Tumor-Targeted Interleukin 2 Boosts the Anticancer Activity of FAP-Directed Radioligand Therapeutics
Andrea Galbiati, Paulina Dorten, Ettore Gilardoni, Florian Gierse, Matilde Bocci, Aureliano Zana, Jacqueline Mock, M. Claesener, Juela Cufe, Florian Büther, Klaus Schäfers, Sven Hermann, Michael Schäfers, Dario Neri, Samuele Cazzamalli, Philipp Backhaus
Abstract
We studied the antitumor efficacy of a combination of 177 Lu-labeled radioligand therapeutics targeting the fibroblast activation protein (FAP) (OncoFAP and BiOncoFAP) with the antibody-cytokine fusion protein L19-interleukin 2 (L19-IL2) providing targeted delivery of interleukin 2 to tumors. Methods: The biodistribution of 177 Lu-OncoFAP and 177 Lu-BiOncoFAP at different molar amounts (3 vs. 250 nmol/kg) of injected ligand was studied via SPECT/CT in mice bearing subcutaneous HT-1080.hFAP tumors, and self-absorbed tumor and organ doses were calculated. The in vivo anticancer effect of 5 MBq of the radiolabeled preparations was evaluated as monotherapy or in combination with L19-IL2 in subcutaneously implanted HT-1080.hFAP and SK-RC-52.hFAP tumors. Tumor samples from animals treated with 177 Lu-BiOncoFAP, L19-IL2, or both were analyzed by mass spectrometry-based proteomics to identify therapeutic signatures on cellular and stromal markers of cancer and on immunomodulatory targets. Results: 177 Lu-BiOncoFAP led to a significantly higher self-absorbed dose in FAP-positive tumors (0.293 6 0.123 Gy/MBq) than did 177 Lu-OncoFAP (0.157 6 0.047 Gy/MBq, P 5 0.01) and demonstrated favorable tumorto-organ ratios at high molar amounts of injected ligand. Administration of L19-IL2 or 177 Lu-BiOncoFAP as single agents led to cancer cures in only a limited number of treated animals. In 177 Lu-BiOncoFAP-plus-L19-IL2 combination therapy, complete remissions were observed in all injected mice (7/7 complete remissions for the HT-1080.hFAP model, and 4/4 complete remissions for the SK-RC-52.hFAP model), suggesting therapeutic synergy. Proteomic studies revealed a mechanism of action based on the activation of natural killer cells, with a significant enhancement of the expression of granzymes and perforin 1 in the tumor microenvironment after combination treatment. Conclusion: The combination of OncoFAP-based radioligand therapeutics with concurrent targeting of interleukin 2 shows synergistic anticancer effects in the treatment of FAP-positive tumors. This experimental finding should be corroborated by future clinical studies.