Phase 1 study of KT-333, a targeted protein degrader, in patients with relapsed or refractory lymphomas, large granular lymphocytic leukemia, and solid tumors.

Abstract

TPS3171 Background: The signal transducer and activator of transcription 3 (STAT3) protein is activated by cytokines and growth factors resulting in tumor growth and promotion and hindering antitumor immunity. Approximately 70% of human cancers including both hematological malignancies and solid tumors exhibit increased levels of phosphorylated STAT3 (pSTAT3). There is evidence of constitutive activation of STAT3 through genetic mutations or aberrant cellular signaling pathways in tumors such as large granular lymphocytic leukemia (LGL-L), peripheral T-cell lymphoma (PTCL), and cutaneous T-cell lymphomas (CTCL). Hyperactivation of STAT3 has been reported in a variety of solid tumors. In several of these cancers, the levels of pSTAT3 and/or activated STAT3 have been shown to correlate with poor clinical prognosis. As with other transcription factors, selective inhibition of STAT3 has been proven to be difficult with conventional therapeutic approaches. KT-333 is a potent highly selective, heterobifunctional small molecule degrader of STAT3. In preclinical studies, durable tumor regressions were seen with weekly KT-333 administration in STAT3-dependent T cell lymphomas, and antitumor activity was seen in solid tumors in combination with anti-PD1 (ASH 2021, SITC 2021). Methods: KT-333 is being evaluated in an open-label, dose escalation (Phase 1a, n = 40) study in patients with lymphomas relapsed or refractory (R/R) to at least two prior systemic treatments or for whom standard therapies are unavailable. Dose escalation will be conducted by accelerated titration followed by a 3+3 design in ascending doses of intravenous KT-333 administered once weekly in 28-day cycles to evaluate safety and define the maximum tolerated dose (MTD)/recommended Phase 2 dose (RP2D) (primary endpoint). Secondary endpoints include pharmacokinetics (PK) in plasma and urine and preliminary pharmacodynamic effects (PD) of KT-333 using blood (peripheral blood mononuclear cells [PBMCs], plasma/serum) and tumor tissue. After confirming the MTD/RP2D in patients with lymphoma, patients with advanced solid tumors will be enrolled in a separate Phase 1a cohort at the MTD/RP2D. In Phase 1b (n = 80), patients with PTCL, CTCL, LGL-L (T-cell LGL-L or chronic lymphoproliferative disorder of natural killer-cells), or solid tumors R/R to at least one prior systemic standard of care treatment or for whom standard therapies are not available, will be enrolled in separate 20 patient cohorts. This will further characterize safety, PK, PD and evaluate the clinical activity of KT-333. Treatment with KT-333 will continue until disease progression, unacceptable toxicity, or patient refusal. KT333-TL-101 began enrolling in January 2022. Clinical trial information: NCT05225584.