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J Baram

Publications and source records attributed to J Baram.

9 recordsLinked to original sources
PubMed1992

[Extraskeletal Ewing's sarcoma].

5 patients diagnosed as having extraskeletal Ewing's sarcoma have been referred to our adult oncology unit since 1980. All were men, ranging in age from 18-57 (mean 32 years). The primary tumor was located on the trunk in 4 and in an extremity in 1. Wide tumor excision was feasible in only 2. 3 died within 27 months and 2 are alive, 13 and 67 months, respectively, following diagnosis. This study demonstrates the highly aggressive nature of extraskeletal Ewing's sarcoma and the need for early diagnosis and efficient chemotherapy.

Adult↗
PubMed1990

Mechanism of leucovorin reversal of methotrexate cytotoxicity in human MCF-7 breast cancer cells.

Previous studies have suggested that metabolic inhibition by methotrexate (MTX) is multifactorial and that cytotoxicity can be reversed by the reduced folate leucovorin. In this report we investigated the mechanism of leucovorin rescue in the MCF-7 human breast cancer cell line. Cells were exposed to various concentrations of MTX (0.5, 1.0, 3.0, and 10.0 microM) for 24 hr followed by rescue with labelled leucovorin (0.5 to 50 microM). The changes in the intracellular folate pools 24 hr following the addition of leucovorin were quantitated by high-pressure liquid chromatographic methods. The changes in the folate pools during rescue were compared with the ability of various concentrations of leucovorin to affect cellular rescue from MTX using a cloning assay. Our studies show that the total labelled intracellular folate pools increased in a log-linear fashion with respect to leucovorin exposure concentrations up to 100 microM. The degree of accumulation at a given leucovorin concentration was not significantly different in the absence or presence of MTX over the concentration range of 0.5 to 10 microM. Individual folate pool levels (tetrahydrofolate, 10-formyl tetrahydrofolate, 5-formyl tetrahydrofolate, 5-methyl tetrahydrofolate, and 5,10-methylene tetrahydrofolate) reached those present in cells not exposed to MTX at concentrations of leucovorin that were not adequate to rescue the MTX-treated cells. With exposure to concentrations of leucovorin capable of rescue, the individual folate pool levels were up to twelve times greater than those found in untreated cells, consistent with competition for catalytic activity at folate-dependent enzymes in addition to dihydrofolate reductase. The dihydrofolate pool also increased with increasing leucovorin concentration: but, unlike the reduced folates, this oxidized folate reached a maximal level that was dependent on the MTX concentration to which the cells had been exposed. This suggests that competition between MTX and leucovorin occurs at the level of dihydrofolate reductase via a competitive interaction with dihydrofolate in this intact cell system. The ability of leucovorin and its metabolites to compete with direct inhibitors of dihydrofolate reductase and other metabolically important folate-dependent enzymes appears to be associated with leucovorin rescue.

Breast Neoplasms↗
PubMed1990

Mechanism of thymidylate synthase inhibition by methotrexate in human neoplastic cell lines and normal human myeloid progenitor cells.

We have studied the roles of 5,10-methylenetetrahydrofolate (5,10-methylene-H4PteGlu) depletion and dihydrofolate (H2PteGlu) accumulation in the inhibition of de novo thymidylate synthesis by methotrexate (MTX) in human MCF-7 breast cancer cells. Using both a high pressure liquid chromatography system and a modification of the 5-fluoro-2'-deoxyuridine-5'-monophosphate radioenzymatic binding assay, we determined that the 5,10-methylene-H4PteGlu pool is 50-60% depleted in human MCF-7 breast cancer cells following exposure to 1 micron MTX for up to 21 h. Similar alterations in the 5,10-methylene-H4PteGlu pools were obtained when human promyelocytic HL-60 leukemia cells and normal human myeloid precursor cells were incubated with 1 micron MTX. The H2PteGlu pools within the MCF-7 cells increased significantly after 15 min of 1 micron MTX exposure, reaching maximal levels by 60 min. Thymidylate synthesis, as measured by labeled deoxyuridine incorporation into DNA, decreased to less than 20% of control activity within 30 min of 1 micron MTX exposure. The inhibition of thymidylate synthesis coincided temporally with the rapid intracellular accumulation of H2PteGlu, a known inhibitor of thymidylate synthase. Furthermore, inhibition of this pathway was associated in a log-linear fashion with the intracellular level of dihydrofolate. These studies provide further evidence that depletion of the thymidylate synthase substrate 5,10-methylene-H4PteGlu is inadequate to account completely for diminished thymidylate synthesis resulting from MTX treatment. Our findings suggest that acute inhibition of de novo thymidylate synthesis is a multifactorial process consisting of partial substrate depletion and direct enzymatic inhibition by H2PteGlu polyglutamates.

Breast Neoplasms↗
PubMed1987

Evidence for direct inhibition of de novo purine synthesis in human MCF-7 breast cells as a principal mode of metabolic inhibition by methotrexate.

We have investigated the role of dihydrofolate (H2PteGlu) accumulation in the inhibition of de novo purine synthesis by methotrexate (MTX) in human MCF-7 breast cancer cells. Previous studies have shown that cytotoxic concentrations of MTX that inhibit dihydrofolate reductase produce only minimal depletion of the reduced folate cofactor, 10-formyltetrahydrofolate, required for purine synthesis. At the same time, de novo purine synthesis is totally inhibited. In these studies, we show that 10 microM MTX causes inhibition of purine synthesis at the step of phosphoribosylaminoimidazolecarboxamide (AICAR) transformylase, as reflected in a 2-3-fold expansion of the intracellular AICAR pool. The inhibition of purine synthesis coincides with the rapid intracellular accumulation of H2PteGlu, a known inhibitor of AICAR transformylase. When the generation of H2PteGlu is blocked by pretreatment with 50 microM 5-fluorodeoxyuridine (FdUrd), an inhibitor of thymidylate synthase, MTX no longer causes inhibition of purine synthesis. Intermediate levels of H2PteGlu produced in the presence of lower (0.1-10 microM) concentrations of FdUrd led to proportional inhibition of purine biosynthesis, and the exogenous addition of H2PteGlu to breast cells in culture re-established the block in purine synthesis in the presence of FdUrd and MTX. The early phases of inhibition of purine biosynthesis could be ascribed only to H2PteGlu accumulation. MTX polyglutamates, also known to inhibit AICAR transformylase, were present in breast cells only after 6 h of incubation with the parent compounds and were not formed in cells preincubated with FdUrd. The lipid-soluble antifolate trimetrexate, which does not form polyglutamates, produced modest 10-formyltetrahydrofolate depletion, but caused marked H2PteGlu accumulation and a parallel inhibition of purine biosynthesis. This evidence leads to the conclusion that MTX and the lipid-soluble analog trimetrexate cause inhibition of purine biosynthesis through the accumulation of H2PteGlu behind the blocked dihydrofolate reductase reaction.

Acyltransferases↗
PubMed1987

Antimetabolites.

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Animals↗