RPR 119990, a novel alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid antagonist: synthesis, pharmacological properties, and activity in an animal model of amyotrophic lateral sclerosis.

Alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptor antagonists are of potential interest for the treatment of certain acute and chronic neurodegenerative diseases, including amyotrophic lateral sclerosis. Here, we describe the synthesis and pharmacological properties of 9-carboxymethyl-4-oxo-5H,10H-imidazo[1,2-a]indeno[1,2-e]pyrazin-2-phosphonic acid (RPR 119990). The compound displaced [3H]AMPA from rat cortex membranes with a K(i) of 107 nM. In oocytes expressing human recombinant AMPA receptors, RPR 119990 depressed ion flux with a K(B) of 71 nM. The antagonist properties of this compound were confirmed on rat native AMPA receptors in cerebella granule neurons in culture and in hippocampal slices where it antagonized electrophysiological responses with IC50 values of 50 and 93 nM, respectively. RPR 119990 antagonized hippocampal evoked responses in vivo, demonstrating brain penetration at active concentrations. RPR 119990 is a potent anticonvulsant in the supramaximal electroshock in the mouse with an ED50 of 2.3 mg/kg 1 h post s.c. administration, giving it a workably long action. Pharmacokinetic studies show good passage into the plasma after subcutaneous administration, whereas brain penetration is low but with slow elimination. This compound was found active in a transgenic mouse model of familial amyotrophic lateral sclerosis (SOD1-G93A) where it was able to improve grip muscle strength and glutamate uptake from spinal synaptosomal preparations, and prolong survival with a daily dose of 3 mg/kg s.c.

Indeno[1,2-b]pyrazin-2,3-diones: a new class of antagonists at the glycine site of the NMDA receptor with potent in vivo activity.

Indeno¿1,2-bpyrazin-2,3-diones have been identified as a novel series of potent ligands on the glycine site of the NMDA receptor. To improve their in vivo activities, an acetic acid-type side chain was introduced to the 5-position, giving water-soluble compounds when formulated as the sodium salt (>10 mg/mL). Introduction of a chlorine atom in the 8-position led to a dramatic improvement of anticonvulsant activity and this was surprising since this change did not improve binding affinity. A plausible explanation is a reduced recognition by a Na(+),K(+)-ATPase active transport system responsible for the excretion of these compounds from the brain and kidney. This promising new chemical series led to the optically active isomer (-)-10i (RPR 118723), a glycine/NMDA antagonist with nanomolar binding affinity and in vivo activity in animal model of convulsions and electrophysiology at doses in the range of 2-3 mg/kg following iv administration.

Substance P-evoked calcium mobilization and ionic current activation in the human astrocytoma cell line U 373 MG: pharmacological characterization.

In the human astrocytoma cell line U 373 MG, application of substance P (SP) leads to a transient increase in cytosolic calcium concentration and to a biphasic current response in voltage-clamped cells. Using these two functional assays we have characterized pharmacologically the SP response in U 373 MG cells. SP and [L-Pro9]SP displayed high potencies in both assays with EC50 values of 2.5 x 10(-9) M and 1 x 10(-9) M on calcium responses and 1 x 10(-9) M and 5 x 10(-9) M on ion current responses, respectively. The high potency of SP and [L-Pro9]SP as well as the low potency of [Lys5,MeLeu9,N-Leu10]neurokinin A(4-10) and the inactivity of senktide demonstrate the NK1-type pharmacology of these responses. Furthermore, the NK1 antagonists (+/-)-CP 96,345, its chloro analogue, (+/-)-cis-3-(2-chlorobenzylamino)-2-benzhydrylquinuclidine, and RP 67580 were potent antagonists of both SP responses. For the calcium mobilization induced by SP (10(-7) M), the IC50 values for the three antagonists were 4 x 10(-10) M, 4 x 10(-9) M, and 9 x 10(-9) M, respectively, whereas on the current response evoked by SP (10(-8) M), the IC50 values were 8 x 10(-9) M, 2.4 x 10(-8) M, and 1.2 x 10(-7) M, respectively. Despite differences in the absolute IC50 values obtained with both techniques, the relative potencies of the three antagonists correlate fairly well.(ABSTRACT TRUNCATED AT 250 WORDS)

Potassium channel openers act through an activation of ATP-sensitive K+ channels in guinea-pig cardiac myocytes.

In a previous article (Escande et al. 1988a), we have shown that cromakalim (BRL 34915), a potassium channel opener (PCO), is a potent activator of ATP-sensitive K+ channels in cardiac cells. In the present article, the influence on K+ channels of two other potassium channel openers chemically unrelated to cromakalim, RP 49356 and pinacidil, has been investigated in patch-clamped isolated cardiac myocytes. In the whole-cell configuration, K+ currents were recorded in the presence of 50 microM TTX and 3 microM nitrendipine or 3 mM cobalt. Like cromakalim, RP 49356 or pinacidil activated a time-independent outward current at 33-35 degrees C but not at 19-21 degrees C, which showed little voltage-dependency in the potential range -60 to +60 mV. Its amplitude was a function of the agonist concentration, e.g. it was 2.1 +/- 0.4 nA at +60 mV with 30 microM RP 49356 and 4.3 +/- 0.8 nA with 300 microM. In control conditions, glibenclamide, a blocker of K+-ATP channels in pancreatic and heart cells, affected neither the inward rectifier, iK1, nor the delayed K+ current, iK. At 3 microM, glibenclamide fully prevented the effects of 300 microM RP 49356 or pinacidil. At lower concentrations, glibenclamide partially counteracted the activation by PCOs of a K+ current. In the cell-attached configuration, externally applied RP 49356 or pinacidil caused opening of large channels which reversed around O mV in a high K+ external medium. In inside-out patches, both RP 49356 or pinacidil activated K+-ATP channels by increasing the time period for which the channels remained in the open state. It is concluded that, like cromakalim, RP 49356 and pinacidil are potent activators of K+-ATP channels in cardiac myocytes.