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

Scott Wadler, Robert Horowitz, Jie Rao, Xun Mao, Kathie Schlesinger, Edward L. Schwartz

Research output: Contribution to journalArticle

15 Scopus citations


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 μM to 215 μM (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 μM) 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.

Original languageEnglish (US)
Pages (from-to)522-528
Number of pages7
JournalCancer Chemotherapy and Pharmacology
Issue number6
Publication statusPublished - Sep 22 1996



  • Colon cancer
  • Drug resistance
  • Hydroxyurea
  • Interferon alfa-2a
  • Ribonucleotide reductase

ASJC Scopus subject areas

  • Oncology
  • Toxicology
  • Pharmacology
  • Cancer Research
  • Pharmacology (medical)

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