Sutro Reports Early STRO-004 Responses in Phase 1
The company posted $9.8 million of second-quarter revenue and $164.3 million of cash as it optimized STRO-004 between 4 and 5 mg/kg.
Sutro Biopharma (STRO), a clinical-stage oncology company developing site-specific antibody-drug conjugates, reported confirmed and ongoing unconfirmed partial responses in its Phase 1 study of STRO-004, a tissue-factor-targeting DAR8 exatecan ADC, after enrolling dose levels 1 through 5 mg/kg faster than expected.
The STRIVE-01 trial, which began in November 2025, is now optimizing between 4 and 5 mg/kg. The maximum tolerated dose has not yet been defined. In the first quarter, the company said it expected initial safety, pharmacokinetic and early activity data in mid-2026; that readout arrived with 49 patients enrolled across those dose levels.
Responses were seen in pancreatic cancer, head and neck cancer, and non-small cell lung cancer at dose levels 3 and 4 mg/kg among RECIST-evaluable patients. The U.S.-only study includes heavily pretreated patients, with a median of three prior lines of therapy (range 1–7), across eight tumor types unselected for tissue-factor expression. In pancreatic and colorectal cancer patients, 100% had received one or more prior irinotecan-containing regimens.
Tolerability was mostly low-grade. The discontinuation rate due to adverse events was 6%. Dose-limiting toxicities occurred only at 5 mg/kg and appeared largely driven by target-related toxicity, resulting in dose reduction but no study-drug discontinuations. All-grade treatment-related adverse events above 15% were nausea (33%), fatigue (29%) and anemia (18%). On-target tissue-factor events such as epistaxis, stomatitis and mucosal inflammation were predominantly grade 1–2. Grade 3 anemia occurred in 14% of patients.
Pharmacokinetics were dose-proportional, with no evidence of target-mediated drug disposition. STRO-004 has a half-life of nearly seven days and preserved 98% DAR8 configuration, while free exatecan remained low, delayed and formation-limited. Chief Scientific Officer Hans-Peter Gerber said the construct delivered 25–50% more ADC exposure with at least 50% less circulating payload concentration versus conventional DAR8 exatecan ADCs, allowing dosing at the highest end of the class range. The next STRIVE-01 update is targeted for the first half of 2027, and initiation of expansion cohorts is planned for the same period.
STRO-006, a next-generation integrin β6-targeting ADC with a DAR8 exatecan payload, is expected to initiate a Phase 1 trial in the third quarter of 2026. In the prior quarter, the company described an IND submission as anticipated in 2026. STRO-227, a wholly owned PTK7-targeting dual-payload ADC combining MMAE and exatecan, remains on track for IND submission in 2026.
Under the Astellas collaboration, the first dual-payload immunostimulatory ADC program, targeting TROP2, continues to dose patients. Sutro received a $10 million milestone payment in April 2026. The second program is expected to enter the clinic by the end of 2026, versus the prior quarter’s description of an IND-enabling toxicology study.
Revenue was $9.8 million for the quarter ended June 30, 2026, compared with $63.7 million a year earlier, with the 2026 amount related principally to the Astellas collaboration. Total research and development and general and administrative expenses were $39.5 million. Research and development expense was $31.7 million and general and administrative expense was $7.8 million. Restructuring and related costs were $0.2 million.
Net loss was $38.5 million, or $2.33 a share, versus $11.5 million, or $1.35 a share, a year earlier. Loss from operations was $29.9 million. Weighted-average shares used in computing basic and diluted loss per share were 16.6 million.
Cash, cash equivalents and marketable securities were $164.3 million as of June 30, 2026, compared with $202.6 million as of March 31, 2026. The balance is expected to support operations into at least the second quarter of 2028.
Chief Executive Officer Jane Chung said the company continued to execute swiftly across its next-generation ADC portfolio, highlighted by the STRO-004 data and rapid enrollment of the initial dose-escalation cohorts in seven months. She said the company is excited to enter the clinic with STRO-006 in the near future, its second clinical program in less than a year.