Takashi Koyano

Naturally occurring small-molecule inhibitors of hedgehog/GLI-mediated transcription.

The aberrant hedgehog (Hh)/GLI signaling pathway causes the formation and progression of a variety of tumors. To search for Hh/GLI inhibitors, we screened for naturally occurring inhibitors of the transcriptional activator GLI1 by using a cell‐based assay. We identified zerumbone (1), zerumbone epoxide (2), staurosporinone (9), 6‐hydroxystaurosporinone (10), arcyriaflavin C (11) and 5,6‐dihydroxyarcyriaflavin A (12) as inhibitors of GLI‐mediated transcription. In addition, we isolated physalins F (17) and B (18) from Physalis minima, which are also potent inhibitors. These compounds also inhibited GLI2‐mediated transactivation. Semiquantitative RT‐PCR and Western blotting analysis further revealed that 1, 9, 17, and 18 decreased Hh‐related component expressions. We also show that inhibitors of GLI‐mediated transactivation reduce the level of the antiapoptosis Bcl2 expression. Finally, these identified compounds were cytotoxic to PANC1 pancreatic cancer cells, which express Hh/GLI components. These results strongly suggest that the cytotoxicity of the compounds to PANC1 cells correlates with their inhibition of GLI‐mediated transcription.

Induction of normal phenotypes in ras-transformed cells by damnacanthal from Morinda citrifolia

We have screened tropical plant extracts for substances that induce normal morphology in K-rasts-NRK cells. As a result we isolated an anthraquinone compound, damnacanthal, from the chloroform extract of the root of Morinda citrifolia. Damnacanthal induced normal morphology and cytoskeletal structure in K-rasts-NRK cells at the permissive temperature, without changing the amount and localization of Ras. The effect of damnacanthal was reversible, and the compound had no effect on the morphology of RSVts-NRK cells expressing the src oncogene. Thus, damnacanthal is a new inhibitor of ras function.

Leishmanicidal alkaloids from Kopsia griffithii

Thirteen alkaloids were isolated from the stem-bark extract of Kopsia griffithii, of which three were new. These were the N(4)-oxides of akuammiline, 16-epi-deacetylakuammiline and 11,12-methylenedioxykopsinaline. Harmane, pleiocarpine and buchtienine showed antileishmanial activity.

New Wnt/β‐Catenin Signaling Inhibitors Isolated from Eleutherine palmifolia

Aberrant Wnt/beta-catenin signaling has recently been implicated in tumorigenesis. On the basis of our screening program targeting inhibition of TCF/beta-catenin transcriptional activity, a plant extract of Eleutherine palmifolia was selected as a hit sample. Activity-guided fractionations led to the isolation of 15 naphthalene derivatives (1-15), including 4 new glucosides, eleutherinosides B-E (1-4), and 10 of the 15 compounds showed strong activities with high viability among 293T cells. Our data showed that 2 and 9 inhibited the transcription of TCF/beta-catenin in SW480 colon cancer cells in a dose-dependent manner. These two compounds also showed selective cytotoxicity against three colorectal cancer cell lines. In addition, treatment with 9 led to a significant decrease in the level of nuclear beta-catenin protein, suggesting this reduction to have resulted in the inhibitory effect of 9 on the transcription of TCF/beta-catenin.

Induction of insulin production in rat pancreatic acinar carcinoma cells by conophylline.

We set up a screening system to detect low-molecular-weight compounds that induce insulin expression in pancreatic acinar carcinoma AR42J cells. They can differentiate into insulin-producing cells with neuron-like morphological change when treated with activin A. We employed this morphological change for the screening of beta-cell inducers among various signal transduction inhibitors. As a result, a vinca alkaloid, conophylline, induced neurite formation at 0.1 approximately 0.3 microg/ml in 72 h, like activin A. Conophylline-treated cells were found to express insulin as measured at both mRNA and protein levels. By RT-PCR analysis, conophylline-treated cells were shown to express neurogenin3 strongly. They also expressed Beta2/NeuroD and Nkx2.2, but not Pax4 and PP. Although activin A induces nuclear translocation of Smad2, conophylline did not. But the latter induced p38 activation, like activin A, as detected by phosphorylation. Pretreatment with a p38-specific inhibitor, SB203580, lowered the conophylline-induced insulin production. Therefore, p38 activation would be involved in the differentiation of AR42J cells into insulin-producing cells. Studies on structure-activity relationship with conophyllidine, conofoline, conophyllinine, and related monomer alkaloids showed that the dimeric aspidosperma structure with the dihydrofuran unit in its center was essential for the differentiation-inducing activity.

Reversal of multidrug resistance (MDR) by aspidofractinine-type indole alkaloids.

A series of indole alkaloids of the aspidofractinine-type was assessed for their potential in reversing MDR in vincristine-resistant KB cells. Of the compounds tested, kopsiflorine, kopsamine, pleiocarpine, 11-methoxykopsilongine, lahadinine A and N-methoxycarbonyl-11,12-methylenedioxy-delta 16,17-kopsinine were found to show appreciable activity.

Terpenoids and a flavonoid glycoside from Acacia pennata leaves as Hedgehog/GLI-mediated transcriptional inhibitors.

Overexpression of glioma-associated oncogene 1 (GLI1), which has been characterized as a terminal effector and a target gene of the Hedgehog (Hh) signaling pathway, is associated with the development of cancer. A cellular screen was applied utilizing of a GLI-dependent luciferase reporter in human keratinocyte cells (HaCaT) and identified two terpenoids (1 and 2) and a flavonoid glycoside (5) from Acacia pennata as Hh/GLI inhibitors. Compounds 1, 2, and 5 exhibited selective cytotoxicity against human pancreatic (PANC1) and prostate (DU145) cancer cells with no toxic effect on normal cells. This result was consistent with a dose-dependent reduction of the protein levels of antiapoptotic BCL-2 and the tumor suppressor patched 1 protein (PTCH). Additionally, treatment of 1 downregulated mRNA expression of Ptch in PANC1, suggesting that the compound has an inhibitory effect on the transcription of Hh/GLI.

Hedgehog/GLI-mediated transcriptional inhibitors from Zizyphus cambodiana.

The aberrant hedgehog (Hh)/GLI signaling pathway causes the formation and progression of a variety of tumors. By screening tropical plant extracts by using our screening system, Zizyphus cambodiana was found to include Hh/GLI signaling inhibitors. Bioassay-guided fractionation of this plant extract led to the isolation of three active pentacyclic triterpenes, colubrinic acid (1), betulinic acid (2) and alphitolic acid (3), as potent inhibitors. The inhibition of GLI-related protein expression with 1 or 2 was observed in HaCaT cells with exogenous GLI1, or human pancreatic cancer cells (PANC1), which express Hh/GLI components aberrantly. The expressions of GLI-related proteins PTCH and BCL2 were clearly inhibited by 1 or 2. We also examined the cytotoxicity of these active compounds against PANC1, human prostate cancer cells (DU145) and mouse embryo fibroblast cells (C3H10T1/2). The cytotoxicity against cancer cells (PANC1 and DU145) by 1 or 2 would be caused by inhibition of the expression of the anti-apoptosis protein BCL2. These pentacyclic triterpene inhibitors showed an important relationship between Hh/GLI signaling inhibition, the decrease of BCL2, and cytotoxicity against cancer cells.

Conodiparines A-D, New bisindoles from Tabernaemontana. Reversal of vincristine-resistance with cultured cells

Four new bisindoles of the vobasine-iboga type, conodiparines A-D were obtained from Tabernaemontana corymbosa which showed appreciable activity in reversing resistance in vincristine-resistant KB cells.

A new bioactive steroidal saponin, furcreastatin, from the plant Furcraea foetida.

Microbial and plant secondary metabolites were screened for compounds that are selectively cytotoxic to mutant p53-expressing mouse fibroblasts. As a result, furcreastatin, a novel steroidal saponin, was isolated from an EtOH extract of the leaves of Furcraea foetida. Furcreastatin consisted of hecogenin as the aglycone and a hexasaccharide containing D-galactose, L-rhamnose and four D-glucose residues. The structure was determined to be (3 beta,5 alpha,25R)- 3-hydroxyspirostan-12-one 3-O-[alpha-L-Rhap-(1-->4)-beta-D-Glcp-(1-->3)-¿beta-D-Glcp-(1-->3) -beta-D- Glcp-(1-->2)¿-beta-D-Glcp-(1-->4)-beta-D-Galp] by extensive NMR spectroscopic studies. Furcreastatin decreased the viability of mutant p53-over-expressing cells with an ED50 of 4.0 micrograms/mL, and decreased that of the parental cell-line with an ED50 of 9.6 micrograms/mL.