Presentation highlights early clinical activity from ACESOT-1051, including partial responses and stable disease in patients across multiple tumor types
Manageable tolerability confirmed across cohorts
Patient expansion into uterine serous carcinoma and platinum-resistant ovarian cancer underway; dose escalation and backfill expansion expected to complete Q2 2027

DOYLESTOWN, Pa., June 01, 2026 (GLOBE NEWSWIRE) -- Aprea Therapeutics, Inc. (NASDAQ:APRE) ("Aprea", or the "Company"), a clinical-stage precision medicine oncology company focused on the discovery and development of targeted therapies for patients with biomarker-defined cancers, announces the presentation of a poster "Early results from the first-in-human phase 1 study of WEE1 inhibitor APR-1051 in patients with advanced solid tumors (ACESOT-1051)" on May 30 at the American Society of Clinical Oncology (ASCO) 2026 annual meeting, taking place in Chicago, Illinois.

APR-1051 is an orally bioavailable, potent, and selective small molecule WEE1 inhibitor with in vivo anti-tumor activity in several cancer models. It exhibits low off-target inhibition of PLK kinases (PLK1, PLK2, PLK3), a property that differentiates it from prior WEE1 inhibitors and may contribute to an improved safety profile. ACESOT-1051 is the ongoing first-in-human Phase 1 study evaluating once-daily APR-1051 in advanced solid tumors harboring cancer-associated gene alterations.

"We are pleased to have the opportunity to present the updated ACESOT-1051 data to the oncology community at this year's ASCO meeting," said Gene Kennedy, M.D., Chief Medical Advisor of Aprea. "The partial responses and disease stabilizations we have observed in this heavily pretreated, biomarker-selected patient population reinforce our confidence in APR-1051's differentiated profile and the potential of our precision medicine strategy. With enrollment now expanding into uterine serous carcinoma and platinum-resistant ovarian cancer, dose escalation and backfill expansion is on track to complete in the second quarter of 2027. Importantly, we believe that we are on a clear path to generating the data that will demonstrate APR-1051's potential."

ACESOT-1051: A Biomarker-Focused, Phase 1 Trial of Oral WEE1 Inhibitor, APR-1051

The poster (Abstract #3107) provides an updated summary of ACESOT-1051 with a data cutoff of May 6, 2026. Key highlights from the presentation include:

Study objectives: The primary objective is to characterize the safety profile, dose-limiting toxicity (DLT), maximum tolerated dose or maximum administered dose, and recommended Phase 2 dose (RP2D) of APR-1051. Secondary objectives include characterization of the PK of APR-1051 and assessment of preliminary efficacy of APR-1051
Clinical activity: Two patients with endometrial cancers have achieved partial responses ("PR"). Six additional patients achieved stable disease, including those with colorectal cancer, HPV+ head and neck squamous cell carcinoma, and endometrial cancer.
Tolerability: APR-1051 has been well tolerated across all dose levels. Treatment-related adverse events were reported in 54% of patients, with nausea (36%) and fatigue (14%) the most common, nearly all Grade 1 or 2.
Pharmacokinetics: APR-1051 exposure is dose-proportional with a half-life of approximately 18 hours, supporting once-daily dosing.
Study status: 28 patients with advanced solid tumors harboring specific cancer-associated gene alterations have been enrolled at doses from 10 mg to 300 mg once daily. Dose escalation is ongoing, with enrollment currently underway in the 300 mg cohort (dose level 9). Aprea is expanding enrollment to include at least 50 patients with uterine serous carcinoma as well as patients with cyclin E-overexpressing, platinum-resistant ovarian cancer. Completion of dose escalation and backfill expansion is anticipated in the second quarter of 2027.

For more information on ACESOT-1051, refer to ClinicalTrials.gov NCT06260514. A copy of the poster will be available on Aprea's corporate website, later today.

About Aprea Therapeutics

Aprea is a clinical-stage precision medicine oncology company focused on the discovery and development of targeted therapies for patients with biomarker-defined cancers. The Company is pioneering a new approach to treat cancer by exploiting vulnerabilities associated with cancer cell mutations. This approach was developed to kill tumors while minimizing the effect on normal, healthy cells. Aprea's technology has potential applications across multiple cancer types, enabling it to target a range of tumors, including ovarian, endometrial, colorectal and head and neck squamous cell carcinoma. The Company's lead programs are APR-1051, an oral, small-molecule inhibitor of WEE1 kinase, and ATRN-119, a small molecule ATR inhibitor, both in clinical development for solid tumor indications. For more information, please visit www.aprea.com.

The Company may use, and intends to use, its investor relations website at https://ir.aprea.com/ as a means of disclosing material nonpublic information and for complying with its disclosure obligations under Regulation FD.

Forward-Looking Statement

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Investor Contact:

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LifeSci Advisors

mmoyer@lifesciadvisors.com

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Russo Partners, LLC

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Aprea Therapeutics Presents Updated Phase 1 Data on WEE1 Inhibitor APR-1051 at ASCO 2026, Demonstrating Early Monotherapy Activity and Manageable Tolerability in Advanced Solid Tumors