lometrexol and edatrexate

Many novel antifolate compounds with unique pharmacologic properties are currently in clinical development. These newer antifolates differ from methotrexate, the most widely used and studied drug in this class, in terms of their lipid solubility and cellular transport affinity, their level of polyglutamation, and their specificity for inhibiting folate-dependent enzymes, such as dihydrofolate reductase, thymidylate synthase, or glycinamide ribonucleotide formyltransferase. The current status (ie, mechanism of action, clinical response rates, and toxicity) of some of the newer antifolate compounds presently in clinical testing, including edatrexate, piritrexim, raltritrexed, LY 231514, AG337, AG331, 1843U89, ZD 9331, and lometrexol, is reviewed.

Topics: Aminopterin; Animals; Antimetabolites, Antineoplastic; Clinical Trials as Topic; Drug Design; Enzyme Inhibitors; Folic Acid Antagonists; Glutamates; Guanine; Humans; Indoles; Isoindoles; Pemetrexed; Pyrimidines; Quinazolines; Tetrahydrofolates; Thiophenes; Thymidylate Synthase

A number of promising new antifolates have been entered in clinical trials in recent years. These agents have been rationally designed based on the current understanding of folate transport and metabolism and of the mechanisms by which cells become resistant to methotrexate. Methotrexate-resistant cell lines are generally sensitive to one or more of the newer antifolates, which differ from methotrexate by being either more lipid soluble, more extensively polyglutamated, or by inhibiting folate-requiring enzymes other than dihydrofolate reductase. Five of the agents furthest along in clinical testing, trimetrexate, piritrexim, edatrexate, lometrexol, and D1694, are discussed. These drugs offer exciting opportunities to expand the role of antifolates in cancer chemotherapy, as well as in antimicrobial and antirheumatic therapy.

Topics: Aminopterin; Animals; Antineoplastic Agents; Chemistry, Pharmaceutical; Clinical Trials as Topic; Drug Evaluation; Folic Acid Antagonists; Forecasting; Humans; Neoplasms; Pyrimidines; Quinazolines; Tetrahydrofolates; Thiophenes; Trimetrexate

Since the clinical introduction of the antifolates aminopterin (AMT) and methotrexate (MTX) many promising analogs have been developed. A common feature of these compounds is their ability to induce bone marrow suppression. However, few studies have been undertaken on the effect of the folic acid analogs on the cells comprising the hematopoietic system.. In this paper we describe the effects of the novel thymidylate synthase (TS) inhibitors raltitrexed (Tomudex, ZD1694), AG337 (nolatrexed, Thymitaq), and the two closely related analogs 5,8-dideazaisofolic acid (IAHQ2a) and 2-desamino-2-methyl 5,8-dideazaisofolic acid (IAHQ2c), the glycinamide-ribonucleosyl (GAR) transformylase inhibitor lometrexol (DDATHF), and the dihydrofolate reductase (DHFR) inhibitors MTX, AMT, trimetrexate (TMTX), and edatrexate (EDX) on purified populations of early and late murine hematopoietic progenitor cells.. All the antifolates inhibited bone marrow proliferation in suspension cultures and all drugs except DDATHF inhibited colony formation by more mature progenitor cells (CFU-C) in clonogenic assays. The lipophilic agents TMTX and AG337 were most toxic, totally abolishing CFU-C colony formation at high concentrations. When IAHQ2c, raltitrexed, DDATHF, and MTX were investigated further for effects on the immature high proliferative potential colony-forming cells (HPP-CFCs) in semisolid and limiting dilution cultures, none of these agents were found to be toxic to the HPP-CFC, but induced a reversible developmental arrest in the progenitor cell population.

Topics: Aminopterin; Animals; Cell Division; Cells, Cultured; Enzyme Inhibitors; Female; Folic Acid; Folic Acid Antagonists; Hematopoietic Stem Cells; Methotrexate; Mice; Mice, Inbred BALB C; Quinazolines; Tetrahydrofolates; Thiophenes; Trimetrexate

Two methotrexate (MTX)-resistant human breast-cancer cell lines with impaired transport via the reduced folate carrier (RFC), one established in vitro (MTX(R)-ZR-75-1) and another inherently resistant (MDA-231), were adapted to grow in medium containing 2 nM folic acid. This induced the expression of previously undetectable membrane folate receptors (MFR) to levels of 8.2 and 2.3 pmol/10(7) cells, respectively. Polymerase chain reaction (PCR) quantitation revealed that MFR messenger-RNA levels of the isoform first described in human nasopharyngeal carcinoma KB cells (MFR-alpha) were increased in low-folate-adapted MTX(R)-ZR-75-1 cells, whereas placental transcripts (MFR-beta) coincided with MFR-alpha expression in low-folate (LF)-adapted MDA-231 cells. These cell lines were used to study the role of MFR in the uptake and growth-inhibitory effects of five different antifolates with varying affinities for MFR: N10-propargyl-5, 8-dideazafolic acid (CB3717) > 5,10-dideazatetra-hydrofolic acid (DDATHF) > N-5-[N-(3,4-dihydro-2-methyl-4-oxoquinazolin-6-methyl) -N-methyl-amino]-2-theonyl}-glutamic acid (ZD1694) >> MTX > edatrexate (EDX). Expression of MFR only slightly decreased the resistant phenotype for MTX, EDX, and ZD1694, suggesting that these drugs are not transported intracellularly to cytotoxic concentrations at these levels of MFR expression. On the other hand, both cell lines became from at least 180- to 400-fold more sensitive to growth inhibition by CB3717 and DDATHF, which may be correlated with their high affinity for MFR. These sensitivity/resistance profiles were largely similar following cell culture in medium containing 1 nM L-leucovorin, a folate with an affinity for MFR 10-fold lower than that of folic acid, the one exception being the increased sensitivity for ZD1694 seen in the LF-adapted cells with the highest level of MFR expression (MTX(R)-ZR-75-1). These results illustrate that the efficacy of MFR in mediating antifolate transport and cytotoxicity depends on their affinity for the folate antagonist, their degree of expression, and the levels of competing folates.

Topics: Aminopterin; Antimetabolites, Antineoplastic; Binding Sites; Breast Neoplasms; Carrier Proteins; Cell Membrane; DNA, Complementary; Female; Folate Receptors, GPI-Anchored; Folic Acid; Folic Acid Antagonists; Humans; Methotrexate; Polymerase Chain Reaction; Quinazolines; Receptors, Cell Surface; RNA, Messenger; Spectrometry, Fluorescence; Structure-Activity Relationship; Tetrahydrofolates; Thiophenes; Tumor Cells, Cultured

The role of a membrane-associated folate binding protein (mFBP) in transport of folate analogues was investigated in three epithelial cell lines that were grown in high folate medium and folate-conditioned medium and express different levels of mFBP: human nasopharyngeal KB cells, monkey kidney MA104 cells, and IGROV-I ovarian carcinoma cells. Folate analogues were selected for which mFBP exhibits a low affinity, i.e., methotrexate (MTX) and 10-ethyl-10-deazaaminopterin (10-EdAM) or a (moderately) high affinity as compared to folic acid, i.e., N-(5[N-(3,4-dihydro-2-methyl-4-oxoquinazolin-6-ylmethyl(-N-m ethylamino]-2-theonyl)-L-glutamic acid (ZD1694), N10-propargyl-5,8-dideazafolic acid (CB3717), and 5,10-dideazatetrahydrofolic acid. Regardless of the medium folate status, growth inhibition studies with IGROV-I and MA104 cells demonstrated a lack of correlation between the affinity of mFBP for the antifolate drugs and their sensitivity profile; both cell lines were highly sensitive to growth inhibition by MTX, 10-EdAM, ZD1694 and 5,10-dideazatetrahydrofolic acid, but were insensitive for CB3717. The same drug sensitivity profile was observed for KB cells, with the exception that these cells were also sensitive to growth inhibition by CB3717 but only in folate-conditioned medium. This overall drug sensitivity profile appeared to correlate with the differential efficiency of drug transport via the "classical" reduced folate/MTX carrier (RFC), rather than by mFBP. Characteristics that further supported functional RFC activity in KB, IGROV-I, and MA104 cells included: (a) the growth inhibitory effects of the drugs could be prevented by the reduced folate leucovorin rather than by folic acid; (b) rates for uptake of [3H]10-EdAM were 2-4-fold higher than for [3H]MTX at 1 microM extracellular concentrations and coincided with the affinity of the RFC for these drugs, rather than those of the mFBP; (c) uptake of [3H]10-EdAM and [3H]leucovorin was markedly inhibited by leucovorin and 10-EdAM, respectively, or by an N-hydroxysuccinimide ester of MTX (irreversibly labeling RFC) but only to a minor extent by folic acid or an N-hydroxysuccinimide ester of folic acid (irreversibly labeling mFBP); and, finally, (d) labeling with an N-hydroxysuccinimide ester of [3H]MTX identified a protein with a molecular weight within the range of that reported for the RFC in human leukemic cells. Altogether, these results indicate that both RFC and mFBP are coexpressed in three epithe

Topics: Aminopterin; Animals; Carrier Proteins; Cell Division; Female; Folate Receptors, GPI-Anchored; Folic Acid; Folic Acid Antagonists; Glutamates; Haplorhini; Humans; Kidney; Leucovorin; Methotrexate; Nasopharyngeal Neoplasms; Ovarian Neoplasms; Quinazolines; Receptors, Cell Surface; Tetrahydrofolates; Thiophenes; Tumor Cells, Cultured

A series of 7 human squamous carcinoma cell lines of the head and neck (HNSCC), grown in standard medium containing high folate concentrations and in "folate-conditioned" medium containing nanomolar concentrations of folates, were all found to be sensitive (IC50: less than or equal to 50 nM) in growth-inhibition studies to methotrexate (MTX) following drug exposure for 7 days. However, when MTX exposure was limited to 24 hr, only 2 out of 7 HNSCC cell lines were sensitive to MTX (IC50: less than 500 nM), 2 were moderately sensitive (IC50: 1-2 microM), and 3 exhibited inherent resistance to MTX (IC50: greater than 250 microM). In these last 3 cell lines, the mechanism of resistance was not correlated with altered membrane transport of MTX or changes in dihydrofolate reductase activity, but rather was associated with a 3-fold lower activity of intracellular folylpolyglutamate synthase (FPGS) activity compared to MTX-sensitive HNSCC cells. The 3 cell lines exhibiting inherent resistance to a short exposure to MTX, however, did not show inherent cross-resistance after exposure for 24 hr to one or more of 3 novel antifolate compounds. These compounds, which appear to be more efficiently transported and polyglutamylated than MTX, include: 10-ethyl-10-deazaaminopterin (10-EdAM), 2-desamino-2-methyl-N10-propargyl-5,8-dideazafolic acid (ICI-198,583), and 5,10-dideazatetrahydrofolic acid (DDATHF). These results indicate that antifolate membrane transport and intracellular FPGS activity are important factors in determining sensitivity or resistance of HNSCC cells to short-term antifolate compound exposures.

Topics: Aminopterin; Biological Transport; Carcinoma, Squamous Cell; Cell Division; Cell Line; Cell Membrane; Drug Resistance; Drug Screening Assays, Antitumor; Folic Acid; Folic Acid Antagonists; Head and Neck Neoplasms; Humans; Methotrexate; Tetrahydrofolate Dehydrogenase; Tetrahydrofolates; Tumor Cells, Cultured