Imaging Mitogen-Activated Protein Kinase Function in Xenograft Models of Prostate Cancer

Abstract

Mitogen-activated protein kinases (MAPK) play important roles in malignancy. The ability to detect and quantitate MAPKs in live animal models of cancer will facilitate an understanding of disease progression. We have developed a gene expression-based imaging system that detects and quantifies MAPK activity in prostate cancer tumors implanted into severe combined immunodeficient mice. The imaging technology uses a modified version of two-step transcriptional amplification (TSTA). The tissue specificity of gene expression is imparted by an enhanced version of the prostate-specific antigen regulatory region that expresses GAL4-ELK1. GAL4-ELK1 confers MAPK specificity by activating a firefly luciferase (FLuc) reporter gene when the Ets-like transcription factor (ELK) 1 activation domain is phosphorylated by MAPK. FLuc activity in live animals was detected using the Xenogen In vivo Imaging System. We validated the TSTA-ELK1 system by analyzing its response to epidermal growth factor treatment in transfected tissue culture cells and in adenovirus (AdTSTA-ELK1)-injected prostate cancer xenograft tumors. We measured MAPK activity in two well-characterized xenograft models, CWR22 and LAPC9. Although no significant differences in MAPK levels were detected between androgendependent and androgen-independent xenografts, the CWR22 models display significantly higher levels of AdTSTA-ELK1 activity versus LAPC9. Western blots of tumor extracts showed that the elevated imaging signal in CWR22 xenografts correlated with elevated levels of phosphorylated extracellular signal-regulated kinase 1/2 but not p38 or c-Jun NH 2 -terminal kinase. We conclude that a gene expression-based optical imaging system can accurately detect and quantify MAPK activity in live animals. (Cancer Res 2006; 66(22): 10778-85)

Silibinin Impairs Constitutively Active TGFα-EGFR Autocrine Loop in Advanced Human Prostate Carcinoma Cells

“…Downstream of EGFR, MAPK/Erk1/2 activation is the key event to drive proliferation, and similar to constitutively active EGFR, an increase in constitutive activation of MAPK/ Erk1/2 signaling has also been reported in human PCA as it progresses to a more advanced and androgen-independent malignancy (24). Furthermore, some studies have also shown that MAPK/Erk1/2 is constitutively active in DU145 cells, and that Erk1/2 kinase activity decides activation of transcription factors for cell proliferation (8)(9)(10).…”

Factors Affecting Residence Time of Mesenchymal Stromal Cells (MSC) Injected into the Myocardium

“…To circumvent these difficulties, in the current study we used in vivo biophotonic imaging technology (IVIS, Xenogen Corp.) that allows monitoring cell survival in vivo within the living animal in a real-time fashion (7,33). IVIS has already been applied for the spatial and temporal detection of cancer cells during drug and gene therapy (13,14,24,42,48) to follow the survival and biodistribution of cell transplants (20,21,40,47) or expression of viral genes (35). We further improved this technique by combining it with retroviral overexpression of the firefly luciferase in the MSC to be injected.…”

Non‐invasive imaging of adaptive immunity using positron emission tomography

“…A significant barrier to targeted expression of a reporter is the relatively weak activity of cellular promoters. One strategy to overcome this obstacle is two‐step transcriptional amplification (TSTA) (40). The basis of TSTA is using weak cellular promoters to express a potent transcriptional activator.…”