Geranylgeraniol causes a decrease in levels of calreticulin and tyrosine phosphorylation of a 36-kDa protein prior to the appearance of apoptotic features in HL-60 cells

Changes in the in vitro activity of platinum drugs when administered in two aliquots

BACKGROUND

The management of ovarian cancer remains a challenge. Because of the lack of early symptoms, it is often diagnosed at a late stage when it is likely to have metastasized beyond ovaries. Currently, platinum based chemotherapy is the primary treatment for the disease. However acquired drug resistance remains an on-going problem. As cisplatin brings about apoptosis by intrinsic and extrinsic pathways, this study aimed to determine changes in activity of platinum drugs when administered in two aliquots as against a bolus and sought to determine association with changes in GSH, speciation of platinum drugs and changes in protein expression.

METHODS

The efficacy of administering cisplatin, carboplatin and oxaliplatin in two aliquots with a time gap was investigated in ovarian A2780, A2780(cisR), A2780(ZD0473R) and SKOV-3 cell lines. The cellular accumulation of platinum, level of platinum - DNA binding and cellular glutathione level were determined, and proteomic studies were carried out to identify key proteins associated with platinum resistance in ovarian A2780(cisR) cancer cell line.

RESULTS

Much greater cell kill was observed with solutions left standing at room temperature than with freshly prepared solutions, indicating that the increase in activity on ageing was related to speciation of the drug in solution. Proteomic studies identified 72 proteins that were differentially expressed in A2780 and A2780(cisR) cell lines; 22 of them were restored back to normal levels as a result of synergistic treatments, indicating their relevance in enhanced drug action.

CONCLUSIONS

The proteins identified are relevant to several different cellular functions including invasion and metastasis, cell cycle regulation and proliferation, metabolic and biosynthesis processes, stress-related proteins and molecular chaperones, mRNA processing, cellular organization/cytoskeleton, cellular communication and signal transduction. This highlights the multifactorial nature of platinum resistance in which many different proteins with diverse functions play key roles. This means multiple strategies can be harnessed to overcome platinum resistance in ovarian cancer. The results of the studies can be significant both from fundamental and clinical view points.

Acyclic retinoid inhibits angiogenesis by suppressing the MAPK pathway

Acyclic retinoid (ACR) is currently under clinical trial as an agent to suppress the recurrence of hepatocellular carcinoma (HCC) through its ability to induce apoptosis in premature HCC cells. ACR has an anticancer effect in vivo as well, although it shows weak apoptosis-inducing activity against mature HCC cells, suggesting the existence of an additional action mechanism. In this study, we investigated the antiangiogenic activity of ACR. ACR inhibited angiogenesis within chicken chorioallantoic membrane (CAM) in as similar a manner as all-trans retinoic acid (atRA). Although suppression of angiogenesis by atRA was partially rescued by the simultaneous addition of angiopoietin-1, suppression of angiogenesis by ACR was not rescued under the same condition at all. Conversely, although suppression of angiogenesis by ACR was partially inverted by the simultaneous addition of vascular endothelial growth factor (VEGF), suppression of angiogenesis by atRA was not affected under the same condition. These results suggested that mechanisms underlying the suppression of angiogenesis by ACR and atRA were different. ACR selectively inhibited the phosphorylation of VEGF receptor 2 (VEGFR2) and of extracellular signal-regulated kinase (ERK) without changing their protein expression levels, and inhibited endothelial cell growth, migration, and tube formation. The inhibition of the phosphorylation of ERK, endothelial growth, migration, tube formation, and angiogenesis by ACR was rescued by the overexpression of constitutively active mitogen-activated protein kinase (MAPK). Finally, ACR, but not atRA, inhibited HCC-induced angiogenesis in a xenografted CAM model. These results delineate the novel activity of ACR as an antiangiogenic through a strong inhibition of the VEGFR2 MAPK pathway.

Plaunotol and geranylgeraniol induce caspase-mediated apoptosis in colon cancer

BACKGROUND

Plaunotol, a kind of isoprenoid extracted from a Thai medical plant, plau-noi, is structurally similar to geranylgeraniol (GGOH), another isoprenoid reported to exert strong anticancer effects. Recently, we have reported on its inhibitory effects on tumor angiogenesis and direct effects on gastric cancer cells. Here, we aimed to test whether plaunotol could have some therapeutic effect on colon cancer.

MATERIALS AND METHODS

Human colon cancer cell line DLD1 was used. Tumor cells were cultured in the presence of plaunotol or GGOH, and their proliferation was measured by MTS assay. Apoptosis was evaluated by Annexin V and propidium iodide double-staining or terminal-deoxynucleotidyl assay. The activation of caspase-3, -8, and -9 was analyzed by flow cytometry and Western blot analysis for PRRP cleavage.

RESULTS

Plaunotol and GGOH strongly inhibited the proliferative activity of DLD1, dependent on induction of apoptosis. The induction of apoptosis by either plaunotol or GGOH was dependent on the activation of both caspase-8 and caspase-9 pathways.

CONCLUSIONS

Plaunotol would be a potential anticancer agent against colon cancer, and since it is already available in Japan and Thailand for clinical use as an anti-ulcer/antigastritis agent, clinical trials will be designed to confirm the present findings.

[Basic studies for the development of anticancer, antidementia, and taste modifier drugs]

We developed various types of differentiation- and apoptosis-inducing agents against tumor cells and also studied the function and structure of synucleins and taste modifiers. Differentiation- and apoptosis-inducing agents are classified into DNA-damaging agents, Na(+), K(+)-ATPase inhibitors, agents affecting the redox states of tumor cells, agents affecting signal transduction pathways, isoprenoid compounds, and ATP-noncompetitive tyrosine kinase inhibitors. These include camptothecin, etoposide, cisplatin, transplantin, bufalin, arsenic trioxide, costunolide, C(2)- ceramide, daidzein, geranylgeranylacetone, geranylgeraniol, vitamin K(2), sophoranone, and beta-hydroxyisovalerylshikonin. The mechanisms of action of these differentiation- and apoptosis-inducing agents are described. The structure and function of synucleins are also reviewed for the development of potential antidementia agents. In addition, the structures of three purified taste modifiers are described.

Isoprenoids: Remarkable diversity of form and function

The isoprenoid biosynthetic pathway is the source of a wide array of products. The pathway has been highly conserved throughout evolution, and isoprenoids are some of the most ancient biomolecules ever identified, playing key roles in many life forms. In this review we focus on C-10 mono-, C-15 sesqui-, and C-20 diterpenes. Evidence for interconversion between the pathway intermediates farnesyl pyrophosphate and geranylgeranyl pyrophosphate and their respective metabolites is examined. The diverse functions of these molecules are discussed in detail, including their ability to regulate expression of the beta-HMG-CoA reductase and Ras-related proteins. Additional topics include the mechanisms underlying the apoptotic effects of select isoprenoids, antiulcer activities, and the disposition and degradation of isoprenoids in the environment. Finally, the significance of pharmacological manipulation of the isoprenoid pathway and clinical correlations are discussed.

Beta-hydroxyisovalerylshikonin is a novel and potent inhibitor of protein tyrosine kinases

Beta-hydroxyisovalerylshikonin (beta-HIVS), a compound isolated from Lithospermium radix, most efficiently induced cell-death in two lines of lung cancer cells, namely, NCI-H522 and DMS114, whereas shikonin was effective against a wide variety of tumor cell lines. During our studies of the mechanism of action of beta-HIVS on tumor cells, we found that this compound inhibited protein tyrosine kinase (PTK) activity. The tyrosine kinase activities of a receptor for EGF (EGFR) and v-Src were strongly inhibited and that of KDR/Flk-1 was weakly inhibited by beta-HIVS. The inhibition by beta-HIVS of the activities of EGFR and v-Src was much stronger than that by shikonin. The IC50 values of beta-HIVS for EGFR and v-Src were approximately 0.7 microM and 1 microM, respectively. Moreover, the inhibition of v-Src by beta-HIVS was non-competitive with respect to ATP. These results strongly suggest that the action of beta-HIVS, as well as that of shikonin, involves the inhibition of PTK, and they also suggest the possibility of producing a novel group of PTK inhibitors based on shikonin as the parent compound.

Geranylgeraniol, an intermediate product in mevalonate pathway, induces apoptotic cell death in human hepatoma cells: death receptor-independent activation of caspase-8 with down-regulation of Bcl-xL expression

Geranylgeraniol (GGOH), an intermediate of mevalonate metabolism, is known to induce apoptosis in various lines of cancer cells. The present study was undertaken to clarify the signaling pathways of apoptosis induced by GGOH in human hepatoma cells. HuH-7 human hepatoma cells were incubated in the absence or presence of GGOH. Activation of caspase-8 /-9 /-3 in HuH-7 cells was found after 8 h treatment with GGOH, at which time DNA fragmentation and loss of mitochondrial transmembrane potential (Deltaphim) occurred. HuH-7 cells do not express Bcl-2; however, down-regulation of Bcl-xL expression preceded activation of the caspase cascade in GGOH-treated HuH-7 cells, while Bax expression was not changed by GGOH treatment. Addition of caspase inhibitors restored the decreased cell viability of HuH-7 cells by GGOH, including Deltaphim, to the baseline level, which indicated that caspase triggers mitochondria-dependent apoptotic pathways in GGOH-treated HuH-7 cells. Similarly, GGOH-mediated apoptosis of HuH-7 cells was clearly prevented by coadministration of ursodeoxycholic acid (UDCA), which led to restoration of the level of Bcl-xL expression. Activation of caspase-8 /-9 /-3, as well as Deltaphim, by GGOH treatment was suppressed by addition of UDCA. Our results indicate that activation of the caspase cascade initiating from caspase-8, which could be accelerated by down-regulation of Bcl-xL expression, plays a key role in an apoptotic process induced by GGOH in human hepatoma cells.

Competitive inhibition of choline phosphotransferase by geranylgeraniol and farnesol inhibits phosphatidylcholine synthesis and induces apoptosis in human lung adenocarcinoma A549 cells

We have previously shown that, among various isoprenoids, farnesol and geranylgeraniol specifically induced actin fiber disorganization, growth inhibition, and apoptosis in human lung adenocarcinoma A549 cells (Miquel, K., Pradines, A., and Favre, G. (1996) Biochem. Biophys. Res. Commun. 225, 869-876). Here we demonstrate that isoprenoid-induced apoptosis was preceded by an arrest in G0/G1 phase. The isoprenoid effects were independent of protein prenylation and of mitogen-activated protein kinase activity. Moreover, geranylgeraniol and farnesol induced a rapid inhibition of phosphatidylcholine biosynthesis at the last step of the CDP-choline pathway controlled by choline phosphotransferase and not at the level of CTP:phosphocholine cytidylyltransferase, the key enzyme of the pathway. Inhibition of choline phosphotransferase was confirmed by in vitro assays on microsomal fractions, which clearly showed that the isoprenoids acted by competitive inhibition with the diacylglycerol binding. Exogenous phosphatidylcholine addition prevented all the biological effects of the isoprenoids, including actin fiber disorganization and apoptosis, suggesting that inhibition of phosphatidylcholine biosynthesis might be the primary event of the isoprenoid action. These data demonstrate the molecular mechanism of geranylgeraniol and farnesol effects and suggest that the mevalonate pathway, leading notably to prenylated proteins, might be linked to the control of cell proliferation through the regulation of phosphatidylcholine biosynthesis.

Calreticulin: an intracellular Ca++-binding protein abundantly expressed and regulated by androgen in prostatic epithelial cells

Calreticulin was identified in a screen for androgen-response genes in the rat ventral prostate. Northern blot and Western blot analyses in the rat model showed that both calreticulin messenger RNA and protein are down-regulated by castration and up-regulated by androgen replacement in the prostate. Northern blot analysis showed that calreticulin expression level in the prostate is much higher than that in seminal vesicles, heart, brain, muscle, kidney, and liver. The regulation of calreticulin expression by androgen is only observed in the prostate and seminal vesicles, two male secondary sex organs. The induction of calreticulin by androgen in prostate organ culture partially resists protein synthesis inhibition, suggesting that calreticulin is a direct androgen-response gene. In situ hybridization and immunohistochemistry studies showed that calreticulin is an intracellular protein in prostatic epithelial cells. Because calreticulin is a major intracellular Ca++-binding protein with 1 high-affinity and 25 low-affinity Ca binding sites, our observations suggest that calreticulin is a promising candidate that mediates androgen regulation of intracellular Ca++ levels and/or signals in prostatic epithelial cells. The expression of calreticulin is also regulated by androgen in the mouse and human prostate, suggesting that androgen regulation and function of calreticulin in the prostate are conserved evolutionarily.

Clinical relevance of calreticulin in systemic lupus erythematosus

Calreticulin is an abundant intracellular protein which is proposed to have numerous biological functions. However, there is increasing evidence to suggest that calreticulin plays a multifunctional role as an autoantigen present in patients with systemic lupus erythematosus. In this review we detail some of the recent evidence which indicate that calreticulin may play a supportive role in the formation of the autoantigen complex-Ro/SS-A. In addition, several proposed mechanisms of release and surface expression of calreticulin are described in relation to SLE mediated responses to the autoantigen. In particular, the generation of autoantibodies to specific regions of the protein and the ability of calreticulin to interfere with complement mediated inflammatory processes.