On January 29, 2026 Aprea Therapeutics, Inc. (Nasdaq: APRE) ("Aprea" or the "Company"), a clinical-stage biopharmaceutical company developing innovative therapies that exploit cancer-specific vulnerabilities while minimizing damage to healthy cells, reported the first unconfirmed partial response (uPR) observed in a patient enrolled in its ongoing Phase 1 ACESOT-1051 dose-escalation study (A Multi-Center Evaluation of WEE1 Inhibitor APR-1051 in Patients with Advanced Solid Tumors).

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This early clinical activity was observed in a patient with PPP2R1A-mutated uterine serous carcinoma, a form of endometrial cancer, treated at the 150 mg dose level of APR-1051, with dose escalation continuing into higher dose cohorts to establish the recommended Phase 2 dose (RP2D). At the protocol-defined 8-week imaging assessment, the patient achieved a 50% reduction in target lesion size per RECIST v1.1 criteria, along with a marked reduction in cancer antigen 125 (CA-125) levels, from 732 to 70 U/mL, a well-recognized tumor marker in endometrial cancer.

In earlier cohorts of ACESOT-1051 study, multiple patients achieved stable disease with 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 (HNSCC) and a 15% reduction in a patient with FBXW7-mutated colon cancer treated at the 100 mg dose. This patient has remained on therapy for over 210 days and is approaching their eighth treatment cycle. In addition, a second patient treated at the 150 mg dose level achieved stable disease at the first follow-up imaging assessment.

Collectively, these findings suggest that APR-1051 may have therapeutic potential across a range of solid tumors. Enrollment in the 220 mg dose level cohort of the study is currently underway, and the company intends to increase enrollment of HPV-positive patients in the ongoing trial.

"These early single-agent data demonstrate that APR-1051 has clinical activity as a single agent," said Anthony Tolcher, MD, FRCPC, Principal Investigator at Next Oncology. "The observation of a partial response on the first scan, together with a decrease in tumor marker at this dose level, supports continued clinical evaluation of APR-1051."

Oren Gilad, PhD, Chief Executive Officer of Aprea Therapeutics, added, "These preliminary results provide early proof-of-concept for single-agent activity of APR-1051 and support our strategy of targeting cancers with specific genomic alterations, including HPV-positive disease and PPP2R1A, FBXW7, CCNE1, TP53 and KRAS mutations. The potential dose-response trend and favorable safety profile observed in the ongoing dose-escalation study reinforce our confidence in the potential of APR-1051 as a differentiated WEE1 inhibitor for patients with advanced solid tumors. We look forward to providing additional updates in the first half of 2026 and completing dose escalation later in the year."

About the ACESOT-1051 Trial

ACESOT-1051 is a first-in-human, open-label Phase 1 study evaluating the safety, pharmacokinetics, pharmacodynamics, and preliminary efficacy of single-agent APR-1051 in patients with advanced solid tumors harboring cancer-associated genetic alterations. The dose-escalation portion of the study is expected to enroll up to 50 patients across nine planned dose cohorts, ranging from10 mg to 300 mg administered once daily. APR-1051 is administered orally once daily in continuous 28-day cycles. To date, enrollment has evaluated doses up to 150 mg, with the 220 mg cohort currently enrolling. For more information, refer to ClinicalTrials.gov ID NCT06260514.

(Press release, Aprea, JAN 29, 2026, View Source [SID1234662349])