Enhancing NSCLC susceptibility to anti-PD-1 - PD-L1 therapy trough PD-L1 ligand-Ir(III) complex conjugates

Immune checkpoint inhibitors (ICIs) targeting the PD-1-PD-L1 axis have revolutionized cancer therapy. However, their limited clinical success and the emergence of resistance mechanisms highlight the need for novel strategies to enhance anti-PD-1-PD-L1 immunotherapy. In this context, Iridium (III) complexes (Ir(III) complexes), have gained increasing attention for their potent anticancer activity and favorable safety profile. They are shown to induce immunogenic cell death (ICD) in non-small cell lung cancer (NSCLC), boosting tumor immunogenicity and improving response to conventional therapy. Here, we investigate whether Ir(III) complexes can synergize with anti-PD-L1 therapy and consequently synthetize a small array of triazine-based PD-L1 ligand-Ir(III) complexes by conjugating our previously reported anti-PD-L1 ligand (compound 10) with a bis-phenyl-pyridine-Ir(III) complex 2. The antitumor and immunomodulatory activity of Ir(III) complex 2 and PD-L1 inhibitor compound 10, as well as of four other PD-L1 ligand-Ir(III) complex conjugates 3-6, was tested in NSCLC cell lines expressing different levels of PD-L1, as well as in co-culture assays with peripheral blood mononuclear cells (PBMCs). Ir(III) complex conjugate 3 significantly enhanced anti-PD-L1-mediated PBMC tumor cell recognition and elimination, by increasing ER stress-mediated calreticulin (CRT) exposure, mitochondrial ROS production, and immunogenic signal release (ATP, HMGB1). More importantly, these effects were abrogated in PD-L1 knockout NSCLC cells incubated with the PD-L1 ligand-Ir(III) complex conjugate 3, validating a PD-L1-mediated selective delivery and dependent mechanism. These findings provide strong evidence that Ir(III) complexes potentiate anti-PD-L1 therapy in NSCLC, supporting the clinical implementation of PD-L1 ligand-Ir(III) conjugates as a novel combinatorial immunotherapeutic strategy for enhancing anti-PD-L1 therapy.