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

Rhea-AI Summary

Sutro Biopharma (NASDAQ: STRO) presented expanded data from the dose-optimization portion of the REFRαME-O1 trial for luveltamab tazevibulin (luvelta) in platinum resistant ovarian cancer at SGO 2025. The study demonstrated:

At the optimized dose of 5.2 mg/kg + G-CSF (followed by 4.3 mg/kg), luvelta achieved:

• 32% overall response rate (ORR) and 96% disease control rate (DCR), compared to 13.8% ORR and 69% DCR at 4.3 mg/kg
• Consistent clinical activity across FRα expression levels ≥25%
• 30.8% ORR and 100% DCR for positive staining 2+ ≥75%
• 33.3% ORR and 91.7% DCR for PS2+ <75%

The safety profile remained consistent across dosing groups, with manageable neutropenia. However, Sutro announced it is deprioritizing luvelta's development across all indications and is seeking out-licensing opportunities.

Positive

• Higher efficacy at optimized dose: 32% ORR vs 13.8% at lower dose
• Strong disease control rate of 96% at optimized dose
• Consistent efficacy across all FRα expression levels ≥25%
• Manageable safety profile with no new safety signals

Negative

• Company deprioritizing luvelta development across all indications
• Seeking out-licensing opportunities indicates strategic shift away from the program

Insights

Financial Analyst

Sutro's clinical data from the REFRαME-O1 trial shows promising efficacy for luveltamab tazevibulin (luvelta) in platinum resistant ovarian cancer, with the optimized dose achieving a 32% overall response rate and 96% disease control rate. However, the strategic decision to deprioritize luvelta across all indications creates significant uncertainty for STRO investors.

This corporate pivot is particularly concerning given the positive clinical data. The company's plan to out-license luvelta suggests either resource constraints or a strategic realignment toward other pipeline assets. For a small-cap biotech with $75.5 million market capitalization, successfully out-licensing this asset could provide important non-dilutive funding, but the timing is puzzling considering the encouraging efficacy data.

The trial results demonstrate meaningful clinical differentiation compared to standard chemotherapy, particularly in patients with FRα expression between 25% and 75%, potentially addressing an unmet medical need. However, investors should be cautious about the disconnect between the positive clinical data and the company's strategic shift away from this program. This decision raises questions about either undisclosed challenges with the asset or significant financial constraints forcing portfolio prioritization.

Oncology Specialist

The REFRαME-O1 trial data for luvelta demonstrates clinically meaningful activity in platinum resistant ovarian cancer, a notoriously difficult-to-treat population. The dose-optimized regimen (5.2 mg/kg + G-CSF for two cycles then 4.3 mg/kg) shows particular promise with its 32% overall response rate and remarkable 96% disease control rate.

What's scientifically significant is luvelta's consistent efficacy across varying levels of FRα expression (25% or greater), including patients with expression below 75% who aren't candidates for the currently approved FRα-targeting ADC. This expands the potential treatment population considerably compared to existing targeted options.

The manageable safety profile with neutropenia apparently well-controlled through G-CSF support indicates a favorable therapeutic window. The 91.7% disease control rate in patients with lower FRα expression addresses a critical treatment gap in precision medicine for ovarian cancer.

Sutro's decision to deprioritize this asset despite these encouraging results is puzzling from a clinical perspective. Given the data's strength and the significant unmet need in platinum-resistant disease, this ADC could represent a valuable therapeutic option if developed by a partner with adequate resources. The strategic pivot away from luvelta suggests either portfolio reprioritization or undisclosed development challenges beyond efficacy and safety.

- 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

FAQ

What were the key efficacy results for STRO's luvelta in the REFRαME-O1 trial?

At 5.2 mg/kg, luvelta achieved 32% ORR and 96% DCR, showing improved efficacy compared to 13.8% ORR and 69% DCR at 4.3 mg/kg dose.

How did luvelta perform in patients with different FRα expression levels?

Luvelta showed consistent efficacy across FRα expression ≥25%, with 30.8% ORR (100% DCR) in PS2+ ≥75% and 33.3% ORR (91.7% DCR) in PS2+ <75%.

What is the optimized dosing regimen for STRO's luvelta?

The optimized dose is 5.2 mg/kg + G-CSF for two cycles, followed by 4.3 mg/kg maintenance dose.

What is Sutro Biopharma's current development strategy for luvelta?

Sutro is deprioritizing luvelta's development across all indications and seeking out-licensing opportunities.