ACUTE MONOCYTIC LEUKEMIA - A MYELOID-LEUKEMIA SUBSET THAT MAY BE SENSITIVE TO METHOTREXATE

Impaired polyglutamylation of methotrexate (MTX) and thus poor retenti on is believed to be the basis of intrinsic resistance in blasts from patients with acute myeloid leukemia (AML) to MTX. We studied addition al samples from patients with this disease, and confirmed that polyglu tamylation of MTX was poor in ANLL blast cells. However, in one subset of ANLL, acute monocytic leukemia, (M5) leukemia blasts were found to be capable of accumulating and forming long-chain MTX polyglutamates. An acute monocytic leukemia cell line, THP-1 also was found to accumu late high levels of MTX polyglutamates and was relatively sensitive to MTX, strengthening the concept that M5 blasts may be sensitive to thi s drug. MTX may be an overlooked drug for the treatment of acute monoc ytic leukemia.