Treatment with HC-070, a potent inhibitor of TRPC4 and TRPC5, leads to anxiolytic and antidepressant effects in mice.

BACKGROUND: Forty million adults in the US suffer from anxiety disorders, making these the most common forms of mental illness. Transient receptor potential channel canonical subfamily (TRPC) members 4 and 5 are non-selective cation channels highly expressed in regions of the cortex and amygdala, areas thought to be important in regulating anxiety. Previous work with null mice suggests that inhibition of TRPC4 and TRPC5 may have anxiolytic effects. HC-070 IN VITRO: To assess the potential of TRPC4/5 inhibitors as an avenue for treatment, we invented a highly potent, small molecule antagonist of TRPC4 and TRPC5 which we call HC-070. HC-070 inhibits recombinant TRPC4 and TRPC5 homomultimers in heterologous expression systems with nanomolar potency. It also inhibits TRPC1/5 and TRPC1/4 heteromultimers with similar potency and reduces responses evoked by cholecystokinin tetrapeptide (CCK-4) in the amygdala. The compound is >400-fold selective over a wide range of molecular targets including ion channels, receptors, and kinases. HC-070 IN VIVO: Upon oral dosing in mice, HC-070 achieves exposure levels in the brain and plasma deemed sufficient to test behavioral activity. Treatment with HC-070 attenuates the anxiogenic effect of CCK-4 in the elevated plus maze (EPM). The compound recapitulates the phenotype observed in both null TRPC4 and TRPC5 mice in a standard EPM. Anxiolytic and anti-depressant effects of HC-070 are also observed in pharmacological in vivo tests including marble burying, tail suspension and forced swim. Furthermore, HC-070 ameliorates the increased fear memory induced by chronic social stress. A careful evaluation of the pharmacokinetic-pharmacodynamic relationship reveals that substantial efficacy is observed at unbound brain levels similar to, or even lower than, the 50% inhibitory concentration (IC50) recorded in vitro, increasing confidence that the observed effects are indeed mediated by TRPC4 and/or TRPC5 inhibition. Together, this experimental data set introduces a novel, high quality, small molecule antagonist of TRPC4 and TRPC5 containing channels and supports the targeting of TRPC4 and TRPC5 channels as a new mechanism of action for the treatment of psychiatric symptoms.

alpha1-Adrenergic modulation of synaptic input to Purkinje neurons in rat cerebellar brain slices.

The inhibitory activity in the cerebellar network, as investigated in acute brain slices from 14-20 days old rats, is modulated by alpha1-adrenergic stimulation. The specific alpha1-adrenoceptor agonist phenylephrine (PhE; 10 microM) or the alpha-adrenoceptor agonist 6-fluoronoradrenaline (10 microM) increases the frequency and the amplitude of spontaneous postsynaptic currents (sPSC) in Purkinje neurons. The effects are sensitive to the alpha1-adrenoceptor antagonists prazosin (30 microM) and phentolamine (10 microM). The PhE-induced augmentation is suppressed when phospholipase C is blocked by preincubation with U73122 (10 microM) but is not affected by inhibition of protein kinases with H7 (10 microM) or GF109203X (10 microM). Involvement of intracellular Ca(2+) stores was shown by a reduced PhE effect after blocking of SERCA pumps with cyclopiazonic acid (30 microM) and thapsigargin (1 microM). The persistence of the PhE effect on the frequency of miniature postsynaptic currents, as recorded in presence of tetrodotoxin, indicates a presynaptic localization of the alpha1-adrenoceptors. A block of voltage-gated Ca(2+) channels with nifedipine, verapamil, or omega-conotoxin MVIIC did not suppress the PhE-induced increase of the frequency and amplitude of sPSC. The results suggest that alpha1-adrenoceptors at presynaptic terminals mediate an increase of the spontaneous synaptic inhibition of Purkinje neurons in the cerebellar cortex via release of Ca(2+) from intracellular stores.