Galactosyltransferase activities in sera of
cancer patients were determined by assaying the formation of
paragloboside from
UDP-galactose and
lactotriaosylceramide immobilized on microtiter plates by means of the
enzyme-linked
immunosorbent assay using a
monoclonal antibody, H-11, directed to
paragloboside.
Enzyme properties were as follows. Optimum pH was 6.8 in
cacodylate buffer, and Km values were 2 microM for
lactotriaosylceramide and 29 microM for
UDP-galactose. The
enzyme activity was inhibited by the addition of
alpha-lactalbumin.
Glucose (20 mM) inhibited the
enzyme activity in the presence of
alpha-lactalbumin (0.1 mg/ml) but not in its absence. These
enzyme properties are similar to those of bovine milk
galactosyltransferase, indicating that the
enzyme in the sera might be
lactose synthetase. The
enzyme activities in sera from patients with
cancer, patients with benign disease, or a reference sample group were assayed. The activity was below the limit of detection (5.5 pmol/25 microliters serum/2 h) in the reference sample group. Remarkable elevations of the
enzyme activity were observed with high incidence in patients with
cancer, especially those with
blood cancer (100%). A high incidence was observed in the progressive stage, and the
enzyme activity was detected at stage 1 in lung, esophagus, stomach, colorectal, and
testis cancer. The
enzyme activity in sera from patients with benign disease was elevated in 22% of the patients. After effective
therapies, the
enzyme activity decreased to below the limit of detection. Release of the
galactosyltransferase into culture medium of
cancer cells could be demonstrated. These observations suggest that the
galactosyltransferase is released from
cancer tissue into the circulation. The present method for the assay of
galactosyltransferase may be useful for the detection of patients with
cancer and for monitoring neoplastic recurrence after
therapy.