This study has aimed at taking information necessary for design of anticancer
prodrugs modified with chiral acyl group, especially about the effect of chirality of the acyl group on its enzymic removal in specific cells. Thus, 13 species of chiral
esters were synthesized and stereoselectivity in their enzymic hydrolysis was investigated with six
cancer cell lines, solid
tumors, and the corresponding normal tissues. Cultured
cancer cells from rat liver, pancreas, and muscle hydrolyzed the R enantiomer of (+/-)-ethyl 2-methoxy-2-phenylacetate (3c) more preferentially than its antipode, whereas this stereoselectivity was reversed in the reaction by homogenate of the corresponding normal tissue of rat. The difference in stereoselectivity between
cancer cells and normal tissue was also found in the hydrolysis of other
esters including those of actual
anticancer agents, p-
hydroxyaniline mustard and
5-fluorouridine. The investigation was expanded to real
tumor to show that the degree of stereoselectivity or the hydrolytic activity was significantly different between a human
brain tumor and its surrounding normal tissue for such substrates as (+/-)-ethyl 2-phenoxypropanoate and N-trifluoroacetylphenylalaninate. The
esterases of rat
liver cancer cells (Anr4) and normal rat liver gave different band patterns in active staining after gel electrophoresis. The
enzymes were fractionated by ion exchange column chromatography and then tested on their stereoselectivity against (+/-)-3c. Comparison of the results and electrophoretograms of the fractions suggests that
esterases with different stereoselectivity are expressed in different ways by normal and
cancer cells. These results show that stereoselectivity in enzymic hydrolysis of some synthetic chiral
esters is different between
cancer and normal cells, leading to the possibility that specific activation of
ester-type anticancer
prodrugs in
cancer cells would be controlled by the chiral structure of the acyl group.