Identification of tetracycline combinations as EphB1 tyrosine kinase inhibitors for treatment of neuropathic pain.

Previous studies have demonstrated that the synaptic EphB1 receptor tyrosine kinase is a major mediator of neuropathic pain, suggesting that targeting the activity of this receptor might be a viable therapeutic option. Therefore, we set out to determine if any FDA-approved drugs can act as inhibitors of the EphB1 intracellular catalytic domain. An in silico screen was first used to identify a number of tetracycline antibiotics which demonstrated potential docking to the ATP-binding catalytic domain of EphB1. Kinase assays showed that demeclocycline, chlortetracycline, and minocycline inhibit EphB1 kinase activity at low micromolar concentrations. In addition, we cocrystallized chlortetracycline and EphB1 receptor, which confirmed its binding to the ATP-binding domain. Finally, in vivo administration of the three-tetracycline combination inhibited the phosphorylation of EphB1 in the brain, spinal cord, and dorsal root ganglion (DRG) and effectively blocked neuropathic pain in mice. These results indicate that demeclocycline, chlortetracycline, and minocycline can be repurposed for treatment of neuropathic pain and potentially for other indications that would benefit from inhibition of EphB1 receptor kinase activity.

A Chemical-Genetic Approach to Generate Selective Covalent Inhibitors of Protein Kinases.

Although a previously developed bump-hole approach has proven powerful in generating specific inhibitors for mapping functions of protein kinases, its application is limited by the intolerance of the large-to-small mutation by certain kinases and the inability to control two kinases separately in the same cells. Herein, we describe the development of an alternative chemical-genetic approach to overcome these limitations. Our approach features the use of an engineered cysteine residue at a particular position as a reactive feature to sensitize a kinase of interest to selective covalent blockade by electrophilic inhibitors and is thus termed the Ele-Cys approach. We successfully applied the Ele-Cys approach to identify selective covalent inhibitors of a receptor tyrosine kinase EphB1 and solved cocrystal structures to determine the mode of covalent binding. Importantly, the Ele-Cys and bump-hole approaches afforded orthogonal inhibition of two distinct kinases in the cell, opening the door to their combined use in the study of multikinase signaling pathways.

Spinal ephrinB/EphB signalling contributed to remifentanil-induced hyperalgesia via NMDA receptor.

BACKGROUND: One of the major unresolved issues in treating pain is the paradoxical hyperalgesia produced by opiates, and accumulating evidence implicate that EphBs receptors and ephrinBs ligands are involved in mediation of spinal nociceptive information and central sensitization, but the manner in which ephrinB/EphB signalling acts on spinal nociceptive information networks to produce hyperalgesia remains enigmatic. The objective of this research was to investigate the role of ephrinB/EphB signalling in remifentanil-induced hyperalgesia (RIH) and its downstream effector. METHODS: We characterized the remifentanil-induced pain behaviours by evaluating thermal hyperalgesia and mechanical allodynia in a rat hind paw incisional model. Protein expression of EphB1 receptor and ephrinB1 ligand in spinal dorsal horn cord was determined by Western blotting, and Fos was determined by immunohistochemistry assay, respectively. To figure out the manner in which ephrinB/EphB signalling acts with N-methyl-d-aspartic acid (NMDA) receptor, we used MK-801, an antagonist of NMDA receptor, trying to suppressed the hyperalgesia induced by ephrinB1-Fc, an agonist of ephrinB/EphB. RESULTS: Continuing infusion of remifentanil produced a thermal hyperalgesia and mechanical allodynia, which was accompanied with increased protein expression of spinal-level EphB1 receptor, ephrinB1 ligand and Fos; what appeared above was suppressed by pretreatment with EphB1-Fc, an antagonist of ephrinB/EphB or MK-801, and increased pain behaviours induced by intrathecal injection of ephrinB1-Fc, an agonist of ephrinB/EphB, were suppressed by MK-801. CONCLUSIONS: Our findings indicated that ephrinB/EphB signalling is involved in RIH. EphrinB/EphB signalling might be the upstream of NMDA receptor.

Blocking EphB1 receptor forward signaling in spinal cord relieves bone cancer pain and rescues analgesic effect of morphine treatment in rodents.

Treating bone cancer pain continues to be a clinical challenge and underlying mechanisms of bone cancer pain remain elusive. Here, we report that EphB1 receptor forward signaling in the spinal cord is critical to the development of bone cancer pain and morphine tolerance in treating bone cancer pain. Tibia bone cavity tumor cell implantation (TCI) produces bone cancer-related thermal hyperalgesia, mechanical allodynia, spontaneous and movement-evoked pain behaviors, and bone destruction. Production and persistence of these pain behaviors are well correlated with TCI-induced upregulation of EphB1 receptor and its ligand ephrinB2 in the dorsal horn and primary sensory neurons. Spinal administration of an EphB1 receptor blocking reagent EphB2-Fc prevents and reverses bone cancer pain behaviors and the associated induction of c-Fos and activation of astrocytes and microglial cells, NR1 and NR2B receptors, Src within the N-methyl-D-aspartate receptor complex, and the subsequent Ca(2+)-dependent signals. The exogenous ligand ephrinB2-Fc upregulates level of phosphorylation of NR1 and NR2B receptors depending on the activation of EphB1 receptor. Spinal administration of EphB2-Fc and ephrinB2-Fc induces downregulation of EphB1 and ephrinB2, respectively, accompanied with increased activity of matrix metalloproteinase (MMP)-2/9. Blocking MMP-2 or MMP-9 reverses EphB1-Fc treatment-induced downregulation of EphB1 receptor. In addition, spinal blocking or targeted mutation of EphB1 receptor reverses morphine tolerance in treating bone cancer pain in rats and defensive pain in mice. These findings show a critical mechanism underlying the pathogenesis of bone cancer pain and suggest a potential target for treating bone cancer pain and improving analgesic effect of morphine clinically.

Involvement of EphB1 receptor/ephrinB1 ligand in bone cancer pain.

In prior studies, Eph/ephrin system was demonstrated to be involved in inflammatory and neuropathic pain modulation. The present study was to investigate whether the spinal Eph/ephrin signaling was involved in modulation of spinal inflammatory cytokines in bone cancer pain (BCP) of rats. BCP was induced by intra-tibial inoculation of Walker 256 mammary gland carcinoma cells. The expressions of EphB1/ephrinB1 in spinal cord (SC) and dorsal root ganglia (DRG) were determined. At 16 days post inoculation, the pain relieving effect and the mRNA levels of inflammatory cytokines were detected after intrathecal administration of EphB1-Fc (blocker of EphB1 receptor, 10µg). The results showed that the EphB1/ephrinB1 expression was significantly increased in SC, but ephrinB1 was decreased in DRG after Walker 256 inoculation. The mechanical allodynia induced by bone cancer was significantly alleviated by intrathecal administration of EphB1-Fc. Furthermore, the RT-PCR analysis showed that the mRNA levels of IL-1ß, IL-6 and TNF-α were significantly increased at 16 days post Walker 256 inoculation and were significantly suppressed by intrathecal administration of EphB1-Fc in SC. We concluded that Eph/ephrin might be involved in the maintenance of mechanical allodynia, via modulating the expression of spinal inflammatory cytokines, in the present rat model of BCP. This study suggested that Eph/ephrin signaling would be a potential target for the treatment of BCP.