Enhancement of the toxicity and DNA incorporation of arabinosyl-5-azacytosine and 1-beta-D-arabinofuranosylcytosine by cyclopentenyl cytosine.
We evaluated the interaction of a biochemically active concentration of cyclopentenyl cytosine (CPE-C), an investigational antimetabolite which inhibits CTP synthetase, on the cytotoxicity of arabinosyl-5-azacytosine (Ara-AC) and 1-beta-D-arabinofuranosylcytosine (Ara-C) in HCT 116 colon carcinoma cells. A 3-h exposure to 0.5 microM CPE-C depleted CTP pools by over 90% and decreased dCTP pools by 57%; the effect on CTP pools persisted for up to 24 h following washout of CPE-C. A 3-h pre-exposure to 0.5 microM CPE-C augmented the growth inhibition resulting from a 24-h exposure to Ara-AC. The combination of 1 microM cytidine and deoxycytidine fully reversed the enhancement associated with CPE-C pretreatment, to a level of growth inhibition expected from either CPE-C or Ara-AC alone. A striking enhancement of toxicity was observed in clonogenic studies with pre-exposure to CPE-C at a nonlethal dose followed by either Ara-AC or Ara-C. CPE-C increased the formation of Ara-AC and Ara-C nucleotides by as much as 3-fold, and this was accompanied by increased incorporation of the arabinosyl nucleotides into methanol-precipitable material. Analysis of purified RNase-treated nucleic acids by cesium sulfate density centrifugation confirmed that a 3-h pre-exposure to CPE-C increased [3H]-Ara-C incorporation into DNA at 4 and 24 h by 2.4- and 2.7-fold, respectively. Thus, these studies indicate that CPE-C can function as a biochemical modulator. Following a brief exposure to a nonlethal concentration, CPE-C is capable of augmenting the cytotoxicity and intracellular metabolism of Ara-AC and Ara-C.
Gastrointestinal Tumor Section, National Cancer Institute, Bethesda, Maryland 20892.
J L
JL
Grem
C J
CJ
Allegra
D000964:Antimetabolites, Antineoplastic / Q000008:administration & dosage* / Q000633:toxicity; D001374:Azacitidine / Q000378:metabolism / Q000633:toxicity* / Q000031:analogs & derivatives; D002470:Cell Survival / Q000187:drug effects; D015179:Colorectal Neoplasms / Q000473:pathology; D003561:Cytarabine / Q000378:metabolism / Q000633:toxicity*; D003570:Cytidine Triphosphate / Q000378:metabolism; D004273:DNA, Neoplasm / Q000378:metabolism; D003845:Deoxycytosine Nucleotides / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D014407:Tumor Cells, Cultured / Q000187:drug effects
D000964:Antimetabolites, Antineoplastic; D004273:DNA, Neoplasm; D003845:Deoxycytosine Nucleotides; D003561:Cytarabine; C024107:2'-deoxycytidine 5'-triphosphate; C022121:fazarabine; D003570:Cytidine Triphosphate; D001374:Azacitidine