Study of Suratadenoturev (OBP-301) in Combination With Pembrolizumab in Esophagogastric Adenocarcinoma

This is a phase II study of suratadenoturev (OBP-301) with pembrolizumab in advanced or metastatic gastric, gastroesophageal junction, or esophageal adenocarcinoma that has progressed on at least 1 line of prior therapy for advanced disease. Patients must have received prior immunotherapy (anti PD-1 therapy). This study will examine the addition of OBP-301 with pembrolizumab patients who are refractory to first line immunotherapy.

Patients will undergo intra-tumoral injection of OBP-301 followed 2-4 days later by the administration of pembrolizumab. The OBP-301 injection will then be repeated every two weeks for 4 planned treatments, and up to one additional optional treatment. Pembrolizumab will be administered every 6 weeks until disease progression.

The primary endpoint is objective response rate, with the target response rate of 20%, to examine the hypothesis that OBP-301 can overcome checkpoint resistance. The expected response to continuing anti-PD-1 therapy in this patient population would anticipated to be <5%. As a key secondary endpoint, the investigators will also examine duration of response and progression free survival. In a previous trial of OBP-301 and pembrolizumab in the third line setting, two patients who had a partial response are now off therapy and without evidence of disease, with a duration of response 33+ months and 20+ months. The third patient with a partial response has been on therapy for 15+ months.

This trial utilizes a Simon's two-stage Minimax design. In the first stage of the trial, 13 patients will be accrued. If there are 0 responses in these 13 patients, the study will be stopped. Otherwise, 14 additional patients will be accrued for a total of 27 patients.

Inclusion criteria

• Histologically or cytologically confirmed advanced or metastatic gastric, gastroesophageal junction, or esophageal adenocarcinoma amenable to intra-tumoral injection (i.e. at least 1 cm in size)
• Tumor must be examined forPD-L1 assessment as defined by a Combined Positive Score (CPS), and approved commercial diagnostic assay
• If the PD-L1 CPS score is > 1, patients must have received at least one line of systemic therapy for advanced disease that includes a PD-1 or PD-L1 inhibitor.

• Patients must have clinical or radiographic disease progression on 1L therapy, or within three months of the last dose of immunotherapy
• Patients must be eligible for immunotherapy (i.e. have not had a Grade 3 or 4 immunotherapy related gastrointestinal or pulmonary toxicity, or other immune-related adverse event that excludes them from receiving future immunotherapy per PI discretion)
• If the PD-L1 CPS score is < 1, patients must not have received prior anti-PD-1 or PD-L1 therapy and must have received at least one line of systemic therapy for advanced disease.

Exclusion criteria

• Is currently participating and receiving study therapy or has participated in a study of an investigational agent and received study therapy within 3 weeks of study Day 1.
• Has an active autoimmune disease that has required systemic treatment in past 2 years except replacement therapy (eg., thyroxine, insulin, or physiologic corticosteroid)
• Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy (greater than equivalent of 20 mg/day) or any other form of immunosuppressive therapy within 7 days prior to study Day 1.
• Has known active central nervous system metastases and/or carcinomatous meningitis.
• Has had prior anti-cancer monoclonal antibody chemotherapy, targeted small molecule therapy, or radiation therapy within 2 weeks prior to study Day 1, who has not recovered from adverse events due to a previously administered agent.
• Has a known additional malignancy within 3 years before the first OBP-301 administration that is progressing or requires active treatment, with the exception of prostate cancer controlled with androgen deprivation therapy.
• Has received a live vaccine or live-attenuated vaccine within 30 days before the first dose of study intervention. Administration of killed vaccines is allowed.
• Is known to have acute or chronic active hepatitis B virus (HBV), hepatitis C virus (HCV) or human immunodeficiency virus (HIV)
• Has a history of (non-infectious) pneumonitis/interstitial lung disease that required steroids or has current pneumonitis/interstitial lung disease.
• Has an active infection requiring systemic therapy within 2 weeks of Day 1.
• Is unable to comply with protocol procedures
• Previous severe hypersensitivity (≥ Grade 3) to any monoclonal antibody
• Has not adequately recovered from major surgery or has ongoing surgical complications.
• Has had an allogenic tissue/solid organ transplant
• Has certain uncontrolled illnesses
• Is pregnant or breastfeeding or planning to become pregnant or start breast feeding during the study time period
• Is expecting to get someone else pregnant during the study time period