Abstract 884: Detection of intratumoral heterogeneity using MR-defined tumor habitats in breast cancer model under melatonin treatment
Authors: Jardim-Perassi Bruna V. , Dominguez-Viqueira William , El-Kenawi Asmaa , Abrahams Dominique F. , Budzevich Mikalai , Ruiz Epifanio , Huang Suning , Enriquez-Navas Pedro M. , Martinez Gary , Zuccari Debora Aparecida Pires de Campos , Gillies Robert J. 
Published: July 2017

Abstract
Breast cancer shows high intratumoral heterogeneity, which can be visualized as localized sub-populations of tumor cells with different malignancy potential and treatment responsiveness. These regions are like “habitats” that contain different combinations of environmental selection forces, such as hypoxia, acidosis, or nutrient availability. Thus, agents that can perturb these forces may be useful in limiting cancer progression. Studies have shown that melatonin can affect tumor metabolism and we hypothesize that this may be a mechanism by which the disruption of circadian melatonin production by light exposure at night (LAN) promotes breast cancer initiation and progression. The aim of this study was to evaluate the effect of melatonin on intratumoral heterogeneity measured by non-invasive MR imaging in a syngeneic mouse model of breast cancer (4T1). To visualize habitats, clusters were generated from combined MR images generated by different pulse sequences. These were co-registered with histology using tumor specific 3-D printed cradles to classify these tumor habitats. Methods: Mice were exposed to LAN (Control) or LAN plus melatonin. The melatonin metabolite 6-sulfatoxymelatonin (6-SMT) was assessed in urine as a measure of melatonin production. Mice were imaged in a 7T MRI system with: 1) anatomical T2 images, 2) T2*, 3) diffusion-weighted MRI (DWI); and 4) T1 weighted dynamic contrast enhanced (DCE). DCE maps were obtained through semi-quantitative analysis of the pre- and post-contrast agent bolus time-series on a pixel-by-pixel basis. These were combined to the corresponding T2, T2* and Apparent Diffusion Coefficient (ADC) values to generate parameter maps. Parameter maps were used to classify multiple clusters, based on a Gaussian mixture model. Following euthanasia, a 3D printed mold based on the T2 tumor isosurface was created in order to co-register the MRI and histology. Tumors were stained with H&E and for pimonidazole (hypoxia) by immunohistochemistry. Results: Melatonin treatment increased the 6-SMT in urine of mice exposed to LAN and statistically reduced tumor growth by day 15 (p&lt;0.05). Distinct hypoxic habitats have been observed by MRI. Habitat clusters with low values in ADC (high cellularity) and low contrast enhancement were associated with positive staining of pimonidazole. Initial results suggest that the melatonin-treated mice had more homogeneous tumors, although additional numbers will be needed to reach statistical significance. Conclusion: These data indicate that the spatial heterogeneity of breast tumors, corroborated by histological features, may be used as a non-invasive imaging method for monitoring the changes in intratumoral heterogeneity following cancer therapy.
Citation Format: Bruna V. Jardim-Perassi, William Dominguez-Viqueira, Asmaa El-Kenawi, Dominique F. Abrahams, Mikalai Budzevich, Epifanio Ruiz, Suning Huang, Pedro M. Enriquez-Navas, Gary Martinez, Debora Aparecida Pires de Campos Zuccari, Robert J. Gillies. Detection of intratumoral heterogeneity using MR-defined tumor habitats in breast cancer model under melatonin treatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 884. doi:10.1158/1538-7445.AM2017-884