Liposome-encapsulated eribulin shows enhanced antitumor activity over eribulin for combination therapy with anti-PD-1 antibody.

Eribulin is a microtubule dynamics inhibitor with tumor microenvironment modulation activity such as vascular remodeling activity. Here, we investigated antitumor and immunomodulatory activities of eribulin and its liposomal formulation (eribulin-LF) as monotherapies or in combination with anti-PD-1 antibody. The antitumor activity of eribulin or eribulin-LF as monotherapy or in combination with anti-PD-1 antibody was examined in a P-glycoprotein-knockout 4T1 model. Eribulin and eribulin-LF showed stronger antitumor activity in immunocompetent mice compared with immunodeficient mice, indicating that they have immunomodulatory activity that underlies its antitumor activity. Combination therapy of eribulin and eribulin-LF with anti-PD-1 antibody showed antitumor activity, and the combination activity of eribulin-LF with anti-PD-1 antibody was observed at a lower dose and longer interval of administration compared with that using eribulin. To examine the immunomodulatory activity of eribulin and eribulin-LF and its underlying mechanisms, we performed flow cytometry, immunohistochemistry, and gene expression profiling. Immunohistochemistry and flow cytometry revealed that eribulin-LF increased microvessel density and intratumoral populations of cytotoxic T cells and natural killer cells rather than eribulin. Gene expression profiling demonstrated that eribulin-LF induces interferon-γ signaling. Furthermore, immunohistochemistry also showed that eribulin-LF increased infiltration of CD8-positive cells together with increased CD31-positive cells. Eribulin-LF also increased ICAM-1 expression, which is essential for lymphocyte adhesion to vascular endothelial cells. In conclusion, eribulin showed combination antitumor activity with anti-PD-1 antibody via immunomodulation due to its vascular remodeling activity, and the liposomal formulation showed improved antitumor activity over the standard formulation.