Target validation to biomarker development: focus on RNA interference

ATAD2 in cancer: a pharmacologically challenging but tractable target

INTRODUCTION

ATAD2 protein is an emerging oncogene that has strongly been linked to the etiology of multiple advanced human cancers. Therapeutically, despite the fact that genetic suppression/knockdown studies have validated it as a compelling drug target for future therapeutic development, recent druggability assessment data suggest that direct targeting of ATAD2's bromodomain (BRD) may be a very challenging task. ATAD2's BRD has been predicted as a 'difficult to drug' or 'least druggable' target due to the concern that its binding pocket, and the areas around it, seem to be unfeasible for ligand binding. Areas covered: In this review, after shedding light on the multifaceted roles of ATAD2 in normal physiology as well as in cancer-etiology, we discuss technical challenges rendered by ATAD2's BRD active site and the recent drug discovery efforts to find small molecule inhibitors against it. Expert opinion: The identification of a novel low-nanomolar semi-permeable chemical probe against ATAD2's BRD by recent drug discovery campaign has demonstrated it to be a pharmacologically tractable target. Nevertheless, the development of high quality bioavailable inhibitors against ATAD2 is still a pending task. Moreover, ATAD2 may also potentially be utilized as a promising target for future development of RNAi-based therapy to treat cancers.

Constitutive expression of short hairpin RNA in vivo triggers buildup of mature hairpin molecules

RNA interference (RNAi) has become the cornerstone technology for studying gene function in mammalian cells. In addition, it is a promising therapeutic treatment for multiple human diseases. Virus-mediated constitutive expression of short hairpin RNA (shRNA) has the potential to provide a permanent source of silencing molecules to tissues, and it is being devised as a strategy for the treatment of liver conditions such as hepatitis B and hepatitis C virus infection. Unintended interaction between silencing molecules and cellular components, leading to toxic effects, has been described in vitro. Despite the enormous interest in using the RNAi technology for in vivo applications, little is known about the safety of constitutively expressing shRNA for multiple weeks. Here we report the effects of in vivo shRNA expression, using helper-dependent adenoviral vectors. We show that gene-specific knockdown is maintained for at least 6 weeks after injection of 1 × 10(11) viral particles. Nonetheless, accumulation of mature shRNA molecules was observed up to weeks 3 and 4, and then declined gradually, suggesting the buildup of mature shRNA molecules induced cell death with concomitant loss of viral DNA and shRNA expression. No evidence of well-characterized innate immunity activation (such as interferon production) or saturation of the exportin-5 pathway was observed. Overall, our data suggest constitutive expression of shRNA results in accumulation of mature shRNA molecules, inducing cellular toxicity at late time points, despite the presence of gene silencing.

The effect on cell growth by Wnt1 RNAi in human neuroblastoma SH-SY5Y cell line

PURPOSE

We tested the hypothesis that Wnt signaling pathways are critical to neuroblastoma development. Our objective was to explore the novel role that Wnt/beta-catenin plays in human neuroblastoma cell line SH-SY5Y, including detection of expression of wnt1 and beta-catenin in SH-SY5Y, and the morphological and proliferative changes after Wnt1 RNAi in SH-SY5Y.

METHODS

PCR, Western blot and immunofluorescence technology were used to detect the expression of Wnt1 in human neuroblastoma SH-SY5Y cell line. RNAi technology was used to knock down the expression of Wnt1in SH-SY5Y. SiRNA targeting Wnt1 was transfected into SH-SY5Y cells by Lipofectamine2000. The protein expression of Wnt1 and beta-catenin were detected by Western blotting 48 h after transfection. The quantity and the morphologic changes of the cells were recorded under light microscope. The growth curve of SH-SY5Y cells after RNAi transfection was drawn through MTT assay.

RESULTS

Wnt1 was expressed in human neuroblastoma SH-SY5Y cells. The SH-SY5Y cell was successfully transfected with siRNA targeting Wnt1 mediated by Lipofectamine in vitro. The proteins expression of Wnt1 and beta-catenin decreased after transfection with siRNA; the numbers of the cells were decreased, accompanying abundant floating and dead cells under the light microscope. SH-SY5Y cells transfected with siRNA targeting Wnt1 showed less viability.

CONCLUSION

Wnt1 and beta-catenin expressed in SH-SY5Y cells. Knockdown of endogenous wnt1 expression could result in cell death and inhibit cell growth. From our study, we suggest that the activated embryonal development-related wnt1/beta-catenin pathway might take part in the oncogenesis and growth of neural crest-derived neuroblastoma.

Target validation and biomarker identification in oncology : the example of aurora kinases

The strong link between gene expression of mitotic Aurora kinases and cancer has stimulated a very high interest in developing Aurora kinase inhibitors for cancer therapy. Validation of Aurora kinases as targets, and development of pharmacodynamic biomarkers for inhibitors of Aurora kinases, provides an example of how target validation can help the drug discovery process, and also of how to interpret results depending on the technology used. In this review, we outline the principal tools, concepts, and strategies of target and biomarker validation for Aurora kinases, with emphasis on validation results derived from RNA-interference experiments. These data were essential for the decision to enter the next steps in drug development and for the selection of the appropriate biomarkers for clinical trials.