DOYLESTOWN, PA — Aprea Therapeutics reported early signs of anti-tumor activity from its ongoing Phase 1 trial of experimental cancer therapy APR-1051, with partial responses observed in patients with advanced endometrial cancer and additional disease stabilization across several tumor types, findings presented at the 2026 American Society of Clinical Oncology Annual Meeting.
The results are significant because APR-1051, a first-in-human WEE1 inhibitor, is being evaluated in patients with advanced solid tumors harboring specific cancer-associated genetic alterations, a population with limited treatment options after prior therapies have failed.
Data from the ACESOT-1051 trial, based on a May 6, 2026 cutoff, showed two patients with endometrial cancer achieved partial responses. Six additional patients experienced stable disease, including patients with colorectal cancer, HPV-positive head and neck squamous cell carcinoma, and endometrial cancer.
The company reported that 28 patients had been enrolled across dose levels ranging from 10 milligrams to 300 milligrams administered once daily. Dose escalation remains ongoing, with enrollment currently taking place in the 300-milligram cohort.
APR-1051 was generally well tolerated across all tested dose levels, according to the company. Treatment-related adverse events were reported in 54% of patients, with nausea and fatigue representing the most common side effects. Nearly all treatment-related adverse events were classified as Grade 1 or Grade 2.
Researchers reported that APR-1051 demonstrated dose-proportional exposure and an approximate 18-hour half-life, supporting once-daily dosing.
Gene Kennedy, Aprea’s chief medical advisor, stated that the responses and disease stabilization observed in heavily pretreated patients support continued development of the drug candidate and expansion into additional tumor types.
The company is expanding enrollment to include at least 50 patients with uterine serous carcinoma and patients with cyclin E-overexpressing, platinum-resistant ovarian cancer. Completion of dose escalation and backfill expansion is expected during the second quarter of 2027.
APR-1051 is designed to selectively inhibit WEE1, a protein involved in regulating cell division and DNA damage repair. Aprea believes the drug’s limited activity against related PLK kinases may contribute to an improved tolerability profile compared with earlier WEE1 inhibitors.
The ACESOT-1051 study is registered on ClinicalTrials.gov under identifier NCT06260514.
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