2-CHLORO-2'-DEOXYADENOSINE (CLADRIBINE) AND ITS ANALOGS ARE GOOD SUBSTRATES AND POTENT SELECTIVE INHIBITORS OF ESCHERICHIA-COLI PURINE-NUCLEOSIDE PHOSPHORYLASE
A. Bzowska et Z. Kazimierczuk, 2-CHLORO-2'-DEOXYADENOSINE (CLADRIBINE) AND ITS ANALOGS ARE GOOD SUBSTRATES AND POTENT SELECTIVE INHIBITORS OF ESCHERICHIA-COLI PURINE-NUCLEOSIDE PHOSPHORYLASE, European journal of biochemistry, 233(3), 1995, pp. 886-890
2-Chloro-2'-deoxyadenosine (CldAdo), a nucleoside that has proven usef
ul in the treatment of several chronic lymphoid malignancies, and its
analogue, 2-bromo-2'-deoxyadenosine, are both effective inhibitors of
the bacterial (Escherichia coli) purine-nucleoside phosphorylase (PNP)
, with K-i values of 4.5 mu M and 6.3 mu M, respectively. The examinat
ion of a series of base-modified analogues of CldAdo has shown that se
veral other compounds have similar inhibitor properties, and has indic
ated that y-2-chloro-9-(2'-deoxy-beta-D-ribofuranosyl)purine is the mo
st potent inhibitor with a K-i value of 0.5 mu M, competitive with res
pect to inosine (Ino). CldAdo itself and its base-modified analogues,
discounting those substituted at C(8), are also substrates for the E.
coli PNP and undergo rapid glycosidic bond cleavage. CldAdo is degrade
d with substrate efficiency, i.e. V-max/K-m similar to that observed f
or Ino (130%), although the individual kinetic constants, K-m and V-ma
x, are both approximately an order of magnitude lower than for Ino. Al
l compounds tested are totally inactive as substrates and inhibitors f
or mammalian (calf spleen) PNP and therefore constitute a new class of
potent selective, although cleavable, inhibitors of bacterial phospho
rylases. 8-Bromo-2-chloro-2'-deoxyadenosine and 8-thio-2-chloro-2'-deo
xyadenosine are the only base-modified CldAdo derivatives showing inhi
bitory activity against MOLT-3 (acute T-cell leukemia) and U-937 (hist
iocytic lymphoma) cells and, as shown in this study, are resistant to
degradation by E. coli PNP. The above-mentioned results suggest that b
oth analogues could be effective as oral cytotoxic agents that are non
cleavable by enteric bacteria.