Immunostimulatory effects of targeted thorium-227 conjugates as single agent and in combination with anti-PD-L1 therapy

• Published in: Journal for immunotherapy of cancer 2021-10, Vol.9 (10), p.e002387
• Main Authors: Lejeune, Pascale, Cruciani, Véronique, Berg-Larsen, Axel, Schlicker, Andreas, Mobergslien, Anne, Bartnitzky, Lisa, Berndt, Sandra, Zitzmann-Kolbe, Sabine, Kamfenkel, Claudia, Stargard, Stefan, Hammer, Stefanie, Jørgensen, Jennifer S, Jackerott, Malene, Nielsen, Carsten H, Schatz, Christoph A, Hennekes, Hartwig, Karlsson, Jenny, Cuthbertson, Alan S, Mumberg, Dominik, Hagemann, Urs B
• Format: Article
• Language: English
• Subjects: Animals; Antibodies; B7-H1 Antigen - antagonists & inhibitors; Basic Tumor Immunology; Cancer; Cancer therapies; Cloning; Cytokines; Flow cytometry; Gene expression; Gene Expression Profiling; Immunoconjugates - pharmacology; Immunoconjugates - therapeutic use; Immunotherapy; Lymphatic system; Lymphocytes; Mice; Ovarian cancer; Radiation; radiotherapy; Thorium - pharmacology; Thorium - therapeutic use; Transfection; Tumors; Xenograft Model Antitumor Assays
• ISSN: 2051-1426; 2051-1426
• DOI: 10.1136/jitc-2021-002387

BackgroundTargeted thorium-227 conjugates (TTCs) are an emerging class of targeted alpha therapies (TATs). Their unique mode of action (MoA) is the induction of difficult-to-repair clustered DNA double-strand breaks. However, thus far, their effects on the immune system are largely unknown. Here, we investigated the immunostimulatory effects of the mesothelin-targeted thorium-227 conjugate (MSLN-TTC) in vitro and in vivo in monotherapy and in combination with an inhibitor of the immune checkpoint programmed death receptor ligand 1 (PD-L1) in immunocompetent mice.MethodsThe murine cell line MC38 was transfected with the human gene encoding for MSLN (hMSLN) to enable binding of the non-cross-reactive MSLN-TTC. The immunostimulatory effects of MSLN-TTC were studied in vitro on human cancer cell lines and MC38-hMSLN cells. The efficacy and MoA of MSLN-TTC were studied in vivo as monotherapy or in combination with anti-PD-L1 in MC38-hMSLN tumor-bearing immunocompetent C57BL/6 mice. Experiments were supported by RNA sequencing, flow cytometry, immunohistochemistry, mesoscale, and TaqMan PCR analyses to study the underlying immunostimulatory effects. In vivo depletion of CD8+ T cells and studies with Rag2/Il2Rg double knockout C57BL/6 mice were conducted to investigate the importance of immune cells to the efficacy of MSLN-TTC.ResultsMSLN-TTC treatment induced upregulation of DNA sensing pathway transcripts (IL-6, CCL20, CXCL10, and stimulator of interferon genes (STING)-related genes) in vitro as determined by RNASeq analysis. The results, including phospho-STING activation, were confirmed on the protein level. Danger-associated molecular pattern molecules were upregulated in parallel, leading to dendritic cell (DC) activation in vitro. MSLN-TTC showed strong antitumor activity (T:C 0.38, p