Note: This story was updated Feb. 8, 2021, to note that the ovarian cancer expansion group will include 40 participants, not 20.
Sutro Biopharma‘s Phase 1 clinical trial has begun testing the recommended dose of STRO-002 in heavily pretreated patients with advanced ovarian cancer.
“We are excited to be part of the STRO-002-GM1 dose-expansion study and to provide additional clinical data to show the potential of this therapeutic for ovarian patients with limited treatment options,” Lainie Martin, MD, trial investigator and leader of the gynecology/oncology program at the Hospital of the University of Pennsylvania, said in a press release.
A total of 40 ovarian cancer patients, being enrolled at multiple sites in the U.S., will be randomly assigned to either 4.3 or 5.2 mg/kg of STRO-002, given every three weeks. A second expansion group including people with endometrial cancer is planned to start later this year.
“We are pleased to advance the clinical development of STRO-002 into dose-expansion studies,” said Arturo Molina, MD, chief medical officer of Sutro. “Results from our STRO-002 dose escalation in a heavily pre-treated ovarian cancer patient population demonstrated improved outcomes.”
STRO-002 is an investigational antibody-drug conjugate. It is made up of an antibody that specifically binds to folate receptor alpha — a protein found at high levels in most types of ovarian cancer — linked to a toxic compound. When the antibody binds to its target, it releases the compound into cells, destroying them.
The Phase 1 trial (NCT03748186) is evaluating the safety, tolerability, and preliminary efficacy of STRO-002 in 160 women with ovarian cancer (including fallopian and primary peritoneal cancer) and endometrial cancer who received prior platinum-based chemotherapy and failed multiple prior therapies.
The trial is divided in two parts: an initial dose-escalation part, in which participants received increasing doses of STRO-002 (0.5 to 6.4 mg/kg given every three weeks) to determine its optimal dose; and a dose expansion part, in which participants will be treated with the recommended dose.
Initial data from the 39 patients included in the study’s dose-escalation phase showed that STRO-002 was generally safe and well-tolerated and showed promising benefits in patients who received doses of 2.9 mg/kg or higher.
“STRO-002 continues to be well-tolerated and we have observed encouraging preliminary activity in patients with advanced platinum-resistant and refractory ovarian cancer,” said Martin.
A third of patients (10 out of 31) receiving such doses responded favorably to treatment, including one complete response, or complete cancer elimination. Stable disease was experienced by an additional 13 patients, meaning that a total of 74% of patients drew some benefit from STRO-002 after a minimum of 12 weeks of treatment — an outcome that is considered clinically relevant in this patient population.
The most common serious side effect was neutropenia (low white blood cell counts). Nearly all side effects (86%) reported were mild or moderate in severity.
“We are hopeful that the dose-expansion study will validate the preliminary signs of efficacy we have seen in dose-escalation and provide valuable data on the treatment paradigm and patient population that will benefit from treatment, bringing us one step closer to offering an important new potential treatment option,” said Molina.