282
fine capillary, producing a fine aerosol of charged particles in an
electric field, or matrix-assisted laser desorption ionization time-of-
flight (MALDI-TOF) MS. In the later, a sample in a highly absorb-
ing matrix is bombarded with a laser to produce ionized species. In
each case, the ionized species then enter the instrument and under
a vacuum travel according to their mass to an ion detector [ 3 , 4 ].
There has been particular interest in using a modification of
MALDI-TOF, the technique of surface-enhanced laser desorp-
tion/ionization time-of-flight SELDI-TOF for the identification
of serum proteomic profiles that can be used in clinical diagnostics.
In this technique, chromatographic separation is achieved on a
protein chip surface, which is then analyzed intact [ 3 ]. A variety of
protein chip surfaces is available which selectively bind according
to specific properties of the proteins. By varying chip surfaces and
binding conditions, large numbers of proteins can be captured.
Once discriminating protein peaks have been detected, the peaks
can be isolated by chromatographic techniques, the isolated pro-
teins are then broken down into peptides by tryptic digests and
peptides analyzed using tandem (MS/MS) mass spectrometry in
which two or more MS analyzers are linked. The analyzers are
linked by a collision cell in which ions are bombarded to produce
fragmentation. These MS/MS techniques, which provide amino
acid sequence data, are now considered to be the most reliable way
of providing unambiguous identification of proteins [ 5 ].
Proteomic profiling by two-dimensional SDS-PAGE has been
used to detect changes between non-neoplastic esophageal mucosa,
Barrett esophagus, and esophageal adenocarcinoma tissue indicat-
ing early changes in the development of adenocarcinoma [ 6 ].
Similar studies have been performed comparing normal and squa-
mous cell carcinoma tissue [ 7 ]. Serum profiling by SELDI-TOF
MS has been used to detect a panel of markers that correctly pre-
dict response to chemotherapy in patients with esophageal squa-
mous cell carcinoma [ 8 ].
The technique has been used to detect markers of response to
chemotherapy by plasma proteomic profiling of human esophageal
adenocarcinoma cell line xenografts and in a cohort of patients
with esophageal adenocarcinoma [ 9 ]. Thus, analysis of plasma pro-
teomic in patients with esophageal adenocarcinoma has the poten-
tial to monitor response and guide chemotherapy in esophageal
adenocarcinoma. In addition, plasma proteins noted in the patients
with esophageal adenocarcinoma are associated with survival of
patients with the cancer [ 10 ].
This chapter describes the methods used to analyze plasma
samples collected from esophageal adenocarcinoma.Peter Kelly