Indocyanine green-/TLR7 agonist-constructed thermosensitive liposome for low-temperature PTT induced synergistic immunotherapy of colorectal cancer

Colorectal cancer (CRC) is a lethal malignancy with a high mortality rate due to its low immunogenicity, the strong immunosuppressive milieu and poor drug permeability. To overcome these obstacles, a cascade synergistic nanosystem (denoted as R837/ICG@Lip) was developed via self-assembly of heater indocyanine green (ICG) and toll-like receptor-7 agonist imiquimod (R837) into thermosensitive liposome for simultaneous induction of immunogenic cell death (ICD) and reversing of suppressive tumor microenvironment. The obtained nanoparticles exhibited NIR-triggered drug release, good photothermal conversion efficiency and phototoxicity towards CT26 colorectal cancer cells. In vivo results reveal that the R837/ICG@Lip could be effectively accumulated in CT26 subcutaneous tumors and the draining lymph nodes. More importantly, R837/ICG@Lip-mediated low-temperature photothermal therapy triggers ICD, promotes the maturation of host dendritic cells (DCs), and subsequently amplifies adaptive antitumor T-cell responses, resulting in 'Cold to Hot' transition. Besides directly affecting immune cells, the secretion of some immune-related cytokines further indirectly boosted anti-cancer immunity. After combining with the indoleamine 2,3-dioxygenase (IDO) inhibitor, the systemic antitumor immune response was further augmented, achieving best tumor inhibition effects. Thus, low-temperature mediated photoimmunotherapy targeting multiple antitumor immune pathways boost synergistic antitumor immunity of tolerance tumors.