Progress and challenges in the development of clinically viable Piezo1 inhibitors

The development of new drugs is required, for example, if resistance to existing therapies has occurred. To avoid cross-resistance, either a substance class with a completely different chemical structure is indicated, or more innovatively, new targets are addressed. The calcium-permeable, mechanosensitive ion channels of the piezo family discovered in 2010 are one of them. Their discovery was honored with the Nobel Prize in Physiology or Medicine in 2021 [1]. Piezo2 plays an essential role primarily in mechanosensory perception [2]. However, Piezo1 in particular appears to be an auspicious target due to its diverse involvement in (patho)physiological processes [3]. Diseases arising due to or promoted by increases in Piezo1 include cardiovascular, neurological, and pulmonary disorders, bone-related skeletal diseases, and cancer among others [4]. The question arises as to what progress has been made in recent years with regard to the development of Piezo1 inhibitors. In order to approach this matter, it should first be ascertained which inhibitors of Piezo1 have been described so far.

One representative is ruthenium red, which exerts a direct pore-blocking action by inhibiting the inward calcium current. Trivalent gadolinium is most likely to act by plugging the ion pore of the channels, competing with permeant calcium and sodium ions in the pore. Though, gadolinium is known to interact with many other cation channels. Since both ruthenium red and gadolinium work nonspecifically, the development of respective metal complexes exerting effects on Piezo1, for example, might appear to be associated with a large number of undesirable events on off-targets [5]. Nevertheless, a sophisticated fine-tuning of the ligands in metal complexes is generally possible to emphasize certain mechanisms of action and thus relativize other less desirable effects [6].

In addition, fatty acids such as saturated n-heptadecanoic acid (margaric acid) or polyunsaturated arachidonic and eicosapentaenoic acids were reported to possess an inhibitory effect on Piezo1. The contribution of such fatty acids to plasma membranes is assumed to have a mechanical influence on membrane proteins [7]. Moreover, polyunsaturated fatty acids modulate gene expression or serve as signaling molecules within a cell instead of just being part of the membrane. Therefore, their potential for the treatment of diseases should not be underestimated [8]. From a chemical point of view, such molecules would be fairly easy to isolate or synthesize. However, due to their abundant roles in physiological processes and certain promiscuity, selectivity could probably be rather questionable.

The issue of selectivity also arises with Grammostola mechanotoxin #4 (GsMTx4). This is a peptide extracted from the poison of tarantulas. GsMTx4 acts as a gating modifier of Piezo1 by changing the membrane tension at the channel given its amphipathic structure. In turn the calcium influx is inhibited. Effects of GsMTx4 on other cationic channels somewhat limit its potential as a lead structure for the development of drug candidates [9]. In this context, a refined design of derivatives of GsMTx4 would be required in order to achieve selectivity toward Piezo1. From a preparative-chemical perspective, this is challenging for a peptide with 35 amino acids. But that is exactly where there is great potential, namely in the modification of the primary sequence and the resulting spatial structure to increase diversity.

Peptide-based drugs are in general recognized for their high potency and selectivity. However, solubility problems and low proteolytic stability are also known, which cause short half-lives in vivo in addition to enhanced glomerular filtration [10]. These issues are known to narrow clinical applications, but can be largely circumvented by smart technological approaches. The cost-intensive production of clinically applicable remedies would still remain as a disadvantage.

Inhibition of Piezo1 by modulating the membrane structure has also been described for amyloid beta peptides, which are involved in the development of Alzheimer’s disease [11]. Again, the amphiphilicity of the peptide appears to play a role in this context. The exact mechanism of regulation has not yet been clarified. A complete understanding of how the peptide interacts with the membrane would be indicated in order to continue with a potential drug design based on this approach of action. At this stage, computer-aided methods such as docking studies could be used. Yet, the lack of a completely resolved structure of the Piezo1 channel compromises such an approach. Therefore, with a view to the potential design of clinically viable inhibitors, it would first be necessary to fully elucidate the architecture of Piezo1. In contrast, Lim and coworkers demonstrated that the amyloid beta peptides Aβ_1–40 enhance the probability of Piezo1 to open on endothelial cells and increase the opening time itself. This enabled an augmented influx mediated by Piezo1 [12]. Overall, more research seems to be needed to elucidate the particular effects of amyloid beta peptides on the Piezo1 channel.

Some natural compounds isolated from medicinal plants have also been described as inhibitors of Piezo1. These include the protoberberine alkaloid jatrorrhizin (obtained from Phellodendri cortex, Coptidis rhizoma) [13], albeit its nature of inhibiting Piezo1 and the selectivity toward the ion channel still need to be enlightened. Further representatives are the triterpenoid saponins escin (extracted from Aesculus hippocastanum) and tubeimoside I (extracted from Bolbostemmatis rhizoma) [5]. Both compounds strongly reduced the calcium flux induced by the Piezo1 agonist Yoda1. Interestingly, tubeimoside I was observed to exert relative selectivity toward Piezo1 compared to other mechanosensitive calcium channels [14]. The polyphenolic compound salvianolic acid B (obtained from Salvia miltiorrhiza) proved to be a reversible inhibitor of Piezo1. It acts by competing with the binding site of the agonist Yoda1 and selectively antagonizing it [15]. There are initial findings that the flavonoid isoquercitrin indirectly interferes with the Piezo1/NLRP3 pathway. So far isoquercetin cannot be regarded as an direct inhibitor of Piezo1 [16].

The four natural compounds mentioned and directly targeting Piezo1 are structurally very diverse in some cases. It is striking that all of them have phenolic or hydroxy groups, which could play a role in the interaction with Piezo1. Since the mechanism of inhibiting the ion channel is not yet clear, it is difficult at present to deduce meaningful structure-activity relationships for future development of clinically viable Piezo1 inhibitors. However, a structural similarity is obvious between the selective Piezo1 antagonist Dooku1 and the agonist Yoda1. While the latter bears a pyrazin-2-yl thiadiazole moiety, the inhibitor has a pyrrole-2-yl oxadiazole core [17]. Regarding the design of Piezo1 inhibitors to be applied in clinics, the small molecule Dooku1 appears to be a suitable drug candidate. The criteria of the traditional “Lipinski’s rule of five” for the general prediction of the potential suitability as an orally administered drug are mostly met. Only the low solubility of Dooku1 in body fluids limits its further in vivo investigation [5]. The organic synthesis of derivatives with improved solubility but at least similar pharmacological effect would be advisable.

The clinically approved drug benzbromarone is used to treat hyperuricemia in gout. It acts by blocking essential renal transporters, thereby promoting the elimination of uric acid and reducing serum urate concentrations. In a sophisticated experimental procedure, Liang et al. found that benzbromarone inhibits Piezo1. Benzbromarone was capable of suppressing the calcium increase caused by Yoda1. The blocking activity on the Piezo1 channel was reversible. In brief, Piezo1-mediated influx of calcium is suppressed and, consequently, the cell surface exposure of phosphatidylserine mediated by TMEM16F CaPLSase (a protein acting as a calcium-activated lipid scramblase and nonselective ion channel) [18]. Since hepatotoxicity is repeatedly discussed with benzbromarone, its suitability as a lead compound for the design of new Piezo1 inhibitors is rather questionable [19].

In summary, the inhibitors described so far can be divided into three subclasses. Direct inhibition of the Piezo1 channel is achieved by ruthenium red and trivalent gadolinium. Due to their amphiphilic character, fatty acids and the peptides GsMTx4 and amyloid beta can be involved in modulating the membrane. By changing the membrane tension, effects are exerted on the mechanosensitive piezo channels. The natural compounds jatrorrhizine, escin, tubeimoside I, and salvianolic acid B, as well as the compound Dooku1 lead to a competitive inhibition. As a result of the blockade of the Piezo1-mediated influx of calcium, subsequent downstream signaling pathways and thus (patho)physiological processes are inhibited. Thus, Piezo1 turned into an auspicious target for medicinal chemistry approaches.

Most of the Piezo1 inhibitors known to date have the issue of nonspecific action. This is very likely to lead to off-target effects. This challenge should definitely be addressed in future drug design. Structurally, the inhibitors show great variety. This can be seen as an opportunity, as the structural diversity of drugs should not lead to cross-resistance later on, for example. However, clear structure-activity relationships cannot yet be derived from the pool of existing Piezo1 inhibitors. This makes it difficult to consistently optimize lead structures into drug candidates for further clinical testing. In order to be supported by computer-aided methods, the underlying mechanisms of ligand binding and inhibition need to be clarified. This also includes the complete elucidation of the structure of Piezo1.

So, what is the current state? Even if the development of Piezo1 inhibitors is still in its infancy, there is still a lot of potential. With the discovery of the piezo channels, very interesting targets have been found. It should be mentioned that the search for suitable agonists for therapeutic purposes is also underway [20]. As the piezo channels are involved in the development of various diseases, their targeting by inhibitors seems promising. However, particular attention must be paid to selectivity in order to avoid inducing undesirable side effects. The antagonist Dooku1 developed in the research group of Beech et al. can be considered a valuable lead structure [17]. Based on this, good progress should be made to overcome the challenges and hopefully to develop clinically viable Piezo1 inhibitors.

Funding Statement

This paper was not funded.

Disclosure statement

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties

Writing assistance

No writing assistance was utilized in the production of this manuscript

Reviewer disclosure

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.