Immune–metabolic PET/MRI uncovers microenvironmental reprogramming under combined immunotherapy and anti-angiogenic therapy

The limited efficacy of immune checkpoint inhibitor (ICI) therapy in triple-negative breast cancer (TNBC) highlights the need for combination strategies that enhance antitumor responses. Sorafenib, a multikinase inhibitor with anti-angiogenic and immunomodulatory activity, represents a rational partner for ICI-based combination therapy. However, therapeutic responses to such combinations are biologically complex and cannot be fully characterized by any single biomarker or imaging modality. Here, we evaluated ICI therapy combined with sorafenib in the aggressive and ICI-refractory orthotopic 4T1 TNBC model. Therapeutic responses were assessed using a unique longitudinal multimodal imaging framework integrating [⁸⁹Zr]Zr-DFO–anti-CD8 minibody and [¹⁸F]FDG PET, as well as perfluorocarbon (PFC)-based ¹⁹F MRI and hyperpolarized ¹³C MRS, together with ex vivo analyses. Only the ICI–sorafenib combination suppressed tumor growth, whereas both monotherapies showed limited antitumor activity. Multimodal imaging, together with complementary ex vivo analyses, uncovered coordinated tumor microenvironment (TME) remodeling, including vascular normalization, elevated CD8⁺ cell presence with modest enrichment in the tumor center, delayed increase in phagocyte-associated ¹⁹F MRI signal coupled with reduced CD206⁺ cell infiltration, and sustained metabolic activity. These findings support ICI–sorafenib combination therapy as a promising therapeutic strategy for TNBC. Therapeutic efficacy reflected coordinated vascular, immune, and metabolic remodeling. This multimodal imaging framework enables non-invasive longitudinal monitoring of these complementary TME changes, providing a comprehensive strategy for treatment assessment in immunotherapy-based combination therapies.