This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Gene therapy has emerged as a potentially promising strategy for treatment of prostate cancer. However, widespread implementation is hindered by difficulties in assessing the success of transfection: in particular, assessing the location, magnitude and persistence of transgene expression. Reporter genes and associated molecules should allow assessment of gene expression. lacZ gene encoding E. coli beta-galactosidase (beta-gal) has already been recognized as the most commonly used reporter system. Moreover, prostate-specific membrane antigen (PSMA), as the most well-established, highly restricted prostate cancer cell surface antigen, has been identified as an ideal antigenic target in prostate cancer. Much elegant research has been directed at developing non-therapeutic reporter genes and imaging protocols to non-invasively in vivo reveal gene expression and cancer itself, such as nuclear imaging (PET, SPECT), fluorescence, bioluminescence and new near infrared reporter molecules. MRI techniques have opened the realm of imaging at very high resolutions in small animals during development and in clinical practice. Recently, a new emerging generation of MRI contrast agents, so-called """"""""smart"""""""" contrast agents of developing MRI tests specific for biomarkers indicative of particular disease states and aiding in the early detection and diagnosis, hold great promise in the gene therapy arena. We propose to develop a novel class of """"""""smart"""""""" Gd3+-based MRI contrast agents for in vivo detection of beta-gal or PSMA activity. This new concept of the """"""""smart"""""""" Gd3+-based MRI contrast agents is composed of three moieties: (A) a signal enhancement group, such as Gd-DOTA or Gd-PCTA;(B) an Fe3+ chelating group;(C) beta-D-galactose or beta-glutamate. Following cleavage by lacZ transgene or PSMA in prostate cancer cells, the released, activated aglycone Fe3+-ligand will spontaneously trap endogenous Fe3+ at the site of enzyme activity forming a highly stable complex. Significantly, this complex will exhibit restricted motion of the Gd3+ chelates enhancing relaxivity. In addition, a paramagnetic chelator based on the Fe3+ will generate strong relaxation. This process will provide contrast based on enzyme beta-gal or PSMA stimulated local accumulation. The combination of Gd3+ and Fe3+ contrast agents for in vivo detection of beta-gal or PSMA activity is fundamentally new approach for in vivo monitoring gene activity or in vivo imaging of prostate cancer. We plan to synthesize series of novel """"""""smart"""""""" MRI contrast agnets well-designed for detecting beta-gal or PSMA activity in prostate cancer cell culture, explore the feasibility of applying the most promising analogies to cells grown in vivo in mice and rats, and compare with vascular extent and necrosis to analyse the correlation of novel """"""""smart'MRI contrast agents response to tumor size and growth. The ultimate objective is to develop a new concept of """"""""smart"""""""" MRI contrast agents for in vivo assessment of beta-gal or PSMA activity, thereby, to establish a novel platform for in vivo monitoring of lacZ transgene expression in prostate cancer gene therapy or in vivo imaging of the prostate cancer itself by assessing PSMA through an extracellular MRI approach. Basically, this novel concept combines all the approaches of reaching the highest possible relaxivities, and the combination of three functional moieties is based on the clinically applied strategies on cancer therapy. We believe the technique translation to clinical investigations with the high promise of in vivo monitoring gene therapy and in vivo imaging of prostate cancer will improve efficacy while reducing side effects and hence improving quality of life for patients with prostate cancer, and the technique will be of widespread utility to investigators probing other diseases.
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