186040-40-4Relevant academic research and scientific papers
Effect of plasma protein binding-on in vivo activity and brain penetration of glycine/NMDA receptor antagonists
Rowley, Michael,Kulagowski, Janusz J.,Watt, Alan P.,Rathbone, Denise,Stevenson, Graeme I.,Carling, Robert W.,Baker, Raymond,Marshall, George R.,Kemp, John A.,Foster, Alan C.,Grimwood, Sarah,Hargreaves, Richard,Hurley, Catherine,Saywell, Kay L.,Tricklebank, Mark D.,Leeson, Paul D.
, p. 4053 - 4068 (2007/10/03)
A major issue in designing drugs as antagonists at the glycine site of the NMDA receptor has been to achieve good in vivo activity. A series of 4- hydroxyquinolone glycine antagonists was found to be active in the DBA/2 mouse anticonvulsant assay, but improvements in in vitro affinity were not mirrored by corresponding increases in anticonvulsant activity. Here we show that binding of the compounds to plasma protein limits their brain penetration. Relative binding to the major plasma protein, albumin, was measured in two different ways: by a radioligand binding experiment or using an HPLC assay, for a wide structural range of glycine/NMDA site ligands. These measures of plasma protein binding correlate well (r = 0.84), and the HPLC assay has been used extensively to quantify plasma protein binding. For the 4-hydroxyquinolone series, binding to plasma protein correlates (r = 0.92) with log P (octanol/pH 7.4 buffer) over a range of log P values from 0 to 5. The anticonvulsant activity increases with in vitro affinity, but the slope of a plot of pED50 versus pIC50 is low (0.40); taking plasma protein binding into account in this plot increases the slope to 0.60. This shows that binding to albumin in plasma reduces the amount of compound free to diffuse across the blood-brain barrier. Further evidence comes from three other experiments: (a) Direct measurements of brain/blood ratios for three compounds (2, 16, 26) show the ratio decreases with increasing log P. (b) Warfarin, which compotes for albumin binding sites dose-dependently, decreased the ED50 of 26 for protection against seizures induced by NMDLA. (c) Direct measurements of brain penetration using an in situ brain perfusion model in rat to measure the amount of drug crossing the blood-brain barrier showed that compounds 2, 26, and 32 penetrate the brain well in the absence of plasma protein, but this is greatly reduced when the drug is delivered in plasma. In the 4-hydroxyquinolones glycine site binding affinity increases with lipophilicity of the 3-substituent up to a maximum at a log P around 3, then does not improve further. When combined with increasing protein binding, this gives a parabolic relationship between predicted in vivo activity and log P, with a maximum log P value of 2.39. Finally, the plasma protein binding studies have been extended to other series of glycine site antagonists, and it is shown that for a given log P these have similar protein binding to the 4-hydroxyquinolones, except for compounds that are not acidic. The results have implications for the design of novel glycine site antagonists, and it is suggested that it is necessary to either keep log P low or pK(a) high to obtain good central nervous system activity.
4-Substituted-3-phenylquinolin-2(1H)-ones: Acidic and nonacidic glycine site N-methyl-D-aspartate antagonists with in vivo activity
Carling, Robert W.,Leeson, Paul D.,Moore, Kevin W.,Moyes, Christopher R.,Duncton, Matthew,Hudson, Martin L.,Baker, Raymond,Foster, Alan C.,Grimwood, Sarah,Kemp, John A.,Marshall, George R.,Tricklebank, Mark D.,Saywell, Kay L.
, p. 754 - 765 (2007/10/03)
4-Substituted-3-phenylquinolin-2(1H)-ones have been synthesized and evaluated in vitro for antagonist activity at the glycine sits on the NMDA (N-methyl-D-aspartate) receptor and in vivo for anticonvulsant activity in the DBA/2 strain of mouse in an audiogenic seizure model. 4-Amino-3- phenylquinolin-2(1H)-one (3) is 40-fold lower in binding affinity but only 4- fold weaker as an anticonvulsant than the acidic 4-hydroxy compound 1. Methylsulfonylation at the 4-position of 3 gives an acidic compound (6, pK(a) = 6.0) where affinity is fully restored but in vivo potency is significantly reduced (Table 1). Methylation at the 4-position of 1 to give 18 results in the abolition of measurable affinity, but the attachment of neutral hydrogen bond-accepting groups to the methyl group of 18 produces compounds with comparable in vitro and in vivo activity to 1 (e.g., 23 and 28, Table 2). Replacement of the 4-hydroxy group of 1 with an ethyl group abolishes activity (42), but again, incorporation of neutral hydrogen bond acceptors to the terminal carbon atom restores affinity (e.g., 36, 39, and 40, Table 3). Replacement of the 4-hydroxy group of the high-affinity compound 2 with an amino group produces a compound with 200-fold reduced affinity (43, IC50 = 0.42 μM, Table 4) which is nevertheless still 10-fold higher in affinity than 3. The results in this paper indicate that anionic functionality is not an absolute requirement for good affinity at the glycine/NMDA site and provide compelling evidence for the existence of a ligand/receptor hydrogen bond interaction between an acceptor attached to the 4-position of the ligand and a hydrogen bond donor attached to the receptor.
