Inhibition of the membrane translocation and activation of protein kinase C, and potentiation of doxorubicin-induced apoptosis of hepatocellular carcinoma cells by tamoxifen

Dissimilar action of tamoxifen and 4-hydroxytamoxifen on phosphatidylcholine model membranes

The anticancer drug tamoxifen and its primary metabolite 4-hydroxytamoxifen tend to accumulate in membranes due to its strong hydrophobic character. Thus, in this work we have carried out a systematic study to investigate their effects on model phosphatidylcholine membranes. Tamoxifen and 4-hydroxytamoxifen affect the phase behaviour of phosphatidylcholine model membranes, giving rise to formation of drug/dipalmitoylphosphatidylcholine domains, which is more evident in the case of 4-hydroxytamoxifen. These drugs have differential effects on the polar and apolar regions of the phospholipid supporting a different location of both compounds within the bilayer. Both compounds induce contents leakage in fluid phosphatidylcholine unilamellar liposomes, the effect of 4-hydroxytamoxifen being negligible as compared to that of tamoxifen. Molecular dynamics confirmed the tendency of both drugs to form clusters, tamoxifen locating all along the bilayer, whereas 4-hydroxytamoxifen mostly locates near the lipid/water interface, which can explain the different effects of both drugs in fluid phosphatidylcholine membranes.

Tamoxifen and oxidative stress: an overlooked connection

Tamoxifen is the gold standard drug for the treatment of breast cancer in pre and post-menopausal women. Its journey from a failing contraceptive to a blockbuster is an example of pharmaceutical innovation challenges. Tamoxifen has a wide range of pharmacological activities; a drug that was initially thought to work via a simple Estrogen receptor (ER) mechanism was proven to mediate its activity through several non-ER mechanisms. Here in we review the previous literature describing ER and non-ER targets of tamoxifen, we highlighted the overlooked connection between tamoxifen, tamoxifen apoptotic effects and oxidative stress.

Does tamoxifen have a therapeutic role outside of breast cancer? A systematic review of the evidence

INTRODUCTION

Tamoxifen is a widely used hormonal based therapy for breast cancer in the adjuvant and metastatic setting, prolonging overall and recurrence-free survival. There has been increasing interest in the potential for novel "off-target" effects of tamoxifen and its metabolite N-desmethyltamoxifen across a number of cancer types. We aim to review the current literature regarding the potential use of tamoxifen in other primary malignancies.

METHOD

A qualitative systematic review was performed according to the PRISMA guidelines using pre-set search criteria across the PubMed, Cochrane and Scopus databases from 1985 to 2019. Additional results were generated from included papers references.

RESULTS

A total of 324 papers were identified, of which 47 were included; a further 29 articles were obtained from additional referencing to give a total of 76 articles. Clinical trials have demonstrated benefits with the use of tamoxifen in isolation and combination, specifically in patients with advanced non-resectable malignancy, however results are not consistent across the literature. In vivo data consistently suggests that off target effects of tamoxifen are mediated through the ceramide pathway or through inhibition of protein kinase C (PKC).

CONCLUSIONS

With increased focus upon the potential of repurposing drugs, tamoxifen may be a candidate for repurposing in the wider cancer setting. There is evidence to suggest that the ceramide or PKC pathway could act as a therapeutic target for tamoxifen or alternative chemotherapeutics and merits further investigation.

Oncolytic Virus-Based Immunotherapies for Hepatocellular Carcinoma

Hepatocellular carcinoma is highly refractory cancer which is resistant to conventional chemotherapy and radiotherapy, carrying a dismal prognosis. Although many anticancer drugs have been developed for treating HCC, sorafenib is the only effective treatment, but it only prolongs survival duration for about 3 months. Recently, oncolytic virotherapy has shown promising results in treating HCCs and the effects can be more enhanced by adopting immune modulatory molecules. This review discusses the current status of treating HCC and the effective strategy of oncolytic virus-based immunotherapy for the treatment of HCCs.

Protein kinase C as a target for new anti-cancer agents

Cancer joins the category of diseases involving abnormalities in the rate of proliferation of cells and is associated with uncontrolled cell division, where cells either generate their own growth-promoting stimuli or neighboring cells or do not respond to growth inhibitory signals. Protein kinase C (PKC) is one of the key elements in the tumor growth signal transduction pathways and is found to be overexpressed in several malignant cell types. A way to control cell proliferation and cell differentiation is by influencing signal transduction pathways by modulation of PKC. PKC encloses 12 different isoenzymes, and each isoenzyme is found to have a different functional property. Because specific PKC isoenzyme types are present in different (malignant) cell species, they may be an attractive target in the development of anti-cancer agents. Classification and identification of the available PKC isoenzymes in different tumor cells could be useful in targeting specific tumors. PKC also tends to be overexpressed in association with the multidrug resistance pheno-type. This concise review deals with the role of PKC isoenzymes in (tumor) cell biology and evaluates the antineoplastic agents interacting on PKC isoenzymes.

Inhibitory effects of tamoxifen and doxorubicin, alone and in combination, on the proliferation of the MG63 human osteosarcoma cell line

The present study aimed to compare the combined effect of tamoxifen (TAM) and doxorubicin (ADM) with the individual effects of TAM and ADM alone on the MG63 human osteosarcoma cell line. Estrogen receptor (ER) expression was detected in the MG63 cells using reverse transcription PCR. The morphological changes during the inhibition of cell growth were observed using an inverted microscope and a 3-(4, 5-dimethy1-2-thiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) colorimetric assay following the individual or combined addition of TAM and ADM. ERα and ERβ expression was detected in the MG63 cells. The typical apoptotic cell morphology was observed in all groups, with the exception of the control group. The MTT colorimetric analysis demonstrated that the rate of inhibition of cell proliferation in the combination group was significantly increased compared with that in the other groups (P<0.05). ERα and ERβ expression was detected in the MG63 human osteosarcoma cells. TAM and ADM alone were able to inhibit cell proliferation. The combination of TAM and ADM significantly enhanced the inhibitory effect, partly through the enhanced sensitivity of the cells to ADM by TAM, which caused the inhibition of cell proliferation and apoptosis.

Tamoxifen non-estrogen receptor mediated molecular targets

Recent experimental studies revealing new biological effects of tamoxifen on tumor cells both expressing and not expressing different types of estrogen receptors (ERα and ERβ) show new aspects of a seemingly well known agent. This review describes tamoxifen targets, the blocking of which leads to inhibition of tumor cell growth and angiogenesis, stimulation of programmed cell death (apoptosis, autophagia and necrosis), inhibition of multidrug resistance, invasion and metastasis. Since outcomes of tamoxifen action on cells are prognostically good from the point of view of both tumor growth/metastasis inhibition and tumor response to drug therapy, the authors believe this is an extremely important addition to tamoxifen antiestrogenic effect. Arguments are provided to consider the strategy of long-term tamoxifen treatment proposed by Professor Craig V. Jordan in the 1970s that is also applicable to the treatment of other tumors. This is, first of all, the fact that expression of estrogen receptor-beta that can also be targeted by tamoxifen therapy in solid tumors of practically all known sites and histologies. The authors believe that molecular biological screening of patients with respect to expression of tamoxifen cellular targets other than ERα and ERβ is needed to use to the full all tamoxifen biological activities other than modulation of estrogen receptors during long-term adjuvant therapy for cancers of various sites.

Tamoxifen inhibits malignant peripheral nerve sheath tumor growth in an estrogen receptor-independent manner

Few therapeutic options are available for malignant peripheral nerve sheath tumors (MPNSTs), the most common malignancy associated with neurofibromatosis type 1 (NF1). Guided by clinical observations suggesting that some NF1-associated nerve sheath tumors are hormonally responsive, we hypothesized that the selective estrogen receptor (ER) modulator tamoxifen would inhibit MPNST tumorigenesis in vitro and in vivo. To test this hypothesis, we examined tamoxifen effects on MPNST cell proliferation and survival, MPNST xenograft growth, and the mechanism by which tamoxifen impeded these processes. We found that 1-5 μM 4-hydroxy-tamoxifen induced MPNST cell death, whereas 0.01-0.1 μM 4-hydroxy-tamoxifen inhibited mitogenesis. Dermal and plexiform neurofibromas, MPNSTs, and MPNST cell lines expressed ERβ and G-protein-coupled ER-1 (GPER); MPNSTs also expressed estrogen biosynthetic enzymes. However, MPNST cells did not secrete 17β-estradiol, exogenous 17β-estradiol did not stimulate mitogenesis or rescue 4-hydroxy-tamoxifen effects on MPNST cells, and the steroidal antiestrogen ICI-182,780 did not mimic tamoxifen effects on MPNST cells. Further, ablation of ERβ and GPER had no effect on MPNST proliferation, survival, or tamoxifen sensitivity, indicating that tamoxifen acts via an ER-independent mechanism. Consistent with this hypothesis, inhibitors of calmodulin (trifluoperazine, W-7), another known tamoxifen target, recapitulated 4-hydroxy-tamoxifen effects on MPNST cells. Tamoxifen was also effective in vivo, demonstrating potent antitumor activity in mice orthotopically xenografted with human MPNST cells. We conclude that 4-hydroxy-tamoxifen inhibits MPNST cell proliferation and survival via an ER-independent mechanism. The in vivo effectiveness of tamoxifen provides a rationale for clinical trials in cases of MPNSTs.

Randomized Study of Paclitaxel and Tamoxifen Deposition into Human Brain Tumors: Implications for the Treatment of Metastatic Brain Tumors

PURPOSE

Drug resistance in brain tumors is partially mediated by the blood-brain barrier of which a key component is P-glycoprotein, which is highly expressed in cerebral capillaries. Tamoxifen is a nontoxic inhibitor of P-glycoprotein. This trial assessed, in primary and metastatic brain tumors, the differential deposition of paclitaxel and whether tamoxifen could increase paclitaxel deposition.

EXPERIMENTAL DESIGN

Patients for surgical resection of their primary or metastatic brain tumors were prospectively randomized to prior paclitaxel alone (175 mg/m(2)/i.v.) or tamoxifen for 5 days followed by paclitaxel. Central and peripheral tumor, surrounding normal brain and plasma, were analyzed for paclitaxel and tamoxifen.

RESULTS

Twenty-seven patients completed the study. Based on a multivariate linear regression model, no significant differences in paclitaxel concentrations between the two study arms were found after adjusting for treatment group (tamoxifen versus control). However, in analysis for tumor type, metastatic brain tumors had higher paclitaxel concentrations in the tumor center (1.93-fold, P = 0.10) and in the tumor periphery (2.46-fold, P = 0.039) compared with primary brain tumors. Pharmacokinetic analyses showed comparable paclitaxel areas under the serum concentration between treatment arms.

CONCLUSIONS

Paclitaxel deposition was not increased with this tamoxifen schedule as the low plasma concentrations were likely secondary to concurrent use of P-450-inducing medications. However, the statistically higher paclitaxel deposition in the periphery of metastatic brain tumors provides functional evidence corroborating reports of decreased P-glycoprotein expression in metastatic versus primary brain tumors. This suggests that metastatic brain tumors may respond to paclitaxel if it has proven clinical efficacy for the primary tumor's histopathology.

Estrogens and the pathophysiology of the biliary tree

The scientific framework concerning estrogen effects on different tissues has expanded enormously during the last decades, when estrogen receptor (ER) subtypes were identified. Estrogens are not only essential for the female reproductive system, but they also control fundamental functions in other tissues including the cardiovascular system, bone, brain and liver. Recently, estrogens have been shown to target the biliary tree, where they modulate the proliferative and secretory activities of cholangiocytes, the epithelial cells lining bile ducts. By acting on both estrogen receptors (ER-α) and (ER-β) subtypes, and by activating either genomic or non-genomic pathways, estrogens play a key role in the complex loop of growth factors and cytokines, which modulates the proliferative response of cholangiocytes to damage. Specifically, estrogens activate intracellular signalling cascades [ERK1/2 (extracellular regulated kinases 1/2, PI3- kinase/AKT (phosphatidylinositol-3’ kinase/AKT)] typical of growth factors such as insulin like growth factor (IGF1), nerve growth factor (NGF) and vascular endothelial growth factor (VEGF), thus potentiating their action. In addition, estrogens stimulate the secretion of different growth factors in proliferating cholangiocytes. This review specifically deals with the recent advances related to the role and mechanisms by which estrogens modulate cholangiocyte functions in normal and pathological conditions.

The role of tamoxifen in combination with cisplatin on oral squamous cell carcinoma cell lines

The purpose of this study was to evaluate the effect of tamoxifen (TAM) when used in combination with cisplatin on oral squamous cell carcinoma (OSCC). For this, the relation between estrogen receptor (ER) expression level and the cytotoxic effect of TAM, the apoptotic effect and its molecular mechanisms of TAM were investigated using OSCC cell lines. Combination treatment demonstrated a superior cytotoxic and apoptotic effect on OSCC cell lines. Considerable amount of ER was detected in some OSCC cell lines, but there were no significant differences of cytotoxic effect of TAM. TAM inhibited PKC activity and up-regulated TGF-beta1 secretion.

Tamoxifen Paradoxically Decreases Paclitaxel Deposition into Cerebrospinal Fluid of Brain Tumor Patients

BACKGROUND

P-glycoprotein (Pgp) mediates, in part, resistance to natural product chemotherapy drugs which constitute over half of the available drugs for cancer treatment. Tamoxifen (TAM) enhances intracellular deposition of natural product chemotherapy in human cell lines by inhibition of Pgp. Pgp is highly expressed in the choroid plexus and is thought to be a key component of the blood-cerebrospinal fluid barrier (BCSFB). We conducted a prospective, randomized study to assess if Pgp inhibition by TAM alters deposition of paclitaxel in cerebrospinal fluid (CSF).

METHODS

Ten patients with either primary or metastatic brain tumors were randomized to: paclitaxel alone (175 mg/m2/IV) or a course of TAM (160 mg/m2 PO BID on Days 1-5) followed by paclitaxel (175 mg/m2/IV on Day 5). CSF and plasma samples were obtained following paclitaxel infusion; paclitaxel and TAM concentrations were measured by high-performance liquid chromatography assays.

RESULTS

Paclitaxel was detected in the CSF of six of the 10 patients. Peak CSF paclitaxel concentrations of the paclitaxel and paclitaxel-TAM groups ranged between 3.5-57.4 and 2.3-24.6 nM, respectively. Though there was a 2.4-fold higher mean CSF paclitaxel concentration and a 3.7-fold higher median peak CSF:plasma paclitaxel ratio for those who received paclitaxel alone as compared to combined paclitaxel-TAM, it was not statistically significant (P = 0.22). In one patient enrolled to both arms, higher CSF concentrations of paclitaxel and higher paclitaxel CSF: plasma ratios were observed when given paclitaxel alone.

CONCLUSIONS

The trend towards lower paclitaxel CSF concentrations when given with TAM is consistent with the published finding that Pgp's localization in the endothelial cells of the choroid plexus works in an opposite direction and keeps drugs in the CSF. Thus, agents which inhibit Pgp, such as TAM, may increase efflux of Pgp substrates out of the BCSFB and may paradoxically lower CSF concentrations of natural product chemotherapy drugs. Conceptually, this finding implies that the Pgp in the BBB and BCSFB keeps natural toxins such as paclitaxel, from entering the brain (BBB) and, if they do enter the brain, keeps them in the CSF (BCSFB) where they may be less harmful than if they re-entered the brain. Thus, our work supports this novel idea and adds to the understanding of the functions of the BCSFB.

Modulation of apoptosis by cancer chemopreventive agents

A review of almost 2000 studies showed that the large majority of 39 putative cancer chemopreventive agents induced "spontaneous" apoptosis. Inhibition of the programmed cell death triggered by a variety of stimuli was consistently reported only with ascorbic acid, alpha-tocopherol, and N-acetylcysteine (NAC). We performed experimental studies in rodents exposed to cigarette smoke, either mainstream (MCS) or environmental (ECS), and UV-A/B-containing light. The nonsteroidal anti-inflammatory drug sulindac did not affect the apoptotic process in the skin of light-exposed mice and in the lungs of ECS-exposed mice. Likewise, 5,6-benzoflavone, indole-3-carbinol, 1,2-dithiole-3-thione and oltipraz failed to modulate apoptosis in the respiratory tract of ECS-exposed rats. Phenethyl isothiocyanate further enhanced the frequency of apoptosis in pulmonary alveolar macrophages and bronchial epithelial cells, and upregulated several genes in the lung of ECS-exposed rats. Both individually and in combination with oltipraz, NAC inhibited apoptosis in the respiratory tract of rats exposed either to MCS or ECS. Moreover, NAC attenuated the ECS-related overexpression of proapoptotic genes and normalized the levels of proapoptotic proteins in rat lung. The transplacental administration of NAC to mice considerably attenuated gene overexpression in the liver of fetuses exposed to ECS throughout pregnancy. Inhibition of apoptosis by chemopreventive agents reflects their ability to counteract certain upstream signals, such as genotoxic damage, redox imbalances, and other forms of cellular stress that trigger apoptosis. On the other hand, enhancement of apoptosis is a double-edged sword, since it represents a protective mechanism in carcinogenesis but may contribute to the pathogenesis of other degenerative diseases. We suggest that stimulation of apoptosis by so many chemopreventive agents, as reported in the literature, may often reflect the occurrence of toxic effects at high doses.

Modulation of multidrug resistance by andrographolid in a HCT-8/5-FU multidrug-resistant colorectal cancer cell line

OBJECTIVE

To develop an HCT-8/5-FU multidrug-resistant colorectal cancer cell line and to elucidate the effect of Andrographolid (AG), an extract from Andrographis paniculate, a medicinal herb on the HCT-8/5-FU multidrug-resistant colorectal cancer cell line.

METHODS

An HCT-8 colorectal cancer cell line was used and a high concentration of 5-Fluorouracid (5-FU) was introduced at the beginning to induce drug resistance, then the concentration of 5-FU was increased in gradients. Approximately 7 months later, the cells grew stably in 2.0 microg/mL of 5-FU, and the cell line was named HCT-8/5-FU multidrug-resistant colorectal cancer cell line. The resistant index of HCT-8/5-FU cells to 5-FU, adriamycin (ADM), cisplatin (DDP) was checked by MTT test, and a growth curve was drawn. The morphological changes were observed by both light and electron microscope. The function of P-170 was detected by rhodamine staining. After the application of AG and co-administration of 5-FU, ADM and DDP, the growth curves and inhibition rate as well as apoptosis rate of HCT-8/5-FU at different concentrations of AG were evaluated by MTT and flow cytometry. Rhodamine staining was used to investigate the possible mechanism involved by AG.

RESULTS

The resistance index of HCT-8/5-FU to 5-FU was 16.6, and a cross-resistance to ADM and DDP was noticed. Compared with parental cells, HCT-8/5-FU cell's growth rate did not change significantly but the cell's morphology was remarkably changed as compared with parental cells. Overexpression of P-170 by HCT-8/5-FU cell was indicated through rhodamine staining. AG at a low concentration showed weak inhibitory effect on HCT-8/5-FU. However, a remarkable inhibitory and apoptosis rate was shown when AG was co-administered with 5-FU, ADM and DDP, respectively. Interestingly AG alone could not induce apoptosis and change the cell cycles. AG might affect the expression of P-170, which was indicated by rhodamine staining.

CONCLUSIONS

The HCT-8/5-FU multidrug-resistant colorectal cancer cell line has been successfully developed and because it has cross-resistance to 5-FU, ADM and DDP, it might serve as an ideal multidrug resistance (MDR) model for colorectal cancer research. The mechanism of HCT-8/5-FU resistance to chemotherapeutic agents might be related to the overexpression of P-170. Low concentrations of AG alone have no significant inhibition on HCT-8/5-FU and fail to induce apoptosis and to change cell cycles. AG might act as a chemosensitizer when co-administered with 5-FU, ADM and DDP, and the mechanism of reversal modulation of multidrug resistance by AG in the HCT-8/5-FU resistant cell line might be related to its downregulation of overexpression of P-170.

Role of protein kinase C-alpha in superficial bladder carcinoma recurrence

OBJECTIVES

To investigate the role of protein kinase C-alpha (PKCalpha) in the recurrence of superficial bladder carcinoma.

METHODS

Expression of PKCalpha was measured by Western blot analysis in 56 samples. A human RT-4 bladder cancer cell line stably expressing green fluorescent protein-PKCalpha (RT-4/PKCalpha) was established. The sensitivity of the RT-4/PKCalpha and parental cells to adriamycin (ADM) was determined by MTT assay. We also observed a change in the sensitivity of RT-4/PKCalpha to ADM under the conditions of PKCalpha upregulation and downregulation.

RESULTS

PKCalpha expression and the ratio of PKCalpha expression in the membrane to that in cytosol were greater in cancerous tissues than in normal tissues (P <0.05). With an increase in tumor grade, the level of PKCalpha expression increased significantly in the membrane (P <0.01) and decreased in cytosol (P <0.01). Patients with superficial bladder carcinoma with a greater membrane/cytosol ratio of PKCalpha had a shorter recurrence-free period than did those with lower levels after standard ADM treatment at 2 years of follow-up (P <0.05). In vitro transfection of PKCalpha increased resistance of RT-4 cells to ADM (P<0.01). Activation of PKCalpha also greatly promoted resistance (P <0.001), and inhibition of PKCalpha decreased resistance (P <0.01).

CONCLUSIONS

Our results have shown the correlation of PKCalpha overexpression/activation in superficial bladder carcinoma with the effect of ADM on tumor recurrence. PKCalpha may play an important role, not only in tumor differentiation, but also in intrinsic resistance to chemotherapy drugs by activation of the PKC pathway.

Genomic approach to identification of mutations affecting caspofungin susceptibility in Saccharomyces cerevisiae

The antifungal agent caspofungin (CAS) specifically interferes with glucan synthesis and cell wall formation. To further study the cellular processes affected by CAS, we analyzed a Saccharomyces cerevisiae mutant collection (4,787 individual knockout mutations) to identify new genes affecting susceptibility to the drug. This collection was screened for increased CAS sensitivity (CAS-IS) or increased CAS resistance (CAS-IR). MICs were determined by the broth microdilution method. Disruption of 20 genes led to CAS-IS (four- to eightfold reductions in the MIC). Eleven of the 20 genes are involved in cell wall and membrane function, notably in the protein kinase C (PKC) integrity pathway (MID2, FKS1, SMI1, and BCK1), chitin and mannan biosynthesis (CHS3, CHS4, CHS7, and MNN10), and ergosterol biosynthesis (ERG5 and ERG6). Four of the 20 genes (TPO1, VPS65, VPS25, and CHC1) are involved in vacuole and transport functions, 3 of the 20 genes (CCR4, POP2, and NPL3) are involved in the control of transcription, and 2 of the 20 genes are of unknown function. Disruption of nine additional genes led to CAS-IR (a fourfold increase of MIC). Five of these nine genes (SLG1, ERG3, VRP1, CSG2, and CKA2) are involved in cell wall function and signal transduction, and two of the nine genes (VPS67 and SAC2) are involved in vacuole function. To assess the specificity of susceptibility to CAS, the MICs of amphotericin B, fluconazole, flucytosine, and calcofluor for the strains were tested. Seven of 20 CAS-IS strains (with disruption of FKS1, SMI1, BCK1, CHS4, ERG5, TPO1, and ILM1) and 1 of 9 CAS-IR strains (with disruption of SLG1) demonstrated selective susceptibility to CAS. To further explore the importance of PKC in CAS susceptibility, the activity of the PKC inhibitor staurosporine in combination with CAS was tested against eight Aspergillus clinical isolates by the microdilution assay. Synergistic or synergistic-to-additive activities were found against all eight isolates by use of both MIC and minimum effective concentration endpoints.

The tamoxifen-induced suppression of telomerase activity in the human hepatoblastoma cell line HepG2: a result of post-translational regulation

PURPOSE

Patients with advanced hepatocellular carcinoma (HCC) have shown to benefit from tamoxifen treatment. The mechanisms of tamoxifen action in HCC, however, are not yet clearly understood. Results from studies on the human hepatoblastoma cell line HepG2 provide evidence that estrogen-receptor-alpha-independent antiproliferative actions of tamoxifen in HCC are mediated by the suppression of telomerase activity [5].

MATERIALS AND METHODS

We investigate the pathway of the tamoxifen-induced down-regulation of telomerase activity, using HepG2 cells incubated over 24 h or 48 h in the presence of 20 microM tamoxifen.

RESULTS

The transcriptional levels of the three telomerase core components-human telomerase RNA (hTR), human telomerase reverse transcriptase (hTERT) (all variants), and telomerase-associated protein (TP1)-did not change during tamoxifen treatment, as revealed by RT-PCR analysis. Furthermore, the hTERT splice pattern was not shifted from the active full-length variant (+alpha/+beta) to the inactive deletion variants (-alpha; -beta; -alpha/-beta) and the level of the 120 kDa hTERT full-length protein remained constant, as shown by Western blot analysis. Protein kinase C (PKC) activity has been suggested to be crucial for post-translational up-regulation of telomerase activity. In HepG2 cells, we observed a tamoxifen-induced suppression of the total protein kinase C (PKC) activity (cytosolic and membrane-bound). Inhibition of PKC with bisindolylmaleimide I resulted in a reduction of telomerase activity, as revealed by TRAP-assay. Alpha-tocopherol (vitamin E) diminished the effects of tamoxifen on PKC-activity as well as on telomerase activity.

CONCLUSIONS

We conclude that the tamoxifen-induced decrease of telomerase activity in HepG2 cells is mediated post-translationally via suppression of PKC-activity.

Tamoxifen induces suppression of cell viability and apoptosis in the human hepatoblastoma cell line HepG2 via down-regulation of telomerase activity

BACKGROUND/AIMS

Antiproliferative action of tamoxifen in the estrogen receptor-alpha-negative human hepatoblastoma cell line HepG2 was investigated.

METHODS

HepG2 cells, seeded at different densities (4000-36 000 cells/cm(2)), were incubated with tamoxifen (1, 10, or 20 microM) or the telomerase inhibitor 3'-azido-3'-deoxythymidine (AZT) (0.6-3.0 mM) up to 72 h. Cell viability was assessed (MTT-test), flow cytometric analysis was performed, and telomerase activity was measured (telomeric repeat amplification protocol assay).

RESULTS

Ten or 20 microM tamoxifen induced a reduction of cell viability. Basically reduction of viability was related to an increase in the fraction of G0/1-phase. When tamoxifen was present at higher concentration (20 microM) or at low cell density (4000/cm(2)) an additional increase of the rate of apoptotic cells occurred with a delay, aggravating the effect of tamoxifen on cell viability substantially. When apoptosis was induced a significant suppression of telomerase activity preceded regularly. Direct inhibition of telomerase activity with AZT resulted in a decrease of cell viability and apoptosis.

CONCLUSION

The tamoxifen-induced reduction of cell viability in HepG2 cells depends on drug concentration and cell density and is due to cytostatic and cytocide effects. The latter may be mediated by a down-regulation of telomerase activity.

Potent Killing of Paclitaxel- and Doxorubicin-resistant Breast Cancer Cells by Calphostin C Accompanied by Cytoplasmic Vacuolization

Drug resistance is a major impediment to the successful treatment of breast cancer using chemotherapy. The photoactivatable drug calphostin C has shown promise in killing select drug-resistant tumor cells lines in vitro. To assess the effectiveness of this agent in killing doxorubicin- or paclitaxel-resistant breast tumor cells and to explore its mode of action, MCF-7 cells were exposed to increasing concentrations of either doxorubicin or paclitaxel until maximum resistance was obtained. This resulted in the creation of isogenic drug-resistant MCF-7TAX and MCF-7DOX cell lines, which were approximately 50- and 65-fold resistant to paclitaxel and doxorubicin, respectively. Interestingly, calphostin C was able to kill MCF-7TAX cells as efficiently as wildtype MCF-7 cells (IC50s were 9.2 and 13.2 nM, respectively), while MCF-7DOX cells required a 5-fold higher concentration of calphostin C to achieve the same killing (IC50 = 64.2 nM). Consistent with their known mechanisms of action, paclitaxel killed tumor cells by inducing mitotic arrest and cell multinucleation, while doxorubicin induced plasma membrane blebbing and decreased nuclear staining with propidium iodide. In contrast, cytoplasmic vacuolization accompanied cell killing by calphostin C in these cell lines, without the induction of caspase-8 or PARP cleavage or the release of cytochrome c from mitochondria. Calphostin C had little effect on the uptake of either paclitaxel or doxorubicin by the cells. Taken together, the above data suggests that calphostin C is able to potently kill drug-resistant breast tumor cells through a mechanism that may involve the induction of cytoplasmic vacuolization, without activation of typical apoptotic pathways. Consequently, calphostin C may prove useful clinically to combat tumor growth in breast cancer patients whose tumors have become unresponsive to anthracyclines or taxanes, particularly in association with photodynamic therapy.

Differential effects of calmodulin and protein kinase C antagonists on bone resorption and acid transport activity

Tamoxifen inhibits bone resorption by disrupting calmodulin-dependent processes. Since tamoxifen inhibits protein kinase C in other cells, we compared the effects of tamoxifen and the PKC inhibitor, bis indolylmaleimide II (bIM), on bone resorption and acid transport activity in isolated membrane vesicles. Bis indolylmaleimide inhibited bone resorption 50% with an IC50 approximately 3 microM, as well as acid transport activity in a concentration -dependent manner with an IC50 of approximately 0.4 IM. The IC50 of bIM for inhibiting acid transport activity was similar to that of calmodulin antagonists. The potassium ionophore, valinomycin, failed to restore bIM or tamoxifen-dependent inhibition of acid transport, suggesting that bIM and tamoxifen both inhibit H(+)-ATPase activity. Half maximal inhibitory concentrations of tamoxifen and bIM were not additive in acid transport assays, suggesting different sites of action. Furthermore, exogenous calmodulin blocked tamoxifen, but not bIM, -dependent inhibition of acid transport. We also compared the effects of tamoxifen and bIM on phosphorylation of proteins in isolated membrane fractions as determined by 32P incorporation and autoradiography. Tamoxifen had no effect on protein phosphorylation in contrast to bIM, which inhibited phosphorylation of eight proteins with different apparent kinetics. The data suggest that, while tamoxifen and bIM both affect H(+)-ATPase activity, the mechanisms of action are different.

Phospholipase C-protein kinase C mediated phospholipase D activation pathway is involved in tamoxifen induced apoptosis

Tamoxifen (TAM) is the endocrine therapeutic agent the most widely used in the treatment of breast cancer, and it operates primarily through the induction of apoptosis. In this study, we attempted to elucidate the non-ER mediated mechanism behind TAM treatment, involving the phospholipase C-protein kinase C (PLC-PKC) mediated phospholipase D (PLD) activation pathway, using multimodality methods. In TAM treated MCF7 cells, the PLC and PLD protein and mRNA levels increased. Phosphatidylethanol (PEt) and diacylglycerol (DAG) generation also increased, showing increased activity of PLD and PLCgamma1. Translocation of PKCalpha, from cytosol to membrane, was observed in TAM treated cells. By showing that both PKC and PLC inhibitors could reduce the effects of TAM-induced PLD activation, we confirmed the role of PKC and PLC as upstream regulators of PLD. Finally, we demonstrated that TAM treatment reduced the viability of MCF7 cells and brought about rapid cell death. From these results, we confirmed the hypothesis that TAM induces apoptosis in breast cancer cells, and that the signal transduction pathway, involving PLD, PLC, and PKC, constitutes one of the possible mechanisms underlying the non-ER mediated effects associated with TAM.

Combination therapy with irinotecan and protein kinase C inhibitors in malignant glioma

The topoisomerase-I inhibitor irinotecan (CPT-11) is currently used in Phase I/II trials for the treatment of patients with recurrent malignant gliomas. Protein kinase C (PKC) inhibitors such as high-dose tamoxifen and hypericin also have been used in the treatment of malignant gliomas. The current study examined the role of PKC inhibitors as chemosensitizers for CPT-11 and their proposed mechanism of action. Two glioma cell lines (A-172 and U-87) and one primary glioma cell culture (LA-567) were used. Proliferation ((3)H-thymidine) and cytotoxicity (methylthiotetrazole) studies were performed using CPT-11 (0-100 microM) alone, 7-ethyl-10-hydroxy camptothecin (SN-38) (0-1000 nM) alone or in the presence of a PKC inhibitor, tamoxifen (10 microM), hypericin (10 microM), calphositin C (400 nM), or staurosporine (10 nM). The terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling(TUNEL) assay was used to determine apoptosis as the mechanism of cytotoxicity; alterations in bcl-2 and bax expression were determined using Western blot analysis. Conversion of CPT-11 to SN-38 by glioma cells was determined using high-performance liquid chromatography (HPLC) analysis. Increasing CPT-11 and SN-38 concentrations induced cytotoxic morphologic changes, decreased proliferation, and increased cytotoxicity on all glioma cell lines tested. These changes were increased in the presence of a PKC inhibitor. The mechanism of the cytotoxicity was determined to be apoptosis by the TUNEL assay. The combination of a PKC inhibitor with CPT-11 or SN-38 led to decreased expression of the antiapoptotic protein bcl-2, and increased expression of the proapoptotic protein bax. HPLC analysis demonstrated conversion of CPT-11 to SN-38 by glioma cells. A combination of CPT-11 or SN-38 with a PKC inhibitor was found to lead to a decrease in proliferation and an increase in apoptosis in malignant glioma cells. The induction of apoptosis was secondary to a decrease in bcl-2 and an increase in bax expression. Glioma cells are capable of converting CPT-11 to SN-38 by intrinsic tumor carboxylesterases.

Characterization of p21Ras-mediated apoptosis induced by protein kinase C inhibition and application to human tumor cell lines

Suppression of PKC activity can selectively induce apoptosis in cells expressing a constitutively activated p21Ras protein. We demonstrate that continued expression of p21Ras activity is required in PKC-mediated apoptosis because farnesyltransferase inhibitors abrogated the loss of viability in p21Ras-transformed cells occurring following PKC inhibition. Studies utilizing gene transfer or viral vectors demonstrate that transient expression of oncogenic p21Ras activity is sufficient for induction of apoptosis by PKC inhibition, whereas physiologic activation of p21Ras by growth factor is not sufficient to induce apoptosis. Mechanistically, the p21Ras-mediated apoptosis induced by PKC inhibition is dependent upon mitochondrial dysregulation, with a concurrent loss of mitochondrial membrane potential (psim). Cyclosporine A, which prevented the loss of psim, also inhibited HMG-induced DNA fragmentation in cells expressing an activated p21Ras. Induction of apoptosis by PKC inhibition in human tumors with oncogenic p21Ras mutations was demonstrated. Inhibition of PKC caused increased apoptosis in MIA-PaCa-2, a human pancreatic tumor line containing a mutated Ki-ras allele, when compared to HS766T, a human pancreatic tumor line with normal Ki-ras alleles. Furthermore, PKC inhibition induced apoptosis in HCT116, a human colorectal tumor line containing an oncogenic Ki-ras allele but not in a subline (Hke3) in which the mutated Ki-ras allele had been disrupted. The PKC inhibitor 1-O-hexadecyl-2-O-methyl-rac-glycerol (HMG), significantly reduced p21Ras-mediated tumor growth in vivo in a nude mouse MIA-PaCa-2 xenograft model. Collectively these studies suggest the therapeutic feasibility of targeting PKC activity in tumors expressing an activated p21Ras oncoprotein.

High-dose tamoxifen in the treatment of inoperable hepatocellular carcinoma: A multicenter randomized controlled trial

In the Asia-Pacific region and elsewhere, almost 85% of patients with hepatocellular carcinoma (HCC) are inoperable at diagnosis and have a dismal prognosis. Tamoxifen (TMX) is believed to inhibit HCC positive for estrogen receptor (ER), but most HCCs are ER negative. Results of previous phase 3 trials in inoperable HCC have been conflicting and inconclusive. At higher doses, however, TMX inhibits HCC through ER-independent mechanisms. A multicenter randomized controlled trial was performed to assess the role of high-dose TMX versus placebo (P) in the treatment of patients with inoperable HCC with respect to survival and quality of life (QoL). A total of 329 patients from 10 centers in 9 countries in the Asia-Pacific region enrolled in a double-blind randomized controlled trial of TMX 120 mg/d (TMX120) against P as a control arm with an intermediate dosage of TMX 60 mg/d (TMX60) to assess possible dose response. An independent data monitoring committee reviewed all aspects of the trial. QoL was assessed using the European Organization for Research and Treatment of Cancer QLQ-C30 questionnaire. Three-month survival rates for the P, TMX60, and TMX120 groups were 44%, 41%, and 35%, respectively, with a statistically significant trend difference in survival across the 3 treatment regimens (P =.011). There was a significantly higher risk of death in the TMX120 group compared with the P group (hazard ratio, 1.39; 95% confidence interval, 1.07-1.81). Adverse drug reactions were reported in 3% (9 patients), and 8 patients were lost to follow-up. In conclusion, TMX does not prolong survival in patients with inoperable HCC and has an increasingly negative impact with increasing dose. No appreciable advantage to QoL with TMX was observed.

Proteomics reveals protein profile changes in doxorubicin--treated MCF-7 human breast cancer cells

MCF-7 cells are extensively used as a cell model to investigate human breast tumors and the cellular mechanism of antitumor drugs such as doxorubicin (DOX), an anthracycline antitumor drug widely used in clinical chemotherapy. To understand the effects of DOX on the protein expression, we perform a comprehensive proteomics to survey global changes in proteins after DOX treatment in MCF-7 cells. Exposure of MCF-7 cells to 0.1 microM DOX for 2 days induced a differentiation-like phenotype with prominent perinuclear autocatalytic vacuoles, abundant filamentous material, and irregular microvilli at the cell surface. In this study, we also present a proteome reference map of MCF-7 cells with 21 identified protein spots via analysis of N-terminal sequencing, mass spectrometry, immunoblot and/or computer matching with protein database. Based on the proteome map, we found that DOX causes a markedly decrease in the levels of three isoforms of heat shock protein 27 (HSP27) whereas the levels of other stress associated proteins including HSP60, calreticulin, and protein disulfide isomerase were not significantly altered in DOX-treated MCF-7 cells. Taken together, we suggest that that action of DOX on breast tumor cells may be partly related to dysregulation of HSP27 expression. Modulation of HSP27 levels may be a clinically useful potential target for design of antitumor drugs and controlling breast tumor growth.

Basal levels and patterns of anticancer drug-induced activation of nuclear factor-kappaB (NF-kappaB), and its attenuation by tamoxifen, dexamethasone, and curcumin in carcinoma cells

Nuclear factor-kappaB (NF-kappaB) has been implicated in the development of drug resistance in cancer cells. We systematically examined the baseline levels of NF-kappaB activity of representative carcinoma cell lines, and the change of NF-kappaB activity in response to a challenge with four major anticancer drugs (doxorubicin, 5-fluorouracil, cisplatin, and paclitaxel). We found that the basal level of NF-kappaB activity was heterogeneous and roughly correlated with drug resistance. When challenged with various drugs, all the cell lines examined responded with a transient activation of NF-kappaB which then declined to basal level despite variation in the concentration of the agent and the timing of the treatment. In contrast to tumor necrosis factor-alpha (TNF-alpha), which activates NF-kappaB in minutes, NF-kappaB activation induced by anticancer drugs usually occurred more than 1hr after stimulation. A gradual increase of total NF-kappaB and its nuclear translocation, and cytoplasmic translocation of nuclear IkappaBalpha and its degradation were involved in this process. In particular, when cells were pretreated with common biologic modulators such as tamoxifen, dexamethasone, and curcumin, the doxorubicin-induced NF-kappaB activation was attenuated significantly. This inhibition may play a role in sensitizing cancer cells to chemotherapeutic drugs. This study has demonstrated that activation of NF-kappaB is a general cellular response to anticancer drugs, and the mechanism of activation appears to be distinct from that induced by TNF-alpha. These observations may have implications for improving the efficacy of systemic chemotherapy for cancer patients.

Tamoxifen elicits its anti-estrogen effects in growth plate chondrocytes by inhibiting protein kinase C

17 beta-Estradiol (E(2)) regulates growth plate cartilage cells via classical nuclear receptor mechanisms, as well as by direct effects on the chondrocyte membrane. These direct effects are stereospecific, causing a rapid increase in protein kinase C (PKC) specific activity, are only found in cells from female rats and are mimicked by E(2)-bovine serum albumin (BSA), which cannot penetrate the cell membrane. E(2) and E(2)-BSA stimulate alkaline phosphatase specific activity and proteoglycan sulfation in female rat costochondral cartilage cell cultures, but traditional nuclear receptors do not appear to be involved. This study examined the effect of the anti-estrogen tamoxifen on these markers of chondrocyte differentiation; the gender-specificity of tamoxifen's effect on PKC, if tamoxifen has an effect on vitamin D metabolite-stimulated PKC, which is mediated via specific membrane receptors (1,25-mVDR; 24,25-mVDR) and whether the effect of tamoxifen is mediated by nuclear estrogen receptors. Tamoxifen dose-dependently inhibited the effect of E(2)-BSA on PKC, alkaline phosphatase and proteoglycan sulfation in confluent cultures of female resting zone (RC) cells and growth zone (GC) (prehypertrophic/upper hypertrophic zones) cells, suggesting that its action is at the membrane and not cell maturation-dependent. Neither the estrogen receptor (ER) antagonist ICI 182780 nor the ER agonist diethylstilbesterol affected E(2) or E(2)-BSA-stimulated PKC in female chondrocytes. Tamoxifen also inhibited the increase in PKC activity due to 1 alpha,25-(OH)(2)D(3) or 24R,25-(OH)(2)D(3) in growth plate cells derived from either female or male rats. Inhibition of PKC by tamoxifen may be a general property of membrane receptors involved in rapid responses to hormones.

Tamoxifen increases photodynamic therapeutic response of U87 and U25ln human glioma cells

We tested the hypothesis that Tamoxifen (TMX), an inhibitor of protein kinase C (PKC), augments the cytotoxicity of photodynamic therapy (PDT) treatment of human (U87) and (U25ln) glioma cells. U87 and U25ln glioma cells were plated and treated with PDT using Photofrin as the sensitizer. Cells were treated with Photofrin at various doses and with various optical (632 nm) irradiation intensities 24 h later. Cells were also treated with Photofrin at a fixed dose alone and with various doses of Tamoxifen and subjected to laser treatment 24 h later. Tumor response was tested using the (3-94,5-dimethyl-2-yl)-2,5-diphenyl-tetrazolium (MTT) method. Total toxicity of U87 cells was achieved with PDT at all doses of Photofrin (1, 2.5, 5, 10 microg/ml) with irradiation densities equal to or greater than 200 mJ/cm2. Using an irradiation intensity of 100 mJ/cm2, U87 and U25ln cells were killed in a Photofrin dose-dependent manner. Significant cytotoxicity was detected with Photofrin doses of 5 microg/ml (p < 0.05) and 10 microg/ml (p < 0.001). Tamoxifen at a dose of 500 microg/ml and higher, significantly increased the toxicity of the PDT response with 5 microg/ml Photofrin and 100 mJ/cm2 (p < 0.05). In summary, our data demonstrate that Tamoxifen significantly enhances the Photofrin PDT activity of U87 and U25ln human glioma cells.

Malnutrition-induced macrophage apoptosis

BACKGROUND

Human and murine studies suggest protein-calorie malnutrition (PCM) results in significant host immunosuppression resulting in increased morbidity and mortality. Apoptosis has been implicated as an important mediator in the immunosuppression observed in several disease states. This study was designed to characterize macrophage apoptosis in a murine model of PCM and investigate components that regulate the apoptotic process, such as protein kinase C (PKC) and Bcl-2 activity.

METHODS

Swiss-Webster mice (n = 50) were randomly assigned to receive either a control (24% protein) or a PCM diet (0% protein) for 7 days. Peritoneal macrophages were harvested and detection of apoptosis was performed by terminal deoxy-transferase-mediated deoxyuridine triphosphate (dUTP) nick-end labeling (TUNEL) and propidium iodide DNA staining under baseline and pro-apoptotic conditions. Pro-apoptotic conditions included cells treated with tumor necrosis factor-alpha (TNF-alpha) (10 ng/mL), interferon-gamma (IFN-gamma) (10 ng/mL), and a combination of both agents. In addition, levels of PKC activity and expression of Bcl-2 and p53 protein were measured.

RESULTS

Peritoneal macrophages from PCM mice had a significantly greater amount of apoptosis at baseline and under stimulated conditions compared with controls. Levels of PCM apoptosis were elevated at baseline by TUNEL staining compared with macrophages from the control group (16.5% +/- 1.4%, versus 4.5% +/- 1.1%, P <.01). In addition, peritoneal macrophages from the malnourished animals were significantly more susceptible to the apoptotic effect of TNF-alpha and the effects of INF-gamma (27.3% +/- 2.1% and 31% +/- 1.4%) compared with control mice (5.5% +/- 0.7% and 7.2% +/- 0.5%, P <.01), respectively. Again, an increase in the baseline apoptosis rate was demonstrated in peritoneal macrophages from PCM mice compared with control fed mice (13.2% +/- 4.4% versus 4.3% +/- 3.1%, P <.01) as measured by propidium iodide staining. The combination of agents, TNF-alpha and INF-gamma, resulted in an additive apoptotic effect in the malnourished host compared with the control animals (43.4% +/- 4.7% versus 10.5% +/- 2.2%, P <.01), respectively. Furthermore, there was a significant decrease in the mean total PKC activity in the malnourished macrophages compared with results in controls (110,000 +/- 8000 versus 60,000 +/- 4000 cpm, P <.01). Similar changes were also observed in PKC cytosolic and membrane activity between both groups. In addition, Bcl-2 protein expression was significantly decreased in PCM animals compared with control animals.

CONCLUSIONS

Thus, peritoneal macrophages from PCM mice exhibit significantly greater levels of apoptosis at baseline and when stimulated with pro-apoptotic agents compared with controls. The propensity of macrophages from PCM mice to undergo apoptosis may be attributable in part to decreased PKC activity and Bcl-2 protein expression. These findings may help to explain the associated immune dysfunction observed in malnutrition.

Modulation of protein kinase C in antitumor treatment

PKC isoenzymes were found to be involved in proliferation, antitumor drug resistance and apoptosis. Therefore, it has been tried to exploit PKC as a target for antitumor treatment. PKC alpha activity was found to be elevated, for example, in breast cancers and malignant gliomas, whereas it seems to be underexpressed in many colon cancers. So it can be expected that inhibition of PKC activity will not show similar antitumor activity in all tumors. In some tumors it seems to be essential to inhibit PKC to reduce growth. However, for inhibition of tumor proliferation it may be an advantage to induce apoptosis. In this case an activation of PKC delta should be achieved. The situation is complicated by the facts that bryostatin leads to the activation of PKC and later to a downmodulation and that the PKC inhibitors available to date are not specific for one PKC isoenzyme. For these reasons, PKC modulation led to many contradicting results. Despite these problems, PKC modulators such as miltefosine, bryostatin, safingol, CGP41251 and UCN-01 are used in the clinic or are in clinical evaluation. The question is whether PKC is the major or the only target of these compounds, because they also interfere with other targets. PKC may also be involved in apoptosis. Oncogenes and growth factors can induce cell proliferation and cell survival, however, they can also induce apoptosis, depending on the cell type or conditions in which the cells or grown. PKC participates in these signalling pathways and cross-talks. Induction of apoptosis is also dependent on many additional factors, such as p53, bcl-2, mdm2, etc. Therefore, there are also many contradicting results on PKC modulation of apoptosis. Similar controversial data have been reported about MDR1-mediated multidrug resistance. At present it seems that PKC inhibition alone without direct interaction with PGP will not lead to successful reversal of PGP-mediated drug efflux. One possibility to improve chemotherapy would be to combine established antitumor drugs with modulators of PKC. However, here also very contrasting results were obtained. Many indicate that inhibition, others, that activation of PKC enhances the antiproliferative activity of anticancer drugs. The problem is that the exact functions of the different PKC isoenzymes are not clear at present. So further investigations into the role of PKC isoenzymes in the complex and interacting signalling pathways are essential. It is a major challenge in the future to reveal whether modulation of PKC can be used for the improvement of cancer therapy.

Epidermal growth factor receptor-dependent control of keratinocyte survival and Bcl-xL expression through a MEK-dependent pathway

Previous work has shown that the epidermal growth factor receptor (EGFR) tyrosine kinase moiety provides protection to normal human keratinocytes against apoptosis. This protection is, at least in part, due to EGFR-dependent expression of the antiapoptotic Bcl-2 family member, Bcl-x(L). Here we focused on intracellular signaling pathways relevant to keratinocyte survival and/or Bcl-x(L) expression. By using pharmacological inhibitors and dominant negative expression constructs, we observed that phosphatidylinositol 3-kinase/AKT and phospholipase C gamma/protein kinase C alpha activation were required for keratinocyte survival independently of EGFR activation or Bcl-x(L) expression. By contrast, MEK activity required EGFR activation and, as shown by use of the MEK inhibitor PD98059 and a dominant negative MEK construct, was necessary for Bcl-x(L) expression and survival. Consistent with an earlier study, blocking SRC kinase activities similarly led to down-regulation of Bcl-x(L) protein expression and impaired keratinocyte survival. In conclusion, our results demonstrate that EGFR-dependent MEK activity contributes to both Bcl-x(L) expression and survival of normal keratinocytes. Other signaling pathways (i.e. phosphatidylinositol 3-kinase/AKT and phospholipase C gamma/protein kinase C alpha) are obligatory to keratinocyte survival but not to Bcl-x(L) expression, and control of these pathways by EGFR activation is not rate-limiting to normal keratinocyte survival.

Oxydation radiolytique du tamoxifène par les radicaux libres ·OH et (ou) HO·2

Tamoxifen is the most widely used antiestrogen in the treatment of breast cancer. In this work, we have studied its antioxidant properties. We have investigated the ability of tamoxifen to scavenge, in vitro, ·OH and (or) HO·2 free radicals that are produced by water radiolysis. Aqueous solutions of tamoxifen of concentrations ranging between 10-5 and 2.5 × 10-5 M have been irradiated (γ 137Cs) in aerated acidic medium (H3PO4 10-3 M or HCOOH 10-1 M). The results show that tamoxifen reacts quantitatively with ·OH free radicals but does not react with HO·2 free radicals under our experimental conditions.Key words: tamoxifen, antioxidant, oxygenated free radicals, radiolysis.

Tamoxifen inhibits phorbol ester stimulated osteoclastic bone resorption: An effect mediated by calmodulin

Tamoxifen inhibits bone resorption by disrupting calmodulin-dependent processes. Since tamoxifen inhibits protein kinase C in other cells, we compared the effects of tamoxifen and the phorbol ester, phorbol myristate acetate, on osteoclast activity. Phorbol esters stimulate bone resorption and calmodulin levels four-fold (k0.5 = 0.1–0.3 µM). In contrast, tamoxifen inhibited osteoclast activity ~60% with an IC50 of 1.5 µM, had no apparent effect on protein kinase C activity in whole-cell lysates, and reduced protein kinase Cα recovered by immunoprecipitation 75%. Phorbol esters stimulated resorption in a time-dependent manner that was closely correlated with a similar-fold increase in calmodulin. Protein kinase Cα, β, δ, ε, and ζ were all down-regulated in response to phorbol ester treatment. Tamoxifen and trifluoperazine inhibited PMA-dependent increases in bone resorption and calmodulin by 85 ± 10%. Down-regulation of protein kinase C isoforms by phorbol esters suggests that the observed increases in bone resorption and calmodulin levels are most likely due to a mechanism independent of protein kinase C and dependent on calmodulin. In conclusion, the data suggest that protein kinase C negatively regulates calmodulin expression and support the hypothesis that the effects of both phorbol esters and tamoxifen on osteoclast activity is mediated by calmodulin.Key words: osteoclast, calmodulin, tamoxifen, osteoporosis, protein kinase C.

Rapid activation of basolateral potassium transport in human colon by oestradiol

1. We investigated the effect of oestradiol on basolateral potassium channels in human colonic epithelium. 2. Ion transport was quantified using short circuit current (I:(sc)) measurements of samples mounted in Ussing chambers. Serosal K transport was studied using nystatin permeabilization of the apical membrane. Intracellular pH changes were quantified using spectroflouresence techniques. 3. Experiments were performed with either 10 nM or 1 microM Ca(2+) in the apical bathing solution. With 10 nM Ca(2+) in the apical bathing solution addition of oestradiol (1 nM) to the basolateral bath produced a rapid increase in current (delta I(K)=11.2+/-1.2 microA.cm(-2), n=6). This response was prevented by treatment of the serosal membrane with tolbutamide (1 microM). With 1 microM Ca(2+) in the apical bathing solution addition of oestradiol produced a rapid fall in current (delta I(K)=-12.8+/-1.4 microA.cm(-2)), this response was prevented by treatment of the basolateral membrane with tetra-pentyl-ammonium (TPeA). These responses were rapid and occurred independently of protein synthesis. 4. Inhibition of basolateral Na(+)/H(+) exchange with either amiloride or a low sodium bathing solution prevented this response. These responses were prevented by inhibition of protein kinase C (PKC) with bis-indolyl-maleimide. 5. Oestradiol (1 nM) produced a rapid intracellular alkanization (mean increase=0.11 pH units; n=6; P<0.01). 6. These results suggest that oestradiol rapidly modulates serosal K transport in human colon. These effects depend upon intact Na(+)/H(+) exchange and protein kinase C. We propose a non-classical, possibly membrane linked, mechanism for oestradiol action in human colonic epithelium.

Role of NAD(P)H oxidase in the tamoxifen-induced generation of reactive oxygen species and apoptosis in HepG2 human hepatoblastoma cells

Previously, tamoxifen (TAM) has been shown to induce apoptosis through elevation of intracellular Ca2+ in HepG2 human hepatoblastoma cells. In this study we investigated the role of reactive oxygen species (ROS) in the TAM-induced apoptosis, and interrelationship between intracellular Ca2+ and ROS. TAM induced a slow and sustained increase in intracellular ROS level. An antioxidant, N-acetylcysteine significantly inhibited both ROS production and apoptosis induced by TAM, suggesting that ROS may play an essential role in the TAM-induced apoptosis. In a time frame ROS generation followed intracellular Ca2+ increase, and the extracellular and intracellular Ca2+ chelation with EGTA and BAPTA/AM, respectively, completely inhibited the TAM-induced ROS production, indicating that intracellular Ca2+ may mediate the ROS generation. Inhibitors of NAD(P)H oxidase, diphenylene iodonium, phenylarsine oxide and neopterine, significantly blocked the TAM-induced ROS generation and apoptosis, implying that this oxidase may act as a source enzyme for the production of ROS. These results suggest that non-phagocytic NAD(P)H oxidase may play a novel role as a mediator of the apoptosis associated with intracellular Ca2+ in HepG2 cells.

Modulation of CPP32 activity and induction of apoptosis in Human CEM X 174 lymphocytes by heptachlor, a chlorinated hydrocarbon insecticide

Heptachlor is an organochlorine insecticide used worldwide for the control of pests both agriculturally and domestically. Its lipophilic structure allows it to bioaccumulate and pass through the food chain, exposing those who come in contact with it to its tumor promoting and possible carcinogenic effects. As a mechanism of tumor promotion, we explored the possibility of heptachlor suppressing the apoptotic process in human CEM x 174 lymphocytes. In this article, we describe the effect of heptachlor on the activity of the apoptosis protease CPP32. We show that heptachlor by itself was able to stimulate CPP32 activity at relatively high concentrations. When combined with the chemotherapeutic agent doxorubicin, a known CPP32 activator, a dual effect was observed. Low concentrations of heptachlor (5 microM-10 microM) suppressed doxorubicin-induced CPP32 activity, and high concentrations of heptachlor (80 microM-120 microM) augmented it. We also showed that heptachlor alone at relatively high concentrations induced apoptosis-associated changes in CEM x 174 cells including high molecular weight (HMW) DNA cleavage and chromatin condensation. From these results, it appears that heptachlor has tumor promoting-like effects at lower concentrations, and at higher concentrations induces apoptosis as a mechanism of cytotoxicity.

Use of tamoxifen in hepatocellular carcinoma: a review and paradigm shift

Hepatocellular carcinoma is often diagnosed at a late, inoperable stage for which there are no uniformly efficacious treatment available presently. The oral anti-oestrogen drug, tamoxifen, has been used in such patients, based on the belief that the growth of hepatocellular carcinoma is promoted by endogenous oestrogen via a receptor-mediated process. In this review, we examine the trials reported in the literature using tamoxifen in hepatocellular carcinoma. Randomized controlled trials with tamoxifen have so far revealed mixed results. We propose that this may be due to the fact that the mechanism of action of tamoxifen in hepatocellular carcinoma is via an oestrogen-receptor independent pathway that requires much higher doses of tamoxifen for activation than those used in the trials so far. Thus there must be a paradigm shift to dissociate the action of tamoxifen from oestrogen receptors in hepatocellular carcinoma. This means that future trials with tamoxifen in hepatocellular carcinoma should use higher doses of tamoxifen, at least four to eight-fold that of the dose that is efficacious in an oestrogen-receptor dependent mechanism.

Effects of tamoxifen on oxyhemoglobin-induced cerebral vasoconstriction

The effect of tamoxifen on oxyhemoglobin-mediated cerebral vasoconstriction was examined. Tamoxifen caused a concentration-dependent relaxation of cerebral artery preparations contracted with oxyhemoglobin and phorbol myristate acetate with the IC(50) values 0.66+/-0.1 and 1.1+/-0.1 microM, respectively. In cerebrovascular smooth muscle cells, oxyhemoglobin and phorbol myristate acetate induced protein kinase C activation, which was 220+/-7% and 203+/-8% of control, respectively. The increase in protein kinase C activity was prevented by tamoxifen. The results suggest that the ability of tamoxifen to reverse vasoconstriction is mediated, at least in part, via inhibition of protein kinase C.

Involvement of Ca2+ influx in the mechanism of tamoxifen-induced apoptosis in HepG2 human hepatoblastoma cells

The signaling mechanism of tamoxifen (TAM)-induced apoptosis was investigated in HepG2 human hepatoblastoma cells which do not express the estrogen receptor (ER). TAM induced cytotoxicity and DNA fragmentation, a hallmark of apoptosis, in a dose-dependent manner. TAM increased the intracellular concentration of Ca2+. This effect was completely inhibited by the extracellular Ca2+ chelation with EGTA. TAM also induced a Mn2+ influx, indicating that TAM activated Ca2+ influx pathways. This action of TAM was significantly inhibited by flufenamic acid (FA), a known non-selective cation channel blocker. Quantitative analysis of apoptosis by flow cytometry revealed that treatment with either FA or BAPTA, an intracellular Ca2+ chelator, significantly inhibited TAM-induced apoptosis. These results suggest that intracellular Ca2+ signals may play a central role in the mechanism of the TAM-induced apoptotic cell death in ER-negative HepG2 cells.

Ziskind-Somerfeld Research Award. Protein kinase C signaling in the brain: molecular transduction of mood stabilization in the treatment of manic-depressive illness

Understanding the biology of the pharmacological stabilization of mood will undoubtedly serve to provide significant insight into the pathophysiology of manic-depressive illness (MDI). Accumulating evidence from our laboratories and those of other researchers has identified the family of protein kinase C isozymes as a shared target in the brain for the long-term action of both lithium and valproate. In rats chronically treated with lithium, there is a reduction in the hippocampus of the expression of two protein kinase isozymes, alpha and epsilon, as well as a reduction in the expression of a major PKC substrate, MARCKS, which has been implicated in long-term neuroplastic events in the developing and adult brain. In addition, we have been investigating the down-stream impact of these mood stabilizers on another kinase system, GSK-3 beta and on the AP-1 family of transcription factors. Further studies have generated promising preliminary data in support of the antimanic action of tamoxifen, and antiestrogen that is also a PKC inhibitor. Future studies must address the therapeutic relevance of these protein targets in the brain using innovative strategies in both animal and clinical investigations to ultimately create opportunities for the discovery of the next generations of mood stabilizers for the treatment of MDI.

Regulation of transforming growth factor-beta1 gene expression and cell proliferation in human hepatocellular carcinoma cells (PLC/PRF/5) by tamoxifen

Hepatocellular carcinoma (HCC) is a common, potentially lethal tumor in human patients. Because the serum levels of transforming growth factor-beta1 (TGF-beta1) correlate with outcome in patients with HCC and because TGFbeta1 mRNA expression is increased in HCC tissues, it raises the possibility that TGF-beta1 may be of importance in the development, growth, and metastases of HCC. Tamoxifen has been used for the treatment of human HCC. However, clinical trials have produced conflicting results. To further delineate whether tamoxifen may be of benefit in altering the course of HCC, we documented the effects of 4-hydroxytamoxifen and 17beta-estradiol on TGF-beta1 mRNA and protein levels and cell proliferation in a human HCC cell line. PLC/PRF/5 cells were treated with carrier (controls), 4-hydroxytamoxifen, 17beta-estradiol, or TGF-beta1. 4-Hydroxytamoxifen and 17beta-estradiol decreased TGF-beta1 mRNA and protein levels in a time- and dose-dependent manner. TGF-beta1 significantly inhibited PLC/PRF/5 cell proliferation, whereas both 4-hydroxytamoxifen and 17beta-estradiol stimulated PLC/PRF/5 cell proliferation. The stimulatory effects of 4-hydroxytamoxifen on PLC/PRF/5 cell proliferation raise concerns regarding its use in the treatment of HCC in human patients and suggest that 4-hydroxytamoxifen may have no beneficial effects in some patients with HCC.