Antiangiogenic and cytotoxic effects are considered the principal mechanisms of action of sorafenib, a multitarget kinase inhibitor approved for the treatment of hepatocellular carcinoma (HCC). We report that sorafenib also acts through direct immune modulation, indispensable for its antitumor activity. In vivo cell depletion experiments in two orthotopic HCC mouse models as well as in vitro analysis identified macrophages (MF) as the key mediators of the antitumoral effect and demonstrate a strong interdependency of MF and natural killer (NK) cells for efficient tumor cell killing. Caspase 1 analysis in sorafenib-treated MF revealed an induction of pyroptosis. As a result, cytotoxic NK cells become activated when cocultured with sorafenib-treated MF, leading to tumor cell death. In addition, sorafenib was found to down-regulate major histocompatibility complex class I expression of tumor cells, which may reduce the tumor responsiveness to immune checkpoint therapies and favor NK-cell response. In vivo cytokine blocking revealed that sorafenib efficacy is abrogated after inhibition of interleukins 1B and 18. Conclusion: We report an immunomodulatory mechanism of sorafenib involving MF pyroptosis and unleashing of an NK-cell response that sets it apart from other spectrum kinase inhibitors as a promising immunotherapy combination partner for the treatment of HCC.

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