Zentalis Pharmaceuticals Reports Third Quarter 2025 Financial Results and Operational Progress (Form 8-K)

Zentalis Pharmaceuticals Reports Third Quarter 2025 Financial Results and Operational Progress

DENALI Phase 2 trial evaluating azenosertib in patients with Cyclin E1-positive PROC remains on track with topline data anticipated by year end 2026, with the potential to support an accelerated approval, subject to FDA feedback

$280.7 million cash, cash equivalents and marketable securities supports runway into late 2027

SAN DIEGO, Calif. - November 10, 2025 - Zentalis® Pharmaceuticals, Inc. (Nasdaq: ZNTL), a clinical-stage biopharmaceutical company developing a potentially first-in-class WEE1 inhibitor for patients with ovarian cancer and other tumor types, announced financial results for the third quarter 2025 and highlighted recent operational progress.

"We are pleased with our continued disciplined execution of the DENALI clinical trial this quarter, supporting late-stage development of azenosertib as a potential treatment for Cyclin E1-positive platinum-resistant ovarian cancer, and positioning us for an anticipated topline data readout by year end 2026. Our engagement with trial investigators and presence at medical conferences is very encouraging and continues to support our development strategy," said Julie Eastland, Chief Executive Officer of Zentalis. "With $280.7 million in cash providing runway into late 2027, we maintain a robust financial foundation to deliver on our azenosertib objectives."

Business Updates

•Phase 2 DENALI clinical trial remains on track and has the potential to support an accelerated approval, subject to FDA feedback.

◦Enrollment is ongoing in DENALI Part 2a of the Phase 2 DENALI clinical trial (NCT05128825) of azenosertib in patients with Cyclin E1-positive PROC. DENALI Part 2a is designed to confirm the primary dose-of-interest with a target enrollment of up to approximately 30 patients at each of two dose levels: 400mg QD 5:2 (intermittent daily dosing with a five days on, two days off dosing schedule) and 300mg QD 5:2. DENALI Part 2b is designed to enroll approximately 70 patients at a single dose, the selection of which will be informed by the Part 2a results.

◦The Company expects to disclose topline data from DENALI Part 2 (Part 2a and Part 2b) by year end 2026. We believe that DENALI Part 2, if successful, has the potential to support an accelerated approval, subject to FDA review.

•Poster Presentations at AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics support Cyclin E1 biomarker-driven strategy for azenosertib.

◦Presentations feature data from first-in-human Phase 1 study, including Cyclin E1 biomarker findings, supporting late-stage development of azenosertib.

•TETON Phase 2 trial in uterine serous carcinoma (USC) completed enrollment.

◦Consistent with the Company's previously announced strategic prioritization of azenosertib for the treatment of patients with Cyclin E1-positive PROC, further development in USC will be limited to partnering or the Company's ability to allocate capital to this indication.

◦The Company will continue to support an ongoing investigator-initiated study to explore potential biomarker enrichment strategy in USC.

◦Results from the TETON trial are planned for publication in the first half of 2026.

Third Quarter 2025 Financial Results

•Cash, Cash Equivalents and Marketable Securities Position: As of September 30, 2025, the Company had cash, cash equivalents and marketable securities of $280.7 million. The Company believes that its existing cash, cash equivalents and marketable securities as of September 30, 2025 will be sufficient to fund its operating expenses requirements into late 2027.

•Research and Development Expenses: Research and development (R&D) expenses for the three months ended September 30, 2025 were $23.0 million, compared to $36.8 million for the three months ended September 30, 2024. The decrease of $13.8 million was primarily due to decreases of $7.6 million for personnel expenses, of which $2.7 million was non-cash stock-based compensation. Decreases of $4.2 million for lab services, $1.2 million for clinical expenses, and $0.8 million for supplies, overhead, and other expense also contributed to the overall reduction in research and development expenses.

•General and Administrative Expenses: General and administrative expenses for the three months ended September 30, 2025 were $10.8 million, compared to $14.6 million during the three months ended September 30, 2024. This decrease of $3.8 million was attributable to a decrease of $3.8 million in personnel expense, of which $2.8 million was non-cash stock-based compensation.

•Operating Expenses: Total operating expenses were $33.7 million for the three months ended September 30, 2025, compared to $51.4 million for the three months ended September 30, 2024.

About Azenosertib

Azenosertib is an investigational, novel, selective, and orally bioavailable inhibitor of WEE1 currently being evaluated as a monotherapy and combination clinical studies in ovarian cancer and additional tumor types. WEE1 acts as a master regulator of the G1-S and G2-M cell cycle checkpoints, through negative regulation of both CDK1 and CDK2, to prevent replication of cells with damaged DNA. By inhibiting WEE1, azenosertib enables cell cycle progression, despite high levels of DNA damage, thereby resulting in the accumulation of DNA damage and leading to mitotic catastrophe and cancer cell death.

About DENALI Clinical Trial

DENALI is a multi-part Phase 2 clinical trial studying azenosertib in platinum-resistant ovarian cancer (PROC) patients. Part 1b enrolled patients with PROC regardless of Cyclin E1 protein expression, all treated at 400mg 5:2 (intermittent daily dosing with a five days on, two days off dosing schedule). Interim results from Part 1b were presented at the Society of Gynecologic Oncology (SGO) 2025 Annual Meeting. Part 2 is ongoing and is enrolling PROC patients with Cyclin E1 protein overexpression based on Zentalis' proprietary immunohistochemistry cutoff. Part 2 includes Part 2a, a dose confirmation portion evaluating two doses, 300mg 5:2 and 400mg 5:2, and Part 2b, a portion designed to complete enrollment at the selected dose. Part 2, in total, is designed for accelerated approval, pending study outcome and discussions with the U.S. Food and Drug Administration.

About Zentalis Pharmaceuticals

Zentalis® Pharmaceuticals, Inc. is a clinical-stage biopharmaceutical company developing azenosertib (ZN-c3), an investigational, potentially first-in-class and best-in-class WEE1 inhibitor for patients with Cyclin E1-positive platinum-resistant ovarian cancer (PROC). Azenosertib is being evaluated as a

monotherapy and in combination across multiple tumor types in clinical trials and has broad franchise potential. In clinical trials, azenosertib has been well tolerated and has demonstrated anti-tumor activity as a single agent across multiple tumor types. The Company is also leveraging its extensive experience and capabilities to translate its science to advance research on additional areas of opportunity for azenosertib outside PROC. Zentalis has operations in San Diego.

For more information, please visit www.zentalis.com. Follow Zentalis on LinkedIn at www.linkedin.com/company/zentalis-pharmaceuticals