Discovery of Apararenone (MT-3995) as a Highly Selective, Potent, and Novel Nonsteroidal Mineralocorticoid Receptor Antagonist.

Overactivation of the mineralocorticoid receptor (MR) is involved in many diseases, such as hypertension, kidney disease, and heart failure. Thus, MR antagonists (MRAs) are expected to be beneficial to patients with these diseases. In order to identify novel nonsteroidal MRAs that overcome the issues of already marketed steroidal MRAs, we searched for new compounds guided by our hypothesis that T-shaped compounds with a hydrophobic core structure, two polar functional groups at both extremities able to interact with MR, and a bulky substituent that can interfere with the folding of the C-terminal helix 12 may exhibit antagonist activity toward MR. We discovered that the novel 1,4-benzoxazin-3-one derivative 19 (apararenone: MT-3995) acted as a highly selective and potent nonsteroidal MRA. Apararenone exhibited a more potent antihypertensive and organ-protective activity than steroidal MRA eplerenone in a primary aldosteronism rat model obtained by infusing aldosterone in uninephrectomized rats.

Synthesis and preclinical evaluation of [11C]MTP38 as a novel PET ligand for phosphodiesterase 7 in the brain.

PURPOSE: Phosphodiesterase (PDE) 7 is a potential therapeutic target for neurological and inflammatory diseases, although in vivo visualization of PDE7 has not been successful. In this study, we aimed to develop [11C]MTP38 as a novel positron emission tomography (PET) ligand for PDE7. METHODS: [11C]MTP38 was radiosynthesized by 11C-cyanation of a bromo precursor with [11C]HCN. PET scans of rat and rhesus monkey brains and in vitro autoradiography of brain sections derived from these species were conducted with [11C]MTP38. In monkeys, dynamic PET data were analyzed with an arterial input function to calculate the total distribution volume (VT). The non-displaceable binding potential (BPND) in the striatum was also determined by a reference tissue model with cerebellar reference. Finally, striatal occupancy of PDE7 by an inhibitor was calculated in monkeys according to changes in BPND. RESULTS: [11C]MTP38 was synthesized with radiochemical purity ≥99.4% and molar activity of 38.6 ± 12.6 GBq/µmol. Autoradiography revealed high radioactivity in the striatum and its reduction by non-radiolabeled ligands, in contrast with unaltered autoradiographic signals in other regions. In vivo PET after radioligand injection to rats and monkeys demonstrated that radioactivity was rapidly distributed to the brain and intensely accumulated in the striatum relative to the cerebellum. Correspondingly, estimated VT values in the monkey striatum and cerebellum were 3.59 and 2.69 mL/cm3, respectively. The cerebellar VT value was unchanged by pretreatment with unlabeled MTP38. Striatal BPND was reduced in a dose-dependent manner after pretreatment with MTP-X, a PDE7 inhibitor. Relationships between PDE7 occupancy by MTP-X and plasma MTP-X concentration could be described by Hill's sigmoidal function. CONCLUSION: We have provided the first successful preclinical demonstration of in vivo PDE7 imaging with a specific PET radioligand. [11C]MTP38 is a feasible radioligand for evaluating PDE7 in the brain and is currently being applied to a first-in-human PET study.

Antipsychotic-like effects of a novel phosphodiesterase 10A inhibitor MT-3014 in rats.

Phosphodiesterase (PDE) 10A is an attractive therapeutic target for schizophrenia. Here, we investigated the antipsychotic-like effects of a novel PDE10A inhibitor, 1-({2-(7-fluoro-3-methylquinoxalin-2-yl)-5-[(3R)-3-fluoropyrrolidin-1-yl]pyrazolo[1,5-α]pyrimidin-7-yl}amino)-2-methylpropan-2-ol hydrochloride (MT-3014) in rats. MT-3014 showed a potent and selective inhibitory effect against PDE10A (IC50 = 0.357 nmol/L). Oral administration of MT-3014 (1.0-10 mg/kg) significantly increased the levels of cAMP, cGMP and cAMP response element-binding protein (CREB) phosphorylation in the rat striatum. MT-3014 decreased MK-801 (0.075 mg/kg)-induced hyperactivity (ED50 = 0.30 mg/kg) in a dose-dependent manner, although it decreased spontaneous locomotion in control rats (ED50 = 0.48 mg/kg); its effects were equivalent to those of risperidone. MT-3014 (0.3-3.0 mg/kg and 0.2 mg/kg) attenuated MK-801-induced prepulse inhibition deficits and cognitive deficits in rats, respectively, whereas risperidone attenuated MK-801-induced prepulse inhibition at only a high dose and failed to improve MK-801-induced cognitive deficits. Similar to risperidone (ID50 = 0.63 mg/kg), MT-3014 suppressed the conditioned avoidance response (ID50 = 0.32 mg/kg). Interestingly, MT-3014 did not elicit catalepsy and plasma prolactin increases at high doses. Furthermore, it also did not affect body weight. A positron emission tomography study using [11C]IMA107 showed a plasma concentration-dependent increase in brain PDE10A occupancy after oral administration of MT-3014 within the pharmacological dose range in rats. Brain PDE10A occupancy corresponding to the ID50 value in the conditioned avoidance response was approximately 60%, predicting the target occupancy in patients with schizophrenia. These results suggest that MT-3014 may be a novel antipsychotic drug, which is expected to have additional effects on cognitive impairment, without the prominent side effects associated with current atypical antipsychotics.

Antipsychotic-like effects of a novel phosphodiesterase 10A inhibitor T-251 in rodents.

Phosphodiesterase 10A (PDE10A) is a dual-substrate PDE that hydrolyzes both cAMP and cGMP. PDE10A is selectively expressed in medium spiny neurons in the striatum, suggesting the potential of PDE10A inhibitors in the treatment of schizophrenia. This study presents the pharmacological profile of a novel PDE10A inhibitor, 2-[(E)-2-(7-fluoro-3-methylquinoxalin-2-yl)vinyl]-6-pyrrolidin-1-yl-N-(tetrahydro-2H-pyran-4-yl)pyrimidin-4-amine hydrochloride (T-251) in rodent models of schizophrenia. T-251 showed a potent inhibitory activity against human PDE10A (IC50 = 0.050 nmol/L) and showed high selectivity over other PDE families which have over 10,000-fold IC50 values. Oral administration of T-251 (0.1-1.0 mg/kg) increased cAMP and cGMP in the striatum in a dose-dependent manner. Oral administration of T-251 attenuated MK-801 induced hyperactivity (ED50 = 0.68 mg/kg) and suppressed conditioned avoidance response (ID50 = 0.87 mg/kg) in rats in a dose dependent manner. Furthermore, T-251 significantly attenuated MK-801 induced prepulse inhibition deficits and cognitive deficits in rats. Unlike haloperidol and olanzapine, T-251 (1.0-30 mg/kg) did not cause catalepsy in rats. Moreover, T-251 (0.6 and 6.0 mg/kg) did not increase plasma levels of prolactin at 1 h after administration, whereas haloperidol and olanzapine significantly increased them. The antipsychotic-like effects and cognitive enhancement of T-251 without catalepsy or plasma prolactin elevation observed in rats suggests that T-251 would be a novel antipsychotic with an improved side-effect profile.

Discovery of a pyrazolo[1,5-a]pyrimidine derivative (MT-3014) as a highly selective PDE10A inhibitor via core structure transformation from the stilbene moiety.

We have developed a new class of PDE10A inhibitor, a pyrazolo[1,5-a]pyrimidine derivative MT-3014 (1). A previous compound introduced was deprioritized due to concerns for E/Z-isomerization and glutathione-adduct formation at the core stilbene structure. We discovered pyrazolo [1,5-a] pyrimidine as a new lead scaffold by structure-based drug design utilizing a co-crystal structure with PDE10A. The lead compound was optimized for in vitro activity, solubility, and selectivity against human ether-á-go-go related gene cardiac channel binding. We observed that MT-3014 shows excellent efficacy in rat conditioned avoidance response test and suitable pharmacokinetic properties in rats, especially high brain penetration.

Inhibition of inducible nitric oxide synthase and interleukin-1ß expression by tunicamycin in cultured glial cells exposed to lipopolysaccharide.

Endoplasmic reticulum (ER) stress has recently been implicated in human diseases such as Alzheimer׳s disease (AD) and Parkinson׳s disease (PD). However, the link between the immune system, ER stress, and the development of neurodegenerative diseases has not yet been clarified in detail. Mouse primary cultured astrocytes were treated with lipopolysaccharide (LPS) and/or tunicamycin (Tm), and inducible nitric oxide synthase (iNOS) and interleukin (IL)-1ß levels were then measured using RT-PCR, ELISA, and Western blotting. Activation of the immune system by LPS triggered inflammatory responses in astrocytes, as measured by the induction of iNOS and IL-1ß. Tm-induced ER stress inhibited the LPS-induced expression of IL-1ß and iNOS at the protein level. On the other hand, ER stress alone did not induce the expression of IL-1ß or iNOS. The inhibitory effect of ER stress on iNOS and IL-1ß may not be mediated transcriptionally as we did not observe inhibition at the mRNA level. LPS-induced iNOS protein levels were attenuated by the Tm post-treatment in the absence of LPS. Overall, these results suggest that ER stress negatively regulates the expression of IL-1ß and iNOS in LPS-activated astrocytes.