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

Abstract

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.

Keywords: PD-L1-targeted immunotoxin; atezolizumab; endosomal escape; immune checkpoint inhibitors; intracellular drug delivery; non-small cell lung cancer; photochemical internalization; photodynamic therapy.