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Biomedical subjects

R Löser

Publications and source records attributed to R Löser.

At least 19 recordsLinked to original sources
PubMed2000

The effects of lifibrol (K12.148) on the cholesterol metabolism of cultured cells: evidence for sterol independent stimulation of the LDL receptor pathway.

Lifibrol (4-(4'-tert. butylphenyl)-1-(4'-carboxyphenoxy)-2-butanol) is a new hypocholesterolemic compound; it effectively lowers low density lipoprotein (LDL) cholesterol. We studied the effects of lifibrol on the cholesterol metabolism of cultured cells. In the hepatoma cell line HepG2, Lifibrol decreased the formation of sterols from [14C]-acetic acid by approximately 25%. Similar to lovastatin, lifibrol had no effect on the synthesis of sterols from [14C]-mevalonic acid. Lifibrol did not inhibit 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase. Instead, cholesterol synthesis inhibition by lifibrol was entirely accounted for by competitive inhibition of HMG-CoA synthase. Lifibrol enhanced the cellular binding, uptake, and degradation of LDL in cultured cells in a dose dependent fashion. The stimulation of LDL receptors was significantly stronger than expected from the effect of lifibrol on sterol synthesis. In parallel, lifibrol increased the amount of immunologically detectable receptor protein. Stimulation of LDL receptor mediated endocytosis was observed both in the presence and in the absence of cholesterol-containing lipoproteins. In the absence of an extracellular source of cholesterol, both lifibrol and lovastatin induced microsomal HMG-CoA reductase. Co-incubation with LDL was sufficient to suppress the lifibrol mediated increase in reductase activity, indicating that lifibrol does not affect the production of the non-sterol derivative(s) which are thought to regulate HMG-CoA reductase activity at the post-transcriptional level. Considered together, the data suggest that the hypolipidemic action of lifibrol may, at least in part, be mediated by sterol-independent stimulation of the LDL receptor pathway. A potential advantage of lifibrol is that therapeutic concentrations do not interfere with the production of mevalonate which is required not only to synthesize sterols but also as a precursor of electron transport moieties, glycoproteins and farnesylated proteins.

Anticholesteremic Agents↗
PubMed1999

2-(diethylamino)thieno1,3ŏxazin-4-ones as stable inhibitors of human leukocyte elastase.

A series of 2-(diethylamino)thieno1,3ŏxazin-4-ones was synthesized and evaluated in vitro for inhibitory activity toward human leukocyte elastase (HLE). The Gewald thiophene synthesis was utilized to obtain several ethyl 2-aminothiophene-3-carboxylates. These precursors were subjected to a five-step route to obtain thieno2,3-d1,3ŏxazin-4-ones bearing various substituents at positions 5 and 6. Both thieno2,3-d and thieno3,2-d fused oxazin-4-ones possess extraordinary chemical stability, which was expressed as rate constants of the alkaline hydrolysis. The kinetic parameters of the HLE inhibition were determined. The most potent compound, 2-(diethylamino)-4H-1benzothieno2,3-d1,3ŏxazin-4-one, exhibited a K(i) value of 5.8 nM. 2-(Diethylamino)thieno1, 3ŏxazin-4-ones act as acyl-enzyme inhibitors of HLE, similar to the inhibition of serine proteases by 4H-3,1-benzoxazin-4-ones. The isosteric benzene-thiophene replacement accounts for an enhanced stability of the acyl-enzyme intermediates.

Enzyme Inhibitors↗
PubMed1998

Effects of pravastatin on cholesterol metabolism of cholesterol-fed heterozygous WHHL rabbits.

1. We administered the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor pravastatin at a daily dose of 1 mg kg(-1) body weight to cholesterol-fed (0.03%) heterozygous Watanabe heritable hyperlipidaemic rabbits, an animal model for heterozygous familial hypercholesterolaemia. 2. After 12 months of cholesterol treatment, immunohistochemistry with the monoclonal antibody 9D9 was used to detect hepatic low density lipoprotein (LDL) receptors, which were quantified by densitometry. In addition we determined LDL receptor mRNA by competitive reverse transcriptase polymerase chain reaction. The cholesterol precursor lathosterol and the plant sterol campesterol were analysed by gas-liquid chromatography. 3. The drug reduced total plasma cholesterol levels by 51% (P=0.04), when compared to the control group. Unexpectedly, hepatic LDL receptor density and mRNA showed no significant differences between the groups. Total plasma levels of lathosterol and campesterol also revealed no significant differences between the groups, if expressed relative to plasma cholesterol. 4. The findings suggest that mechanisms other than induced hepatic LDL receptors are responsible for the cholesterol-lowering effect of pravastatin in this animal model. We propose a reduced cholesterol absorption efficiency compatible with similar campesterol levels between both groups observed in our study.

Animals↗
PubMed1998

In vitro efficacy of known P-glycoprotein modulators compared to droloxifene E and Z: studies on a human T-cell leukemia cell line and their resistant variants.

P-glycoprotein(P-gp)- related resistance is one of the major obstacles in treating leukemia patients. Therefore, it is of clinical interest to find new potential modulators and compare their P-gp-modulating efficacy. The present analysis investigated the influence of P-gp modulators, such as verapamil, tamoxifen, droloxifene E, droloxifene Z, SDZ PSC 833 (PSC 833) and dexniguldipine in a leukemic T-cell line (CCRF-CEM) and its P-gp-resistant counterparts (CCRF-CEM/ACT400 and CCRF-CEM/VCR1000). P-gp expression was assessed with an immunocytological technique using the monoclonal antibody 4E3.16. It was characterized as the percentage of P-gp positive cells and also expressed as a D value by using the Kolmogorov Smirnov statistic. The efficacy of P-gp modulators was determined with the rhodamine-123 accumulation test and the MTT test. An in vitro modulator concentration between 0.1 microM and 3 microM was determined, where no genuine antiproliferative effect was apparent. The modulators PSC 833 and dexniguldipine were the significant (p<C0.05) most potent chemosensitizers followed by verapamil, droloxifene Z, tamoxifen and droloxifene E in descending order. In addition to the modulators PSC 833 and dexniguldipine, droloxifene Z should especially be considered as a candidate for future ex vivo and in vivo studies. The main advantage of droloxifene Z could be the low rate of expected side effects. This fact permits the use of high Drol Z dosage in order to achieve a relevant modulating effect in vivo and to use this drug in combination with a further modulator so as to reach maximum efficacy with tolerable side effects.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1995

Intracellular localization, vesicular accumulation and kinetics of daunorubicin in sensitive and multidrug-resistant gastric carcinoma EPG85-257 cells.

In the human gastric carcinoma cell line EPG85-257P (parent) induction of resistance to daunorubicin (DAU) was achieved by selection with stepwise increased concentrations of the drug. The new variant was named EPG85-257DAU and was shown to overexpress the mdr1 gene product 170 kDa P-glycoprotein (P-Gp) as demonstrated by immunocytochemistry and mdr1-specific RT-PCR. To investigate the intracellular pathway of DAU the subcellular distribution of this autofluorescent drug was studied in the resistant cells and compared to its chemosensitive counterpart EPG85-257P. When sensitive cells were exposed to DAU the drug rapidly accumulated in the nucleus until cell death. No redistribution of DAU to the cytoplasm was observed. In resistant cells exposed to the drug DAU also accumulated in the nucleus but to a lesser extent than in parent cells. Following exposure, nuclear fluorescence was observed to decrease over a time period of up to 48 h. Six hours after DAU exposure formation of fluorescent vesicle formation started in the perinuclear region and increased continuously. After 48 h nuclear fluorescence was no longer detectable and DAU was located exclusively in vesicles. During this period the vesicles moved from the region of origin to the cell periphery. A pulse chase experiment showed, that vesicles may contain DAU derived from the nucleus. Treatment of EPG85-257DAU cells with DAU in conjunction with the chemosensitizer cyclosporin A (CsA) increased nuclear fluorescence without impairing vesicle formation. Disruption of microtubules by nocodazole led to an accumulation of vesicles in the perinuclear region indicating that microtubules are involved in vesicular transport. Treatment of EPG85-257DAU cells with the actin disruptor cytochalasin B led to accumulation of vesicles in the cell periphery indicating that actin may be involved in exocytosis. Uptake and efflux of DAU and rhodamin (RH) were determined in sensitive and resistant cells using a fluorescence activated cell sorter. Uptake of both compounds was distinctly lower in resistant than in sensitive cells. When resistant cells preloaded for 2 h with RH subsequently were incubated in drug free medium the substance was rapidly released indicating transmembrane transport by P-Gp. In contrast, despite expression of P-Gp in resistant cells no considerable release of DAU was observed for up to 2 h under the same experimental protocol. This indicates that in resistant cells intracellular DAU at least in part may be inaccessible for P-Gp and that vesicular drug transport appears to contribute to DAU resistance by removing intracellular DAU via exocytosis.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1995

A novel assay for cytosolic 3-hydroxy-3-methylglutaryl-coenzyme A synthase activity using reversed-phase ion-pair chromatography: demonstration that Lifibrol (K12.148) modulates the enzyme activity.

Cytosolic HMG-CoA synthase and microsomal 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase catalyze two sequential steps in the mevalonate pathway. Both enzymes are negatively regulated by cholesterol. Cytosolic HMG-CoA synthase is responsible for the generation of HMG-CoA from acetyl-CoA and acetoacetyl-CoA). We have developed a new method to determine HMG-CoA synthase activity. In this assay, HMG-CoA is formed from acetoacetyl-CoA and labeled acetyl-CoA. The HMG-CoA product is isolated from the reaction mixture by means of reversed-phase ion-pair chromatography. The recovery of the product was always greater than 90%. The average within-batch coefficient of variation for HMG-CoA synthase activity was 5.1%. Using the new assay, we demonstrate that Lifibrol (K12.148), a new hypolipidemic compound, inhibits HMG-CoA synthase. Because our assay is accurate and precise it may become useful in future studies on the regulation and the pharmacological modulation of cytosolic HMG-CoA synthase.

Animals↗
PubMed1994

Preclinical data for Droloxifene.

The new antiestrogen Droloxifene has a 10-60-fold higher binding affinity to the estrogen receptor (ER) compared to the related compound Tamoxifen. A similar relationship was found in growth inhibition studies which showed that Droloxifene inhibited the different ER positive human breast cancer cells more effectively than Tamoxifen, predominantly in drug concentrations which are found in humans during therapy. As another consequence of the high stability of the complex formed by Droloxifene binding to the ER, intermittent exposures with clinically relevant concentrations of Droloxifene brought about effective growth inhibition of human ER positive tumor cells even after short-term application. Droloxifene was found, like Tamoxifen, to block human breast cancer cells in G1-phase of the cell cycle. Moreover, cell-cycle data confirmed the superior growth-inhibiting potency of Droloxifene compared to Tamoxifen. Droloxifene was also found to effectively induce expression of the negative growth factor TGF-beta, to inhibit IGF-I stimulated cell growth and to prevent estrogen-stimulated proto-oncogene c-myc expression. Unlike Tamoxifen, Droloxifene is a potent inhibitor of protein biosynthesis in ER-positive breast cancer cells at physiologically relevant concentrations. Lower estrogenic and higher antiestrogenic effects on immature rat uterus indicate a higher therapeutic index for Droloxifene compared to Tamoxifen. In vivo, Droloxifene displayed increased growth inhibition of different tumors of animal (R3230AC and 13762) and human origin (T61). Furthermore, it was found that the two structurally similar drugs differ in their toxicologic characteristics in the following important respects: Droloxifene is devoid of any in vivo or in vitro carcinogenic or mutagenic effects, whereas Tamoxifen causes liver tumors in rats, induces DNA adduct formation in rats and hamsters and shows transforming activity in SHE-cells (Syrian hamster embryo fibroblasts). Considerably less toxicity and a lower level of intrinsic estrogenicity was observed even after maximum long-term exposure of different animal species to Droloxifene, in comparison with Tamoxifen. Therefore, it can be assumed that Droloxifene may represent an important step forward in the treatment of mammary carcinomas in women through its better tolerability and increased efficacy compared with Tamoxifen. For long-term adjuvant or preventive treatment of breast cancer, Droloxifene may well be the safer choice.

Animals↗
PubMed1993

Inhibition of growth-factor-activated proliferation by anti-estrogens and effects on early gene expression of MCF-7 cells.

Recently, it was reported that the anti-estrogen tamoxifen not only inhibits estradiol-stimulated growth of MCF-7 cells but also significantly reduces the proliferation rate of cells stimulated by growth factors. We have confirmed this finding and also shown that the new anti-estrogen droloxifene inhibits the proliferation of epidermal growth factor (EGF) and insulin-like growth factor-I (IGF-I)-stimulated MCF-7 cells. The growth-factor-induced proliferation was inhibited in a dose-dependent manner by the anti-estrogens in the complete absence of estrogen and FCS. Of the anti-estrogens, droloxifene was considerably more potent than tamoxifen. Because the expression of the proto-oncogenes c-fos and c-myc has been considered a key event in development of the mitogenic response, we examined the effects of anti-estrogens on c-myc and c-fos gene expression. We included in these investigations the steroidal anti-estrogen ICI 164,384 because this compound has no or very little estrogenic activity. The studies revealed that all 3 anti-estrogens transiently induced c-myc mRNA expression. However, the anti-estrogens inhibited estradiol-induced c-myc mRNA expression, although with different potencies. Pre-incubation of MCF-7 cells with droloxifene and tamoxifen resulted in elevated levels of growth-factor-induced c-myc mRNA expression. In contrast, the anti-estrogens did not induce c-fos mRNA or affect the expression of c-fos mRNA induced by growth factors. In conclusion, non-steroidal anti-estrogens inhibit growth-factor-stimulated proliferation of MCF-7 cells without inhibiting growth-factor-induced c-myc or c-fos mRNA expression.

Breast Neoplasms↗
PubMed1992

Inhibition of cholesterol synthesis in vitro by extracts and isolated compounds prepared from garlic and wild garlic.

Using a modified liver homogenate model to assay for the inhibition of cholesterol biosynthesis, different garlic and wild garlic extracts as well as pure compounds isolated from them were investigated for their influence on cholesterol synthesis. Chloroform and acetone/chloroform extracts of garlic and wild garlic inhibited cholesterol synthesis 44-52% at a concentration of 166 micrograms/ml, while the 5 individual sulfur-containing compounds ajoene, methylajoene, allicin, 2-vinyl-4H-1,3-dithiin and diallydisulfide inhibited cholesterol synthesis by 37-72% (10(-3) M corresponding to 234, 208, 162, 144, 146 micrograms/ml, respectively). Ajoene, 2-vinyl-4H-1,3-dithiin and allicin show IC50 values of 6.4, 7.2 and 9.4 x 10(-4) M, respectively. The results demonstrate that garlic and wild garlic may reduce serum cholesterol levels primarily by inhibiting cholesterol synthesis if taken in sufficient amount and that this effect arises from a mixture of multiple compounds from the sulfur-containing class of thiosulfinates, ajoenes and dithiines. Wild garlic extracts showed nearly identical efficiency to garlic extracts.

Animals↗
PubMed1990

Flow cytometric analysis of virus-infected cells and its potential use for screening antiviral agents.

Virus-infected cells were analyzed using multiparameter flow cytometry. Two virus-cell systems were investigated: HSV-1-infected VF cells and influenza C virus JHB/1/66-infected MDCK cells. Analysis included the measurement of the appearance of virus specific antigens. On individual cells, with polyclonal antibodies, antigens were first detected at 12 h p.i., and the numbers of labeled cells were followed up to 96 h p.i. The efficacy of four antiviral agents was tested with this system. The results were in good agreement with those of plaque reduction tests and indicated that this new method may be extremely useful for the correlation of viral and cellular events with antiviral activity. Finally, it was demonstrated that infected cells in both systems have a considerably greater volume than non-infected cells.

Animals↗
PubMed1990

The hypolipidemic effect of lifibrol during a long term treatment of pigs.

We investigated the hypolipidemic property of lifibrol in male and female minipigs in a long term trial over a treatment period of 6 months. Oral dosages between 12.5 mg/kg BW and 100 mg/kg BW lifibrol resulted in a strong reduction of serum cholesterol after only two weeks of treatment. The hypocholesterolemic effect was not counterbalanced and reached -76% at the end of the trial in the male pigs and -70% in the female pigs (100 mg/kg BW lifibrol). The reduction of serum cholesterol was mainly brought about by the reduction of LDL-cholesterol. Serum triglycerides seemed to be less influenced by lifibrol than serum cholesterol. The application of lifibrol had no significant influence on the weight gain of the pigs and did not alter the serum levels of AST and ALT. Lifibrol was well tolerated and the animals showed no symptoms of incompatibility.

Alanine Transaminase↗
PubMed1989

Effect of continuous vs intermittent application of 3-OH-tamoxifen or tamoxifen on the proliferation of the human breast cancer cell line MCF-7 M1.

The antiproliferative potency of 5 x 10(-7) M tamoxifen (TAM) and 3-hydroxytamoxifen (3-OH-TAM) was investigated during continuous (8 days) or intermittent (2 h every 2nd or 3rd day, respectively) application to the oestrogen-receptor-positive, estradiol-sensitive human mammary carcinoma cell line MCF-7 M1, a variant of MCF-7 wild type. Growth modulation was evaluated in parallel by counting cells and by measuring DNA content. Continuous incubation resulted in a growth inhibition to 21.8 +/- 3.2% by 3-OH-TAM and to 39.5 +/- 4.8% by TAM when compared with control cultures defined as 100%. Intermittent addition induced a growth reduction to 23.0 +/- 2.1% by 3-OH-TAM and to 41.2 +/- 2.4% by TAM in relation to 100% controls. Addition of 3-OH-TAM for 2 h only at day 1 resulted in an inhibition to 70.3 +/- 3.2%, again in relation to 100% controls. When TAM was administered once for 2 h at day 1 it induced an inhibition to 79.0 +/- 4.9% at day 8. The in vitro results indicate that (a) at 5 x 10(-7) M 3-OH-TAM has a better antiproliferative effectiveness than TAM, (b) the intermittent application is as effective as continuous application (no significant difference), and (c) the addition once a week reveals only a slight growth reduction after 8 days of culture. Application of the long-living TAM results in continuously high serum concentrations, which have been shown to create resistant cell clones. Compared to TAM the 3-OH metabolite has a considerably shorter half-life and its application in vivo reveals rise and fall of its serum concentrations. Since the presented data demonstrate that 3-OH-TAM is more potent than TAM and that the intermittent application is as effective as the continuous form, interval therapy with 3-OH-TAM may slow down the process of acquiring resistance to antioestrogens.

Breast Neoplasms↗
PubMed1989

Hypolipemic activity of K12.148 in rats, marmosets and pigs.

The hypolipemic effect of K12.148, a new hypolipemic compound, was examined in normolipemic rats, marmosets and pigs. It could be demonstrated that this compound reduced serum lipids, and in particular serum cholesterol, very effectively in all tested animal species. The analysis of the lipids of the pig give evidence that the hypocholesterolemic effect is due to a reduction of LDL only. In vitro experiments with rat liver homogenates suggest that the hypocholesterolemic effect is brought about by the inhibition of hepatic cholesterol synthesis.

Animals↗
PubMed1987

Circadian variation of the hypocholesterolemic effect of K13.004 in rats.

The hypocholesterolemic effect in rats of the new lipid-lowering agent K13.004 was dependent on the time of day of its application. This dependence was shifted together with the time of peak activity of hepatic cholesterol synthesis (CS) when the feeding time of the animals was changed. This compound considerably reduced serum cholesterol only if given before the peak of hepatic CS, whereas application afterwards was ineffective. Our finding suggests that this hypolipidemic compound lowers serum cholesterol by inhibition of hepatic CS. Drugs acting in such a way should be administered prior to the maximum of hepatic sterol synthesis.

1-Propanol↗
PubMed1985

No loss of estrogenic or anti-estrogenic activity after demethylation of droloxifene (3-OH-tamoxifen).

The binding affinity of 3-OH-Tamoxifen (Droloxifene or DROL) and N-demethyl-droloxifene (ND-DROL) to the cystosolic estrogen receptor of rabbit uteri was 10 times higher than that of Tamoxifen. Both compounds exhibited similar stimulation (estrogenic effect) and inhibition (anti-estrogenic effect) of uterine growth of immature female rats. 3H-Uridine incorporation into the RNA of MCF-7 and ZR-75 cells as a measure of anti-estrogenic activity was equally inhibited by concentrations of 0.05-1.0 mumol/l of both compounds. Thus, the pharmacological properties of DROL were not changed by N-demethylation.

Animals↗
PubMed1985

In vivo and in vitro antiestrogenic action of 3-hydroxytamoxifen, tamoxifen and 4-hydroxytamoxifen.

This study demonstrates in vivo and in vitro properties of the non-steroidal antiestrogens tamoxifen (TAM), 4-OH-tamoxifen (4-OH-TAM) and 3-OH-tamoxifen (K 060 E). In immature rabbit uteri 4-OH-TAM and K 060 E bound to the respective estrogen receptors with a ten-fold higher affinity than TAM. Furthermore, K 060 E exhibited less agonistic (estrogenic) but higher antagonistic (antiestrogenic) activity in the immature rat uterus than TAM and 4-OH-TAM (change of uterine weight). The ratio of agonistic vs antagonistic effect of K 060 E was distinctly lower than in TAM and 4-OH-TAM. In addition, K 060 E reduced by approximately 45% the growth of the transplantable Fisher rat mammary tumor (R 3230 AC) as compared with TAM (33%). We assume that, due to the higher antitumor activity, K 060 E (3-OH-TAM) is a better antiestrogen than TAM.

Adenocarcinoma↗
PubMed1983

Antiestrogenic action of 3-hydroxytamoxifen in the human breast cancer cell line MCF-7.

The antiestrogenic action of 3-hydroxytamoxifen [trans-1-(4-beta-dimethylaminoethoxyphenyl)-1-(3-hydroxyphenyl)-2 -phenylbut-1-ene] was characterized in vitro and compared with that of tamoxifen [trans-1-(4-beta-dimethylaminoethoxyphenyl)-1,2-diphenylbut-1-ene]. The relative binding affinities of 3-hydroxytamoxifen to estrogen receptor were 3.3% in cytosol of MCF-7 cells and 1.5% in human mammary carcinoma cytosol compared to values of 0.2 and 0.3% for tamoxifen (the affinity of 17 beta-estradiol considered to be 100%). The concentration of 3-hydroxytamoxifen necessary to suppress the 17 beta-estradiol-induced growth stimulation of MCF-7 cells was about tenfold lower than that for tamoxifen. The induction of progesterone receptor in MCF-7 cells by 17 beta-estradiol was inhibited by 3-hydroxytamoxifen. In the absence of 17 beta-estradiol, 3-hydroxytamoxifen gave rise to a moderate increase in the progesterone receptor levels, which demonstrates the partially estrogenic character of hydroxytamoxifen.

Binding, Competitive↗