Characterization of a specific signal from human pancreatic tumors heterotransplanted into nude mice

Summary

In a previous study, we demonstrated the existence of a 3.2 ± 0.2 ppm peak in the¹H NMR spectrum at 60 MHz from human pancreatic adenocarcinomas (Capan-1 cell) heterotransplanted intonude mice. This peak, which is not present in normal human pancreas, was attributed to enhanced membrane fluidity and/ or an increase in phospholipid turnover. The present study was designed to identify this signal by comparing the¹H NMR spectra recorded in vivo at 100 MHz from Capan-1 tumors, after suppression of the tissular water proton peak, to those recorded from normal pancreatic tissue, and to those recorded at 300 MHz from lipid extracts. The¹H NMR spectra at 100 MHz of the Capan-1 tumors in vivo exhibited three main peaks in the 3.2 ± 0.2 ppm region: 1. A peak at 2.8 ± 0.1 ppm from CH₂ protons of the acyl chains of unsaturated phospholipids; 2. A peak at 3.2 ± 0.1 ppm from the protons of the N(CH₃)₃ group of choline; and 3 A peak at 3.5 ± 0.1 ppm attributed to GPC.

The NMR¹H 300 MHz spectrum of phospholipid extracts of Capan-1 tumors displayed 12 principal resonances, of which only the N(CH₃)₃ peak of PC had a similar chemical shift to that observed at low resolution (3.2 ± 0.2 ppm). This peak had a higher intensity in the xenografts than in normal human pancreatic tissue. HPLC analysis of the same lipid extracts from Capan-1 cells in culture, of tumors derived from these cells and from normal pancreas showed: 1. Identical concentrations of the different phospholipids from cancerous human pancreatic cells in vivo and in culture; and 2. A significantly higher level of PC in the extracts of normal human pancreatic tissue.

The increase in intensity of the N(CH₃)₃ peak of PC in the Capan-1 tumors was not thought to be caused by an increase in PC concentration, but to a difference in conformation or mobility of the PC protons in the xenografts. The increase in relaxation time in cancerous tissue (from 60 to 125 ms) was also taken to be evidence in favor of a high mobility of protons. The peak observed at 3.2 ± 0.2 ppm in the low resolution NMR spectra from the Capan-1 tumors in vivo thus represents a combination of several phenomena: 1. An