Abstract 4198: Optoacoustic imaging of blood vasculature and study of angiogenesis in orthotopic breast cancer models
Authors: Quiros-Gonzalez Isabel , Tomaszewski Michal , Joseph James , Bohndiek Sarah E. 
Published: July 2016

Abstract
The outcomes of anti-angiogenic drugs in breast cancer have been disappointing. There is an urgent clinical need to better understand the existing and emerging anti-angiogenic therapies in order to: select appropriate patients therapy; define ‘windows’ for combination therapy; and reduce healthcare costs of ‘precision medicine’. MultiSpectral Optoacoustic Tomography (MSOT) is emerging as a new imaging modality, cheaper and less toxic than existing functional imaging methods. It is based on the absorption of laser energy in tissues, which produces pressure waves detectable by ultrasound. MSOT can detect binding of O2 to haemoglobin (Hb and HbO2) based on changes in the optical absorption spectrum, making it a very useful tool to image blood vasculature and measure tissue oxygenation.
We have used MSOT to study blood vessel formation in a breast cancer xenograft model (MCF7, Estrogen Receptor+, n = 10). MSOT images were acquired at 3 and 6 weeks after innoculation and at 6 weeks, tumours were collected for histopathological study. The endothelial protein CD31 was use to identify blood vessel density. Serum levels of vascular endothelial growth factor (VEGF) were measured at 3 and 6 weeks. Presence/absence of VEGF receptor levels were assessed in MCF7 cell line by WB and IF.
The MSOT parameters mean intensity (MI) and maximum intensity (MaI) for total Hb (THb) and O2 saturation (SO2, HbO2/(HbO2+Hb)) did not change significantly during tumour development (p-values: Hb = 0.952, 0.716; HbO2 = 0.102, 0.19; mean/max respectively, SO2 = 0.12), indicating that there is no substantial change in blood vessel density in this tumour model despite a size increase (mean, cm3 3w = 0.139 and 6w = 0.458, p-value = 0.04). The serum levels of the pro-angiogenic cytokine VEGF were significantly decreased (mean, pg/ml 3w = 116.97 and 6w = 86.24). The decrease in VEGF could explain the apparent lack of further blood vessel formation by 6 weeks. Unexpectedly, although the mean intensity for total Hb is lower in the tumour than the reference (cava artery-vein), there is no difference in SO2. Finally, comparing measurements from MSOT to histopathology, HbO2 MI correlates with CD31 staining intensity (CD31si) (Spearman correlation r = 0.57 p-value = 0.041) indicating that both measurements mark presence of blood vessel in the tumour. Microvessel density and CD31si do trend towards correlation with THb MI but this is not statistically significant at present.
In conclusion, MSOT is a direct method to image blood vasculature in our tumour model non-invasively and indirectly to determine blood vessel density. The xenograft mouse model from MCF-7 cell line shows good vascularization, oxygenation and stability during tumour growth. In the next steps, we will investigate in this xenograft model the utility of MSOT biomarkers to monitor response to anti-angiogenic therapies, hence establishing the potential of the technique as a companion diagnostic.
Citation Format: Isabel Quiros-Gonzalez, Michal Tomaszewski, James Joseph, Sarah E. Bohndiek. Optoacoustic imaging of blood vasculature and study of angiogenesis in orthotopic breast cancer models. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4198.