Morphological Aspects of Tumor Angiogenesis and Microcirculation

Study on tumor microvasculature damage induced by alternate cooling and heating

Tumor vasculature damage induced by various thermal treatments has been studied in vivo via laser confocal microscopy. Murine mammary carcinoma 4T1 was implanted in the nude mice dorsal skin fold window chamber. The implanted tumor was treated by alternate cooling and heating. Results showed that the treatment was much more effective as compared with that of cooling or heating alone, especially in damaging the tumor vasculature. In general, tumor vascular response to thermal stimuli was heterogeneous. All the treatments of hyperthermia at 42 degrees C (for 1 h), alternate cooling at 1 degrees C and heating at 42 degrees C (for 1/2 h each) and that of -10 degrees C/42 degrees C (for 1/2 h each) enhanced liposome extravasation. Pre-cooling tumor at 1 degrees C preserved most of the vascular integrity but partially inhibited the effect of post-hyperthermia at 42 degrees C. On the other hand, cooling at -10 degrees C for 1/2 h before heating at 42 degrees C caused severe vessel damage. Histo-pathological analyses further confirmed the effect as rare tumor vessel recurrence and large necrotic tumor tissue areas shown on the 7th day after the treatment.

Thalidomide Radiosensitizes Tumors through Early Changes in the Tumor Microenvironment

Purpose: The aim of this work was to study changes in the tumor microenvironment early after an antiangiogenic treatment using thalidomide (a promising angiogenesis inhibitor in a variety of cancers), with special focus on a possible “normalization” of the tumor vasculature that could be exploited to improve radiotherapy.

Experimental Design: Tumor oxygenation, perfusion, permeability, interstitial fluid pressure (IFP), and radiation sensitivity were studied in an FSAII tumor model. Mice were treated by daily i.p. injection of thalidomide at a dose of 200 mg/kg. Measurements of the partial pressure of oxygen (pO2) were carried out using electron paramagnetic resonance oximetry. Three complementary techniques were used to assess the blood flow inside the tumor: dynamic contrast-enhanced magnetic resonance imaging, Patent Blue staining, and laser Doppler imaging. IFP was measured by a “wick-in-needle” technique.

Results: Our results show that thalidomide induces tumor reoxygenation within 2 days. This reoxygenation is correlated with a reduction in IFP and an increase in perfusion. These changes can be attributed to extensive vascular remodeling that we observed using CD31 labeling.

Conclusions: In summary, the microenvironmental changes induced by thalidomide were sufficient to radiosensitize tumors. The fact that thalidomide radiosensitization was not observed in vitro, and that in vivo radiosensitization occurred in a narrow time window, lead us to believe that initial vascular normalization by thalidomide accounts for tumor radiosensitization.