Abstract CT040: SOT101, an IL-2/IL-15 Rβγ superagonist, in combination with pembrolizumab in patients with advanced solid tumors: Interim safety and efficacy results from the AURELIO-03 dose escalation trial

Abstract Introduction: SOT101 (previously SO-C101), a fusion protein of IL-15 and the IL-15 receptor α sushi+ domain, was investigated in an open-label, multicenter, dose-escalation study as monotherapy and in combination with pembrolizumab in patients with selected advanced tumors (NCT04234113). Here we report an update on the safety and efficacy of the combination treatment. Methods Dose escalation followed a standard 3+3 design. Objectives were to determine the maximum tolerated dose (MTD) and the recommended phase 2 dose (RP2D). The evaluation period for dose-limiting toxicities in each dose step was 21 days. The RP2D was defined as the MTD or a dose below, considering pharmacokinetic and pharmacodynamic parameters. The study is ongoing (data cut-off 26 January 2022). Results: Twenty-one patients with a median of 2 (range 1-6) lines of previous systemic therapies were treated with 1.5, 3.0, 6.0, 9.0, and 12.0 μg/kg of SOT101 subcutaneously in combination with pembrolizumab. The MTD was not yet reached at the ongoing dose level 12.0 µg/kg, which is the RP2D in SOT101 monotherapy. The most common treatment-emergent adverse events were transient and included pyrexia, chills, injection site reaction, anemia, transaminase elevation, vomiting, and lymphopenia. One dose-limiting toxicity with rash, hypotension, and oliguria was reported at 6.0 µg/kg. The event resolved within 2 days and the patient continued with SOT101 at a lower dose. No treatment-related death was reported. One patient achieved a confirmed complete response (CR): mesothelioma at 9.0 µg/kg, on treatment 20 weeks with CR. This patient was immune checkpoint blocker (ICB)-naïve. Four patients achieved a partial response (PR): thyroid gland carcinoma at 3.0 µg/kg, ICB-naïve, on treatment 61 weeks with PR; skin squamous cell carcinoma at 6.0 µg/kg, ICB-relapsed, with PR and disappearance of target lesions, then fluctuating lesions, and on treatment 46 weeks with significant clinical benefit; skin melanoma at 6.0 µg/kg, ICB-relapsed, on treatment 41 weeks with PR; cervical melanoma at 9.0 µg/kg, ICB-pretreated, discontinued treatment after 8 weeks while still on PR. Five patients had confirmed stable disease (SD): anal squamous cell carcinoma (anal SCC) at 1.5 µg/kg, gastric cancer at 3.0 µg/kg, cervical cancer at 6.0 µg/kg, liver cancer at 6.0 µg/kg, and colorectal cancer at 9.0 µg/kg, with 1 patient (anal SCC) having a long-lasting SD over 40 weeks. In this heavily pretreated population, the observed preliminary clinical benefit rate was 63%. Conclusions: SOT101 in combination with pembrolizumab showed a favorable safety profile. Highly promising efficacy signals were reported in ICB-naïve and ICB pre-treated patients, including ICB-resistant tumors. Citation Format: Stephane Champiat, Aurelien Marabelle, Vladimir Galvao, Patricia LoRusso, Peter Grell, Philippe Cassier, Carlos Gomez-Roca, Iphigenie Korakis, Aung Naing, Lenka Palova Jelinkova, Irena Adkins, Ulrich Moebius, Richard Sachse, Sascha Tillmanns, David Bechard, Joachim Kiemle-Kallee, Elena Garralda. SOT101, an IL-2/IL-15 Rβγ superagonist, in combination with pembrolizumab in patients with advanced solid tumors: Interim safety and efficacy results from the AURELIO-03 dose escalation trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT040.