Abstract CT185: Phase I dose-escalation study of endoscopic intratumoral injection of OBP-301 (telomelysin) with radiotherapy in esophageal cancer patients unfit for standard treatments

Abstract

Abstract Background: OBP-301 (telomelysin) is an attenuated type-5 adenovirus with oncolytic potency that contains the human telomerase reverse transcriptase (hTERT) promoter to regulate viral replication. OBP-301 causes selective replication and lysis of a variety of cancer cells, and a phase I study has confirmed the safety and biological activity of OBP-301 alone in patients with advanced solid tumors in the US. We have also completed the preclinical study demonstrating that OBP-301 inhibits the repair of radiation-induced DNA double-strand breaks, leading to radiosensitization. To further determine the feasibility, efficacy, and pharmacokinetics of OBP-301 in combination with radiotherapy, a clinical trial was designed in esophageal cancer patients unfit for standard treatments such as in elderly.Methods: An open-label, phase I dose-escalation study of OBP-301 with radiotherapy (UMIN 000010158) was conducted in 13 histologically confirmed esophageal cancer patients who deemed unfit to receive standard surgery or chemotherapy. Study treatment consisted of intratumoral OBP-301 injections on days 1, 18, and 32 of treatments. Radiation therapy was administered concurrently over 6 weeks, beginning on day 4, to a total of 60 Gy. Virus administration was performed by intratumoral needle injection of the primary tumor through a flexible endoscope. Patients were also monitored for virus distribution and shedding into the body fluids. The primary and secondary end points were incidence of dose-limiting toxicities and objective response rate.Results: Of 13 patients, 7, 3, and 3 patients were treated in the cohorts with 10e10, 10e11, and 10e12 virus particles (vp) of OBP-301, respectively. The patients comprised 10 males and 3 females, with median age of 79.7 years (range, 53 to 92 years). Common grade 1 and 2 toxicities included fever, esophagitis, pneumonitis, anorexia, constipation, and gastroesophageal reflux. All patients developed a transient, self-limited lymphopenia. Distribution studies revealed that viral DNA was detected in 5 out of 6 patents received with10e11 and 10e12 vp of OBP-301, but rarely in the gargle, saliva, and urine. Eight patients had local complete response (CR); all of them exhibited pathologically no viable malignant cells in biopsy specimens, and 3 had partial response. The objective response rate was 84.6%. The clinical CR rate was 80.0% in stage I and 66.7% in stage II/III, respectively. Histopathologic examination in post-treatment specimens showed massive infiltration of CD8+ cells in 3 partially responded tumors.Conclusions: Multiple courses of endoscopic OBP-301 injection with radiotherapy were feasible and provided definite clinical benefits in patients with esophageal cancer, especially who are unfit for standard treatments. Citation Format: Toshiyoshi Fujiwara, Shunsuke Tanabe, Hiroshi Tazawa, Nobuhiko Kanaya, Kazuhiro Noma, Shunsuke Kagawa, Shinji Kuroda, Yasuo Urata, Yasuhiro Shirakawa. Phase I dose-escalation study of endoscopic intratumoral injection of OBP-301 (telomelysin) with radiotherapy in esophageal cancer patients unfit for standard treatments [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr CT185.