Oncolys BioPharma announced the results from an investigator-initiated phase II clinical trial for Telomelysin™? (OBP-301) in combination with pembrolizumab in advanced gastric and gastroesophageal junction (GEA) adenocarcinoma confirm promising safety and preliminary efficacy of OBP-301 in combination with pembrolizaumb as presented at ASCO 2023. The objectives of this clinical trial were to evaluate the safety and efficacy of Telomelysin (OBP-301), an oncolytic virus in combination with pembrolIZumab, an anti-PD-1 antibody, for patients with PD-L1 positive advanced gastric and gastro-esophageal junction (GEJ) adenocarcinomas, and is led by Dr. Manish Shah at Weill Cornell Medicine, Meyer Cancer Center, in New York, NY.

Patients received OBP-301 at 2x1012 viral particles via direct tumor injection every two weeks x 4 injections as well as pembrolizumab 200 mg IV every 3 weeks for up to 2 years. The primary endpoint was objective response rate (ORR). The null hypothesis that the ORR is < 15% was tested against the Ha ORR > 30%.

The trial included 16 patients who had received at least 2 lines of prior therapy. The investigators observed clinical responses in 3 patients (ORR 19%). Two patients are without evidence of disease: one patient with brain metastases achieved a complete response and remains without evidence of disease for 3 years.

Another patient with prolonged partial response proceeded to resection and remains without evidence of disease at 20 months. The third patient had a prolonged partial response of 15 months. All patients were PD-L1 positive, but mismatch repair proficient.

One patient (with complete response) had progressed on pembrolizumab monotherapy, suggesting that OBP-301 could salvage immunotherapy refractory disease. OBP-301 viral particle injection into the tumor was well tolerated. Adverse events attributed to OBP-301 were limited to total grade 2-3 fatigue (37.5%), grade 2-3 fever (12.5%), grade 2-3 elevated LFT (12.5%), and a single incidence each of grade 2 nausea, grade 2 maculopapular rash, grade 2 mucositis, grade 3 anemia and grade 3 upper GI bleed.

A formal phase II study of OBP-301 + checkpoint inhibitor in IO refractory GEA patients will be initiated later this year.