In situ injectable hydrogel-loaded drugs induce anti-tumor immune responses in melanoma immunochemotherapy

Melanoma is a highly aggressive tumor located in the skin, with limited traditional therapies. In order to reduce the side effects caused by traditional administration method and amplify the killing effect of immune system against tumor cells, an in situ injectable hydrogel drug delivery system is developed for the first time which co-delivers doxorubicin (Dox) and imiquimod (R837) for the synergistic therapy of melanoma. The mechanical properties and stability of the hydrogel are characterized and the optimal doses of hydrogel and drugs are also identified. As a result, the co-delivery system effectively suppresses melanoma growth and metastatic progression both in vitro and in vivo. Further studies show that the co-delivery system causes immunogenic cell death, activation of antigen presenting cells, comprising dendritic cells and M1 macrophages, and secretion of related cytokines consisted of tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ), subsequently with the activation of T lymphocytes and natural killer cells in spleen and tumor area. The co-delivery system also decreases the suppressive immune responses, including infiltration of M2 macrophages and secretion of interleukin-10 (IL-10), in vivo. Besides, other death modes are induced by the co-delivery system, including apoptosis and non-apoptotic cell death. In a word, this co-delivery system induces melanoma cell death directly and activates immune system for further tumor killing simultaneously, which shows probability for precise targeted tumor therapy.