Liposomal Irinotecan Achieves Significant Survival and Tumor Burden Control in a Triple Negative Breast Cancer Model of Spontaneous Metastasis

Triple negative breast cancer (TNBC) represents a significant therapeutic challenge due to its highly aggressive nature and lack of effective treatment options. Liposomal irinotecan (nal-IRI, ONIVYDE) was approved in 2015 (by the Food and Drug Administration, European Medicines Agency, and Therapeutic Goods Administration) and is a topoisomerase inhibitor indicated, in combination with fluorouracil and leucovorin, for the treatment of patients with metastatic adenocarcinoma of the pancreas after disease progression following gemcitabine-based therapy. This study investigates the potential therapeutic benefit of nal-IRI for the treatment of advanced TNBC in a clinically relevant mouse model of spontaneous metastasis (LM2-4). Female SCID mice were orthotopically inoculated with TNBC LM2-4-luc cells in the lower mammary fat pad. Following primary tumor resection, bioluminescence imaging (BLI) was used to monitor both metastasis formation and spread as well as response to treatment with nal-IRI. Weekly treatment with 10 mg/kg of nal-IRI provided a 4.9-times longer median survival compared to both 50 mg/kg irinotecan treated and untreated animals. The survival benefit was supported by a significant delay in the regrowth of the primary tumor, effective control, and eventual regression of metastases assessed using longitudinal BLI, which was confirmed at the study end point with magnetic resonance (MR) imaging and post-mortem observation. This preclinical investigation demonstrates that, at a five-times lower dose compared to the free drug, liposomal irinotecan provides significant survival benefit and effective management of metastatic disease burden in a clinically relevant model of spontaneous TNBC metastases. These findings support the evaluation of nal-IRI in patients with advanced and metastatic TNBC.