Calmodulin antagonists stimulate LDL receptor synthesis in human skin fibroblasts

Cytotoxic effects of antipsychotic drugs implicate cholesterol homeostasis as a novel chemotherapeutic target

The reported reduction in cancer risk in those suffering from schizophrenia may be because antipsychotic medications have antineoplastic effects. In this study, 6 antipsychotic agents with a range of structural and pharmacological properties (reserpine, chlorpromazine, haloperidol, pimozide, risperidone and olanzapine), were screened for their effect on the viability of cell lines derived from lymphoblastoma, neuroblastoma, non-small cell lung cancer and breast adenocarcinoma. We aimed to determine if antipsychotic drugs in general possess cancer-specific cytotoxic potential, and whether it can be attributed to a common mode of action. With the exception of risperidone, all drugs tested displayed selective inhibition of the viability of cancer cell lines compared with normal cells. Using Affymetrix expression microarrays and quantitative real-time polymerase chain reaction, we found that for the antipsychotic drugs, olanzapine and pimozide, cytotoxicity appeared to be mediated via effects on cholesterol homeostasis. The role of cholesterol metabolism in the selective cytotoxicity of these drugs was supported by demonstration of their increased lethality when coadministered with a cholesterol synthesis inhibitor, mevastatin. Also, pimozide and olanzapine showed accelerating cytotoxic effects from 12 to 48 hr in time course studies, mirroring the time-dependent onset of cytotoxicity induced by the amphiphile, U18666A. On the basis of these results, we concluded that the Class II cationic amphiphilic properties of antipsychotic drugs contribute to their cytotoxic effects by acting on cholesterol homeostasis and altering the biophysical properties of cellular membranes, and that drugs affecting membrane-related cholesterol pathways warrant further investigation as potential augmentors of standard cancer chemotherapy.

Early induction of LDL receptor gene during rat liver regeneration

After partial hepatectomy in the rat, there is substantial lipid accumulation in the liver. No information is available on the possible role of receptor-mediated endocytosis in this process. Since the low density lipoprotein (LDL) receptor is stimulated as a part of an early growth response in cell culture (Ellsworth et al.: Biochem. J. 279:175-187, 1991), the metabolism of this receptor during liver regeneration was studied. The mRNA and membrane protein level of the receptor were measured in the liver and in the adrenal glands at different times after partial hepatectomy, corresponding to different phases of the cell cycle. A discontinuous pattern of receptor expression is detectable in the regenerating liver; a large increase of mRNA and membrane protein occurs at an early time (2-4 h), suggesting that there is induction of LDL receptor gene transcription shortly after partial hepatectomy. This response seems specific for the liver following injury since the adrenal receptor does not show a different pattern in partially hepatectomized rats and sham-operated controls. After returning to control levels, the LDL receptor again increases slightly above control at 24 h, a time when cell replication begins.

Evidence for sterol-independent regulation of low-density lipoprotein receptor activity in Hep-G2 cells

The relationship between the serum factor(s)-mediated induction of low-density lipoprotein (LDL) receptor activity and changes in cellular cholesterol metabolism was examined in the human hepatoma cell line Hep-G2. Relative to incubation with serum-free media [Eagle's minimal essential medium (MEM) control], short-term (less than 8 h) incubation with medium containing 15% of either calf serum (MEM + serum) or the d greater than 1.25 fraction of calf serum (MEM + d greater than 1.25) produced a time- and concentration-dependent increase in the uptake of 125I-LDL. Immunoblotting with anti-(LDL receptor) antibodies demonstrated that this was correlated with a 2-fold increase in the amount of the mature 136,000 Da LDL receptor protein in detergent-solubilized Hep-G2 cell membranes. Incubation with MEM + serum, but not MEM + d greater than 1.25, increased the efflux of radiolabelled cholesterol from Hep-G2 cells. However, the induction of 125I-LDL uptake by MEM + d greater than 1.25 (2.3-fold) and MEM + serum (2.2-fold) was virtually identical. Addition of the d less than 1.063 lipoproteins of calf serum to MEM + d greater than 1.25 at their original or three times their serum concentration decreased the induction of 125I-LDL uptake by MEM + d greater than 1.25 by only 20-30%. Together, these results suggest that the stimulation of 125I-LDL uptake was not due to the presence of high-density lipoprotein, the absence of LDL or the stimulation of cholesterol efflux. MEM + serum stimulated 125I-LDL uptake in cells cholesterol-loaded by incubation with rat very-low-density lipoprotein with beta electrophoretic mobility (beta-VLDL). Compared to incubation with the MEM control, either MEM + serum or MEM + d greater than 1.25 produced time-dependent increases in the activity of 3-hydroxy-3-methylglutaryl-CoA reductase which also occurred in cholesterol-loaded cells. However, cholesterol biosynthesis, whether measured from 3H2O, [14C]acetate or [3H]mevalonic acid, was not increased. Incubation with MEM + serum or MEM + d greater than 1.25 did not affect [3H]oleate incorporation into cellular cholesteryl esters, hydrolysis of intracellular [3H]cholesteryl esters or the cellular mass of unesterified or esterified cholesterol. Incubation with MEM + serum or MEM + d greater than 1.25 produced a transient increase in the level of LDL receptor mRNA, reaching a maximum of 5-10-fold by 2 h and decreasing to near baseline levels by 4 h. Actinomycin D blocked the serum-factor-mediated induction of LDL receptor mRNA.(ABSTRACT TRUNCATED AT 400 WORDS)

Nature of aortic smooth muscle cellular activity induced by cholesterol incorporation through an LDL-receptor-independent pathway: preventive role of trifluoperazine on such activity

The present study was addressed to understand two specific issues: (a) whether atherogenic activity of smooth muscle cells could be initiated by incorporating cholesterol within their membranes through a LDL-receptor-independent pathway; and (b) whether trifluoperazine, which we had recently shown to prevent the cholesterol-induced atherogenesis in an experimental animal model system, could prevent such activity of these cells induced by cholesterol in vitro. The results of such a study revealed that trifluoperazine could prevent the cholesterol-induced stimulation of (a) DNA synthesis, (b) cholesterol synthesis, (c) intracellular cGMP levels, (d) intracellular free and esterified cholesterol accumulation, and (e) collagen secretion. Furthermore, the drug caused stimulation of cholesterol-induced suppression of LDL-receptor synthesis. On this basis, we suggest that acquisition of cholesterol by smooth muscle cells through the LDL-receptor-independent pathway may be the fundamental process responsible for atherogenic activity of these cells and that the drug trifluoperazine has the inherent capacity to prevent the membrane-cholesterol-modulated atherogenic activity of smooth muscle cells in vitro.

Effect of trifluoperazine on DNA and LDL-receptor synthesis in smooth muscle cells exposed to hypercholesterolemic medium in vitro

We recently demonstrated that calmodulin and/or protein kinase C may play a crucial role in cholesterol-induced atherogenesis in experimental animal model system. The present study, which was undertaken to elucidate the effect of trifluoperazine (known as a potent inhibitor of calmodulin and protein kinase C) on DNA and LDL-receptor synthesis of aortic smooth muscle cells exposed to hypercholesterolemic medium, revealed that (a) trifluoperazine at a concentration of 25 microM caused an approximately threefold increase in the [35S]methionine-incorporated LDL-receptor protein as compared with values found in control cells; (b) the drug at concentrations greater than or equal to 0.1 microM caused inhibition of DNA synthesis as compared with values found in control cells. These results demonstrate that the preventive effect of trifluoperazine on the atherogenic activity of smooth muscle cells may be due to its ability to increase LDL-receptors synthesis as well as concomitant inhibitory action on DNA synthesis of smooth muscle cells exposed to hypercholesterolemic medium.

In vitro inhibition of arterial myocyte growth and stimulation of low density lipoprotein metabolism by SIM 6080, a new calcium antagonist

We have investigated the in vitro effect of the new calcium antagonist SIM 6080 on proliferation of rat aortic smooth muscle cells and on LDL receptor-mediated catabolism in human fibroblasts. Verapamil was used as the reference compound. SIM 6080 inhibited the proliferation of rat aortic myocytes in concentrations ranging between 1 and 20 microM. The inhibition, evaluated as cell number and nuclear incorporation of [3H]thymidine, was dose and time dependent; the cell doubling time increased with drug concentrations up to 69 h versus 20 h for controls. Similar results on both LDL pathway and smooth muscle cell proliferation were achieved with verapamil, but higher concentrations were needed. The specific uptake and degradation of 125I-LDL was evaluated in human fibroblasts after 48 h incubation with SIM 6080 (1-10 microM). The compound dose dependently enhanced the receptor-mediated 125I-LDL uptake, with a fourfold increase as a maximal effect (10 microM); LDL degradation was less sensitive to the drug. The present results provide evidence that the new calcium antagonist SIM 6080 interferes in vitro with processes involved in atherogenesis.

Inhibition of mitochondrial palmitate oxidation by calmodulin antagonists

1. The effect of calmodulin antagonists on the rate of palmitate oxidation by isolated rat liver mitochondria was studied. 2. In the presence of 100 microM amitriptyline, chlorpromazine, prenylamine, N-(4-aminobutyl)-5-chloro-2-naphthalenesulfonamide or N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide, palmitate oxidation was inhibited by 17, 34, 49, 31 and 37%, respectively. 3. The degree of inhibition of palmitate oxidation exerted by these chemical compounds did not appear to correlate appreciably with changes in mitochondrial membrane fluidity.

Calmodulin regulates the interleukin 1-induced procollagenase production in human uterine cervical fibroblasts

Interleukin 1 (IL-1) stimulates the synthesis of collagenase in human uterine cervical fibroblasts. This inductive effect of IL-1 on collagenase production was augmented by N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), a specific inhibitor of calmodulin, in a dose-dependent manner. The apparent collagenase activity observed in the culture medium of the cells treated with IL-1 and 40 microM W-7 was about three times higher than that produced by the cells treated with IL-1 alone. The immunoblotting with the specific antibody against human collagenase showed that the increased collagenase activity resulted from the accelerated biosynthesis of collagenase. Another calmodulin inhibitor, trifluoperazine, enhanced the effect of IL-1 on collagenase production similarly. However, the effect of N-(6-aminohexyl)-1-naphthalenesulfonamide, the weakest inhibitor of calmodulin, was negligible. These results suggest that W-7 enhances the collagenase production by specifically inhibiting calmodulin and that calmodulin may act as a suppressor of the IL-1-induced collagenase production in human uterine cervical fibroblasts.

Determination of the LDL receptor binding capacity of human lymphocytes by immunocytofluorimetric assay

The determination of the LDL receptor binding capacity of human blood lymphocytes was assessed by indirect immunocytofluorimetric assay. To produce the maximal synthesis of the LDL receptor, the cholesterol efflux was enhanced by incubation of lymphocytes with HDL3 subfractions. The binding capacity of the LDL receptor was measured by incubation at 4 degrees C either with LDL and rabbit anti-LDL immunoglobulins or with peptide receptor antibody (ARP-Ig) raised against the NH2-terminal sequence of the LDL receptor. Thereafter complexes were incubated with fluorescein-labelled anti-rabbit immunoglobulin (FITC-Ig). Fluorescence flow cytometry was used to quantify the number of fluorescent lymphocytes and results were expressed as the percentage of lymphocytes with a fluorescent intensity above the threshold. Using preimmune rabbit immunoglobulin and then FITC-Ig, only 5-10% of cells were fluorescent. Neither LDL nor ARP-Ig could bind to homozygous familial hypercholesterolemia (FH) lymphocytes. Normal lymphocytes preincubated with HDL3 could bind LDL or ARP-Ig, the number of fluorescent cells being 59 and 39.2% respectively. Subjects with confirmed or suspected heterozygous FH demonstrated cell fluorescence at about half the normal level.

Induction of histamine release and calmodulin antagonism are two distinct properties of compound 48/80

Compound 48/80, a mixture of oligomers, was fractionated by passing it in the presence of Ca2+ over a calmodulin-Sepharose column. The fraction not retained by the gel was shown by mass spectrometry to consist mainly of trimers, tetramers and pentamers. A second fraction consisting of hexamers and heptamers was eluted from the column at high ionic strength in the presence of Ca2+. Finally, in the presence of EGTA at high ionic strength, a third fraction eluted mainly consisting of higher oligomers (hexamers to dodecamers). The different fractions were characterized by testing their influence on calmodulin-sensitive Ca2+-transporting ATPase and their ability to elicit histamine release from mast cells. The third fraction showed the highest potency as calmodulin antagonist, however, the second fraction was the most potent in inducing histamine secretion. This would imply that the ability of compound 48/80 to evoke histamine release and to inhibit the function of calmodulin are distinct properties of the agent which are unrelated.

Calmodulin antagonists increase the amount of mRNA for the low-density-lipoprotein receptor in skin fibroblasts

The effects of calmodulin antagonists on the amount of LDL receptor (LDL-R) mRNA in cultured human fibroblasts was examined by hybridization with a fragment of LDL-R cDNA. In a 'Northern' blot the fragment hybridized to a 5.3-kilobase RNA, as expected for LDL-R mRNA. The concentration of this RNA was increased in preparations from cells that were treated with trifluoperazine or W-7 [N-(6-aminohexyl)-5-chloronaphthalene-1-sulphonamide]. The selectivity of the increase was established by using a probe for beta-actin mRNA. In dot-blot hybridization it was observed that the calmodulin antagonists cause 2-4-fold relative increase in the amount of LDL-R mRNA.

Calmodulin antagonists suppress cholesterol synthesis by inhibiting sterol delta 24 reductase

Preincubation of hepatoma cells and human skin fibroblasts in the presence of the calmodulin antagonists trifluoperazine and N-(6-aminohexyl)-5-chloro-1-naphthalene sulfonamide resulted in a dose-dependent suppression of [14C]mevalonolactone incorporation into cholesterol. At a calmodulin antagonist concentration of 25 mumol, the incorporation of [14C]mevalonolactone into cellular cholesterol was suppressed to about 30% (hepatoma cells) and 10% (human skin fibroblasts) of control values. When the total nonsaponifiable [14C]lipids were separated and analyzed by two-dimensional thin layer chromatography, an accumulation of [14C]desmosterol was observed along with reduced formation of [14C]cholesterol. However, when cells were preincubated in the presence of [14C]dihydrolanosterol, [14C]cholesterol formation was not inhibited by the calmodulin antagonists. About 25% of the cell-associated dihydrolanosterol radioactivity was converted to cholesterol in both control and calmodulin antagonist-pretreated cells. The data suggest that calmodulin antagonists prevent the conversion of desmosterol into cholesterol by inhibiting sterol delta 24 reductase and that the enzymes catalyzing sterol ring modifications are not affected by the inhibitors.

Antiatherogenic properties of calcium antagonists

A generalized accumulation of cholesterol, calcium and matrix materials (collagen, elastin and proteoglycans) occurs in an age-dependent manner in major arteries. Human atherogenesis is a disease of arteries characterized by a focal accumulation of fibrous matrix elements, lipids and calcium at lesion sites. Studies in cholesterol-fed animal models have indicated that calcium competitors and chelating agents can reduce calcium, lipid and matrix accumulation in arterial lesions and reduce the extent of lesion formation. These agents generally alter soft and hard tissue calcium pools or have deleterious side-effect profiles. Antiatherogenic studies with calcium antagonists (which have been shown to be safe in human clinical studies) have created confusion because of conflicting results. It is apparent, however, that high doses of calcium antagonists can significantly decrease atherogenic lesion development in cholesterol-fed rabbits. The antiatherogenic effects of calcium antagonists may be the result of changes in intracellular calcium pools within smooth muscle cells, which may lead to alterations in cellular metabolic activity or may be due to activities not related to calcium channel effects. Several mechanisms involving regulation of lipoprotein receptor synthesis, lipoprotein uptake or degradation, cholesterol ester hydrolytic activity and arterial matrix synthesis are discussed as potential sites of activity for calcium antagonists. A dihydropyridine channel antagonist, PN 200-110 (isradipine), has been shown to be a very potent antiatherogenic agent in the rabbit and also to be a potent inhibitor of smooth muscle cell matrix synthesis.