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PubMed1982

The metabolism of 5-methyltetrahydropteroyl-L-glutamic acid and its oxidation products in the rat.

Folate metabolism in the rat was investigated using radiolabelled 5-methyltetrahydropteroylglutamate (5-CH3-H4PteGlu) and its oxidation products. 5-CH3-H4PteGlu is absorbed completely from the intestine, although in some preparations it is an equimolecular mixture of C-6 epimers, only one of which is naturally present in biological systems. The methyl group is incorporated into non-folate compounds, including methionine and creatine. No evidence was observed for the oxidation of the methyl group of 5-CH3-H4PteGlu to form other folate types. The tetrahydrofolate moiety of 5-CH3-H4PteGlu is metabolized in a similar manner to folic acid, forming formyl folates and tissue polyglutamates, and is catabolized by scission. The triazine oxidation product of 5-CH3-H4PteGlu is not metabolized by the rat or its gut microflora. 5-Methyl-5,6-dihydropteroylglutamate, however, is assimilated into the folate pool, but is substantially broken down by passage through the gut. The possible implication of this in scorbutic diets is discussed.

Animals↗
PubMed1995

Mechanisms of acquired resistance to the quinazoline thymidylate synthase inhibitor ZD1694 (Tomudex) in one mouse and three human cell lines.

Four cell lines, the mouse L1210 leukaemia, the human W1L2 lymphoblastoid and two human ovarian (CH1 and 41M) cell lines, were made resistant to ZD1694 (Tomudex) by continual exposure to incremental doses of the drug. A 500-fold increase in thymidylate synthase (TS) activity is the primary mechanism of resistance to ZD1694 in the W1L2:RD1694 cell line, which is consequently highly cross-resistant to other folate-based TS inhibitors, including BW1843U89, LY231514 and AG337, but sensitive to antifolates with other enzyme targets. The CH1:RD1694 cell line is 14-fold resistant to ZD1694, largely accounted for by the 4.2-fold increase in TS activity. Cross-resistance was observed to other TS inhibitors, including 5-fluorodeoxyuridine (FdUrd). 41M:RD1694 cells, when exposed to 0.1 microM [3H]ZD1694, accumulated approximately 20-fold less 3H-labelled material over 24 h than the parental line. Data are consistent with this being the result of impaired transport of the drug via the reduced folate/methotrexate carrier. Resistance was therefore observed to methotrexate but not to CB3717, a compound known to use this transport mechanism poorly. The mouse L1210:RD1694 cell line does not accumulate ZD1694 or Methotrexate (MTX) polyglutamates. Folylpolyglutamate synthetase substrate activity (using ZD1694 as the substrate) was decreased to approximately 13% of that observed in the parental line. Cross-resistance was found to those compounds known to be active through polyglutamation.

Animals↗
PubMed2000

Accessory tubules and axonemal microtubules of Apis mellifera sperm flagellum differ in their tubulin isoform content.

In the insect sperm flagellum, an extra set of nine additional microtubules, named accessory tubules, is present surrounding the axoneme. Using a sarcosyl/urea extraction, we were able to fractionate the microtubular cytoskeleton of the sperm flagellum of the insect Apis mellifera resulting in the dissociation of the axonemal microtubule protein components and the accessory tubules. This has allowed us to compare the tubulin isoform content of axonemal microtubules and accessory tubules by immunoelectron microscopy and immunoblotting using a panel of monoclonal antibodies directed against different tubulin post-translational modifications (PTMs). All the PTMs occurring in axonemal tubulin are also present in accessory tubules, which indicates the close relativeness of accessory tubules to axonemal rather than to cytoplasmic microtubules. However, our results demonstrate the presence of significant differences in the tubulin isoform content of axonemal microtubules and accessory tubules. First, the tubulin tyrosination extent of accessory tubules is far lower than that of axonemal microtubules, thus confirming at the molecular level their morphogenetic origin as outgrowths from the B-subtubule of each microtubular doublet. Second, although polyglycylation seems to occurr at the same extent in both microtubular systems, alpha-tubulin exhibits a larger amount of monoglycylated sites in axonemal microtubules than in accessory tubules. Third, a greater amount of beta-tubulin molecules is glutamylated in axonemal microtubules than in accessory tubules. Moreover, highly acidic isoforms, likely molecules with longer polyglutamate side chains, are present only in axonemal microtubules. Taken together, our data are indicative of a higher level of tubulin heterogeneity in axonemal microtubules than in accessory tubules. They also show a segregation of post-translationally modified isoforms between accessory tubules and axonemal microtubules and suggest the implication of PTMs in the functional specialization of the two microtubular systems.

Acetylation↗
PubMed1983

Methotrexate metabolism by bone marrow cells from patients with leukemia.

Bone marrow cells from children with leukemia in remission and lymphoblasts and myeloblasts from children with early and late-stage leukemia all accumulated methotrexate during short-term culture and converted it to poly-gamma-glutamyl derivatives. This metabolism was time and dose-dependent. Leukemia cells from two patients with chronic myelocytic leukemia also synthesized methotrexate polyglutamates. Patients varied one from another in the quantity of total non-exchangeable methotrexate and methotrexate polyglutamates present in cells, but highest levels of each of these were seen in late acute lymphoblastic leukemia and in acute myeloblastic leukemia. Co-incubation of leukemic cells with both methotrexate and a ten-fold excess of folinic acid decreased accumulation and polyglutamylation of methotrexate to the same extent as achieved by reducing methotrexate concentration ten-fold. Co-incubation with methotrexate and a ten-fold excess of vincristine did not increase total cell methotrexate and methotrexate polyglutamates in leukemic cells in culture. Such an increase had been anticipated from earlier studies with other cells. Indeed, levels of methotrexate and its derivatives were modestly reduced.

Bone Marrow↗
PubMed1985

Turnover of the methyl moiety of 5-methyltetrahydropteroylglutamic acid in the cobalamin-inactivated rat.

The metabolism of the methyl group of 5-methyltetrahydrofolate was studied in rats in which cobalamin had been inactivated by exposure to nitrous oxide and in air-breathing control animals. Methylfolate labeled with [14C] in the methyl group and with [3H] in the pteridine-PABA portion was injected and the disappearance of [14C]H3- relative to [3H]folate was measured in liver. The half-time of the methyl group in the livers of control rats was two hours. There was no turnover of the methyl group for the first 72 hours after cobalamin inactivation. After 72 hours, there was a slow turnover of the methyl group, with a half-time of 43 hours. In control rats, it is assumed that the methyl group was metabolized by transfer to homocysteine to form methionine. In cobalamin-inactivated rats, it was shown that methylfolate was used as the substrate for forming folate polyglutamate, and analogues with 3, 4, and 5 glutamic acid residues were present. It is likely that oxidation of the methyl group by methylene tetrahydrofolate reductase occurs from folate polyglutamate containing six and seven glutamic acid residues, (Brody et al, Biochemistry 21: 276, 1982), since we were unable to demonstrate labeled methyl in longer chain analogues.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗
PubMed1986

Methotrexate analogues. 29. Effect of gamma-aminobutyric acid spacers between the pteroyl and glutamate moieties on enzyme binding and cell growth inhibition.

A series of "stretched" methotrexate (MTX) analogues containing up to five 4-aminobutyryl (Gab) spacers between the 4-amino-4-deoxy-N10-methylpteroyl (MeAPA) moiety and the glutamate (Glu) side chain was prepared. Interest in these compounds stemmed from their relationship to MTX gamma-polyglutamates, from which they differ only in lacking "internal" alpha-carboxyl groups. The ability of the MeAPA-Gabn-Glu derivatives to inhibit dihydrofolate reductase (DHFR) and thymidylate synthase (TS) in vitro and to inhibit the growth of tumor cells in culture was evaluated. The IC50 for DHFR inhibition increased progressively from 0.082 to 0.84 microM as the number of Gab spacers was varied from one to five. At the same time the introduction of Gab spacers was found to produce substantial TS inhibition (Ki 0.1-0.4 microM) similar to that reported for MTX polyglutamates. Despite the activity of the MeAPA-Gabn-Glu derivatives as combined inhibitors of TS and DHFR, there was a steep loss of cell growth inhibitory potency as the number of Gab spacers was increased. This most likely reflects low cell uptake and the fact that when n greater than 1 there is almost total abolition of substrate activity for folylpolyglutamate synthetase, which had previously been observed with n = 1.

Animals↗
PubMed1984

Mechanisms of folate homeostasis.

Recent work has provided information that allows the delineation of the mechanisms by which folate homeostasis is maintained. Dietary folates are converted to monoglutamates in the gut, absorbed by an active process, and distributed to tissues by the enterohepatic cycle, possibly utilizing folic acid binding proteins. During short periods of dietary deprivation, supply is maintained in the monoglutamate pools in the enterohepatic cycle as well as within cells. A net increase in available folate results from a decrease in tissue uptake and in subsequent polyglutamate synthesis, coupled with a fixed rate of conversion of polyglutamate to monoglutamate and release from the cell. The liver exerts substantial regulatory effect because of its mass, relatively rapid folate turnover, and the large folate flux through the enterohepatic cycle. In addition, there is a substantial, if more long-term, contribution from tissues that die and release folates (e.g., red blood cells), and a pathway exists that is capable of salvaging this folate and returning it to the liver for subsequent redistribution to actively proliferating cells.

Folic Acid↗
PubMed1996

The role of dietary folate in modulation of folate receptor expression, folylpolyglutamate synthetase activity and the efficacy and toxicity of lometrexol.

We have studied the molecular effects of a LFD in a murine model in order to better define the biochemical changes associated with folate deficiency. In addition, we have demonstrated the effect of a LFD on the pharmacokinetic profile and therapeutic activity and toxicity of lometrexol. These studies showed increased density of FR in tumors implanted in LFD mice and a decrease in the affinity of these receptors for folic acid. The results suggest that tumors can compensate for low folate bioavailability by up-regulation of a second FR with slightly lower affinity for folic acid. The higher density of this FR would provide greater capacity for garnering serum folate. FPGS activity increased in several tumors and liver and kidney of LFD mice. The increase in this enzyme activity would result in enhanced polyglutamation of folates and classical antifolates and thus increased cellular retention. Consistent with these changes in liver FPGS, mice injected i.v. with a single dose of lometrexol accumulated significantly more drug in liver and tumors of LFD animals compared to SD mice. Also, higher liver concentrations of lometrexol persisted longer in LFD mice. Polyglutamate analysis showed that longer polyglutamate forms appeared earlier in liver of LFD mice. After 7 days, longer polyglutamyl forms were recovered from liver of LFD mice (octa- and hepta-glutamyl lometrexol) compared to those on SD. A comparison of the efficacy and toxicity of lometrexol in C3H mammary tumor-bearing mice showed that in mice on LFD, lometrexol treatment produced a delayed toxicity with an LD50 of 0.1-0.3 mg/kg, a 3000-fold increase in lethality compared to SD mice. Supplementation of mice with folic acid restored anti-tumor activity and increased the therapeutic dose-range over which efficacy could be assessed. These studies support the use of folic acid supplementation for cancer patients treated with antifolate therapy in order to prevent the biochemical changes in FR and FPGS associated with folate deficiency, prevent delayed toxicity to GARFT inhibitors and enhance the therapeutic potential of this class of drugs.

Acyltransferases↗
PubMed1995

Insulin-dependent suppression in glutamyl hydrolase activity and elevated cellular methotrexate polyglutamates.

Folates and antifolates are converted to polyglutamates, which are better retained in cells and may also bind more tightly to cellular proteins than the parent compounds. The regulation of the process of polyglutamate formation and breakdown is not fully clarified yet and is being studied by a number of approaches. An early observation concerning the potential regulation of polyglutamate formation was that insulin caused a marked increase in the rate and accumulation of polyglutamates of methotrexate (MTX) in rat hepatoma cells. The present study demonstrated that insulin caused a decrease in the activity of gamma-glutamyl hydrolase (GH), the enzyme that degrades polyglutamates, that was inversely commensurate with the increase in the synthesis of MTX polyglutamates. The effects of insulin on GH activity with regard to concentration, time of onset, and the effect of N6, O2' dibutyryl cAMP and theophylline were consistent with the reduction in GH being responsible for the increase in cellular MTX polyglutamate accumulation. Insulin addition also led to an increase in folate polyglutamates. The insulin effects were also seen with H35D cells, a subline with enhanced glutamyl hydrolase activity as a result of having been made resistant to 5, 10-dideazatetrahydrofolic acid. When H35 cells with insulin were compared with H35D cells lacking insulin, there was an 8-fold increase in GH and a 44-fold decrease in the number of gamma-glutamate residues added to MTX.

Animals↗
PubMed1997

LY231514, a pyrrolo[2,3-d]pyrimidine-based antifolate that inhibits multiple folate-requiring enzymes.

N-[4-[2-(2-amino-3,4-dihydro-4-oxo-7H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl ]-benzoyl]-L-glutamic acid (LY231514) is a novel pyrrolo[2,3-d]pyrimidine-based antifolate currently undergoing extensive Phase II clinical trials. Previous studies have established that LY231514 and its synthetic gamma-polyglutamates (glu3 and glu5) exert potent inhibition against thymidylate synthase (TS). We now report that LY231514 and its polyglutamates also markedly inhibit other key folate-requiring enzymes, including dihydrofolate reductase (DHFR) and glycinamide ribonucleotide formyltransferase (GARFT). For example, the Ki values of the pentaglutamate of LY231514 are 1.3, 7.2, and 65 nM for inhibition against TS, DHFR, and GARFT, respectively. In contrast, although a similar high level of inhibitory potency was observed for the parent monoglutamate against DHFR (7.0 nM), the inhibition constants (Ki) for the parent monoglutamate are significantly weaker for TS (109 nM) and GARFT (9,300 nM). The effects of LY231514 and its polyglutamates on aminoimidazole carboxamide ribonucleotide formyltransferase, 5,10-methylenetetrahydrofolate dehydrogenase, and 10-formyltetrahydrofolate synthetase were also evaluated. The end product reversal studies conducted in human cell lines further support the concept that multiple enzyme-inhibitory mechanisms are involved in cytotoxicity. The reversal pattern of LY231514 suggests that although TS may be a major site of action for LY231514 at concentrations near the IC50, higher concentrations can lead to inhibition of DHFR and/or other enzymes along the purine de novo pathway. Studies with mutant cell lines demonstrated that LY231514 requires polyglutamation and transport via the reduced folate carrier for cytotoxic potency. Therefore, our data suggest that LY231514 is a novel classical antifolate, the antitumor activity of which may result from simultaneous and multiple inhibition of several key folate-requiring enzymes via its polyglutamated metabolites.

5,10-Methylenetetrahydrofolate Reductase (FADH2)↗
PubMed1988

Identification of the second chromophore of Escherichia coli and yeast DNA photolyases as 5,10-methenyltetrahydrofolate.

Denaturation of DNA photolyase (deoxyribodipyrimidine photolyase, EC 4.1.99.3) from Escherichia coli with guanidine hydrochloride or acidification to pH 2 released, in addition to FAD, a chromophore with the spectral and chromatographic properties of a reduced pterin. Treatment of the enzyme with iodine prior to acidification converted the chromophore to a stable, oxidized derivative, which was resolved by HPLC into four species with identical spectral properties. The same species, in the same distribution, were obtained from the yeast enzyme. The material isolated from the iodine-oxidized enzyme was shown to be a pterin by conversion to pterin-6-carboxylic acid with alkaline permanganate and was found to release glutamate upon acid hydrolysis. The presence of 10-formylfolate in the isolated, oxidized chromophore was demonstrated by absorption and fluorescence spectroscopy and by deformylation and conversion to folic acid. Analysis of the distribution of polyglutamates revealed that the four species identified by HPLC corresponded to the tri-, tetra-, penta-, and hexaglutamate derivatives of 10-formylfolate. The results were consistent with gamma linkages in the triglutamate derivative with additional glutamates linked via the alpha-carboxyl group of the preceding residue. Treatment with rat plasma hydrolase produced the monoglutamate derivative of 10-formylfolate. The native, enzyme-bound form of the folate cofactor was identified as 5,10-methenyltetrahydrofolylpolyglutamate by effecting release and isolation at low pH to protect the 5,10-methenyl bridge and preserve the reduced pyrazine ring structure.

Bacterial Proteins↗
PubMed1987

Folate and methotrexate polyglutamate tissue levels in rhesus monkeys following chronic low-dose methotrexate.

Methotrexate (MTX), a mainstay in the treatment of acute lymphoblastic leukemia, is associated with both hepatic and neurologic toxicity. Like a folate, MTX is metabolized to polyglutamated derivatives (MTXGlun) with long intracellular half-lives. These metabolites may contribute to MTX toxicity through a direct effect on cellular metabolism or indirectly through a perturbation of folate homeostasis. To better define the effects of chronic MTX treatment, tissue levels of MTX, MTXGlun, and folate were measured in three monkeys treated with weekly intramuscular MTX for 1 year. Greater than 80% of the total tissue MTX found was in the form of polyglutamated derivatives. Most of these derivatives were MTXGlu3-5 but Glu6-7 were easily detectable. Total tissue folates were measured in liver, kidney, brain and testis with MTX treated animals having a 90% loss of total folate in brain tissue. This is of special interest since inborn errors of folate metabolism are often associated with severe neurologic abnormalities.

Animals↗
PubMed1988

Cytotoxicity, uptake, polyglutamate formation, and antileukemic effects of 8-deaza analogues of methotrexate and aminopterin in mice.

In contrast to methotrexate (MTX) and aminopterin (AMT), the 8-deaza analogues of these antifolates are not substrates for rabbit liver aldehyde oxidase. Since they are not converted to 7-hydroxy derivatives, they have been investigated with regard to their cytotoxicity for CCRF-CEM cells, transport into these cells, and conversion to polyglutamate forms. For this purpose 3H-labeled analogues were synthesized. The drug concentrations of the analogues required to inhibit cell growth by 50% are significantly lower than for the parent compounds particularly for a short exposure of cells to the drug. Vmax and Km for unidirectional influx do not differ greatly among the four drugs, but amounts of uptake over 1 h are markedly different and increase in the order MTX less than 8-deazaMTX less than AMT less than 8-deazaAMT. During 1 h of uptake a much greater proportion of the 8-deaza analogues is converted to polyglutamate forms than in the case of parent drugs. Only 52% of MTX is converted to polyglutamates, whereas in the case of the other three compounds the conversion is greater than or equal to 90%. However, MTX is relatively efficient in adding two glutamate residues, whereas the other drugs predominantly accumulate as forms with only one additional glutamate (+Glu1). During 1 h of efflux the drugs without additional glutamates decrease to low concentrations and there is also a major loss of +Glu1 form, but there is also an increase in longer chain forms, especially in the case of MTX. The net result is a still greater disparity in total intracellular levels of the four drugs after the period of efflux. MTX has much lower toxicity in mice in vivo than the other three compounds, 8-deazaAMT being the most toxic. At the maximum tolerated dose MTX produced a considerably greater increase in life span for mice bearing P388 than any of the other drugs, and a somewhat greater increase for mice bearing L1210. Thus the 8-deaza analogues do not offer a therapeutic advantage over MTX against leukemias in the mouse, primarily due to their much greater toxicity.

Aminopterin↗
PubMed1988

Synthesis and biological evaluation of poly-gamma-glutamyl metabolites of 10-deazaaminopterin and 10-ethyl-10-deazaaminopterin.

The chemical synthesis of a series of poly-gamma-glutamyl metabolites of the experimental anticancer drugs 10-deazaaminopterin (10-DAAM) and 10-ethyl-10-deazaaminopterin (10-EDAAM) has been carried out by the solid-phase procedure. The synthetic products were identical with the poly-gamma-glutamyl metabolites of radiolabeled 10-DAAM and 10-EDAAM produced by normal mouse tissues with regard to elution volume from [(diethylamino)ethyl]cellulose columns and susceptibility to hydrolysis by human plasma folylpolyglutamate hydrolase. Poly-gamma-glutamyl metabolites with a glutamate chain length of up to four glutamate residues were detected in the tissues. The antifolate activity was evaluated with methotrexate (MTX) sensitive and MTX-resistant strains of Lactobacillus casei and Streptococcus faecium. In general, inhibitory potency decreases with increasing Glu chain length. However there are two exceptions. Addition of one Glu residue to 10-DAAM enhances its potency for MTX-resistant L. casei and addition of one Glu residue to 10-EDAAM enhances its potency for the MTX-sensitive L. casei. As shown earlier for MTX polyglutamates, polyglutamylation greatly enhances the inhibitory potency of 10-DAAM and 10-EDAAM for L. casei thymidylate synthase. MTX polyglutamates are 15-30 times more inhibitory than the corresponding 10-DAAM derivatives and 30-60 times more inhibitory than the corresponding 10-EDAAM derivatives. Polyglutamylation of 10-DAAM had little influence on its ability to inhibit L. casei dihydrofolate reductase; however, with 10-EDAAM, addition of one or two Glu residues enhanced its inhibitory potency 2.3-fold.

Aminopterin↗
PubMed2001

Marked suppression of the activity of some, but not all, antifolate compounds by augmentation of folate cofactor pools within tumor cells.

Folates have been co-administered with some antifolates to diminish host toxicity; however, the extent to which this will reduce antitumor activity is not known. To further clarify this issue, studies were undertaken to characterize and quantitate the impact of alterations in intracellular folate levels on the activities of a variety of antifolates in L1210 murine leukemia cells. Intracellular folate cofactor levels increased almost in proportion to the increase in extracellular 5-formyltetrahydrofolate (5-CHO-THF) over a concentration range that encompassed physiological levels of 5-methyltetrahydrofolate. This resulted in a spectrum of increases in the ic50 values of antifolates upon continuous exposure to drugs [Lometrexol (DDATHF) (70x) > trimetrexate (TMQ) (30x), multitargeted antifolate, LY231514 (ALIMTA) (30x) > Raltitrexed, Tomudex (ZD1694) (10x), 6R-2',5'-thienyl-5,10-dideazatetrahydrofolic acid (LY309887) (10x) > methotrexate (MTX) (6x) > (2S)-2-[o-fluoro-p-[N-(2,7-dimethyl-4-oxo-3,4-dihydroquinazolin-6-ylmethyl)-N-(prop-2-ynyl)amino]benzamido]-4-(tetrazol-5-yl) butyric acid (ZD9331) (3x), N(alpha)-(4-amino-4-deoxypteroyl)-N(delta)-hemiphthaloyl-l-ornithine (PT523) (3x)]. Upon a 4-hr pulse exposure to drug, the ic50 values for DDATHF and ALIMTA were increased > 180- and 5-fold, respectively, with only a 2.5-fold increase in the extracellular 5-CHO-THF level within the physiological range. The reductions in drug sensitivities could be attributed to decreases in accumulation of polyglutamate derivatives of ALIMTA and DDATHF. Hence, in these studies, natural folates diminished the activity of agents that undergo polyglutamation by suppression of the formation of these active congeners at the level of folylpolyglutamate synthetase. For inhibitors of dihydrofolate reductase, the suppressive effect of endogenous folates appears to be due to competition between the antifolate and dihydrofolate at the level of the target enzyme. These data should be carefully considered in the design of regimens with antifolates, which incorporate co-administration of folates.

Animals↗
PubMed1986

Enhancement of methotrexate cytotoxicity towards the MDA.MB.436 human breast cancer cell line by dipyridamole. The role of methotrexate polyglutamates.

MTX and dipyridamole are synergistic in their toxicity towards the MDA.MB.436 human breast cancer cell line. Dipyridamole increases net MTX uptake into the cells and increases the intracellular levels of MTXG7 to G10, the highest molecular weight polyglutamyl derivatives of MTX detected. During a recovery period, after completion of exposure to MTX with and without dipyridamole, levels of MTXG7 to G10 remained elevated in dipyridamole treated cells by comparison with controls. Dipyridamole, which has no intrinsic effect on cell growth, transforms a cytostatic response of MDA.MB.436 cells towards MTX into a cytotoxic response. The effect of dipyridamole is not mediated through an increase in prostacyclin biosynthesis.

Arachidonic Acid↗
PubMed1993

Reduction in microtubule dynamics in vitro by brain microtubule-associated proteins and by a microtubule-associated protein-2 second repeated sequence analogue.

Microtubule-associated protein (MAP) binding to assembled microtubules (MTs) can be reduced by the addition of polyglutamate without significant MT depolymerization or interference with MT elongation reactions. Ensuing polymer length redistribution in MAP-depleted MTs occurs on a time scale characteristic of that observed with MAP-free MTs. The redistribution phase occurs even in the absence of mechanical shearing and without appreciable effects from end-to-end annealing, as indicated by the time course of incremental changes in polymer length and MT number concentration. We also observed higher rates of MT length redistribution when the [MAP]/[tubulin] ratio was decreased. Together, these results demonstrate that MT length redistribution rates are greatly influenced by MAP content, and the data are compatible with the dynamic instability model. We also found that a peptide analogue corresponding to the second repeated sequence in the MT-binding region of MAP-2 can also markedly retard MT length redistribution kinetics, a finding that accords with the ability of this peptide to promote tubulin polymerization in the absence of MAPs and to displace MAP-2 from MTs. These results provide further evidence that MAPs can modulate MT assembly/disassembly dynamics and that peptide analogues can mimic the action of intact MAPs without the need for three contiguous repeated sequences in the MT-binding region.

Amino Acid Sequence↗
PubMed2005

Folate pathway gene expression differs in subtypes of acute lymphoblastic leukemia and influences methotrexate pharmacodynamics.

The ability of leukemia cells to accumulate methotrexate polyglutamate (MTXPG) is an important determinant of the antileukemic effects of methotrexate (MTX). We measured in vivo MTXPG accumulation in leukemia cells from 101 children with acute lymphoblastic leukemia (ALL) and established that B-lineage ALL with either TEL-AML1 or E2A-PBX1 gene fusion, or T-lineage ALL, accumulates significantly lower MTXPG compared with B-lineage ALL without these genetic abnormalities or compared with hyperdiploid (fewer than 50 chromosomes) ALL. To elucidate mechanisms underlying these differences in MTXPG accumulation, we used oligonucleotide microarrays to analyze expression of 32 folate pathway genes in diagnostic leukemia cells from 197 children. This revealed ALL subtype-specific patterns of folate pathway gene expression that were significantly related to MTXPG accumulation. We found significantly lower expression of the reduced folate carrier (SLC19A1, an MTX uptake transporter) in E2A-PBX1 ALL, significantly higher expression of breast cancer resistance protein (ABCG2, an MTX efflux transporter) in TEL-AML1 ALL, and lower expression of FPGS (which catalyzes formation of MTXPG) in T-lineage ALL, consistent with lower MTXPG accumulation in these ALL subtypes. These findings reveal distinct mechanisms of subtype-specific differences in MTXPG accumulation and point to new strategies to overcome these potential causes of treatment failure in childhood ALL.

Cluster Analysis↗