Aprea Therapeutics reported that a second patient in its Phase 1 ACESOT‑1051 study of the oral WEE1 inhibitor APR‑1051 achieved an unconfirmed partial response. The patient, who had advanced endometrial cancer, received the 220 mg dose and experienced a 50 % reduction in target lesions on the first on‑treatment scan, accompanied by an 87 % fall in the tumor biomarker CA‑125 from 362 U/mL to 47 U/mL.
The response was observed in a tumor harboring a PPP2R1A mutation and the patient reported only Grade 1 treatment‑emergent adverse events, underscoring the drug’s tolerability profile at this dose level. Aprea’s Chief Medical Advisor Eugene Kennedy noted, “We are encouraged to see a second patient in the ongoing ACESOT trial achieve an unconfirmed partial response. We believe the magnitude of tumor reduction and the substantial drop in CA‑125 in this patient provides further evidence of APR‑1051’s biologic activity and potential therapeutic impact.”
The finding reinforces an early clinical trend in the trial, where two patients with PPP2R1A‑altered tumors have achieved disease control. PPP2R1A mutations are increasingly recognized as predictive biomarkers for response to targeted therapies and immunotherapy, positioning APR‑1051 within a growing precision‑oncology strategy that targets genomically defined solid tumors.
Aprea plans to continue enrolling patients in the 220 mg cohort and to expand enrollment of PPP2R1A‑positive endometrial and HPV‑positive head‑and‑neck squamous cell carcinoma patients. The company expects to provide further updates on the trial in the second quarter of 2026, which will clarify whether the early signals translate into confirmed responses.
While the company remains a pre‑revenue, clinical‑stage biopharmaceutical with a market capitalization of roughly $4.1 million and a cash runway extended to Q4 2026, the positive data are critical for its ability to secure future financing and advance its pipeline. The early activity in a biomarker‑selected population offers a potential competitive advantage in the crowded WEE1 inhibitor landscape, where other agents such as AZD1775 and azenosertib are also in development.
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