We synthesized various 4-benzylamino-1-chloro-6-substituted phthalazines (15) and 4-benzylamino-1-chloro-7-substituted phthalazines (16) and evaluated their inhibitory activity toward phosphodiesterase 5 (PDE5) purified from porcine platelets. The PDE5-inhibitory activities of 15 were greater than those of the isomers (16). The preferred substituent at the 4-position of phthalazine was a (3-chloro-4-methoxybenzyl)amino group, and those at the 6-position were cyano, nitro, and trifluoromethyl groups. Compounds 15a (IC50 = 4.8 nM), 15f (3.5 nM), and 15i (5.3 nM) were more potent inhibitors than E4021 (8.6 nM). Compounds 15a and 15f also showed vasorelaxant activity in isolated porcine coronary arteries precontracted with prostaglandin F2alpha (10(-5) M). The EC50 values for vasorelaxant action of 15a, 15f, and E4021 were 150, 160, and 980 nM, respectively. These results show that novel PDE5 inhibitors possessing a potent vasorelaxant effect may exist among phthalazine derivatives.

Abbreviations: SA-J schweinfurthin A-J; TGN trans-Golgi-network; PTEN phosphatase and tensin homolog; DLBCL diffuse large B cell lymphoma; mTOR mammalian target of rapamycin; PDK1 phosphoinositide-dependent kinase 1; PIP3 phosphatidylinositol (3,4,5)-triphosphate; WGA wheat germ agglutinin; ConA concanavalin; MAA Maackia amurensis agglutinin; PNA peanut agglutinin; ORPs oxysterol-binding protein related family proteins Natural compound schweinfurthins are of considerable interest for novel therapy development because of their selective anti-proliferative activity against human cancer cells. We previously reported the isolation of highly active schweinfurthins E-H, and in the present study, mechanisms of the potent and selective anti-proliferation were investigated. We found that schweinfurthins preferentially inhibited the proliferation of PTEN deficient cancer cells by indirect inhibition of AKT phosphorylation. Mechanistically, schweinfurthins and their analogs arrested trans-Golginetwork trafficking, an intracellular vesicular trafficking system, resulting in the induction of endoplasmic reticulum stress and the suppression of both lipid raft-mediated PI3K activation and mTOR/RheB complex formation, which collectively led to an effective inhibition of mTOR/AKT signaling. The trans-Golgi-network traffic arresting effect of schweinfurthins was associated with their in vitro binding activity to oxysterol-binding proteins that are known to regulate intracellular vesicular trafficking. Moreover, schweinfurthins were found to be highly toxic toward PTENdeficient B cell lymphoma cells, and displayed 2 orders of magnitude lower activity toward normal human peripheral blood mononuclear cells and primary fibroblasts in vitro. These results revealed a previously unrecognized role of schweinfurthins in regulating trans-Golgi-network trafficking, and linked mechanistically this cellular effect with mTOR/ AKT signaling and with cancer cell survival and growth. Our findings suggest the schweinfurthin class of compounds as a novel approach to modulate oncogenic mTOR/AKT signaling for cancer treatment.

The Saccharomyces cerevisiae mRNA capping enzyme consists of two subunits: an RNA 5-triphosphatase (Cet1) and an mRNA guanylyltransferase (Ceg1). In yeast, the capping enzyme is recruited to the RNA polymerase II (Pol II) transcription complex via an interaction between Ceg1 and the phosphorylated carboxyterminal domain of the Pol II largest subunit. Previous in vitro experiments showed that the Cet1 carboxyterminal region (amino acids 265 to 549) carries RNA triphosphatase activity, while the region containing amino acids 205 to 265 of Cet1 has two functions: it mediates dimerization with Ceg1, but it also allosterically activates Ceg1 guanylyltransferase activity in the context of Pol II binding. Here we characterize several Cet1 mutants in vivo. Mutations or deletions of Cet1 that disrupt interaction with Ceg1 are lethal, showing that this interaction is essential for proper capping enzyme function in vivo. Remarkably, the interaction region of Ceg1 becomes completely dispensable when Ceg1 is substituted by the mouse guanylyltransferase, which does not require allosteric activation by Cet1. Although no interaction between Cet1 and mouse guanylyltransferase is detectable, both proteins are present at yeast promoters in vivo. These results strongly suggest that the primary physiological role of the Ceg1-Cet1 interaction is to allosterically activate Ceg1, rather than to recruit Cet1 to the Pol II complex.Eukaryotic and viral mRNAs are modified at their 5Ј end by a cap structure which consists of a 7-methylguanosine moiety attached to the 5Ј terminus via a 5Ј-5Ј linkage. Cellular mRNA capping enzyme is a bifunctional enzyme: RNA 5Ј-triphosphatase removes the ␥-phosphate from the 5Ј end of the RNA substrate to leave a diphosphate end, and GTP::mRNA guanylyltransferase subsequently transfers GMP from GTP to the 5Ј-diphosphate RNA end. A separate enzyme, RNA (guanine-7-)-methyltransferase, adds a methyl group to the N-7 position of the guanine cap to leave m 7 GpppN 1 -(35). Capping enzyme from Saccharomyces cerevisiae is a heterodimer of RNA triphosphatase and guanylyltransferase subunits (20) encoded by the CET1 and CEG1 genes, respectively. Both genes are essential for cell viability (34, 39). CET1 and CEG1 homologs from Schizosaccharomyces pombe and Candida albicans functionally replace the S. cerevisiae genes (36,42,44). The fungal guanylyltransferase subunits have amino acid similarity to viral and metazoan guanylyltransferases, indicating a common reaction mechanism (11, 41). In contrast to the two subunit yeast enzymes, capping enzyme from higher eukaryotes are a single polypeptide consisting of an aminoterminal RNA triphosphatase domain and a carboxy-terminal guanylyltransferase domain. Both mouse (MCE or MCE1) and human (HCE or HCE1) enzymes can replace CEG1 and CET1 in vivo (16,17,24,43,47). Interestingly, the higher eukaryotic RNA triphosphatase domains belong to the PTP (protein tyrosine phosphatase) superfamily (27, 38, 47) and do not resemble the fungal phosphatases (39, 44).Cellular capping enzymes ...

We synthesized various 4-[[3,4-(methylenedioxy)benzyl]amino]quinazolines substituted at the 5- to 8-positions and evaluated their inhibitory activities toward cyclic GMP phosphodiesterase (cGMP-PDE) from porcine aorta. Monosubstitution at the 6-position was essential for the inhibitory activity, and the preferred substituents were compact and hydrophobic: methoxy (3b, IC50 = 0.23 microM), methyl (3c, 0.10 microM), chloro (3d, 0.019 microM), thiomethyl (3f, 0.031 microM), and cyano (3p, 0.090 microM) groups. Compounds 3b-d,f,p lacked inhibitory activity toward other PDE isozymes (all IC50 values > 100 microM), and their relaxing activities in porcine coronary arteries were well correlated with the inhibitory activities toward cGMP-PDE (r = 0.88, p < 0.05). One of these compounds, 3b, elevated the intracellular cGMP level in isolated porcine coronary arteries without causing any change in the cAMP level. We consider that this series of compounds dilates coronary arteries via potent and specific inhibition of cGMP-PDE.

The Saccharomyces cerevisiae mRNA capping enzyme consists of two subunits: an RNA 5-triphosphatase (RTPase) and GTP::mRNA guanylyltransferase (GTase). The GTase subunit (Ceg1) binds to the phosphorylated carboxyl-terminal domain of the largest subunit (CTD-P) of RNA polymerase II (pol II), coupling capping with transcription. Ceg1 bound to the CTD-P is inactive unless allosterically activated by interaction with the RTPase subunit (Cet1). For purposes of comparison, we characterize here the related GTases and RTPases from the yeasts Schizosaccharomyces pombe and Candida albicans. Surprisingly, the S. pombe capping enzyme subunits do not interact with each other. Both can independently interact with CTD-P of pol II, and the GTase is not repressed by CTD-P binding. The S. pombe RTPase gene (pct1 ؉ ) is essential for viability. Pct1 can replace the S. cerevisiae RTPase when GTase activity is supplied by the S. pombe or mouse enzymes but not by the S. cerevisiae GTase. The C. albicans capping enzyme subunits do interact with each other. However, this interaction is not essential in vivo. Our results reveal an unexpected diversity among the fungal capping machineries.