Safety, pharmacokinetics (PK), pharmacodynamics (PD) and efficacy of KT-253, a targeted protein degrader of MDM2, in patients with relapsed/refractory (R/R) solid tumors, lymphoma, high grade myeloid malignancies and acute lymphoblastic leukemia (ALL).
Authors: M. Rizwan Rizwan-ul-Haq Khawaja, Abdul Rafeh Naqash, Reva Schneider, Aditi Shastri, Maximilian Stahl, Justin C Moser, Nagla Fawzy Abdel Karim, Yazan Madanat, Brian Andrew Jonas, Eytan Stein, Shirish M. Gadgeel, James K. McCloskey, Ashwin Gollerkeri, Rachelle Perea, Yogesh Chutake, Sagar Agarwal, Patrick Henrick, Kelvin Shi, Naval Guastad Daver
Journal: Journal of Clinical Oncology (2024)

3084 Background: The tumor suppressor p53 is mutated in approximately 50% of cancers. In those cancers with wild-type p53, its activity is controlled by mouse double minute 2 (MDM2), an E3 ligase that tags p53 for degradation. KT-253 is a novel, highly potent heterobifunctional MDM2 degrader that upregulates p53 activity and overcomes the p53-MDM2 feedback loop, resulting in &gt;200-fold higher potency compared to MDM2 inhibitors. In preclinical PDX models of sensitive p53 WT solid tumors, AML and ALL, KT-253 robustly activates p53, induces apoptosis, and results in tumor regressions with every 3-week dosing. The ability to rapidly induce an acute apoptotic response and dose intermittently may result in a therapeutic index that has eluded previous MDM2 targeting agents. Methods: The ongoing open-label Phase 1 study evaluates safety, PK, PD and preliminary efficacy of IV KT-253 administered on Day 1 of 21-day cycles. Patients (pts) with advanced (≥2 prior therapies) solid tumors (ST)/lymphomas (Arm A) and relapsed/refractory (R/R) high grade myeloid malignancies (AML, high/very-high risk myelodysplastic syndrome (MDS), MDS/myeloproliferative neoplasms) and ALL (Arm B) are eligible. Blood samples are collected for KT-253 PK/PD analyses. Results: As of 26 January 2024, 18 pts have been treated, 13 in Arm A dose levels (A: DL) 1-4 and 5 in Arm B dose levels (B: DL) 1-2, with mean number of 3 and 2 doses, respectively. The most common solid tumor types were Merkel cell carcinoma ((MCC) n=3), adenoid cystic carcinoma ((ACC) n=2) and uveal melanoma (n=2). Arm B included 5 pts with R/R AML. The median age was 61 years (yrs) (range 42, 81) in Arm A and 66 yrs (range 57, 70) in Arm B. The most common adverse events (AEs) in &gt; 20% of pts included nausea, fatigue, headache, and vomiting. There was 1 DLT of AEs leading to discontinuation that included Grade (G) 2 nausea and fatigue in A: DL4. There were no neutropenia or thrombocytopenia AEs in either arm. KT-253 related SAEs included G3 hypotension in a pt with decreased oral intake (A: DL1). Overall best response: 1 CR (B: DL2, AML); 2 PRs (A: DL1, MCC; B: DL1, AML); 3 SD (A: DL1, fibromyxoid sarcoma; DL2, ACC; DL3, renal cell cancer). PD data from A: DL1-4 and B: DL1-2 demonstrated rapid upregulation of plasma GDF-15 protein and upregulation of CDKN1A and PHLDA3 mRNA levels in blood. KT-253 demonstrated dose-dependent increase in plasma exposure with levels approximating efficacious doses. Conclusions: KT-253 results in potent upregulation of p53-dependent biomarkers and has demonstrated early signs of anti-tumor activity including objective responses in MCC and AML at doses that are well tolerated. Dose escalation is ongoing at DL4 in Arm A and at DL2 in Arm B and analyses from additional pts will be presented at the meeting. Clinical trial information: NCT05775406 .