Some signs of life for new IL-2 variants
The annual AACR meeting was held last week. Below I highlight a couple of data readouts from two players in the once-hot IL-2 variant space
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There was a ton of intriguing clinical and preclinical data unveiled at last week's annual AACR meeting. Given the novelty of the molecules, mechanisms of action, and combinations presented, this conference is always a challenge to synthesize completely.
For today's post, I chose to spotlight one specific area – IL-2 variants – and dive into a couple of compelling data readouts from emerging players in this space.
The IL-2 Conundrum
Many companies have tried and failed to harness IL-2 as an effective oncology treatment, most notably Nektar, whose once-promising bempegaldesleukin (pegylated IL-2) program catastrophically flamed out in a phase 3 study in first-line melanoma. The primary stumbling block with leveraging IL-2 in an oncology context is its broad activation profile, which includes the intended stimulation of effector T cells, but also the undesirable activation of regulatory T cells (Tregs), largely driven by engagement of the alpha subunit of the IL-2 receptor (aka CD25). This indiscriminate activation can precipitate potentially lethal side effects while simultaneously undermining efficacy if Tregs become overstimulated.
These limitations have spawned a multitude of players tinkering with modifications to the IL-2 molecule, generating IL-2 variants, in an effort to skew its mechanism of action toward preferentially activating effector T cells while limiting Treg stimulation. Two companies - Medicenna and Synthekine - advancing IL-2 variants as their lead programs, presented early clinical data at AACR, each showcasing a distinct spin on engineering the IL-2 molecule.
Synthekine and Medicenna: Divergent IL-2 Variant Designs Yield Intriguing Early Results
Synthekine presented first clinical data from its lead program, STK-012, a first-in-class alpha/beta-IL-2R biased partial agonist. The molecule has been designed to preferentially bind the high-affinity IL-2Rs while reducing binding to the IL-2R gamma chain, with Synthekine's hypothesis being that this design selectively activates antigen-primed T cells. Across a wide range of heavily pre-treated solid tumor patients, STK-012 monotherapy delivered 3 partial responses (PRs) in renal cell carcinoma, head and neck squamous cell carcinoma, and non-small cell lung cancer, along with 12 instances of stable disease. Mechanistically, Synthekine demonstrated STK-012's selectivity for CD25-expressing cells, dose-dependent increases in IFN-gamma secretion, and limited expansion of off-target cell subsets like NK cells and Tregs.
While these initial three responses represent an encouraging early sign in traditionally immunotherapy-sensitive tumor types, the pivotal path for STK-012, like most IL-2 variant programs, will likely involve combination regimens with checkpoint inhibitors. Nonetheless, demonstrating monotherapy responses helps allay potential efficacy concerns ahead of future combination-focused studies. Safety was relatively clean aside from some grade 3 GI toxicities at the highest 3mg dose level and one grade 4 anaphylactic reaction that rapidly resolved.
Medicenna also presented updated phase 1 data for its IL-2 variant, MDNA11, in 38 patients. MDNA11 is engineered as a "beta-enhanced, not-alpha" IL-2 construct fused to albumin to extend its half-life. Medicenna believes this design enables MDNA11 to selectively activate CD8+ T cells and NK cells while minimally engaging Tregs. The company reported 4 PRs across difficult-to-treat tumor types like pancreatic ductal adenocarcinoma, small bowel cancer, and melanoma. Medicenna somewhat clumsily characterized this as a 28.6% response rate in "phase 2 eligible" patients receiving doses ≥60 mcg/kg, though a more conservative calculation pegs the ORR closer to 18%.