Development of Thiochroman Dioxide Analogues of Benzothiadiazine Dioxides as New Positive Allosteric Modulators of α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptors.

On the basis of the activity of 1,2,4-benzothiadiazine 1,1-dioxides as positive allosteric modulators of AMPA receptors, thiochroman 1,1-dioxides were designed applying the isosteric replacement concept. The new compounds expressed strong modulatory activity on AMPA receptors in vitro, although lower than their corresponding benzothiadiazine analogues. The pharmacokinetic profile of three thiochroman 1,1-dioxides (12a, 12b, 12e) was examined in vivo after oral administration, showing that these compounds freely cross the blood-brain barrier. Structural analysis was achieved using X-ray crystallography after cocrystallization of the racemic compound 12b in complex with the ligand-binding domain of GluA2 (L504Y/N775S). Interestingly, both enantiomers of 12b were found to interact with the GluA2 dimer interface, almost identically to its benzothiadiazine analogue, BPAM344 (4). The interactions of the two enantiomers in the cocrystal were further analyzed (mapping Hirshfeld surfaces and 2D fingerprint) and compared to those of 4. Taken together, these data explain the lower affinity on AMPA receptors of thiochroman 1,1-dioxides compared to their corresponding 1,2,4-benzothiadiazine 1,1-dioxides.

Pharmacological characterisation of S 47445, a novel positive allosteric modulator of AMPA receptors.

S 47445 is a novel positive allosteric modulator of alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptors (AMPA-PAM). S 47445 enhanced glutamate's action at AMPA receptors on human and rat receptors and was inactive at NMDA and kainate receptors. Potentiation did not differ among the different AMPA receptors subtypes (GluA1/2/4 flip and flop variants) (EC50 between 2.5-5.4 µM), except a higher EC50 value for GluA4 flop (0.7 µM) and a greater amount of potentiation on GluA1 flop. A low concentration of S 47445 (0.1 µM) decreased receptor response decay time of GluA1flop/GluA2flip AMPA receptors and increased the sensitivity to glutamate. Furthermore, S 47445 (0.1 and 0.3 µM) in presence of repetitive glutamate pulses induced a progressive potentiation of the glutamate-evoked currents from the second pulse of glutamate confirming a rapid-enhancing effect of S 47445 at low concentrations. The potentiating effect of S 47445 (1 µM) was concentration-dependently reversed by the selective AMPA receptor antagonist GYKI52466 demonstrating the selective modulatory effect of S 47445 on AMPA receptors. Using an AMPA-kainate chimera approach, it was confirmed that S 47445 binds to the common binding pocket of AMPA-PAMs. S 47445 did not demonstrate neurotoxic effect against glutamate-mediated excitotoxicity in vitro, in contrast significantly protected rat cortical neurons at 10 µM. S 47445 was shown to improve both episodic and spatial working memory in adult rodents at 0.3 mg/kg, as measured in the natural forgetting condition of object recognition and T-maze tasks. Finally, no deleterious effect on spontaneous locomotion and general behavior was observed up to 1000 mg/kg of S 47445 given acutely in rodents, neither occurrence of convulsion or tremors. Collectively, these results indicate that S 47445 is a potent and selective AMPA-PAM presenting procognitive and potential neuroprotective properties. This drug is currently evaluated in clinical phase 2 studies in Alzheimer's disease and in Major Depressive Disorder.

In vivo pharmacological profile of S 38093, a novel histamine H3 receptor inverse agonist.

S 38093, a novel histamine H3 receptor inverse agonist, was tested in a series of neurochemical and behavioral paradigms designed to evaluate its procognitive and arousal properties. In intracerebral microdialysis studies performed in rats, S 38093 dose-dependently increased histamine extracellular levels in the prefrontal cortex and facilitated cholinergic transmission in the prefrontal cortex and hippocampus of rats after acute and chronic administration (10mg/kg i.p.). Acute oral administration of S 38093 at 0.1mg/kg significantly improved spatial working memory in rats in the Morris water maze test. The compound also displayed cognition enhancing properties in the two-trial object recognition task in rats, in a natural forgetting paradigm at 0.3 and 1mg/kg p.o. and in a scopolamine-induced memory deficit situation at 3mg/kg p.o. The property of S 38093 to promote episodic memory was confirmed in a social recognition test in rats at 0.3 and 1mg/kg i.p. Arousal properties of S 38093 were assessed in freely moving rats by using electroencephalographic recordings: at 3 and 10mg/kg i.p., S 38093 significantly reduced slow wave sleep delta power and induced at the highest dose a delay in sleep latency. S 38093 at 10mg/kg p.o. also decreased the barbital-induced sleeping time in rats. Taken together these data indicate that S 38093, a novel H3 inverse agonist, displays cognition enhancing at low doses and arousal properties at higher doses in rodents.

Positive allosteric modulators of 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid receptors belonging to 4-cyclopropyl-3,4-dihydro-2h-1,2,4-pyridothiadiazine dioxides and diversely chloro-substituted 4-cyclopropyl-3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxides.

Two 4-ethyl-substituted pyridothiadiazine dioxides belonging to α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor positive allosteric modulators were cocrystallized with the GluA2 ligand binding domain in order to decipher the impact of the position of the nitrogen atom on their binding mode at the AMPA receptors. The latter was found to be very similar to that of previously described benzothiadiazine-type AMPA receptor modulators. The affinity of the two compounds for the receptor was determined by isothermal titration calorimetry. Accordingly, the synthesis and biological evaluation of novel 4-cyclopropyl-substituted pyridothiadiazine dioxides was performed and completed with the synthesis of the corresponding chloro-substituted 4-cyclopropyl-3,4-dihydro-2H-benzothiadiazine 1,1-dioxides. The "8-aza" compound 32 was found to be the most potent pyridothiadiazine-type AMPA receptor potentiator in vitro, whereas the 7-chloro-substituted compound 36c emerged as the most promising benzothiadiazine dioxide. Due to proper drug-likeness and low in vivo acute toxicity in mice, 36c was chosen for a more complete preclinical evaluation. The compound was able to easily cross the blood-brain barrier. In an in vivo object recognition test with CD1 mice, oral administration of 36c was found to significantly improve cognition performance at doses as low as 1 mg/kg.

DRUG FOCUS: S 18986: A positive allosteric modulator of AMPA-type glutamate receptors pharmacological profile of a novel cognitive enhancer.

Alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) type glutamate receptors are critical for synaptic plasticity and induction of long-term potentiation (LTP), considered as one of the synaptic mechanisms underlying learning and memory. Positive allosteric modulators of AMPA receptors could provide a therapeutic approach to the treatment of cognitive disorders resulting from aging and/or neurodegenerative diseases, such as Alzheimer disease (AD). Several AMPA potentiators have been described in the last decade, but for the moment their clinical efficacy has not been demonstrated due to the complexity of the target, AMPA receptors, and the difficulty in studying cognition in animals and humans. A better understanding of the mechanism of action of this type of drug remains an important issue, if knowledge of these compounds is to be increased and if this novel therapeutic approach is to be an interesting research area. Among the AMPA potentiators, S 18986 is emerging as a new selective positive allosteric modulator of AMPA-type glutamate receptors. S 18986, as with other positive AMPA receptor modulators, increased induction and maintenance of LTP in the hippocampus as well as the expression of brain-derived neurotrophic factor (BDNF) both in vitro and in vivo. Its cognitive-enhancing properties have been demonstrated in various behavioral models (procedural, spatial, "episodic," working, and relational/declarative memory) in young-adult and aged rodents. It is interesting to note that memory-enhancing effects appeared more robust in middle-aged animals compared with aged ones and in "episodic" and spatial memory tasks. From these results, S 18986 is expected to treat memory deficits associated with early cerebral aging and neurological diseases in elderly people.

New fluorinated 1,2,4-benzothiadiazine 1,1-dioxides: discovery of an orally active cognitive enhancer acting through potentiation of the 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid receptors.

In the search of a potent cognitive enhancer, a series of 3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxides have been synthesized and evaluated as positive allosteric modulators of the AMPA receptors. In the present work, we focused our efforts on the insertion of mono- or polyfluoro-substituted alkyl chains at the 4-position of the thiadiazine ring in an attempt to enhance the pharmacokinetic behavior of previously described compounds. Among all the described compounds, 7-chloro-4-(2-fluoroethyl)-3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxide, 12b, was shown to exert a strong activity on AMPA receptors in vitro and a marked cognitive-enhancing effect in vivo after oral administration to Wistar rats. Considering its in vivo activity, the metabolic degradation of 12b was studied and compared to that of its nonfluorinated analogue 9b. Taken together, results of this study clearly validated the positive impact of the fluorine atom on the alkyl chain at the 4-position of benzothiadiazine dioxides on activity and metabolic stability.

Synthesis and pharmacological evaluation of a second generation of pyridothiadiazine 1,1-dioxides acting as AMPA potentiators.

Taking into account structure-activity relationships obtained with our previous series, new diversely substituted 1,2,4-pyridothiadiazine 1,1-dioxides were designed to obtain novel AMPA potentiators. The aim of this work was focused on the improvement of lipophilicity, which is well known as a critical parameter to obtain in vivo active central nervous system agents. For this purpose, two positions on the pyridine ring were privileged to insert selected groups. Among the synthesized compounds emerged 7-chloro-4-ethyl-3,4-dihydro-2H-pyrido[2,3-e]-[1,2,4]-thiadiazine 1,1-dioxide (12d), which was evaluated in two memory tests in Wistar rats and showed cognition enhancing effects after intraperitoneal injection at doses as low as 0.3mg/kg.

Design, synthesis, and pharmacology of novel 7-substituted 3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxides as positive allosteric modulators of AMPA receptors.

A series of 3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxides have been synthesized and evaluated as potentiators of AMPA receptors. Attention was paid to the impact of the substituent introduced at the 7-position of the heterocycle. The biological evaluation was achieved by measuring the AMPA current in rat cortex mRNA-injected Xenopus oocytes. The most potent compound, 4-ethyl-7-fluoro-3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxide (12a) was found to be active in an object recognition test in rats demonstrating cognition enhancing effects in vivo after oral administration.

Novel quinolinone-phosphonic acid AMPA antagonists devoid of nephrotoxicity.

We reported previously the synthesis and structure-activity relationships (SAR) in a series of 2-(1H)-oxoquinolines bearing different acidic functions in the 3-position. Exploiting these SAR, we were able to identify 6,7-dichloro-2-(1H)-oxoquinoline-3-phosphonic acid compound 3 (S 17625) as a potent, in vivo active AMPA antagonist. Unfortunately, during the course of the development, nephrotoxicity was manifest at therapeutically effective doses. Considering that some similitude exists between S 17625 and probenecid, a compound known to protect against the nephrotoxicity and/or slow the clearance of different drugs, we decided to synthesise some new analogues of S 17625 incorporating some of the salient features of probenecid. Replacement of the chlorine in position 6 by a sulfonylamine led to very potent AMPA antagonists endowed with good in vivo activity and lacking nephrotoxicity potential. Amongst the compounds evaluated, derivatives 7a and 7s appear to be the most promising and are currently evaluated in therapeutically relevant stroke models.