Structural requirements for anion substrates of the methotrexate transport system in L1210 cells

Henderson, Gary B.; Zevely, Edward M.

doi:10.1016/0003-9861(83)90162-5

Cited by 79 publications

(61 citation statements)

References 17 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The inhibitory effects of nitrate and nitrite were even smaller (∼15%) but still significant (P , 0.01). These results are consistent with prior observations on the inhibitory effect of anions on RFC-mediated transport (Henderson and Zevely, 1983;Yang et al, 1984). However, no significant difference was observed between bisulfite and sulfate or between nitrate and nitrite, in contrast to what was observed for PCFT-mediated 5-CHO-THF influx.…”

Section: Resultssupporting

confidence: 92%

“…This is quite opposite to the high K i for folic acid and very low K i for PT523 for RFC-mediated transport (Rosowsky et al, 1998;Zhao et al, 2011a). Unlike PCFT, which is a proton-coupled process that operates optimally at low pH (Qiu et al, 2006;Nakai et al, 2007;Umapathy et al, 2007;Inoue et al, 2008), RFC is an anion exchanger that operates most efficiently at pH 7.4 and is inhibited by inorganic and organic anions (Henderson and Zevely, 1983;Yang et al, 1984;Zhao et al, 2001). Although some organic anions are weak inhibitors of PCFTmediated transport, with inhibitor constants in the submillimolar to millimolar range (Inoue et al, 2008), little is known about the impact of inorganic anions on PCFTmediated transport, particularly anions that have physiologic relevance.…”

Section: Introductionmentioning

confidence: 86%

See 1 more Smart Citation

Inhibition of the Proton-Coupled Folate Transporter (PCFT-SLC46A1) by Bicarbonate and Other Anions

et al. 2013

View full text Add to dashboard Cite

The proton-coupled folate transporter (PCFT) plays a key role in intestinal folate absorption, and loss-of-function mutations in the gene encoding this transporter are the molecular basis for hereditary folate malabsorption. Using a stable transfectant with high expression of PCFT, physiologic levels of bicarbonate produced potent and rapidly reversible inhibition of PCFT-mediated transport at neutral pH. Bisulfite and nitrite also inhibited PCFT function at neutral pH, whereas sulfate, nitrate, and phosphate had no impact at all. At weakly acidic pH (6.5), bisulfite and nitrite exhibited much stronger inhibition of PCFT-mediated transport, whereas sulfate and nitrate remained noninhibitory. Inhibition by bisulfite and nitrite at pH 6.5 was associated with a marked decrease in the influx V max and collapse of the transmembrane proton gradient attributed to the diffusion of the protonated forms into these cells. Monocarboxylates such as pyruvate and acetate also collapsed the pH gradient and were also inhibitory, whereas citrate and glycine neither altered the proton gradient nor inhibited PCFTmediated transport. These observations add another dimension to the unfavorable pH environment for PCFT function in systemic tissues: the presence of high concentrations of bicarbonate.

show abstract

Section: Resultssupporting

confidence: 92%

Section: Introductionmentioning

confidence: 86%

Inhibition of the Proton-Coupled Folate Transporter (PCFT-SLC46A1) by Bicarbonate and Other Anions

et al. 2013

View full text Add to dashboard Cite

show abstract

“…Similarly, influx of radiolabeled MTX by RFC is significantly enhanced ("trans-stimulated") in cells preloaded with high concentrations of 5-formyl or 5-methyl tetrahydrofolate (Goldman, 1971a, b). In anion-free buffers without glucose, the rate of MTX efflux from cells is inhibited but can be stimulated with both inorganic and organic anions (e.g., folic acid, 5-formyl tetrahydrofolate, AMP, ADP, thiamine pyrophosphate, phosphate, sulfate, and chloride) (Henderson and Zevely, 1980, 1983b. The anion concentrations required for half-maximal stimulation of efflux were similar to their Ki values for inhibition of influx by RFC.…”

Section: Functional Properties Of Rfcmentioning

confidence: 68%

Chapter 5 Structure and Function of the Reduced Folate Carrier

Matherly

Hou

2008

Vitamins &Amp; Hormones

View full text Add to dashboard Cite

Folates are essential for life and folate deficiency contributes to a host of health problems including cardiovascular disease, fetal abnormalities, neurologic disorders, and cancer. Antifolates, represented by methotrexate, continue to occupy a unique niche among the modern day pharmacopoeia for cancer along with other pathologic conditions. This review focuses on the biology of the membrane transport system termed the "reduced folate carrier" or RFC with a particular emphasis on RFC structure and function. The ubiquitously expressed RFC is the major transporter for folates in mammalian cells and tissues. Loss of RFC expression or function portends potentially profound physiologic or developmental consequences. For chemotherapeutic antifolates used for cancer, loss of RFC expression or synthesis of mutant RFC protein with impaired function results in antifolate resistance due to incomplete inhibition of cellular enzyme targets and low levels of substrate for polyglutamate synthesis. The functional properties for RFC were first documented nearly 40 years ago in murine leukemia cells. Since 1994, when RFC was first cloned, tremendous advances in the molecular biology of RFC and biochemical approaches for studying the structure of polytopic membrane proteins have led to an increasingly detailed picture of the molecular structure of the carrier, including its membrane topology, its Nglycosylation, identification of functionally and structurally important domains and amino acids, and helix packing associations. Although no crystal structure for RFC is yet available, biochemical and molecular studies, combined with homology modeling, based on homologous bacterial Major Facilitator Superfamily transporters such as LacY, now permit the development of experimentally testable hypotheses designed to establish RFC structure and mechanism.

show abstract

“…Cocarboxylase (or thiamine pyrophosphate, Sigma), a potent inhibitor of the reduced folate/MTX transport system (Henderson & Zevely, 1983), had no effect on the cytotoxicity of the MHT6C1 conjugate against R120 cells, indicating that none of the cytotoxicity observed was due to free drug released from the conjugate extracellularly. Furthermore, by use of agents able to inhibit lysosomal protein degradation (ammonium chloride (Ohkuma & Poole, 1978) and leupeptin (Seglen et al, 1979)), it was shown that, once internalised, the MTX-HSA-791T/36 conjugates require lysosomal degradation to release free MTX in order to exert their cytotoxic effect, also shown previously for such conjugates (Garnett et al, 1985).…”

Section: Competitive Effect Offree Antibodymentioning

confidence: 99%

Monoclonal antibody targeting of methotrexate (MTX) against MTX-resistant tumour cell lines

Affleck

Embleton²

1992

Br J Cancer

View full text Add to dashboard Cite

Structural requirements for anion substrates of the methotrexate transport system in L1210 cells

Cited by 79 publications

References 17 publications

Inhibition of the Proton-Coupled Folate Transporter (PCFT-SLC46A1) by Bicarbonate and Other Anions

Inhibition of the Proton-Coupled Folate Transporter (PCFT-SLC46A1) by Bicarbonate and Other Anions

Chapter 5 Structure and Function of the Reduced Folate Carrier

Monoclonal antibody targeting of methotrexate (MTX) against MTX-resistant tumour cell lines

Contact Info

Product

Resources

About