Amino-terminal isoforms of the human glycine transporter GlyT1 exhibit similar pharmacology.

Alternative promoter usage and mRNA precursor splicing produce three amino-terminal isoforms of the human glycine transporter type 1 (GlyT1). To enable discovery of pharmacological tools that might distinguish them, each of these isoforms was stably expressed in CHO-K1 cells and clonal isolates were generated by limiting dilution. Glycine uptake assays were validated for two lines for each isoform, one low and one high expressor. The data show a modest trend for lower potency against higher expressing lines. IC(50) values for reference GlyT1 inhibitors ALX-5407 (Allelix), (S)-13h (Merck), and SSR504734 (Sanofi-Synthelabo) were similar across isoforms. The greatest variation was observed for ALX-5407, and its IC(50) values across isoforms were still within one log unit of each other. Antipsychotics previously shown to be weak inhibitors of GlyT1 likewise had similar potency against all three isoforms. The cell lines validated here are tools for discovering inhibitors that might distinguish among GlyT1 isoforms.

Glycine transporter (GlyT1) inhibitors with reduced residence time increase prepulse inhibition without inducing hyperlocomotion in DBA/2 mice.

Inhibition of the glycine transporter type 1 (GlyT1) leading to potentiation of the glycine site (GlyB) on the N-methyl-d-aspartate (NMDA) receptor has been proposed as a novel therapeutic approach for schizophrenia. However, sarcosine-based GlyT1 inhibitors produce undesirable side effects including compulsive walking and respiratory distress. The influence of specific biochemical properties of GlyT1 inhibitors, such as mode of inhibition and residence time, on adverse effects is unknown. Two GlyT1 inhibitors that contain a sarcosine moiety, sarcosine and ALX-5407, and two compounds that do not contain a sarcosine moiety, Roche-7 and Merck (S)-13h, were evaluated for their potency, mode of inhibition, and target residence times in vitro, and modulation of prepulse inhibition (PPI) and locomotor activity in vivo. (S)-13h and sarcosine were competitive inhibitors while ALX-5407 and Roche-7 demonstrated mixed noncompetitive inhibition. Potency of GlyT1 inhibition (ALX-5407>(S)-13h>Roche-7≫sarcosine) did not correlate with residence time on GlyT1 (sarcosine=Roche-7≪(S)-13h

ALK mutants in the kinase domain exhibit altered kinase activity and differential sensitivity to small molecule ALK inhibitors.

Abnormal expression of constitutively active anaplastic lymphoma kinase (ALK) chimeric proteins in the pathogenesis of anaplastic large-cell lymphoma (ALCL) is well established. Recent studies with small molecule kinase inhibitors have provided solid proof-of-concept validation that inhibition of ALK is sufficient to attenuate the growth and proliferation of ALK (+) ALCL cells. In this study, several missense mutants of ALK in the phosphate anchor and gatekeeper regions were generated and their kinase activity was measured. NPM-ALK L182M, L182V, and L256M mutants displayed kinase activity in cells comparable to or higher than that of NPM-ALK wild type (WT) and rendered BaF3 cells into IL-3-independent growth, while NPM-ALK L182R, L256R, L256V, L256P, and L256Q displayed much weaker or little kinase activity in cells. Similar kinase activities were obtained with corresponding GST-ALK mutants with in vitro kinase assays. With regard to inhibitor response, NPM-ALK L182M and L182V exhibited sensitivity to a fused pyrrolocarbazole (FP)-derived ALK inhibitor comparable to that of NPM-ALK WT but were dramatically less sensitive to a diaminopyrimidine (DAP)-derived ALK inhibitor. On the other hand, NPM-ALK L256M exhibited >30-fold lower sensitivity to both FP-derived and DAP-derived ALK inhibitors. The growth inhibition and cytotoxicity of BaF3/NPM-ALK mutant cells induced by ALK inhibitors were consistent with inhibition of cellular NPM-ALK autophosphorylation. In a mouse survival model, treatment with the orally bioavailable DAP-ALK inhibitor substantially extended the survival of the mice inoculated with BaF3/NPM-ALK WT cells but not those inoculated with BaF3/NPM-ALK L256M cells. Binding of ALK inhibitors to ALK WT and mutants was analyzed using ALK homology models. In summary, several potential active ALK mutants were identified, and our data indicate that some of these mutants are resistant to select small molecule ALK inhibitors. Further characterization of these mutants may help to identify and develop potent ALK inhibitors active against both WT and resistant mutants of ALK.

Mixed-lineage kinase 1 and mixed-lineage kinase 3 subtype-selective dihydronaphthyl[3,4-a]pyrrolo[3,4-c]carbazole-5-ones: optimization, mixed-lineage kinase 1 crystallography, and oral in vivo activity in 1-methyl-4-phenyltetrahydropyridine models.

The optimization of the dihydronaphthyl[3,4-a]pyrrolo[3,4-c]carbazole-5-one R(2) and R(12) positions led to the identification of the first MLK1 and MLK3 subtype-selective inhibitors within the MLK family. Compounds 14 (CEP-5104) and 16 (CEP-6331) displayed good potency for MLK1 and MLK3 inhibition with a greater than 30- to 100-fold selectivity for related family members MLK2 and DLK. Compounds 14 and 16 were orally active in vivo in a mouse MPTP biochemical efficacy model that was comparable to the first-generation pan-MLK inhibitor 1 (CEP-1347). The MLK1 structure-activity relationships were supported by the first-reported X-ray crystal structure of MLK1 bound with 16.

Phosphoregulation of mixed-lineage kinase 1 activity by multiple phosphorylation in the activation loop.

Mixed-lineage kinase 1 (MLK1) is a mitogen-activated protein kinase kinase kinase capable of activating the c-Jun NH(2)-terminal kinase (JNK) pathway. Full-length MLK1 has 1104 amino acids and a domain structure identical to MLK2 and MLK3. Immunoblot and mass spectrometry show that MLK1 is threonine (and possibly serine) phosphorylated in or near the activation loop. A kinase-dead mutant is not, consistent with autophosphorylation. Mutation to alanine of any of the four serine or threonine residues in the activation loop reduces both the activity of the recombinant kinase domain and JNK pathway activation driven by full-length MLK1 expressed in mammalian cells. Furthermore, the gel mobility of the mutant MLK1s is closer to that of the kinase-dead than wild type, consistent with reduced phosphorylation. Thr312 is the key residue: MLK1[T312A] retains only basal activity (about 1-2% of wild type), and its gel mobility is indistinguishable from kinase-dead. Thr312 does not suffice, however; phosphorylation of multiple sites is necessary for full activation of MLK1. An activation mechanism consistent with these data involves phosphorylation of multiple sites in the activation loop, with phosphorylation of Thr312 required for full phosphorylation. This mechanism is broadly similar to that previously reported for MLK3 [Leung, I. W., and Lassam, N. (2001) J. Biol. Chem. 276, 1961-1967], but the key residue differs.