Aprea Therapeutics Highlights Positive Emerging Clinical Activity for WEE1 Inhibitor, APR-1051, with a Confirmed Partial Response in the Ongoing Phase 1 ACESOT-1051 Trial

Rhea-AI Summary

Aprea (Nasdaq: APRE) reported a confirmed partial response (PR) to WEE1 inhibitor APR-1051 in the Phase 1 ACESOT-1051 trial at the 220 mg once-daily dose.

The patient with PPP2R1A-mutated endometrial cancer had a 50% reduction in target lesion size at first scan, a further 9.5% reduction at confirmation, and CA-125 fell from 362 U/mL to 40.2 U/mL. To date 24 patients received 10–220 mg; two PRs (one confirmed) and five stable disease responses reported. Dose escalation will progress toward 300 mg once daily in Q2 2026.

Positive

• Confirmed PR at 220 mg with sustained tumor reduction
• CA-125 fell from 362 U/mL to 40.2 U/mL in responder
• Two partial responses observed among 24 patients treated
• Safety profile generally Grade 1–2 adverse events only

Negative

• Limited sample size: only 24 patients treated to date
• Only one confirmed partial response so far
• Dose escalation ongoing, efficacy and tolerability not fully defined

Key Figures

Dose level: 220 mg once daily Initial lesion reduction: 50% reduction Additional lesion reduction: 9.5% reduction +5 more

8 metrics

Dose level 220 mg once daily Dose with confirmed partial response in ACESOT-1051

Initial lesion reduction 50% reduction Target lesion size at first imaging assessment

Additional lesion reduction 9.5% reduction Further target lesion decrease at second assessment

CA-125 at follow-up 40.2 U/mL Confirmed responder’s CA-125 level at second assessment

Baseline CA-125 362 U/mL Baseline CA-125 level in responding patient

Patients treated 24 patients Total enrolled in ACESOT-1051 to date

Partial responses 2 patients Endometrial cancers with PPP2R1A mutations in ACESOT-1051

Planned next dose 300 mg once daily Planned Dose Level 9 escalation in Q2 2026

Market Reality Check

Price: $0.7466 Vol: Volume 72,584 is below th...

normal vol

$0.7466 Last Close

Volume Volume 72,584 is below the 20-day average of 85,895, suggesting limited pre-news positioning. normal

Technical Shares at 0.699 are trading below the 200-day MA of 1.26 and about 70.1% under the 52-week high.

Peers on Argus

APRE was down 2.43% while scanner peers were mixed: two up (e.g., PCSA, CLDI) an...

2 Up 1 Down

APRE was down 2.43% while scanner peers were mixed: two up (e.g., PCSA, CLDI) and one down (INAB). Affinity peers also showed both gains and losses, pointing to stock-specific trading rather than a coordinated biotech move.

Previous Clinical trial Reports

5 past events · Latest: Oct 15 (Positive)

Same Type Pattern 5 events

Date	Event	Sentiment	Move	Catalyst
Oct 15	ATRN-119 RP2D set	Positive	-1.3%	Set ATRN-119 RP2D at 1,100 mg and shifted focus to combinations.
Jun 25	APR-1051 early data	Positive	+10.1%	Reported antiproliferative effects and early stable disease in HPV+ HNSCC.
Dec 11	ATRN-119 BID dosing	Positive	+3.3%	Initiated 550 mg BID dosing to optimize ATRN-119 exposure and outcomes.
Oct 09	WEE1 advisor added	Positive	-1.6%	Engaged senior advisor to lead APR-1051 WEE1 clinical development.
Jun 17	ACESOT-1051 first dose	Positive	-4.7%	Dosed first patient in ACESOT-1051 Phase 1 WEE1 inhibitor trial.

Pattern Detected

Clinical trial updates have drawn mixed reactions: more events showed price divergence than alignment despite generally positive clinical narratives.

Recent Company History

Over the past two years, Aprea has steadily advanced its DNA damage response pipeline. ATRN-119 reached a recommended Phase 2 dose of 1,100 mg once daily, with strategy shifting toward combinations. For APR-1051, the ACESOT-1051 Phase 1 trial progressed from first-patient dosing in June 2024 to biomarker-focused efficacy signals and now confirmed partial response. Multiple clinical updates produced both positive and negative single-day moves, showing that encouraging data have not consistently translated into strong price gains.

Historical Comparison

+1.2% avg move · Past clinical trial updates for APRE moved the stock by an average of 1.16%. Today’s -2.43% pre-news...

clinical trial

+1.2%

Average Historical Move clinical trial

Past clinical trial updates for APRE moved the stock by an average of 1.16%. Today’s -2.43% pre-news move is modest and opposite in direction to that average.

Clinical releases show a progression from first dosing in ACESOT-1051 to early disease-stabilization data, and now to confirmed partial response in biomarker-selected endometrial cancer, alongside ATRN-119 advancing to a defined Phase 2 dose and BID strategies.

Regulatory & Risk Context

Active S-3 Shelf

Shelf Active

Active S-3 Shelf Registration 2026-03-17

An effective S-3/A shelf dated 2026-03-17 is in place, with at least one usage via a 424B3 on 2026-03-19 registering 12,577,714 resale shares from a January 2026 private placement. The company would receive cash only upon warrant exercises.

Market Pulse Summary

This announcement highlights a confirmed partial response and additional stable disease signals for ...

Analysis

This announcement highlights a confirmed partial response and additional stable disease signals for APR-1051 in the Phase 1 ACESOT-1051 trial, with 24 patients treated across doses up to 220 mg. Safety has remained mostly Grade 1–2, and dose escalation toward 300 mg is planned. Historically, Aprea’s clinical trial news around APR-1051 and ATRN-119 has produced mixed single-day price reactions, so investors may watch future updates in Q2 2026 and any subsequent regulatory or financing actions closely.

Key Terms

partial response, RECIST, CA-125, PPP2R1A, +3 more

7 terms

partial response medical

"Aprea announced the confirmation of a partial response (PR) in its ongoing ACESOT-1051 trial"

A partial response is a clinical outcome where a treatment produces a clear, measurable improvement in a disease — for example a substantial shrinkage of a tumor or reduction in symptom measures — but does not eliminate the disease entirely. For investors it signals meaningful efficacy that can support regulatory progress, further trials, or commercial potential, like seeing a product gain market traction even though it hasn’t achieved a complete cure.

RECIST medical

"50% reduction in target lesion size (meeting RECIST criteria for partial response)"

RECIST (Response Evaluation Criteria In Solid Tumors) is a standardized set of rules doctors and researchers use to measure how solid tumors change over time on medical scans, categorizing whether a tumor shrinks, grows, or stays the same. Investors pay attention because RECIST-based results often serve as clear, comparable trial endpoints that influence drug approvals, market expectations and company valuations—like using a reliable ruler to track progress in a development program.

CA-125 medical

"a reduction in CA-125 to 40.2U/ml (from 362 U/mL at baseline)"

CA-125 is a protein measured in the blood that often rises when certain cancers, especially ovarian cancer, are present or returning; doctors use it like a dashboard warning light to monitor disease activity, treatment response, and possible relapse rather than as a definitive diagnostic test. For investors, changes in CA-125 levels can affect clinical trial outcomes, regulatory decisions, and demand for diagnostic tests or therapies, so it can influence a company’s clinical progress and market prospects.

PPP2R1A medical

"patient with PPP2R1A-mutated endometrial cancer who is currently being treated"

PPP2R1A is a human gene that makes a key part of a molecular “brake” inside cells that helps control growth and repair by turning off certain biochemical signals. Mutations or abnormal activity in this gene are linked to some cancers and other diseases, so it matters to investors because it can be a target for drugs, affect the value of diagnostics or therapies, and influence the commercial outlook of biomedical projects.

pharmacokinetics medical

"designed to evaluate the safety, tolerability, pharmacokinetics, and preliminary anti-tumor activity"

Pharmacokinetics is the study of how a substance, such as a drug or chemical, moves through and is processed by the body over time. It tracks how it is absorbed, distributed, broken down, and eventually eliminated. For investors, understanding pharmacokinetics helps gauge the effectiveness, safety, and potential risks of new medications or treatments, which can influence a company’s success and valuation in the healthcare industry.

adverse events medical

"most common adverse events reported as Grade 1 or 2, primarily consisting of nausea"

Adverse events are any harmful or unwanted medical occurrences experienced by people using a drug, device, or undergoing a treatment, whether or not the problem is caused by the product. Think of them as complaints or breakdowns noticed during a trial or after a product is on the market; regulators record and investigate them. Investors care because clusters or serious adverse events can delay approvals, trigger costly studies or recalls, change labeling, and quickly alter a company’s revenue and risk profile.

Phase 1 medical

"ACESOT-1051 is a biomarker focused Phase 1 trial designed to evaluate the safety"

Phase 1 is the first stage of testing a new drug or medical treatment in people, focused primarily on safety, how the body handles the product, and finding a tolerated dose. Think of it as a short, tightly controlled experiment with a small group to check for dangerous side effects before wider testing; for investors it is an early milestone that reduces some uncertainty but still carries high risk and potential for both big value changes and setbacks.

AI-generated analysis. Not financial advice.

• Confirmed partial response at 220 mg indicates anti-tumor activity of APR-1051 in biomarker-defined cancers
• Early clinical data suggest the potential of APR-1051 as a best-in-class WEE1 inhibitor
• Emerging clinical proof of concept responses without class-limiting toxicity to date support Aprea’s development strategy of differentiated WEE1 inhibition with an improved therapeutic index
• A further update from the trial is expected in the second quarter of 2026

DOYLESTOWN, Pa., March 30, 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, today announced the confirmation of a partial response (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, 2026 that, at their first imaging assessment, this patient achieved a 50% reduction in target lesion size (meeting RECIST criteria for partial response) 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 (from 362 U/mL at baseline).

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 (HNSCC), 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.

“The data emerging from the ACESOT-1051 trial continue to support the clinical potential of APR-1051, with confirmation of a partial response in the 220 mg cohort indicating evidence of sustained anti-tumor activity,” said Eugene Kennedy, MD, Chief Medical Advisor at Aprea. “APR-1051 appears to be generally well-tolerated with an encouraging therapeutic window and overall, these findings strengthen our confidence in the ability of this candidate to successfully target WEE1 in genetically defined cancers, where patients face significant unmet need.”

Dose escalation is ongoing, with plans to advance to Dose Level 9 (300 mg once daily) 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 (a subset of endometrial), colorectal and HPV+ tumors. For more information on ACESOT-1051, refer to ClinicalTrials.gov NCT06260514.

About Aprea

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 the company website at 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

Certain information contained in this press release includes “forward-looking statements”, within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended related to our study analyses, clinical trials, regulatory submissions, and projected cash position. We may, in some cases use terms such as “future,” “predicts,” “believes,” “potential,” “continue,” “anticipates,” “estimates,” “expects,” “plans,” “intends,” “targeting,” “confidence,” “may,” “could,” “might,” “likely,” “will,” “should” or other words that convey uncertainty of the future events or outcomes to identify these forward-looking statements. Our forward-looking statements are based on current beliefs and expectations of our management team and on information currently available to management that involve risks, potential changes in circumstances, assumptions, and uncertainties. All statements contained in this press release other than statements of historical fact are forward-looking statements, including statements regarding our ability to develop, commercialize, and achieve market acceptance of our current and planned products and services, our research and development efforts, including timing considerations and other matters regarding our business strategies, use of capital, results of operations and financial position, and plans and objectives for future operations. Any or all of the forward-looking statements may turn out to be wrong or be affected by inaccurate assumptions we might make or by known or unknown risks and uncertainties. These forward-looking statements are subject to risks and uncertainties including, without limitation, risks related to the success, timing, and cost of our ongoing clinical trials and anticipated clinical trials for our current product candidates, including statements regarding the timing of initiation, pace of enrollment and completion of the trials (including our ability to fully fund our disclosed clinical trials, which assumes no material changes to our currently projected expenses), futility analyses, presentations at conferences and data reported in an abstract, and receipt of interim or preliminary results (including, without limitation, any preclinical results or data), which are not necessarily indicative of the final results of our ongoing clinical trials, our understanding of product candidates mechanisms of action and interpretation of preclinical and early clinical results from its clinical development programs, and our ability to predict clinical outcomes based on such preclinical and early clinical results, our ability to continue as a going concern, and the other risks, uncertainties, and other factors described under “Risk Factors,” “Management’s Discussion and Analysis of Financial Condition and Results of Operations” and elsewhere in the documents we file with the U.S. Securities and Exchange Commission. For all these reasons, actual results and developments could be materially different from those expressed in or implied by our forward-looking statements. You are cautioned not to place undue reliance on these forward-looking statements, which are made only as of the date of this press release. We undertake no obligation to update such forward-looking statements for any reason, except as required by law.

Investor Contact:

Mike Moyer
LifeSci Advisors
mmoyer@lifesciadvisors.com

FAQ

What did Aprea (APRE) report about APR-1051 in the March 30, 2026 update?

Aprea confirmed a partial response to APR-1051 at 220 mg once daily in a PPP2R1A-mutated endometrial cancer patient. According to the company, the response showed an initial 50% lesion reduction, a further 9.5% decline at confirmation, and CA-125 fell to 40.2 U/mL.

How many patients and responses are reported in Aprea's ACESOT-1051 trial (APRE)?

A total of 24 patients have been treated so far across 10–220 mg dose levels, with two partial responses observed. According to the company, one PR is confirmed and five additional patients achieved stable disease.

What safety profile did Aprea (APRE) describe for APR-1051 in the ACESOT-1051 trial?

APR-1051 has been generally safe and well tolerated with mostly Grade 1–2 events such as nausea and fatigue. According to the company, no class-limiting toxicities have emerged to date in the enrolled patients.

What are Aprea's (APRE) next clinical steps for APR-1051 and timing?

Dose escalation will continue toward Dose Level 9 (300 mg once daily) in Q2 2026, with additional patient enrollment per protocol. According to the company, they will prioritize biomarker-defined tumor types like uterine serous and HPV+ tumors.

What evidence supports APR-1051's anti-tumor activity in Aprea's (APRE) trial?

Evidence includes a confirmed PR at 220 mg with objective radiologic shrinkage and a CA-125 biomarker drop from 362 to 40.2 U/mL. According to the company, these findings indicate emerging clinical proof of concept without class-limiting toxicity.