Abstract: Verteporfin (VP) is a benzoporphyrin derivative traditionally utilized as a photosensitizer in photodynamic therapy (PDT) for the treatment of age-related macular degeneration (AMD) and various solid tumors. Recently, Verteporfin has garnered significant attention for its light-independent pharmacological properties, most notably its ability to act as a direct inhibitor of the Yes-associated protein (YAP) and Transcriptional co-activator with PDZ-binding motif (TAZ). YAP and TAZ are core effectors of the Hippo signaling pathway, playing critical roles in mechanotransduction, tissue regeneration, extracellular matrix (ECM) regulation, and the expression of pro-fibrotic genes such as Connective Tissue Growth Factor (CTGF). By physically binding to YAP and disrupting the YAP-TEAD transcriptional complex, Verteporfin downregulates key mechanotransduction elements including Focal Adhesion Kinase (FAK), integrins, and CTGF. Furthermore, VP exhibits anti-inflammatory properties and modulates protein polymerization. These mechanisms provide a strong molecular rationale for repositioning Verteporfin as a targeted therapeutic agent for scarless wound healing and anti-fibrosis.
1. Introduction
Verteporfin (commercially known as Visudyne) is an FDA-approved, second-generation liposomal photosensitizer originally developed for the treatment of ocular neovascular diseases, such as age-related macular degeneration (AMD), through photodynamic therapy (PDT) [1][3]. Chemically, it is a benzoporphyrin derivative (C41H42N4O8) that, upon activation by a 690 nm laser, generates reactive oxygen species (ROS) leading to localized cellular apoptosis and vascular occlusion [7][8].
Beyond its established role in PDT, recent research has uncovered that Verteporfin exerts profound biological effects even in the absence of photoactivation. Most prominently, it has been identified as a potent inhibitor of Yes-associated protein (YAP) and Transcriptional co-activator with PDZ-binding motif (TAZ), which are the core downstream effectors of the Hippo signaling pathway [1][10]. The Hippo-YAP/TAZ pathway is a fundamental regulator of tissue homeostasis, organ size, and cellular plasticity [1][4]. Because YAP and TAZ communicate extracellular biophysical cues to the nucleus to regulate cytoskeletal and extracellular matrix (ECM) components, their aberrant activation is heavily implicated in fibrotic diseases and abnormal wound healing [4]. Consequently, the ability of Verteporfin to pharmacologically disrupt YAP-TEAD interactions has opened a novel research direction exploring its utility in scarless wound healing and anti-fibrotic therapies.
2. Pharmacological Activity
While much of the literature focuses on Verteporfin's anti-tumorigenic properties, its pharmacological activities are highly relevant to the mechanisms underlying fibrosis and wound healing:
Inhibition of Pro-Fibrotic Gene Expression: YAP and TAZ transcriptionally regulate the expression of Connective Tissue Growth Factor (CTGF) and Cysteine-Rich Angiogenic Inducer 61 (CYR61) [1]. CTGF is a critical mediator in the "angiofibrotic switch" and drives the excessive deposition of ECM seen in fibrotic conditions [9]. By blocking YAP/TAZ, Verteporfin significantly downregulates the expression of CTGF and CYR61, thereby removing a primary driver of fibrogenesis [1].
Modulation of Mechanotransduction and Cellular Adhesion: Fibrosis is characterized by altered mechanosignaling and cellular stiffening. Verteporfin has been shown to downregulate Focal Adhesion Kinase (FAK) and phosphorylated FAK (p-FAK), along with other critical focal adhesion proteins such as β1-integrin, paxillin, and zyxin [1]. It also affects the FAT1 adhesion molecule [12]. By dismantling these mechanotransduction networks, Verteporfin can potentially prevent the mechanical activation of fibroblasts that leads to scarring.
Anti-Inflammatory Effects: Chronic inflammation is a well-known precursor to fibrosis. Non-photoactivated Verteporfin inhibits the production of the pro-inflammatory cytokine IL-17A by targeting germinal center kinase-like kinase (GLK) and disrupting the AhR-RORγt complex. This suggests a therapeutic potential against autoimmune and inflammatory conditions that often culminate in tissue fibrosis [1].
Class Effect of YAP Inhibition in Fibrosis: The anti-fibrotic potential of YAP inhibition is supported by studies on other YAP inhibitors. For instance, Celastrol, another compound identified as a YAP-TEAD inhibitor, has demonstrated potent anti-fibrotic effects in systemic sclerosis and corneal stromal fibrosis by inhibiting the TGF-β1/Smad2/3-YAP/TAZ signaling axis [2]. As a direct YAP inhibitor, Verteporfin shares this mechanistic capacity to halt fibrotic progression.
3. Molecular Mechanism of Action
Verteporfin exerts its anti-fibrotic and cellular regulatory effects through several distinct molecular mechanisms:
Disruption of the YAP-TEAD Complex: In the absence of light, Verteporfin selectively binds to YAP, inducing a conformational change that physically precludes its interaction with Transcriptional Enhanced Associate Domain (TEAD) transcription factors [10][12]. Furthermore, Verteporfin upregulates the 14-3-3σ protein, which sequesters YAP in the cytoplasm, preventing its nuclear translocation and subsequent activation of target genes [4][7].
Protein Polymerization and Autophagy Inhibition: Verteporfin directly targets p62 (SQSTM1), a crucial cargo receptor in autophagy. It induces the formation of covalently crosslinked, high-molecular-weight p62 oligomers. This polymerization, mediated by low-level singlet oxygen production even in ambient light, impairs p62's ability to bind polyubiquitinated proteins, thereby blocking autophagosome formation [5]. Additionally, Verteporfin induces the oligomerization of STAT3 (decreasing STAT3 signaling) and nuclear lamins (lamin A/C and B1), which alters nuclear organization and gene expression [5].
Modulation of p53 Family Proteins and Oxidative Stress: Verteporfin stabilizes the TAp73 protein (a p53 homolog) and acts as an efficient inhibitor of thioredoxin reductase (TrxR), a key component of the cellular antioxidant system. This inhibition leads to the accumulation of ROS and subsequent cellular apoptosis [6].
4. Structure-Activity Relationship (SAR)
Verteporfin is a benzoporphyrin derivative, and its structure dictates both its photoactivated and non-photoactivated properties. The porphyrin ring (C41H42N4O8) is highly efficient at absorbing light (specifically at 690 nm) to excite electrons to a triplet state, which then transfer energy to oxygen to produce cytotoxic singlet oxygen and ROS [3][7].
In its non-photoactivated role, the structural conformation of Verteporfin allows it to act as a small-molecule inhibitor of protein-protein interactions. The YAP-TEAD complex relies on three highly conserved binding interfaces (including an anti-parallel β-sheet and an α-helix motif fitting into a hydrophobic groove) [1]. Verteporfin selectively binds to YAP, altering its three-dimensional conformation and sterically hindering its ability to engage with these TEAD interfaces [10]. Additionally, its structural similarity to iron-binding porphyrins may contribute to its ability to interfere with intracellular iron metabolism and induce oxidative stress independently of the YAP pathway [7].
5. Current Limitations
Despite its therapeutic promise, several limitations hinder the immediate translation of Verteporfin into standard anti-fibrotic clinical practice:
Pharmacokinetics and Bioavailability: Verteporfin is highly hydrophobic and has a short systemic half-life of approximately 5 to 6 hours [3][4]. It requires specialized lipid-based delivery systems (such as the liposomal formulation Visudyne) to remain soluble and achieve adequate tissue penetration [7][8].
Photosensitivity: Because Verteporfin is a potent photosensitizer, patients and animal models treated with the drug must be kept in the dark for extended periods (e.g., 24 hours post-injection) to avoid severe phototoxic reactions, such as edema, inflammation, and tissue hemorrhage upon exposure to ambient light [1][3].
Off-Target Protein Crosslinking: The ability of Verteporfin to induce widespread covalent crosslinking of various proteins (including p62, STAT3, and lamins) raises concerns about off-target proteotoxicity. This broad impact on cellular proteostasis could lead to the accumulation of dysfunctional proteins and unintended cellular damage in healthy tissues [5].
6. Future Perspectives
The repositioning of Verteporfin from an ophthalmological photosensitizer to a targeted YAP-TEAD inhibitor presents a highly promising avenue for the treatment of fibrosis and the promotion of scarless wound healing. Future research must focus on decoupling its YAP-inhibitory effects from its ROS-generating photodynamic properties. This could be achieved through the structural modification of the benzoporphyrin ring to eliminate photosensitivity while retaining YAP-binding affinity.
Furthermore, advancements in drug delivery will be critical. The development of localized, sustained-release formulations—such as hydrogels, nanostructured lipid carriers (NLCs), or mesoporous silica nanoparticles (MSNs)—could allow for the topical application of Verteporfin directly to wound beds [1]. This would maximize local YAP inhibition to prevent scarring while minimizing systemic exposure and the associated risks of phototoxicity. As our understanding of the Hippo pathway's role in mechanotransduction and ECM deposition deepens, Verteporfin stands out as a premier pharmacological tool to modulate these processes for regenerative medicine.
