Mass profiling of serum to distinguish mice with pancreatic cancer induced by a transgenic Kras mutation

Abstract

Mass spectrometry (MS) has the unique ability to profile, in an easily accessible body tissue (peripheral blood/serum,) the sizes and relative amounts of a wide variety of biomolecules in a single platform setting. Using electrospray ionization (ESI)-MS, we distinguished individual serum from wild-type control mice from serum of mice containing an oncogenic Kras mutation, which leads to development of pancreatic ductal adenocarcinoma (PDAC) similar to that observed in humans. Identification of differences in significant ESI-MS sera mass peaks between Kras-activated mice and control mice was performed using t tests and a "nested leave one out" cross-validation procedure. Peak distributions in serum of control mice from mice with Kras-mutant-dependent PDAC were distinguished from those of pancreatic intraepithelial neoplasia (PanIN) lesions (p = 0.00024). In addition, Kras mutant mice with PDAC were distinguished from Kras mutant mice with PanIN alone (p = 0.0057). Test specificity, a measure of the false positives, was greater for the control vs. Kras mutated mice, and the test sensitivity, a measure of false negatives, was greater for the PDAC vs. PanIN containing mice. Receiver-operating characteristic (ROC) curve discriminatory values were 0.85 for both comparisons. These studies indicate ESI-MS serum mass profiling can detect physiological changes associated with pancreatic cancer initiation and development in a GEM (genetic engineered mouse) model that mimics pancreatic cancer development in humans. Such technology has the potential to aid in early detection of pancreatic cancer and in developing therapeutic drug interventions.

Keywords: Kras mutation; early detection; electrospray mass spectrometry; genetically engineered mouse; pancreatic cancer; serum profiling.

Figure 1

Gross morphology and histology of pancreas tissue from control and Kras GEM animals. Panels A and B, mouse control pancreas and pancreas with ductal adenocarcinoma (PDAC); panels C and D, mouse pancreas control and PDAC histology; panels E and F, mouse PanIN 1a and PanIN 3, range of PanIN observed in this study.

Figure 2

Physiological parameters associated with the Kras GEM model. Panels A and B, average body and pancreata weights for control (wild-type) and Kras mice; Panel C, % of mice with pancreatic ductal adenocarcinoma; Panel D, % normal pancreata present; Panel E, numbers of PanIN lesions by grade in Kras mice.

Figure 3

Electrospray MS m/Z peaks distinguishing sera from mouse controls versus sera from GEM animals and model peak analysis. ESI-MS was performed as described in Materials and Methods. Panel A, mass peaks are averages from 5 individual serum samples per category. Panel B, model of electrospray MS methodology used to identify, quantify, and classify significant sera m/Z peaks into mouse pancreatic cancer (PDAC or PanIN) or control descriptors.

Figure 4

Distinguishing sera between GEM KrasG12D animals and wild-type (non-disease) mice using ESI-MS profiling. Panel A, distinguishing sera from GEM animals from control mice based on significant "% GEM sera peaks identified" using the mass peak analyses described in the Materials and Methods and Fig. 3B. Panel B, ROC area under the curve discriminating sera from wild-type mice versus GEM animals.

Figure 5

ESI-MS analysis distinguishing sera from GEM animals with PDAC and without PDAC. Panel A, distribution differences based on "% GEM+PDAC sera peaks identified" between PDAC mice and GEM animals without PDAC using the mass peak analyses described in the Materials and Methods and Fig. 3. Panel B, ROC area under the curve discriminating sera from these two cohorts.