以C26腫瘤細胞之動物模式來探討台灣紫芝多醣體合併化學療法的抗腫瘤效果

Abstract

台灣紫芝(Ganoderma formosanum)為台灣特有靈芝品種，本實驗室利用液態深層醱酵培養法所生產的台灣紫芝胞外多醣體，進行膠體過濾層析純化可分離得PS-F1、PS-F2 和PS-F3 三個主要分劃。實驗室先前的研究發現在接種腫瘤前後持續給予小鼠PS-F2可活化其抗腫瘤免疫反應。本篇研究更進一步探討單獨給予小鼠PS-F2以及合併PS-F2和化療藥物5-FU，對於已形成之C26腫瘤的治療成效。研究結果發現，單獨給予C26腫瘤小鼠PS-F2仍然可抑制腫瘤的生長，而5-FU合併PS-F2的療程對於抑制腫瘤的生長具有加乘的效果。5-FU和PS-F2合併療法的抗腫瘤機制是藉由促進脾臟內的Th1細胞、毒殺型T細胞以及自然殺手細胞的活化，另一方面降低多型核骨髓衍生抑制細胞和調節型T細胞的比例。此外，合併療法也可有效降低腫瘤微環境內的具有免疫抑制能力的骨髓衍生抑制細胞和腫瘤相關巨噬細胞的比例。而在體外試驗中，發現PS-F2的刺激會單核型骨髓衍生抑制細胞對於T細胞增生的抑制能力。綜合以上結果，我們發現PS-F2和5-FU的合併療法可藉由活化體內的抗腫瘤免疫反應，同時削弱顯示免疫調節細胞的抑制免應系統的能力，以達到加乘性的抗腫瘤效果，因此也顯示了PS-F2可單獨做為抗腫瘤的免疫輔助療法，並且也可和化療藥物搭配施用而產生更強的抗腫瘤效果。

Ganoderma formosanum is a native species of Ganoderma, first isolated in Taiwan. The extracellular polysaccharides purified from the submerged culture of G. formosanum can be separated into three main fractions PS-F1, PS-F2 and PS-F3 according to their sizes by gel filtration. We have reported previously that PS-F2 can elicit antitumor immune responses when given to mice continuously before and after tumor grafting. In this study, we continued to investigate the antitumor efficacy of PS-F2 monotherapy and combined treatment of PS-F2 and chemotherapy drug 5-fluorouracil (5-FU) in mice with established colon 26 (C26) adenocarcinoma. We found that PS-F2 treatment alone could suppress the growth of established tumor, and combined treatment of PS-F2 and 5-FU could further suppress tumor growth synergistically. The inhibition of tumor growth by PS-F2 and 5-FU was associated with the activation of Th1 cells, cytotoxic T cells and natural killer (NK) cells in the spleen, while the accumulation of polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) and regulatory T (Treg) cells was suppressed by the treatment. In the tumor, PS-F2 and 5-FU treatment effectively suppressed the accumulation of PMN-MDSCs, monocytic MDSCc (M-MDSCs), and tumor-associated macrophages (TAMs). In addition, PS-F2 treatment could decrease the immunosuppressive function of M-MDSCs in vitro. Overall, our data demonstrated that PS-F2 and 5-FU could synergistically suppress the growth of established tumor via activating antitumor immune responses and alleviating immunosuppressive effects of immunoregulatory cells, indicating that PS-F2 has the potential to be used in adjuvant immunotherapy alone or in combination with chemotherapy for the treatment of cancer.