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Oncology (Williston Park, N.Y.) Jul 1995Numerous new antifolate drugs have been developed in an attempt to overcome the potential mechanisms of tumor cell resistance to methotrexate, which can include... (Review)
Review
Numerous new antifolate drugs have been developed in an attempt to overcome the potential mechanisms of tumor cell resistance to methotrexate, which can include decreased drug transport into cells; decreased polyglutamation, leading to increased drug efflux from cells; decreased drug affinity for folate-dependent enzymes; mutations of dihydrofolate reductase (DHFR), a key enzyme required for the maintenance of adequate intracellular reduced folate levels that is inhibited by methotrexate; and increased expression of the DHFR protein. Promising antifolate compounds undergoing clinical testing as anticancer agents include trimetrexate (which was recently approved by the FDA for the treatment of Pneumocystis carinii pneumonia), edatrexate, piritrexim, Tomudex, and lometrexol. The mechanisms of action, dosage, pharmacokinetics, clinical toxicity, and antitumor activity of these drugs are profiled.
Topics: Aminopterin; Antimetabolites, Antineoplastic; Antineoplastic Agents; Drugs, Investigational; Folic Acid Antagonists; Humans; Neoplasms; Pyrimidines; Quinazolines; Thiophenes; Trimetrexate
PubMed: 8924375
DOI: No ID Found -
Annals of Oncology : Official Journal... May 2007The prognosis for any patient with progressive or recurrent invasive transitional cell carcinoma remains poor. In this context, the focus of clinical research in these... (Review)
Review
The prognosis for any patient with progressive or recurrent invasive transitional cell carcinoma remains poor. In this context, the focus of clinical research in these invasive cancers concentrates on identifying systemic treatment options and new agents in order to improve survival of patients. Cisplatin-based chemotherapy is standard treatment of patients with metastatic urothelial cancer; however, despite regimens as the cisplatin-gemcitabine combination, the overall response rates vary between 40% and 65%, with complete response in 15%-25% with survivals up to 16 months. This survival is frequently achieved with severe and life-threatening side effects. None the less, almost all responding patients relapse within the first year; therefore, the need for development of new and tolerable agents is urgent. This review highlights some new active chemotherapeutic as new platinum compounds (oxaliplatin, lobaplatin), gallium nitrate, ifosfamide, the antifolates piritrexim and pemetrexed (Alimta, LY231514), vinflunine and molecular targeting agents such as farnesyltransferase inhibitors (lonafarnib, R115777, SCH66336), ribozyme (RPI.4610), histone deacetylase inhibitor (CI-994) and monoclonal antibodies (epidermal growth factor receptor, Her 2/neu).
Topics: Antibodies, Monoclonal; Antineoplastic Agents; Antineoplastic Combined Chemotherapy Protocols; Carcinoma, Transitional Cell; Clinical Trials as Topic; Enzyme Inhibitors; Humans; Multicenter Studies as Topic; Neoplasm Metastasis; Neoplasm Recurrence, Local
PubMed: 17018703
DOI: 10.1093/annonc/mdl331 -
Antimicrobial Agents and Chemotherapy Apr 1988Piritrexim, a lipid-soluble antifolate, was evaluated for its activity against Pneumocystis carinii and Toxoplasma gondii. The concentration of piritrexim needed to...
Piritrexim, a lipid-soluble antifolate, was evaluated for its activity against Pneumocystis carinii and Toxoplasma gondii. The concentration of piritrexim needed to inhibit 50% of the catalytic activity of P. carinii dihydrofolate reductase (DHFR) was 19.3 nM, and that for T. gondii DHFR was 17.0 nM, concentrations that were 40- to over 1,000-fold less than those needed for the inhibition of activity by trimethoprim and pyrimethamine, the antifolates conventionally used in treating these organisms. Piritrexim was able to inhibit replication of T. gondii in a mouse peritoneal macrophage model at concentrations of 0.1 to 1.0 microM. Leucovorin, a reduced folate that can bypass the inhibition of DHFR by antifols in mammalian cells but not in protozoa, did not affect the ability of piritrexim to inhibit T. gondii replication. The addition of sulfadiazine, which alone was ineffective, to piritrexim allowed inhibition of T. gondii replication at lower concentrations of piritrexim than when piritrexim was used alone. These results suggest that piritrexim, alone or combined with a sulfonamide, may be a highly potent antitoxoplasma and antipneumocystis agent that could provide major pharmacologic and clinical advantages over available agents.
Topics: Animals; Folic Acid Antagonists; Mice; Mice, Inbred BALB C; Pneumocystis; Pyrimethamine; Pyrimidines; Quinazolines; Rats; Rats, Inbred Strains; Toxoplasma; Trimetrexate
PubMed: 2967669
DOI: 10.1128/AAC.32.4.430 -
British Journal of Cancer Feb 1993Piritrexim is a lipid-soluble inhibitor of dihydrofolate reductase (DHFR) that enters tumour cells rapidly by passive diffusion, cannot be polyglutamated, and is as... (Clinical Trial)
Clinical Trial
Piritrexim is a lipid-soluble inhibitor of dihydrofolate reductase (DHFR) that enters tumour cells rapidly by passive diffusion, cannot be polyglutamated, and is as effective as methotrexate in inhibiting DHFR. Bioavailability after oral dosing is approximately 75%. We performed a phase II study with oral piritrexim in non-chemotherapy pretreated patients with metastatic urothelial cancer. Thirty-three patients were treated with 25 mg three times daily for 5 consecutive days, repeated weekly, with provision for dose escalation or reduction according to the toxicity observed. Of 29 evaluable patients, one patient achieved a complete response of 19+ weeks duration, and ten patients achieved a partial response with a median duration of 22 weeks (range 16-48), for a total response rate of 38%. Piritrexim was generally well tolerated, with myelosuppression as the major toxicity, that frequently required dose modification. We conclude that piritrexim appears to be an active agent in patients with metastatic urothelial cancer when administered as a 5-day, low-dose oral schedule. It would be attractive to investigate the combination of piritrexim and cisplatin.
Topics: Administration, Oral; Adult; Aged; Antineoplastic Agents; Antineoplastic Combined Chemotherapy Protocols; Carcinoma, Transitional Cell; Cisplatin; Female; Humans; Male; Methotrexate; Middle Aged; Pyrimidines; Urologic Neoplasms
PubMed: 8431372
DOI: 10.1038/bjc.1993.71 -
British Journal of Cancer Sep 1993Piritrexim is a lipid-soluble antifolate which, like methotrexate, has a potent capacity to inhibit dihydrofolate reductase. We performed a multicentre phase II study... (Clinical Trial)
Clinical Trial
Piritrexim is a lipid-soluble antifolate which, like methotrexate, has a potent capacity to inhibit dihydrofolate reductase. We performed a multicentre phase II study with piritrexim in patients with locally advanced or metastatic breast cancer. Twenty-four patients of which sixteen had received prior chemotherapy, were initially treated with 25 mg piritrexim orally administered trice daily for four days, repeated weekly, with provision for dose escalation or reduction according to observed toxicity. Of twenty-one patients evaluable for tumour response, one patient achieved a partial response which lasted for 24 weeks. Three patients had stable disease during 12 weeks of treatment, seventeen had progressive disease. Pirtrexim was generally well tolerated, in eighteen patients the dose could be escalated. Myelotoxicity was the most frequent observed toxicity of this piritrexim regimen. Leucopenia and thrombocytopenia grade 3/4 occurred in 38% of the patients sometime during treatment. Pharmacokinetic analysis of piritrexim in three patients during the first treatment cycle, revealed peak levels 1 to 2 h after an oral dose, with a trend towards a higher peak plasma levels and AUCs on the fourth dosing day compared with the first dosing day. In conclusion, orally administered piritrexim appears to be a regimen with little activity in patients with locally advanced or metastatic breast carcinoma.
Topics: Administration, Oral; Adult; Aged; Breast Neoplasms; Drug Evaluation; Female; Humans; Leukopenia; Middle Aged; Neoplasm Metastasis; Pyrimidines; Thrombocytopenia
PubMed: 8353055
DOI: 10.1038/bjc.1993.400 -
The Journal of Biological Chemistry Nov 1989We describe the development of resistance to trimetrexate and piritrexim (BW 301U) by a stepwise selection protocol in Chinese hamster ovary cells. Selection in... (Comparative Study)
Comparative Study
Sequential amplification of dihydrofolate reductase and multidrug resistance genes in Chinese hamster ovary cells selected for stepwise resistance to the lipid-soluble antifolate trimetrexate.
We describe the development of resistance to trimetrexate and piritrexim (BW 301U) by a stepwise selection protocol in Chinese hamster ovary cells. Selection in trimetrexate resulted in initial resistance as a result of dihydrofolate reductase gene amplification. Several trimetrexate-resistant variants that display 250-340-fold and 25-50-fold resistance to lipophilic and hydrophilic antifolates, respectively, were established. Increased antifolate resistance was associated with a prominent overexpression of dihydrofolate reductase as determined from the elevated folate reductase activity, cellular labeling with fluorescein-methotrexate, and steady-state mRNA levels as a result of a consistent dihydrofolate reductase gene amplification. However, upon subsequent incremental increases in trimetrexate, further resistance was also associated with amplification of the multidrug resistance gene. This resulted in overexpression of P-glycoprotein and a subsequent 20-50-fold collateral resistance to pleiotropic drugs such as adriamycin, actinomycin D, vinca alkaloids, etoposide, and colchicine. In contrast, initial resistance following selection with low piritrexim concentrations resulted from an unknown mechanism(s) not involving overproduction of either dihydrofolate reductase or P-glycoprotein. This piritrexim resistance was shared with trimetrexate but not with methotrexate. Upon further selection with piritrexim, resistant variants emerge with amplified dihydrofolate reductase but not with multidrug resistance genes. These variants were subsequently resistant to both hydrophilic and lipophilic folate antagonists but retained sensitivity to pleiotropic drugs. The pattern of resistance with methotrexate, trimetrexate, and piritrexim shared a common mechanism, dihydrofolate reductase gene amplification, but differed regarding the additional amplification of the multidrug resistance gene in trimetrexate-resistant cells as well as the emergence of an additional unknown mechanism(s) of resistance to lipid-soluble antifolates upon initial selection in piritrexim.
Topics: ATP Binding Cassette Transporter, Subfamily B, Member 1; Animals; Cell Line; Cricetinae; Drug Resistance; Fluorescein; Fluoresceins; Folic Acid Antagonists; Gene Amplification; Gene Expression; Membrane Glycoproteins; Methotrexate; Pyrimidines; Quinazolines; RNA, Messenger; Tetrahydrofolate Dehydrogenase; Trimetrexate
PubMed: 2572592
DOI: No ID Found -
Antimicrobial Agents and Chemotherapy Oct 1989Three sulfonamides and four dihydrofolate reductase inhibitors were tested alone and in combination to determine their in vitro effects on two strains of Toxoplasma...
Three sulfonamides and four dihydrofolate reductase inhibitors were tested alone and in combination to determine their in vitro effects on two strains of Toxoplasma gondii grown in MRC5 fibroblast tissue culture. Toxoplasma growth was quantitated by an enzyme immunoassay performed directly on the fixed cultures, and linear regression models were used to quantify the relationship between the optical density values generated by the enzyme-linked immunosorbent assay and the concentrations of the antimicrobial agents in the culture medium. The cytopathic effects of antimicrobial agents on T. gondii were examined in Giemsa-stained cultures. Sulfonamides and dihydrofolate reductase inhibitors exhibited similar patterns of inhibition, consisting of an important increase of the inhibitory effect within a narrow range of concentrations. Sulfadiazine, sulfamethoxazole, and sulfisoxazole were all found to have important inhibitory effects on T. gondii; the 50% inhibitory concentrations estimated from the regression models were 2.5 micrograms/ml for sulfadiazine, 1.1 micrograms/ml for sulfamethoxazole, and 6.4 micrograms/ml for sulfisoxazole. This inhibition of growth was associated with a reduction of the number of parasitized cells and intracellular parasites that were morphologically normal. With dihydrofolate reductase inhibitors, including pyrimethamine, trimethoprim, trimetrexate-glycuronate, and piritrexim, a strong inhibition of Toxoplasma growth was observed, which was associated with striking morphological changes of the parasites. The 50% inhibitory concentrations were 0.04 microgram/ml for pyrimethamine, 2.3 micrograms/ml for trimethoprim, 0.16 ng/ml for trimetrexate-glycuronate, and 6.9 ng/ml for piritrexim. When sulfonamides and dihydrofolate reductase inhibitors were used in combination, a synergistic effect was observed with sulfadiazine combined with pyrimethamine, trimetrexate-glycuronate, and piritrexim; sulfisoxazole combined with pyrimethamine; and trimethoprim combined with sulfamethoxazole. These results were analyzed in comparison with human pharmacokinetics data.
Topics: Animals; Enzyme-Linked Immunosorbent Assay; Folic Acid Antagonists; Microbial Sensitivity Tests; Pyrimethamine; Pyrimidines; Quinazolines; Sulfamethoxazole; Sulfisoxazole; Toxoplasma; Trimethoprim; Trimetrexate
PubMed: 2531568
DOI: 10.1128/AAC.33.10.1753 -
Virology Mar 2000Kaposi's sarcoma-associated herpesvirus (KSHV) is the first human virus known to encode dihydrofolate reductase (DHFR), an enzyme required for nucleotide and methionine... (Comparative Study)
Comparative Study
Kaposi's sarcoma-associated herpesvirus (KSHV) is the first human virus known to encode dihydrofolate reductase (DHFR), an enzyme required for nucleotide and methionine biosynthesis. We have studied the purified KSHV-DHFR enzyme in vitro and analyzed its expression in cultured B-cell lines derived from primary effusion lymphoma (PEL), an AIDS-associated malignancy. The amino acid sequence of KSHV-DHFR is most similar to human DHFR (hDHFR), but the viral enzyme contains an additional 23 amino acids at the carboxyl-terminus. The viral DHFR, overexpressed and purified from E. coli, was catalytically active in vitro. The K(m) of KSHV-DHFR for dihydrofolate (FH(2)) was 2.4 microM, which is significantly higher than the K(m) of recombinant hDHFR (rhDHFR) for FH(2) (390 nM). K(m) values for NADPH were similar for the two enzymes, about 1 microM. KSHV-DHFR was inhibited by folate antagonists such as methotrexate (K(i): 200 pM), aminopterin (K(i): 610 pM), pyrimethamine (K(i): 29 nM), trimethoprim (K(i): 2.3 microM), and piritrexim (K(i): 3.9 nM). In all cases, K(i) values for these folate antagonists were higher for KSHV-DHFR than for rhDHFR. The viral enzyme was expressed at levels two- to tenfold higher than hDHFR in PEL cell lines as an early lytic cycle gene. KSHV-DHFR mRNA and protein appeared from 6 to 24 h after chemical induction of the KSHV lytic cycle. Epitope-tagged KSHV-DHFR and rhDHFR both localized to the nucleus of transfected cells, while other KSHV nucleotide metabolism genes localized to the cytoplasm. DHFR activity was not essential for viral replication in cultured PEL cells. Since hDHFR was not detectable in peripheral blood mononuclear cells (PBMCs), KSHV-DHFR may function to provide increased DHFR activity in vivo in infected cells that have little or none of their own enzyme.
Topics: Amino Acid Sequence; Aminopterin; Butyrates; CD3 Complex; Enzyme Inhibitors; Herpesvirus 8, Human; Humans; Kinetics; Leukocytes, Mononuclear; Lymphoma, B-Cell; Molecular Sequence Data; RNA, Messenger; Sequence Analysis, Protein; Tetrahydrofolate Dehydrogenase; Tumor Cells, Cultured; Virus Replication
PubMed: 10683342
DOI: 10.1006/viro.1999.0165 -
Antimicrobial Agents and Chemotherapy Jan 1995Twenty-eight 2,4-diaminopteridines with alkyl and aralkyl groups at the 6- and 7-positions, five 1,3-diamino-7,8,9,10-tetrahydropyrimido [4,5-c]isoquinolines with an...
Twenty-eight 2,4-diaminopteridines with alkyl and aralkyl groups at the 6- and 7-positions, five 1,3-diamino-7,8,9,10-tetrahydropyrimido [4,5-c]isoquinolines with an alkyl, alkylthio, or aryl group at the 6-position, and nine 4,6-diamino-1,2-dihydro-s-triazines with one or two alkyl groups at the 2-position and a substituted phenyl or naphthyl group at the 1-position were evaluated as inhibitors of dihydrofolate reductase enzymes from Pneumocystis carinii, Toxoplasma gondii, and rat liver. Halogen substitution at the 5- or 6-position of 2,4-diaminoquinazoline favored selective binding to the P. carinii enzyme but not the T. gondii enzyme. For example, the 50% inhibitory concentrations of 2,4-diamino-6-chloroquinazoline as an inhibitor of P. carinii, T. gondii, and rat liver dihydrofolate reductase were 3.6, 14 and 29 microM, respectively, corresponding to 12-fold selectivity for the P. carinii enzyme but only marginal selectivity for the T. gondii enzyme. Greater than fivefold selectivity for P. carinii but not T. gondii dihydrofolate reductase was also observed for the 2,4-diaminoquinazolines with 5-methyl, 5-fluoro, 5- and 6-bromo, 6-chloro, and 5-chloro-6-bromo substitution. In contrast, alkyl and aralkyl substitution at the 6- and 7-positions of 2,4-diaminopteridines was found to be a favorable feature for selective inhibition of the T. gondii enzyme and, in two cases, for both enzymes. Nine of the fifty-one compounds tested against P. carinii dihydrofolate reductase and four of the thirty compounds tested against T. gondii dihydrofolate reductase displayed fivefold or greater selectivity for the microbial enzyme versus the rat liver enzyme. The most selective against both enzymes was 2,4-diamino-6,7-bis(cyclohexylmethyl) pteridine, with a selectivity ratio 2 orders of magnitude greater than the value reported for trimetrexate and piritrexim. Since substitution at the 7-position is generally considered to be detrimental to the binding of 2,4-diaminop-teridines and related compounds to mammalian dihydrofolate reductase, the selectivity observed in this study with the 6,7-bis(cyclohexylmethyl) analog may represent a useful approach to enhancing selective inhibition of the enzyme from nonmammalian species.
Topics: Animals; Enzyme Inhibitors; Folic Acid Antagonists; Liver; Pneumocystis; Pteridines; Quinazolines; Rats; Structure-Activity Relationship; Toxoplasma
PubMed: 7695334
DOI: 10.1128/AAC.39.1.79 -
Bioorganic & Medicinal Chemistry Letters Aug 2019Pneumocystis pneumonia (PCP) caused by Pneumocystis jirovecii (pj) can lead to serious health consequences in patients with an immunocompromised system. Trimethoprim...
Pneumocystis pneumonia (PCP) caused by Pneumocystis jirovecii (pj) can lead to serious health consequences in patients with an immunocompromised system. Trimethoprim (TMP), used as first-line therapy in combination with sulfamethoxazole, is a selective but only moderately potent pj dihydrofolate reductase (pjDHFR) inhibitor, whereas non-clinical pjDHFR inhibitors, such as, piritrexim and trimetrexate are potent but non-selective pjDHFR inhibitors. To meet the clinical needs for a potent and selective pjDHFR inhibitor for PCP treatment, fourteen 6-substituted pyrido[3,2-d]pyrimidines were developed. Comparison of the amino acid residues in the active site of pjDHFR and human DHFR (hDHFR) revealed prominent amino acid differences which could be exploited to structurally design potent and selective pjDHFR inhibitors. Molecular modeling followed by enzyme assays of the compounds revealed 15 as the best compound of the series with an IC of 80 nM and 28-fold selectivity for inhibiting pjDHFR over hDHFR. Compound 15 serves as the lead analog for further structural variations to afford more potent and selective pjDHFR inhibitors.
Topics: Folic Acid Antagonists; Humans; Models, Molecular; Pneumocystis; Pneumocystis carinii; Pyrimidines; Structure-Activity Relationship; Trimethoprim
PubMed: 31176699
DOI: 10.1016/j.bmcl.2019.06.004