Selective Blockade of HCN1/HCN2 Channels as a Potential Pharmacological Strategy Against Pain

Abstract

A prominent role of hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels has been suggested based on their expression and (dys)function in dorsal root ganglion (DRG) neurons, being likely involved in peripheral nociception. Using HCN blockers as antinociceptive drugs is prevented by the widespread distribution of these channels. However, tissue-specific expression of HCN isoforms varies significantly, HCN1 and HCN2 being considered as major players in DRG excitability. We characterized the pharmacological effect of a novel compound, MEL55A, able to block selectively HCN1/HCN2 isoforms, on DRG neuron excitability in-vitro and for its antiallodynic properties in-vivo. HEK293 cells expressing HCN1, HCN2, or HCN4 isoforms were used to verify drug selectivity. The pharmacological profile of MEL55A was tested on mouse DRG neurons by patch-clamp recordings, and in-vivo in oxaliplatin-induced neuropathy by means of thermal hypersensitivity. Results were compared to the non-isoform-selective drug, ivabradine. MEL55A showed a marked preference toward HCN1 and HCN2 isoforms expressed in HEK293, with respect to HCN4. In cultured DRG, MEL55A reduced Ih amplitude, both in basic conditions and after stimulation by forskolin, and cell excitability, its effect being quantitatively similar to that observed with ivabradine. MEL55A was able to relieve chemotherapy-induced neuropathic pain. In conclusion, selective blockade of HCN1/HCN2 channels, over HCN4 isoform, was able to modulate electrophysiological properties of DRG neurons similarly to that reported for classical Ih blockers, ivabradine, resulting in a pain-relieving activity. The availability of small molecules with selectivity toward HCN channel isoforms involved in nociception might represent a safe and effective strategy against chronic pain.

Characterization in Dual Activation by Oxaliplatin, a Platinum-Based Chemotherapeutic Agent of Hyperpolarization-Activated Cation and Electroporation-Induced Currents

“…As HCN2, HCN3, or mixed HCN2 + HCN3 channels are functionally expressed in GH 3 cells [24], OXAL-induced stimulation of I h in native cells does not tend to be isoform specific, although our experimental results showed that OXAL could modify the amplitude and gating of I h in GH 3 and R1220 cells. Because of the importance of I h (i.e., HCNx-encoded currents) in contributing to excitability and automaticity of electrically excitable cells [18,22,28,38,40,50], findings from the present results could provide novel insights into electrophysiological and pharmacological properties of OXAL or other structurally related compounds [19,20].…”

“…For example, OXAL has been demonstrated to suppress different types of voltage-gated K + or Na + currents in various preparations, such as myelinated axons, sciatic-nerve preparations, and motoneuron-like cells [11,[13][14][15][16]. Of interest, this agent was also recently reported to activate I h in isolated dorsal root ganglion neurons, and this action is thought to be implicated in its modifications of pain sensation [17][18][19][20].…”

“…Generation of HCN1-, HCN2-, and HCN4-deficient mice has highlighted the important role of these channels in regulation of pacemaker activity [26,29]. Of interest, previous reports have shown the ability of either MEL55A, an inhibitor of I h , or dexmedetomidine to ameliorate OXAL-induced pain sensation [18,19,30].…”

Inhibitory Effective Perturbations of Cilobradine (DK-AH269), A Blocker of HCN Channels, on the Amplitude and Gating of Both Hyperpolarization-Activated Cation and Delayed-Rectifier Potassium Currents

“…It is also necessary to point out that the potential of HCN blockers in cardiac pathologies and in the management of pain is well established and that the compounds able to increase I h (e.g., oxaliplatin) may have the therapeutic potential [42,43]. Caution thus entails being raised in attributing the action of CIL on either cardiac function or neuronal networks widely to the block of I h [2,18,19,30,[34][35][36]44,45].…”

Characterization of Inhibitory Effectiveness in Hyperpolarization-Activated Cation Currents by a Group of ent-Kaurane-Type Diterpenoids from Croton tonkinensis

“…In the next set of experiments, we examined and compared the effects of croton-03, YS-035, zatebradine, croton-03 plus SQ-22536, and croton-03 plus oxaliplatin on I h amplitude in GH 3 cells. YS-035 or zatebradine was recognized as an inhibitor of I h [19,29], oxaliplatin was recently demonstrated to stimulate I h [30,31], and SQ-22536 is an inhibitor adenylate cyclase. As illustrated in Figure 4, similar to the effect of croton-03 on I h described above, the addition of either YS-053 (3 µM) or zatebradine (3 µM) was effective at depressing I h amplitude.…”