Abstract. An shRNA tumor suppressor panel was screened using reverse infection of an A549 tumorigenic cell line and exposing it to a predetermined concentration of paclitaxel, an anticancer drug. The shRNAs targeting a positive control gene, MDR1, were found to effectively decrease mRNA levels and cause cells to become more sensitive to the chemotherapeutic drug. A set of genes were identified in the screen of a panel of tumor suppressors which, when down-regulated, were found to increase or decrease cell sensitivity in regards to treatment with paclitaxel. In many cases, there were multiple clones to a single gene that provided a positive result. The shRNAs targeting SMAD4, LZTS2, ST14 and VHL all increased the cell's sensitivity to paclitaxel. The loss of other tumor suppressors such as GLTSCR2, LATS1, NF1, PTEN, TP53 and WT1 induced a protective effect in the cell, making it more resistant to the effect of the drug. Further investigation of VHL mRNA levels after down-regulation with shRNA show a direct correlation between gene expression levels and paclitaxel sensitivity. This study credits the identified genes with the potential to act as prognostic biomarkers for use in genetic profiling, or even as targets in pathways of tumorigenesis yet to be fully understood.
IntroductionLung cancer is a leading cause of death in the United States, with an estimated number of over 172,000 new cases and 163,000 deaths in 2005. Lung cancer accounts for almost 30% of all cancer related deaths in the United States (1). The incidence of lung cancer has declined in recent years, largely due to a decrease in smoking rates. Yet lung cancer is a serious disease, with a low 5-year survival rate and very few patients receiving effective chemotherapy (reviewed in 2).Paclitaxel, produced by Bristol-Meyers Oncology, is an antimicrotubule agent that works by stabilizing tubulin polymer formation and shifting the equilibrium in cancer cells towards microtubule assembly. The normal function of the microtubule network is thus disrupted, resulting in abnormal mitotic processes. Early treatment regimens examining the effectiveness of paclitaxel in non-small cell lung cancer (NSCLC) showed response rates of 21 to 24% (3,4) and an improved one-year survival rate, approaching 40% of patients treated. Due to the initial success of this chemotherapy, several combination trials have been executed, or are in the process, in the hope of finding paclitaxel combinations with increased efficacy, including paclitaxel combined with cisplatin (5), paclitaxel with carboplatin (reviewed in 6) and paclitaxel with radiation therapy (7).One way to improve the response rates to chemotherapies such as paclitaxel, other than by a combination with multiple therapies, is to predict the chemosensitivity of individual patients to therapy. This requires, in part, an understanding of the individual genes involved in therapy response. It also requires an effective and integrated use of a variety of genomic-based tools. Over the past few years, significant use has been...