Abstract OT2-01-03: Trial in progress: Phase 2 study of intratumoral plasmid interleukin-12 (tavokinogene telseplasmid; TAVO™) plus electroporation in combination with pembrolizumab with or without chemotherapy in patients with inoperable locally advanced or metastatic triple-negative breast cancer (KEYNOTE-890/OMS-I141)

Abstract BACKGROUND: Interleukin-12 (IL-12) is a potent immunoregulatory cytokine that plays a key role in the crosstalk between innate (dendritic, macrophage, and natural killer) and adaptive (T and B) cells promoting anti-tumor immune responses. DNA plasmid-based IL-12 delivered to accessible tumors by intratumoral injection and electroporation (TAVO-EP) has been shown to induce activation of innate and adaptive tumor-infiltrating and peripheral immune cells, regression of treated and distant untreated lesions (abscopal effect), and expression of PD-L1 in patients with melanoma or triple-negative breast cancer (TNBC), without the systemic toxicity that has limited therapeutic use of IL-12 historically. The combination of TAVO-EP and pembrolizumab has demonstrated durable responses in melanoma patients with immunologically “cold” tumors or with prior progression on anti-PD1 therapy. Early clinical data indicate similar potential for eliciting strengthened immunogenic responses in TNBC. KEYNOTE-890 (OMS-I141) is a Phase 2 study in patients with metastatic TNBC to evaluate the safety and efficacy of TAVO-EP + pembrolizumab in the second-line or later (2L+) treatment setting (Cohort 1) or TAVO-EP + pembrolizumab + chemotherapy in the first-line (1L) setting (Cohort 2). Cohort 1 data are presented in a separate abstract. Enrollment in Cohort 2 is ongoing. METHODS: Cohort 2 of this Phase 2, open-label, multicenter study will be assessing the safety and efficacy of TAVO-EP in combination with pembrolizumab and chemotherapy as a first-line treatment for metastatic TNBC. Eligible patients are adults with metastatic TNBC (ER and PR staining <10%, HER2 0 to 1+ or [F]ISH-negative), no prior systemic therapy for advanced disease (neo/adjuvant therapy allowed if at least 6-month disease-free interval from last treatment), measurable disease by RECIST v1.1, at least one lesion accessible for TAVO-EP treatment, and biopsy tissue available for post-hoc central determination of PD-L1 expression. Patients will receive pembrolizumab (200 mg IV) every 3 weeks, TAVO-EP (0.5 mg/mL at dose volume of ~1/4 lesion volume) on Days 1, 5, and 8 every 6 weeks, and nab-paclitaxel (100 mg/m2 IV) on Days 1, 8, and 15 every 4 weeks. Additional chemotherapy options may be introduced in future protocol amendments. Tumor assessments will be performed every 12 weeks. On-study biopsies will be collected approximately 3 weeks after start of treatment and at disease progression. The primary endpoint will be ORR assessed by blinded independent review per RECIST v1.1. Additional endpoints will include safety and tolerability, duration of response, immune ORR, progression-free survival (PFS), immune PFS, disease control rate, and overall survival. Planned enrollment in Cohort 2 is 40 patients. Based on positive efficacy data in Cohort 1, additional cohorts are being planned and will be presented. ClinicalTrials.gov: NCT03567720 Citation Format: Melinda Telli, Bianca Devitt, Katharine Cuff, Shaveta Vinayak, Rita Nanda, Alberto J. Montero, Rina Hui, David A. Canton, Christopher Twitty, Sunny Xie, Donna Bannavong, Bridget O'Keeffe, Sandra Aung, Rohit Joshi. Trial in progress: Phase 2 study of intratumoral plasmid interleukin-12 (tavokinogene telseplasmid; TAVO™) plus electroporation in combination with pembrolizumab with or without chemotherapy in patients with inoperable locally advanced or metastatic triple-negative breast cancer (KEYNOTE-890/OMS-I141) [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr OT2-01-03.