TM-5614

Plasminogen activator inhibitor-1 (PAI-1) is a serine protease inhibitor that plays a critical role in cancer progression, particularly in skin cancers. PAI-1 is widely recognized for its role in inhibiting fibrinolysis; however, emerging evidence suggests that it also contributes to tumor progression through multiple mechanisms, including tumor angiogenesis, immunomodulation, and stromal cell regulation. In the tumor microenvironment (TME), PAI-1 influences tumor-associated macrophages (TAMs) and cancer-associated fibroblasts (CAFs), promoting an immunosuppressive environment that supports cancer growth and therapy resistance. Furthermore, PAI-1 has been implicated in the regulation of programmed death-ligand 1 (PD-L1) expression via the JAK/STAT signaling pathway, thereby influencing immune evasion in various skin cancers. The significance of PAI-1 as a therapeutic target has been demonstrated in melanoma and other cutaneous malignancies, where inhibition of PAI-1 has shown promise in overcoming resistance to immune checkpoint inhibitors. Additionally, clinical trials evaluating PAI-1 inhibitors, such as TM5614, highlight its potential as an adjunctive therapy for melanoma and cutaneous angiosarcoma. This review comprehensively explores PAI-1's role in skin cancer progression, its influence on tumor-stromal interactions, and its potential as a therapeutic target.

Plasminogen activator inhibitor-1 (PAI-1) plays a multifaceted and central role in the tumor biology of various skin malignancies. Beyond its classical function in fibrinolysis, PAI-1 contributes to tumor progression by promoting immunosuppression, angiogenesis, cellular senescence, and tissue remodeling. Its expression is particularly elevated in aggressive disease stages across cutaneous melanoma, cutaneous squamous cell carcinoma (cSCC), cutaneous angiosarcoma (CAS), and mycosis fungoides (MF), and is associated with poor clinical outcomes. The ability of PAI-1 to induce senescence-associated secretory phenotype (SASP), modulate PD-L1 expression, and recruit tumor-associated macrophages (TAMs) and cancer-associated fibroblasts (CAFs) suggests a key role in shaping the immunosuppressive tumor microenvironment (TME). This positions PAI-1 as both a potential biomarker for disease progression and a therapeutic target for restoring immune responsiveness, especially in tumors resistant to immune checkpoint inhibitors (ICIs). The PAI-1 inhibitor TM5614 has demonstrated promising activity in early clinical studies, particularly in anti-PD-1-refractory melanoma, and is currently under evaluation in multiple Phase II and III trials. Future strategies should focus on patient stratification using biomarkers such as SASP factors and PAI-1 levels, as well as rational combination therapies targeting interconnected pathways like IL-17/IL-23, AhR, and senescence signaling. Overall, PAI-1 inhibition offers a novel and mechanistically grounded approach to improve outcomes in skin cancers characterized by therapy resistance and an immunosuppressive microenvironment.