Abstract CT183: Initial results from a phase 1a/1b study of STK-012, a first-in-class α/β IL-2 receptor biased partial agonist in advanced solid tumors (NCT05098132)

Abstract Background: STK-012 is a first-in-class α/β-IL-2R biased partial agonist designed to drive antitumor activity by selectively stimulating CD25+ antigen activated T cells, while avoiding hallmark IL-2 toxicities by sparing pleotropic activation of lymphocytes including NK cells. Methods: STK-012-101 is a Phase 1a/b study of STK-012 administered subcutaneously in subjects with advanced, relapsed/refractory (r/r) solid tumors. During Phase 1a, subjects are enrolled in a 3+3 dose escalation to STK-012 as monotherapy (QW or Q3W) or STK-012 + pembrolizumab (Q3W) followed by Phase 1b expansions. Results: Phase 1a and preliminary Phase 1b data are being presented for STK-012 monotherapy. As of Oct 23rd, 2023, 45 subjects were treated at 7 dose levels (DL) across 2 schedules (QW at 0. 375 mg and 0. 75mg; Q3W at 0. 75mg-3mg). The most common tumors were NSCLC (35. 6%) and RCC (20%). The most common treatment related AEs (TRAEs) were maculo-papular rash (38%), injection site reactions (28. 9%), fatigue (28. 9%), and nausea (24. 4%). Grade 3 TRAEs occurred in 12 subjects (26. 6%) and included maculo-papular rash (4), vomiting (2), nausea (1), diarrhea (1), enterocolitis (1), arthralgia (1), urticaria (1), periorbital edema (1), blood creatinine increase (1) and leukocytosis (1). One subject had a Grade 4 TRAE of anaphylaxis in Cycle 9 after the data extract date. TRAEs were reversible, and no subjects had Grade 5 TRAEs. No subjects had capillary leak syndrome and 5% experienced other IL-2 hallmark TRAEs (hypotension 4. 4%, AST/ALT increase 0%, pyrexia 4. 4%, peripheral edema 4. 4%). No DLTs were observed. The maximum administered dose of STK-012 was 3mg Q3W. A DL of 2. 25mg Q3W was advanced into Phase 1b based on safety, pharmacokinetic (PK) and pharmacodynamic (PD) data. Peripheral PD data showed STAT5 phosphorylation in CD25+ T cells and a dose dependent increase in activated T cells (Ki-67+CD38+CD8+) and serum IFNγ. Expansion of NK cells and Tregs was limited. STK-012 has a half-life of 4 days. Of 38 efficacy evaluable subjects, 3 had a partial response (PR) and 17 had stable disease as best overall response by RECIST V1. 1. The PRs included 2 confirmed (anti-PD-1 r/r NSCLC and RCC) and 1 unconfirmed (anti-PD-1 r/r SCCHN) with the RCC subject in response for over 9 months with treatment ongoing. After the data extract date, a fourth subject achieved a PR (confirmed) with 80% reduction in target lesions (anti-PD-1/CTLA-4 and TKI r/r RCC) with treatment ongoing. Monotherapy Phase 1b dose expansions in r/r NSCLC and r/r RCC are ongoing. Conclusions: In our ongoing Phase 1a/b trial, STK-012 demonstrated a favorable safety, PK, and PD profile which is distinct from that of aldesleukin and non-α IL-2 analogues. Peripheral PD and PK data support selectivity for IL-2R α/β. Preliminary monotherapy efficacy in subjects who are r/r to prior immunotherapy warrants further development. Citation Format: Benjamin Izar, Dmitriy Zamarin, David R. Spigel, Christopher J. Hoimes, David F. McDermott, Kartik Sehgal, Yana G. Najjar, Adam J. Schoenfeld, Edward B. Garon, Ryan J. Sullivan, Brian S. Henick, Ticiana A. Leal, Michael E. Hurwitz, Rana R. McKay, Natalie Busby, Anita Mehta-Damani, Alex Azrilevich, Tony Tran, Naiyer Rizvi, Martin Oft, Alexander I. Spira. Initial results from a phase 1a/1b study of STK-012, a first-in-class α/β IL-2 receptor biased partial agonist in advanced solid tumors (NCT05098132) abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (7Suppl): Abstract nr CT183.