Updated Interim Data from Phase I Trial of STRO-002 Show Promise in Ovarian Cancer

Updated interim data from the ongoing phase I clinical trial of the folate receptor alpha (FolRα) antibody drug-conjugate (ADC) STRO-002 regarding safety and anti-tumor activity results in heavily pre-treated patients with ovarian cancer were reported by Sutro Biopharm, the agent’s developer.¹

The ongoing open-label, multicenter, dose escalation trial with dose expansion of STRO-002 is designed to identify the maximum tolerated dose (MTD), the recommended phase II clinical dose, and to evaluate the safety, tolerability, and preliminary anti-tumor activity of STRO-002 in adults with advanced epithelial ovarian cancer, including fallopian or primary peritoneal cancer, and endometrial cancer. 

Patients were administered 2.9 mg/kg of STRO-002 or higher. One patient experienced an ongoing confirmed partial response (36 weeks), 5 patients had confirmed stable disease (3 up to 18 weeks, 2 up to 27 weeks), and 7 ongoing patients have confirmed stable disease at the 6-week assessment point.

“STRO-002 is the first ADC generated with cell-free protein synthesis technology to be tested in patients with solid tumors,” R. Wendel Naumann, MD, of the Levine Cancer Institute, said in a poster presentation of the data at the American Association for Cancer Research (AACR) Virtual Annual Meeting 2020.² “The preliminary evidence of antitumor activity and clinical benefit starting at the 2.9 mg/kg dose is encouraging, particularly in this heavily pretreated patient population that is resistant or refractory to platinum and has not been enriched for FolRα expression.” 

Ultimately, 62% of the participants saw a reduction in CA-125 levels of 50% or more or a normalization of CA-125 levels. Moreover, 35% of the patients who were evaluable for progression have remained on the study for longer than 24 weeks and 11 patients dosed at 5.2 mg/kg or higher are continuing the study and have not yet reached 24 weeks. 

STRO-002 was generally well tolerated and was most patients only experienced mild adverse events (AEs). Overall, 89% of AEs were grade 1 or grade 2, and prophylactic corticosteroid eye drops have not yet been necessary. Additionally, grade 3 treatment emergent AEs included fatigue, neutropenia, arthralgia, diarrhea, peripheral neuropathy, and myalgia. The only grade 4 treatment AE that emerged was neutropenia, and all neutropenias were found to be reversible within 1 week. 

“Follow-up at higher dose levels is early, and response data is pending in 22% of patients,” said Naumann. “The maximum tolerated dose and recommended phase II dose have not been determined. Enrollment is ongoing.”

As of April 20, 2020, the phase I trial has enrolled 30 patients with recurrent platinum resistant or refractory ovarian cancer. Further, a dose expansion phase of this trial is anticipated to begin in the second half of 2020. Though an MTD has not yet been reached, the company indicated that they continue to evaluate the 5.2 mg/kg to 6.0 mg/kg dose levels as they await a recommended phase II dose. 

References:

1. Sutro Biopharma. Sutro Biopharma Announces Encouraging Interim Phase I Clinical Data for a Dose Escalation Study of STRO-002 Antibody-Drug Conjugate in Ovarian Cancer [news release]. Published April 27, 2020. sutrobio.com/sutro-biopharma-announces-encouraging-interim-phase-1-clinical-data-for-a-dose-escalation-study-of-stro-002-antibody-drug-conjugate-in-ovarian-cancer/. Accessed April 27, 2020. 

2. Sutro Biopharma. Dr. Wendel Naumann of The Levine Cancer Institute, Virtual Presentation of STRO-002 Antibody-Drug Conjugate (ADC) at the American Association for Cancer Research (AACR) Virtual Annual Meeting 2020. Published April 27, 2020. sutrobio.com/dr-wendel-naumann-of-the-levine-cancer-institute-virtual-presentation-of-stro-002-antibody-drug-conjugate-adc-at-the-american-association-for-cancer-research-aacr-virtual-annual-meeting-2020/. Accessed April 27, 2020.