Chimeric 5/35 adenovirus-mediated Dickkopf-1 overexpression suppressed tumorigenicity of CD44⁺ gastric cancer cells via attenuating Wnt signaling.

BACKGROUND: Gastric cancer stem cells (CSCs), which require activation of Wnt signaling to maintain their self-renewal and tumorigenicity, are proposed to be critical targets for effective therapy of gastric carcinomas. Gene therapies that are delivered by adenovirus of serotype 5 (Ad5) or chimeric 5/35(Ad5/35) adenovirus have shown promise for treating various cancers. Here we aimed to develop a gene therapy strategy that targeted gastric CSCs (CD44⁺ cells). METHODS: CD44⁺ cells were isolated by fluorescence activated cell sorting from both primary gastric cancer cells and cell lines. Expression of adenovirus receptors was examined in CD44⁺ and CD44⁻ cells. A potent Wnt antagonist Dickkopf-1 (DKK1) was delivered into CD44⁺ cells using Ad5/35 (Ad5/35-DKK1). The therapeutic outcomes were evaluated. RESULTS: Expression of Coxsakievirus adenovirus receptor for Ad5 was significantly reduced, while abundance of CD46, the receptor for Ad5/35, was slightly higher in CD44⁺ cells. Accordingly, CD44⁺ cells were sensitive to Ad5/35 infection, but not to Ad5. Ad5/35-DKK1 introduced DKK1 into CD44⁺ cells and deactivated endogenous Wnt/ß-catenin signaling efficiently. Overexpression of DKK1 inhibited survival, anchorage-independent colony formation, and invasion of CD44⁺ cells, which were restored by a GSK-3 specific inhibitor BIO-acetoxime. More importantly, introduction of DKK1 abrogated the tumorigenicity of CD44⁺ cells in vivo. However, Ad5/35-DKK1 only showed minimal cytotoxicity to normal tissue-derived cells, L-02 and GES-1. CONCLUSIONS: We developed, for the first time, a novel Ad5/35-DKK1-based approach to abrogate Wnt signaling in CSCs and demonstrated that gastric CSC-targeting gene therapy was effective in preclinical experiments.