Pharmacology of PIEZO1 channels

Abstract

PIEZO1 is a eukaryotic membrane protein that assembles as trimers to form calcium-permeable, non-selective cation channels with exquisite capabilities for mechanical force sensing and transduction of force into effect in diverse cell types that include blood cells, endothelial cells, epithelial cells, fibroblasts and stem cells and diverse systems that include bone, lymphatics and muscle. The channel has wide-ranging roles and is considered as a target for novel therapeutics in ailments spanning cancers and cardiovascular, dental, gastrointestinal, hepatobiliary, infectious, musculoskeletal, nervous system, ocular, pregnancy, renal, respiratory and urological disorders. The identification of PIEZO1 modulators is in its infancy but useful experimental tools emerged for activating, and to a lesser extent inhibiting, the channels. Elementary structure-activity relationships are known for the Yoda series of small molecule agonists, which show the potential for diverse physicochemical and pharmacological properties. Intriguing effects of Yoda1 include the stimulated removal of excess cerebrospinal fluid. Despite PIEZO1's broad expression, opportunities are suggested for selective positive or negative modulation without intolerable adverse effects. Here we provide a focused, non-systematic, narrative review of progress with this pharmacology and discuss potential future directions for research in the area.

Keywords: calcium ion; ion channel; mechanical force; non‐selective cation channel; pharmacology; pressure; shear stress; small molecule modulator.

Figure 1. Structures of Yoda series compounds.

Chemical differences of analogues compared with Yoda1 are indicated in colour. (a) Yoda1. The 2,6-dichlorophenyl moiety is shown on the right side of the molecule and its pyrazine moiety on the left. The central core is thiadiazole. (b) Compound 2 g. Chemically the same as Yoda1 except for a fluorine (indicated in red) in place of a chlorine in the right-hand ring. Compared with Yoda1, it is a weak agonist of PIEZO1. (c) KC124. Chemically the same as Yoda1 except for methyl groups (indicated in red) in place of the chlorines in the right-hand ring. It has similar or slightly weaker agonist capability at PIEZO1 compared with Yoda1. (d) KC159. Chemically the same as Yoda1 except for a 4-substituted phenyl carboxylic acid (4-benzoic acid group) (indicated in blue) in place of Yoda1’s pyrazine group on the left side. It has similar or stronger agonist capability at PIEZO1 compared with Yoda1. It has better aqueous solubility and other physicochemical properties compared with Yoda1. (e) Yoda2 (KC289). The potassium salt of KC159, also showing improved properties compared with Yoda1. (f) KC157. Chemically the same as Yoda1 except for a two-substituted phenyl carboxylic acid (indicated in blue) in place of Yoda1’s pyrazine group on the left side. It has no or very weak agonist capability at PIEZO1. (g) CHR-1871-032. It is chemically the same as Yoda1 except for a 4-substituted phenyl carboxylic acid (indicated in blue) in place of Yoda1’s pyrazine group on the left side and a monoazole (thiazole) instead of a diazole (thiadiazole) in the central core (indicated in orange). It has slightly stronger agonist capability at PIEZO1 compared with Yoda1 and better capability to rescue loss-of-function variant PIEZO1 channel function. (h) Compound 11. Chemically the same as Yoda1 except for an oxadiazole in the central core (indicated in orange). Compared with Yoda1 it is a slightly less effective agonist at PIEZO1. (i) Yaddle1. Chemically similar to Yoda1 except for the oxadiazole and 2-chloro-6-trifluoromethyl substitution in the phenyl ring. (j) Dooku1. It is chemically the same as Yoda1 except for an oxadiazole in the central core (indicated in orange) and a 2-pyrrolyl instead of pyrazine group on the left. At overexpressed hPIEZO1 channels it lacked agonist activity but it inhibited the action of Yoda1. Additional PIEZO1-related effects of Dooku1 occur (as described in the main text), suggesting that it may have partial agonist capability (i.e., inhibitor or weak agonist capability) depending on context.

Figure 2. Concepts for cell/ tissue type-specific effects of PIEZO1 agonists.

Diagram of contexts predicted to result in weak (a) or strong (b) effects of Yoda series agonists. (a) Organ/ tissue with one or more of: low PIEZO1 channel expression; weak PIEZO1 force sensitivity (e.g., due to loss-of-function PIEZO1 mutation; low force environment (e.g., due to sparse and/or soft extracellular matrix, weak cell–cell contact, little or no shear stress); fast PIEZO1 inactivation (i.e., reducing PIEZO1 channel functional capability); low lipid regulation (e.g., loss of PIEZO1 activity due to depletion of phosphatidylinositol 1, 4, 5-triphosphate; or weak downstream pathways (e.g., due to depleted calpain). An example of Cell type 1 may be physiological cardiac myocytes which, although experiencing a high force context because of the heartbeat, may express very little PIEZO1. (b) Organ/tissue with one or more of: strong PIEZO1 channel expression; strong PIEZO1 force sensitivity (e.g., due to gain-of-function PIEZO1 mutation); strong force environment (e.g., due to dense and/or stiff extracellular matrix, strong cell–cell contact, fluid shear stress); slow or disabled PIEZO1 inactivation (i.e., due to sphingomyelinase activity or MyoD Family Inhibitor Domain Containing protein); high lipid regulation (e.g., due to ω-3 fatty acids); or strong downstream pathways (e.g., due to coupling to nitric oxide synthase). An example of Cell type 2 may be lymphatic endothelial cells.

Figure 3. Possible clinical indications for modulators.

(a) Positive modulators. The potential uses are suggested based on effects of Yoda series agonists observed in in vivo or ex vivo preclinical experimental studies. (b) Negative modulators. The potential uses are suggested based on effects of PIEZO1 genetic depletion or inhibitors. Potential uses of negative modulators may also be inferred from the suggested contraindications and adverse effects of Yoda series agonists, which are specified in the main text. (a, b) Supporting studies are described and referenced in the main text. The indications are exemplars and not an exhaustive list of what might be possible.

Figure 4. Model of how PIEZO1 inhibitor (negative modulator) therapy might work.

The model is adapted from Beech (2023). PIEZO1 expression or activity is assumed to be low in the healthy tissue of the patient but elevated in diseased tissue, in which there may also be increased PIEZO1 expression and/or activity and increased mechanical stress and tissue fibrosis (e.g., in the heart in heart failure). In the model, PIEZO1 inhibitor inhibits the excess PIEZO1, leading to therapeutic benefit. Healthy PIEZO1 may also be suppressed by the inhibitor but adverse (unwanted) effects of the inhibitor (i.e., on healthy tissue) may occur only at supra-therapeutic inhibitor concentrations when there is more than 50% PIEZO1 inhibition. Human genetic studies suggest that 50% loss of PIEZO1 does not have obvious adverse effect. In this model, the partial inhibition of ‘Diseased PIEZO1’ and sparing of some ‘Healthy PIEZO1’ enables a therapeutic window within a specified concentration range of the inhibitor (i.e., depending on dose of the inhibitor and the protocol for its administration). It may, therefore, be possible to achieve therapeutic benefit without unacceptable adverse effects.

Figure 5. Concepts for PIEZO1 modulation by small molecules.

Examples of how small molecule modulation of PIEZO1 may occur. (a) Modulation by Yoda series molecules (or equivalents) that stabilise compact or loose channel conformations that favour ion pore closure (compact conformation) or ion pore opening (loose conformation). PIEZO1 channel (blue) is shown in simple schematic form in helicopter perspective (from above). An agonist such as Yoda1 is suggested to act like a wedge, facilitating activation of the channel by mechanical force. Yoda1 analogues such as Dooku1 may do the reverse: stabilising the compact conformation, yet acting via a similar or overlapping binding pocket. (b) Depiction of the proposed mechanism of PIEZO1 inhibition by OB-1 and OB-2 small molecules, acting via the STOML3 protein. With this mechanism, the inhibition occurs slowly via STOML3 disruption and depends on STOML3 (or a similar molecule) expressed with PIEZO1 (e.g., in tactile neurones).

Figure 6. Summary list of PIEZO1 modulators.

The blue schematic in the middle is a side-view sketch of the PIEZO1 channel in a lipid membrane, with cations above in the extracellular medium potentially going through the ion pore of the channel once open. The main physiological activator of the channels is mechanical force (e.g., increased membrane tension). Listed on the left in green are substances that have been suggested to activate or enhance PIEZO1 activity by whatever mechanism. Listed on the right in red are substances that have been suggested to inhibit PIEZO1 activity by whatever mechanism. The substances do not necessarily act directly or specifically on PIEZO1. Several independent results and complex data sets are available for some of the substances, whereas for others there may only be one experimental result available. Details of the underlying studies and notes of caution and interpretation are available via the main text. Potential additional modulators have been suggested from results of chemical screens. Other approaches to altering PIEZO1 include RNA interference and gene modification. Anti-PIEZO1 antibody has been used to direct chemical to cells. The side-view sketch of PIEZO1 channel was generated from BioRender.