以化學酵素法合成Globo H衍生物作為癌症疫苗用之研究

Abstract

大部分癌症細胞表面會表現多量的特定醣抗原，Globo H (Fucα1→2Galβ1→ 3GalNAcβ1→ 3Galα1→4Galβ1→ 4Glc)六碳醣是其中一種，以Globo H為基礎的治療疫苗已經在應用在 乳癌、前列腺癌、卵巢癌、胰腺癌、大腸直腸癌及肺癌。在這篇研究中，我們合成一系列Globo H衍生物以提升癌症疫苗的免疫性。Globo H衍生物是由酵素法合成而來並和載體蛋白(CRM) 197 (DT)接合，並搭配C34醣脂類為佐劑(adjuvant)。在注射完Balb/c老鼠實驗，免疫的反應由醣晶片來分析，結果顯示在Globo H還原端六號位上的glucose修飾氟化（F），疊氮基(N3)，苯基（phenyl)和在Globo H非還原端六號位上的fucose修飾疊氮基(N3)亦有強烈的IgG免疫球蛋白反應辨認Globo H 和Gb5 和SSEA4。上述的疫苗可以辨認Globo H表現的癌細胞(MCF-7)和具有補體依賴的細胞毒殺能力。由上述資料顯示這樣的化學修飾癌症醣抗原可以促進癌症疫苗的發展。

Globo H-based therapeutic cancer vaccines have been tested in clinical trials for the treatment of late stage breast, ovarian and prostate cancers. In this study, we explored Globo H analogue antigens with an attempt to enhance the antigenic properties in vaccine design. The Globo H analogues with modification at the reducing or non-reducing end were synthesized using chemoenzymatic methods, and these modified Globo H antigens were then conjugated with the carrier protein diphtheria toxoid cross-reactive material (CRM) 197 (DT), and combined with a glycolipid C34 as an adjuvant designed to induce a class switch of antibody to form the vaccine candidates. The immune response was studied by a glycan array and the results showed that modification at the C-6 position of reducing end glucose of Globo H with the fluoro, azido or phenyl group elicited robust IgG antibody response to specifically recognize Globo H (GH) and the GH-related epitopes, stage-specific embryonic antigen 3 (SSEA3) (also called Gb5) and stage-specific embryonic antigen 4 (SSEA4). However, only the modification of Globo H with the azido group at the C-6 position of the non-reducing end fucose could elicit strong IgG immune response. Moreover, the antibodies induced by theses vaccines were shown to recognize GH expressing tumor cells (MCF-7) and mediate the complement-dependent cell cytotoxicity against tumor cells. Our data suggest a new potential approach to cancer vaccine development.