Abstract LB-381: A multi-modal imaging technique to identify metabolites in hypoxic regions of a human breast cancer model

Abstract

Abstract Tumor hypoxia triggers signaling cascades that significantly impact on biological outcomes, resulting in resistance to radio- and chemotherapy. Therefore, understanding the hypoxic response of tumors is critical. In this study, we investigated links between hypoxia and different metabolites, such as lactate/lipid and total choline (tCho), in a human breast cancer model by combining in vivo magnetic resonance spectroscopic imaging (MRSI) with ex vivo optical imaging. Human MDA-MB-231-HRE-Tdtomato breast cancer cells, which were genetically engineered to express red fluorescent Tdtomato protein under the transcriptional control of hypoxia response elements (HREs) under hypoxic conditions, were orthotopically grown in female athymic nude mice. Both 3-dimensional (3D) water-unsuppressed chemical shift imaging (CSI) to determine tumor shape, and water-suppressed 3D CSI to detect metabolites, was performed. Each tumor was removed and sectioned to obtain serial slices throughout the tumor. Before sectioning, the tumor was embedded in a gelatine block containing straight fiducial marker lines for 3D reconstruction of serial optical images. Bright-field and Tdtomato fluorescence images of the same field of view were acquired from each tumor slice on a microscope to visualize hypoxia. We performed 3D reconstruction and registration of MRSI and optical images of 4 tumors. All metabolites were 3D-reconstructed from MRSI data with a 0.4 ppm spectral window size. Bright-field images from each serial section were aligned to each other by rigid body transformation based on the locations of fiducial markers. The tumor's edges were then detected and interpolated to reconstruct the 3D shape of the tumor. Accordingly, the 3D hypoxic region in the tumor was also reconstructed given the inherent co-registration of bright-field and fluorescence imaging. Then, the 3D tumor shape and the corresponding 3D hypoxic region were registered to 3D MRSI images of water-unsuppressed signal along with 3D metabolite images. Regions where hypoxia overlaps with a given metabolite were measured. tCho, glutamate/glutamine, lipid/lactate CH3, lipid CH2 and myo-inositol were detected by MRSI. The overlapping region between those metabolites and hypoxia was 35.1%, 12.7%, 9.8%, 16.7%, and 23.7% of the hypoxic region, respectively. A large proportion of high tCho-containing and myo-inositol-containing regions colocalized with the Tdtomato fluorescence in hypoxic regions, indicating that hypoxia can up-regulate tCho and myo-inositol levels in this breast tumor model. Hypoxia-driven up-regulation of choline kinase and tCho was previously shown by us in a prostate tumor model. Combining 3D MRSI and optical imaging proved useful to delineate the effects of tumor hypoxia on MRS-detectable metabolites, some of which may, in the future, serve as surrogate markers for hypoxia. This work was supported by NIH R01 CA134695. 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 LB-381.