Abstract
The herpes simplex virus thymidine kinase/ganciclovir (HSV TK/GCV) system is one of the best studied cancer suicide gene therapy systems. Our previous study showed that caspase 3 expression was upregulated and bladder tumor growth was significantly reduced in rats treated with a combination of Bifidobacterium (BF) and HSV TK/GCV (BF-rTK/GCV). However, it was raised whether the BF-mediated recombinant thymidine kinase combined with ganciclovir (BF-rTK/GCV) was safe to administer via venous for cancer gene therapy. To answer this question, the antitumor effects of BF-rTK/GCV were mainly evaluated in a xenograft nude mouse model bearing MKN-45 gastric tumor cells. The immune response, including analysis of cytokine profiles, was analyzed to evaluate the safety of intramuscular and intravenous injection of BF-rTK in BALB/c mice. The results suggested that gastric tumor growth was significantly inhibited in vivo by BF-rTK/GCV. However, the BF-rTK/GCV had no effect on mouse body weight, indicating that the treatment was safe for the host. The results of cytokine profile analysis indicated that intravenous injection of a low dose of BF-rTK resulted in a weaker cytokine response than that obtained with intramuscular injection. Furthermore, immunohistochemical analysis showed that intravenous administration did not affect the expression of immune-associated TLR2 and TLR4. Finally, the BF-rTK/GCV inhibited vascular endothelial growth factor (VEGF) expression in mouse model, which is helpful for inhibiting of tumor angiogenesis. That meant intravenous administration of BF-rTK/GCV was an effective and safe way for cancer gene therapy.
Highlights
Gastric cancer is the fifth most common cancer, with the highest morbidity and mortality rate in the world [1]
We previously found that caspase 3 expression was upregulated and bladder tumor growth was significantly reduced in rats treated with a combination of BF and HSV TK/GCV (BF-rTK/GCV) for 15 days [10]
When we compared the cytokine ratio of BF-rTK/E. coli DH5α, the results indicated that only GM-CSF and IL-10 were significantly upregulated more than 20-fold following IV injection of the low dose of BF-rTK (Figure 3)
Summary
Gastric cancer is the fifth most common cancer, with the highest morbidity and mortality rate in the world [1]. Despite significant progress in reconstructing vectors [2,10,11,12,13], several hurdles still prevent success in the clinic, including non-specific expression, low-efficiency delivery, and biosafety [6,14,15,16,17]; the safety of gene carriers remains the biggest obstacle for tumor gene therapy [6,18]. We previously found that caspase 3 expression was upregulated and bladder tumor growth was significantly reduced in rats treated with a combination of BF and HSV TK/GCV (BF-rTK/GCV) for 15 days [10] It was always questioned whether it is safe to administer live BF-rTK into the blood for cancer gene therapy. The universality of the antitumor mechanism of BF-rTK/GCV was confirmed in human an intestinal cancer colo320 xenograft model using quantitative real-time PCR (qPCR)
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