Aprea Therapeutics confirms partial response in ongoing ACESOT-1051 trial

Aprea Therapeutics (APRE) announced the confirmation of a partial response, or PR, in its ongoing ACESOT-1051 trial evaluating APR-1051, a potent and selective WEE1 kinase inhibitor. The confirmed PR was observed in a patient with PPP2R1A-mutated endometrial cancer who is currently being treated at the 220 mg once daily dose level. Aprea announced on February 18 that, at their first imaging assessment, this patient achieved a 50% reduction in target lesion size as well as a reduction in CA-125 levels. This response was subsequently confirmed at the second image assessment, with an additional 9.5% reduction in target lesion size, and a reduction in CA-125 to 40.2U/ml. ACESOT-1051 is a biomarker focused Phase 1 trial designed to evaluate the safety, tolerability, pharmacokinetics, and preliminary anti-tumor activity of APR-1051 in patients with advanced solid tumors harboring cancer-associated genetic alterations. A total of 24 patients have been treated to date, at doses ranging from 10 mg to 220 mg once daily. Two patients have achieved partial responses, both with endometrial cancers harboring PPP2R1A mutations. One of these responses has been confirmed, as described above. Both patients remain on treatment. Five other patients in ACESOT-1051 have achieved a best overall response of stable disease, including patients with HPV+ head and neck squamous cell carcinoma, colorectal and endometrial cancers with relevant genomic alternations. APR-1051 has been generally safe and well tolerated with the most common adverse events reported as Grade 1 or 2, primarily consisting of nausea and fatigue. Dose escalation is ongoing, with plans to advance to Dose Level 9 in the second quarter of 2026. In parallel, the company plans to enroll additional patients as specified in the protocol based on the understanding that their tumor types or specific mutations gives them an increased probability of responding to this class of potential therapeutics. This includes patients with uterine serous carcinoma, colorectal and HPV+ tumors.