STRO-002 Shows Early Efficacy, Safety in Heavily Pretreated Epithelial Ovarian Cancer – OncLive September 2020

Sep 11, 2020

The novel anti-folate receptor alpha antibody-drug conjugate STRO-002 demonstrated encouraging efficacy with a tolerable safety profile in patients with advanced platinum-resistant or refractory epithelial ovarian cancer.

The novel anti-folate receptor alpha (FolRα) antibody-drug conjugate (ADC) STRO-002 demonstrated encouraging efficacy with a tolerable safety profile in patients with advanced platinum-resistant or refractory epithelial ovarian cancer, according to updated interim results from the phase 1 STRO-002-GM1 trial (NCT03748186).1

Results showed that the ADC elicited an overall response rate (ORR) of 24% in a total of 33 evaluable patients who had post-baseline scans available. Durability of response was demonstrated in 44% of patients who received treatment for 16 weeks or more and 12% of those who received treatment for 1 year or longer. The disease control rate (DCR) with STRO-002 was 47% (n = 14/30).

“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,” Arturo Molina, MD, MS, chief medical officer of Sutro Biopharma, stated in a press release.

STRO-002 is the first ADC to be produced with cell-free protein synthesis technology for testing in patients with solid tumors. STRO-002 contains an anti-FolRα human IgG1 antibody, SP8166, which is conjugated to a cleavable DBCO-3-aminophenyl-hemiasterlin drug-linker through site-directed conjugation technology to develop an ADC with the predominant species that has a drug-antibody ratio of 4.2

The open-label, dose-escalation/expansion phase 1 trial was launched in March 2019 and is being conducted across 10 clinical sites throughout the United States. Patients with recurrent platinum-resistant or -refractory ovarian cancer and those who received treatment with at least 2 previous platinum regimens have been enrolled. Notably, an all-comer population was enrolled to the trial, irrespective of their level of FRα expression. There was no limit to the number or previous lines of chemotherapy regimens a patient had received.3

The primary end point of the dose-expansion portion of the STRO-002-GM1 trial is ORR to determine the antitumor activity of the ADC. A secondary objective in the dose-escalation phase was to characterize the pharmacokinetics (PK) and immunogenicity of the drug. Key secondary objectives in the dose-expansion phase include duration of response, progression-free survival, as well as additional safety and PK. The exploratory objectives in the dose-escalation phase include preliminary efficacy, pharmacokinetic correlation with efficacy, and biomarkers; objectives in the dose-expansion phase include further PK correlation with efficacy and biomarkers.

To date, a total of 39 patients have been enrolled on the trial; 77% (n =30) have endothelial ovarian cancer, 18% (n = 7) have fallopian tube, and 5% (n = 2) have primary peritoneal. The median age of participants is 61 years. Moreover, the majority of participants, or 59% (n = 23), have an ECOG performance status of 0, while 41% (n = 16) have a status of 1.

The median time from diagnosis to treatment was 3.9 years and the median prior lines of treatment was 5. All patients had previously received treatment with platinum-based chemotherapy and 36% had received 3 more previous platinum-containing regimens. Additionally, 97% (n = 38) of patients received prior taxane treatment, 79% (n = 31) received bevacizumab (Avastin), 59% (n = 23) had PARP inhibitors, 21% (n = 8) had checkpoint inhibitors, and 34% (n = 13) had received experimental therapy.

Additional results showed that in the 30 patients evaluable for RECIST response, 8 patients achieved partial responses (PRs) with STRO-002; 2 were confirmed and 6 were unconfirmed. Moreover, 7 patients with PRs and 13 patients who achieved stable disease experienced a DCR of 60% at 12 weeks or greater.

Twenty-nine percent of patients who received STRO-002 at a dose of 2.9 mg/kg or higher continued on the study for longer than 24 weeks. Forty-one percent of patients remained on study for over 16 weeks, 15% for longer than 45 weeks, and 6% for over 1 year. Forty-seven percent of patients remain on treatment with the ADC.

Additionally, in those who received a dose of 2.9 mg/kg or higher and were evaluable for CA-125 response (n = 24), 67% (n = 16/24) experienced a 50% or greater reduction in CA-125 and 42% (n = 10/24) had confirmed CA-125 response per Gynecologic Cancer Intergroup criteria. Eight percent (n = 2/24) have an ongoing response with confirmation pending or possible, while 21% (n = 5/24) have discontinued without confirmation.

With regard to safety, those who received STRO-002 were found to have mostly mild adverse effects; 88% of toxicities reported were either grade 1 or 2 in severity. Of the 39 patients, 67% (n = 26) experienced fatigue, 59% (n = 23) reported nausea, 51% (n = 20) experienced neutropenia/neutrophil count decrease, 44% (n = 17) had arthralgia, 44% (n = 17) had decreased appetite, 31% (n = 12) experienced abdominal pain, 31% (n = 12) had increased aspartate aminotransferase, 29% (n = 11) had diarrhea, 26% (n = 10) reported peripheral neuropathy, and 26% (n = 10) experienced vomiting.

Two dose-limiting toxicities were reported: 1 patient who received the agent at 6.0 mg/kg experienced neuropathy and 1 patient who was given the agent at a dose of 6.4 mg/kg reported bone pain. Only 1 case of grade 3 febrile neutropenia was reported. One grade 5 event of death on day 12 of cycle 1 was reported, although no cause was reported, and it was not determined to be related to study treatment per investigator assessment.

Notably, a low rate of keratitis was observed with long-term dosing of the ADC. Only 1 patient required therapeutic corticosteroid eyedrops.

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


  1. Sutro Biopharma presents promising STRO-002 interim phase 1 clinical data in ovarian cancer at the 2020 IGCS Annual Global Meeting. News release. Sutro Biopharma. September 9, 2020. Accessed September 11, 2020.
  2. Naumann RW, Braiteh FS, Diaz JP, et al. 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. Presented at: 2020 International Gynecologic Cancer Society Virtual Healthcare Conference; September 10-13, 2020; Virtual.
  3. Naumann RW, Uyar D, Moroney JW, et al. STRO-002-GM1, a first in human, phase 1 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), including fallopian tube or primary peritoneal cancers. Presented at: 2020 AACR Virtual Annual Meeting I; April 27-28, 2020. Abstract CT125.