Cellular and molecular mechanisms of the bone marrow sparing effects of the
glucose chloroethylnitrosourea chlorozotocin
P Byrne, K Tew, J Jemionek, T MacVittie, L Erickson and P Schein
1,(2-Chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) and other
chloroethylnitrosourea anticancer agents in clinical use produce severe and
cumulative bone marrow toxicity. Chlorozotocin, a glucose analogue, has
demonstrated reduced hematologic toxicity while retaining full antitumor
activity. The biochemical-pharmacologic properties of chlorozotocin and
CCNU were compared in human bone marrow. After a 2-hr incubation with a
0.1-mM drug concentration, total cellular uptake of chlorozotocin in whole
marrow was 2.47 +/- 0.80 pmole/10(4) cells and was not significantly
different compared to the uptake of 1.94 +/- 0.53 pmole/10(4) cells with
CCNU. The quantitative alkylation of bone marrow DNA by chlorozotocin, 22.8
+/- 1.2 pmole/mg DNA, was equivalent to that produced by CCNU, 22.9 +/- 0.5
pmole/mg DNA. Bone marrow was separated into 14 fractions by centrifugal
elutriation. CCNU uptake was found to be greater than that of chlorozotocin
in 3 fractions that were primarily composed of lymphocytes, monocytes, and
normoblasts. Chlorozotocin uptake was greater than CCNU in 6 fractions that
contained primarily mature and immature myeloid cells as well as the
highest CFU-GM activity. The two drugs produced a comparable degree of DNA
strand breakage and DNA-protein cross-linking as measured by alkaline
elution of pooled fractions of elutriated bone marrow. DNA interstrand
crosslinking was not found with either drug. The most significant finding
of this study is the differences in the site of drug alkylation by
chlorozotocin and CCNU in bone marrow chromatin. Endonuclease digestions
with MCN, DNase I, and DNase II showed nonrandom alkylation of specific
regions of chromatin by the two drugs: CCNU demonstrated a preferential
binding to the transcriptionally active regions of chromatin, whereas
chlorozotocin predominantly alkylated the transcriptionally inactive
regions. These data suggest that the lethal damage of nitrosourea
alkylation in human bone marrow is principally expressed in
transcriptionally active regions of chromatin.
Volume 63,
Issue 4,
pp. 759-767,
04/01/1984
Copyright © 1984 by The American Society of Hematology
