Glutamate carboxypeptidase II (GCPII) inhibitor displays anti-glutamate and anti-cocaine effects in an invertebrate assay

Nicotine-induced C-shape movements in planarians are reduced by antinociceptive drugs: Implications for pain in planarian paroxysm etiology?

C-shapes are stereotyped movements in planarians that are elicited by diverse stimuli (e.g. acidity, excitatory neurotransmitters, psychostimulants, and pro-convulsants). Muscle contraction and seizure contribute to the expression of C-shape movements, but a causative role for pain is understudied and unclear. Here, using nicotine-induced C-shapes as the endpoint, we tested the efficacy of three classes of antinociceptive compounds - an opioid, NSAID (non-steroidal anti-inflammatory drug), and transient receptor potential ankyrin 1 (TRPA1) channel antagonist. For comparison we also tested effects of a neuromuscular blocker. Nicotine (0.1-10 mM) concentration-dependently increased C-shapes. DAMGO (1-10 µM), a selective µ-opioid agonist, inhibited nicotine (5 mM)-induced C-shapes. Naloxone (0.1-10 µM), an opioid receptor antagonist, prevented the DAMGO (1 µM)-induced reduction of nicotine (5 mM)-evoked C-shapes, suggesting an opioid receptor mechanism. C-shapes induced by nicotine (5 mM) were also reduced by meloxicam (10-100 µM), a NSAID; HC 030,031 (1-10 µM), a TRPA1 antagonist; and pancuronium (10-100 µM), a neuromuscular blocker. Evidence that nicotine-induced C-shapes are reduced by antinociceptive drugs from different classes, and require opioid receptor and TRPA1 channel activation, suggest C-shape etiology involves a pain component.

The therapeutic and diagnostic potential of the prostate specific membrane antigen/glutamate carboxypeptidase II (PSMA/GCPII) in cancer and neurological disease

Prostate specific membrane antigen (PSMA) otherwise known as glutamate carboxypeptidase II (GCPII) is a membrane bound protein that is highly expressed in prostate cancer and in the neovasculature of a wide variety of tumours including glioblastomas, breast and bladder cancers. This protein is also involved in a variety of neurological diseases including schizophrenia and ALS. In recent years, there has been a surge in the development of both diagnostics and therapeutics that take advantage of the expression and activity of PSMA/GCPII. These include gene therapy, immunotherapy, chemotherapy and radiotherapy. In this review, we discuss the biological roles that PSMA/GCPII plays, both in normal and diseased tissues, and the current therapies exploiting its activity that are at the preclinical stage. We conclude by giving an expert opinion on the future direction of PSMA/GCPII based therapies and diagnostics and hurdles that need to be overcome to make them effective and viable.

Riluzole attenuates the effects of chemoconvulsants acting on glutamatergic and GABAergic neurotransmission in the planarian Dugesia tigrina

Planarians, the non-parasitic flatworms, display dose-dependent, distinct (C-like and corkscrew-like) hyperkinesias upon exposure to 0.001-10 mM aqueous solutions of glutamatergic agonists (L-glutamate and N-methyl-D-aspartate (NMDA)) and 0.001-5 mM concentrations of the glutamate decarboxylase (GAD) inhibitor (semicarbazide). In the planarian seizure-like activity (PSLA) experiments the three chemoconvulsants displayed the following order of potency (EC50): L-glutamate (0.6mM)>NMDA (1.4 mM)>semicarbazide (4.5mM). Planarian hyperkinesias behavior counting experiments also revealed that riluzole (0.001 to 1mM), an anti-convulsive agent, displayed no significant behavioral activity by itself, but attenuated hyperkinesias elicited by the three chemoconvulsants targeting either glutamatergic or GABAergic neurotransmission with the following order of potency (IC50): NMDA (44.7 µM)>semicarbazide (88.3 µM)>L-glutamate (160 µM). Further, (+)-MK-801, a specific NMDA antagonist, alleviated 3mM NMDA (47%) or 3mM L-glutamate (27%) induced planarian hyperkinesias. The results provide pharmacological evidence for the presence of glutamatergic receptor-like and semicarbazide sensitive functional GAD enzyme-like proteins in planaria in addition to demonstrating, for the first time, the anti-convulsive effects of riluzole in an invertebrate model. High performance liquid chromatography coupled with fluorescence detection (HPLC-F) analysis performed on planarian extracts post no drug treatment (control) or treatment with 3mM semicarbazide, combination of 3mM semicarbazide and 0.1 mM riluzole, or 0.1 mM riluzole revealed that 3 mM semicarbazide induced 35% decrease in the GABA levels and a combination of 3mM semicarbazide and 0.1 mM riluzole induced 42% decrease in glutamate levels with respect to the control group.

In vivo comparison of harmine efficacy against psychostimulants: preferential inhibition of the cocaine response through a glutamatergic mechanism

Harmine is a β-carboline compound that targets glutamatergic, monoaminergic, and GABAergic pathways underlying drug addiction. We compared the efficacy of harmine against different psychoactive drugs using an invertebrate (planarian) assay designed to quantify 'C-shape' responses. Harmine itself (0.01-10 μM) did not produce C-shapes. However, when applied over the same concentration range, harmine significantly inhibited C-shapes elicited by cocaine, with a concentration of 0.1 μM producing almost 90% inhibition. Consistent with its putative actions, harmine produced a similar, though less efficacious, inhibition of C-shapes elicited by the substituted amphetamines methamphetamine and mephedrone (4-methylmethcathinone) but was much less effective against nicotine. When tested in the presence of the glutamate transporter inhibitor dihydrokainate (DHK) (0.1, 1 μM), harmine (0.1 μM) efficacy against cocaine-induced C-shapes was significantly reduced. Harmine also attenuated C-shapes elicited by N-methyl-d-aspartate (NMDA) and by glutamate itself. The present data suggest that harmine displays preferential efficacy against different addictive substances (cocaine>amphetamines>nicotine) and, at least for cocaine, is dependent on the glutamate system.