A New Inducible RNAi Model for Cancer Target Validation In Vivo
KeywordsTumor Response Significant Response Tumor Regression Efficacy Evaluation Regulate RNAi
Human xenograft tumor models are widely used for evaluation of potential cancer targets, by assessing the anti-tumor effects of specific agents, such as siRNA. siRNA is usually stably introduced into tumor cells prior to transplantation. However, oncogene silencing results in reduced cell growth/survival in vitro and/or failure to establish tumors in vivo, thus hindering tumor response-based efficacy evaluation that is more clinically relevant. We therefore explored a new tumor response model based on regulated RNAi.
A unique RNAi vector was generated to express shRNA only after induction with doxycylcine. Using this vector, we created a novel xenograft tumor model, in which tumors are established under non-induced conditions, followed by induced target inactivation upon oral dosing of the inducer. Three genes were evaluated, a known oncogene (mTOR), and two novel cancer targets (HE7 and HE26), by assessing the tumor response to their silencing.
We demonstrate a significant response of staged tumor regression to silencing of all three target genes. For early staged tumors, inactivation of each of the three targets caused dramatic tumor regression (100% regressed and 50% became tumor-free for both mTOR and HE7, and 100% for HE26). Advanced staged tumors also demonstrated significant responses (100% regression for mTOR, and 75% for HE7, 85% HE26).
Our results demonstrate the utility of this unique and powerful model for efficacy evaluation of cancer targets; our data also provide robust in vivo efficacy validations of HE7 and HE26 as novel cancer therapeutic targets.