3 research outputs found
Dynamics of antifolate transport via the reduced folate carrier and the membrane folate receptor in murine leukaemia cells in vitro and in vivo
Murine L1210 leukaemia cells expressing
either the reduced folate carrier (RFC) or the membrane
folate receptor (MFR) were studied in vitro and in vivo to
assess the dynamics of membrane transport of two categories
antifolates; folate-based inhibitors of dihydrofolate
reductase (methotrexate, edatrexate, aminopterin, PT523,
and PT644) and thymidylate synthase (TS) [CB3717, raltitrexed,
plevitrexed (BGC9331), pemetrexed and
GW1843]. The potency of in situ inhibition of TS was used
as an endpoint to analyze the in vitro dynamics of RFC/
MFR-membrane transport of these antifolates. Both for
L1210-RFC and L1210-MFR cells, the potency of in situ
TS inhibition was closely correlated with increasing aYnities
of these transporters for the antifolates (r = 0.64,
P < 0.05 and r = ¡0.65, P < 0.05, respectively). Within the
group of antifolates for which MFR had a low binding
aYnity, those that had the ability to become polyglutamylated,
were more potent inhibitors of TS in situ activity than
non-polyglutamatable antifolates. In vivo activity of methotrexate,
edatrexate, raltitrexed and pemetrexed was
assessed in L1210-RFC and L1210-MFR bearing mice that
were fed either a standard or a folate-deWcient chow. Dietary
folate depletion signiWcantly reduced the MTD for
methotrexate (sevenfold), edatrexate (sevenfold), raltitrexed
(50-fold) and pemetrexed (150-fold). Based on
increased life spans, antitumor eVects of methotrexate and
edatrexate were markedly better in L1210-RFC bearing
mice on the folate-deWcient chow (ILS: 455 and 544%,
respectively) than on standard chow (ILS: 213 and 263%,
respectively). No therapeutic eVects of methotrexate and
edatrexate were observed for L1210-MFR bearing mice on
either chow condition, which may be consistent with the
low binding aYnity for MFR. Irrespective of the folate diet
status, pemetrexed and raltitrexed were inactive against
both L1210-RFC and L1210-MFR bearing mice, which
may be due to high circulating plasma thymidine levels.
Collectively, this study underscores that modulation of dietary
folate status can provide a basis within which the therapeutic
eVect of antifolates may be further improved
Dynamics of antifolate transport via the reduced folate carrier and the membrane folate receptor in murine leukaemia cells in vitro and in vivo
Effect of dexamethasone on the antileukemic effect of cytarabine: role of deoxycytidine kinase
Dexamethasone (DEX) is often used in the initial treatment of leukemia. Earlier we demonstrated that DEX decreased the activity of deoxycytidine kinase (dCK) which is essential for the activation of cytarabine (ara-C). Therefore we investigated the effect of DEX on the in vivo sensitivity of acute myeloid leukemia (AML) to ara-C and another deoxycytidine analog, gemcitabine, in the Brown Norway Myeloid Leukemia (BNML) rat model for AML, and its ara-C resistant variant B-araC, in relation to the effects on dCK activity. The antileukemic effect was evaluated as survival of the rats, while dCK activity was measured in leukemic spleen (completely consisting of BNML cells) with liver as representative normal tissue, 24 hr after treatment with ara-C or DEX with radioactive deoxycytidine (CdR) as a substrate. Treatment with ara-C increased life-span of BNML by 200%, which was not affected by DEX. Gemcitabine was ineffective. In the liver of BNML bearing rats DEX decreased dCK activity 33%, while ara-C increased dCK activity slightly (to 129%), but in the combination of ara-C/DEX dCK activity was also decreased. In the livers of Bara-C bearing rats dCK was 2.7-fold higher compared to BNML rats, which was increased 179% in the gemcitabine-DEX treated rats. In BNML leukemic spleens DEX decreased dCK activity 41% and gem/dex 46%, but ara-C increased dCK activity to 123%, but in the combination this effect was neutralized. In Bara-C spleens only ara-C/dex decreased dCK activity (32%). In conclusion; in an AML rat model DEX did not affect the antileukemic effect of ara-C, nor the dCK activity