Robust prostate-specific expression for targeted gene therapy based on thehuman kallikrein 2 promoter

Tissue-specific transcriptional regulatory elements can increase the safety of gene therapy vectors. Unlike prostate-specific antigen (PSA/hK3), whose expression displays an inverse correlation with prostate cancer grade and stage, human glandular kallikrein 2 (hK2) is upregulated in higher grade an d stage disease. Therefore, our goal was to develop a strong and prostate-s pecific hK2-based promoter for targeted gene therapy. We identified the min imum "full-strength" hK2 enhancer and built transcriptional regulatory elem ents composed of multiple tandem copies of this 1.2-kb enhancer, fused to t he hK2 minimal promoter. Relative to the weak induction of the minimal hK2 promoter by androgen analog (R1881) in androgen receptor (AR)-positive LNCa P cells, transcriptional activity was increased by 25-, 44-, 81-, and 114-f old when one to four enhancers were spliced to the hK2 promoter, respective ly. In contrast, the enhancer/promoter elements were inactive in the AR(-) prostate cancer line PC-3 and in a panel of nonprostate lines, including 29 3, U87, MCF-7, HuH-7, and HeLa cells. Furthermore, we generated a recombina nt adenovirus, ADV.hK2-E3/P-EGFP, expressing enhanced green fluorescent pro tein (EGFP) under the control of the hK2 triplicate enhancer/promoter, and compared its properties with ADV.CMV-EGFP expressing EGFP under the control of the cytomegalovirus (CMV) enhancer/promoter. Unlike the CMV promoter, t he hK2-E3/P promoter was at least 100-fold inducible by R1881 in the adenov iral backbone. Compared with in situ injection of subcutaneous LNCaP tumors with ADV.CMV-EGFP, which led to detectable EGFP expression in tumor, Liver , and brain tissue, ADV.hK2-E3/P-EGFP injection led to robust but tumor-res tricted EGFP expression. These results suggest that the hk2 multienhancer/p romoter should be a powerful novel reagent for safer targeted gene therapy of prostate cancer.