Phase I dose-escalation study of endoscopic intratumoral injection of OBP-301 (Telomelysin) with radiotherapy in oesophageal cancer patients unfit for standard treatments

Purpose: OBP-301 (Telomelysin) is an attenuated type-5 adenovirus that contains the human telomerase reverse transcriptase promoter to regulate viral replication. OBP-301 sensitises human cancer cells to ionising radiation by inhibiting DNA repair, and radiation enhances coxsackievirus and adenovirus receptor–mediated OBP-301 infection on the contrary. We assessed OBP-301 with radiotherapy in oesophageal cancer patients unfit for standard chemoradiation treatments. Methods: A phase I dose-escalation study of OBP-301 with radiotherapy was conducted in 13 histologically confirmed oesophageal cancer patients deemed unfit to undergo surgery or chemotherapy. Study treatment consisted of OBP-301 administration by intratumoural needle injection using a flexible endoscope on days 1, 18 and 32. Radiotherapy was administered concurrently over 6 weeks, beginning on day 4, to a total of 60 Gy. Results: Of the 13 patients, 7, 3 and 3 patients were treated with 10¹⁰, 10¹¹ and 10¹² virus particles, respectively. Study group comprised 10 males and 3 females, with a median age of 82 years (range, 53–91 years). All patients developed a transient, self-limited lymphopenia. Distribution studies revealed transient virus shedding in the plasma. Eight patients had local complete response (CR); all of them exhibited no pathologically viable malignant cells in biopsy specimens, and 3 patients had a partial response. The objective response rate was 91.7%. The clinical CR rate was 83.3% in stage I and 60.0% in stage II/III. Histopathological examination revealed massive infiltration of CD8⁺ cells and increased PD-L1 expression. Conclusion: Multiple courses of endoscopic intratumoural OBP-301 injection with radiotherapy are feasible and provide clinical benefits in patients with oesophageal cancer unfit for standard treatments.