A patient is described with acute myelocytic leukemia refractory to conventional therapy, who also became highly resistant to methotrexate (MTX) after repeated courses of this drug. Leukemia cells from this patient were found to contain an elevated level of dihydrofolate reductase (DHFR) activity, with no change in the affinity of the enzyme for MTX. A sensitive "dot blot" assay revealed a fourfold increase in the gene copy number of DHFR. Southern blot analysis with a human DHFR cDNA probe confirmed this increase in the gene copy number, and demonstrated a similar restriction pattern with Eco R1, Hind III, and Pst 1 as seen with a highly amplified human leukemia cell line, K562. Additional DHFR fragments were detected, not seen in the K562 blot, suggesting the presence of pseudogenes, or a result of gene rearrangements occurring as part of the amplification process. Resistance to MTX in this patient was therefore ascribed to gene amplification and overproduction of DHFR.
To determine the safety and efficacy of mitoxantrone use in hyperbilirubinemic breast cancer patients, a prospectively determined dosage schedule was evaluated in a multi-center trial. Pretreatment bilirubin prospectively defined three groups: Controls (with normal bilirubin) and two Study groups (with either moderate or severe bilirubin increase). Bilirubin determined initial mitoxantrone dose as well: bilirubin less than 3.5 mg/dl, 14 mg/m2; and bilirubin greater than or equal to 3.5 mg/dl, 8 mg/m2. Mitoxantrone at 14 mg/m2 was well tolerated in patients with moderate hepatic dysfunction. Patients with severe hepatic dysfunction demonstrated a mixed toxicity picture, with performance status (ECOG level 3) defining a population with limiting myelosuppression and/or early death. The survival of Study patients with severe hepatic dysfunction (median 17 days) was significantly worse than both Control (p less than 0.01) and Study (p less than 0.05) patients with lower bilirubin. Entry performance status (ECOG level 0-2 versus level 3) profoundly influenced survival (median survival 222 days versus 25 days, respectively, p less than 0.0001). Objective responses were seen in patients with both normal and elevated bilirubin. Bilirubin reduction following mitoxantrone commonly occurred, representing at least an indicator of favorable prognosis. Recommendations for mitoxantrone use include: 1. Patients with moderate bilirubinemia tolerate 14 mg/m2 mitoxantrone with reasonable chance for benefit. 2. Patients with severe hepatic dysfunction and poor performance status should not be given mitoxantrone. A definitive recommendation regarding use of reduced 8 mg/m2 mitoxantrone in patients with severe hyperbilirubinemia and favorable performance status requires further study.
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