Abstract CT192: Phase IIa open-label clinical study of intratumoural administration of BO-112 in combination with pembrolizumab in subjects with liver metastasis from colorectal cancer or gastric/gastro-oesophageal junction cancer

Protocol tittle: Study of BO-112 with pembrolizumab for colorectal or gastric/GEJ cancer with liver metastasis.Background: Gastric (GC), oesophagogastric junction (EGJC) and colorectal tumors (CRC) with microsatellite stability (MSS) are poorly responders to PD(L)-1 inhibition, due to low CD8+ T cell infiltration and PD-L1 expression. Therefore, modulation of the tumor microenvironment (TME) could increase disease control. In these tumors the presence of liver lesions is difficult to control because of the hepatic immune tolerance. Control of the hepatic disease could increase survival.BO-112 is a non-coding dsRNA agonist of TLR3, MDA5 and RIG-I which activates the innate and adaptative immune response, inducing apoptosis and immunogenic cell death, with a local and a systemic effect. A prior Phase I trial showed that the combination of pembrolizumab and intratumoral (IT) BO-112 has a good safety profile and encouraging activity. Study design: This is a single arm phase IIa trial to assess the efficacy of intrahepatic IT BO-112 and iv pembrolizumab in 3W cycles in patients with MSS CRC, GC or EGJ tumors. Up to 69 patients with at least one liver lesion and 2 prior lines for CRC and 1 for GC/EGJC will be enrolled. Primary endpoints: ORR and related TEAEs ≥ grade 3. Secondary endpoints: ORR (iRECIST), PFS, 6-months OS and safety. Exploratory endpoint: Changes in TME (PD-L1 expression and CD8+ T cell infiltration) from baseline to C2D1.Results: A total of 11 CRC and 7 GC/EGJC patients were enrolled since July 2020. This abstract focuses on the CRC patients´ biomarker expression. These patients had low PD-L1 CPS (combined positive score) expression and CD8+ T cell infiltration with a median value of 5 and 4%, respectively, in the TME at baseline. Following two IT BO-112 injections, an important increase in PD-L1 expression and CD8+ T cell infiltration was observed in 5 and 7 patients, respectively. PD-L1 CPS median value increased to 37.9 while CD8+ T cell infiltration median values raised to 12.9%.Conclusions: A meaningful increase in PD-L1 expression and CD8+ T cell infiltration was achieved in MSS CRC patients after one cycle of BO-112-pembrolizumab. Citation Format: Mariano Ponz-Sarvise, Elena Elez, Andres Munoz, Marc Van den Eynde, Antonio Gaetano Rampoldi, Alain Hendlisz, Hans Prenen, Mercedes Rodriguez, Maria Teresa Cano, Marya Chaney, Helena Escuin, Vanesa Pons, Marisol Quintero, Andres Cervantes. Phase IIa open-label clinical study of intratumoural administration of BO-112 in combination with pembrolizumab in subjects with liver metastasis from colorectal cancer or gastric/gastro-oesophageal junction cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr CT192.