Investigating PD-1/PD-L1 Checkpoint Inhibition as a Treatment for Platinum-Resistant Ovarian Cancer



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Ovarian cancer is the deadliest cancer of the female reproductive system, with the majority of patients experiencing relapse on first-line platinum-based chemotherapies. Therefore, identifying potential targets for additional second-line therapies is critical for treating platinum-resistant ovarian cancer. To that end, the evolution of platinum resistance in a cell-based model of ovarian cancer was monitored via characterization of proteomic changes in cancer-derived extracellular vesicles (EVs) after progressive rounds of cisplatin treatment. The content of cancer-derived EVs was analyzed via mass spectrometry, reverse phase protein array, and Western blotting to identify pathways that could be targeted by second-line therapies. Several therapeutically relevant markers were identified in EVs collected after cisplatin treatment, including PD-L1 and other proteins regulating PD-L1 export. Monoclonal antibody-based therapies (mAbs) targeting PD-1/PD-L1 have been deployed successfully as second-line treatments for a variety of cancers, but their success has yet to be translated to ovarian cancer. Current mAb-based immunotherapies suffer from several pitfalls, including difficulties in managing immune-related adverse events and poor tumor penetration. As an alternative to anti-PD-1/PD-L1 mAb-based immunotherapies, a small interfering peptide for PD-1/PD-L1 was designed based on the interface region of PD-L1. This lead peptide underwent several rounds of in silico optimization and in vitro validation to identify and screen modifications that could improve affinity for PD-1 or stability in serum. Serum stability studies indicated the modifications dramatically improved stability, with peptide abundance still quantifiable via mass spectrometry after 72 hours. The peptide was also shown to block PD-1/PD-L1 complex formation via Amplified Luminescent Proximity Homogeneous Assay screening. The stabilized peptide, MN1.4, was chosen for further efficacy testing in a cell-based model. An ovarian cancer cell line was co-cultured with human peripheral blood mononuclear cells to measure markers of T cell activation via ELISA after MN1.4 treatment. Results showed that MN1.4 had immunosuppressive effects similar to those of full-length PD-L1, suggesting that MN1.4 was an agonist for PD-1 rather than an inhibitor as was initially hypothesized. Therefore, this peptide could have several applications for treating autoimmune disorders, including those that arise as side effects from mAb-based immunotherapies.



Cancer immunotherapy, Drug resistance, Extracellular vesicles, PD-1/PD-L1