Liposomal honokiol inhibits glioblastoma growth through regulating macrophage polarization

Background: Glioblastoma is a type of aggressive brain tumor-related to infiltrating microglia/ macrophages. Various studies have identified antitumor properties of a bioactive plant compound named honokiol, originating from the Magnolia species. This beneficial characteristic of honokiol has been discovered in many malignant tumors. Methods: We investigated the molecular mechanisms behind the anti-glioma effects of liposomal honokiol (Lip-HNK) using qRT-PCR, Western blot, co-culture, and in vivo animal experiments. Results: It was discovered that the expression of M1 markers such as CD11c, inducible nitric oxide synthase (iNOS), and major histocompatibility complex (MHC) II (IA/IE subregions) induced by lipopolysaccharide (LPS)/IFN-gamma was increased by Lip-HNK, and M2 markers Arg1 and CD206 induced by interleukin (IL)-4 had reduced expression, thus inhibiting tumor cell growth through co-culture experiments. After Lip-HNK treatment, a considerable increase in signal transducer and activator of transcription 1 (STAT1) activation was observed, and in contrast, STAT6 activation was suppressed. STAT1 and STAT6 are the key signaling molecules mediating M1 and M2 polarization, respectively. Furthermore, the percentage of CD11c-positive M1 macrophages was increased by Lip-HNK in G422 xenograft mice, while Lip-HNK treatment reduced the CD206-positive M2 macrophage distribution in tumor tissues. These findings are consistent with the decline in tumor volume seen in mice treated with Lip-HNK. Conclusions: Lip-HNK inhibits the growth of glioblastoma by upregulating M1 macrophages and limiting M2 phenotypic macrophages.