The activity of
folylpolyglutamate synthetase was measured in extracts of head and neck
squamous carcinoma cell lines and in surgical specimens utilizing a new rapid method to separate free [3H]
glutamate from [3H]
glutamate incorporated into
methotrexate, used as a substrate for the
enzyme. The validity of this new method, based on reversed phase chromatography via a Sep-Pack C18 cartridge, was observed between both methods, but the Sep Pack C18 assay has the advantage that it can be accomplished in less than 5 min, whereas the DE-52 procedure requires approximately 2 hr. In seven head and neck cell lines, activity of folylpoly-
glutamate synthetase varied from 335-1305 pmol [3H]
glutamate incorporated/mg
protein/hr. In nine head and neck
tumor biopsies, a broad range in activity of
folylpolyglutamate synthetase was observed (25-1827 pmol/mg/hr) which partly overlapped the
enzyme activity in 'normal' tissue (7-297 pmol/mg/hr). For six patients,
folylpolyglutamate synthetase was measured in the center of the
tumor, in the transitional region from
tumor to 'normal' tissue, and in the 'normal' tissue. The
enzyme activity was higher in
tumor tissue vs 'normal' tissue in four of six cases, whereas in all cases, the
enzyme activity in the transitional region was higher than in 'normal' tissue. The results of this study provide further support for the concept that putative differences in
folylpolyglutamate synthetase activity between
tumor tissue and normal tissue can be exploited to improve the effectiveness of
antifolate-based
chemotherapy in general, and in
head and neck cancer in particular.