Changes of mitochondrial respiration, mitochondrial content and cell size after induction of apoptosis in leukemia cells.

Mitochondrial damage with release of cytochrome c is implicated in cell death signalling pathways. To examine mitochondrial function in apoptotic cells, we applied high-resolution respirometry to human leukemia cells arrested in the G1- and S-phase by exposure to the glucocorticoid dexamethasone and nucleotide analogue gemcitabine. At 30% apoptosis, opposite effects were observed on respiratory capacity (71% and 131% of controls, respectively). These changes correlated with alterations in cell size, cytosolic, and mitochondrial marker enzymes. Mitochondrial ATP production and membrane potential were maintained in all treatments, as deduced from high respiratory uncoupling control ratios (UCR). Bcl-2 over-expression did not prevent apoptosis after gemcitabine-treatment, but protected dexamethasone-treated cells from apoptosis, without fully preventing the decline of respiration and cell size. These results, therefore, provide conclusive evidence that alterations in respiratory capacity and enzyme activities per cell are mainly caused by opposite changes in cell size, occurring upon cell cycle arrest triggered by dexamethasone and gemcitabine in the early phase of apoptosis.

In vitro studies on the immunosuppressive effect of 2',2'-difluorodeoxycytidine (dFdC) and its metabolite 2',2'-difluorodeoxyuridine (dFdU).

The effect of 2',2'-difluorodeoxycytidine (dFdC) on in vitro human lymphocyte response was assessed in comparison with that of its major metabolite 2',2'-difluorodeoxyuridine (dFdU). Peripheral blood mononuclear cells (PBMNC) from healthy human volunteers were used for assay of mixed lymphocyte reaction (MLR), blastogenesis and colony forming by PHA. Both substances inhibited mitogen and alloantigen responses of PBMNC in a dose-dependent manner, but dFdU was up to 10,000-fold less potent than its parent compound dFdC. The data indicate that activation by alloantigen is more sensitive to the action of dFdU and dFdC than the response to PHA. Thus, dFdU inhibits MLR-induced response at significantly lower doses than PHA-induced proliferation (IC50 +/- SD, 23.55 +/- 8 microM versus 133.2 +/- 12 microM) (p = 0.0003). dFdC also proved to be about 12.3-fold more potent against alloantigen response compared to PHA-induced proliferation of PBMNC (IC50 +/- SD, 2.28 +/- 0.5 nM versus 28.1 +/- 0.5 nM) (p = 0.0001). To get an insight into the toxic profile of dFdU and dFdC, both substances were additionally tested on the in vitro clonal growth of CD34+ cells. Cells were cultured in methylcellulose in the continuous presence of dFdU and dFdC in doses up to 640 microM and 16 nM, respectively. The results show a marked inhibition of erythroid (BFU-E) and myeloid progenitors (CFU-GM) in a dose-dependent manner, but BFU-E was more sensitive to the action of dFdU and dFdC than CFU-GM (p=0.0001). Compared to T-lymphocytes, however, similar or even higher doses of dFdU and dFdC were required for complete inhibition of colony formation obtained from CD34+ cells. To test the role of deoxycytidine kinase (dCK) in the metabolism of dFdU in comparison to that of dFdC, reversal studies with deoxycytidine (dCyd), the natural substrate of dCK, were performed on dFdU- and dFdC-treated HL-60 cells. The data show that relatively low concentrations of dCyd (10 microM) were sufficient to protect HL-60 cells from cytotoxicity of lethal doses of dFdU (160 microM), whereas 100-fold higher concentrations of deoxycytidine (dCyd) (1 mM) were required for a complete reversal of dFdC-mediated toxicity. This suggests that activation of dFdU is due to its phosphorylation by dCK, but dFdU has low affinity to dCK. These effects of dFdU and dFdC in relation to T-lymphocytes and CD34+ cells suggest their possible use as immunosuppressive agents.

Oxindole alkaloids from Uncaria tomentosa induce apoptosis in proliferating, G0/G1-arrested and bcl-2-expressing acute lymphoblastic leukaemia cells.

Natural products are still an untapped source of promising lead compounds for the generation of antineoplastic drugs. Here, we investigated for the first time the antiproliferative and apoptotic effects of highly purified oxindole alkaloids, namely isopteropodine (A1), pteropodine (A2), isomitraphylline (A3), uncarine F (A4) and mitraphylline (A5) obtained from Uncaria tomentosa, a South American Rubiaceae, on human lymphoblastic leukaemia T cells (CCRF-CEM-C7H2). Four of the five tested alkaloids inhibited proliferation of acute lymphoblastic leukaemia cells. Furthermore, the antiproliferative effect of the most potent alkaloids pteropodine (A2) and uncarine F (A4) correlated with induction of apoptosis. After 48 h, 100 micromol/l A2 or A4 increased apoptotic cells by 57%. CEM-C7H2 sublines with tetracycline-regulated expression of bcl-2, p16ink4A or constitutively expressing the cowpox virus protein crm-A were used for further studies of the apoptosis-inducing properties of these alkaloids. Neither overexpression of bcl-2 or crm-A nor cell-cycle arrest in G0/G1 phase by tetracycline-regulated expression of p16INK4A could prevent alkaloid-induced apoptosis. Our results show the strong apoptotic effects of pteropodine and uncarine F on acute leukaemic lymphoblasts and recommend the alkaloids for further studies in xenograft models.

Phagocytosis of human retinal pigment epithelial cells: evidence of a diurnal rhythm, involvement of the cytoskeleton and interference of antiviral drugs.

Retinal pigment epithelial (RPE) cells provide crucial functions for the maintenance of the retinal environment. We investigated the phagocytotic mechanisms of RPE cells evaluating the question whether particle uptake underlies a diurnal rhythm. Additionally, a possible connection of volume regulation and the phagocytotic function of RPE cells was studied. As antiviral nucleoside analogues influence cell-volume-regulating mechanisms, we tested several antiviral drugs. Cultured primary RPE cells and a permanent cell line (ARPE-19) were tested for uptake of europium-labeled microspheres quantified by time-resolved fluorometry. Cells were also exposed to cyclic illumination or continuous light and dark culture conditions. Inhibitors of cytoskeleton (microtubuli, actin) and osmotic swelling were also tested. Ingested FITC-labeled microparticles were found in phagosomes strongly associated which the cytoskeleton as they could not be easily moved by laser tweezer microscopy. Phagocytosis was observed predominately during dark intervals and was reduced by continuous light exposure. The diurnal rhythm of unsynchronized RPE cultures was abolished by microtubule inhibitors although no inhibition of overall particle uptake by cytoskeletal blockers was observed. Hypoosmotic swelling of RPE also decreased phagocytosis. Acyclovir was found inhibitory in ARPE-19 cells, whereas azidothymidine showed a protracted inhibiting activity on primary RPE cells and ganciclovir was inactive in both cell types. The presence of a diurnal rhythm also in culture indicates genetic determination of light-regulated particle uptake. This mechanism appears to be influenced by the regulation of cell volume and microtubule function. Inhibition of RPE function by antiviral drugs is a novel finding and in accordance with interferences of the tested drugs with cellular chloride channels described earlier. It may give a hint towards possible ocular side effects in the long-term use of nucleoside-analogous substances.

The immunomodulator FTY720 interferes with effector functions of human monocyte-derived dendritic cells.

The potent immunomodulator FTY720 elicits immunosuppression via acting on sphingosine 1-phosphate receptors (S1PR), thereby leading to an entrapment of lymphocytes in the secondary lymphoid tissue. To elucidate the potential in vitro effects of this drug on human monocyte-derived DC, we used low nanomolar therapeutic concentrations of FTY720 and phosphorylated FTY720 (FTY720-P) and investigated their influence on DC surface marker expression, protein levels of S1PR and DC effector functions: antigen uptake, chemotaxis, cytokine production, allostimulatory and Th-priming capacity. We report that both FTY720 and FTY720-P reduce chemotaxis of immature and mature DC. Mature DC generated in the presence of FTY720 or FTY720-P showed an impaired immunostimmulatory capacity and reduced IL-12 but increased IL-10 production. T cells cultured in the presence of FTY720- or FTY720-P-treated DC showed an altered cytokine production profile indicating a shift from Th1 toward Th2 differentiation. In treated immature and mature DC, expression levels for two S1PR proteins, S1P1 and S1P4, were reduced. We conclude that in vitro treatment with FTY720 affects DC features that are essential for serving their role as antigen-presenting cells. This might represent a new aspect of the overall immunosuppressive action of FTY720 and makes DC potential targets of further sphingolipid-derived drugs.

Ability of PSA-positive circulating macrophages to detect prostate cancer.

BACKGROUND: Prostate-specific antigen (PSA) is a widely used serum marker for prostate cancer, but has a poor specificity for early detection at levels below 10 ng/ml, because it can also result from benign conditions. Our aim was to determine the frequencies of circulating PSA+ macrophages in a blinded study and to examine the suitability of this new method for differentiating between benign and malignant prostate disease. METHODS: Between October 2002 and February 2003, 126 patients undergoing transrectal biopsy were enrolled in this study. Peripheral blood macrophages were stained for intracellular content of PSA in all patients. Ten patients' peripheral blood mononulear cells (PBMCs) were also supplementarily stained for cytokeratin (CK) and epithelial membrane antigen (EMA). Macrophages were analysed by flow cytometry. Patients were grouped according to their biopsy histology and bone scan results. FINDINGS: Based on histological data, patients were classified as having no evidence of malignancy (NEM) (n = 59), prostatitis (n = 20), or localised prostate cancer (n = 37). Significantly higher levels of circulating PSA+ macrophages were found in prostate cancer compared to benign conditions. Calculating a 2% cut-off level enabled the detection of localised prostate cancer with 89% sensitivity and 80% specificity. In a subset of patients (65%) with a serum PSA below 4 ng/ml and confirmed prostate cancer, the percentage of PSA+ macrophages was significantly higher compared to NEM and prostatitis. Macrophages of ten patients tested with prostate cancer contained significantly higher amounts of PSA, EMA, and CK compared to ten with NEM. INTERPRETATION: Intracellular PSA in combination with CK and EMA can be found in permeabilized blood macrophages, indicating phagocytosis of complete cancer cells. This study further suggests, that this new method might be suitable for differentiating between prostate cancer and benign conditions especially in patients with low serum PSA.

Delayed addition of deoxycytidine protects normal CD34+ cells against cytotoxicity of gemcitabine without compromising its activity against human leukemic cells.

In phase I and II clinical trials, the deoxycytidine analogue 2',2' difluorodeoxycytidine (dFdC, gemcitabine) has shown promising antitumor activity in leukemia as well as in solid tumors. Preclinical and clinical studies of gemcitabine suggested that myelosuppression was the dose-limiting toxicity. The present investigations were designed to test the effect of continuously administered gemcitabine on the in vitro clonal growth of normal CD34(+) cells isolated from peripheral blood and the promyelocytic cell line, HL-60. For this purpose, CD34(+) and HL-60 cells were cultured in methylcellulose in the continuous presence of 0.1-16 nM of gemcitabine. The results show a dose-dependent inhibition of colony growth of normal as well as leukemic cells. However, HL-60 cells were up to 12-fold more sensitive towards gemcitabine than normal progenitors. For rescue experiments, the natural pyrimidine deoxycytidine (dCyd) was added to CD34(+) and HL-60 cells simultaneously or with delay. Coadministration of 1mM dCyd to separate cultures resulted in complete restoration of colony formation capacity of CD34(+) and HL-60 cells. Delayed addition of 1 mM dCyd after 48 and 72 hours recovered up to 90% and 40%, respectively, of stem cell proliferation, whereas HL-60 cells remained substantially inhibited (4.5% +/- 3.5% versus 0%). Delayed addition after 48 and 72 hours protected about 80% and 50%, respectively, of myelopoietic and erythropoetic colony formation, whereas colony formation obtained from HL-60 cells remained significantly inhibited (9.6% +/- 4.17% versus 0%). These in vitro data suggest that there is a marked difference in the susceptibility of leukemic and normal CD34(+) cells to gemcitabine and that delayed administration of dCyd may further reduce the bone marrow cytotoxicity of gemcitabine without impairing its antitumor effect.