Gene therapy with tumor-specific promoter mediated suicide gene plus IL-12 gene enhanced tumor inhibition and prolonged host survival in a murine model of Lewis lung carcinoma

BACKGROUND: Gene therapy is a promising therapeutic approach for cancer. Targeted expression of desired therapeutic proteins within the tumor is the best approach to reduce toxicity and improve survival. This study is to establish a more effective and less toxic gene therapy of cancer. METHODS: Combined gene therapy strategy with recombinant adenovirus expressing horseradish peroxidase (HRP) mediated by human telomerase reverse transcriptase (hTERT) promoter (AdhTERTHRP) and murine interleukin-12 (mIL-12) under the control of Cytomegalovirus (CMV) promoter (AdCMVmIL-12) was developed and evaluated against Lewis lung carcinoma (LLC) both in vivo and in vitro. The mechanism of action and systemic toxicities were also investigated. RESULTS: The combination of AdhTERTHRP/indole-3-acetic acid (IAA) treatment and AdCMVmIL-12 resulted in significant tumor growth inhibition and survival improvement compared with AdhTERTHRP/IAA alone (tumor volume, 427.4 ± 48.7 mm(3 )vs 581.9 ± 46.9 mm(3), p = 0.005 on day 15; median overall survival (OS), 51 d vs 33 d) or AdCMVmIL-12 alone (tumor volume, 362.2 ± 33.8 mm(3 )vs 494.4 ± 70.2 mm(3), p = 0.046 on day 12; median OS, 51 d vs 36 d). The combination treatment stimulated more CD4(+ )and CD8(+ )T lymphocyte infiltration in tumors, compared with either AdCMVmIL-12 alone (1.3-fold increase for CD4(+ )T cells and 1.2-fold increase for CD8(+ )T cells, P < 0.01) or AdhTERTHRP alone (2.1-fold increase for CD4(+ )T cells and 2.2-fold increase for CD8(+ )T cells, P < 0.01). The apoptotic cells in combination group were significantly increased in comparison with AdCMVmIL-12 alone group (2.8-fold increase, P < 0.01) or AdhTERTHRP alone group (1.6-fold increase, P < 0.01). No significant systematic toxicities were observed. CONCLUSIONS: Combination gene therapy with AdhTERTHRP/IAA and AdCMVmIL-12 could significantly inhibit tumor growth and improve host survival in LLC model, without significant systemic adverse effects.