Abstract 1484: Pancreatic cancer and normal pancreas water content and its impact in metabolite quantification
Authors: Penet Marie-France , Krishnamachary Balaji , Shah Tariq , Mironchik Yelena , Maitra Anirban , Bhujwalla Zaver M. 
Published: August 2015

Abstract
The absence of early symptoms in pancreatic cancer creates a critical need for identifying new noninvasive biomarkers. Magnetic resonance spectroscopy (MRS) and spectroscopic imaging (MRSI) are being evaluated in the diagnosis of several solid malignancies. A hallmark of most solid tumors is the detection of elevated phosphocholine (PC) and total choline (tCho). We previously observed elevated levels of tCho in several pancreatic cancer cell lines and tumor xenografts (1). Initial single voxel studies performed in humans suggest that the tCho signal normalized to water may be relatively high in normal pancreas compared to pancreatic tumor (2). Since metabolites are normalized to the water signal it is important to determine differences in its content for accurate quantification. Here, we quantified tCho in orthotopic and subcutaneous Panc1 pancreatic xenografts, and in normal pancreas. 1H MRSI acquired on a 9.4T spectrometer showed heterogeneous tCho signal in orthotopic tumors. To further determine differences in tCho, tumor tissues and pancreas were embedded in agarose and imaged ex vivo with 1H MRSI. Concentration of tCho was 3.38 ± 0.95 mM in orthotopic tumors, 1.32 ± 0.59 mM in subcutaneous tumors, and 1.27 ± 0.52 mM in normal pancreas (n = 2), when using the uncorrected water signal for normalization. Despite a much higher tCho signal in the subcutaneous tumors, tCho concentrations were comparable to the pancreas.
We next estimated the water content of the tumors and the pancreas as a ratio of wet weight to dry weight (measured after 72h of lyophilization) and confirmed a significantly higher water content in tumors compared to the pancreas (wet to dry weight ratio of ∼ 6 vs ∼ 4). A separate set of tumors were freeze-clamped and used for high-resolution 1H MRS. Tumor and pancreas extracts were obtained using a dual-phase extraction method and 1H MR spectra were acquired as previously described (3). To determine the tCho concentration, peak integrations from spectra for choline, PC and glycerophosphocholine were compared to an internal standard. Integrals of the metabolites of interest were determined and normalized first to the tissue wet weight. Once the tCho concentration in tumors and pancreas was corrected for differences in water content, a two-fold higher tCho concentration was observed in tumor tissue compared to normal pancreas. These data support the use of 1H MRSI that provides a tCho map rather than the placement of single voxels to address heterogeneities in the pancreas and in pancreatic cancers. The results highlight the importance of quantifying water content in the calculation of metabolite concentration when comparing different tissues.
Work supported by NIH P50CA103175. (1) Penet et al., Clin Cancer Res (2014). (2) Ma et al., Journal of computer assisted tomography (2011). (3) Shah et al., NMR Biomed (2012).
Citation Format: Marie-France Penet, Balaji Krishnamachary, Tariq Shah, Yelena Mironchik, Anirban Maitra, Zaver M. Bhujwalla. Pancreatic cancer and normal pancreas water content and its impact in metabolite quantification. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1484. doi:10.1158/1538-7445.AM2015-1484