Photochemical enhancement of PD-L1-SAP immunotoxin efficacy in non-small cell lung cancer cell lines

Introduction Resistance to immune checkpoint inhibitors (ICIs) targeting the programmed cell death protein 1/programmed death ligand 1 (PD–1/PD–L1) axis remains a major obstacle in non–small cell lung cancer (NSCLC). Materials and methods To address this, we investigated photochemical internalization (PCI), a light–controlled endosomal escape technology, as a strategy to enhance intracellular delivery and efficacy of a PD–L1–targeted immunotoxin (anti–PD–L1–SAP). Results NSCLC cell lines with high (NCI–H1975) and low (A549) PD–L1 expression were subjected to PCI, resulting in a pronounced increase in cytotoxicity with picomolar potency (30 pM), while A549 cells required a higher dose (1000 pM) for a similar effect. Specificity was confirmed via receptor blockade and non–targeted controls. Confocal microscopy demonstrated lysosomal and endosomal localization of anti–PD–L1–SAP, and flow cytometry showed time–dependent intracellular accumulation, consistent with PCI’s requirement for endosomal sequestration prior to light–induced release. Importantly, co–treatment with the immune checkpoint inhibitor atezolizumab (Tecentriq ® ) reduced PCI efficacy in PD–L1^ high ^ cells, underscoring the importance of receptor accessibility. Conclusions These findings demonstrate that PCI enhances delivery and activity of PD–L1–targeted biologics and may help overcome resistance mechanisms. Overall, PCI expands the therapeutic window of PD–L1–targeted immunotoxins and may complement current immunotherapies, supporting further preclinical evaluation in NSCLC.