Synergistic lethality of combination treatment with Trop2-directed antibody-drug conjugate sacituzumab govitecan and TRAIL agonists in triple negative breast cancer.

BACKGROUND: Sacituzumab govitecan (SG) is an antibody drug conjugate targeting trophoblast cell surface antigen 2 (Trop2) that is approved for treatment of patients with metastatic triple negative breast cancer (TNBC). Tumor necrosis factor-related apoptosis inducing ligand (TRAIL) agonists are antitumor agents that interact with death receptors on the cell surface to induce apoptosis in cancer cells, often sparing normal cells. In this study, we investigated whether combination treatment with SG and TRAIL agonists inhibit TNBC cell growth. METHODS: In vitro, 10 human TNBC cell lines and 4 non-modified, low passage patient derived TNBC cells were treated with SG and the TRAIL agonist Apo2L. Cell death was assessed via a propidium iodide-based assay while cell proliferation was measured using an ATP cell viability assay. The mode of cell death elicited by combination treatment was investigated by using inhibitors of apoptosis, necroptosis and ferroptosis. The drug effect on cell cycle was analyzed with flow cytometry. In vivo, NCr athymic nude (nu/nu) female mice bearing HCC1806 TNBC xenografts were treated with SG and TRAIL agonists after which the effect of treatment on tumor growth and survival was evaluated. RESULTS: SG and TRAIL acted synergistically in all 10 TNBC cell lines as well as all 4 patient derived TNBC cells tested. Synergistic cell death and growth inhibition was observed in both Trop2 high-expressing and low-expressing cells, with data suggesting that the linker deconjugation and bystander effects of SG contribute to the efficacy in Trop2 low-expressing cells. Caspase-3/7 assays as well as cell death assays using cell death inhibitors demonstrated that the lethality of dual treatment is primarily mediated by apoptosis. Additionally, SG alone and in combination with Apo2L induced cycle arrest at the G2/M phase. Finally, xenograft models using HCC1806 bearing mice showed that dual treatment with SG and TRAIL agonists significantly inhibited tumor growth and caused a borderline significant benefit on survival with no toxicities noted for both drug treatments. CONCLUSIONS: Combination treatment with SG and TRAIL agonists induces synergistic lethality in TNBC cells in vitro and inhibits tumor growth in vivo, suggesting a potential clinical benefit of the combination therapy in TNBC.