Plasminogen Activator Inhibitor-1 Mediates Tolerance to Anti–PD-1 Immunotherapy in Non–Small Cell Lung Cancer

Immune checkpoint inhibitors (ICI) have improved the prognosis of patients with non-small cell lung cancer (NSCLC), but the cure rate remains low because tolerant persister cancer cells can survive within the tumor during ICI treatment. We have previously reported that plasminogen activator inhibitor-1 (PAI-1) is involved in tolerance acquisition to osimertinib in EGFR-mutated NSCLC. This study aimed to examine the role of PAI-1 in ICI tolerance and whether PAI-1 may be a therapeutic target to overcome this tolerance. In a mouse subcutaneous tumor model using Lewis lung carcinoma or KLN205 cells, cancer cells surviving within the tumor 7 days after anti-PD-1 (aPD-1) antibody treatment were defined as aPD-1 antibody-tolerant persister cells (aPD-1-TP). PAI-1 and mesenchymal gene expression levels were higher in aPD-1-TPs than in control cells. IHC analyses showed higher numbers of tumor-associated macrophages, expression of PD-L1 in cancer cells, and degree of angiogenesis. In contrast, the number of tumor-infiltrating lymphocytes was lower in aPD-1 antibody-tolerant tumors than in control tumors. Combination treatment with an aPD-1 antibody and the PAI-1 inhibitor, TM5614 decreased mesenchymal gene expression, PD-L1 expression, tumor-associated macrophage numbers, and angiogenesis and increased tumor-infiltrating lymphocyte counts in tolerant tumors. Furthermore, it resulted in prolonged inhibition of tumor growth. In conclusion, this study underscores the involvement of PAI-1 in the survival of aPD-1-TPs via epithelial-mesenchymal transition and alteration of the tumor microenvironment. Combination treatment with an aPD-1 antibody and TM5614 can be a new therapeutic strategy for NSCLC.