Growth factor and oncogene signalling pathways as targets for rational anticancer drug development

Isoflavones inhibit intestinal epithelial cell proliferation and induce apoptosis in vitro

There have been many reports that high soya-based diets reduce the risk of certain types of cancer. This effect may be due to the presence of high levels of isoflavones derived from the soya bean, particularly genistein which has been shown to be a protein tyrosine kinase (PTK) inhibitor and have both oestrogenic and anti-oestrogenic properties. We have examined the effect of genistein and a number of novel synthetic analogues on both normal (IEC6, IEC18) and transformed (SW620, HT29) intestinal epithelial cell lines. Responses were compared to those elicited by oestradiol, the anti-oestrogen tamoxifen, and the tyrosine kinase inhibitor tyrphostin. Genistein and tamoxifen were potent inhibitors of cell proliferation. Of seven novel isoflavones tested, none were more potent inhibitors than genistein, and all displayed similar relative activities across the different cell lines. In addition to inhibiting cell proliferation, cell death via apoptosis was observed when the cells were exposed to the isoflavones and all but one exhibited PTK inhibitory activity. These data suggest that by reducing proliferation and inducing apoptosis, possibly due in part to PTK inhibition, isoflavones may have a role in protecting normal intestinal epithelium from tumour development (reducing the risk) and may reduce colonic tumour growth.

Effect of curcumin on cell cycle progression and apoptosis in vascular smooth muscle cells

1. The possible mechanisms of the antiproliferative and apoptotic effects of curcumin (diferuloylmethane), a polyphenol in the spice turmeric, on vascular smooth muscle cells were studied in rat aortic smooth muscle cell line (A7r5). 2. The proliferative response was determined from the uptake of [3H]-thymidine. Curcumin (10(-6)-10(-4) M) inhibited serum-stimulated [3H]-thymidine incorporation of both A7r5 cells and rabbit cultured vascular smooth muscle cells in a concentration-dependent manner. Cell viability, as determined by the trypan blue dye exclusion method, was unaffected by curcumin at the concentration range 10(-6) to 10(-5) M in A7r5 cells. However, the number of viable cells after 10(-4) M curcumin treatment was less than the basal value (2 x 10(5) cells). 3. To analyse the various stages of the cell cycle, [3H]-thymidine incorporation into DNA was determined every 3 h. After stimulation with foetal calf serum, quiescent A7r5 cells started DNA synthesis in 9 to 12 h (G1/S phase), then reached a maximum at 15 to 18 h (S phase). Curcumin (10(-6)-10(-4) M) added during either the G1/S phase or S phase significantly inhibited [3H]-thymidine incorporation. 4. Following curcumin (10(-6)-10(-4) M) treatment, cell cycle analysis utilizing flow cytometry of propidium iodide stained cells revealed a G0/G1 arrest and a reduction in the percentage of cells in S phase. Curcumin at 10(-4) M also induced cell apoptosis. It is suggested that curcumin arrested cell proliferation and induced cell apoptosis, and hence reduced the [3H]-thymidine incorporation. 5. The apoptotic effect of 10(-4) M curcumin was also demonstrated by haematoxylin-eosin staining, TdT-mediated dUTP nick end labelling (TUNEL), and DNA laddering. Curcumin (10(-4) M) induced cell shrinkage, chromatin condensation, and DNA fragmentation. 6. The membranous protein tyrosine kinase activity stimulated by serum in A7r5 cells was significantly reduced by curcumin at the concentration range 10(-5) to 10(-4) M. On the other hand, the cytosolic protein kinase C activity stimulated by phorbol ester was reduced by 10(-4) M curcumin, but unaffected by lower concentrations (10(-6)-10(-5) M). 7. The levels of c-myc, p53 and bcl-2 mRNA were analysed using a reverse transcription-polymerase chain reaction (RT-PCR) technique. The level of c-myc mRNA was significantly reduced by curcumin (10(-5)-10(-4) M) treatment. And, the level of bcl-2 mRNA was significantly reduced by 10(-4) M curcumin. However, the alteration of the p53 mRNA level by curcumin (10(-5)-10(-4) M) treatment did not achieve significance. The effects of curcumin on the levels of c-myc and bcl-2 mRNA were then confirmed by Northern blotting. 8. Our results demonstrate that curcumin inhibited cell proliferation, arrested the cell cycle progression and induced cell apoptosis in vascular smooth muscle cells. Curcumin may be useful as a template for the development of drugs to prevent the pathological changes of atherosclerosis and post-angioplasty restenosis. Our results suggest that the antiproliferative effect of curcumin may partly be mediated through inhibition of protein tyrosine kinase activity and c-myc mRNA expression. And, the apoptotic effect may partly be mediated through inhibition of protein tyrosine kinase activity, protein kinase C activity, c-myc mRNA expression and bcl-2 mRNA expression.

Epigallocatechin suppression of proliferation of vascular smooth muscle cells: correlation with c-jun and JNK

1. The mechanisms of the antiproliferative effect of epigallocatechin, one of the catechin derivatives found in green tea, in vascular smooth muscle cells were studied. The proliferative response was determined from the uptake of tritiated thymidine. 2. In the concentration range of 10(-6) to 10(-4) M, catechin, epicatechin, epigallocatechin, epicatechin gallate and epigallocatechin, epigallocatechin gallate, concentration-dependently inhibited the proliferative response stimulated by serum in rabbit cultured vascular smooth muscle cells. Catechin and epicatechin were less effective in inhibiting the serum-stimulated smooth muscle cell proliferation, indicating that the galloyl group may be important for full inhibitory activity. 3. Epigallocatechin (EGC) inhibited the proliferative responses in different cells including rat aortic smooth muscle cells (A7r5 cells), rabbit cultured aortic smooth muscle cells, human coronary artery smooth muscle cells, and human CEM lymphocytes in a concentration-dependent manner. The possible mechanisms of the antiproliferative effect of EGC were further studied in A7r5 cells. 4. The membranous protein tyrosine kinase activity stimulated by serum in A7r5 cells was significantly reduced by 10(-5) M EGC. In contrast, the cytosolic protein kinase C activity stimulated by phorbol ester was unaffected by directly incubating with EGC (10(-6)-10(-4) M). 5. We also performed Western blot analysis using the anti-phosphotyrosine monoclonal antibody PY20. EGC (10(-5) M) reduced the levels of tyrosine phosphorylated proteins with different molecular weights, indicating that EGC may inhibit the protein tyrosine kinase activity or stimulate the protein phosphatase activity. 6. Reverse transcription-polymerase chain reaction analysis of c-fos, c-jun and c-myc mRNA levels demonstrated that c-jun mRNA level after serum-stimulation was significantly reduced by 10(-5) M EGC. However, the reduction of c-fos and c-myc mRNA levels by 10(-5) M EGC did not achieve significance. 7. Western blot analysis using the antibody against JNK (c-jun N-terminal kinase) and ERK (extracellular signal-regulated kinase) demonstrated that the level of phosphorylated JNK1, but not phosphorylated ERK1 and ERK2, was reduced by 10(-5) M EGC. Direct measurement of kinase activity by immune complex kinase assay confirmed that JNK1 activity was inhibited by EGC treatment. These results demonstrate that EGC preferentially reduced the activation of JNK/SAPK (stress-activated protein kinase) signal transduction pathway. 8. It is suggested that the antiproliferative effect of epigallocatechin on vascular smooth muscle cells may partly be mediated through inhibition of protein tyrosine kinase activity, reducing c-jun mRNA expression and inhibiting JNK1 activation. Tea catechins may be useful as a template for the development of drugs to prevent the pathological changes of atherosclerosis and post-angioplasty restenosis.

The possible mechanisms of the antiproliferative effect of fullerenol, polyhydroxylated C60, on vascular smooth muscle cells

1. The possible mechanisms of the antiproliferative effect of polyhydroxylated fullerene (fullerenol), a novel free radical trapper, were studied in rat vascular smooth muscle cells (A7r5 cells) and compared with the effect of ascorbic acid. 2. Fullerenol-1 and ascorbic acid inhibited the proliferative responses in a number of cells, including rat aortic smooth muscle cells (A7r5 cells), human coronary artery smooth muscle cells, and human CEM lymphocytes (CEM cells) in a concentration dependent manner. 3. At the concentration range of 10(-6) to 10(-2) M, fullerenol-1 and ascorbic acid concentration-dependently inhibited the proliferative responses stimulated by serum in A7r5 cells. Fullerenol-1 was more potent than ascorbic acid. 4. The production of O2- induced by alloxan, a diabetogenic compound, was reduced by fullerenol-1 (10(-4) M) in the presence of A7r5 cells. 5. The cytosolic protein kinase C activity of A7r5 cells stimulated by phorbol ester was reduced by 10(-3) M fullerenol-1, but not ascorbic acid (10(-4)-10(-2) M) and fullerenol-1 at lower concentrations (10(-6)-10(-4) M). 6. In contrast, the membraneous protein tyrosine kinase activity of A7r5 cells stimulated by foetal calf serum was significantly reduced by fullerenol-1 (10(-6)-10(-3) M) and ascorbic acid (10(-4)-10(-2) M). Again, the inhibitory activity of fullerenol-1 was greater than that of ascorbic acid. 7. Our results demonstrate that fullerenol-1 and ascorbic acid exhibit inhibitory effects on transduction signals in addition to their antioxidative property. It is suggested that the antiproliferative effect of fullerenol-1 on vascular smooth muscle cells may partly be mediated through the inhibition of protein tyrosine kinase.

The causes of cancer: implications for prevention and treatment

The final clinical manifestation of cancer is a result of complex series of changes in a single cell. This review summarizes some of the new concepts and hypotheses that explain the evolution of cancers. The emphasis is on cancer as a disease of the stem cells within a tissue that undergo initiation as a result of mutational insult to one or more genes that are critical for cell growth. During the second stage (promotion stage) the initiated cells acquire proliferative capacity due to epigenetic changes, i.e., altered expression of genes whose products play a central role in signal transduction. This requires continued exposure to agents and events causing such changes. This stage is, therefore, reversible and the various components of this stage are central targets for the development of mechanism based anti-cancer drugs. During the stage of progression, the neoplastic lesions acquire additional genetic alterations and become clinically manifestable malignant neoplasms. At the biochemical and molecular level, neoplastic transformation involves aberrations in the expression and regulation of oncogenes, tumor suppression genes, transcription factors and components of the cell signal transduction cascades. The understanding of the various cellular biochemical and molecular events that metamorphose a normal cell into a cancer cell is central to the development of rational new drugs that are targeted against the various components. Such drugs in combination with the conventional chemotherapeutic agents that are currently used, provide a more effective control of cancer without the risk of toxic side effects.

Specific inhibition of cyclic AMP-dependent protein kinase by warangalone and robustic acid

The prenylated isoflavone warangalone from the insecticidal plant Derris scandens is a selective and potent inhibitor of rat liver cyclic AMP-dependent protein kinase catalytic subunit (cAK) (IC50 3.5 microM). The inhibition of rat liver cAK by warangalone is non-competitive with respect to both ATP and the synthetic peptide substrate (LRRASLG) employed in this study. Warangalone is a poor inhibitor of avian calmodulin-dependent myosin light chain kinase (MLCK), rat brain Ca(2+)- and phospholipid-dependent protein kinase C (PKC) and wheat embryo Ca(2+)-dependent protein kinase (CDPK). The related plant derived prenylisoflavones are also potent cAK inhibitors. Thus, 8-gamma-gamma-dimethylallylwighteone, 3' -gamma-gamma-dimethlallylwighteone and nallanin are inhibitors of cAK with IC50 values in the range 20-33 microM. The prenyl-substituted isoflavones tested in this study are ineffective or poor as inhibitors of PKC. Thus nallanin is a poor PKC inhibitor (IC50 value of 120 microM). The related isoflavones biochanin A and genistein are poor inhibitors of cAK (IC50 values 100 microM and 126 microM, respectively). Genistein inhibits MLCK (IC50 value 14 microM) but biochanin A is a poor MLCK inhibitor (IC50 value 300 microM). The D. scandens prenyl-isoflavones and related isoflavones are ineffective inhibitors of wheat embryo Ca(2+)-dependent protein kinase (CDPK). The 4-methoxy-3-phenyl-coumarin robustic acid is a potent inhibitor of rat liver cAK (IC50 value 10 microM) but is a poor inhibitor of rat brain PKC, avian MLCK and wheat embryo CDPK. The coumarins 5-methoxypsoralen and 4,4'-di-O-methyl scandenin are poor cAK inhibitors (IC50 values 240 and 248 microM, respectively). All of the non-prenylated coumarins examined are ineffective as inhibitors of the eukaryote signal-regulated protein kinases cAK, MLCK, PKC and CDPK. The selective, high affinity interaction of warangalone and robustic acid with cAK may contribute to their biological effects in vivo and to the insecticidal activity of the plant D. scandens.

Selective inhibition of cyclic AMP-dependent protein kinase by isoquinoline derivatives

A large series of isoquinoline derivatives was synthesised including derivatives of isoquinoline, isoquinolino[3,4-c]furazan, 1,2-dihydro-1-oxoisoquinoline, 6-oxopyrimido[1,2-d]isoquinoline, benzo[c][1,8]-naphthyridine, pyrazino[2,3-c]isoquinoline and benzimidazo[2,1-a]isoquinoline as well as further structurally related isoquinoline derivatives and pyrido-2,3-furazans. Representatives of all of these classes of isoquinolines are potent and selective inhibitors of the cyclic AMP-dependent protein kinase (PKA) catalytic subunit (cAK) from rat liver. The most effective cAK inhibitors are a series of 1,3-di-substituted and 1,3,4-tri-substituted isoquinolines (IC50 values 30-50 nM) (compounds A1, A2, A3, A4 and A5) and 2-ethylcarboxy-3-amino-5,6-dihydro-6-oxobenzo[c] [1,8]naphthyridine (E1) (IC50 0.08 microM). Compounds A1-A5 inhibit cAK in a fashion that is competitive with respect to ATP as substrate. The isoquinoline inhibitors A1-A5 are ineffective or very poor inhibitors of wheat embryo Ca(2+)-dependent protein kinase (CDPK) and rat brain Ca(2+)-dependent protein kinase C (PKC), chicken gizzard myosin light chain kinase (MLCK) and potato tuber cyclic nucleotide-binding phosphatase (Pase). E1 is a moderately effective inhibitor of CDPK and PKC (IC50 values 30 and 61 microM, respectively). The bisisoquinoline-1(2H)-one compound B7 inhibits cAK, CDPK, PKC and MLCK (IC50 values 8, 95, 24 and 7 microM, respectively) as does J1 [2-(p-bromophenyl)pyrrolo-[2,3-c]isoquinoline-5(4H)-one] (IC50 values 2, 50, 44 and 7 microM, respectively). The very potent isoquinoline-derived cAK inhibitors found here involve substitution of the N-containing isoquinoline ring system and these inhibitors show high specificity for cAK.

Inhibition of cyclic AMP-dependent protein kinase by curcumin

Curcumin [diferuloylmethane; 1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione], a major bioactive secondary metabolite found in the rhizomes of turmeric (Curcuma longa), is an inhibitor of Ca(2+)- and phospholipid-dependent protein kinase C (PKC) and of the catalytic subunit (cAK) of cyclic AMP-dependent protein kinase (IC50 values 15 and 4.8 microM, respectively). Curcumin inhibits plant Ca(2+)-dependent protein kinase (CDPK) (IC50 41 microM), but does not inhibit myosin light chain kinase or a high affinity 3',5'-cyclic AMP-binding phosphatase. Curcumin inhibits cAK, PKC and CDPK in a fashion that is competitive with respect to both ATP and the synthetic peptide substrate employed. The IC50 values for inhibition of cAK by curcumin are very similar when measured with kemptide (LRRASLG) (in the presence or absence of ovalbumin) or with casein or histone III-S as substrates. However, the presence of bovine serum albumin (0.8 mg ml-1) largely overcomes inhibition of cAK by curcumin.

Selective inhibition of cyclic AMP-dependent protein kinase by amphiphilic triterpenoids and related compounds

A set of plant- and animal-derived amphiphilic triterpenoids have been shown to be potent and selective inhibitors of the catalytic subunit of rat liver cyclic AMP-dependent protein kinase (cAK). Thus plant-derived 18 alpha- and 18 beta-glycyrrhetinic acid, ursolic acid, oleanolic acid and betulin and animal-derived lithocholic acid, 5-cholenic acid and lithocholic acid methyl ester are inhibitors of cAK with IC50 values (concentrations for 50% inhibition) in the range 4-20 microM. These compounds are ineffective or relatively ineffective as inhibitors of various other eukaryote signal-regulated protein kinases namely wheat embryo Ca(2+)-dependent protein kinase (CDPK), avian calmodulin-dependent myosin light chain kinase (MLCK) and rat brain Ca(2+)- and phospholipid-dependent protein kinase C (PKC). These naturally occurring triterpenoids have a common structural motif involving polar residues located at opposite ends of an otherwise non-polar triterpenoid nucleus. A variety of triterpenoids not possessing this structural motif are relatively inactive as inhibitors of cAK and of CDPK, PKC and MLCK. The terpenoid amphiphilic compound crocetin is also a potent and relatively selective inhibitor of cAK (IC50 value for cAK 3.0 microM). 12-Hydroxystearic acid and 10-hydroxydecanoic acid do not inhibit CDPK, PKC or MLCK but are selective inhibitors of cAK (IC50 values 127 and 138 microM, respectively), consistent with a simple model for amphiphile inhibition of cAK involving two polar groups separated by a non-polar region. However, laurylgallate and 15-pentadecanolide are also potent and selective inhibitors of cAK (IC50 values 1.5 and 20 microM, respectively) although the structures of both of these compounds involve a large non-polar portion associated with only one polar region. Crocetin and the plant-derived amphiphilic triterpenoids described here are the most potent non-aromatic plant-derived inhibitors of cAK yet found.

Potential applications of apoptosis in modifying the biological behavior of therapeutically refractory cancers

Recent information about apoptosis or programmed cell death, the anti-apoptotic gene, BCL2, its interaction with reactive oxygen species and the role of these agents in senescence and apoptosis, suggests a discussion of their relationships could be of interest. Such information may eventually provide alternative approaches to modifying the biological behavior of therapeutically resistant cancers. Some of these comments probably are self-evident, others may be less so and provide ideas for further studies.

Tyrosine protein kinase inhibition and cancer

The various aspects of the research on tyrosine protein kinase inhibition and its connections with cancer are presented. The emphasis was made on the theoretical low toxic side effects of specific tyrosine protein kinase inhibitors. Particularly, the strategy of finding peptidic substrate-derived inhibitors or modulators is discussed, with an almost complete compendium of the tyrosine protein kinase peptidic substrates published so far. A series of data has been gathered that may serve as a basis for the discovery of selective and specific tyrosine protein kinase inhibitors by screening on molecular and cellular models. The potential of SH2 domain-interfering agents are also presented as a promising route to new anticancer compounds.

Specific inhibition of cyclic AMP-dependent protein kinase by the antimalarial halofantrine and by related phenanthrenes

The phenanthrenemethanol antimalarial halofantrine is a potent inhibitor of bovine heart and rat liver cyclic AMP-dependent protein kinase catalytic subunit (cAK) (IC50 values 2.1 microM and 0.6 microM, respectively). The inhibition of rat liver cAK by halofantrine is non-competitive with respect to both ATP and to the synthetic peptide substrate employed (LRRASLG). Halofantrine is a poor inhibitor of calmodulin-dependent myosin light chain kinase (MLCK) and wheat embryo Ca(2+)-dependent protein kinase (CDPK) and does not inhibit rat brain Ca(2+)- and phospholipid-dependent protein kinase C (PKC). In contrast, the acridine-based antimalarial quinacrine and a variety of quinoline-based antimalarials are very poor inhibitors of cAK, the best inhibitor being chloroquine (IC50 for bovine heart cAK, 80 microM). Quinacrine and the quinoline-based antimalarials variously inhibit CDPK, PKC and MLCK albeit at relatively high concentrations (about 1 to 4 x 10(-4) M), the best inhibitors found being primaquine, pentaquine and mefloquine (IC50 values for MLCK 49, 103 and 33 microM, respectively). A number of phenanthrene derivatives having a 9-hydroxy or 9-keto substituent, namely phenanthrenequinone, 6(5H)-phenanthridinone and 9-phenanthrol are potent inhibitors of bovine heart cAK (IC50 values 8, 10 and 10 microM, respectively) and of MLCK (IC50 values 6, 53 and 10 microM, respectively). The selective, high affinity interaction of halofantrine with cAK may contribute to biological effects in vivo of this clinically-employed antimalarial compound.

Effects of baicalein and esculetin on transduction signals and growth factors expression in T-lymphoid leukemia cells

The possible mechanisms of antiproliferative effect of baicalein were studied in human T-lymphoid leukemia cells (CEM cells) and compared with those of esculetin. Baicalein, esculetin and related compounds, baicalein, wogonin, esculin and scoparone, inhibited CEM cell proliferation. Baicalein exhibited the greatest antiproliferative activity with an IC50 of 4.7 +/- 0.5 microM and the maximal suppression of 91.5 +/- 1.4% in CEM cells. The protein tyrosine kinase activity in the CEM cells was significantly reduced by baicalein (10(-6)-10(-4) M) and esculetin (10(-4) M). Baicalein exhibited a greater inhibitory activity on the protein tyrosine kinase than did esculetin (74.1 +/- 3.3% vs. 64.6 +/- 2.8% inhibition at 10(-4) M). On the other hand, the protein kinase C activity stimulated by phorbol-12-myristate 13-acetate was reduced by directly incubating with baicalein (10(-6)-10(-4) M) and esculetin (10(-4) M). However, the inhibitory activities on protein kinase C did not show a dose-dependency. The reverse transcription-polymerase chain reaction analysis of platelet-derived growth factor-A (PDGF-A) and transforming growth factor-beta 1 (TGF-beta 1) messenger RNA levels demonstrates that baicalein and esculetin reduced the PDGF-A mRNA level, but less affected the TGF-beta 1 mRNA. Baicalein exhibited the greater reduction on the expression of PDGF-A mRNA than did esculetin. It is suggested that baicalein and esculetin may affect cell proliferation by direct inhibition of growth-related signal, protein tyrosine kinase, as well as reduction of mRNA expression of growth factor, platelet-derived growth factor.

Differential inhibition of cyclic AMP-dependent protein kinase, myosin light chain kinase and protein kinase C by azaacridine and acridine derivatives

A series of 72 acridine and azaacridine derivatives have been tested as inhibitors of Ca(2+)- and phospholipid-activated protein kinase C (PKC), the catalytic subunit of cyclic AMP-dependent protein kinase (cAK) and Ca(2+)-calmodulin-dependent myosin light chain kinase (MLCK). A series of monomethyl derivatives of N-(2-dimethylaminoethyl)-acridine-4-carboxamide that have anti-tumour activity are good inhibitors of MLCK (IC50 values ranging from 4-138 microM) but these same compounds are ineffective or relatively poor inhibitors of PKC or cAK. With only several exceptions, the effective azaacridine inhibitors of PKC and MLCK (IC50 values < 200 microM) have basic or neutral 4-substituents whereas the effective azaacridine inhibitors of cAK have either neutral or acidic 4-substituents. The four exceptions found to this generality are effective inhibitors of all three protein kinases with IC50 values of about 100 microM or less. With several exceptions azaacridine inhibitors of PKC are also inhibitors of MLCK but effective inhibitors of cAK are relatively poor inhibitors of MLCK and PKC and vice versa. 4-N-(2-dimethylaminoethyl)-6-azaacridone-4-carboxamide is a competitive inhibitor of MLCK with respect to both the peptide substrate and ATP. All other acridines and azaacridines examined are non-competitive inhibitors of both MLCK and cAK with respect to both ATP and peptide substrate. All azaacridine PKC inhibitors examined are competitive with respect to ATP and noncompetitive with respect to peptide substrate suggesting that binding of these inhibitors is at or near the enzyme active site. The inhibition of MLCK (but not cAK or PKC) by anti-tumour acridine carboxamides suggests a novel site of in vivo biological action and a useful criterion for the detection of potential antitumour compounds.

Analysis of c-erbB-2 amplification in salivary gland tumours by differential polymerase chain reaction

DNA samples extracted from 22 normal salivary glands, 38 salivary pleomorphic adenomas and 20 other salivary gland neoplasms were screened for amplification of the c-erbB-2 oncogene by a differential polymerase chain reaction (PCR). The samples were PCR amplified with primers specific for the c-erbB-2 oncogene and for a reference gene (interferon-gamma). A breast carcinoma cell line SKBR-3 known to contain c-erbB-2 amplification was used as positive control. Following gel electrophoresis, the intensity of the amplified DNA bands was determined by laser densitometry and the level of amplification of the c-erbB-2 oncogene was assessed from the intensity of the c-erbB-2 specific band relative to that of the interferon-gamma band. Of all the tumours detected, only the two poorly differentiated adenocarcinomas, two of the pleomorphic adenomas and one of the Warthin's tumours showed gene amplification at levels comparable to the breast carcinoma cell line. None of the normal salivary gland tissues was found to have amplification. Within the group of pleomorphic adenomas the average level of amplification was not significantly different from that observed in the normal salivary gland, or in total genomic DNA from unrelated tissue (P < or = 0.001, determined by a general linear model of statistical analysis). These results indicate that amplification of the c-erbB-2 oncogene is infrequent in salivary neoplasia. Thus, gene amplification alone cannot account for the high prevalence of c-erbB-2 overexpression demonstrated previously in salivary gland tumours. When present, c-erbB-2 amplification may be associated with a more aggressive behaviour.

Design of a potent peptide inhibitor of the epidermal growth factor receptor tyrosine kinase utilizing sequences based on the natural phosphorylation sites of phospholipase C-gamma 1

Peptides that possess primary sequences identical to segments surrounding the natural phosphorylation sites of phospholipase C-gamma 1 (i.e., tyrosines 472, 771, 783, and 1284) have been synthesized and evaluated with respect to substrate kinetics for the epidermal growth factor receptor tyrosine kinase. A peptide that was based on tyrosine 472 was the superior substrate in terms of lowest Km value at 37 microM and had the following amino acid sequence: Lys-His-Lys-Lys-Leu-Ala-Glu-Gly-Ser-Ala-Tyr472-Glu-Glu-Val. This peptide sequence was used as a foundation to make amino acid substitutions and/or chemical modifications directed toward the synthesis of a potent peptide inhibitor. As a result, a nine amino acid peptide was synthesized having a K(i) of 10 microM.

Conformationally constrained analogues of diacylglycerol (DAG)--II. Differential interaction of delta-lactones and gamma-lactones with protein kinase C (PK-C)

Starting with L- or D-tri-O-acetylglucal, the corresponding L- and D-isomers of 4-O-tetradecanoyl-2,3-dideoxyglucono-1,5-lactone (2a and 2b) were synthesized as rigid diacylglycerol (DAG) analogues. Consistent with results obtained previously with the equivalent L- and D-1,4-lactones (1a and 1b), the L-isomer (2a) was more potent in activating protein kinase C (PK-C) and inhibiting the binding of [3H]phorbol-12,13-dibutyrate to the enzyme's regulatory domain. In these experiments the difference in potency observed between the optical antipodes of the gluconolactones (2a and 2b) was greatly increased relative to the corresponding ribonolactones (1a and 1b). These results indicate that PK-C is more able to discriminate between optical antipodes, in favor of the L-isomer, as the lactone ring increases from five to six.

Antiproliferative effect of esculetin on vascular smooth muscle cells: possible roles of signal transduction pathways

The effect of esculetin, a coumarin derivative with lipoxygenase inhibitor activity, on the proliferation response of cultured rabbit vascular smooth muscle cells was studied. Proliferation response was determined by the uptake of tritiated thymidine. Esculetin (10(-5)-10(-4) M) dose dependently inhibited the enhanced proliferation stimulated by 5% fetal calf serum. The structure-activity relationship of esculetin and eight other coumarin derivatives indicates that two adjacent phenolic hydroxyl groups at the C-6 and C-7 positions in the coumarin skeleton are necessary for the potent antiproliferative effect. The antiproliferative effects of other lipoxygenase inhibitors, 5,8,11,14-eicosatetraynoic acid (ETYA) and ketoconazole, were comparable to the effect of esculetin. However, esculetin exhibited the greatest maximal suppression. The enhanced releases of 12-hydroxyeicosatetraenoic acid (12-HETE), prostaglandin E2 and 6-keto-prostaglandin F1 alpha in the culture medium of smooth muscle cells stimulated by 5% fetal calf serum were significantly reduced by esculetin. Furthermore, the fetal calf serum-stimulated protein tyrosine kinase activity was reduced by esculetin (10(-5)-10(-4) M) in a dose-dependent manner. In contrast, the protein kinase C activity stimulated by phorbol-12-myristate-13-acetate was not affected by esculetin (10(-6)-10(-4) M). These results suggest that the antiproliferative effect of esculetin on vascular smooth muscle cells may be partly mediated through inhibition of protein tyrosine kinase and modulated by inhibition of lipoxygenase.

Cytotoxic and cytostatic effects of antitumor agents induced at the plasma membrane level

A variety of antitumor agents inhibit cell proliferation by interacting with the plasma membrane. They act as growth factor antagonists, growth factor receptor blockers, interfere with mitogenic signal transduction or exert direct cytotoxic effects. The P-glycoprotein encoded by the MDR1 gene represents a transmembrane protein which catalyzes the efflux of various antitumor agents. This membrane protein is the target of compounds acting as Multi-Drug Resistance (MDR)-modulators. Finally, several established antitumor agents which are considered to represent DNA-targeted drugs, including anthracyclines, platinum complexes and alkylating agents, cause a variety of membrane lesions. Their contribution to the antitumor activity of these drugs is discussed.