zd-9331 and nolatrexed

Thymidylate synthase (TS) is a folate-dependent enzyme that catalyzes the reductive methylation of 2'-deoxyuridine-5'-monophosphate to 2'-deoxythymidine-5'-monophosphate. This pathway provides the sole intracellular de novo source of 2'-deoxythymidine-5'-triphosphate; therefore, TS represents a critical target in cancer chemotherapy. 5-Fluorouracil (5-FU) was synthesized in 1957 and represents the first class of antineoplastic agents to be developed as inhibitors of TS. While 5-FU has been widely used to treat various human malignancies, its overall clinical efficacy is limited. Therefore, significant efforts have focused on the design of novel, more potent inhibitor compounds of TS. These agents fall into two main categories: folate analogs and nucleotide analogs. Five antifolate analogs are currently being evaluated in the clinic: raltitrexed, pemetrexed, nolatrexed, ZD9331, and GS7904L. Our laboratory has identified a novel mechanism of resistance that develops to TS inhibitor compounds, namely drug-mediated acute induction of new TS synthesis; this mechanism is directly controlled at the translational level. The ability of cancer cells to acutely induce the expression of TS may represent a novel mechanism for the development of cellular drug resistance. The future success of TS inhibitor compounds in the clinic may depend on novel strategies to selectively inhibit TS and on novel combination therapies to overcome cellular drug resistance.

Topics: Antineoplastic Agents; Enzyme Inhibitors; Humans; Indoles; Isoindoles; Neoplasms; Quinazolines; Randomized Controlled Trials as Topic; Thiophenes; Thymidylate Synthase

Topics: Antineoplastic Agents; Clinical Trials as Topic; Colorectal Neoplasms; Enzyme Inhibitors; Folic Acid; Glutamates; Guanine; Humans; Pemetrexed; Quinazolines; Thiophenes; Thymidylate Synthase

Thymidylate synthase (TS) is a critical enzyme for DNA replication and cell growth because it is the only de novo source of thymine nucleotide precursors for DNA synthesis. TS is the primary target of 5-fluorouracil (5-FU), which has been used for cancer treatment for more than 40 years. However, dissatisfaction with the overall activity of 5-FU against the major cancers, and the recognition that TS still remains an attractive target for anticancer drugs because of its central position in the pathway of DNA synthesis, led to a search for new inhibitors of TS structurally analogous to 5,10-methylenetetrahydrofolate, the second substrate of TS. TS inhibitory antifolates developed to date that are in various stages of clinical evaluation are ZD 1694 and ZD9331 (Astra-Zeneca, London, UK), (Eli Lilly, Indianapolis, IN), LY231514 (BW1843U89 (Glaxo-Wellcome, Research Triangle Park, NC), and AG337 and AG331 (Agouron, La Jolla, CA). Although each of these compounds has TS as its major intracellular site of action, they differ in propensity for polyglutamylation and for transport by the reduced folate carrier. LY231514 also has secondary target enzymes. As a result, each compound is likely to have a different spectrum of antitumor activity and toxicity. This review will summarize the development and properties of this new class of TS inhibitors.

Topics: Animals; Antimetabolites, Antineoplastic; Colorectal Neoplasms; Enzyme Inhibitors; Folic Acid; Folic Acid Antagonists; Glutamates; Guanine; Humans; Indoles; Isoindoles; Pemetrexed; Quinazolines; Thiophenes; Thymidylate Synthase

Thymidylate synthase (TS), an enzyme that catalyses the conversion of dUMP to dTMP, has been the focus of interest as a target in cancer chemotherapy for more than two decades. Over the last 10 years much research has been devoted to the design and development of nonpolyglutamatable inhibitors of TS as antitumour agents, mainly to over-come resistance due to unfavourable expression of folylpolyglutamate synthetase (FPGS). Lipophilic inhibitors of the enzyme were expected not to depend on the reduced folate carrier transporter (RFC) for cellular uptake, thus avoiding resistance due to an impaired RFC. Compounds of this type can be classified in three groups: A: nonclassical lipophilic inhibitors of TS, mainly folate-based analogues lacking the glutamate side chain; B: folate-based analogues in which the glutamate side chain has been modified in such a way that polyglutamation is precluded; and C: nonpolyglutamatable glutamate-containing inhibitors of TS. Compounds of group A included 5- or 6-substituted quinazolin-4-ones, benzo[flquinazolines, imidazotetrahydroquinoline- and benz[cd]indole-based inhibitors. The second group is mainly related to a series of g-linked dipeptide derivatives of ICIl98583, or analogues of this inhibitor where the glutamate residue was replaced with a range of a-amino acids. The third group is concerned with some 7-substituted derivatives of ICI198583 and the pyrrolo[3, 2-d]pyrimidine-based inhibitor 175. A large number of structurally diverse nonpolyglutamatable inhibitors of TS were synthesised some of which were potent inhibitors of the enzyme (human or E. coli) and in vitro cell growth. Three compounds, i.e. 49 (AG 337), 83 (AG 331), 123 (ZD9331) have reached the stage of clinical evaluation.

Topics: Antimetabolites, Antineoplastic; Cell Division; Excitatory Amino Acid Antagonists; Folic Acid Antagonists; Humans; Indoles; Peptide Synthases; Quinazolines; Structure-Activity Relationship; Thymidylate Synthase

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

Thymidylate synthase (TS) is an important target for cancer chemotherapy. However, several mechanisms of resistance to TS inhibitors have been described. One mechanism that may be relevant to short-term exposure to TS inhibitors occurs as a result of disruption of the autoregulatory loop, which allows TS to control its own translation. This disruption leads to up-regulation of TS protein and is generally thought to decrease efficacy. This study has investigated TS protein up-regulation using a range of TS inhibitors in both tumor and nonmalignant cell lines in vitro and in vivo. Up-regulation of TS protein showed a time-, dose-, and cell-type-specific response to treatment with ZD9331. This response was observed in W1L2 cells treated for 24 h at equitoxic doses of raltitrexed (6-fold), ZD9331 (10-fold), fluorouracil (5-fold), LY231514 (7-fold), AG337 (7-fold), and BW1843U89 (3-fold). Up-regulation was observed over a range of doses. Elevation of TS protein only persisted up to 12 h after removal of drug. The extent of induction does not depend on basal TS levels. Nontransformed human fibroblasts showed significantly greater up-regulation of TS protein than tumor cells exposed to an equitoxic dose of ZD9331. In vivo experiments using the L5178Y thymidine kinase -/- mouse lymphoma implanted into DBA2 mice also showed greater up-regulation of TS protein in normal intestinal epithelial cells compared with tumor cells. These results confirm that TS up-regulation is a common feature of TS inhibition in tumor cells and that it may occur to a greater extent in normal tissues, although the clinical implications of these findings remain to be determined.

Topics: Analysis of Variance; Animals; Antimetabolites, Antineoplastic; Antineoplastic Agents; Blotting, Western; Dose-Response Relationship, Drug; Enzyme-Linked Immunosorbent Assay; Female; Fibroblasts; Flow Cytometry; Fluorouracil; Glutamates; Guanine; Humans; Indoles; Inhibitory Concentration 50; Isoindoles; Mice; Mice, Inbred DBA; Microscopy, Confocal; Neoplasm Transplantation; Pemetrexed; Quinazolines; Thiophenes; Thymidylate Synthase; Time Factors; Tumor Cells, Cultured; Up-Regulation