Further elucidation of mechanism of resistance to vincristine in myeloid cells: role of hypochlorous acid in degradation of vincristine by myeloperoxidase
U. Ozgen et al., Further elucidation of mechanism of resistance to vincristine in myeloid cells: role of hypochlorous acid in degradation of vincristine by myeloperoxidase, LEUKEMIA, 14(1), 2000, pp. 47-51
Inherent resistance of myeloblasts to vincristine (VCR) has been related to
the activity of myeloperoxidase (MPO) which can degrade VCR in the presenc
e of hydrogen peroxide (H2O2). We investigated the relationship between VCR
degradation and hypochlorous acid (HOCI) generation from the reaction of H
2O2 with chlorine (CI) as catalyzed by MPG. A cell-free system, three human
leukemia cell lines (CEM/CCRF, HL-60, U937) and 15 bone marrow samples fro
m children with acute myeloid leukemia (AML) were studied. VCR cytotoxicity
was evaluated by MTT assay and by quantitative measurement of apoptosis. I
n vitro levels of VCR in cell-free systems were measured by high performanc
e liquid chromatography (HPLC), and intracellular HOCI levels by oxidation
of 5-thio-2-nitrobenzoic acid with the accompanying decrease in the absorbe
ncy at 412 nm. VCR was degraded by increasing concentrations of HOCI in cel
l-free systems and this activity was inhibited by taurine, which is known t
o block HOCI activity. This finding was confirmed by the VCR cytotoxicity s
tudies on cell lines. The HOCI-producing myeloblasts from patients were res
istant to VCR. In five samples out of eight HOCI was also detected extracel
lularly. These results suggest that oxidation by HOCI may be the final step
in VCR degradation catalyzed by MPO through its action on intracellular H2
O2 and CI.