibiting translation, resulting in a decreased level of phospho-KIT and abrogating its constitutive downstream signaling. Imatinib-sensitive HMC-1.1 cells harboring the mutation V560G in the juxtamembrane domain of KIT, imatinib-resistant HMC-1.2 cells harboring both V560G and D816V mutations, and murine P815 cells were treated with HHT and analyzed in terms of growth, apoptosis, and signal transduction. The in vivo antitumor activity was evaluated by using the murine mast cell leukemia model. Our results indicated that HHT effectively inhibited the growth and induced apoptosis in cells bearing both V560G and D816V or D814Y KIT. Additionally, HHT inhibited the KIT-dependent phosphorylation of downstream signaling molecules Akt, signal transducer and activator of transcription 3 and 5, and extracellular signal-regulated kinase 1/2. Furthermore, HHT significantly prolonged the survival duration of mice with aggressive SM or mast cell leukemia by inhibiting the expansion and infiltration of imatinib-resistant mast tumor cells harboring imatinib-resistant D814Y KIT. Collectively, we show that HHT circumvents D816V KIT-elicited imatinib resistance. Our findings warrant a clinical trial of HHT in patients with SM harboring D816V or D814Y KIT.

Homoharringtonine induces apoptosis and growth arrest in human myeloma cells

Homoharringtonine (HHT) is a plant alkaloid with antileukemic activity which is currently being used for treatment of acute and chronic leukemias. The present studies have evaluated the effect of HHT on proliferation and apoptosis in human myeloma cells. Myeloma cell viability was measured by 3-(4,5-dimethylthiazol-2-yl)- 2,5-diphenyl tetrazolium bromide (MTT) assay. Apoptotic cells and cell cycle were evaluated by flow cytometry. Level of caspase-8, caspase-9, caspase-3, and DNA repair enzyme poly (ADP-ribose) polymerase (PARP), were investigated using Western blot analysis. We found that HHT significantly inhibited the proliferation of human multiple myeloma (MM) cell lines and tumor cells from patients with relapsed refractory MM in a dose-dependent manner. HHT also induced apoptosis in myeloma cells as evidenced by flow cytometric detection of annexin V binding assay. This apoptotic process was associated with the activation of caspase-8, caspase-9, caspase-3 and PARP. The results also demonstrate that HHT potentiates dexamethasone-induced killing of MM cells. These findings indicate that HHT may be effective in the treatment of MM.

Homoharringtonine inhibits the AKT pathway and induces in vitro and in vivo cytotoxicity in human multiple myeloma cells

Involvement of phosphatidylinositol 3-kinase/Akt-1 in cell survival and proliferation of multiple myeloma (MM) has been well established. In this study, we demonstrate that homoharringtonine (HHT), an antileukemic drug first isolated from the Chinese evergreen Cephalotaxus harringtonia, induces significant cytotoxicity in dexamethasone-sensitive and -resistant and chemotherapy-sensitive MM cell lines in a time and dose-dependent manner. HHT also triggers apoptosis in chemotherapy-resistant patient's myeloma cells. Contrary to dexamethasone, the cytotoxicity of HHT on myeloma is independent of interleukin-6. The mechanism of HHT cytotoxicity is related to down-regulation of Akt phosphorylation/activation and various target genes of Akt including nuclear factor kappa B, XIAP, cIAP and cyclin D1. Moreover, in vivo antitumor activity of HHT is demonstrated in RPMI8226 myeloma xenograft model. Importantly, an additive effect of antitumor is confirmed in the myeloma cells treated with HHT and bortezomib concomitantly with inhibition of phosphorylated Akt. Together, these findings obtained with HHT should give useful insights into a novel antimyeloma chemotherapy.

Anti-myeloma effect of homoharringtonine with concomitant targeting of the myeloma-promoting molecules, Mcl-1, XIAP, and beta-catenin

Since a variety of cell intrinsic and extrinsic molecular abnormalities cooperatively promote tumor formation in multiple myeloma (MM), therapeutic approaches that concomitantly target more than one molecule are increasingly attractive. We herein demonstrate the anti-myeloma effect of a cephalotaxus alkaloid, homoharringtonine (HHT), an inhibitor of protein synthesis, through the induction of apoptosis. HHT significantly reduced Mcl-1, a crucial protein involved in myeloma cell survival, in all three myeloma cell lines examined, whereas certain BH3-only proteins, such as Bim, Bik, and Puma, remained unchanged following HHT treatment, and their expression levels depended on the cell type. HHT also reduced the levels of c-FLIP(L/S), activated caspase-8, and induced active truncated-Bid. Thus, HHT-induced apoptosis appears to be mediated via both intrinsic and extrinsic apoptosis pathways, and the resultant imbalance between BH3-only proteins and Mcl-1 may be pivotal for apoptosis by HHT. In addition, HHT treatment resulted in reduced levels of beta-catenin and XIAP proteins, which also contribute to disease progression and resistance to chemotherapy in MM. In combination, HHT enhanced the effects of melphalan, bortezomib, and ABT-737. These results suggest that HHT could constitute an attractive option for MM treatment though its ability to simultaneously target multiple tumor-promoting molecules.

Preclinical assessment of FHIT gene replacement therapy in human leukemia using a chimeric adenovirus, Ad5/F35

PURPOSE

Expression of the FHIT protein is lost or reduced in most solid tumors and a significant fraction of hematopoietic malignancies. Adenovirus 5 (Ad5) virus or adeno-associated viral vectors have been used to study the tumor suppressor function of FHIT in solid tumors, but these tools have not been effective in leukemias. We have generated a chimeric FHIT-containing adenovirus composed of Ad5 and the group B adenovirus called F35 with which we have been able to efficiently infect hematopoietic cells.

EXPERIMENTAL DESIGN

Infection efficiency of Ad5/F35-FHIT and Ad5/F35-GFP viruses was tested in leukemia cell lines that lacked FHIT expression, and biological effects of successful infection were assessed. An acute myelogenous leukemia, a chronic myelogenous leukemia, and four acute lymphoblastic leukemia human cell lines were examined as well as two EBV-transformed B lymphoblastoid cell lines that expressed endogenous FHIT.

RESULTS

Two of four acute lymphoblastic leukemia cell lines, Jurkat and MV4;11, which were efficiently infected with Ad5/F35-FHIT, underwent growth suppression and massive induction of apoptosis without apparent activation of caspase-8 or caspase-2 and late activation of caspase-3. Treatment of infected cells with caspase-9 and caspase-3 inhibitors partially blocked FHIT-induced apoptosis. The two remaining infected acute lymphoblastic leukemia cell lines, Molt-3 and RS4;11, were apparently unaffected. Restoration of FHIT expression in the chronic myelogenous leukemia K562 cell line and the acute myelogenous leukemia KG1a cell line also induced apoptosis but at later time points than seen in the acute lymphoblastic leukemia Jurkat and MV4;11 cell lines. I.v. injection of Ad5/F35-FHIT-infected Jurkat cells resulted in abrogation of tumorigenicity in the NOD/SCID xenogeneic engraftment model.

CONCLUSION

FHIT restoration in some FHIT-deficient leukemia cells induces both antiproliferative and proapoptotic effects involving the intrinsic caspase apoptotic pathway.

Homoharringtonine-induced apoptosis of MDS cell line MUTZ-1 cells is mediated by the endoplasmic reticulum stress pathway

Homoharringtonine has been shown to lead to apoptosis of leukemic cells in several studies. Here we showed that the endoplasmic reticulum (ER) may be the initial site of apoptotic signal induced by homoharringtonine in MUTZ-1 cells. After incubation with homoharringtonine, the percentage of apoptotic MUTZ-1 cells increased in a time-dependent manner, Ca(2+) translocated from ER pool to cytosol, the mitochondrial membrane potential decreased, and Bid protein translocated from ER to mitochondria. The activation of ER stress-associated proapoptotic factor CHOP and ER chaperones BiP and XBP1 genes followed by cleavage of caspase-3 but not caspase-4 protein were also observed.

A phase I dose-finding and pharmacokinetic study of subcutaneous semisynthetic homoharringtonine (ssHHT) in patients with advanced acute myeloid leukaemia

To determine the maximum-tolerated dose (MTD), dose-limiting toxicities and pharmacokinetic of semisynthetic homoharringtonine (ssHHT), given as a twice daily subcutaneous (s.c.) injections for 9 days, in patients with advanced acute leukaemia, 18 patients with advanced acute myeloid leukaemia were included in this sequential Bayesian phase I dose-finding trial. A starting dose of 0.5 mg m⁻² day⁻¹ was explored with subsequent dose escalations of 1, 3, 5 and 6 mg m⁻² day⁻¹. Myelosuppression was constant. The MTD was estimated as the dose level of 5 mg m⁻² day⁻¹ for 9 consecutive days by s.c. route. Dose-limiting toxicities were hyperglycaemia with hyperosmolar coma at 3 mg m⁻², and (i) one anasarque and haematemesis, (ii) one life-threatening pulmonary aspergillosis, (iii) one skin rash and (iv) one scalp pain at dose level of 5 mg m⁻² day⁻¹. The mean half-life of ssHHT was 11.01±3.4 h, the volume of distribution at steady state was 2±1.4 l kg⁻¹ and the plasma clearance was 11.6±10.4 l h⁻¹. Eleven of the 12 patients with circulating leukaemic cells had blood blast clearance, two achieved complete remission and one with blast crisis of CMML returned in chronic phase. The recommended daily dose of ssHHT on the 9-day schedule is 5 mg m⁻² day⁻¹.

Berbamine: A novel inhibitor of bcr/abl fusion gene with potent anti-leukemia activity

Gleevec, which is an inhibitor of the bcr/abl tyrosine kinase, has been a remarkable success for the treatment of chronic myelogenous leukemia (CML). However, a significant proportion of patients chronically treated with Gleevec develop resistance. Here we describe the activity of a natural small molecular compound, berbamine from plant Berberis amurensis that can selectively induce cell death of both Gleevec-sensitive and -resistant Ph+ CML cells. The IC50 values of berbamine were 8.80 microg/ml in Gleevec-sensitive Ph+ CML cells, 11.34 microg/ml in Gleevec-resistant Ph+ CML cells, and 54.40 microg/ml in Ph- KG-1 cells, respectively. Similarly, berbamine was also found to display a selective anti-proliferative activity of primary leukemia cells from CML patients, and its IC50 values were 4.20-10.50 microg/ml in primary CML cells, and 185.20 microg/ml in normal bone marrow cells, respectively. More importantly, our studies demonstrate that berbamine down-regulates p210bcr/abl oncoprotein level, and induces apoptosis of bcr/abl+ cells through caspase-3-dependent pathway. These data suggest that berbamine might be a novel bcr/abl inhibitor with potent anti-leukemia activity.

Mitochondrial-dependent, reactive oxygen species-independent apoptosis by myricetin: roles of protein kinase C, cytochrome c, and caspase cascade

Abrogation of mitochondrial permeability and induction of reactive oxygen species (ROS) production have been observed in chemical-induced apoptosis; however, the relationship between the mitochondria and intracellular ROS levels in apoptosis is still unclear. In the present study, myricetin (ME) but not its respective glycoside, myricitrin (MI; myricetin-3-O-rhamnose) reduced the viability of human leukemia HL-60 cells via apoptosis, characterized by the occurrence of DNA ladders and hypodiploid cells. Results of Western blotting and caspase activity assays showed that activation of caspases 3 and 9 but not caspases 1, 6 or 8 with cleavage of PARP and D4-GDI proteins is involved in ME-induced apoptosis. A reduction in mitochondrial functions characterized by a decrease in the Bcl-2/Bax protein ratio and translocation of cytochrome c (cyt c) from the mitochondria to the cytosol in accordance with a decrease in mitochondrial membrane potential were observed in ME-treated HL-60 cells. No significant induction of intracellular ROS levels by ME was observed by the DCHF-DA assay, DPPH assay or plasmid digestion assay, and antioxidants including N-acetyl-cysteine (NAC), catalase (CAT), superoxide dismutase (SOD), and tiron (TIR) showed no protective effects on ME-induced apoptosis. A PKC activator, 12-O-tetradecaoylphorbol-13-acetate (TPA) significantly attenuated ME-induced apoptosis via preventing cytochrome c release to the cytosol and maintaining the mitochondrial membrane potential by inhibiting the decrease in the Bcl-2/Bax protein ratio; these effects were blocked by protein kinase C (PKC) inhibitors including GF-109203X, H7, and staurosporin. Removing mitochondria by ethidium bromide (EtBr) treatment reduced the apoptotic effect of ME. Results of SAR studies showed that the presence of OH at C3', C4', and C5' is important for the apoptosis-inducing activities of ME, and that ME induces apoptosis in another leukemia cell line, Jurkat cells, but not in primary human polymorphonuclear (PMN) cells or in murine peritoneal macrophages (PMs). The results of the present study suggest that apoptosis induced by ME occurs through a novel mitochondrion-dependent, ROS-independent pathway; TPA protects cells from ME-induced apoptosis via PKC activation which prevents the occurrence of mitochondrial destruction during apoptosis.

Stress-induced activation of the p53 tumor suppressor in leukemia cells and normal lymphocytes requires mitochondrial activity and reactive oxygen species

The p53 system is highly stress sensitive and integrates diverse intracellular signals in a complex and poorly defined manner. We report on the high dependence of stress-induced p53 activation on mitochondrial activity. Down-regulation of mitochondrial transmembrane potential (MTMP) by inhibitors of electron transport (rotenone, thenoyltrifluoroacetone (TTFA)) and adenosine triphosphate (ATP) synthesis (oligomycin) prevented stress-induced p53 protein accumulation and abrogated p53-dependent apoptosis in a wild-type p53 leukemia cell line MOLT-3, in primary leukemia cells and in normal T lymphocytes. Using genome-wide gene expression analysis, stress-induced up-regulation of the p53 transcriptional targets and their specific inhibition by oligomycin has been demonstrated. Oligomycin did not impair p53-independent apoptosis and caused only a slight reduction of intracellular ATP levels. Reactive oxygen species (ROS) localized to mitochondria decreased in the presence of oligomycin, and stress-induced p53 activation showed strong ROS sensitivity both in leukemic and normal cells. These observations identify mitochondrial activity, described by MTMP and ROS levels, as a critical intracellular determinant of the p53 stress sensitivity and suggest potential implications of this linkage in the mechanisms of chemoresistance of acute leukemia cells.

Homoharringtonine: a new treatment option for myeloid leukemia

HHT, one of the alkaloids from a Chinese natural plant, Cephalotaxus, has shown its potential in leukemia treatment. This compound demonstrated strong growth-inhibiting activities in vitro and in animal experiments, and obtained encouraging results in some clonal proliferative disease such as in chronic myeloid leukemia (CML) and in polycythemia vera. Evidences also confirmed HHT as an apoptosis inducer in tumor cell lines and fresh cells from cancer patients. The CR rate reported with HHT-based regimen in acute nonlymphocytic leukemia showed no statistic differences from that with DNR-based regimen, although the case number was limited. While used in clinical trial, the drug often cause noticeably cardiovascular disturbances if be given rapidly by intravenous infusion. Myelosuppression is the common complication in HHT-based chemotherapy. Although with the anti-growth activity in vitro and praisable achievement in acute and chronic myeloid leukemia treatment, the drug shows no beneficial effect in lymphocytic leukemia and solid tumors. The underlying mechanism for the discrepancy of efficacy keeps unknown. This review will present with the preclinical research data including the action mechanism, pharmacokinetics and drug resistance of HHT as well as the result from the clinical trial with HHT in China and the United States.

Asiatic acid induces apoptosis in SK-MEL-2 human melanoma cells

Asiatic acid (AA) is a pentacyclic triterpene found in Centella asiatica. In the present study, the mechanism of anticancer effect of AA on skin cancer was investigated. AA decreased viability and induced apoptosis in human melanoma SK-MEL-2 cells in a time- and dose-dependent manner. AA also markedly increased intracellular reactive oxygen species (ROS) level and enhanced the expression of Bax but not Bcl-2 protein in the cells. In addition, AA-induced activation of caspase-3 activity in a dose-dependent manner. Pretreatment with Trolox, an antioxidant, significantly blocked the induction of Bax and activation of caspase-3 in AA-treated cells. Furthermore, Ac-DEVD-CHO, a specific caspase-3 inhibitor, and Trolox prevented the AA-induced apoptosis. AA did not elevate p53 nuclear protein levels that are present in a mutant form in SK-MEL-2 cells. These results suggest that AA-induced apoptosis may be mediated through generation of ROS, alteration of Bax/Bcl-2 ratio and activation of caspase-3, but p53-independent. These results further suggest that AA may be a good candidate for the therapeutic intervention of human skin cancer.

Homoharringtonine mediates myeloid cell apoptosis via upregulation of pro-apoptotic bax and inducing caspase-3-mediated cleavage of poly(ADP-ribose) polymerase (PARP)

Homoharringtonine (HHT) is a plant alkaloid with antileukemia activity that is currently being used for treatment of acute, chronic leukemias and MDS. In this study, we show that HHT can induce apoptosis in a variety of human myeloid leukemia cell lines (U937, HL-60, HEL, THP, and K562). U937 and HL60 cells undergo rapid apoptosis on treatment with HHT, as indicated by increased annexin V binding capacity, caspase-3 activation, and cleavage of poly(ADP-ribose) polymerase (PARP). In addition, the expression of bax is upregulated during HHT-induced cell death, whereas the expression of bcl-2 is only slightly decreased. Importantly, treatment of primary leukemic cells, obtained from acute myeloid leukemia patients, resulted in rapid apoptosis. Thus, our data provide the mechanism of HHT and justify the use of HHT in the treatment of human myeloid leukemia.

Structure-activity relation for synthetic phenoxazone drugs

The structure-activity relations of a series of synthetic phenoxazone drugs with aminoalkyl side chains of variable length and different terminal groups were investigated by examining their biological activity and DNA complexation affinity. Biological activity was determined from their ability to induce apoptosis and cell cycle perturbations (activation of cell cycle checkpoints) using the human malignant MOLT-3 cell line. The thermodynamic parameters of drug-DNA complexation were determined by differential scanning calorimetry. By comparing the activities of compounds with different terminal groups (amino, dimethylamino and diethylamino), we found that the existence of a terminal dimethylamino group in the alkylamino side chain is an important factor for anti-tumour activity. Minor modifications in the dimethylaminoalkyl side chain (e.g. elongation by one methylene group) led to notable changes in both the anti-tumour activity and DNA-binding properties of the drug, providing unambiguous evidence of a marked structure-activity relation.

Reactive oxygen species mediate doxorubicin induced p53-independent apoptosis

Doxorubicin (DOX) is a common anticancer drug. The mechanisms of DOX induced apoptosis and the involvement of reactive oxygen species (ROS) in apoptotic signaling were investigated in p53-null human osteosarcoma Saos-2 cells. Accumulation of pre-G1 phase cells and induction of DNA laddering, which are the hallmarks of apoptosis, were detected in cells at 48 h upon DOX treatment. Furthermore, DOX increased the intracellular hydrogen peroxide and superoxide levels, followed by mitochondrial membrane depolarization, cytochrome c release, caspase-3 activation, prior to DNA laddering in Saos-2 cells. In addition, DOX treatment also upregulated Bax and downregulated Bcl-2 levels in the cells. The role of ROS in DOX induced cell death was confirmed by the suppression effect of catalase on DOX induced ROS formation, mitochondrial cytochrome c release, procaspase-3 cleavage, and apoptosis in Saos-2 cells. The catalase treatment however only suppressed DOX induced Bax upregulation but had no effect on Bcl-2 downregulation. Results from the present study suggested that ROS might act as the signal molecules for DOX induced cell death and the process is still functional even in the absence of p53.

Early induction of secondary injury factors causing activation of calpain and mitochondria-mediated neuronal apoptosis following spinal cord injury in rats

To investigate a potential relationship between calpain and mitochondrial damage in spinal cord injury (SCI), a 40 gram-centimeter force (g-cm) injury was induced in rats by a weight-drop method and allowed to progress for 4 hr. One-centimeter segments of spinal cord tissue representing the adjacent rostral, lesion, and adjacent caudal areas were then removed for various analyses. Calcium green 2-AM staining of the lesion and penumbra sections showed an increase in intracellular free calcium (Ca(2+)) levels following injury, compared with corresponding tissue sections from sham-operated (control) animals. Western blot analysis showed increased calpain expression and activity in the lesion and penumbra segments following SCI. Double-immunofluorescent labeling indicated that increased calpain expression occurred in neurons in injured segments. Western blot analysis also showed an increased Bax:Bcl-2 ratio, indicating the induction of the mitochondria-mediated cell death pathway in the lesion and penumbra. The morphology of mitochondria was altered in lesion and penumbra following SCI: mostly hydropic change (swelling) in the lesion, with the penumbra shrunken or normal. At 4 hr after induction of injury, a substantial amount of cytochrome c had been released into the cytoplasm, suggesting a trigger for apoptosis through caspase 3 activation. Neuronal death after 4 hr of injury was detected by a combined TUNEL and double-immunofluoresence assay in the lesion and penumbra sections of injured cord, compared with sham controls. These results suggest that an early induction of secondary factors is involved in the pathogenesis of SCI. The increased Ca(2+) levels could activate calpain and mediate mitochondrial damage leading to neuronal death in lesion and penumbra following injury. Thus, secondary injury processes mediating cell death are induced as early as 4 hr after the injury, and calpain and caspase inhibitors may provide neuroprotection.

Beta-phenylethylamines and the isoquinoline alkaloids

This review covers beta-phenylethylamines and isoquinoline alkaloids and compounds derived from them, including further products of oxidation, condensation with formaldehyde and rearrangement, some of which do not contain an isoquinoline system, together with naphthylisoquinoline alkaloids, which have a different biogenetic origin. The occurrence of the alkaloids, with the structures of new bases, together with their reactions, syntheses and biological activities are reported. The literature from July 2001 to June 2002 is reviewed, with 581 references cited.

Ham-Wasserman Lecture

Conventional treatment of acute leukemia involves the use of cytotoxic agents (chemotherapy), but other strategies have been explored. All-trans retinoic acid (ATRA) and arsenic have clearly been effective in the treatment of acute promyelocytic leukemia (APL), which creates the possibility that other types of acute leukemia can be conquered by selectively inducing differentiation and/or apoptosis. A great number of investigations have been performed to elucidate the mechanisms and search for effective agents in the treatment of other types of acute leukemia by these new strategies. Progress at the molecular level has been achieved in explaining the mechanisms of action of ATRA and arsenic compounds, and several new agents have emerged, although their clinical effectiveness remains to be confirmed. Mechanism-/gene-based targeted therapy and a combination of different strategies will improve the treatment of acute leukemia.

Ham-Wasserman Lecture

Conventional treatment of acute leukemia involves the use of cytotoxic agents (chemotherapy), but other strategies have been explored. All-trans retinoic acid (ATRA) and arsenic have clearly been effective in the treatment of acute promyelocytic leukemia (APL), which creates the possibility that other types of acute leukemia can be conquered by selectively inducing differentiation and/or apoptosis. A great number of investigations have been performed to elucidate the mechanisms and search for effective agents in the treatment of other types of acute leukemia by these new strategies. Progress at the molecular level has been achieved in explaining the mechanisms of action of ATRA and arsenic compounds, and several new agents have emerged, although their clinical effectiveness remains to be confirmed. Mechanism-/gene-based targeted therapy and a combination of different strategies will improve the treatment of acute leukemia.

Modulation of caspase activation and p27(Kip1) degradation in the p53-induced apoptosis in IW32 erythroleukemia cells

To examine the p53-mediated biological activities and signalling pathways, we generated stable transfectants of the p53-null IW32 murine erythroleukemia cells expressing the temperature-sensitive p53 mutant DNA, tsp53(val135). Two clones with different levels of p53 protein expression were selected for further characterization. At permissive temperature, clone 1-5 cells differentiated along the erythroid pathway, and clone 3-2 cells that produced greater levels (3.5-fold) of p53 underwent apoptosis. Apoptosis of 3-2 cells was accompanied by mitochondrial cytochrome c release and caspase activation as well as by cleavage of caspase substrates. Bax protein was induced to a similar extent in these clones by wild-type p53; expression of p21(Cip1/Waf1) and p27(Kip1) proteins was also increased. However, significantly lesser extent of induction for both CDK inhibitors was detected in the apoptotic 3-2 clone. The general caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (z-VAD.fmk) blocked the p53-induced apoptosis in 3-2 cells, with a concomitant elevation of p27(Kip1), suggesting that p27(Kip1) protein underwent caspase-dependent proteolysis in the apoptotic 3-2 cells. Together these results linked a pathway involving cytochrome c release, caspase activation and p27(Kip1) degradation to the p53-induced apoptosis in IW32 erythroleukemia cells.

Diversity of the apoptotic response to chemotherapy in childhood leukemia

Apoptosis is the primary mechanism through which most chemotherapeutic agents induce tumor cell death. The purpose of this study was to determine the extent to which blasts from children with leukemia undergo a uniform apoptotic death pathway in vivo. The expression of pro- and anti-apoptotic proteins p53, p21, MDM-2, BCL-2, BCL-X(L), BCL-X(S), and BAX, and caspase-3 activity was determined in circulating blasts collected from the peripheral blood of children with leukemia prior to, and at serial time points following chemotherapy. Culturing blasts ex vivo for 12 h assessed spontaneous apoptosis and the increment induced by chemotherapy. Baseline apoptosis varied between 3% and 29%. Twenty-four hours following chemotherapy the increase in the percentage of cells undergoing apoptosis ranged from <1% to 38%. Eleven of 20 patients who received initial treatment with a p53-dependent drug showed an increase in p53 expression. In these patients, the levels of p53 target genes were also increased. A uniform pattern of BCL-2 family protein expression was not observed and only a minority of samples showed a change that would favor apoptosis. We conclude that that the initial apoptotic response to chemotherapy in children with leukemia is variable involving both p53-dependent and p53-independent pathways.