Anti-PD-L1 F(ab) Conjugated PEG-PLGA Nanoparticle Enhances Immune Checkpoint Therapy.

Background: Immune checkpoint therapies are effective in the treatment of a subset of patients in many different cancers. Immunotherapy offers limited efficacy in part because of rapid drug clearance and off-target associated toxicity. PEG-PLGA is a FDA approved, safe, biodegradable polymer with flexible size control. The delivery of immune checkpoint inhibitors such as anti-PD-L1 (α-PD-L1) via PEG-PLGA polymer has the potential to increase bioavailability and reduce immune clearance to enhance clinical efficacy and reduce toxicity. Methods: The Fc truncated F(ab) portion of α-PD-L1 monoclonal antibody (α-PD-L1 mAb) was attached to a PEG-PLGA polymer. α-PD-L1 F(ab)-PEG-PLGA polymers were incubated in oil-in-water emulsion to form a α-PD-L1 F(ab)-PEG-PLGA nanoparticle (α-PD-L1 NP). α-PD-L1 NP was characterized for size, polarity, toxicity and stability. The relative efficacy of α-PD-L1 NP to α-PD-L1 mAb was measured when delivered either intraperitoneally (IP) or intravenously (IV) in a subcutaneous mouse colon cancer model (MC38). Antibody retention was measured using fluorescence imaging. Immune profile in mice was examined by flow cytometry and immunohistochemistry. Results: Engineered α-PD-L1 NP was found to have pharmacological properties that are potentially advantageous compared to α-PD-L1 mAb. The surface charge of α-PD-L1 NP was optimal for both tumor cell uptake and reduced self-aggregation. The modified size of α-PD-L1 NP reduced renal excretion and mononuclear phagocyte uptake, which allowed the NP to be retained in the host system longer. α-PD-L1 NP was non-toxic in vitro and in vivo. α-PD-L1 NP comparably suppressed MC38 tumor growth. α-PD-L1 NP appeared to elicit an increased immune response as measured by increase in germinal center area in the spleen and in innate immune cell activation in the tumor. Finally, we observed that generally, for both α-PD-L1 NP and α-PD-L1 mAb, the IP route was more effective than IV route for tumor reduction. Conclusion: α-PD-L1 NP is a non-toxic, biocompatible synthetic polymer that can extend α-PD-L1 antibody circulation and reduce renal clearance while retaining anti-cancer activity and potentially enhancing immune activation.