The antiglutamine agent
acivicin, L-(alpha S,5S)-alpha-amino-3-chloro-4,5-dihydro-5-isoxazoleacetic
acid, inhibited the growth of
hepatoma 3924A cells in culture. After 7 days of incubation with the
drug, an LC50 of 1.4 microM was observed by determination of colony forming ability. A combination of
cytidine (1 mM),
deoxycytidine (10 microM) and
guanosine (10 microM) completely protected the
hepatoma cells against the cytotoxic action of
acivicin, but each
nucleoside by itself had no effect.
Acivicin (0.1 mM) inhibited the incorporation of
uridine and
thymidine into macromolecules, but not that of
leucine.
Acivicin depressed the pools of
CTP,
GTP,
dCTP,
dGTP and
dTTP to 46, 62, 40, 64 and 53%, respectively, but it increased
UTP level to 152% of the values of untreated
cancer cells. The activity of a highly purified
CTP synthetase (EC 6.3.4.2) from rat liver and
hepatoma 3924A was inhibited by
acivicin. The inhibition was competitive with respect to
L-glutamine, and the Ki values with liver and
hepatoma enzymes, determined by Dixon and reciprocal plots, were 1.1 and 3.6 microM respectively. The hydroxy analog of
acivicin was also a competitive inhibitor, but it was less effective than
acivicin, with a Ki value of 1.8 mM for the
hepatoma enzyme. Our observations on the impact of
acivicin on the behavior of pools of
ribonucleotides and
deoxyribonucleotides and the competitive inhibition of purified
CTP synthetase from
hepatoma cells suggest that a major mechanism of action for this
drug is the inhibition of
CTP synthetase and
GMP synthetase (EC 6.3.5.2).