ORIGINAL ARTICLE Use of the PSA enhancer core element to modulate the expression of prostate- and non-prostate-specific basal promoters in a lentiviral vector context S Chapel-Fernandes 1 , F Jordier 1 , F Lauro 2 , N Maitland 2 , J Chiaroni 1 , P de Micco 1 , P Mannoni 1 and C Bagnis 1 1 EFS Alpes Me ´diterrane ´e, Marseille, France and 2 Prostate Cancer: Initiative for Gene Therapy (PIG), YCR Cancer Research Unit, Department of Biology (Area 13), University of York Heslington, York, UK Composite promoters combining the prostate-specific antigen (PSA) enhancer core element with promoter elements derived from gene coding for human prostate-specific transglutaminase gene, prostate-specific membrane antigen gene, prostate-specific antigen, rat probasin or phosphoglycerate kinase were characterized for their ability to specifically express the enhanced green fluorescent protein (EGFP) gene in prostate versus non-prostate cancer cell lines when transferred with a human immunodeficiency virus-1-based lentiviral vector. By themselves minimal proximal promoter elements were found to inefficiently promote relevant tissue-specific expression; in all the vectors tested, addition of the PSA enhancer core element markedly improved EGFP expression in LnCaP, a cancer prostate cell line used as a model for prostate cancer. The composite promoter was inactive in HuH7, a hepatocarcinoma cell line used as a model of neighboring non-prostate cancer cells. Among the promoters tested, the combination of the PSA enhancer and the rat probasin promoter showed both high specificity and a strong EGFP expression. Neither a high viral input nor the presence of the cPPT/CTS sequence affected composite promoter behavior. Our data suggest that composite prostate- specific promoters constructed by combining key elements from various promoters can improve and/or confer tissue specific expression in a lentiviral vector context. Cancer Gene Therapy (2006) 13, 919–929. doi:10.1038/sj.cgt.7700966; published online 2 June 2006 Keywords: lentiviral vector; prostate cancer; specific expression; PSA Introduction Prostate cancer is the second leading cause of cancer death in men. 1 Although the most recent data suggest that the incidence of death from this disease is on the decline owing to the advent of the prostate-specific antigen (PSA) test and subsequent early intervention, once a patient becomes hormone refractory, there are few treatment choices available. 2 Treatment options for early-stage disease include ‘watchful waiting’ with deferred treatment, radical surgery, radical radiotherapy, hormone therapy and combinations of these options. As all of these options have substantial drawbacks, alternative treatment strate- gies are urgently needed. Gene therapy approaches to prostate cancer are attractive because they allow selective targeting of the affected tissue. Selective targeting avoids toxicity associated with treatments such as cytotoxic chemotherapy, which has so far proven to be of limited benefit in prostate cancer. In addition, because the prostate is a non-essential organ that can be removed, treatment can be targeted with tissue-specific rather than tumor-specific promoters. Tissue-specific gene regulatory sequences have impor- tant potential applications in gene therapy as they enable the targeted expression of introduced genes to specific cells, minimizing unwanted side effects of expression at other sites. High prostate tissue specificity has been demonstrated for several promoters in plasmid vectors and may provide interesting alternatives to ubiquitous promoters. 3 Particularly promising candidate for transcriptional targeting of prostate cancer cells invivo include promoters driving the expression of genes coding for PSA, prostate- specific membrane antigen (PSMA), human prostate- specific transglutaminase (pTG) and rat probasin. pTG is expressed in prostate and is androgen regulated, the expression being lost both in prostate cancer and most of the metastatic tumors. 4–6 Expression of PSMA was found in the epithelial cells of normal prostate independently of the presence of androgens. The PSMA promoter presents two advantages for gene therapy. First it is expressed in the tumor itself, in metastasis and also in the Received 23 September 2005; revised 22 January 2006; accepted 26 March 2006; published online 2 June 2006 Correspondence: Dr C Bagnis, EFS Alpes Me´diterrane´e, 149 Bd Baille, Marseille na 13005, France. E-mail: claude.bagnis@gmail.com Cancer Gene Therapy (2006) 13, 919–929 r 2006 Nature Publishing Group All rights reserved 0929-1903/06 $30.00 www.nature.com/cgt