Abstract 2373: Heterogeneity of permeability in a preclinical model of brain metastases of breast cancer does not correlate with vascular density, HIF-1α expression, or tumor survival

Abstract

Abstract Introduction: High vascular density of brain metastases of breast cancer has been correlated with both poor patient prognosis and with potential chemotherapeutic success. Inversely a low vascular density implies there would be decreased distribution of anti-cancer chemotherapeutics, and over time reduced efficacy of tumor kill. Given that there is heterogeneity in response to chemotherapeutics in human brain metastases and metastases are different than primary tumors; we used a novel brain metastases of breast cancer model to characterize vascular density, and corresponding changes in tumor permeability, hypoxia and survival. Methods: Brain seeking metastatic tumor lines MDA-MB-231-Br and 4T1-Br5 were injected via the left cardiac ventricle in separate experiments and brain metastases developed for ∼28 days and ∼15 days respectively. After development, both 14C-AIB and indocyanine green (ICG) were injected and allowed to circulate for 10 and 1 min respectively. Near infrared imaging was used to identify ICG filled vessels to quantify vascular density of lesions compared to normal brain. To determine permeability, concentrations of 14C-AIB in blood and brain tissue were calculated using autoradiography. Immunofluorescent analysis was performed using anti-HIF-1α and anti Ki67 antibodies and co-stained with DAPI. Results: A significant amount of metastatic lesions were observed to have developed in each model. Lesions varied in size from 0.028 to 2.3mm2. Vascular density was significantly decreased (MDA 176 ± 96 and 4T1 201 ± 76) compared to control brain (429 ± 25) and to an RG2 implanted glioma used as a positive control (736 ± 168). Based on accumulation of 14C-AIB, metastases (range: 22 nCi/g to 1682 nCi/g) were considered to be either permeable (3 fold or greater uptake compared to adjacent control tissue) or non-permeable. There was no strong correlation between lesion size and permeability (r2=0.23) or vascular density (r2 = 0.06). HIF-1α was expressed in both permeable and non-permeable lesions. Lastly, no significant difference was seen in the percentage of Ki67 positive cells in the MDA (permeable 41 ± 2.9, n=7; and non-permeable 40.8 ± 2.7, n=14) and 4T1 model (permeable 52.0 ± 4.6, n=6; and non-permeable 45.0 ± 2.8, n=6). Discussion: This data provides a correlation of permeability to vascular density, HIF-1α and Ki67 in a brain metastases model. While, both brain model systems exhibited a high degree of heterogeneous permeability, in neither model did permeability strongly correlate with vascular density, lesion size, HIF-1α expression and positivity for Ki67. Based upon the data, this experimental model may reflect the heterogeneity seen in human brain metastases of breast cancer and suggests there are other biological factors besides vascular density which correlate with drug distribution and or tumor/survival growth. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2373.