Kymera Therapeutics, Inc. announced that new preclinical data showing the structural and molecular mechanisms underlying anti-tumor activity of its novel STAT3 degrader, KT-333, were presented in a late-breaking research poster session at the AACR Annual Meeting taking place April 5-10, 2024, in San Diego, California. Additionally, Nello Mainolfi, PhD, Founder, President and CEO, will present in the Major Symposium at the conference highlighting the Company?s unique target selection strategy and strong preclinical to clinical translation observed across the Company?s first-in-class oncology programs, KT-333 and KT-253, a potent and selective degrader of MDM2. STAT3 is recognized as a key component of the JAK-STAT signaling pathway with both tumor cell intrinsic and tumor cell extrinsic effects on the tumor microenvironment.

Although multiple drugs have been approved that target upstream effectors signaling through STAT3, no known drugs selectively block STAT3 broadly across all relevant cell types or address both phosphorylation-dependent and -independent functions of STAT3. For these reasons, STAT3 degraders may provide a solution to the development of targeted and selective drugs to address multiple STAT3 dependent pathologies. New findings presented for the first time show KT-333 induces a strong ternary complex between STAT3 and the VHL E3 ligase in a positively cooperative manner, exhibiting properties of native protein complexes, leading to potent, selective, rapid, and consistent degradation as observed in vitro and in vivo.

Innovative structure-based design with cryo-electron microscopy, biochemical, and proteomics techniques provide mechanistic and structural insights further validating VHL as the E3 ligase of choice for STAT3 degradation in cancer. In the STAT3-dependent SUDHL-1 lymphoma xenograft model, reduced expression of canonical STAT3 targets and down-regulation of cytokine-mediated signaling and cell cycle signature genes indicated that cell cycle arrest and subsequent apoptosis were the main drivers of efficacy for KT-333. Additionally, this unique mechanism of action led to induction of proinflammatory anti-tumorigenic transcriptional signatures in the tumor microenvironment.

This has resulted in robust antitumor activity in patients, as reported in the Company?s latest clinical update at the American Society of Hematology (ASH) Annual Meeting in December 2023. About KT-333 STAT3 Degrader KT-333 is a potent, highly selective degrader of STAT3 in development for the treatment of multiple STAT3-dependent pathologies, including hematological malignancies and solid tumors. STAT3 is an undrugged transcription factor activated through a variety of different cytokine and growth factor receptors via Janus kinases (JAKs), as well as through oncogenic fusion proteins and mutations in STAT3 itself.

In certain malignant cells, STAT3 activation is set into overdrive, leading to a dampened immune response, tumor progression, and metastasis. STAT3?s role as a cancer driver and tumor microenvironment modulator has been validated in a multitude of studies, making it a strong candidate to target in the treatment of cancer. KT-333 was the first degrader against an undrugged transcription factor to enter the clinic and the Phase 1 clinical trial is designed to evaluate the safety, tolerability, pharmacokinetics (PK), pharmacodynamics (PD), and clinical activity of KT-333 dosed weekly in adult patients with relapsed and/or refractory lymphomas, leukemias, and solid tumors.

Clinical data from the KT-333 Phase 1 trial has shown evidence of STAT3 targeted protein degradation in humans with associated STAT3 pathway inhibition, along with early signs of antitumor activity, highlighting the potential of heterobifunctional degraders for targeting this previously undruggable transcription factor. Dose escalation in the KT-333 Phase 1 study is ongoing. About KT-253 MDM2 Degrader: KT-253 targets MDM2, the crucial regulator of the most common tumor suppressor, p53.

P53 remains intact (wild type) in close to 50% of cancers, meaning that it retains its ability to modulate cancer cell growth. While small molecule inhibitors (SMIs) have been developed to stabilize and upregulate p53 expression, they have been unable to show meaningful clinical benefits of p53 stabilization, with acceptable safety margins, likely due to their inability to overcome a feedback loop that increases MDM2 protein levels when p53 is upregulated. In preclinical studies, KT-253 has shown the ability to overcome the MDM2 feedback loop and rapidly induce cancer cell death with brief exposures, providing the opportunity for an improved efficacy and safety profile.

The Phase 1 study of KT-253 will evaluate the safety, tolerability, pharmacokinetics/pharmacodynamics, and clinical activity of KT-253 in patients with relapsed or refractory high grade myeloid malignancies, including acute myeloid leukemia (AML), acute lymphocytic leukemia (ALL), lymphomas, and solid tumors. KT-253 has achieved clinical proof-of-mechanism in the Phase 1 trial and shown early signs of anti-tumor activity. Dose escalation in the KT-253 Phase 1 study is ongoing.