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      TRP Channels as Potential Drug Targets

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      Annual Review of Pharmacology and Toxicology
      Annual Reviews

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          Abstract

          The transient receptor potential (TRP) superfamily of channels comprises a diverse group of cation channels. Four TRP channel subunits coassemble to form functional homo- or heterotetramers that pass sodium, calcium, or both in the inward direction. Modulating TRP channel activity provides an important way to impact cellular function by regulating both membrane excitability and intracellular calcium levels. The import of these channels is underscored by the number of genetic diseases caused when they are mutated: Skeletal, skin, sensory, ocular, cardiac, and neuronal disturbances all arise from aberrant TRP function. Not surprisingly, there has been significant pharmaceutical interest in targeting these fascinating channels. Compounds that modulate TRP vanilloid 1 (TRPV1), TRPV3, TRPV4, TRP ankyrin 1 (TRPA1), and TRP melastatin 8 (TRPM8) have all entered clinical trials. The goal of this review is to familiarize the readers with the rationale behind the pursuit of these channels in drug discovery and the status of those efforts.

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          Most cited references141

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          Structure of the TRPV1 ion channel determined by electron cryo-microscopy

          Transient receptor potential (TRP) channels are sensors for a wide range of cellular and environmental signals, but elucidating how these channels respond to physical and chemical stimuli has been hampered by a lack of detailed structural information. Here, we exploit advances in electron cryo-microscopy to determine the structure of a mammalian TRP channel, TRPV1, at 3.4Å resolution, breaking the side-chain resolution barrier for membrane proteins without crystallization. Like voltage-gated channels, TRPV1 exhibits four-fold symmetry around a central ion pathway formed by transmembrane helices S5–S6 and the intervening pore loop, which is flanked by S1–S4 voltage sensor-like domains. TRPV1 has a wide extracellular ‘mouth’ with short selectivity filter. The conserved ‘TRP domain’ interacts with the S4–S5 linker, consistent with its contribution to allosteric modulation. Subunit organization is facilitated by interactions among cytoplasmic domains, including N-terminal ankyrin repeats. These observations provide a structural blueprint for understanding unique aspects of TRP channel function.
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            TRPA1 mediates the inflammatory actions of environmental irritants and proalgesic agents.

            TRPA1 is an excitatory ion channel targeted by pungent irritants from mustard and garlic. TRPA1 has been proposed to function in diverse sensory processes, including thermal (cold) nociception, hearing, and inflammatory pain. Using TRPA1-deficient mice, we now show that this channel is the sole target through which mustard oil and garlic activate primary afferent nociceptors to produce inflammatory pain. TRPA1 is also targeted by environmental irritants, such as acrolein, that account for toxic and inflammatory actions of tear gas, vehicle exhaust, and metabolic byproducts of chemotherapeutic agents. TRPA1-deficient mice display normal cold sensitivity and unimpaired auditory function, suggesting that this channel is not required for the initial detection of noxious cold or sound. However, TRPA1-deficient mice exhibit pronounced deficits in bradykinin-evoked nociceptor excitation and pain hypersensitivity. Thus, TRPA1 is an important component of the transduction machinery through which environmental irritants and endogenous proalgesic agents depolarize nociceptors to elicit inflammatory pain.
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              The menthol receptor TRPM8 is the principal detector of environmental cold.

              Sensory nerve fibres can detect changes in temperature over a remarkably wide range, a process that has been proposed to involve direct activation of thermosensitive excitatory transient receptor potential (TRP) ion channels. One such channel--TRP melastatin 8 (TRPM8) or cold and menthol receptor 1 (CMR1)--is activated by chemical cooling agents (such as menthol) or when ambient temperatures drop below approximately 26 degrees C, suggesting that it mediates the detection of cold thermal stimuli by primary afferent sensory neurons. However, some studies have questioned the contribution of TRPM8 to cold detection or proposed that other excitatory or inhibitory channels are more critical to this sensory modality in vivo. Here we show that cultured sensory neurons and intact sensory nerve fibres from TRPM8-deficient mice exhibit profoundly diminished responses to cold. These animals also show clear behavioural deficits in their ability to discriminate between cold and warm surfaces, or to respond to evaporative cooling. At the same time, TRPM8 mutant mice are not completely insensitive to cold as they avoid contact with surfaces below 10 degrees C, albeit with reduced efficiency. Thus, our findings demonstrate an essential and predominant role for TRPM8 in thermosensation over a wide range of cold temperatures, validating the hypothesis that TRP channels are the principal sensors of thermal stimuli in the peripheral nervous system.
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                Author and article information

                Journal
                Annual Review of Pharmacology and Toxicology
                Annu. Rev. Pharmacol. Toxicol.
                Annual Reviews
                0362-1642
                1545-4304
                January 06 2018
                January 06 2018
                : 58
                : 1
                : 309-330
                Affiliations
                [1 ]Hydra Biosciences, Cambridge, Massachusetts 02138, USA;
                Article
                10.1146/annurev-pharmtox-010617-052832
                28945977
                6068d2ba-bca9-4ad7-8185-f59f72c60260
                © 2018
                History

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