Cationic Peptide Conjugation Enhances Intratumoral Retention and Antitumor Efficacy of Immune Checkpoint Blockade Antibodies

The tumor extracellular matrix (ECM) forms a net negatively charged network that interacts with and hinders the transport of molecules, partly based on electrostatic interactions. The focus on drug delivery in solid tumors has traditionally been on developing neutral charge coatings to minimize interactions with the ECM for improved transport. In contrast to prior work, we recently found a cationic peptide that interacted electrostatically with the negatively charged components of the ECM, resulting in enhanced uptake and retention of nanoparticles in the tumor ECM and tumor tissue. Based on this previous study, here, we hypothesize that the electrostatically driven interactions of the cationic peptide will improve the binding and retention of immune checkpoint blockade antibodies (ICBs), ultimately enhancing their antitumor immunogenic responses. We prepared peptide-antibody conjugates by conjugating the cationic peptide to anti-Cytotoxic T-Lymphocyte Antigen 4 (α-CTLA4) and anti-Programmed cell Death Ligand-1 (α-PD-L1) ICBs using copper-free click chemistry. We confirmed an average of 1–2 peptides per antibody. The cationic peptide electrostatically interacted with the net negatively charged tumor ECM and improved the binding of the antibodies to the tumor ECM without affecting their ability to recognize their antigens. Modifying the antibodies with cationic peptides reduced the systemic exposure of the antibodies and did not induce treatment-related toxicities. The conjugation of ICBs with cationic peptides improved their retention in the tumor microenvironment, resulting in improved antitumor efficacy compared to unconjugated ICBs. These results suggest that leveraging simple electrostatic interactions between cationic peptide anchors and the tumor microenvironment can ultimately improve the antitumor efficacy of immune checkpoint blockade antibodies.