The extracellular signal-regulated kinase mitogen-activated protein kinase/ribosomal S6 protein kinase 1 cascade phosphorylates cAMP response element-binding protein to induce MUC5B gene expression via D-prostanoid receptor signaling.

Mucus hypersecretion is a prominent feature of respiratory diseases, and MUC5B is a major airway mucin. Mucin gene expression can be affected by inflammatory mediators, including prostaglandin (PG) D(2,) an inflammatory mediator synthesized by hematopoietic PGD synthase (H-PGDS). PGD(2) binds to either D-prostanoid receptor (DP1) or chemoattractant receptor homologous molecule expressed on T-helper type 2 cells (CRTH2). We investigated the mechanisms by which PGD(2) induces MUC5B gene expression in airway epithelial cells. Western blot analysis showed that H-PGDS was highly expressed in nasal polyps. Similar results were obtained for PGD(2) expression. In addition, we could clearly detect the expressions of both H-PGDS and DP1 in nasal epithelial cells but not CRTH2. We demonstrated that PGD(2) increased MUC5B gene expression in normal human nasal epithelial cells as well as in NCI-H292 cells in vitro. S5751, a DP1 antagonist, inhibited PGD(2)-induced MUC5B expression, whereas a CRTH2 antagonist (OC0459) did not. These data suggest that PGD(2) induced MUC5B expression via DP1. Pretreatment with extracellular signal-regulated kinase (ERK) inhibitor (PD98059) blocked both PGD(2)-induced ERK mitogen-activated protein kinase (MAPK) activation and MUC5B expression. Proximity ligation assays showed direct interaction between RSK1 and cAMP response element-binding protein (CREB). Stimulation with PGD(2) caused an increase in intracellular cAMP levels, whereas intracellular Ca(2+) did not have such an effect. PGD(2)-induced MUC5B mRNA levels were regulated by CREB via direct interaction with two cAMP-response element sites (-921/-914 and -900/-893). Finally, we demonstrated that PGD(2) can induce MUC5B overproduction via ERK MAPK/RSK1/CREB signaling and that DP1 receptor may have suppressive effects in controlling MUC5B overproduction in the airway.

Cyclopropane-based stereochemical diversity-oriented conformational restriction strategy: histamine H3 and/or H4 receptor ligands with the 2,3-methanobutane backbone.

The stereochemical diversity-oriented conformational restriction strategy can be an efficient method for developing specific ligands for drug target proteins. To develop potent histamine H(3) and/or H(4) receptor ligands, a series of conformationally restricted analogs of histamine with a chiral trans- or cis-4-amino-2,3-methano-1-(1H-imidazol-4-yl)butane structure was designed based on this strategy. These stereochemically diverse compounds were synthesized from previously developed versatile chiral cyclopropane units. Among these analogs, a trans-cyclopropane-type compound, (2S,3R)-4-(4-chlorobenzylamino)-2,3-methano-1-(1H-imidazol-4-yl)butane (5b), has remarkable antagonistic activity to both the H(3) (K(i) = 4.4 nM) and H(4) (K(i) = 5.5 nM) receptors, and a cis-cyclopropane-type compound, (2R,3R)-4-amino-2,3-methano-1-(1H-imidazol-4-yl)butane (6a), is a potent and selective H(3) receptor partial agonist (K(i) = 5.4 nM). Although (2S,3R)-4-amino-2,3-methano-1-(1H-imidazol-4-yl)butane (5a) does not have a hydrophobic group which the usual H(3) receptor antagonists have, it was found to be a potent H(3) receptor antagonist (K(i) = 20.1 nM). Thus, a variety of compounds with different pharmacological properties depending on the cyclopropane backbones and also on the side-chain functional groups were identified. In addition to the previously used 1,2-methanobutane backbone, the 2,3-methanobutane backbone also worked effectively as a cyclopropane-based conformational restriction structure. Therefore, the combination of these two cyclopropane backbones increases the stereochemical and three-dimensional diversity of compounds in this strategy, which can provide a variety of useful compounds with different pharmacological properties.

A nucleoside anticancer drug, 1-(3-C-ethynyl-ß-D-ribo-pentofuranosyl)cytosine (TAS106), sensitizes cells to radiation by suppressing BRCA2 expression.

BACKGROUND: A novel anticancer drug 1-(3-C-ethynyl-ß-D-ribo-pentofuranosyl)cytosine (ECyd, TAS106) has been shown to radiosensitize tumor cells and to improve the therapeutic efficiency of X-irradiation. However, the effect of TAS106 on cellular DNA repair capacity has not been elucidated. Our aim in this study was to examine whether TAS106 modified the repair capacity of DNA double-strand breaks (DSBs) in tumor cells. METHODS: Various cultured cell lines treated with TAS106 were irradiated and then survival fraction was examined by the clonogenic survival assays. Repair of sublethal damage (SLD), which indicates DSBs repair capacity, was measured as an increase of surviving cells after split dose irradiation with an interval of incubation. To assess the effect of TAS106 on the DSBs repair activity, the time courses of γ-H2AX and 53BP1 foci formation were examined by using immunocytochemistry. The expression of DNA-repair-related proteins was also examined by Western blot analysis and semi-quantitative RT-PCR analysis. RESULTS: In clonogenic survival assays, pretreatment of TAS106 showed radiosensitizing effects in various cell lines. TAS106 inhibited SLD repair and delayed the disappearance of γ-H2AX and 53BP1 foci, suggesting that DSB repair occurred in A549 cells. Western blot analysis demonstrated that TAS106 down-regulated the expression of BRCA2 and Rad51, which are known as keys among DNA repair proteins in the homologous recombination (HR) pathway. Although a significant radiosensitizing effect of TAS106 was observed in the parental V79 cells, pretreatment with TAS106 did not induce any radiosensitizing effects in BRCA2-deficient V-C8 cells. CONCLUSIONS: Our results indicate that TAS106 induces the down-regulation of BRCA2 and the subsequent abrogation of the HR pathway, leading to a radiosensitizing effect. Therefore, this study suggests that inhibition of the HR pathway may be useful to improve the therapeutic efficiency of radiotherapy for solid tumors.

Contribution of AP-1 interference induced by TAC-101 to tumor growth suppression in a hepatocellular carcinoma model.

TAC-101, 4-[3,5-bis(trimethylsilyl)benzamido] benzoic acid, is a synthetic ligand for retinoic acid receptor (RAR)-alpha. Here, we demonstrate the contribution of TAC-101-induced AP-1 interference to stabilization of tumor growth. TAC-101 induced transcriptional activation of RAR, resulting in marked elevation of RARbeta, a representative retinoid response marker, and it also significantly repressed the transcriptional activity of AP-1 in JHH-7 cells. In contrast to JHH-7, JHH-6 is another RARalpha-expressing human hepatocellular carcinoma (HCC) cell line with constitutive activation of AP-1, but it is retinoid insensitive and did not respond to the TAC-101-induced RAR signal. TAC-101 did not inhibit AP-1 activity of the JHH-6 cell line, showing that AP-1 interference by TAC-101 must be in parallel with RAR activation. Interleukin-8 (IL-8), one of the AP-1-regulated factors which correlate with a poor prognosis in HCC patients, was found to be overexpressed in JHH-7 cells. TAC-101 reduced IL-8 production without cytotoxicity and inhibited the progression of HCC in the orthotopic mouse model with decreased tumor IL-8 level. These results suggest that downregulation of the extracellular biomarker for AP-1 interference via the induction of retinoid signals will enhance the pharmacological effect of TAC-101 on HCC and it could be useful as a surrogate biomarker of therapeutic efficacy.

Augmentation of chemotherapeutic infusion effect by TSU-68, an oral targeted antiangiogenic agent, in a rabbit VX2 liver tumor model.

PURPOSE: This study was designed to investigate the in vivo effects of combination therapy with TSU-68 and chemotherapeutic infusion in a rabbit VX2 liver tumor model. METHODS: This study was approved by the animal care committee at our institute. Three weeks before chemotherapeutic infusion, VX2 carcinoma was implanted into the livers of 32 rabbits. One week after chemotherapeutic infusion, vehicle was administered orally for 3 weeks in the control group (n = 16), and TSU-68 was administered orally at a daily dose of 200 mg/kg for 3 weeks in the treated group (n = 16). Computed tomography (CT) was performed before and 1, 2, 3, and 4 weeks after chemotherapeutic infusion. Tumor response was assessed according to the Response Evaluation Criteria in Solid Tumors (RECIST) on CT scan. The maximum thickness of viable tumor was measured on microscopic sections. RESULTS: According to the RECIST, stable disease was observed in 9 (56%) rabbits and progressive disease in 7 (44%) in the control group, whereas partial response was observed in 1 (6%) rabbit and stable disease in 15 (94%) in the treated group. On pathologic examination, a viable lesion was present in 12 (75%) rabbits in the control group and in 6 (38%) rabbits in the treated group (P = 0.073). The mean maximum thickness of viable tumor in the treated group was significantly smaller than that in the control group (0.74 mm vs. 3.39 mm; P = 0.02). CONCLUSIONS: Oral administration of TSU-68 augmented the effect of chemotherapeutic infusion in a rabbit VX2 liver tumor model.

Investigation of the bioactive conformation of histamine H3 receptor antagonists by the cyclopropylic strain-based conformational restriction strategy.

We previously identified the highly potent histamine H(3) receptor antagonists (1R,2S)-2-[2-(4-chlorobenzylamino)ethyl]-1-(1H-imidazol-4-yl)cyclopropane (1) and its enantiomer ent-1. Although the conformations of 1 and ent-1 are restricted by the central cyclopropane ring, the 2-(4-chlorobenzylamino)ethyl side chain essential for the H(3) receptor binding may somewhat freely rotate. To investigate the bioactive conformation, the 1'-ethyl-substituted derivatives 2a and 2b and their enantiomers ent-2a and ent-2b were designed as side chain conformation-restricted analogues of 1 and ent-1, based on the cyclopropylic strain. These compounds were synthesized, and their analysis by NMR and calculations suggested that the side chain moiety was effectively restricted in a syn-form or an anti-form by the cyclopropylic strain as expected. Pharmacological evaluation and docking simulation showed that the bioactive conformations of 1 and ent-1 appear to be the syn-form and the anti-form, respectively. Thus, the cyclopropylic strain can be effectively used for conformational restriction of the side chain moiety of cyclopropane compounds.

An RNA-directed nucleoside anti-metabolite, 1-(3-C-ethynyl-beta-d-ribo-pentofuranosyl)cytosine (ECyd), elicits antitumor effect via TP53-induced Glycolysis and Apoptosis Regulator (TIGAR) downregulation.

1-(3-C-ethynyl-beta-d-ribo-pentofuranosyl)cytosine (ECyd) is a ribose-modified nucleoside analog of cytidine with potent anticancer activity in several cancers. The main antitumor mechanism of this promising RNA-directed nucleoside anti-metabolite is efficient blockade of RNA synthesis in cancer cells. Here, we examined the therapeutic potential of this RNA-directed anti-metabolite in in vitro models of nasopharyngeal cancer (NPC). In a panel of 6 NPC cell lines, ECyd effectively inhibited cellular proliferation at nM concentrations (IC(50): approximately 13-44nM). Moreover, cisplatin-resistant NPC cells were highly sensitive to ECyd (at nM concentration). The ECyd-mediated growth inhibition was associated with G(2)/M cell cycle arrest, PARP cleavage (a hallmark of apoptosis) and Bcl-2 downregulation, indicating induction of apoptosis by ECyd in NPC cells. Unexpectedly, ECyd-induced significant downregulation of TIGAR, a newly described dual regulator of apoptosis and glycolysis. More importantly, this novel action of ECyd on TIGAR was accompanied by marked depletion of NADPH, the major reducing power critically required for cell proliferation and survival. We hypothesized that ECyd-induced TIGAR downregulation was crucially involved in the antitumor activity of ECyd. Indeed, overexpression of TIGAR was able to rescue NPC cells from ECyd-induced growth inhibition, demonstrating a novel mechanistic action of ECyd on TIGAR. We demonstrated for the first time that an RNA-directed nucleoside analog, ECyd, exerts its antitumor activity via downregulation of a novel regulator of apoptosis, TIGAR. Moreover, ECyd may represent a novel therapy for NPC.

Cellular localization and functional characterization of the equilibrative nucleoside transporters of antitumor nucleosides.

Nucleoside transporters play an important role in the disposition of nucleosides and their analogs. To elucidate the relationship between chemosensitivity to antitumor nucleosides and the functional expression of equilibrative nucleoside transporters (ENT), we established stable cell lines of human fibrosarcoma HT-1080 and gastric carcinoma TMK-1 that constitutively overexpressed green fluorescent protein-tagged hENT1, hENT2, hENT3 and hENT4. Both hENT1 and hENT2 were predictably localized to the plasma membrane, whereas hENT3 and hENT4 were localized to the intracellular organelles. The chemosensitivity of TMK-1 cells expressing hENT1 and hENT2 to cytarabine and 1-(3-C-ethynyl-beta-D-ribopentofuranosyl) cytosine increased markedly in comparison to that of mock cells. However, no remarkable changes in sensitivity to antitumor nucleosides were observed in cell lines that expressed both hENT3 and hENT4. These data suggest that hENT3 and hENT4, which are mainly located in the intracellular organelles, are not prominent nucleoside transporters like hENT1 and hENT2, which are responsible for antitumor nucleoside uptake.