Troponin I overexpression inhibits tumor growth, perfusion, and vascularization of morris hepatoma.

UNLABELLED Antiangiogenic gene transfer inhibiting growth of new blood vessels is a promising approach in cancer therapy. Human troponin I (TnI) efficiently inhibits endothelial cell proliferation, migration, as well as angiogenesis and tumor growth in vivo. However, little is known about its effects on perfusion and tumor biology. METHODS Stable Morris hepatoma (MH3924A) cells overexpressing human TnI (TnI-MH3924A) were cocultured with human umbilical vein endothelial cells (HUVECs) followed by measurements of endothelial apoptosis and proliferation. Furthermore, tumor growth and perfusion were determined using H(2)(15)O and (68)Ga-DOTA-albumin (DOTA is 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid) PET as well as functional MRI. Additionally, histologic measurements of vascularization, apoptosis, proliferation, and gene array analyses were performed. RESULTS Apoptosis of HUVECs was increased and proliferation was decreased after coculture with TnI-MH3924A cells. TnI-MH3924A tumors showed a significant inhibition of growth (90%) and a decreased perfusion (25%), whereas blood volume remained unchanged. MRI investigations demonstrated a significant decrease of the rate constant k(ep). Immunohistochemical analyses showed decreased microvessel density and proliferation and significant induction of apoptosis. Furthermore, TnI-expressing hepatomas demonstrated changes in the expression of genes related to angiogenesis, apoptosis, signal transduction, or stress. CONCLUSION TnI regulates tumor growth by modulating vascularization including apoptosis induction and decrease of proliferation. In addition, changes in expression of genes associated with angiogenesis, apoptosis, signal transduction, or stress were found. The upregulation of angiogenesis and stress-related genes indicates a cross-talk of different mechanisms as part of the tumor's reaction to TnI. Because the decrease of vascularization led to lower perfusion values as measured by PET and MRI, these noninvasive methods are promising tools for the monitoring of antiangiogenic gene therapy.