Expression of poliovirus receptor-related proteins PRR1 and PRR2 in acute myeloid leukemia: first report of surface marker analysis, contribution to diagnosis, prognosis and implications for future therapeutical strategies

Poliovirus receptor-related (PRR) proteins belong to the Nectin-adhesion molecules' group, are expressed on endothelial cells and on CD34(+) stem cells and mediate the organization of endothelial and epithelial junctions. There is evidence to suggest, that those receptors could have a role in leukemia. We have studied the expression of PRR molecules PRR1 and PRR2 on mononuclear bone marrow (BM) cells of 55 patients with acute myeloid leukemia (AML) at first diagnosis by FACS-analysis using directly Phycoerythrin-labeled markers (PRR1 clone R1.302.12; PRR2 clone R2.477.1) in combination with other Fluorescein conjugated antibodies to evaluate the blast phenotype in AML. The leukemic gate included blasts and residual monocytes and lymphocytes. A case was defined as positive, if more than 20% of the gated cells expressed the regarding receptor. We could demonstrate, that on average 35% PRR1(+) or 45% PRR2(+) cells in AML were found. Within FAB-types we observed a high PRR1 expression in cases with M3 and M4 and lowest expressions in M0 and M5; a high PRR2 expression was found in cases with M3, M4, M5 and M1 and lowest expressions in M0 and M2. Separating our patients' cohorts in cytogenetic risk groups we could detect a significant higher proportion of PRR1(+) cases (73% vs. 25% of cases, P = 0.009) or PRR1(+) cells (57% vs. 18% of cases, P = 0.001) in the cytogenetic favorable risk vs. poor risk group (75% vs. 32% PRR2(+) cases). Moreover cut-off-values with a maximum probability for a significant differentiation between cases with higher or lower levels of these markers could be found: cases with >78% PRR1(+) and cases with >77% PRR2(+) cells were characterized by a tendency for longer relapse free survival times. Qui-square analyses showed, that 3 of 4 cases with FAB-type M3 (P = 0.03) or a favorable karyotype (P = 0.04) were found in the group with >7% PRR1(+) cells, due to only few cases available a similar correlation, however, could not be found in cases with >78% PRR2(+) cells. We can conclude, that blasts in AML regularly express PRR1 and PRR2. Cases with a high expression of PRR1 or PRR2 are characterized by a more favorable prognosis. With respect to the individual PRR-status the benefit of biological response modifiers as priming agents, differentiation mediators or factors influencing cellular metabolisms inducing factors can be discussed under a new point of view.

Low-dose cytosine arabinoside (LD-AraC) vs LD-AraC plus granulocyte/macrophage colony stimulating factor vs LD-AraC plus Interleukin-3 for myelodysplastic syndrome patients with a high risk of developing acute leukemia: final results of a randomized phase III study (06903) of the EORTC Leukemia Cooperative Group

In this randomized phase III study of the EORTC Leukemia Cooperative Group, patients with myelodysplastic syndromes (MDS) with 10-30% bone marrow blasts and hematopoietic failure were treated with low-dose cytosine arabinoside (LD-AraC) (2 x 10 mg/m2/day subcutaneously (s.c.) days 1-14) either alone or in combination with rhGM-CSF or interleukin-3 (IL-3) both given s.c. at a dose of 150 microg/day from day 8 to 21. A total of 180 evaluable patients with a median age of 65 years and refractory anemia with an excess of blasts (RAEB, n = 107) or RAEB in transformation (RAEBt, n = 73) were randomized. There were no differences among the three treatment regimens with respect to numbers of courses applied or treatment delays. Hemorrhage occurred in approximately 40% in all arms, whereas infection rates were higher in the granulocyte/macrophage colony stimulating factor (GM-CSF)- or IL3-containing arm. The overall response rate was 38.6% with no statistically significant difference among the three arms. In summary, a substantial proportion of patients had achieved relatively durable responses in all the three arms. No influence of either growth factor was detected on the grade of cytopenia. Thus, the combination of LD-AraC with GM-CSF or IL-3 cannot be recommended for routine use in a high-risk MDS population.

Leukemia-Derived Dendritic Cells can be Generated from Blood or Bone Marrow Cells from Patients with Acute Myeloid Leukaemia: A Methodological Approach under Serum-Free Culture Conditions

Functional dendritic cells (DC) are professional antigen-presenting cells (APC) and can be generated in vitro from healthy as well as from leukaemic cells from acute myeloid leukemia (AML) patients giving rise to APC of leukaemic origin-presenting leukaemic antigens. We describe the generation and characterization of DC from different mononuclear cell (MNC) fractions from 50 AML patients under different serum-free culture conditions, determine the optimal culture conditions and compare the results with that from 23 healthy donors. In parallel cultures, we compared DC harvests after 7- or 14-day culture, with total or adherent MNC or T-cell depleted MNC or peripheral blood (PB) or bone marrow-MNC (BM-MNC), thawn or fresh MNC, in Xvivo or CellGro serum-free media, +/-10% autologous plasma or +/-FL. In detail, we could show that AML-DC harvests were higher after 10-14 days culture (healthy DC: 7 days); total or adherent PB or BM-MNC fractions yield comparable DC counts, however, from magnetic cell sorting (MACS)-depleted MNC fractions or thawn MNC lower DC counts can be generated. Whereas the addition of FL increases the DC harvest, the addition of autologous plasma in many cases has inhibitory influence on DC maturation. CellGro and Xvivo media yield comparable DC counts. Optimal harvest of vital and mature DC from AML samples was obtained with a granulocyte/macrophage-colony stimulating factor, interleukin-4, FL and tumour necrosis factor-alpha-containing serum-free Xvivo medium after 10-14 days of culture (36/26% DC; 38/64% vital DC; 46/51% mature DC were generated from AML/healthy MNC samples). Surface marker profiles (e.g. costimulatory antigen expressing) of DC obtained from AML samples were comparable with that of healthy DC. The leukaemic derivation of AML-DC was demonstrated by the persistence of the clonal cytogenetic aberration in the DC or by coexpression of leukaemic antigens on DC. Autologous T-cell activation of leukaemia-derived DC was demonstrated in cases with AML. Autologous T cells proliferate and upregulate DC-contact-relevant antigens. We demonstrate that the generation of leukaemia-derived DC is feasable in AML under serum-free culture conditions giving rise to DC with comparable characteristics as healthy DC and offering an anti-leukaemia-directed immunotherapeutical vaccination strategy in AML.

Low l -selectin (CD62L) expression in acute myeloid leukemia correlates with a bad cytogenetic risk

OBJECTIVES

Interactions between hemopoietic cells and the stromal microenvironment or immunoreactive cells are mediated by specific cell surface receptors. The expression of those molecules may alter the adhesive qualities (mobility and homing) as well as immune response behavior of leukemic blasts. L-Selectin (CD62L) is suggested to play a role in the redistribution and homing of hemopoietic progenitor cells to the bone marrow (BM). Down-regulation of L-selectin is responsible for mobilization of blasts from the BM into the circulation and ligation of L-selectin stimulates proliferation of progenitor cells. This could have an influence on the process of leukemia.

METHOD

We have studied the expression of L-selectin on mononuclear BM cells of 36 acute myeloid leukemia (AML) patients at first diagnosis by FACS analysis using a directly fluorescein isothiocyanate conjugated antibody (clone DRE G56).

RESULTS

On average the patients presented with 88% blasts in the BM. The expression tended to be higher in primary (p) AML compared with secondary (s) AML. L-Selectin was very heterogenously expressed in all FAB groups. Highest expression was found in cases with AML-M4 with four of nine cases presenting with an inv(16) karyotype. Separating our patient cohort in cytogenetic risk groups we could detect a significantly higher expression of L-selectin in cases with a 'good risk' karyotype and a very low expression in cases with a 'bad risk' karyotype (P = 0.037). Comparing patients who achieved remission after double induction therapy (responders) with patients who showed persisting disease (non-responders) we found a higher percentage of L-selectin+ cases or cells in the responder group than in the non-responder group, although the differences were not significant because of only five cases in the 'non-responder' group. Evaluating cut-off points greatest differences in relapse-free survival probabilities were found in patients who presented with > or = 30% L-selectin+ BM cells compared with cases with < 30%: 86% of cases with > or = 30% L-selectin+ cells were still in remission after a mean follow up time of only 8 months compared with only 46% in the group with < 30% L-selectin+ cells.

CONCLUSIONS

We can conclude that (i) expression of L-selectin on AML blasts is variable. This reveals the great diversitiy of immunophenotypes in AML and might contribute to identify individual blast phenotypes in order to detect minimal residual disease in remission. (ii) Low L-selectin expression correlates with a bad cytogenetic risk, with a lower probability to achieve remission and with a shorter relapse-free survival time. This might reflect a decreased homing of the blasts to the BM as well as an impaired cytotoxic T-cell reaction against leukemic cells. The expression of L-selectin on leukemic blasts might be influenced by different cytokine therapies (e.g. with interferon alpha) and this might result in an altered hematologic reconstitution after cytotoxic therapies as well as in an altered immunologic recognition of blasts.

Cytoprotective features of selenazofurin in hematopoietic cells

OBJECTIVES

Antineoplastic activity of tiazofurin (Tz) and selenazofurin (Se) depends on their conversion to substances which are analogs of NAD. NAD performs pleiotropic and essential cellular functions, both as a cofactor in oxidation-reduction reactions and as a substrate for poly- and mono-ADP-ribosylation reactions. The therapeutic potential of modulating intracellular NAD levels and activity of NAD-dependent enzymes by concomitant administration of conventional anticancer agents merits further research. Our aim was to investigate the cytotoxic effects of Tz and Se in hematopoietic cells and to test their ability to potentiate the effects of DNA strand-disrupting agents.

MATERIAL

THP-1, a cell line, derived from human acute monoblastic leukemia, was used. CLL lymphocytes were obtained from 8 patients with CLL.

METHODS

The WST-l test was used to detect the function of NAD(P)-dependent dehydrogenases after exposure of THP-1 cells to Tz or Se. Cytotoxicity of Tz, Se, MNNG and chlorambucil was assessed using the membrane permeability assay (PI test).

RESULTS

THP-1 cells were sensitive to cytotoxic effects of Tz and Se, with IC50 values of 2.5 x 10(-5) M for Tz and 2 x 10(-6) M for Se, as determined with the WST-1 test; 10 microM Se induced cell membrane disruption in more than 20% of THP-1 cells 48 hours after commencement of treatment, whereas the same concentration of Tz failed to increase membrane permeability. Pretreatment of THP-1 cells with 0.5 - 1.5 microM Se had no effect on the time course of cell death, induced by treatment with the DNA-damaging agent 1-methyl-3-nitro-1 - nitrosoguanidinium (MNNG) for 36 hours. However, when incubation of THP-1 cells with MNNG was prolonged (72 hours) without changing the incubation medium, pretreatment with Se had the following effects: the relative number of cells that died spontaneously decreased, and the cytotoxicity of MNNG was diminished. This effect was also demonstrated ex vivo in 6 of 8 cases of CLL, treated with MNNG and chlorambucil.

CONCLUSIONS

Contrary to other investigations, we here demonstrate that preincubation with Se may partially protect cells from cell death induced by the alkylating agents MNNG and chlorambucil in the THP-1 cell line and in CLL lymphocytes presumably by affecting spontaneous cell death.

Soluble CD137 (4-1BB) ligand is released following leukocyte activation and is found in sera of patients with hematological malignancies

Expression of CD137 ligand (4-1BBL), a member of the TNF family of proteins, has been reported on several types of APCs, various carcinoma cells, and can be induced on activated T cells. In this study, we report that the soluble ligand was released constitutively at low levels from leukocytes and at higher levels following cellular activation. Release from cells was blocked by addition of a metalloproteinase inhibitor which concomitantly caused the accumulation of 4-1BBL on the cell surface. In addition, we show that a soluble form of 4-1BBL was present at high levels in the sera of some patients with various hematological diseases, but only at low levels in healthy donors. Soluble 4-1BBL was active in that it competed with recombinant 4-1BBL for binding to the 4-1BB receptor and was able to costimulate IL-2 and IFN-gamma release from peripheral T cells. These results indicate that the release of soluble 4-1BBL from the cell surface is mediated by one or more sheddases and likely regulates 4-1BB-4-1BBL interactions between cells in vivo. Cleavage of 4-1BBL to an active soluble form would alter both proximal and distal cellular responses, including cell survival and costimulatory or inflammatory responses, that are mediated through the 4-1BB pathway. This, in turn, would likely alter disease progression or outcome.

Bcl-2, bax and bcl-xL expression in human sensitive and resistant leukemia cell lines

With the growing understanding of cytostatic drug-induced programmed cell death new drug-resistance mechanisms based on the altered ability of cells to die by apoptosis have been defined. At first, the sensitive and P-glycoprotein (P-gp)-related resistant cell lines were tested to induce apoptosis by a non-P-gp transported drug, such as cytosine arabinoside (ara-C). It was demonstrated that ara-C induces apoptosis in sensitive as well as in P-gp-related resistant cell lines, as expected. Furthermore, the role of bcl-2 and bcl-xL apoptosis inhibitors as well as bax expression (apoptosis inducer) in human sensitive leukemic cell lines (CCRF-CEM and HL-60) as compared to their resistant variants such as CCRF-CEM/ACT400, CCRF-CEM/VCR1000, HL-60/IDA40, HL-60/DNR250 was evaluated. In addition to the P-gp-related resistance, a possible multidrug resistance-associated protein (MRP) and the lung resistance protein (LRP)-related resistance were assessed by flow cytometry using the monoclonal antibodies 4E3.16, MRPr1 and LRP56. Furthermore, the function of P-gp was determined with the rhodamine-123 (R-123) accumulation test. Bcl-2 and bax were analyzed by both flow cytometry and ECL Western blot, bcl-xL by ECL-Western blot alone. Comparison of the two sensitive cell lines demonstrated different bcl-2, bax and bcl-xL patterns. The common characteristic was the increased expression of one of the apoptosis inhibitor proteins, such as bcl-2 or bcl-xL. The sensitive CCRF-CEM showed a high bax level, where a decrease of about 75% in resistant variants was measured. Compared to their sensitive counterpart HL-60, a low bax expression was analyzed, which increased in the resistant variant. The common characteristic of all resistant cell lines was the decreased expression of bax compared to bcl-2 or bcl-xL. In the P-gp-related resistant HL-60/DNR250 only an increase in bcl-xL was seen, whereas in the LRP-expressing as well as P-gp and MRP negative resistant HL-60/IDA40 both apoptotic inhibitor proteins bcl-2 and bcL-xL showed maximum increase, compared to the other resistant cell lines. The P-gp-related resistant cell lines CCRF-CEM/ACT400 and CCRF-CEM/VCR1000 also showed an increased expression of both bcl-2 and bcl-xL. Summarizing these results, it was shown that the examined sensitive human leukemic cell lines and their resistant variants demonstrated a different pattern of markers for preventing and promoting apoptosis. An association between P-gp and possible LRP-expressing leukemic cells as well as apoptosis-preventing markers (bcl-2, bcl-xL) seems to exist. The clinical relevance of the coexpression of various resistance mechanisms remains to be confirmed in large leukemia patient groups.

Molecular effects of topoisomerase II inhibitors in AML cell lines: correlation of apoptosis with topoisomerase II activity but not with DNA damage

We examined the cellular effects of topo II inhibitors in two human myeloid cell lines, HL-60 and KG-1 cells, with the purpose of finding molecular markers for the sensitivity of leukemia cells to topo II inhibitors. These cell lines are widely used, well characterized and they differ in their sensitivities to topo II inhibitors. Despite the fact that HL-60 cells are p53-negative, they are much more sensitive than KG-1 cells. Three different topo II inhibitors with distinct molecular ways of action have been used. Daunorubicin and aclarubicin are DNA intercalators that secondarily interact with topo II; etoposide, on the other hand, directly binds to the enzyme. In contrast to daunorubicin, which induces protein-associated DNA double-strand breaks due to the blockage of topo II action, aclarubicin inhibits the access of DNA by topo II. No correlation could be established between the drug-induced DNA damage and apoptosis. In fact, the amount and pattern of DNA damage examined with the 'comet assay' was characteristic for each drug in both cell lines. The DNA binding of daunorubicin was slightly higher in HL-60 cells, but there was no notable variance between the cell lines for aclarubicin. The most striking difference could be found for the nuclear topo II activity, which was about half in KG-1 cells and, additionally, less than 1% of the nuclear topo II activity was bound to the DNA in KG-1 cells when compared to HL-60 cells. This fraction of topo II interacts with the inhibitors; subsequently these findings might well explain the variance in the cellular sensitivity. Additional factors are alterations of the apoptotic pathways, eg loss of p53 in HL-60 cells. Although we found no differences in the quantity of DNA damage between the cell lines after drug treatment, the quality of DNA damage appeared to be distinct for each topo II inhibitor. The morphological appearance of the comet tails after treatment was characteristic for each drug. Further studies are necessary to decide whether these in vitro data are compatible with the clinical situation.

Endogenous FLT-3 ligand serum levels are associated with disease stage in patients with myelodysplastic syndromes

Myelodysplastic syndromes (MDS) caused by a clonal hematopoietic stem cell disorder progress to either overt leukemia or cytopenia, which leads to lethal infection or bleeding. Although several clinical trials have attempted to reverse cytopenia by using hematopoietic growth factors (HGF), success has been limited due in part to a limited understanding of the role of HGF in MDS progression. The FLT3 ligand, which binds to and activates the FLT3 receptor, does not have a stimulatory effect on hematopoietic cells, but can synergize with other HGF to support the expansion of both immature and committed progenitors. Using ELISA technology we measured endogenous serum levels in 93 patients with MDS: 29 RA, 1 RARS, 31 RAEB, 23 RAEBt, 9 CMML. 48.3% of RA patients' sera had significantly elevated FLT3 ligand levels ranging from 404 to 5735 pg/ml, whereas none of the RAEB, RAEBt, or CMML patients sera had levels different from controls. No significant correlation was found between FLT3 ligand levels and peripheral blood counts, bone marrow cellularity, age, cytogenetic abnormalities, or survival. Our data suggest that FLT3 ligand levels can be upregulated early in the course of MDS, which may represent an appropriate response to a decreased number of normal progenitors, or alternatively a dysregulated HGF system.

Endogenous serum thrombopoietin concentrations in patients with myelodysplastic syndromes

Prognosis in patients with myelodysplastic syndromes (MDS) is closely correlated with cytopenia. To date, no factor is available which is able to reliably stimulate megakaryopoiesis in vivo. Recently, the ligand of the mpl receptor was cloned and found to be thrombopoietin (TPO). We measured endogenous TPO serum levels in 69 patients suffering from MDS using an TPO receptor-based ELISA. Twenty-six of the patients suffered from refractory anemia (RA), 12 from RA with excess of blasts (RAEB), 25 from RAEB in transition (RAEBt), and six from chronic myelomonocytic leukemia (CMML). This assay uses a chimeric molecule consisting of the human TPO receptor fused to the Fc portion of human IgG as the capture reagent. Biotinylated antibody to TPO IgG was used for detection and the lower detection limit in serum was found to be 160 pg/ml. Samples obtained from healthy individuals with a normal platelet number were shown to be below detectable levels. In patients with RA, high endogenous serum TPO concentrations correlated with low platelet count and significantly elevated TPO concentrations were only found when megakaryopoiesis was absent or decreased in the bone marrow. This correlation was not detected in RAEB and RAEBt patients and no detectable TPO serum concentrations were found in six CMML patients whether they showed decreased or normal platelet count. Our data show that endogenous TPO production is upregulated by decreased circulating platelet count only in patients with refractory anemia. In the more advanced stages of MDS where the leukemic clone has further progressed, an inadequate TPO response occurs, possibly due to overexpression of the mpl receptor by the malignant clone.

Functional P-gp expression in multiple myeloma patients at primary diagnosis and relapse or progressive disease

In this study, 25 multiple myeloma (MM) patients at primary diagnosis and 18 MM patients at relapse or progressive disease (PD) were examined in order to investigate the incidence of P-glycoprotein (P-gp) expression at initial diagnosis and relapse or PD. Furthermore, P-gp expression in relation to VAD regimen response was determined. P-gp expression in the myeloma cells was determined using monoclonal antibody 4E3.16 and the rhodamine 123 functional test. The percentage of patients with P-gp overexpression at primary diagnosis ranged between 0 and 41% in the literature vs 32% in our study. The percentage of P-gp positive patients at relapse or PD ranged between 29 and 59% in the literature vs 33% in this analysis. All P-gp positive patients had a functional P-gp, ie a pumping P-gp. A significant difference concerning response (50 vs 58.3%) to VAD treatment and median survival (10 vs 12.5 months) between P-gp positive and P-gp negative patients could not be determined. Six of 12 P-gp negative MM patients at relapse or PD developed after VAD therapy a relapse combined with P-gp overexpression. These results do not confirm the suggestions that P-gp overexpression influences response to VAD treatment. However, the results described in the literature and our own emphasize the need for careful accompanying research programmes aimed at detecting the complexity of chemotherapy resistance in the light of developing a risk-adapting therapy for MM patients.

Expression and functional activity of P-glycoprotein in adult acute myelogenous leukemia patients

Expression and functional activity of P-glycoprotein (P-gp) were measured in 182 acute myelogenous leukemia (AML) patients: 136 patients were treated with the AML-6 protocol (EORTC), containing daunorubicin, vincristine, and conventional-dose cytarabine (ara-C), and 21 patients received idarubicin, vepeside, and conventional-dose ara-C (ICE-AML-10 protocol/EORTC). An additional 25 patients were treated with a dose of idarubicin and ara-C, modified as compared with the ICE protocol, but with the same dose of etopside (ICE-I protocol). P-gp was determined using monoclonal antibody 4E3.16 and functional activity using the rhodamine 123 accumulation test. P-gp positivity was defined as a Kolmogorov Smirnov (KS) D value > or = 0.15, P-gp negativity as a KS D value < 0.15. P-gp activity was defined as a ratio of mean rhodamine 123 accumulation with/without verapamil. In AML patients at primary diagnosis and early relapse/refractoriness a significant (p < 0.05) difference between P-gp-positive and P-gp-negative patients was ascertained using the AML-6 protocol; the difference corresponded to the complete remission rate. For ICE- and ICE-I-treated AML patients at primary diagnosis this significance was not shown. Compared with AML patients at primary diagnosis and patients at early relapse or refractoriness, a significantly (p < 0.05) increased incidence of non-pumping P-gp and a trend (p = 0.054) to a higher percentage of non-P-gp-related mechanisms in AML patients at late relapse was determined. When the AML-6 protocol is used, age, activated P-gp, and CD34 expression are independent prognostic factors in AML patients. A test system which determines a functional P-gp overexpression is a major tool for identifying a group of AML patients with a poor prognosis. In order to effectively use so-called P-gp modulator substances, the degree of P-gp expression, the activated or nonactivated P-gp condition, and detection of non-P-gp-related resistance mechanisms are of utmost interest for optimal design and analysis of P-gp modulator trials and for understanding the complexity of chemotherapy-related resistance mechanisms in patients.

Effects of progesterone and leukotriene receptor antagonists in experimental models of P-glycoprotein-related resistance

P-glycoprotein (P-gp)-related resistance is one of the most intensively investigated mechanisms of multidrug resistance, but the search for better modulators and better modulator combinations has just begun. The present work was performed to determine whether leukotriene LTD4 /LTE4 receptor antagonists such as FPL-55712, Ly-163443, Ly-171883, MK-571 and the progesterone receptor antagonist RU-38486 are potential P-gp modulators in models of P-gp-related resistance. Additionally, the P-gp modulating potency of the combination of RU-38486 and verapamil was investigated. P-gp expression was determined with the monoclonal antibody 4E3.16, and functional activity was assessed by the Rhodamine123 (R123) accumulation assay. Efficacy of the modulators was determined with the MTT test and the R123 accumulation assay. The in vitro examinations were done in the P-gp-resistant human T-lymphoblastic cell lines CCRF-CEM/ ACT400 and CCRF-CEM/VCR1000. No P-gp-modulating effect was observed with Ly-163443, Ly-171883, FPL-55712 or MK-571. A significant (p<0.05) cytotoxicity of the examined modulators per se (without actinomycin D or vincristine) was demonstrated only for verapamil at a concentration of 10 microM. At a concentration of 10 microM a significant (p<0.05) P-gp modulating effect was observed with RU-38486, which was even more pronounced than the effect of verapamil as determined by the MTT test. Using the R123 accumulation assay it was shown that the combination of RU-38486 (6 microM and 10 microM) and verapamil additively increased (p<0.05) the percentage of accumulating cells. This additive effect was reflected by a significantly (p<0.05) enhanced efficacy of the combination of drugs with respect to inhibition of cell proliferation. The data presented advocate testing of new potential P-gp modulator combinations, such as RU-38486 and verapamil, with the aim of increasing efficacy and simultaneously reducing side effects.

Phase I and pharmacokinetic study of the P-glycoprotein modulator dexniguldipine-HCL

Dexniguldipine (DNIG) is the R-enantiomer of the dihydropyridine derivate niguldipine. DNIG showed a binding affinity to the P-glycoprotein (P-gp) and therefore it is to be assumed to block the P-gp pumping mechanism. This open phase I study was conducted to determine the maximal tolerated dose (MTD) and safety of intravenously administered DNIG alone and in combination with vinblastine in patients with a metastatic or locally advanced cancer. Additionally, serum levels of DNIG were assessed and compared between dosage groups to investigate the intravenous dose linearity. The study was divided into two parts concerning DNIG administration. In part I the patients received DNIG for four hours daily over four consecutive days and additionally 0.15 mg/kg vinblastine at day 3. Treatment was started with 1 mg/kg/4h, and whenever the drug was well tolerated the dosage was increased. In part II the patients received up to three courses of a four-hour infusion (5 and 7 mg/kg/4h) of DNIG followed by a continuous infusion for 48 hours (5 and 7 mg/kg/24h). Twenty-six patients entered this trial and were given at least one infusion of DNIG; vinblastine was given immediately after the 4-hour infusion. One to seven courses and dosages from 1-11 mg/kg were administered. In five patients the dose limiting toxicity was seen in cardiovascular adverse events such as a drop in blood pressure, decreased heart rate and in one patient an AV block III. Most frequent adverse events were nausea, dizziness, vomiting, peripheral paresthesia, atactic gait, mild constipation, polyuria, hypocalcemia; all disappeared within 24 hours after discontinuation of infusion. A linear increase in DNIG serum concentration with increasing doses was found following intravenous infusion of DNIG over a four-hour period. Long-term infusion regimes over a period of two or five days resulted in reasonably constant DNIG serum levels. MTD was determined at 5 mg/kg/4h. It is to be assumed that the MTD for continuous infusion of DNIG is higher than 5 mg/kg/24h, but this was not followed up in the study and must be the aim of a later trial.

Topoisomerase II activities in AML blasts and their correlation with cellular sensitivity to anthracyclines and epipodophyllotoxines

We have developed a method to quantify topoisomerase (topo) II activities in partially purified nuclear extracts from human leukemia cells. By virtue of their different pH optima in the reaction buffer, two different topo II activities were found with activity optima at pH 7.9 and at pH 8.9 under high stringency conditions. The activities could be identified as topo II beta activity (pH 7.9) and topo II alpha activity (pH 8.9) by their different sensitivities to topo II alpha inhibitors, dephosphorylation experiments and immunoprecipitation with polyclonal antibodies. Seventy-two bone marrow or blood samples from patients with acute myeloid leukemias have been examined and their in vitro sensitivities to anthracyclines and epipodophyllotoxines correlated to the activities of topo II alpha and topo II beta. Although the topo II alpha activity could be directly inhibited by incubation of the cells with the mentioned drugs, no correlation between the topo II alpha activity and the sensitivity of the cells could be found. In contrast, the topo II beta activity which was not substantially inhibited by the drugs inversely correlated with the sensitivity of the cells. These findings were statistically significant for idarubicin (P=0.017) and daunorubicin (P=0.006). Vice versa, resistant cells (IC90 > median) had a higher topo II beta activity. Clinical relevance might be indicated by the finding that cells from patients that relapsed after initial treatment with anthracyclin-containing regiments had a significantly higher topo II alpha/beta activity ratio (P=0.0276). Obviously, the sensitivity of AML cells is substantially influenced by the activity of the resistant topo II (topo II beta) which gives evidence that the remaining topo II activity after treatment helps the cell to survive the DNA repair phase.

Topoisomerase II activities in AML and their correlation with cellular sensitivity to anthracyclines and epipodophyllotoxines

We have developed a method to quantify topoisomerase (topo) II activities in partially purified nuclear extracts from human leukemia cells. By virtue of their different pH optima in the reaction buffer, two different topo II activities were found with activity optima at pH 7.9 and at pH 8.9 under high stringency conditions. The activities could be identified as topo II beta activity (pH 7.9) and topo II alpha activity (pH 8.9) by their different sensitivities to topo II alpha inhibitors, dephosphorylation experiments and immunoprecipitation with polyclonal antibodies. Seventy-two bone marrow or blood samples from patients with acute myeloid leukemias have been examined and their in vitro sensitivities to anthracyclines and epipodophyllotoxines correlated to the activities of topo II alpha and topo II beta. Although the topo II alpha activity could be directly inhibited by incubation of the cells with the mentioned drugs, no correlation between the topo II alpha activity and the sensitivity of the cells could be found. In contrast, the topo II beta activity which was not substantially inhibited by the drugs inversely correlated with the sensitivity of the cells. These findings were statistically significant for idarubicin (P= 0.017) and daunorubicin (P = 0.006). Vice versa, resistant cells (IC50 > median) had a higher topo II beta activity. Clinical relevance might be indicated by the finding that cells from patients that relapsed after initial treatment with anthracyclin-containing regiments had a significantly higher topo II alpha/beta activity ratio (P=0.0276). Obviously, the sensitivity of AML cells is substantially influenced by the activity of the resistant topo II (topo II beta) which gives evidence that the remaining topo II activity after treatment helps the cell to survive the DNA repair phase.