Polysaccharide Lentinan Attenuates Tumor Vascular Function Via IFN-? Production

Background: Tumor angiogenesis is a hallmark of cancer,because new blood vessels must be developed to nourish tumors that grow to ? 2 mm3 and to facilitate metastasis.Thus,blockade of pro-angiogenic signaling pathways has been investigated and developed as anti-angiogenic therapy aiming to starve tumor cell to death.Currently,anti-angiogenic therapies are widely used in non-small cell lung cancer(NSCLC),colorectal cancer,and several other solid tumors,however,the clinical benefits are modest and transient and usually followed by the rapid emergence of drug resistance.Several recent reports suggest that immune stimulation can also modulate tumor angiogenesis.Lentinan(LNT),a biological active ingredient extracted from Lentinus edodes(L.edodes),is an immunopotentiator.However,whether LNT can affect tumor angiogenesis remains unclear.Objective: In this study,we aimed to investigate the effects and mechanism of LNT treatments on the tumor vasculature in LAP0297 lung and CT26 colorectal tumor models.Methods: By establishing LAP0297 lung or CT26 colorectal cancer models,we evaluated the dose effects of LNT treatments on tumor growth.At the end of LNT treatments,tumor tissues were collected,digested and stained with fluorochrome-conjugated antibodies.Next the labeled cells were analyzed on a Gallios flow cytometer(FCM).The function of tumor vessels was determined by histological analysis of the intravenously injected perfusion marker Hoechst33342.The levels of m RNA transcription of angiogenesis-related genes were determined by a high-throughput fluorescence quantitative PCR meter.We also inoculated LAP0297 lung cancer in nude mice to determine the roles of T cells in LNT treatments.Moreover,we investigated the roles of IFN-? in LNT treatments by using neutralizing anti-IFN-? antibody.In addition,we performed the long-term LNT treatment experiments to evaluate its drug resistance.Finally,we determined the direct effects of LNT on the proliferation of LAP0279 lung cancer cell and the tube formation of HUVEC endothelial cells in vitro.Results: In both models of LAP0279 lung cancer and CT26 colorectal cancer,relatively lower dosage,such as 1.0 mg/kg,showed better antitumor effect than higher dosage,such as ?4.0 mg/kg.LNT treatments significantly decreased tumor vascular function,while it didn't alter vessel density and function in normal tissues.Consistent to the reduction of tumor vascular function,the necrotic area in LNT-treated group was increased compared to control group.Gene expression analysis showed that LNT treatments upregulated the levels of IFN-?,TNF?,chemokine(C-X-C motif)ligand 9(CXCL9),Angiopoietin-1(Ang1),Timp1,and Thrombospondin-1(TSP1).Flow cytometer analysis data showed that LNT treatment increased the proportions of CD4+ T cells,CD8a+ T cells,NKs and neutrophils,and increased their IFN-? production,except of tumor-associated macrophages(TAMs).In nude mice,LNT treatments still inhibited tumor growth,reduced tumor vascular function and tumor vessel density in LAP0297 lung cancer.Although IFN-? neutralization only partially reversed the inhibition of LNT treatments on tumor growth,it completely reversed the effect of LNT treatments on tumor vascular function in LAP0297 lung cancer.Long-term LNT treatments persistently suppressed tumor growth and induced regression of more than 98 % tumors 45 days post of LNT treatment in LAP0297 lung cancer model.In vitro experiments showed that LNT treatments did not inhibit LAP0297 lung cancer cell proliferation and HUVEC tube formation.Conclusion: LNT treatments inhibited tumor growth and reduced tumor vascular function in lung and colorectal cancer models.The effects of LNT treatments on tumor vascular function were mediated by elevated IFN-? production,but in a T cell independent manner.Moreover,persistent LNT administration continuously exhibited antitumor effects without developing drug resistance,thus,LNT could be served as a new kind of antiangiogenic agent for long-term treatments.Taken together,LNT could affect tumor growth via multiple different mechanisms,including the modulation of immune system and the suppression of tumor angiogenesis.