Imiquimod-Loaded Phospholipid-Free Unilamellar Vesicles Activate the Tumor Immune Microenvironment to Treat Liver Cancer and Liver Metastases

Liver cancers are often diagnosed at advanced stages and the fourth most common cause of cancer death globally. Addition to primary tumours, liver metastases are also common from other cancer sites like colorectal cancers, where 66% of patients develop this condition. Immunotherapies for these diseases have been hindered by the immunosuppressive microenvironment. Our lab has developed phospholipid-free unilamellar vesicles (PFSUV) to localize a toll-like receptor 7 agonist Imiquimod (IMQ), to the hepatocytes. PFSUV is composed of 83 mol% cholesterol and 17 mol% Tween80 and IMQ was loaded inside the aqueous core of these 75-nm particles. When administered intravenously (i.v.), PFSUV-IMQ was found to sustain IFN-α levels in the liver over 24 hours, with significantly lower plasma IFN-α levels compared to free IMQ. In a mouse model of liver metastasis from a colorectal cancer origin generated with CT26 cells, mice treated with PFSUV-IMQ in combination with Oxaliplatin showed a significant reduction in tumour size, with increases in CD8+ T cell and a higher percentage of apoptotic cells in the tumour compared to controls. In a mouse model of primary liver cancer using HCA-1 cells, the same treatment combination also showed a significant decrease in tumour burden, increased apoptotic cell percentage in the tumour, and significantly reduced lung metastasis from the liver compared to controls. Flow cytometry analysis showed tumours treated with PFSUV-IMQ had increased infiltration of CD86+/MHC-II+ dendritic cells and IFN-y+ CD8+ T cells. RNA-seq showed an enrichment of innate immune activation genes after a single dose of PFSUV-IMQ. Overall, these data suggest that the activation of the tumour immune microenvironment through this targeted delivery of IMQ resulted in a decrease in tumour burden across both liver tumour models.