Targeting TRP channels for pain relief: A review of current evidence from bench to bedside.

Several decades of research support the involvement of transient receptor potential (TRP) channels in nociception. Despite the disappointments of early TRPV1 antagonist programs, the TRP family remains a promising therapeutic target in pain disorders. High-dose capsaicin patches are already in clinical use to relieve neuropathic pain. At present, localized injections of the side-directed TRPV1 agonist capsaicin and resiniferatoxin are undergoing clinical trials in patients with osteoarthritis and bone cancer pain. TRPA1, TRPM3, and TRPC5 channels are also of significant interest. This review discusses the role of TRP channels in human pain conditions.

Advances in TRP channel drug discovery: from target validation to clinical studies.

Transient receptor potential (TRP) channels are multifunctional signalling molecules with many roles in sensory perception and cellular physiology. Therefore, it is not surprising that TRP channels have been implicated in numerous diseases, including hereditary disorders caused by defects in genes encoding TRP channels (TRP channelopathies). Most TRP channels are located at the cell surface, which makes them generally accessible drug targets. Early drug discovery efforts to target TRP channels focused on pain, but as our knowledge of TRP channels and their role in health and disease has grown, these efforts have expanded into new clinical indications, ranging from respiratory disorders through neurological and psychiatric diseases to diabetes and cancer. In this Review, we discuss recent findings in TRP channel structural biology that can affect both drug development and clinical indications. We also discuss the clinical promise of novel TRP channel modulators, aimed at both established and emerging targets. Last, we address the challenges that these compounds may face in clinical practice, including the need for carefully targeted approaches to minimize potential side-effects due to the multifunctional roles of TRP channels.

Model for long QT syndrome type 2 using human iPS cells demonstrates arrhythmogenic characteristics in cell culture.

Long QT syndrome (LQTS) is caused by functional alterations in cardiac ion channels and is associated with prolonged cardiac repolarization time and increased risk of ventricular arrhythmias. Inherited type 2 LQTS (LQT2) and drug-induced LQTS both result from altered function of the hERG channel. We investigated whether the electrophysiological characteristics of LQT2 can be recapitulated in vitro using induced pluripotent stem cell (iPSC) technology. Spontaneously beating cardiomyocytes were differentiated from two iPSC lines derived from an individual with LQT2 carrying the R176W mutation in the KCNH2 (HERG) gene. The individual had been asymptomatic except for occasional palpitations, but his sister and father had died suddenly at an early age. Electrophysiological properties of LQT2-specific cardiomyocytes were studied using microelectrode array and patch-clamp, and were compared with those of cardiomyocytes derived from control cells. The action potential duration of LQT2-specific cardiomyocytes was significantly longer than that of control cardiomyocytes, and the rapid delayed potassium channel (I(Kr)) density of the LQT2 cardiomyocytes was significantly reduced. Additionally, LQT2-derived cardiac cells were more sensitive than controls to potentially arrhythmogenic drugs, including sotalol, and demonstrated arrhythmogenic electrical activity. Consistent with clinical observations, the LQT2 cardiomyocytes demonstrated a more pronounced inverse correlation between the beating rate and repolarization time compared with control cells. Prolonged action potential is present in LQT2-specific cardiomyocytes derived from a mutation carrier and arrhythmias can be triggered by a commonly used drug. Thus, the iPSC-derived, disease-specific cardiomyocytes could serve as an important platform to study pathophysiological mechanisms and drug sensitivity in LQT2.

Differentiation dependent expression of TRPA1 and TRPM8 channels in IMR-32 human neuroblastoma cells.

TRPA1 and TRPM8 are transient receptor potential (TRP) channels involved in sensory perception. TRPA1 is a non-selective calcium permeable channel activated by irritants and proalgesic agents. TRPM8 reacts to chemical cooling agents such as menthol. The human neuroblastoma cell line IMR-32 undergoes a remarkable differentiation in response to treatment with 5-bromo-2-deoxyuridine. The cells acquire a neuronal morphology with increased expression of N-type voltage gated calcium channels and neurotransmitters. Here we show using RT-PCR, that mRNA for TRPA1 and TRPM8 are strongly upregulated in differentiating IMR-32 cells. Using whole cell patch clamp recordings, we demonstrate that activators of these channels, wasabi, allyl-isothiocyanate (AITC) and menthol activate membrane currents in differentiated cells. Calcium imaging experiments demonstrated that AITC mediated elevation of intracellular calcium levels were attenuated by ruthenium red, spermine, and HC-030031 as well as by siRNA directed against the channel. This indicates that the detected mRNA level correlate with the presence of functional channels of both types in the membrane of differentiated cells. Although the differentiated IMR-32 cells responded to cooling many of the cells showing this response did not respond to TRPA1/TRPM8 channel activators (60% and 90% for AITC and menthol respectively). Conversely many of the cells responding to these activators did not respond to cooling (30%). This suggests that these channels have also other functions than cold perception in these cells. Furthermore, our results suggest that IMR-32 cells have sensory characteristics and can be used to study native TRPA1 and TRPM8 channel function as well as developmental expression.