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Background: 3-Aminopyridine-2-carboxaldehydethiosemicarbazone (3-AP) is a novel small molecule ribonucleotide reductase (RR) inhibitor which is more potent than hydroxyurea, the prototype of RR inhibitors. 3-AP enhances the cellular uptake and DNA incorporation of gemcitabine in tumor cell lines. We evaluated the combination of 3-AP plus gemcitabine in advanced biliary tract adenocarcinoma. Methods: Thirty-three patients with advanced adenocarcinoma of the gall bladder or biliary tract received gemcitabine (1,000 mg/m on days 1, 8, and 15 every 28 days) 1 h after completing a 4-h infusion of 3-AP given at a dose of 105 mg/m in patients with normal liver function (stratum A) or 80 mg/m if abnormal liver function (stratum B). The trial was designed to determine whether the response rate was at least 30% in stratum A and 20% in stratum B. Results: Objective response occurred in 3 of 23 patients (13%, 95% confidence intervals [CI] 3, 34%) with normal liver function, and in 0 of 10 patients with abnormal liver function. The most common grade 3-4 adverse events in all patients included neutropenia (42%), infection (33%), thrombocytopenia (27%), anemia (18%), and fatigue (15%). Fine needle aspiration of tumor samples obtained before and 24 h after 3-AP therapy showed increased R2 mRNA expression by in situ RT-PCR, suggesting RR inhibition. Conclusions: Despite evidence for RR inhibition in vivo, the 3-AP plus gemcitabine combination is not likely to be associated with a response rate exceeding 30% in patients with adenocarcinoma of the biliary tract. [ABSTRACT FROM AUTHOR]