Conjugation of Listeriolysin O to Anti-CD47 mAb: Harnessing Listeria Toxin to Weaponize Macrophages against Tumor Cells

Abstract

<h3>Purpose/Objective(s)</h3> CD47 is expressed on various tumor types including breast, prostate, glioblastoma, non-Hodgkin lymphoma, and hepatocellular carcinoma. Interrupting the CD47-SIRP alpha axis by monoclonal antibodies fosters macrophage-mediated phagocytosis of solid and hematopoietic tumor cells. The pore-forming toxin listeriolysin O (LLO) is activated in the acidic vacuoles of bone marrow-derived macrophages. We hypothesize that LLO conjugation to the anti-CD47 mAb enhances the release of autophagic cargo within macrophages thereby augmenting cGAS-STING activation, antigen presentation, and tumor phagocytosis. <h3>Materials/Methods</h3> The anti-CD47 mAb was conjugated to the LLO toxin using a water-soluble SPDP crosslinker and purified by affinity chromatography. The cytotoxicity of anti-CD47-LLO mAb relative to anti-CD47 mAb was tested in the mouse breast cancer cell line E0771, the human breast cancer cell line MDA-MB-468, the mouse lung cancer cell line LLC, and the human leukemia monocytic cell line THP-1. C57B6 mouse bone marrow-derived macrophages (BMDM) co-cultured with tumor cell lines were analyzed in the presence of anti-CD47-LLO mAb and anti-CD47 mAb to determine the efficiency of BMDM tumor cell phagocytosis, STING activation, and antigen presentation. Tumor growth of E0771-bearing wildtype mice was measured following intratumoral injection of anti-CD47 mAb and anti-CD47-LLO mAB. <h3>Results</h3> The anti-CD47-LLO mAb conjugate enhanced BMDM phagocytosis of LLC and E0771 tumor cells in a dose dependent manner that was significantly higher than cells treated with the anti-CD47 mAb alone. The anti-CD47-LLO mAb significantly increased BMDM levels of phosphorylated STING, interferon-stimulated genes, and antigen presentation relative to anti-CD47 mAb treatment. At doses compatible with preserved animal total body weight, red blood cell counts, and lymphocyte counts, intratumoral injection of anti-CD47-LLO mAb significantly suppressed tumor growth of E0771-bearing wildtype mice relative to the anti-CD47 mAb. <h3>Conclusion</h3> Conjugation of the LLO toxin to anti-CD47 mAb enhances macrophage cGAS-STING activation, antigen presentation, and tumor cell phagocytosis. This novel CD47 antibody builds on clinical interest in targeting macrophages for the treatment of malignancy and may be studied as a supplemental therapy for patients with tumors resistant or refractory to checkpoint therapy.