Abstract C048: Novel master checkpoint Cbl-b siRNA-based adoptive cellular therapy: Superior antitumor efficacy in a syngeneic murine hepatocellular carcinoma Hepa1-6 model following APN401 monotherapy and synergistic effects with anti-PD1
Authors: Gaweco Anderson , Thell Kathrin , Urban Maria , Harrauer Julia , Haslinger Isabella , Dohnal Alexander , Lametschwandtner Guenther , Drobits Karin , Gugenberger Romana , Muehleisen Hannes , Penninger Josef , Becerra Carlos , Chung Vincent , El-Khoueiry Anthony 
Published: March 2020

Introduction: The E3 ubiquitin ligase Cbl-b is an intracellular master checkpoint which negatively regulates both adaptive and innate anti-tumor immune responses. Selective targeting of Cbl-b not only induces anti-tumor activity in vivo but also overrides immune regulation by the PD-L1/PD-1 pathway in vitro (2017 Fujiwara et al). Human APN401 is an autologous adoptive cellular therapy of ex vivo Cbl-b-silenced human PBMCs currently in a clinical Phase 1b multiple dose study demonstrating early clinical safety and tolerability in patients with advanced solid tumors. Herein the preclinical Proof of Concept efficacy of murine APN401 immunotherapy is established in the syngeneic mouse hepatocellular carcinoma Hepa1-6 model. Experimental Procedure: Hepa1-6-C57/BL6-tumor bearing mice were treated with murine APN401 ex vivo silenced immune cells with Cbl-b specific siRNA as monotherapy or in combination with anti-PD1 (clone RMP1-14) versus control siRNA. Mice were treated for 14 d starting on D7 after inoculation of Hepa1-6 cells and tumor volume was measured daily. Results: Murine APN401 treatment alone significantly suppressed Hepa1-6 tumor growth by 56% (p&lt;0.0001) versus control siRNA-treated mice. Combination therapy of APN401 with anti-PD1 induced profound synergistic anti-tumor efficacy with tumor growth inhibition of 76% (p&lt;0.0001) versus anti-PD1 alone with control siRNA. APN401 was well tolerated and APN401-treated mice were unremarkable with optimal body conditions. Conclusion: APN401 monotherapy demonstrates striking anti-tumor efficacy in suppressing tumor growth in a murine hepatocellular carcinoma Hepa1-6 model. The preclinical synergistic effects of APN401 with anti-PD1 support its therapeutic utility as a combination therapy with immune checkpoint anti-PD1 treatment. These findings highlight the potential promise of selective Cbl-b silencing by APN401 as a novel immunotherapy for cancer.

Citation Format: Anderson Gaweco, Kathrin Thell, Maria Urban, Julia Harrauer, Isabella Haslinger, Alexander Dohnal, Guenther Lametschwandtner, Karin Drobits, Romana Gugenberger, Hannes Muehleisen, Josef Penninger, Carlos Becerra, Vincent Chung, Anthony El-Khoueiry. Novel master checkpoint Cbl-b siRNA-based adoptive cellular therapy: Superior antitumor efficacy in a syngeneic murine hepatocellular carcinoma Hepa1-6 model following APN401 monotherapy and synergistic effects with anti-PD1 [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr C048. doi:10.1158/1535-7163.TARG-19-C048