ABSTRACT
Patient survival in small cell lung cancer (SCLC) is limited by acquired chemoresistance. Here we report the use of a biologically relevant model to identify novel candidate genes mediating in vivo acquired resistance to etoposide. Candidate genes derived from a cDNA microarray analysis were cloned and transiently overexpressed to evaluate their potential functional roles. We identified two promising genes in the DNA repair enzyme DNA polymerase ß and in the neuroendocrine transcription factor NKX2.2. Specific inhibition of DNA polymerase ß reduced the numbers of cells surviving treatment with etoposide and increased the amount of DNA damage in cells. Conversely, stable overexpression of NKX2.2 increased cell survival in response to etoposide in SCLC cell lines. Consistent with these findings, we found that an absence of nuclear staining for NKX2.2 in SCLC primary tumors was an independent predictor of improved outcomes in chemotherapy-treated patients. Taken together, our findings justify future prospective studies to confirm the roles of these molecules in mediating chemotherapy resistance in SCLC.
Subject(s)
Antineoplastic Agents, Phytogenic/pharmacology , DNA Polymerase beta/metabolism , Etoposide/pharmacology , Homeodomain Proteins/metabolism , Lung Neoplasms/drug therapy , Small Cell Lung Carcinoma/drug therapy , Small Cell Lung Carcinoma/metabolism , Transcription Factors/metabolism , Cell Line, Tumor , DNA Polymerase beta/biosynthesis , DNA Polymerase beta/genetics , Drug Resistance, Neoplasm , Female , Gene Expression , Homeobox Protein Nkx-2.2 , Homeodomain Proteins/biosynthesis , Homeodomain Proteins/genetics , Humans , Lung Neoplasms/genetics , Lung Neoplasms/metabolism , Nuclear Proteins , Small Cell Lung Carcinoma/genetics , Transcription Factors/biosynthesis , Transcription Factors/genetics , Zebrafish ProteinsABSTRACT
INTRODUCTION: There is a clear need to develop a practical approach to obtain high quality RNA for gene expression analysis from lung cancer patients. Current approaches are restricted to using material from surgical resection specimens. We systematically investigated whether high quality RNA could be obtained from routine lung cancer diagnostic biopsies to determine the optimum method. METHODS: Extra biopsies were taken at diagnosis from patients later confirmed to have lung cancer. Comparisons were made between RNA extracted from samples snap frozen in liquid nitrogen and those treated with an RNA preservative before freezing. Further comparisons were made between biopsies taken by different methods. RESULTS: Acceptable RNA for gene expression analysis was extracted from 72% of lung cancer biopsies. Use of an RNA preservative for storage allowed the extraction of higher quality, more intact RNA from biopsies gathered by both endobronchial forceps and transbronchial needle aspiration. High quality RNA could also be extracted from computed tomography-guided needle core biopsies. CONCLUSION: Banking lung cancer biopsy specimens by storage in an RNA preservative solution will allow use of a broader spectrum of lung cancers for gene expression analysis. We describe a model that makes personalized medicine for lung cancer patients a more practical proposition.