Abstract 3513: INBRX-121, a safe and efficacious molecular targeted cytokine that enhances NK cell-mediated tumor killing
Authors: Kinkead Heather , Sulzmaier Florian J. , Polovina Anya , Kern Nadja , Sanabria Angelica , Ho Jason , Macedo Chelsie , Henderson Ryan , Hussain Abrahim , Pandit Rajay , Crago William , Rowell Emily , Eckelman Brendan P. 
Published: June 2022

Abstract
IL-2 is a powerful cytokine that enhances the activity of and induces the expansion of tumoricidal effector cells including T and NK cells. Despite promising signs of activity, the clinical utility of IL-2 is limited due to severe treatment-associated toxicities including vascular leak syndrome and the concurrent expansion of immunosuppressive regulatory T cells, which blunts efficacy. We developed a molecular targeted cytokine (MTC) platform that combines an engineered IL-2 variant with reduced affinity for the IL-2 receptor and high affinity single-domain antibodies (sdAb) to restrict IL-2 receptor signaling to cells expressing the target antigen (termed cis-signaling).
INBRX-121 is an MTC designed to deliver IL-2 to NK cells using an NKp46-specific sdAb as the targeting moiety. In vitro, INBRX-121 induces dose-dependent STAT5 phosphorylation and proliferation in NK cells with comparable potency to wild-type IL-2, while showing no NKp46-independent activity at concentrations of more than three magnitudes higher than that required for NK cell activity. INBRX-121 enhances NK cell activation and cytotoxic capacity, thereby reducing the NK-to-target cell ratio as well as the target receptor density needed for optimal tumor cell killing. Furthermore, INBRX-121 lowers the threshold for antibody-dependent cellular cytotoxicity (ADCC) and increases maximal target cell killing in combination with ADCC-competent antibodies to an extent that may lessen the need for Fc engineering to enhance binding to the low affinity CD16A variant. In vivo, INBRX-121 demonstrates potent anti-tumor activity with increased intra-tumoral NK cell accumulation and upregulation of NK cell activation markers. INBRX-121 monotherapy reduces primary tumor growth and the formation of metastasis, while combination with ADCC-competent antibodies further increases NK cell activity to convert tumor growth suppression into complete tumor elimination. INBRX-121 is well tolerated in rodents and non-human primates and no overt signs of toxicity have been observed in cynomolgus monkeys up to the highest administered dose of 30 mg/kg.
Our MTC platform provides a novel path to overcoming the limitations of IL-2 therapy through the pinpointed delivery of IL-2 activity to target cells of interest. In the case of INBRX-121 this ensures potent enhancement of the naturally broad anti-tumor activity of NK cells, which have distinct advantages over T cell therapeutics. Unlike T cells, tumor recognition by NK cells is independent of MHC-presented antigens and can elicit immediate cytotoxic activity. Further, many of the toxicities associated with T cell therapeutics have not been observed with NK-centric treatments. INBRX-121 therefore provides a promising safe and efficacious treatment option for a broad array of cancer indications both as a monotherapy and in combination with ADCC-enabled antibodies.
Citation Format: Heather Kinkead, Florian J. Sulzmaier, Anya Polovina, Nadja Kern, Angelica Sanabria, Jason Ho, Chelsie Macedo, Ryan Henderson, Abrahim Hussain, Rajay Pandit, William Crago, Emily Rowell, Brendan P. Eckelman. INBRX-121, a safe and efficacious molecular targeted cytokine that enhances NK cell-mediated tumor killing [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 3513.