Controllability Study Of TRAIL Tumor Biotherapy

Tumor necrosis factor-related apoptosis-inducing ligand (sTRAIL) functions as a cytokine to selectively kill various cancer cells without toxicity to most normal cells. Numerous of studies have demonstrated the potential use of TRAIL as a cancer therapeutic. In our previous study, we aslo showed that administration of the recombinant adeno-associated virus (rAAV) vector expressing sTRAIL resulted in efficient suppression of tumor growth in vivo.However, the potential utility and safety of TRAIL has recently been questioned because its potential toxicity on normal human cells (e.g. hepatocytes) and the mechanism of the related toxicity still hangs in doubt. Furthermore, the physilogical function of TRAIL is much less well understood. From a point of clinical view, safety is the most crictical problem in developing drugs. One of the key issues in successfully implementing gene therapies or biological therapies in the clinical setting is to be able to regulate gene expression very tightly and consistently as and when it is needed.In the present study, we introduced Tet-On regulable gene expression system into the rAAV vector (AAV-TRE-TRAIL&AAV-Tet-On) to control the sTRAIL expression in transcriptional level and evaluate the efficiency of the system in cancer gene therapy. We observed that the expression or secretion of sTRAIL could be tightly controlled by the Tet-On regulable promoter TRE in both normal and cancer cells. Transduction of a variety of human cancer cell lines with AAV-TRE-TRAIL&AAV-Tet-On under the presence of doxycycline (Dox) led to considerable apoptosis compared with the absence of the inducer.We further investigated the effect of AAV-TRE-TRAIL&AAV-Tet-On administration on tumor growth in BALB/c nude mice transplanted with MDA-MB-231 human breast cancer cells. Intravenous injection of virus showed that sTRAIL protein was predominantly expressed in liver and tumor under induced conditions but not under uninduced conditions. The therapeutic efficacy was evaluated according to the weight and volume of the tumor tissue. The tumor weights and volumes were obviously smaller in animals given AAV-TRE-TRAIL&AAV-Tet-On intravenously and Dox orally compared with those given AAV-TRE-TRAIL&AAV-Tet-On without Dox and those given AAV-TRE-eGFP&AAV-Tet-On. The activation of caspase-3 and capase-8 in tumor tissue demonstrated that the mechanism of tumor growth suppression mediated by intravenous administration of AAV-TRE-TRAIL&AAV-Tet-On was apoptosis.Moreover, our data showed that sTRAIL expression intensity and tumor suppress efficacy of AAV-TRE-TRAIL&AAV-Tet-On is similar compared with AAV-CAG-TRAIL, an AAV vector with constitutive intensive promoter CAG, both in vitro and in vivo.These results suggest that AAV-mediated sTRAIL expression under the control of Tet-On system is a promising strategy for the safety requirement in cancer biological therapy.