SPD 502: a water-soluble and in vivo long-lasting AMPA antagonist with neuroprotective activity

Accumulating preclinical data suggest that compounds that block the excitatory effect of glutamate on excitatory amino acid receptors may have neuroprotective effects and utility for the treatment of neurodegeneration after brain ischemia. In the present study, the in vitro and in vivo pharmacological properties of the novel glutamate antagonist SPD 502 [8-methyl-5(4-(N,N-dimethylsulfamoyl)phenyl)-6,7, 8,9,-tetrahydro-1H-pyrrolo[3,2-h]-isoquinoline-2, 3-dione-3-O-(4-hydroxybutyric acid-2-yl)oxime] are described. In binding studies, SPD 502 was shown to display selectivity for the [3H]alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-binding site (IC50 = 0.043 microM) compared with the [3H]kainate- (IC50 = 81 microM), [3H]cis-4-phosphonomethyl-2-piperidine carboxylic acid-(CGS 19755), and [3H]glycine-binding sites (IC50 > 30 microM) in rat cortical membranes. In an in vitro functional assay, SPD 502 blocked the AMPA-induced release of [3H]gamma-aminobutyric acid from cultured mouse cortical neurons in a competitive manner with an IC50 value of 0.23 microM. Furthermore, SPD 502 potently and selectively inhibited AMPA-induced currents in cortical neurons with an IC50 value of 0.15 microM. In in vivo electrophysiology, SPD 502 blocked AMPA-evoked spike activity in rat hippocampus after i.v. administration with an ED50 value of 6.1 mg/kg and with a duration of action of more than 1 h. Furthermore, SPD 502 increased the seizure threshold for electroshock-induced tonic seizures in mice at i.v doses of 40 mg/kg and higher. In the two-vessel occlusion model of transient forebrain ischemia in gerbils, SPD 502 (10 mg/kg bolus injection followed by a 10 mg/kg/h infusion for 2 h) resulted in a highly significant protection against the ischemia-induced damage in the hippocampal CA1 pyramidal neurons.

Characterization of the binding of [3H]NS 257, a novel competitive AMPA receptor antagonist, to rat brain membranes and brain sections

The binding of [3H]NS 257 (1,2,3,6,7,8-hexahydro-3-(hydroxyimino)-N,N-[3H]dimethyl-7-methyl- 2- oxobenzo[2,1-b:3,4-c']dipyrrole-5-sulfonamide) to rat cortical membranes was characterized in the absence and presence of thiocyanate. Specific [3H]NS 257 binding was saturable and reversible, and the stimulating effect of thiocyanate on binding was optimal at 100 mM. In the presence of thiocyanate [3H]NS 257 bound to a single population of binding sites with an affinity of 225 +/- 8 nM and a binding site density of 0.61 +/- 0.04 pmol/mg of original tissue. Thiocyanate increased the affinity of the binding site labeled by [3H]NS 257 for both alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) and L-glutamate by a factor of 20 and 5, respectively. However, the affinity of the agonist domoate and the antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(f)-quinoxaline (NBQX) was decreased in the presence of thiocyanate. Apparently, the affinities of antagonists as well as agonists for the AMPA receptor can be either increased or decreased by thiocyanate. The rank order of potency of the putative agonists quisqualate > AMPA > L-glutamate > domoate > kainate and of the antagonists NBQX > CNQX is consistent with the labeling of AMPA receptors. Autoradiographic studies showed that the distribution of [3H]NS 257 binding sites in rat brain was similar to that of [3H]AMPA binding sites. NS 257 is the first AMPA antagonist to be described showing an increased affinity for the AMPA receptor in the presence of thiocyanate.

NS 004--an activator of Ca(2+)-dependent K+ channels in cerebellar granule cells

The large-conductance Ca(2+)-dependent K+ channels or BK channels in cerebellar granule cells were studied by patch-clamp technique, and the effects on channel activity of the molecule NS 004 (1-(2-hydroxy-5-chlorophenyl)-5-trifluoromethyl-2- benzimidazolone) were investigated. The channels had a unit conductance of 187 pS, were blocked by charybdotoxin and activated by internal Ca2+. NS 004 (10-30 microM) significantly increased the single channel opening frequency as well as the mean open time. In whole-cell recordings the compound shifted the BK current-voltage relationship by up to 40 mV towards negative membrane potentials. NS 004 is an efficient BK channel opener, which may represent a novel approach to relaxation of neuronal cells expressing this type of K+ channel.

A novel non-NMDA receptor antagonist shows selective displacement of low-affinity [3H]kainate binding

5-Nitro-6,7,8,9-tetrahydrobenzo[G]indole-2,3-dione-3-oxime (NS-102), a new competitive glutamate receptor antagonist displaced binding to non-N-methyl-D-aspartate (non-NMDA) binding sites with no activity at the NMDA and strychnine-insensitive glycine binding sites. Under experimental conditions in which both high- and low-affinity sites were labelled, NS-102 only partially inhibited the binding of [3H]kainate. Studies of NS-102 displacement of high-affinity versus low-affinity [3H]kainate binding showed a high selectivity of NS-102 for the low-affinity [3H]kainate binding site (Ki = 0.6 microM) compared to the high-affinity [3H]kainate binding site (Ki > 10 microM). NS-102 was a relatively weak inhibitor of 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) binding (IC50 = 7.2 microM). NS-102 and related compounds with similar pharmacological profiles may become valuable tools in the characterization of the functional importance of the low-affinity [3H]kainate binding site.

Synthesis, tissue distribution and cytostatic properties of two new daunorubicin derivatives of 2-thiouracil containing a guanidine bridge

In further attempts to utilize the affinity of 2-thiouracil for melanin-producing tissues in the design of drugs active against malignant melanomas, guanidine-bridged adducts of the anthraquinone drug daunorubicin (1a) with 2-thiouracil were prepared (Scheme 3). The expected adduct (4), and a by-product in its preparation (5) (Scheme 3), were inactive against murine melanoma, in vivo, and did not show affinity for melanin-producing tissues. They were efficient DNA intercalating agents, but were much less cytostatic than daunorubicin against Cloudman melanoma, and were inactive, in vitro, against human cervical carcinoma MS 751. The coupling chemistry employed may have application in current attempts to effect binding of drugs to high molecular weight targeting antigens.

Affinity therapeutics. 1. Selective incorporation of 2-thiouracil derivatives in murine melanomas. Cytostatic activity of 2-thiouracil arotinoids, 2-thiouracil retinoids, arotinoids, and retinoids

The incorporation of 2-[35S]thiouracil and two of its derivatives into murine melanomas, in vivo, was studied. It was confirmed [J. R. Whittaker, J. Biol. Chem., 246, 6217--6226 (1971)] that 2-thiouracil has a marked affinity for melanin-producing tissue and that an affinity for such tissue could be sustained by 5-substituted 2-thiouracils. A series of derivatives of arotinoids and retinoids, with or without a 2-thiouracil group as a potential carrier to obtain affinity for melanomas, was examined for cytostatic activity, in vitro. None of these showed significant activity against murine melanomas.