DOYLESTOWN, PA — Aprea Therapeutics, Inc. (Nasdaq: APRE) reported its first unconfirmed partial response in a Phase 1 study of its experimental cancer drug APR-1051, an early signal the company says provides proof-of-concept for single-agent activity in patients with advanced solid tumors.
The response was observed in a patient with PPP2R1A-mutated uterine serous carcinoma, a rare and aggressive form of endometrial cancer, enrolled in Aprea’s ongoing ACESOT-1051 dose-escalation trial. At the protocol-defined eight-week imaging assessment, the patient achieved a roughly 50% reduction in target lesion size under RECIST v1.1 criteria, along with a dramatic drop in the tumor marker CA-125, which fell more than 90% from 732 to 70 U/mL at the 150 mg dose level.
The unconfirmed partial response first noted on the initial scan was achieved at the 150 mg dose, while enrollment is now underway in a higher 220 mg cohort as the study continues toward identifying a recommended Phase 2 dose.
Earlier cohorts in the trial also showed signs of activity. Aprea said multiple patients achieved stable disease with measurable reductions in tumor burden, including a 5% reduction at the 70 mg dose in a patient with HPV-positive head and neck squamous cell carcinoma and a 15% reduction at the 100 mg dose in a patient with FBXW7-mutated colon cancer. That patient has remained on therapy for more than 210 days and is nearing an eighth treatment cycle. A second patient treated at the 150 mg dose achieved stable disease at the first follow-up imaging assessment.
Taken together, the company said the data suggest a potential dose-response trend, with increasing single-agent activity observed across the 70 mg, 100 mg, and 150 mg cohorts, and point to broader therapeutic potential across multiple solid tumor types.
“These early single-agent data demonstrate that APR-1051 has clinical activity as a single agent,” said Anthony Tolcher, principal investigator at Next Oncology. He said the observed tumor response and reduction in cancer markers support continued clinical evaluation of the drug.
Chief Executive Officer Oren Gilad said the findings reinforce Aprea’s strategy of targeting tumors with specific genomic alterations, including HPV-positive disease and mutations involving PPP2R1A, FBXW7, CCNE1, TP53, and KRAS. He said the emerging dose-response pattern and favorable safety profile strengthen confidence in APR-1051 as a differentiated WEE1 inhibitor and that the company expects to provide additional updates in the first half of 2026.
ACESOT-1051 is a first-in-human, open-label Phase 1 study evaluating the safety, pharmacokinetics, pharmacodynamics, and preliminary efficacy of APR-1051 as a single agent in patients with advanced solid tumors. The dose-escalation portion is expected to enroll up to 50 patients across nine planned dose levels ranging from 10 mg to 300 mg, administered orally once daily in continuous 28-day cycles. The trial is registered at ClinicalTrials.gov under identifier NCT06260514.
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