Comparison of the membrane-related effects of cytarabine and other agents on model membranes

Treatment strategies for pediatric acute myeloid leukemia

Therapeutic strategies utilized in recently completed Phase III clinical trials in children with de novo acute myeloid leukemia have led to long-term disease-free survival in 50 - 60% of children. This review describes the contributions from early intensification of therapy and postremission intensification using highly myelosuppressive chemotherapy strategies and discusses the controversial roles of allogeneic bone marrow transplantation, maintenance therapy and CNS irradiation. Current strategies focusing on the identification of critical biologic features and measurements of early response to therapy allow for greatly improved risk group stratification. Future improvements in the treatment of children with acute myeloid leukemia will depend on a better understanding of the biology of the disease, targeted therapeutic approaches directed to specific biologic targets, selective use of allogeneic transplantation and innovative clinical trial designs that will allow for the testing of an increasing number of new agents in increasingly small numbers of patients in defined risk groups.

Erufosine, a novel alkylphosphocholine, in acute myeloid leukemia: single activity and combination with other antileukemic drugs

PURPOSE

Alkylphosphocholines represent a new class of cytostatic drugs with a novel mode of action. Erufosine (ErPC3), the first compound of this class that can be administered intravenously, has recently been shown to be active against human tumor and leukemic cell lines.

METHODS

In order to evaluate the antileukemic potential of ErPC3 in acute myeloid leukemia (AML) the lethal concentration 50% (LC 50) was determined using WST-1 assay. For analysis of cell death, staining for Annexin V and activated caspase 3 was performed. An interaction analysis was performed by calculation of combination index and construction of isobolograms.

RESULTS

The LC 50 was 7.4 microg/ml after 24 h and 3.2 microg/ml after 72 h in HL 60 cells and 30.1 and 8.6 microg/ml, respectively, in 19 fresh samples from patients with AML. ErPC3 was found to be cytotoxic in HL60 cells with distinct activation of caspase 3. ErPC3 was not cross-resistant with cytarabine, idarubicine and etoposide as shown by the linear relation of respective LC 50s. The latter agents, however, exerted an additive cytotoxicity in combination with ErPC3 as revealed by isobologram analysis and combination index, although results are uneven for idarubicine.

CONCLUSION

Based on these data ErPC3 appears as a novel antileukemic candidate drug, which needs to be explored further in the treatment of AML.

The pharmacodynamic basis for the increased antileukaemic efficacy of cytosine arabinoside-based treatment regimens in acute myeloid leukaemia with a high proliferative activity

The current study was initiated to explore the mechanisms underlying the previously demonstrated association between the proliferative activity of leukaemic blasts and the response to cytosine arabinoside (AraC)-based therapy in de novo acute myeloid leukaemia (AML). The activity of key enzymes of AraC metabolism-deoxycytidine kinase (DCK), cytidine deaminase (DCD) and polymerase alpha (PolyA) were determined in blast cells from 33 patients. In addition, formation and retention of intracellular levels of AraC triphosphate (AraCTP) and DNA incorporation of AraC were measured, as was the proliferative activity of leukaemic blasts by [3H]-TdR incorporation before and after stimulation with granulocyte-macrophage colony-stimulating factor (GM-CSF) or granulocyte CSF (G-CSF) for 48 h. AraC incorporation into the DNA (median 0.60 pmol/105 cells) was significantly related to the proliferative activity of AML blasts (r = 0.74, P < 0.001). Similarly, priming with GM-CSF or G-CSF increased both the proliferative activity of AML blasts by a median of 1.84- and 1.64-fold, respectively, and the incorporation of AraC into the DNA (1.29- and 1.40-fold respectively). In contrast, no relationship was found between the endogenous proliferative activity (EPA) and enzyme activities regulating AraC activation (DCK; median 4.70 pmol/min/mg protein), inactivation (DCD; median 2.92 pmol/min/mg protein) or inhibitory effects (PolyA; median 1.50 pmol/min/mg protein), nor the formation or retention of AraCTP (median 306.1 ng/107 cell and 1.6 h respectively). When samples were grouped according to EPA (more than or less than the median), slowly proliferating specimens had a higher response to cytokine priming for proliferative activity and incorporation of AraC into DNA. Clinical data of 15 patients were available. Although all eight patients with a high endogenous proliferative activity reached complete remission, only four out of seven patients with a low proliferative activity responded, whereas the other three patients were non-responders (P = 0.077).

The parkinsonian neurotoxin MPP+ opens the mitochondrial permeability transition pore and releases cytochrome c in isolated mitochondria via an oxidative mechanism

The mitochondrial transition pore (MTP) is implicated as a mediator of cell injury and death in many situations. The MTP opens in response to stimuli including reactive oxygen species and inhibition of the electron transport chain. Sporadic Parkinson's disease (PD) is characterized by oxidative stress and specifically involves a defect in complex I of the electron transport chain. To explore the possible involvement of the MTP in PD models, we tested the effects of the complex I inhibitor and apoptosis-inducing toxin N-methyl-4-phenylpyridinium (MPP+) on cyclosporin A (CsA)-sensitive mitochondrial swelling and release of cytochrome c. In the presence of Ca2+ and Pi, MPP+ induced a permeability transition in both liver and brain mitochondria. MPP+ also caused release of cytochrome c from liver mitochondria. Rotenone, a classic non-competitive complex I inhibitor, completely inhibited MPP(+)-induced swelling and release of cytochrome c. The MPP(+)-induced permeability transition was synergistic with nitric oxide and the adenine nucleotide translocator inhibitor atractyloside, and additive with phenyl arsine oxide cross-linking of dithiol residues. MPP(+)-induced pore opening and cytochrome c release were blocked by CsA, the Ca2+ uniporter inhibitor ruthenium red, the hydrophobic disulfide reagent N-ethylmaleimide, butacaine, and the free radical scavenging enzymes catalase and superoxide dismutase. MPP+ neurotoxicity may derive from not only its inhibition of complex I and consequent ATP depletion, but also from its ability to open the MTP and to release mitochondrial factors including Ca2+ and cytochrome c known to be involved in apoptosis.

An evaluation of the role of mitochondria in neurodegenerative diseases: mitochondrial mutations and oxidative pathology, protective nuclear responses, and cell death in neurodegeneration

There is mounting evidence for mitochondrial involvement in neurodegenerative diseases including Alzheimer's and Parkinson's disease and amyotrophic lateral sclerosis. Mitochondrial DNA mutations, whether inherited or acquired, lead to impaired electron transport chain (ETC) functioning. Impaired electron transport, in turn, leads to decreased ATP production, formation of damaging free-radicals, and altered calcium handling. These toxic consequences of ETC dysfunction lead to further mitochondrial damage including oxidation of mitochondrial DNA, proteins, and lipids, and opening of the mitochondrial permeability transition pore, an event linked to cell death in numerous model systems. Although protective nuclear responses such as antioxidant enzymes and bcl-2 may be induced to combat these pathological changes, such a vicious cycle of increasing oxidative damage may insidiously damage neurons over a period of years, eventually leading to neuronal cell death. This hypothesis, a synthesis of the mitochondrial mutations and oxidative stress hypotheses of neurodegeneration, is readily tested experimentally, and clearly points out many potential therapeutic targets for preventing or ameliorating these diseases.

Differential regulation of phospholipase A2 in human leukemia cells by the etherphospholipid analogue hexadecylphosphocholine

Hexadecylphosphocholine (HePC) is the main representative of a new group of antineoplastic agents, the alkylphosphocholines, which were originally derived from cytotoxic etherlysophospholipids. HePC shows antiproliferative action against a whole variety of tumor cells and tumors in vitro and in vivo. Furthermore, it also induces differentiation in some hematologic cell lines and prevents invasive growth of neoplastic cells in vitro. To date, the precise molecular mechanisms mediating the biological effects of HePC have not been identified yet. As etherlysophospholipids seem to inhibit some pathways of lipid-dependent intracellular signalling, similar effects may be relevant for HePC. We therefore investigated the influence of HePC on phospholipase A2 (PLA2-EC 3.1.1) in the human leukemia cell line U 937. HePC seems to inhibit enzyme activity independently of protein kinase C (PKC) in differentiated U 937 cells stimulated by tumor necrosis factor alpha (TNFalpha). Inhibition of purified secretory PLA2 from snake venom (EC 3.1.1.4) in vitro shows characteristics of a non-competitive mode. In contrast, HePC leads to an enhancement of PLA2 activity in immature cells which cannot be explained by changes in membrane composition. Our data suggest that PLA, inhibition is most probably not the mechanism by which HePC mediates its antiproliferative effects.

Effects of the lipophilic anticancer drug teniposide (VM-26) on membrane transport

The epipodophyllotoxin glucopyranosides have previously been shown to interact with membrane lipids and to alter the activity of several lipid-embedded membrane proteins. To determine if these agents are acting as general membrane perturbants, we have further examined their effects on membrane processes in Ehrlich ascites tumor cells. [3H]VM-26 and [3H]VP-16 were taken up rapidly and concentrated within the cells in proportion to their lipophilicity. Neither agent was found to have any significant effect on the influx of L-[3H]leucine or alpha-[3H]aminoisobutyric acid. Likewise, these drugs had no significant effects on the hexose transporter. The nucleoside transporter, which is structurally and functionally similar to the hexose transporter, was dramatically affected, however. VM-26 was a non-competitive inhibitor of equilibrium-exchange influx of cytosine arabinoside in Ehrlich cells with a Ki of 15 microM. Equilibrium-exchange influx increased with temperature in control cells (Q10 = 2) but not in VM-26-treated cells; thus, VM-26 was a more potent inhibitor at higher temperatures. VM-26 also significantly reduced zero-trans influx in Ehrlich, P388, L5178Y, and ML-1 cells, and these effects were immediate in onset. VM-26 inhibited high-affinity binding of the nucleoside transport inhibitor nitrobenzylmercaptopurine riboside (NBMPR), but VM-26 enhanced non-specific NBMPR binding to Ehrlich cells. The apparent specificity of the epipodophyllotoxins for the nucleoside transporter is discussed.