Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0023418 (leukemia)
 93,477 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The activity of microsomal HMG-CoA reductase in freshly isolated leukocytes from patients with a variety of hematologic malignancies was significantly increased (up to 20-fold) when compared to enzyme activity in leukocytes from normal subjects (average 10.3 +/- 0.8 pmol/min per mg). Increased enzyme activity was not due to nonspecific leukocyte stimulation or to the presence of a malignancy, since normal enzyme activity was observed in subjects with either viral illnesses or solid tumors. Increased HMG-CoA reductase activity accompanying hematologic malignancy could also not be attributed to alterations in enzyme-substrate kinetic parameters (Km), or to alterations in the phosphorylation state or thiol-disulfide status of the enzyme, nor was it correlated with differences in serum lipid or lipoprotein concentrations. The increase (3.6-fold) in HMG-CoA reductase activity in leukocytes from patients with preleukemia was due entirely to a rise in enzyme catalytic efficiency (specific activity), whereas the increase (4.3-fold) observed in leukocytes from patients with overt leukemia or non-Hodgkin's lymphoma was due to a concomitant increase in both enzyme catalytic efficiency (2.5-fold) and enzyme protein concentration (1.6-fold). Similar increases in HMG-CoA reductase activity and catalytic efficiency were also noted for both transformed, nonmalignant, and malignant cultured leukocytes, suggesting that increased enzyme catalytic efficiency is not a nonspecific consequence of physiological changes occurring in response to the malignancy but may be an integral aspect of the malignant phenotype. HMG-CoA reductase protein concentrations, however, were not elevated in either transformed, nonmalignant, or malignant cultured leukocytes, suggesting that increases in enzyme protein levels may be secondary to other physiological changes that occur during the development of overt leukemia. Taken together, these observations suggest that an increase in the activity of HMG-CoA reductase, the rate-controlling enzyme in cholesterol synthesis, is a common occurrence in human hematologic malignancies and that a biphasic elevation of enzyme activity may exist in malignant leukocytes, such that changes in catalytic activity may occur early in tumorigenesis and may be followed by secondary changes in enzyme levels.
 ...
PMID:In vivo regulation of human leukocyte 3-hydroxy-3-methylglutaryl coenzyme A reductase: increased enzyme protein concentration and catalytic efficiency in human leukemia and lymphoma. 177 Mar 7

In the 2H3 subline of rat basophilic leukemia cells (RBL-2H3), IgE receptor cross-linking stimulates a signal transduction pathway that leads to the secretion of histamine, serotonin, and other inflammatory mediators; the assembly of F-actin; and the transformation of the cell surface from a microvillous to a lamellar or ruffled architecture. We report here that 20 h incubation of RBL-2H3 cells with 10 microM lovastatin, an inhibitor of 3-hydroxy-3-methyl-glutaryl coenzyme A reductase (HMG CoA reductase), inhibits both the secretory and morphologic responses to IgE receptor cross-linking. Ag-induced Ca2+ mobilization, determined from the influx and efflux of 45Ca2+, and Ag-induced 1,4,5-inositol trisphosphate production are also inhibited in lovastatin-treated RBL-2H3 cells. Under the same conditions, lovastatin does not alter cell proliferation or IgE receptor expression, and it causes only a small impairment of responses initiated by drugs that bypass the earliest steps in the receptor-activated transduction pathway (ionomycin-induced secretion and PMA-induced membrane ruffling). Receptor-mediated Ca2+ mobilization, secretion, and ruffling are all restored by 0.5- to 4-h incubation of lovastatin-treated cells with mevalonic acid, the product of HMG CoA reductase and the first committed intermediate of the isoprenoid biosynthetic pathway. In contrast, dolichol and cholesterol, which are synthesized from products of the isoprenoid pathway, do not restore receptor-activated responses. These data implicate an isoprenoid pathway intermediate in an early step in the IgE receptor-activated signal-transduction sequence. We postulate that this intermediate is required for a newly described post-translational modification of proteins, their post-synthetic isoprenylation. The substrates for this modification include the ras family of GTP-binding proteins and the gamma subunits of the heterotrimeric guanine nucleotide-binding protein.
 ...
PMID:Role of isoprenoid metabolism in IgE receptor-mediated signal transduction. 182 87

The effects of competitive inhibition of hydroxymethylglutaryl coenzyme A (HMG CoA) reductase by compactin on the in vitro proliferation of peripheral blood myeloid leukemia cells were studied using the cells from 45 patients with acute myeloid leukemia or chronic myelogenous leukemia in blast phase. The cells from 58% of these patients showed a dose-related inhibition of DNA synthesis when incubated with compactin. Unexpectedly, cells from 18% of the patients were resistant to the inhibitory effects of compactin on DNA synthesis and responded to the HMG CoA reductase inhibition with an actual increase in the incorporation of 14C-labeled thymidine into DNA. Another 18% of the patients studied displayed both inhibition and stimulation of DNA synthesis in a biphasic response depending on the particular concentration of compactin used. The maximum enhanced rates of cellular DNA synthesis were observed with lower compactin concentrations (5 x 10(-7) mol/L) than were required for maximum inhibition of DNA synthesis (10(-5) mol/L). Leukemia cells displaying a stimulated response to compactin had a significantly lower baseline DNA synthetic rate than did cells that showed an inhibitory response of DNA synthesis to compactin. There was no correlation between these cells' varying DNA synthetic response to compactin and measures of baseline HMG CoA reductase activity or acetate conversion to cholesterol. Whereas the observation of cellular DNA synthesis stimulation by HMG CoA reductase inhibition has not been observed in other mammalian cells and seems paradoxical, explanations may emerge in light of our growing knowledge concerning the importance of isoprenylation for the function of certain cell regulatory proteins.
 ...
PMID:Inhibition of hydroxymethylglutaryl coenzyme A reductase activity induces a paradoxical increase in DNA synthesis in myeloid leukemia cells. 199 91

Of the many varieties of drug interactions, which occur when the disposition or actions of one drug are changed by another, only a few are serious or potentially fatal. A representative outline of some of these illustrates the problem. Precipitant drugs are those which produce the interaction, and object drugs are those whose effects are changed. The interactions which are usually significant are those which alter the metabolism, involve renal excretion, or change the effects of the object drug, especially when the object drug has a low therapeutic index (cardiovascular drugs, anticoagulants, drugs acting on the brain, hypoglycemic drugs, hormones, and cytotoxic drugs). Warfarin toxicity, for example, is produced by aspirin, phenylbutazone, and azapropazone. The dosage requirements of warfarin are reduced by chloramphenicol, ciprofloxacin and other quinolones, erythromycin and some of the other macrolides, metronidazole and other imidazoles, tetracyclines, amiodarone, cimetidine (but not ranitidine), and fibrates. Potassium-depleting drugs can potentiate the action of digoxin, and the elimination of digoxin can be reduced by amiodarone, propafenone, quinidine, and verapamil. Combined oral contraceptives can lose effectiveness through the interaction of carbamazepine, griseofulvin, phenytoin, or rifampicin, which increase estrogen metabolism. In addition, broad-spectrum antibiotics such as ampicillin or tetracyclines also reduce contraceptive effectiveness by altering gut absorption. Even a single drink of an alcoholic beverage may be dangerous to people taking antidepressants, antihistamines, antipsychotic drugs, benzodiazepines, or lithium. Antihistamines suffer inhibited metabolism in the liver if taken in conjunction with the antifungal imidazoles and some of the macrolide antibiotics. Cardiotoxicity of antihistamines is also enhanced by drugs with similar cardiotoxic effects. Lithium potentiation is enhanced by the new serotonin-reuptake inhibitors, and lithium excretion can be reduced by diuretics or fluoxetine. When drugs such as antifungal imidazoles, azapropazone, or phenylbutazone are permitted to inhibit the metabolism of sulphonylureas, hypoglycemic effects are enhanced and, if unnoticed, may cause brain damage. Fibrates should not be combined with HMG-CoA reductase inhibitors because of the increased risk of myopathy. Patients taking non-selective monoamine oxidase inhibitors should avoid amine-containing foods and drugs such as matured cheeses, meat, yeast extracts, some wines, unfresh protein, and cold-curing medications. The metabolism of azathioprine is inhibited by allopurinol, and this combination requires a reduced dosage of azathioprine. Mercaptopurine, used in the treatment of leukemia, is also a metabolite of azathioprine. Sources of comprehensive information on drug interactions are 1) the "British National Formulary," appendix 1; 2) Chapter 10 of "The Oxford Textbook of Clinical Pharmacology and Drug Therapy"; and 3) a monograph by Stockley entitled "Drug Interactions."
 ...
PMID:Serious drug interactions. 790 48

Altered cholesterol homeostasis has been noted in malignant cells, which led us to explore the regulation of cholesterol metabolism in normal and leukemic cells. The mean low-density lipoprotein (LDL) receptor and 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activities were fivefold and threefold higher in mononuclear blood cells from 33 patients with leukemia, compared with cells from 23 healthy subjects, whereas elevations in RNA levels were twofold and 40% only. The activities of the two proteins correlated in normal cells (r = .46), whereas an inverse correlation was found in leukemic cells (r = -.40). Relatively weak correlations were found between LDL receptor RNA levels and receptor activity in normal (r = .48) and leukemic cells (r = .49), and HMG-CoA reductase RNA levels correlated (r = .53) with reductase activity in leukemic cells only. The ratios of protein activities to RNA levels in cells were constant during consecutive blood samplings and similar in leukemic blood and bone marrow cells from the same individual. During cholesterol deprivation, protein activities increased more than RNA levels, and leukemic cells with high LDL receptor activity showed a partial resistance to the suppressing effect of sterols on LDL receptor gene expression. The results demonstrate that LDL receptor RNA levels alone can not explain variation in receptor activity, suggesting post-RNA regulation of LDL receptor expression, similar to what has been described for HMG-CoA reductase. Taken together, the present results suggest multilevel regulation of both proteins and demonstrate that each cell clone, normal or malignant, has a unique ratio of protein activity to RNA level. Leukemic cells, in contrast to normal cells, can meet increased cholesterol requirements by either elevated LDL receptor activity or increased cholesterol synthesis, which is of potential interest for diagnosis and specific treatment of leukemia.
 ...
PMID:Multilevel regulation of low-density lipoprotein receptor and 3-hydroxy-3-methylglutaryl coenzyme A reductase gene expression in normal and leukemic cells. 791 82

Chronic lymphocytic leukemia (CLL) cells express lower low density lipoprotein (LDL) receptor activity and higher 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase activity than normal mononuclear blood cells indicating that CLL cells may depend on cholesterol synthesis for their proliferation. We studied the effects of competitive inhibitors of HMG-CoA reductase on malignant lymphocyte proliferation in vitro and in vivo. Tumor B-cells from 13 patients with CLL, hairy cell leukemia, or immunoblastic B-cell lymphoma were cultured for 4 d in the presence of B-cell mitogens and cholesterol synthesis inhibitors. Simvastatin and lovastatin suppressed, in a concentration-dependent manner, the mitogen-induced cellular thymidin uptake in medium with 10% human AB-serum or lipoprotein-deficient serum. Pravastatin was active only in medium with lipoprotein-deficient serum. Ten previously untreated patients with CLL received simvastatin orally, 40 mg daily for 12 wk. Mean reductions in total plasma and LDL cholesterol were 30% (range 9-46%) and 37% (range 16-63%), respectively. Cells from four patients showed moderate to minor increases in the degradation rate of 1251-LDL suggesting that the need for exogenous cholesterol had increased, three patients showed an increase in HMG-CoA reductase activity, and the cells from one patient showed both. There was no significant change in the clinical disease status during medication. However, four of the ten patients developed a therapy-demanding progressive disease during the subsequent year. Further clinical studies with cholesterol synthesis inhibitors in leukemia are warranted.
 ...
PMID:Simvastatin impairs mitogen-induced proliferation of malignant B-lymphocytes from humans--in vitro and in vivo studies. 907 62

Simvastatin is an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase and also selectively inhibits the growth of leukaemic progenitor cells. The antileukaemic action of simvastatin was compared in vitro with that of lovastatin and pravastatin, chemically related compounds which are also competitive inhibitors of HMG-CoA reductase. After 18 hours incubation with 2.5-20 microM of inhibitor, no effect was observed by any of the compounds on the subsequent clonogenic growth of normal bone marrow (BM) progenitor cells from 4 donors and BM cells from one patient in remission. However, simvastatin and lovastatin produced inhibition of acute myeloid leukaemia (AML) progenitor cell growth of between 25% and 100% in 5 populations tested (4 primary AMLs and the HL60 cell line). Pravastatin showed similar growth inhibitory effects to simvastatin and lovastatin in 2 out of 3 primary AMLs but was less active against one primary AML cell population and HL60 cells. These results indicate that, in addition to simvastatin, lovastatin and pravastatin are also selective inhibitors of leukaemic cell growth, however simvastatin was chosen for clinical trial in patients with leukaemia.
 ...
PMID:A comparison of the effect of the 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors simvastatin, lovastatin and pravastatin on leukaemic and normal bone marrow progenitors. 908 43

Lovastatin, an inhibitor of 3-hydroxy-3-methylglutaryl (HMG) CoA reductase, and 6-fluoromevalonate (Fmev), an inhibitor of diphosphomevalonate decarboxylase, blocked the synthesis of downstream mevalonate products, including prenyl-derived lipids, and prevented membrane localization of Ras in the myeloid cell line U-937. In contrast to lovastatin, which induced cytosol localization of Ras in U-937 cells, Fmev failed to increase cytosolic Ras and also completely prevented the proliferation of U-937 cells. Growth of U-937 cells was restored by the addition of lovastatin to Fmev-blocked cells. These results implied that a product of mevalonate metabolism proximal to isopentenyl diphosphate was responsible for the suppression of proliferation. To delineate the action of this endogenous inhibitor of cell proliferation and determine the relationship between its impact on Ras localization and cell proliferation, the effect of Fmev on a variety of leukemia- and lymphoma-derived cells was examined. Whereas Fmev blocked the growth of these cell lines, there were more than 50-fold differences in the concentrations required to inhibit the growth of individual cell lines by 90%. Regardless of its effect on cell proliferation, the biochemical effect of Fmev was similar. Thus, Fmev uniformly prevented the conversion of radiolabeled mevalonate to isopentenyl diphosphate and other downstream products, including synthesis of sterol and nonsterol lipids and prenylation of proteins. A correlation was noted between higher intrinsic rates of mevalonate synthesis by a cell and susceptibility to inhibition by Fmev. Thus, sensitivity of a cell line to inhibition by Fmev was associated with markedly increased rates of HMG CoA reductase activity that were further increased by incubation with Fmev. Whereas Fmev depleted cellular levels of the prenylated protein Ras in the sensitive cell line U-937, there was no depletion of cellular Ras levels in the resistant cell line EL-4, but rather, there was a shift of Ras from membrane to cytosol, as expected for inhibition of prenylation. These results suggest that leukemic cells with increased HMG CoA reductase activity produce increased levels of an endogenous mevalonate-derived inhibitor that leads to Ras depletion and suppression of cell growth. As a result, inhibition of the growth of these transformed cells might be specifically accomplished by Fmev.
 ...
PMID:Regulation of proliferation and Ras localization in transformed cells by products of mevalonate metabolism. 927 19

Lovastatin, a competitive inhibitor of HMG-CoA reductase, reportedly inhibits proliferation and induces apoptosis of tumor cells with MDR-1 coded P-glycoprotein (Pgp) expression. In this study we investigated the sensitivity to lovastatin of eight myeloid leukemia cell lines: K562, NOMO-1, NB4 and its retinoic acid (RA) resistant subline NB4/RA, and their multidrug-resistant (MDR) sublines: K562/ADR, NOMO-1/ADR, NB4/MDR and NB4/RA/MDR. MTT and apoptosis assays revealed that K562/ADR, NOMO-1/ADR and NB4/RA/MDR were more sensitive to lovastatin than their parental cell lines, while NB4/MDR showed the same level of sensitivity as parental NB4 cells, which already were very sensitive to lovastatin. Significant elevation of transcript levels of HMG-CoA reductase was observed by semiquantitative RT-PCR analysis in more than three lovastatin-sensitive MDR sublines, but not in NB4/MDR compared with the parental cell lines. HMG-CoA reductase mRNA levels were up-regulated more than two-fold by the exposure to lovastatin in all of the parental non-Pgp-expressing cell lines. In NB4/MDR, HMG-CoA reductase mRNA level was elevated to a similar extent as in parental NB4, whereas in three other MDR sublines which showed preferential sensitivity to lovastatin, their HMG-CoA reductase mRNA levels were not significantly elevated after 24- and 48-h treatment with lovastatin. These results indicate a connection between drug resistance and regulation of the mevalonate pathway, and further strengthen the clinical possibility that drug resistant leukemias would be susceptible to treatment with lovastatin.
Leukemia 2000 Aug
PMID:Increased sensitivity of multidrug-resistant myeloid leukemia cell lines to lovastatin. 1094 41

3-Hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase is the rate-limiting enzyme of the mevalonate pathway, the diverse array of end products of which are vital for a variety of cellular functions, including cholesterol synthesis and cell cycle progression. We showed previously that this enzyme holds a critical role in regulating tumor cell fate, including cell death, as its expression is down-regulated in response to retinoic acid, a potent anticancer therapeutic. Indeed, direct inhibition of HMG-CoA reductase with lovastatin, a competitive inhibitor of this enzyme, induced a pronounced apoptotic response in neuroblastoma and acute myeloid leukemic cells. We have now extended this work and evaluated a wide variety and large number of tumor-derived cell lines for their sensitivity to lovastatin-induced apoptosis. These cell lines were exposed to a wide range (0-100 microM) of lovastatin for 2 days and assayed for cell viability using the 3,4,5-dimethyl thiazlyl-2,2,5-diphenyltetrazolium bromide assay and the induction of apoptosis by flow cytometric and ultrastructural analyses. Lovastatin induced a pronounced apoptotic response in cells derived from juvenile monomyelocytic leukemia, pediatric solid malignancies (rhabdomyosarcoma and medulloblastoma), and squamous cell carcinoma of the cervix and of the head and neck. Interestingly, the subset of malignancies that are particularly sensitive to lovastatin-induced apoptosis correspond to those tumor subtypes that are sensitive to the biological and antiproliferative effects of retinoids in vitro. The nature of the biologically active form of lovastatin has been challenged recently as the growth-inhibitory effects of this drug were attributed to its prodrug lactone form that does not inhibit HMG-CoA reductase function. In this report, we demonstrate that the apoptotic properties of lovastatin are triggered by the open ring acid form that is a potent inhibitor of HMG-CoA reductase activity. Thus, we have identified a subset of tumors that are sensitive to lovastatin-induced apoptosis and show HMG-CoA reductase as a potential therapeutic target of these cancers.
 ...
PMID:Differential sensitivity of various pediatric cancers and squamous cell carcinomas to lovastatin-induced apoptosis: therapeutic implications. 1120 4


1 2 3 Next >>