Imaging matrix metalloproteinase expression in tumors.

metastatic Matrix metalloproteinases (MMPs) are zinc-dependent secreted or transmembrane enzymes constituting a family of over 21 proteolytic members that are capable of selectively digesting a wide spectrum of both extracellular matrix (ECM) and nonmatrix proteins. MMPs play a critical role in tumor growth, angiogenesis, and metastatic processes. MMP inhibitors (MMPIs) have been extensively investigated as anti-tumor drugs, although the clinical trials thus far have been disappointing. In order to better understand the role of MMPs in cancer growth and metastasis, as well as improve the therapeutic efficacy of MMPIs, there is a need to develop new procedures to assess and/or monitor MMP activity in vivo. In addition to determining whether MMPs are present in tumors, it would be desirable to have an imaging agent that better probes other processes associated with MMP overproduction, including angiogenesis and the establishment of the growth of metastatic lesions in distant organ sites. In this paper we review the studies relating to the recent development of in vivo imaging of MMP expression. One of the purposes of this review is to discuss the current status of imaging MMP expression, which includes the types of tracers being developed and the types of imaging modalities available. Although imaging MMP expression is a relatively new area of research, the progress thus far is highly promising.