Innovative applications of reporter genes and gene reporters in prostate cancer

Background: Reporter genes can provide insight into tumor development, progression, and response to therapy. When appropriate substrate reporter molecules are administered, non-invasive imaging becomes feasible. Here, we discuss novel applications of luciferase and novel reporters for lacZ with respect to expression in prostate cancer. Methods: Bioluminescent imaging (BLI) is perhaps the simplest tool for investigating tumor growth and the luciferase transgene is widely used. We have developed dynamic BLI based on blocking vascular delivery of luciferin substrate to assess the time course and efficacy of vascular disrupting agents. Specifically, we show the response of PC3-luc prostate tumors growing in nude mice to arsenic trioxide (ATO). We also demonstrate the ability to detect β-galactosidase expression based on the lacZ transgene stably transfected into PC3 cells using bioluminescence in tandem with luciferase, as well as directly using novel substrates for chemiluminescence (CLI) and magnetic resonance imaging (MRI). Results: Following luciferin injection, highly reproducible light emission was observed from PC3-luc tumors by BLI. However, significant vascular shutdown was seen within 2 hours of administering ATO at 8 mg/kg. Light emission, which corresponds to tumor vascular perfusion remained depressed after 6 hours, but showed some recovery after 24 hours. LacZ expression was observed following IP delivery of D-Luciferin-6-O-β-D-Galactopyranoside (Lugal) to PC3-lacZ-luc cells or IV delivery of Galacton-Star™ (dioxetane (3-chloro-5-(5'-chloro-4-methoxy spiro [1,2-dioxetane-3,2'-tricyclo [3.3.1.13,7]decan]-4-yl) phenyl β-D-galactopyrano side) to PC3-lacZ. ¹H MRI following direct intra tumor injection of S-Gal™ + ferric ammonium citrate revealed β-gal activity in both PC3-lacZ-luc and PC3-lacZ tumors. Conclusion: Optical imaging of luciferase activity provides insight into tumor growth, vascular patency, and gene expression in vivo, which is cheap, robust, and easy to implement. Novel substrates facilitate detection of lacZ expression using CLI, BLI, or MRI. Investigation of signal dynamics can further provide insights into tumor pathophysiology and efficacy of vascular disrupting agents.