An Open-Label Clinical Trial of RP2 and RP3 Oncolytic Immunotherapy in Combination with Atezolizumab and Bevacizumab for the Treatment of Patients with Advanced Colorectal Carcinoma

TPS3628 Background: Colorectal cancer (CRC) is the third most frequently diagnosed cancer and the second leading cause of cancer-related mortality worldwide. PD-1/PD-L1 inhibition, in combination with other modalities, has demonstrated significant benefit in patients (pts) with microsatellite instability-high or mismatch repair deficient CRC. However, these agents have limited, if any, clinical benefit in pts with microsatellite stable (MSS) or mismatch repair proficient (pMMR) CRC. RP2 is an enhanced potency oncolytic herpes simplex virus type 1 which expresses the fusogenic gibbon ape leukemia virus glycoprotein with the R sequence deleted (GALV-GP-R–), granulocyte-macrophage colony-stimulating factor (GM-CSF), and an anti–CTLA-4 antibody-like molecule; RP3 additionally expresses 4-1BB and CD40 activating ligands, but does not express GM-CSF. Both agents have demonstrated preliminary safety and efficacy in pts with solid tumors. This study will evaluate the safety and efficacy of RP2 and RP3 in combination with atezolizumab (Atezo) and bevacizumab (Bev) in pts with advanced MSS and pMMR CRC. Methods: Pts with a histologic diagnosis of unresectable and/or metastatic CRC, with documented MSS or pMMR status, and previously treated with up to 3 standard-of-care systemic regimens will be enrolled in the RP2 + Atezo + Bev or RP3 + Atezo + Bev treatment groups (30 pts per group). Further key inclusion criteria include Eastern Cooperative Oncology Group performance status 0–1 and adequate hepatic, renal, and hematologic function. RP2/RP3 will be injected into tumors by direct (including via colonoscope) or image-guided injection. Pts will receive 8 total doses of up to 10 mL of RP2 or RP3, with a first dose concentration of 1 × 10 6 plaque-forming units (PFU)/mL, followed by 3 doses of 1 × 10 7 PFU/mL every 2 weeks, and then 4 doses of 1 × 10 7 PFU/mL every 3 weeks. Pts may receive a second course of up to 8 injections of RP2/RP3 if study criteria are met. Bev will be administered starting on day 1 (with first dose of RP2/RP3); Atezo will be administered starting week 7 on the same days as RP2/RP3. The primary endpoint is objective response rate; secondary endpoints are safety, overall survival, progression-free survival, duration of response, and complete response rate. Antitumor activity will be evaluated using Response Evaluation Criteria in Solid Tumors version 1.1 as modified for this study. Safety will be assessed by physical examination, clinical laboratory evaluations, vital signs, and monitoring for adverse events (AEs; including serious AEs). Clinical trial information: NCT05733611 .