Takumi Sumida

Characterization of a novel nonpeptide vasopressin V2‐agonist, OPC‐51803, in cells transfected human vasopressin receptor subtypes

We discovered the first nonpeptide arginine‐vasopressin (AVP) V2‐receptor agonist, OPC‐51803. Pharmacological properties of OPC‐51803 were elucidated using HeLa cells expressing human AVP receptor subtypes (V2, V1a and V1b) and compared with those of 1‐desamino‐8‐D‐arginine vasopressin (dDAVP), a peptide V2‐receptor agonist. OPC‐51803 and dDAVP displaced [3H]‐AVP binding to human V2‐ and V1a‐receptors with Ki values of 91.9±10.8 nM (n=6) and 3.12±0.38 nM (n=6) for V2‐receptors, and 819±39 nM (n=6) and 41.5±9.9 nM (n=6) for V1a‐receptors, indicating that OPC‐51803 was about nine times more selective for V2‐receptors, similar to the selectivity of dDAVP. OPC‐51803 scarcely displaced [3H]‐AVP binding to human V1b‐receptors even at 10−4 M, while dDAVP showed potent affinity to human V1b‐receptors with the Ki value of 13.7±3.2 nM (n=4). OPC‐51803 concentration‐dependently increased cyclic adenosine 3′, 5′‐monophosphate (cyclic AMP) production in HeLa cells expressing human V2‐receptors with an EC50 value of 189±14 nM (n=6). The concentration‐response curve for cyclic AMP production induced by OPC‐51803 was shifted to the right in the presence of a V2‐antagonist, OPC‐31260. At 10−5 M, OPC‐51803 did not increase the intracellular Ca2+ concentration ([Ca2+]i) in HeLa cells expressing human V1a‐receptors. On the other hand, dDAVP increased [Ca2+]i in HeLa cells expressing human V1a‐ and V1b‐receptors in a concentration‐dependent fashion. From these results, OPC‐51803 has been confirmed to be the first nonpeptide agonist for human AVP V2‐receptors without agonistic activities for V1a‐ and V1b‐receptors. OPC‐51803 may be useful for the treatment of AVP‐deficient pathophysiological states and as a tool for AVP researches.

Pranidipine, a new 1, 4-dihydropyridine calcium channel blocker, enhances cyclic GMP-independent nitric oxide-induced relaxation of the rat aorta

Pranidipine, a new calcium channel modulator, prolonged endothelium-dependent relaxation induced by acetylcholine in a aortic ring preparation, contracted with prostaglandin F2α. This action was not shared by amlodipine. The effect was not modified by indomethacin, suggesting that the action of pranidipine does not involve prostanoid metabolism. NG-nitro-L-arginine completely prevented the action of Pranidipine. The drug affected neither nitric oxide (NO) synthase activity nor the level of cyclic GMP in the vessel. Pranidipine did not affect the sensitivity of the contractile proteins to calcium. Pranidipine also did not alter cyclic GMP-induced relaxation in a-toxinskinned vascular preparations. Pranidipine also prolonged glyceryl trinitrate-induced relaxation in the endothelium denuded rat aorta. Furthermore, pranidipine enhanced relaxation of the aorta induced by glyceryl trinitrate even in the presence of methylene blue, a guanylyl cyclase inhibitor. This action was not modified by iberiotoxin or by charybdotoxin, two inhibitors of the calciumactivated potassium channel. The results strongly suggest that pranidipine enhances cyclic GMPindependent NO-induced relaxation of smooth muscle by a mechanism other than through NOinduced hyperpolarization. These effects were in direct contrast to amlodipine, another new 1,4dihydropyridine calcium antagonist.

Pathogenesis of obesity by food restriction in OLETF rats-increased intestinal monoacylglycerol acyltransferase activities may be a crucial factor

UNLABELLED Obesity was considered to be one of the causes of non-insulin-dependent diabetes mellitus (NIDDM). However, the mechanism responsible for obesity has not yet been fully elucidated. In this study, we first examined the relationship between food intake amount and obesity in a NIDDM model animal, and then we focused on triacylglycerol (TG) synthetase activity, which play important roles in hypertriglyceridemia (HTG) associated with obesity. Otsuka Long-Evans Tokushima Fatty (OLETF) rat is an animal model of NIDDM, characterized by obesity, HTG and insulin resistance. In this study, OLETF rats were allocated to a food-satiated group (satiated) or food-restricted group (to eliminate the effects of hyperphagia on obesity, amount of daily food intake was the same as that in their control strain Long-Evans Tokushima Otsuka (LETO) rats). Changes in body weight, body fat, intraabdominal fat weight, and TG content in liver were measured and biochemical blood tests and activity assay of TG synthetase (monoacylglycerol acyltransferase (MGAT) and diacylglycerol acyltransferase (DGAT)) were performed. RESULTS (1) The body weight in the restricted OLETF rats was significantly decreased to 71.7% of that in the satiated OLETF rats, which was almost the same value as that in the LETO rats. However, body fat and intraabdominal fat weight were significantly increased in restricted OLETF rats and satiated OLETF rats compared with LETO rats. (2) Plasma TG, insulin, glucose, leptin and hepatic TG content were significantly higher in OLETF rats than the values in LETO rats. (3) MGAT activity in the small intestine from both satiated and restricted OLETF rats was significantly higher than that in LETO rats. DGAT activity in OLETF rats was not significantly different from that in LETO rats. In conclusion, the body fat weight and plasma TG were still significantly accelerated in OLETF rats at the same food intake as LETO rats. MGAT activity in the small intestine from OLETF rats was also significantly higher than those of LETO rats. Therefore, high MGAT activity in the small intestine may play an important role in HTG and obesity, subsequently hastening the development of NIDDM in OLETF rats.

Differential properties of the optical‐isomers of pranidipine, a 1,4‐dihydropyridine calcium channel modulator

Abstract— Pranidipine is an optically‐active 1,4‐dihydropyridine (DHP) voltage‐dependent L‐type calcium channel inhibitor. Certain enantiomeric pairs display opposite effects, i.e., inhibition and activation of the calcium channel while others exhibit the same qualitative actions. We investigated pranidipine, a new DHP, using a paradigm of vascular smooth muscle reactivity. In isolated rat aorta, depolarized with 80 mM KCl, both isomers of pranidipine caused a right‐ward shift of the concentration‐contraction curves for extracellular Ca2+. The apparent pA2 values of the S‐isomer and R‐isomer were 10.03 and 8.36, respectively, providing evidence that the calcium channel blocking action of the S‐isomer was 50 times more potent than that of the R‐isomer. Antihypertensive actions of these two isomers studied in pentobarbital‐anaesthetized spontaneously hypertensive rats, revealed that the S‐isomer, at doses of 3–30 μg/kg i.v. decreased blood pressure in a dose‐dependent manner, while the R‐isomer had no effect on blood pressure at those doses. We conclude that the pair of enantiomers of pranidipine qualitatively display the same Ca2+channel blocking action and that neither isomer exhibits Bay K 8644‐like activation. Pranidipine may be useful in studies on the architecture of the DHP receptor ‘pocket’.

Abstract B56: A phase 1, open-label, dose escalation, nonrandomized study to assess the maximum tolerated dose, dose limiting toxicity, and pharmacokinetics of OPB-31121 in subjects with advanced solid tumors.

Background: OPB-31121 is a novel compound exhibiting potent growth inhibition of cancer cell lines in vitro and xenografts in vivo. The exact mechanism of action of OPB-31121 has not been fully characterized, but studies indicate that a major effect is inhibition of STAT3 phosphorylation. STAT3 is frequently activated in a variety of solid and hematologic malignancies and may present an important target for antitumor therapy. Methods: Open-label, non-randomized, multi-center study in subjects with advanced solid tumors, using a 3+3 dose escalation design. OPB-31121 was administered orally for 21 days followed by 7 days rest per cycle (28-day cycle). The starting dose was 50 mg BID with escalations planned until the dose-limiting toxicity (DLT) was reached. The primary endpoint was determination of maximum tolerated dose (MTD). Additional endpoints included safety, pharmacokinetics, and anti-tumor effect of OPB-31121. Results: 30 subjects received treatment with OPB-31121. Most common tumor types were colorectal cancer (15), breast (3) and thyroid (2). Mean age was 55.9 (range 35–80) years and 17 of the patients were female. Most common adverse events (AEs) potentially attributed to treatment were gastrointestinal: nausea (80%), vomiting (73%), diarrhea (63%), anorexia (20%), and constipation (17%). Most AEs were CTCAE grades 1–2 and manageable with supportive treatment. Three DLTs were observed: one at 300 mg BID (grade 3 lactic acidosis), and two at 350 mg BID (a grade 3 diarrhea and a grade 3 vomiting); the MTD was 300 mg BID. All patients recovered from DLTs after discontinuing the drug. Six additional (9 total) subjects discontinued during the first cycle. Eight subjects completed only one cycle and 13 completed two cycles. No objective responses were observed. Disease progression was observed in all evaluable patients at first restaging. Pharmacokinetic measurements showed low and transient plasma levels of OPB-31121. Inter-patient variability was high. Exposure was low - area-under-the-curve (AUC) values were 2–3 orders of magnitude lower than those measured at active doses in mouse models. Analysis of metabolites in plasma samples indicates extensive CYP3A4 metabolism and suggests a large first-pass effect in humans, which had not been observed in rodents. Conclusions: OPB-31121 does not show potential as a therapeutic option for most malignancies. The extensive first-pass metabolism and dose-limiting gastrointestinal AEs limit the level of systemic exposure that can be achieved with this agent. Further studies may be warranted in cancers of organs where local concentrations of the compound may be higher (e.g., liver) and an exploratory study in hepatocellular carcinoma is ongoing in Asia. Because STAT3 remains an attractive antitumor target, chemically related compounds with similar pharmacologic activities are currently being evaluated preclinically. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B56.