Phytogalactolipid dLGG Inhibits Mouse Melanoma Brain Metastasis through Regulating Oxylipin Activity and Re-Programming Macrophage Polarity in the Tumor Microenvironment

SIMPLE SUMMARY: Metastatic brain melanoma is a common metastatic cancer with a high mortality rate. Current clinical regimens use the anti-angiogenesis drug bevacizumab (Avastin) and/or Lipo-DOX, a drug capable penetrating the blood–brain barrier; however, both commonly result in adverse side effects and limited treatment results. This study provides evidence to support the function of a phyto-glyceroglycolipid, 1,2-di-O-α-linolenoyl-3-O-β-galactopyranosyl-sn-glycerol (dLGG) in inhibiting melanoma brain metastasis (MBM) in mice through reprogramming the tumor microenvironment and interacting with melanoma cells and macrophages. The novel function of oxylipin 9,10-EpOMEs + 12,13-EpOMEs in preventing melanoma cell invasion and microglia/macrophage distribution and polarization in the tumor microenvironment is presented. The novel anti-melanoma function and underlying molecular mechanism of dLGG proposed herein can be considered as a novel therapeutic strategy to combat MBM. ABSTRACT: Current conventional cancer therapies for melanoma brain metastasis (MBM) remain ineffective. In this study, we demonstrated the bioefficacy of a phyto-glyceroglycolipid, 1,2-di-O-α-linolenoyl-3-O-β-galactopyranosyl-sn-glycerol (dLGG) alone, or in combination with liposomal doxorubicin (Lip-DOX) or Avastin against MBM in a syngeneic B16BM4(COX−2/Luc) brain-seeking melanoma mouse model. Treatment with dLGG–10, dLGG–25, dLGG–10 + Avastin–5, Lipo-DOX–2, dLGG–10 + Lipo-DOX–2 or Lipo-DOX–2 + Avastin–5 suppressed, respectively, 17.9%, 59.1%, 55.7%, 16.2%, 44.5% and 72.4% of MBM in mice relative to the untreated tumor control. Metastatic PD-L1+ melanoma cells, infiltration of M2-like macrophages and CD31+ endothelial cells, and high expression levels of 15-LOX/CYP450 4A enzymes in the brain tumor microenvironment of the tumor control mice were significantly attenuated in dLGG-treated mice; conversely, M1-like resident microglia and cytotoxic T cells were increased. A lipidomics study showed that dLGG promoted B16BM4 cells to secrete oxylipins 9,10-/12,13-EpOMEs into the culture medium. Furthermore, the conditioned medium of B16BM4 cells pretreated with dLGG or 9,10-EpOMEs + 12,13-EpOMEs drove M2-like macrophages to polarize into M1-like macrophages in vitro. An ex vivo 3D-culture assay further demonstrated that dLGG, 9,10-EpOME or 9,10-EpOME + 12,13-EpOME pretreatment attenuated B16BM4 cells invading brain tissue, and prevented microglia/macrophages infiltrating into the interface of melanoma plug and brain organ/tissue. In summary, this report provides a novel therapeutic strategy and mechanistic insights into phytogalactolipid dLGG for combating MBM.