Abstract CT107: Phase Ib Study of Pembrolizumab in Combination with Intratumoral Injection of Clostridium novyi-NT in Patients with Advanced Solid Tumors

Abstract BACKGROUND: Intra-tumoral Clostridium novyi-NT (non-toxic) is an attenuated strain of C. novyi lacking alpha toxin replication within hypoxic tumor regions, causing tumor cell lysis and inflammation. Immunotherapy (IO) augments anticancer activity with intratumoral agents in prior preclinical and clinical studies. This phase 1b dose escalation study assessed safety and potential synergistic effects of pembrolizumab and C. novyi-NT in advanced solid tumors. METHODS: We enrolled patients with percutaneous injectable, solid tumors to receive single intratumoral injection of C. novyi-NT administered on Day 8 across 4 dose cohorts (3 × 10^4 to 100 × 10^4 spores, 3+3 design) with pembrolizumab 200mg IV Q3weekly starting on Day 0 up to 24 months. Primary objectives: Safety, tolerability and maximum tolerated dose (MTD) of combination. Secondary objectives: anti-tumor activity of combination in the injected tumor lesion and overall response by iRECIST 1.1. RESULTS: At data cutoff on October 24, 2022, 16 patients were enrolled and evaluable for toxicity and efficacy. It was well tolerated across all cohorts without dose limiting toxicities with median number of 5 cycles administered (1-34). 10 patients (63%) experienced progression; 1 withdrew consent; 1 completed therapy; 1 came off trial due to toxicity (immune related dermatitis) and 3 patients remain on trial. Median age was 62.5 years (40-71) while all patients (100%) had performance status of 1. 8 (50%) received prior IO and 7 (44%) had > 4 lines of prior therapies. Confirmed overall objective response rate (ORR) was 25% in 4 patients [non-keratinizing undifferentiated nasopharyngeal squamous carcinoma (NPC), human papilloma virus positive squamous cell carcinoma of base of tongue, vulvar melanoma and chordoma] with 3 partial responses (PR) and 1 complete response (CR). Among responders, median duration of response was 8.18 months and 1/4 (25%) had prior IO. NPC patient completed 24 months on trial to completion with best response at PR (-87%) while vulvar melanoma patient remains on trial with best response at CR (-100%). Median injected tumor size was 2.65cm (1-11) with confirmed ORR in injected lesions at 19% with 2 PRs and 1 CR. Most prevalent grade 1 and 2 adverse events were injection site reaction (25%), pyrexia (19%), pruritus (13%), leukopenia (13%) and anemia (13%). No grade 3 or 4 treatment related adverse events noted. Signs and symptoms of C. novyi-NT germination (infection) including fever, injection site pain, erythema, swelling, tenderness, and in some cases, ulceration, spontaneous drainage, tissue sloughing, bleeding, and malodor were observed in 5 patients. CONCLUSIONS: Intratumoral C. novyi-NT with pembrolizumab demonstrates clinical activity with favorable tolerability in patients regardless of tumor histology. This study is ongoing to define the recommended phase 2 dose (NCT03435952). Citation Format: Blessie Elizabeth Nelson, Filip Janku, Siqing Fu, Ecaterina I. Dumbrava, David S. Hong, Daniel Karp, Aung Naing, Jordi Rodon, Apostolia Tsimberidou, Rodabe N. Amaria, Anthony Conley, Senthil Damodaran, Kanwal P. Raghav, Brent L. Kreider, David Tung, Mary Varterasian, Khashayarsha Khazaie, Sarina Piha-Paul. Phase Ib Study of Pembrolizumab in Combination with Intratumoral Injection of Clostridium novyi-NT in Patients with Advanced Solid Tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT107.