Purpose: New strategies to detect tumor angiogenesis and monitor response of tumor vasculature to therapy are needed. Contrast ultrasound imaging using microbubbles targeted to tumor endothelium offers a noninvasive method for monitoring and quantifying vascular effects of antitumor therapy.We investigated the use of targeted microbubbles to follow vascular response of therapy in a mouse model of pancreatic adenocarcinoma. Experimental Design: Microbubbles conjugated to monoclonal antibodies were used to image and quantify vascular effects of two different antitumor therapies in s.c. and orthotopic pancreatic tumors in mice. Tumor-bearing mice were treated with anti-vascular endothelial growth factor (VEGF) monoclonal antibodies and/or gemcitabine, and the localization of microbubbles to endoglin (CD105), VEGF receptor 2 (VEGFR2), or VEGF-activated blood vessels (the VEGF-VEGFR complex) was monitored by contrast ultrasound. Results: Targeted microbubbles showed significant enhancement of tumor vasculature when compared with untargeted or control IgG^targeted microbubbles.Video intensity from targeted microbubbles correlated with the level of expression of the target (CD105, VEGFR2, or the VEGF-VEGFR complex) and with microvessel density in tumors under antiangiogenic or cytotoxic therapy. Conclusions: We conclude that targeted microbubbles represent a novel and attractive tool for noninvasive, vascular-targeted molecular imaging of tumor angiogenesis and for monitoring vascular effects specific to antitumor therapy in vivo.

Pancreatic cancer is the fourth leading cause of cancer-related death in the USA and little improvement has been seen over the last 20 years in the 5-year survival rate, which remains at 5% (Surveillance, Epidemiology, and End Results, SEER, http://seer.cancer.gov). Historically, studies have focused on cell-autonomous behavior or the molecular biology of cancer cells. However, focus is shifting to the interaction of cancer cells with their microenvironment. In particular, desmoplasia (or stromal response) is prominent in pancreatic adenocarcinoma (Korc, 2007). Crosstalk between malignant epithelial cells and the stromal compartment can promote extracellular matrix (ECM) remodeling, angiogenesis, immune cell recruitment and metastasis (Desmouliere et al

There is growing evidence that anti-angiogenic therapy stimulates cancer cell invasion and metastasis. However, the underlying molecular mechanisms responsible for these changes have not been fully defined. Here we report that anti-VEGF therapy promotes local invasion and metastasis by inducing collagen signaling in cancer cells. We show that chronic VEGF inhibition in a genetically engineered mouse model (GEMM) of pancreatic ductal adenocarcinoma (PDA) induces hypoxia, a less differentiated mesenchymal-like tumor cell phenotype, TGFβ expression, and collagen deposition and signaling. Additionally, we show that collagen signaling is critical for pro-tumorigenic activity of TGFβ in vitro. To further model the impact of collagen signaling in tumors, we evaluated PDA in mice lacking Sparc, a protein that reduces collagen binding to cell surface receptors. Importantly, we show that loss of Sparc increases collagen signaling and tumor progression. Together, these findings suggest that collagen actively promotes PDA spread and that enhanced disease progression associated with anti-VEGF therapy can arise from elevated ECM-mediated signaling.