An open-label, multicenter study investigating RP2 oncolytic immunotherapy in combination with second-line systemic atezolizumab combined with bevacizumab in patients with locally advanced unresectable or metastatic hepatocellular carcinoma.

TPS4191 Background: Despite advances in treatment for unresectable hepatocellular carcinoma (HCC), long-term survival rates remain poor. The combination of atezolizumab (Atezo) plus bevacizumab (Bev) is approved as frontline therapy for advanced HCC, but only a minority of patients (pts) respond and secondary resistance usually occurs within months. HCC has an immune-suppressed tumor microenvironment (TME), mediated by activated immune checkpoint signaling and angiogenesis pathways, which may contribute to therapeutic resistance. RP2 is an enhanced potency oncolytic herpes simplex virus type 1 (HSV-1) that expresses the fusogenic gibbon ape leukemia virus glycoprotein with the R sequence deleted (GALV-GP-R–), GM-CSF, and an anti–CTLA-4 antibody-like molecule. The direct oncolytic effect coupled with immune stimulation by RP2 in the TME is intended to provide systemic antitumor activity and synergize with anti–PD-1/PD-L1 agents, such as Atezo. Preclinical data have demonstrated improved distribution of oncolytic HSV within tumors in combination with Bev, supporting the clinical combination of RP2 with Bev. This study will evaluate the safety and efficacy of RP2 combined with Atezo plus Bev as second-line systemic therapy for unresectable and advanced HCC (NCT05733598). Methods: This is an open-label, single arm, phase 2 trial. Up to 30 pts will be enrolled and receive RP2 in combination with Atezo plus Bev. Key inclusion criteria include advanced unresectable HCC with ≥1 measurable tumor of ≥1 cm in longest diameter, Child-Pugh class A, an Eastern Cooperative Oncology Group performance status of 0 to 1, and progression on 1 prior systemic treatment, which must have included a PD-1/PD-L1–directed agent. Key exclusion criteria include untreated/incompletely treated esophageal and/or gastric varices with bleeding or at high risk for bleeding and macroscopic invasion of the tumor into any major blood vessel(s) and/or main bile ducts. Pts will receive intratumoral RP2 Q2W for 4 doses, then Q3W for up to 4 doses. Bev will be given at 10 mg/kg Q2W starting with the first dose of RP2 then at 15 mg/kg Q3W starting with cycle 4; Atezo will be given at 840 mg Q2W for cycles 2 and 3, then at 1200 mg Q3W starting with cycle 4. Pts will receive treatment until confirmed progressive disease, loss of clinical benefit, or unacceptable toxicity. The primary endpoint is overall response rate (ORR), defined as the proportion of pts achieving a best overall response of complete response or partial response per Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1 as modified for this study. Secondary endpoints are safety, ORR using HCC-modified RECIST, duration of response, complete response rate, and progression-free survival. Clinical trial information: NCT05733598 .