The protein kinase Cβ-selective inhibitor, enzastaurin, attenuates amphetamine-stimulated locomotor activity and self-administration behaviors in rats

RATIONALE

Pathological amphetamine (AMPH) use is a serious public health concern with no pharmacological treatment options. Protein kinase Cβ (PKCβ) has been implicated in the mechanism of action of AMPH, such that inhibition of PKCβ attenuates AMPH-stimulated dopamine efflux in vivo. With this in mind, inhibition of PKCβ may be a viable therapeutic target for AMPH use disorder.

OBJECTIVE

The purpose of this study is to demonstrate that selective pharmacological inhibition of PKCβ alters AMPH-stimulated behaviors in rats.

METHODS

Rats were administered intracerebroventricular (i.c.v.) injections of the PKCβ-selective inhibitor enzastaurin 0.5, 3, 6, or 18 h before evaluating AMPH-stimulated locomotion (0.32-3.2 mg/kg). Rats were trained to make responses for different doses of AMPH infusions or sucrose under a fixed ratio 5 schedule of reinforcement, and the effects of enzastaurin pretreatment 3 or 18 h prior to a self-administration session were determined. Also, the effect of enzastaurin on AMPH-stimulated PKC activity in the ventral striatum was evaluated.

RESULTS

A large dose of enzastaurin (1 nmol) decreased AMPH-stimulated locomotor activity 0.5 h following enzastaurin administration. Small doses of enzastaurin (10-30 pmol) attenuated AMPH-stimulated locomotor activity and shifted the AMPH dose-effect curve to the right following an 18-h pretreatment. Rats pretreated with enzastaurin 18 h, but not 3, prior to a self-administration session showed a decrease in the number of responses for AMPH, shifted the ascending limb of the amphetamine dose effect curve, and produced no change in responses for sucrose. AMPH-stimulated PKC activity was decreased following a 0.5- or 18-h pretreatment, but not a 3-h pretreatment of enzastaurin.

CONCLUSIONS

These results demonstrate that inhibition of PKCβ will decrease AMPH-stimulated behaviors and neurobiological changes and suggest that PKCβ is potentially a viable target for AMPH use disorder.

Disruption of pre-B-cell receptor signaling jams the WNT/β-catenin pathway and induces cell death in B-cell acute lymphoblastic leukemia cell lines

Targeting components of the B-cell receptor (BCR) pathway have dramatically improved clinical outcomes in a variety of B-cell malignancies. Despite the well-documented pathogenic role of BCR precursor (pre-BCR) pathway in B-cell acute lymphoblastic leukemia (B-ALL), there is limited available data of therapies that aim to disrupt this pathway. To investigate the role of protein kinase Cβ (PKCβ), a crucial mediator of BCR and pre-BCR signaling, in B-ALL survival, we studied the activity of the PKCβ selective inhibitor enzastaurin (ENZ) in seven B-ALL cell lines. Treatment with ENZ resulted in a dose- and time-dependent growth inhibition in all cell lines with a relatively higher efficacy in pro-B ALL with translocation t(4;11)(q21;q23). The mechanism of growth inhibition was by apoptotic induction and cell cycle arrest. A rapid reduction in phosphorylation of AKT and its downstream target glycogen synthase kinase 3β (GSK3β) were observed at 30min after treatment and remaining for 48h. The reduction in GSK3β phosphorylation was associated with a paradoxical accumulation of β-catenin, which was due to a transient loss of β-catenin phosphorylation at ser33-37. In addition, accumulation of β-catenin was associated with downregulation of c-Myc, upregulatiuon of c-Jun, and a subsequent protective effect on the tumor suppressor p73. Data in this paper were presented in part at 2012 American Society of Hematology Annual Meeting, abstract 1350.