Abstract 1707: Increasing immune cell infiltration in hepatocellular carcinoma tumors using a novel GPC3-targeting aptamer conjugate

Glypican 3 (GPC3) is a cell membrane-bound heparin sulfate proteoglycan, expressed at the cell surface of many cancer types. It has emerged as a leading target for hepatocellular carcinoma treatment due to its overexpression in aberrant liver cells and low expression in healthy adult tissues. One of the major challenges in treating hepatocellular carcinoma with current immunotherapies is turning cold tumors into immunogenic ones. Unmethylated CpG oligodeoxynucleotides (ODNs) are known immune stimulators, however their use in combination therapy for cancer treatment is limited due to the requirement of intra tumoral injections to prevent systemic toxicity. Here, we describe a unique GPC3-specific aptamer, able to target GPC3-expressing cancer cells in vivo as a means to deliver the immunostimulatory CpG 7909. Systemic administration through intra peritoneal (i.p.) injection of the GPC3 aptamer-CpG conjugate (GRX51) decreases Hep3B tumor volume in a Balb/c nude mouse xenograft model by ~30-50% depending on treatment schedule, while also increasing immune cell infiltration. Final tumor volumes of GRX51-treated animals are consistent with tumor volumes of animals treated with the standard of care compound, sorafenib tosylate. Due to its GPC3-targeting capacity, systemic dosing of GRX51 (15 mg/kg) is less toxic than systemic administration with equimolar amounts of CpG 7909 alone (5 mg/kg), with a comparable effect on tumor shrinkage. While both GRX51 and CpG 7909 induce immune cell recruitment, GRX51 treated mice had a final immune:tumor cell ratio of 2.45 ± 0.56, while CpG 7909-treated animals had a ratio of 1.51 ± 0.95 relative to the vehicle control after a 7-day on/7-day off daily dosing schedule. Using the Hep3B xenograft in CD34+ humanized mice, we also showed GRX51 primes tumors for combination treatments with FDA approved checkpoint inhibitors. Mice were treated with GRX51 (7.5 mg/kg daily i.p. dose, 11 days), the PD-1R inhibitor pembrolizumab (10 mg/kg once every 3 days i.p., 11 days), or a combination of the two drugs. The GRX51 treatment alone outperformed pembrolizumab alone, reducing tumor size by 33% and 18% respectively. Notably, the combination of GRX51 with pembrolizumab reduced tumor size by 63%. Together, our data show that GRX51 is a novel GPC3-targeting molecule capable of reducing tumor size and priming GPC3-positive tumors for combination immunotherapy, without inducing major systemic toxicity with i.p. injection.Citation Format: Christina McGuire, Jin Yuan, Aaron Ball, Justin Sonberg, Yuxun Wang, Kristin Thompson, Shuhao Zhu. Increasing immune cell infiltration in hepatocellular carcinoma tumors using a novel GPC3-targeting aptamer conjugate [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 1707.