Martin Spitaler

Detection of activity of P-glycoprotein in human tumour samples using rhodamine 123

Summary Based on the fluorescent properties of the dye rhodamine 123 (Rh123), which is transported by the membrane efflux pump P‐glycoprotein (P‐gp), we developed a functional flow cytometric assay for the detection of multidrug‐resistant (MDR) cells. Using drug sensitive cell lines (KB‐3–1) and MDR mutants (KB‐8–5, KB‐C1) experimental conditions were established that enabled demonstration of significant differences in Rhl23 efflux and accumulation. Subsequently we investigated the applicability of this functional assay for the prediction of MDR in human peripheral blood and bone marrow samples. Using two‐colour flow cytometry, the leukaemic blast cells of six patients suffering from acute myeloid leukaemia (AML) were analysed. In three cases the blast cells showed a rapid and marked Rh123 efflux. In the presence of MDR inhibitors these cells retained Rh123. To determine whether the efflux of Rhl23 was associated with P‐gp expression, the leukaemic cells were stained with the monoclonal antibody MRK‐16. In addition extracted RNA was analysed by polymerase chain reaction to evaluate the expression of mdr 1 mRNA. In all three Rh123+ cases mdr 1 mRNA was detectable whereas only one AML case expressed P‐gp. In comparing Rh123 with daunorubicin, which also allows the detection of MDR cells, accumulation studies proved Rh123 to be the more sensitive drug for flow cytometric MDR screening. Additionally, two‐colour flow cytometry was much easier to perform with Rh123 than with daunorubicin.

Effects of miltefosine on various biochemical parameters in a panel of tumor cell lines with different sensitivities

We investigated endocytosis activity, uptake of miltefosine (hexadecylphosphocholine), phospholipid and cholesterol content, the cell cycle, and apoptosis in 13 tumor cell lines (MCF7, MCF7/ADR, KB-3-1, KB-8-5, KB-C1, HeLa, HeLa-MDR1-G185, HeLa-MDR1-V185, CCRF/CEM, CCRF/VCR1000, CCRF/ADR5000, HL-60, HL-60/AR) with different sensitivities to treatment with the antitumor phospholipid analogues miltefosine and D-21266 (octadecyl-(N,N-dimethyl-piperidino-4-yl)-phosphate). In this panel of cell lines, MDR1 (multidrug resistance gene 1)- and MRP1 (multidrug resistance-associated protein)-expressing cells were found to be slightly more resistant to both compounds than sensitive parental cells. No correlation was found between resistance to miltefosine and endocytosis, intracellular concentration of miltefosine, the phospholipid and cholesterol content, induction of apoptosis, or cell cycle alterations in all the cell lines tested. Wild-type p53 containing WMN Burkitts lymphoma cells and wild type p53-deficient CA46 exhibited similar sensitivities to miltefosine. The low percentage of apoptosis induced in MCF7 cells lacking caspase 3 indicated that caspase 3 seems to play an essential role in miltefosine-induced apoptosis.

Reversal of multidrug resistance by B859-35, a metabolite of B859-35, niguldipine, verapamil and nitrendipine.

SummaryIt has been shown previously that verapamil and other calcium antagonists and calmodulin inhibitors can reverse multidrug resistance. We compared the potency of the dihydropyridine derivatives (4R)-3-[3-(4,4-diphenyl-l-piperadinyl)-propyl]-5-methyl-1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-pyridine-3,5-dicarboxylate-hydrochloride (B859-35), a metabolite of B859-35, niguldipine and (R)-nitrendipine to that of (RS)-verapamil in reversing multidrug resistance. The accumulation of the fluorescent dye rhodamine 123, which is transported by the P-glycoprotein, was determined by a flow cytometer. Multidrug-resistant human HeLa KB-8-5 and Walker rat carcinoma cells were incubated in the presence and in absence of the drugs indicated above. We found that 0.1 μM B859-35 increases the accumulation of rhodamine 123 in multidrug-resistant KB-8-5 and Walker cells more effectively than 1 μM (RS)-verapamil. In sensitive KB-3-1 cells addition of the drugs had no significant influence on the accumulation of rhodamine 123. In KB-8-5 cells, 10 nM Adriamycin caused a reduction of cell growth to 85% compared to untreated controls (=100%). If 1 μM B859-35, B859-35 metabolite, niguldipine, verapamil or (R)-nitrendipine was added to 10 nM Adriamycin, growth reduction compared with untreated controls increased to 12%, 11%, 23%, 63%, and 82% respectively. The effect of 0.1 μM B859-35 was a reduction in proliferation to 38%, that of 0.1 μM verapamil to 72%. These data illustrate that B859-35, a compound with antitumor activity in several tumors, is at least ten times more potent than racemic verapamil in reversing multidrug resistance.

Unique structural and functional properties of the ATP-binding domain of atypical protein kinase C-iota.

Atypical protein kinase C-ι (aPKCι) plays an important role in mitogenic signaling, actin cytoskeleton organization, and cell survival. Apart from the differences in the regulatory domain, the catalytic domain of aPKCι differs considerably from other known kinases, because it contains a modification within the glycine-rich loop motif (GXGXXG) that is found in the nucleotide-binding fold of virtually all nucleotide-binding proteins including PKCs, Ras, adenylate kinase, and the mitochondrial F1-ATPase. We have used site-directed mutagenesis and kinetic analysis to investigate whether these sequence differences affect the nucleotide binding properties and catalytic activity of aPKCι. When lysine 274, a residue essential for ATP binding and activity conserved in most protein kinases, was replaced by arginine (K274R mutant), aPKCι retained its normal kinase activity. This is in sharp contrast to results published for any other PKC or even distantly related kinases like phosphoinositide 3-kinase γ, where the same mutation completely abrogated the kinase activity. Furthermore, the sensitivity of aPKCι for inhibition by GF109203X, a substance acting on the ATP-binding site, was not altered in the K274R mutant. In contrast, replacement of Lys-274 by tryptophan (K274W) completely abolished the kinase activity of PKCι. In accordance with results obtained with other kinase-defective PKC mutants, in cultured cells aPKCι-K274W acted in a dominant negative fashion on signal transduction pathways involving endogenous aPKCι, whereas the effect of the catalytically active K274R mutant was identical to the wild type enzyme. In summary, aPKCι differs from classical and novel PKCs also in the catalytic domain. This information could be of significant value for the development of specific inhibitors of aPKCι as a key factor in central signaling pathways.

Multidrug resistance in acute leukemia: a comparison of different diagnostic methods.

Accurate measurement of P-glycoprotein (P-170) expression in clinical samples still remains a controversial issue. In this study tumor cell P-170 expression was assessed in 29 patients suffering from acute leukemia (17 acute myeloid leukemia (AML) and 12 acute lymphoblastic leukemia (ALL)) using three different techniques: flow cytometry measuring rhodamine 123 (Rh123) efflux (functional level), immunocytochemistry (protein level) and RT-PCR (mRNA level). Rh123 efflux was detectable in 10/29 (34%) of all cases, in 9/17 (53%) of AML and in 1/12 (8%) of ALL samples. In AML patients a significant association of CD34 expression and P-170 activity was observed (P < 0.02). all aml patients with the fab subtype m5 were rh123 negative (P < 0.007). cytospin preparations were analyzed for staining with monoclonal antibodies jsb1 and mm4.17. eight of 16 (50%) aml and 0/9 (0%) all cases expressed the multidrug resistance (mdr) protein assessed by jsb1. with mm4.17 87% of aml and 50% of all patients were scored positive. agreement between both antibodies was found in only 13/23 (57%) samples. extracted rna from 12 patients was analyzed by rt-pcr to evaluate the expression of mdr1 and multidrug resistance-associated protein (mrp) mrna. an increased level of mdr1 mrna was detectable in 4/7 aml and 0/5 all cases. mrp expression was found in 3/7 aml and 0/5 all patients. comparison of rh123 assay and immunocytochemistry revealed a very good correlation when using moab jsb1 (P < 0.004) but not with mm4.17 (not significant (ns)). jsb1 also showed a much better association with the pcr results (P < 0.05) than mm4.17 (ns). finally, we compared the results of the functional rh123 assay and rt-pcr and observed a high correlation for rh123/mdr1 (r = 0.819, P < 0.001) but low for rh123/mrp (r = 0.562, NS). We conclude that measurement of Rh123 efflux and immunocytochemical staining of cytospin preparations with JSB1 allows the accurate monitoring of P-170 expression in acute leukemia. The simplicity of these two MDR assays suggests their use for routine MDR screening.

PKC-independent modulation of multidrug resistance in cells with mutant (V185) but not wild-type (G185) p-glycoprotein by bryostatin 1

Bryostatin 1 is a new antitumor agent which modulates the enzyme activity of protein kinase C (PKC, phospholipid-Ca2+-dependent ATP:protein transferase, EC 2.7.1.37). Several reports have suggested that the pumping activity of the multidrug resistance gene 1 (MDR1)-encoded multidrug transporter P-glycoprotein (PGP) is enhanced by a PKC-mediated phosphorylation. It was shown here that bryostatin 1 was a potent modulator of multidrug resistance in two cell lines over-expressing a mutant MDR1-encoded PGP, namely KB-C1 cells and HeLa cells transfected with an MDR1-V185 construct (HeLa-MDR1-V185) in which glycine at position 185 (G185) was substituted for valine (V185). Bryostatin 1 is not able to reverse the resistance of cells over-expressing the wild-type form (G185) of PGP, namely CCRF-ADR5000 cells and HeLa cells transfected with a MDR1-G185 construct (HeLa-MDR1-G185). Treatment of HeLa-MDR1-V185 cells with bryostatin 1 was accompanied by an increase in the intracellular accumulation of rhodamine 123, whereas no such effect could be observed in HeLa-MDR1-G185 cells. HeLa-MDR1-V185 cells expressed the PKC isoforms alpha, delta and zeta. Down-modulation of PKC alpha and delta by 12-O-tetradecanoylphorbol-13-acetate (TPA) did not affect the drug accumulation by bryostatin 1. Bryostatin 1 depleted PKC alpha completely and PKC delta partially. In HeLa-MDR1-V185 cells, short-term exposure to bryostatin 1, which led to a PKC activation, was as efficient in modulating the pumping activity of PGP as long-term exposure leading to PKC depletion. Bryostatin 1 competed with azidopine for binding to PGP in cells expressing the MDR1-V185 and MDR1-G185 forms of PGP. It is concluded that bryostatin 1: i) interacts with both the mutated MDR1-V185 and the wild-type MDR1-G185; ii) reverses multidrug resistance and inhibits drug efflux only in PGP-V185 mutants; and iii) that this effect is not due to an interference of PKC with PGP. For gene therapy, it is important to reverse the specific resistance of a mutant in the presence of a wild-type transporter and vice versa. Our results show that it is possible to reverse a specific mutant PGP.

Regulation of phospholipase D isoenzymes by transforming Ras and atypical protein kinase C-iota.

The activation of phospholipase D (PLD) by transforming Ras is well documented. Although two distinct PLD isoforms, PLD1 and PLD2, have been cloned from mammalian cells, it has remained unclear whether both isoenzymes are activated by Ras and, if this is the case, whether they are stimulated by a common mechanism. In the present study we show that expression of transforming Ras in HC11 mouse mammary epithelial cells enhanced the activity of endogenous PLD. Co-expression of Ras with either PLD1b or PLD2 resulted in elevated activities of both PLD isoenzymes in HC11 cells, indicating that transforming Ras was capable of activating both PLD isoforms in vivo. Ras-induced activation of PLD was resistant to the protein kinase C (PKC) inhibitor GF109203X, which preferentially affects conventional- and novel-type PKCs, but sensitive to Ro-31-8220, which inhibits atypical PKCs more effectively. Co-transfection of atypical PKC-iota with either PLD1b or PLD2 led to a selective activation of PLD2 by PKC-iota, whereas PLD1b was not affected. PLD1b, however, was found to be a potent activator of PKC-iota, whereas PLD2 was less effective in this respect. The data suggest that PKC-iota acts upstream of PLD2 and that PLD1b is implicated in the activation of PKC-iota. The data are discussed as indicating a putative signalling cascade comprising Ras-->PLD1b-->PKC-iota-->PLD2. Evidence for the implication of this pathway in the transcriptional regulation of cyclin D1 is also presented.

Reversal of multidrug resistance by the staurosporine derivatives CGP 41251 and CGP 42700

It has been shown previously that the staurosporine derivative CGP 41251, a specific inhibitor of protein kinase C (IC50 = 50 nM), exhibits antitumor activity and reverses mdr1‐mediated multidrug resistance. At present, the compound is evaluated as an anticancer drug in clinical phase I trials. We compared the effects of CGP 41251 with CGP 42700, another staurosporine derivative, which exhibits low protein kinase C inhibiting activity (IC50 = >100 μM). We found that in contrast to CGP 41251, CGP 42700 does not show antiproliferative activity in HeLa and KB cells in tissue culture (up to a concentration of 10 μM). We compared both compounds for their ability to reverse mdr1‐mediated resistance in KB‐C1 and in HeLa‐MDR1 cells (transfected with the mdr1 gene). CGP 42700 is able to reverse mdr1‐mediated resistance to a similar extent as CGP 41251. The intracellular accumulation of rhodamine 123 in KB‐C1 cells following pretreatment with CGP 41251 for 30 min was higher than that following treatment with CGP 42700 if determined in medium without serum. However, quantitation of rhodamine efflux in an ex vivo assay using human CD8+ cells in serum showed that CGP 42700 is more effective in inhibiting the efflux of rhodamine 123 than CGP 41251. We conclude from our results that (1) CGP 42700 is more effective in reversal of multidrug resistance in serum than CGP 41251, indicating that the compound may be useful for treatment of patients, and (2) CGP 42700 does not inhibit protein kinase C and cell proliferation and, therefore, may be less toxic and elicit less side effects in humans than other chemosensitizers. Int. J. Cancer 77:64–69, 1998.© 1998 Wiley‐Liss, Inc.

The New Anticancer Drug Ilmofosine Enhances the Activity of CIS-Platin and Reverses Multidrug Resistance

It is well established that the alkyllysophospholipid ilmofosine (BM 41 440) exhibits antiproliferative activity on tumor cells, but not on bone marrow. Here we demonstrate synergism in antitumor activities of a combination of ilmofosine with cis-platin. We also show that 0.1 μM ilmofosine reverses the multidrug resistance of KB-8-5 cells to the sensitivity of KB-3-1 cells.

Elements of Signal Transduction in Drug Discovery with Special Reference to Inhibitors of Protein Kinase C

Although for a few malignancies, such as childhood leukaemia, Hodgkin’s disease, and testicular cancer, impressive progress has been achieved, cancer mortality as a whole has remained almost unchanged during the last two decades despite enormous worldwide efforts. This is particularly surprising in view of the tremendous progress that has been achieved during the last 20–25 years with regard to our understanding of the molecular mechanisms underlying the regulation of normal growth and dysregulation of malignant growth. Major scientific breakthroughs — the discovery of oncogenes, tumour suppressor genes, mechanisms of angiogenesis, and apoptosis — have occurred during the last two to three decades, but these have not led to any major progress in cancer treatment.