Radiotherapy Decreases Vascular Density and Causes Hypoxia with Macrophage Aggregation in TRAMP-C1 Prostate Tumors

Fang-Hsin Chen, Chi-Shiun Chiang, Chun-Chieh Wang, Chien-Sheng Tsai, Shih-Ming Jung, Chung-Chi Lee, William H. McBride and Ji-Hong Hong

Purpose: To investigate how single or fractionated doses of radiation change the microenvironment in transgenic adenocarcinoma of the mouse prostate (TRAMP)-C1 tumors with respect to vascularity, hypoxia, and macrophage infiltrates.

Experimental Design: Murine prostate TRAMP-C1 tumors were grown in C57BL/6J mice to 4 mm tumor diameter and were irradiated with either 25 Gy in a single dose or 60 Gy in 15 fractions. Changes in vascularity, hypoxia, and macrophage infiltrates were assessed by immunohistochemistry and molecular assays.

Results: Tumor growth was delayed for 1 week after both radiation schedules. Tumor microvascular density (MVD) progressively decreased over a 3-week period to nadirs of 25% and 40% of unirradiated tumors for single or fractionated treatment, respectively. In accord with the decrease in MVDs, mRNA levels of endothelial markers, such as CD31, endoglin, and TIE, decreased over the same time period after irradiation. Central dilated vessels developed surrounded by avascularized hypoxic regions that became infiltrated with aggregates of CD68+ tumor-associated macrophages, reaching a maximum at 3 weeks after irradiation. Necrotic regions decreased and were more dispersed.

Conclusion: Irradiation of TRAMP-C1 tumors with either single or fractionated doses decreases MVD, leading to the development of disperse chronic hypoxic regions, which are infiltrated with CD68+ tumor-associated macrophages. Approaches to interfere in the development of these effects are promising strategies to enhance the efficacy of cancer radiotherapy.

Heterozygous Deficiency of PHD2 Restores Tumor Oxygenation and Inhibits Metastasis via Endothelial Normalization

Massimiliano Mazzone, Daniela Dettori, Rodrigo Leite de Oliveira, Sonja Loges, Thomas Schmidt, Bart Jonckx, Ya-Min Tian, Anthony A. Lanahan, Patrick Pollard, Carmen Ruiz de Almodovar, Frederik De Smet, Stefan Vinckier, Julián Aragonés, Koen Debackere, Aernout Luttun, Sabine Wyns, Benedicte Jordan, Alberto Pisacane, Bernard Gallez, Maria Grazia Lampugnani, Elisabetta Dejana, Michael Simons, Peter Ratcliffe, Patrick Maxwell and Peter Carmeliet

A key function of blood vessels, to supply oxygen, is impaired in tumors because of abnormalities in their endothelial lining. PHD proteins serve as oxygen sensors and may regulate oxygen delivery. We therefore studied the role of endothelial PHD2 in vessel shaping by implanting tumors in PHD2+/ mice. Haplodeficiency of PHD2 did not affect tumor vessel density or lumen size, but normalized the endothelial lining and vessel maturation. This resulted in improved tumor perfusion and oxygenation and inhibited tumor cell invasion, intravasation, and metastasis. Haplodeficiency of PHD2 redirected the specification of endothelial tip cells to a more quiescent cell type, lacking filopodia and arrayed in a phalanx formation. This transition relied on HIF-driven upregulation of (soluble) VEGFR-1 and VE-cadherin. Thus, decreased activity of an oxygen sensor in hypoxic conditions prompts endothelial cells to readjust their shape and phenotype to restore oxygen supply. Inhibition of PHD2 may offer alternative therapeutic opportunities for anticancer therapy.

Endothelial Cells Form a Phalanx to Block Tumor Metastasis

Victoria L. Bautch

Tumor blood vessels deliver oxygen poorly, thereby contributing to tumor hypoxia and upregulation of proangiogenic cytokines in an escalating feedback loop. Mazzone et al. (2009) now show that reducing the amount of a protein involved in endothelial oxygen sensing leads to changes in endothelial cell shape that interrupt this feedback loop and reduce tumor metastasis.

Regulation of CD151 by Hypoxia Controls Cell Adhesion and Metastasis in Colorectal Cancer

Chun-Wei Chien, Shih-Chieh Lin, Yen-Yu Lai, Bo-Wen Lin, Shao-Chieh Lin, Jenq-Chang Lee and Shaw-Jenq Tsai

Purpose: The first step of metastasis is the detachment of cancer cells from the surrounding matrix and neighboring cells; however, how cancer cells accomplish this process remains unclear. Thus, we aimed to investigate the underlying mechanism that controls the early event of metastasis.

Experimental Design: One hundred and thirty-seven paired colorectal carcinoma and normal colon tissues were examined by immunohistochemical staining and Western blot for the expression of CD151, a member of the tetraspanin family that plays important roles in cell adhesion and motility. The effect of CD151 on cancer cell adhesion was investigated under normoxia and hypoxia conditions.

Results: The level of CD151 was down-regulated in colon cancer compared with the paired normal counterparts. Expression of CD151 was negatively regulated by hypoxia inducible factor-1–dependent hypoxic stress. Suppression of CD151 by hypoxia caused the detachment of cancer cells from the surrounding matrix and neighboring cells whereas restoration of CD151 expression during reoxygenation facilitated the adhesion capacity. Clinical examination further showed that metastasized cancer cells expressed a greater level of CD151 compared with that of primary tumor.

Conclusion: Regulation of CD151 by oxygen tension may play an important role in cancer metastasis by regulating the detachment from the primary site and homing in the secondary site.

Does Loss of CD151 Expression Promote the Metastasis of Hypoxic Colon Cancer Cells?

Gregg L. Semenza

Intratumoral hypoxia increases invasion and metastasis through multiple mechanisms, including changes in gene expression that are mediated by hypoxia-inducible factor 1. In hypoxic colon cancer cells, hypoxia-inducible factor 1 inhibits the expression of CD151, a cell surface molecule that normally tethers epithelial cells to the basement membrane, which may promote metastasis.