Updated results of a phase 1/2 study of AU-007, a monoclonal antibody (mAb) that binds to IL-2 and inhibits CD25 binding, in patients with advanced solid tumors.
Authors: Rasco Drew W. , McKean Meredith , Haydon Andrew Mark , Weickhardt Andrew James , Frentzas Sophia , Ahern Elizabeth Stephanie , Powderly John D. , Wyant Timothy , Tang Jenny , Richards Lori , Knickerbocker Aron , Amit Inbar , Ofran Yanay , Vasselli James Robert 
Published: June 2024

2527 Background: AU-007 is a computationally designed human mAb that binds interleukin-2 (IL-2) on its CD25 binding epitope. AU-007 bound IL-2 cannot bind trimeric (CD25, CD122, CD132) IL-2 receptors (IL-2R) on regulatory T cells (Tregs), vascular endothelium, or eosinophils, but IL-2’s binding to dimeric IL-2R (CD122, CD132) on effector T (T eff) and NK cells is unhindered. AU-007 thus redirects IL-2 towards T eff and NK cell activation, while diminishing Treg activation and vascular leak. AU-007 uniquely redirects IL-2 generated from T eff cell expansion, converting a Treg-mediated autoinhibitory loop into an immune stimulating loop. Methods: The study consists of three dose escalation arms followed by cohort expansion. Arm 1A evaluates escalating doses (0.5 – 12 mg/kg) of AU-007 (IV every 2 weeks [Q2W]). Arm 1B evaluates AU-007 Q2W + escalating doses (15K – 270K IU/kg) of one aldesleukin subcutaneous (SC) dose. Arm 1C evaluates AU-007 + escalating doses of SC aldesleukin, both Q2W. Nineteen solid tumor types are allowed in escalation. Cohort expansion Arm 2B evaluates 9 mg/kg AU-007 + one 135K IU/kg aldesleukin dose. Results: Fifty-three patients were enrolled as of 23 January 2024: 15 in Arm 1A, 12 in Arm 1B, 25 in Arm 1C, and 1 in cohort expansion. AU-007 (+/- aldesleukin) was well-tolerated, with no dose limiting toxicities through all Arm 1A and 1B cohorts and the 3rd cohort (of 4) in 1C. Enrollment is ongoing in the final Arm 1C cohort and Arm 2B expansion. All drug related adverse events (AE) were Grade 1 or 2 except for 4 patients with transient lymphopenia (Grade 3 and 4) and 1 patient with Grade 3 anemia. The most common drug-related AEs were pyrexia (18%), fatigue (16%), nausea (14%), lymphopenia (8%), and chills (6%). Two patients had transient Grade 2 drug-related serious AEs: pyrexia Arm 1B and cytokine release syndrome Arm 1C; both patients continued therapy. A confirmed partial response (32% decrease) occurred in a nasopharyngeal carcinoma patient in Arm 1C who progressed on anti-PD-1 therapy. Tumor shrinkage occurred in patients with non-small cell lung, bladder, head and neck, colorectal (CRC), and renal cancer. A melanoma patient (Arm 1B) who progressed on anti-CTLA-4 + anti-PD-1 therapy had a 48% decrease in target tumors; a small brain metastasis was found and irradiated at week 16 and the patient remains on treatment. A patient with microsatellite stable CRC had a 26% tumor shrinkage after the first cycle (Arm 1C). Serum Tregs and eosinophils decreased in patients while NK and CD8 cell counts trended upwards. The CD8:Treg ratio trends upward in all cohorts. Conclusions: The mild toxicity profile and promising early efficacy observed in dose escalation across multiple tumor types in heavily pretreated patients, along with initial pharmacodynamic data, warrant continued evaluation of AU-007 + low dose SC aldesleukin in the Phase 2 expansion cohorts of the study. Clinical trial information: NCT05267626 .