Organisation der Langfristplanung

Depletion of cytidine triphosphate as a consequence of cellular uridine triphosphate deficiency

“…Combination of uridylate trapping by GalN with a blockade of de novo pyrimidine synthesis led to a depletion of UTP within 2 h (fig.1). UTP levels and time course were almost identical as in previous Decrease in CTP and UTP contents of AS-30D hepatoma cells incubated as in[ 7,8] in the presence of GalN(0.5 mmol/l) and 6-azauridine (6-AzaUrd; 0.2 mmol/l). CTP and UTP were analyzed as in section 2.3.…”

Increased formation of nucleotide derivatives of 5‐fluorouridine in hepatoma cells treated with inhibitors of pyrimidine synthesis and D‐galactosamine

“…Different UTP levels in ascites hepatoma cells were adjusted by incubation of the cells in the presence of: (a) GalN that lowers the UTP concentration by its uridylate trapping action [4,5] together with PALA [ 161 or 6-aza-Urd [4,10] , both combinations leading to a depletion of UTP pools in vitro and in vivo. Incubation of AS-30D cells in the presence of these inhibitors for3 h asin section 2.2. resulted in the following average UTP contents relative to control cells (100%): GalN, 60%; PALA, 45%; 6-aza-Urd, 24%; GalN + PALA, 7%; GalN + 6-aza-Urd, 5% ( fig.1) [4,16] . The corresponding factors of increase in uptake of labeled 5-FUrd during 15 min relative to control cells (1 .O) were 1.5 in cells treated with GalN, 2.5 with 6-aza-Urd, 3.1 with PALA, 3.3 with GalN + 6-aza-Urd, and 4.3 with GatN + PALA ( fig.2).…”

“…Paper chromatography of the acid-soluble metabolites of 5-F [ t4C] Urd indicated that >93% were phosphorylated derivatives when the UTP pool had been reduced below 10% before the addition of 5-FUrd. Induction of selective UTP deficiency [4] followed by addition of 5-FUrd resulted in a replenishment of the cellular UTP pool with FUTP ( fig.1). However, the level of FUTP t UTP remained lower in the presence of GalN ( fig.1).…”

“…The formation [ 181 and accumulation [ 191 of UDP-galactosamine and UDP-glucosamine (UDP-HexN) and of UDP-~-acetylglucosamine and UDP-~-acetylgalactosamine {UDPHex~Ac) as metabolites of GalN has been described in liver and hepatoma cells [4,5,10]. Labelling of these amino sugar nucleotides with 5-F [2-14C]Urd has now established the formation and accumulation of FUDP-HexN and FOP-HexNAc ( fig.3).…”

“…The feedback regulation of uridine kinase by UTP [2] can be used for an increase in the cell-specific uptake of some pyrimidine analogs after depletion of the cellular UTP pools [3] . Induction of selective UTP deficiency by D-galactosamine (GalN) and 6azauridine (6aza-Urd) in hepatoma cells [4] is associated with an increased formation of phosphorylated derivatives of 5-FUrd [3]. This approach [3] has the following implications: (i) Considerable selectivity for hepatoma cells and hepatocytes is based on the action of GalN [3,5] ; (ii) The increased activity of uridine kinase [6,7] and the high rate of de nova pyrimidine nucleotide synthesis in hepatoma cells relative to liver [7-IO] makes these malignant cells more susceptible to the action of 6aza-Urd.…”