STRO-002 Trial Update Supports Its Safety, Activity in Advanced Cancer

STRO-002 Trial Update Supports Its Safety, Activity in Advanced Cancer

Updated interim data from a Phase 1 clinical trial continues to support the safety and anti-tumor activity of Sutro Biopharma’s STRO-002 for heavily pre-treated women with advanced ovarian cancer.

About one-quarter of patients receiving a dose of 2.9 mg/kg or higher responded to this investigational antibody-drug conjugate, and nearly half (44%) had responses lasting at least 16 weeks, results showed.

These findings were presented by Wendel Naumann, MD, the trial’s principal investigator, in a virtual poster, “Phase 1 Dose-Escalation Study of STRO-002, An Anti-Folate Receptor Alpha (FRα) Antibody Drug Conjugate (ADC), in Patients with Advanced Platinum-Resistant/Refractory Epithelial Ovarian Cancer (OC)” at the 2020 xDigital Annual Global Meeting of the International Gynecologic Cancer Society (IGCS) on Sept. 10.

STRO-002, an antibody-drug conjugate, is made of an antibody that specifically binds to folate receptor alpha (FRα), a protein found at high levels in most types of ovarian cancer. The binding is designed to trigger the release of a toxic compound that kills tumor cells, while leaving healthy cells unharmed.

The open-label Phase 1 trial (NCT03748186) is assessing the safety, tolerability, and preliminary efficacy of STRO-002 in women with ovarian cancer (including fallopian and primary peritoneal cancer) and endometrial cancer who received prior platinum-based chemotherapy.

In the study’s first part, women were given increasing doses of STRO-002 — ranging from 0.5 mg/kg to 6.4 mg/kg — to determine the therapy’s optimal dose. This is being followed by a dose expansion part, in which participants will be treated with the recommended dose.

As of Aug. 31, a total of 39 heavily pre-treated women (median of five prior chemotherapy regimens) had been enrolled in the dose-escalation part of the study, which is now complete.

Patients were enrolled regardless of their FRα levels and the number of prior chemotherapy regimens, according to Naumann.

Thirty-four patients were given STRO-002 at a dose of 2.9 mg/kg or higher.

In agreement with earlier data, updated findings from 33 of these patients showed that eight (24%) responded in part to the treatment. An additional 13 patients attained disease stabilization, for a disease control rate of 60% after a minimum of 12 treatment weeks.

“We continue to see an encouraging efficacy and safety profile for STRO-002 in this heavily pretreated patient population,” Naumann, a gynecologic oncologist at Levine Cancer Institute, said in a press release.

A total of 44% patients have been on treatment for at least 16 weeks, and 12% for one year or more. The levels of CA-125, a cancer biomarker, fell by 50% or more in 16 of 24 patients evaluated (67%), with the reduction correlating with disease control.

“We are pleased to observe improved efficacy outcomes as our data mature with longer follow-up, and the observed rate of objective response, stable disease and overall disease control during this study suggest that STRO-002 is potentially superior to other targeted ADC therapies being studied currently in ovarian cancer,” said Arturo Molina, MD, chief medical officer of Sutro.

Treatment was safe and well-tolerated, with 87% of the adverse events reported being mild (grade 1) or moderate (grade 2) in severity. Serious adverse events included joint painperipheral neuropathy (nerve damage), and neutropenia (low white blood cell counts). Neutropenia resolved within one week.

The company will continue to explore dose optimization in the dose expansion part, now with less heavily pre-treated patients. Investigators expect that the recommended dose for Phase 2 testing will be in the 4.3 to 5.2 mg/kg range.

“We believe that STRO-002 will be a potent and well-tolerated treatment option for patients. Next up, we plan to initiate a dose expansion trial in patients with less heavily pretreated ovarian cancer in the fourth quarter of 2020,” Molina said.