title: Interferon augments the cytotoxicity of hydroxyurea without enhancing its activity against the M2 subunit of ribonucleotide reductase: effects in wild-type and resistant human colon cancer cells.
abstract: The effects of prolonged exposure to the ribonucleotide reductase (RR) inhibitor, hydroxyurea (HU), were assessed in the presence or absence of recombinant interferon alfa-2a (IFN) in wild-type human colon cancer cells (HT-29) and variants expressing low-level resistance to HU (R200). IFN at nontoxic concentrations decreased the IC50 of HU from 368 microM to 215 microM (P < 0.01) in wild-type cells, but not in the resistant variants. Potential cellular targets for the HU/IFN interaction were examined. In wild-type, but not resistant cells, treatment with HU at clinically achievable concentrations (1000 microM) resulted in rapid early inhibition of RR activity between 4 and 24 h after treatment with a maximal decrease of 65% at 12 h, decreases in cellular levels of dATP, dCTP and dGTP by 50-90% over the same time course, and a two- to fourfold increase in the level of mRNA for both the M1 and M2 subunits of RR, at 24, but not between 1 and 4 h, which probably represents a response to the earlier decrease in RR activity. IFN at a clinically achievable concentration (500 U/ml) failed to augment the effects of HU on RR protein, RR mRNA levels or RR enzyme activity in either the wild-type or resistant cells, suggesting that the mechanism by which IFN augments the effects of HU in the wild-type cells is independent of the effects of HU on M2.
authors.affiliation: Albert Einstein Cancer Center, Albert Einstein College of Medicine, Bronx, New York, USA.
authors.forename: S
authors.initials: S
authors.lastname: Wadler
authors.forename: R
authors.initials: R
authors.lastname: Horowitz
authors.forename: J
authors.initials: J
authors.lastname: Rao
authors.forename: X
authors.initials: X
authors.lastname: Mao
authors.forename: K
authors.initials: K
authors.lastname: Schlesinger
authors.forename: E L
authors.initials: EL
authors.lastname: Schwartz
mesh_terms: D001483:Base Sequence; D002470:Cell Survival / Q000187:drug effects; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000201:enzymology; D019008:Drug Resistance, Neoplasm; D004357:Drug Synergism; D006801:Humans; D006918:Hydroxyurea / Q000494:pharmacology*; D000077190:Interferon alpha-2; D016898:Interferon-alpha / Q000494:pharmacology*; D012333:RNA, Messenger / Q000032:analysis; D011994:Recombinant Proteins; D012264:Ribonucleotide Reductases / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000187:drug effects
chemical_list: D000077190:Interferon alpha-2; D016898:Interferon-alpha; D012333:RNA, Messenger; D011994:Recombinant Proteins; D012264:Ribonucleotide Reductases; D006918:Hydroxyurea