Sutro Biopharma Presents Data from Dose-Optimization Portion of REFRαME-O1 Trial in Patients with Platinum Resistant Ovarian Cancer at SGO 2025

– The late-breaking oral presentation at SGO 2025 highlights consistent response rates observed in patients across all levels of FRα expression of 25% or greater –

SOUTH SAN FRANCISCO, Calif., March 15, 2025 (GLOBE NEWSWIRE) — Sutro Biopharma, Inc. (Sutro or the Company) (NASDAQ: STRO), an oncology company pioneering site-specific and novel-format antibody drug conjugates (ADCs), today announced expanded data in a late-breaking oral presentation from the dose-optimization portion of the REFRαME-O1 trial with luveltamab tazevibulin (luvelta) in patients with platinum resistant ovarian cancer (PROC) at the Society of Gynecologic Oncology (SGO) Annual Meeting on Women’s Cancer^®. The SGO Annual Meeting will take place from March 14-17, 2025 in Seattle, Washington.

In this study, luvelta demonstrated encouraging antitumor activity in patients with late-stage ovarian cancer across all levels of Folate Receptor-α (FRα) expression of 25% or greater, including an improved overall response rate (ORR), a low discontinuation rate, and a consistent safety profile across dose levels. Based on these findings, Sutro selected the optimized dose of luvelta: 5.2 mg/kg + G-CSF for two cycles then continued on 4.3 mg/kg.

“These data demonstrate the potential for improved patient responses compared to standard chemotherapy in PROC, especially patients whose FRα expression falls within the range of at least 25% to less than 75% 2+, which remains an important unmet medical need,” commented Dr. Jung Yun Lee, Professor, Gynecologic Oncologist, Yonsei Cancer Center and Severance Hospital, Yonsei University College of Medicine, Seoul, Republic of Korea.

Late-Breaking Oral Presentation Highlights:

• At the selected optimized dose (5.2 mg/kg), luvelta achieved an ORR of 32%¹ and a disease control rate (DCR) of 96% compared to an ORR of 13.8% and a DCR of 69% for the 4.3 mg/kg group.
• The demonstrated clinical activity in the 5.2 mg/kg group was consistent in patients across all levels of FRα expression of 25% or greater, with an ORR of 30.8% and a DCR of 100% for positive staining (PS) 2+ ≥75% (eligible for approved FRα-targeting ADC) and an ORR of 33.3%¹ and DCR of 91.7%¹ for PS2+ < 75%.
• Safety was consistent across dosing groups, with no new safety signals observed and neutropenia well-managed.
• The majority of patients across both dose cohorts received prior bevacizumab.

The presentation will be accessible through the News & Events page of the Investor Relations section of the company’s website at www.sutrobio.com.

The Company recently announced that it is deprioritizing investment into the development of luvelta across all indications. Sutro continues to explore out-licensing opportunities to deliver the promise of luvelta’s benefit to patients with unmet need in platinum resistant ovarian cancer and beyond.

¹ Immediately after data extraction, one additional patient experienced a confirmed PR and is included in the analysis.

About Luveltamab Tazevibulin

Luveltamab tazevibulin, abbreviated as “luvelta” and formerly known as STRO-002, is a FRα-targeting antibody-drug conjugate (ADC) designed to treat a broad range of patients with ovarian cancer, including those with lower FRα-expression who are not eligible for approved treatment options targeting FRα. Developed and manufactured with Sutro’s cell-free XpressCF^® platform, luvelta is a homogeneous ADC with four hemiasterlin cytotoxins per antibody, precisely positioned to efficiently deliver to the tumor while ensuring systemic stability after dosing. The U.S. Food and Drug Administration (FDA) has granted luvelta a Fast Track designation for Ovarian Cancer, as well as Orphan and Rare Pediatric Disease designations for CBF/GLIS2 Pediatric AML.

About Sutro Biopharma  
Sutro Biopharma, Inc., is relentlessly focused on the discovery and development of precisely designed cancer therapeutics to transform what science can do for patients. Sutro’s fit-for-purpose technology, including cell-free XpressCF^®, provides the opportunity for broader patient benefit and an improved patient experience. Sutro is advancing a robust early-stage pipeline of novel exatecan and dual-payload antibody drug conjugates (ADCs), coupled with high-value collaborations and industry partnerships, which validate its continuous product innovation. Sutro is headquartered in South San Francisco. For more information, follow Sutro on social media @Sutrobio, or visit www.sutrobio.com. 

Forward-Looking Statements
This press release contains forward-looking statements within the meaning of the “safe harbor” provisions of the Private Securities Litigation Reform Act of 1995, including, but not limited to, anticipated preclinical and clinical development activities, including enrollment and site activation; timing of announcements of clinical results, trial initiation, and regulatory filings; outcome of discussions with regulatory authorities; potential benefits of luvelta and the Company’s other product candidates and platform; potential business development and partnering transactions; potential market opportunities for luvelta and the Company’s other product candidates. All statements other than statements of historical fact are statements that could be deemed forward-looking statements. Although the Company believes that the expectations reflected in such forward-looking statements are reasonable, the Company cannot guarantee future events, results, actions, levels of activity, performance or achievements, and the timing and results of biotechnology development and potential regulatory approval is inherently uncertain. Forward-looking statements are subject to risks and uncertainties that may cause the Company’s actual activities or results to differ significantly from those expressed in any forward-looking statement, including risks and uncertainties related to the Company’s ability to advance its product candidates, the receipt and timing of potential regulatory designations, approvals and commercialization of product candidates, the market size for the Company’s product candidates to be smaller than anticipated, clinical trial sites, supply chain and manufacturing facilities, the Company’s ability to maintain and recognize the benefits of certain designations received by product candidates, the timing and results of preclinical and clinical trials, the Company’s ability to fund development activities and achieve development goals, the Company’s ability to protect intellectual property, and the Company’s commercial collaborations with third parties and other risks and uncertainties described under the heading “Risk Factors” in documents the Company files from time to time with the Securities and Exchange Commission. These forward-looking statements speak only as of the date of this press release, and the Company undertakes no obligation to revise or update any forward-looking statements to reflect events or circumstances after the date hereof. 

Investor Contact
Emily White
Sutro Biopharma
(650) 823-7681
ewhite@sutrobio.com

Media Contact
Amy Bonanno
Lyra Strategic Advisory
abonanno@lyraadvisory.com