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Results for “Reduced Folate Carrier Protein”

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At least 127 records · Page 7Linked to original sources
PubMed2005

Pharmacogenetic and metabolite measurements are associated with clinical status in patients with rheumatoid arthritis treated with methotrexate: results of a multicentred cross sectional observational study.

OBJECTIVE: To investigate the contribution of red blood cell (RBC) methotrexate polyglutamates (MTX PGs), RBC folate polyglutamates (folate PGs), and a pharmacogenetic index to the clinical status of patients with rheumatoid arthritis treated with MTX. METHODS: 226 adult patients treated with weekly MTX for more than 3 months were enrolled at three sites in a multicentred cross sectional observational study. Clinical status was assessed by the number of joint counts, physician's global assessment of disease activity, and a modified Health Assessment Questionnaire (mHAQ). RBC MTX PG and folate PG metabolite levels were measured by high performance liquid chromatography fluorometry and radioassay, respectively. A composite pharmacogenetic index comprising low penetrance genetic polymorphisms in reduced folate carrier (RFC-1 G80A), AICAR transformylase (ATIC C347G), and thymidylate synthase (TSER*2/*3) was calculated. Statistical analyses were by multivariate linear regression with clinical measures as dependent variables and metabolite levels and the pharmacogenetic index as independent variables after adjustment for other covariates. RESULTS: Multivariate analysis showed that lower RBC MTX PG levels (median 40 nmol/l) and a lower pharmacogenetic index (median 2) were associated with a higher number of joint counts, higher disease activity, and higher mHAQ (p<0.09). Multivariate analysis also established that higher RBC folate PG levels (median 1062 nmol/l) were associated with a higher number of tender and swollen joints after adjustment for RBC MTX PG levels and the pharmacogenetic index (p<0.05). CONCLUSION: Pharmacogenetic and metabolite measurements may be useful in optimising MTX treatment. Prospective studies are warranted to investigate the predictive value of these markers for MTX efficacy.

Aged↗
PubMed1996

Methotrexate pharmacology and resistance in childhood acute lymphoblastic leukemia.

Impressive gains have been made in the therapy of childhood acute lymphoblastic leukemia (ALL) in recent years such that remissions today are commonly achieved in up to 95% of patients and long term disease-free survival rates approach 70%. Methotrexate is a key component in ALL consolidation and maintenance therapies and is administered intrathecally in the prophylaxis and treatment of central nervous system leukemia. Critical determinants of methotrexate sensitivity and resistance (dihydrofolate reductase levels, methotrexate membrane transport, methotrexate polyglutamylation) previously described in cultured cells have recently been identified in lymphoblasts from children with ALL. Heterogenous expressions of increased dihydrofolate reductase or impaired methotrexate transport can be detected in both diagnostic and relapsed ALL specimens by flow cytometry with fluorescent methotrexate analogues. Lymphoblasts from children with ALL synthesize long chain polyglutamates and correlations have been established between the accumulation of methotrexate polyglutamates in ALL blasts and characteristic patient prognostic features. Variations in methotrexate polyglutamate accumulation may reflect changes in polyglutamate synthetic or degradative enzymes, or may be secondary to changes in methotrexate influx or dihydrofolate reductase levels. Other critical elements in treatment response to methotrexate include the dose and route of methotrexate administration, its catabolism to 7-hydroxymethotrexate, and the rate of methotrexate plasma clearance. A unique relationship exists between chromosome 21 and ALL leukemogenesis, and response to treatment including methotrexate. A better understanding of the molecular bases of methotrexate response and the development of methotrexate resistance in childhood ALL should facilitate further improvements in the effectiveness of methotrexate-based chemotherapy for this disease.

Adult↗
PubMed2003

Homocysteine, pharmacogenetics, and neurotoxicity in children with leukemia.

PURPOSE: Despite its clinical success, methotrexate (MTX) therapy is associated with toxicities such as seizures, the pathogenesis of which remains unclear. It has been suggested that hyperhomocysteinemia is caused by MTX and is responsible for its neurotoxic effects. The purposes of this study were to explore whether hyperhomocysteinemia was related to MTX administration and toxicity and whether homocysteine or MTX toxicity differed by methylenetetrahydrofolate reductase (MTHFR) or reduced folate carrier (RFC) genetic polymorphisms. PATIENTS AND METHODS: We studied 53 children with newly diagnosed acute lymphoblastic leukemia who were consecutively treated on a single clinical protocol that included two courses of high-dose MTX (high-dose methotrexate [HDMTX]; 2.5 or 5.0 g/m2 per day) as consolidation therapy. RESULTS: The study participants' median plasma homocysteine concentrations at 23 and 44 hours after HDMTX (9.00 micromol/L and 10.12 micromol/L, respectively) were greater than the concentrations immediately before HDMTX (5.77 micromol/L, P <.0001 for both comparisons). Seven days after HDMTX treatment, their plasma concentration returned to baseline. Nine patients experienced seizures, and five patients experienced thrombosis during the first 15 months of therapy, with a tendency for there to be higher plasma homocysteine in patients with seizures across all time points (P =.063) but not in patients with thrombosis (P =.59). We observed no significant differences in plasma or cerebrospinal fluid homocysteine levels or in toxicity based on the MTHFR 677C/T or RFC 80G/A genotypes. CONCLUSION: We conclude that homocysteine was transiently elevated after HDMTX and may be related to seizure risk in children with leukemia.

Carrier Proteins↗
PubMed2004

Reduced folate carrier mutations are not the mechanism underlying methotrexate resistance in childhood acute lymphoblastic leukemia.

BACKGROUND: Although the majority of children with acute lymphoblastic leukemia (ALL) are cured with combination chemotherapy containing methotrexate (MTX), drug resistance contributes to treatment failure for a substantial fraction of patients. The primary transporter for folates and MTX is the reduced folate carrier (RFC). Impaired drug transport is a documented mechanism of MTX resistance in patients with ALL; however, to the authors' knowledge it is not known whether inactivating RFC mutations are a contributing factor. METHODS: The authors devised a genomic polymerase chain reaction-single strand conformational polymorphism assay followed by sequencing and screened the entire RFC coding region for sequence alterations in DNA from 246 leukemia specimens from patients with diverse ethnic variation, 24 at the time of recurrence and the rest at the time of diagnosis. This cohort was comprised of 203 B-precursor ALL specimens (82.5%), 32 T-lineage ALL specimens (13%), and 11 acute myeloblastic leukemia specimens (4.5%). RESULTS: Of 246 DNA samples, only 3 diagnosis B-precursor ALL specimens (1.2%) were found to harbor alterations in the RFC gene, including heterozygous single nucleotide changes resulting in D56H and D522N substitutions in the first extracellular loop and the C-terminus of this transporter, respectively. The third sample had a sequence alteration in exon 3 that could not be identified because of the lack of availability of DNA. CONCLUSIONS: Whereas inactivating RFC mutations are a frequent mechanism of MTX resistance in human leukemia cell lines and in patients with osteosarcoma, they are not common and do not appear to play any significant role in intrinsic or acquired resistance to MTX in childhood leukemia. This is the first study of RFC mutations in multiple pediatric leukemia specimens.

Antimetabolites, Antineoplastic↗
PubMed2006

Reduced folate carrier gene G80A polymorphism is associated with an increased risk of gastroesophageal cancers in a Chinese population.

Low folate intake has been associated with an increased risk of both oesophageal and gastric cancers. Reduced folate carrier (RFC1, also named SLC19A1) is an essential folate transporter and functions as a bidirectional anion exchanger, taking up folate cofactors and exporting various organic anions. A G80A polymorphism in RFC1 gene has been shown to be associated with alterations in folate and homocysteine metabolism in healthy individuals. In this study, we hypothesised that genetic variants in RFC1 may modulate risk of oesophageal cancer (EC) and gastric cancer (GC). To test this hypothesis, we evaluated the associations of the G80A polymorphism of RFC1 with EC and GC risk in a case-control study of 216 EC and 633 GC cases and 673 cancer-free controls in a Chinese population. We found that compared with the 80GG/GA genotypes in the recessive model, the variant homozygote RFC1 80AA was associated with a significantly increased risk of EC (adjusted odds ratio (OR)=1.80, 95% confidence interval (CI)=1.29-2.51), GC (adjusted OR=1.59, 95% CI=1.25-2.02) and EC and GC combined (adjusted OR=1.63, 95% CI=1.30-2.04). In the dominant model, the risk associated with RFC1 80AA was also elevated in EC (OR=1.35, 95% CI=0.91-1.99), GC (OR=1.43, 95% CI=1.07-1.91) and EC and GC combined (adjusted OR=1.40, 95% CI=1.07-1.83), compared with the 80GG genotype. The stratification analyses showed that effects of the RFC1 80AA genotype were more evident in subgroups of relatively older (60 years), female, non-smokers, and non-drinkers both in EC and GC. Although the exact biological mechanism of this association remains to be explored, our findings suggest possible involvement of RFC1 variant in the susceptibility of EC and GC. Further large and functional studies are needed to confirm our findings.

Adult↗
PubMed2005

Low expression of reduced folate carrier-1 and folylpolyglutamate synthase correlates with lack of a deleted in colorectal carcinoma mRNA splice variant in normal-appearing mucosa of colorectal carcinoma patients.

BACKGROUND: Cellular folate deficiency leads to DNA strand breaks, mutations, and aberrant methylation and might be a risk factor for colorectal cancer (CRC). The putative tumor suppressor gene deleted in colorectal carcinoma (DCC) is one of several genes the expression of which seems to be affected by the folate concentration at the tissue level. Decreased expression of DCC may be caused by LOH or hypermethylation, i.e. by events that might be linked to folate deficiency. The purpose of this study was to analyze if the folate level and the gene expression levels of reduced folate carrier (RFC-1) and folylpolyglutamate synthase (FPGS) had impact on the expression of DCC splice variants. METHODS: Quantification of RFC-1 and FPGS expression in mucosa of 53 CRC patients was performed using real-time PCR whereas DCC splicing variants were detected by automated capillary gel electrophoresis. Total reduced folate concentration was measured with the FdUMP-binding assay (n = 22). RESULTS: Significantly higher expression levels of RFC-1 (p = 0.026) and FPGS (p = 0.05) were found in mucosa expressing the splice variant DCC342 compared to mucosa that did not. Furthermore, multivariate analysis showed that RFC-1 and FPGS (r = 0.49, p = 0.01) as well as folate and RFC-1 (r = 0.56, p = 0.023) were correlated only in mucosa expressing DCC342. CONCLUSIONS: In conclusion, the present study points to a potential influence of folates in regulating DCC expression at multiple levels involving post-transcriptional pathways. The results may provide a basis for a detailed investigation of molecular mechanisms involved in folate regulation of DCC expression.

Adenocarcinoma↗
PubMed2005

Folate-related genes and omphalocele.

Women who take folic acid in the periconceptional period greatly reduce their chances of having a child with a neural tube defect (NTD). Using multivitamins may also reduce the risk of having a child with an omphalocele. In this study, we tested single nucleotide polymorphisms in folate-related enzyme genes for association with omphalocele. Polymorphisms in methylenetetrahydrofolate reductase (MTHFR), methylenetetrahydrofolate dehydrogenase (MTHFD1), the reduced folate carrier (SLC19A1), and transcobalamin II (TCN2) were examined in 25 children with euploid omphalocele and 59 matched controls. Omphalocele cases were significantly more likely to carry the T allele of MTHFR 677C-->T, a known risk factor for NTDs (odds ratio 3.50, 95% confidence interval 1.07-11.47, P=0.035). The MTHFD1 R653Q, SLC19A1 R27H, and TCN2 P259R polymorphisms showed no significant association with omphalocele. In this small study, the thermolabile variant of MTHFR, 677C-->T, was associated with an increased risk for omphalocele. This variant causes reduced enzyme activity, thus suggesting a mechanism by which multivitamins with folic acid might prevent omphalocele. Additional investigation is required.

Adult↗
PubMed2005

Polymorphisms in folate metabolic genes and lung cancer risk in Xuan Wei, China.

The aim of this study is to investigate the role of genetic polymorphisms in twelve folate metabolism genes on the risk of lung cancer in Xuan Wei, China, where the lung cancer mortality rate is among the highest and is mainly caused by indoor smoky coal emissions. A total of 122 incident primary lung cancer cases and 122 matched controls were enrolled. Three single nucleotide polymorphisms were associated with increased risk of lung cancer including homozygotes of the C allele of CBS Ala360Ala (OR: 4.02; 95% CI: 1.64-9.87), the 222Val allele of MTHFR (OR: 2.32; 95% CI: 1.34-4.03), and the C allele of SLC19A1 Pro232Pro (OR: 1.83; 95% CI: 1.02-3.28). The distribution of CBS and MTHFR haplotypes differed between cases and controls (P=0.002 and P=0.07, respectively). In summary, three genetic variants in folate metabolism genes are associated with an increased risk of lung cancer in Xuan Wei, China.

Adult↗
PubMed1998

Chromosomal localization of the murine RFC-1 gene encoding a folate transporter and its amplification in an antifolate resistant variant overproducing the transporter.

A variant of the L1210 cell (L1210/R83) selected in the presence of the lipophilic antifolate, metoprine, and a concentration of the natural diastereoisomer of 5-formyltetrahydrofolate, lL5CHO-folateH4, suboptimum for growth exhibited a 35-fold increase compared to parental L1210 cells in one-carbon, reduced folate transport. This was evidenced by the increase in Vmax for [3H]MTX (methotrexate) influx and a commensurate increase in the amount of the 46 kilodalton (kDa) transport protein and reduced folate carrier (RFC-1) mRNA. The variant is resistant to lipophilic antifolates, but shows collateral sensitivity to classical folate analogues. Karyotype analysis of L1210/R83 cells revealed the presence of several new chromosome abnormalities. One of these was a large, submetacentric marker chromosome comprising a normal #10 and a longer, abnormally banded arm of uncertain origin which exhibited an interstitial, palely staining, HSR-like segment. The results of Southern and Northern blotting showed that the RFC-1 gene copy number and RNA transcript level were markedly increased (30-35 fold) in L1210/R83 cells. Fluorescence in situ hybridization (FISH) analysis revealed that the HSR-like segment in these cells was the site of amplified RFC-1 genes. Independent revertant subclones, obtained following growth in the absence of selection pressure, showed four- to 12-fold decreases in [3H]MTX influx Vmax and in amount of NHS (N-hydroxysuccinimide)-[3H]MTX affinity labeled one-carbon, reduced folate transporter compared to L1210/R83 cells. RFC-1 gene copy number also decreased, and the mean length of the HSR in these revertants declined 1.6- to 5-fold. Based upon genomic nucleotide sequencing, the RFC-1 gene in the normal mouse genome was localized to chromosome 10 in close association with the alpha 1 (Col18a1) collagen gene at 10B3(locus 41cM). The close association of these genes was confirmed by other data showing that the alpha 1 collagen gene was co-amplified in L1210/R83 cells. These results document the amplification at the site of a putative HSR in an L1210 cell variant of the RFC-1 gene regulating expression of the one-carbon, reduced folate transporter.

Animals↗
PubMed2002

Cytoplasmic domains of the reduced folate carrier are essential for trafficking, but not function.

The reduced folate carrier (RFC) protein has a secondary structure consistent with the predicted 12 transmembrane (TM) domains, intracellular N- and C-termini and a large cytoplasmic loop between TM6 and TM7. In the present study, the role of the cytoplasmic domains in substrate transport and protein biogenesis were examined using an array of hamster RFC deletion mutants fused to enhanced green fluorescent protein and expressed in Chinese hamster ovary cells. The N- and C-terminal tails were removed both individually and together, or the large cytoplasmic loop was modified such that the domain size and role of conserved sequences could be examined. The loss of the N- or C-terminal tails did not appear to significantly disrupt protein function, although both termini appeared to have a role in the efficiency with which molecules exited the endoplasmic reticulum to localize at the plasma membrane. There appeared to be both size and sequence requirements for the intracellular loop, which are able to drastically affect protein stability and function unless met. Furthermore, there might be an indirect role for the loop in substrate translocation, since even moderate changes significantly reduced the V(max) for methotrexate transport. Although these cytoplasmic domains do not appear to be absolutely essential for substrate transport, each one is important for biogenesis and localization.

Amino Acid Sequence↗
PubMed1997

Cellular and molecular mechanisms of resistance to antifolate drugs: new analogues and approaches to overcome the resistance.

A number of antifolate drugs, which inhibit the key enzymes in the 'thymidylate cycle', dihydrofolate reductase (DHFR) and thymidylate synthase (TS), have been developed as part of the search for analogues with superior antitumor efficacy to a 'classical' antifolate, methotrexate (MTX), and those which are active against the MTX-resistant tumor cells. Recent development of newer classes of antifolate drugs is based on the extensive understanding of the relationship between chemical structures and biological properties and of analogue interactions with target enzymes, transport proteins and folate metabolizing enzyme, folylpolyglutamate synthetase (FPGS). Tumor cells may develop resistance to an antifolate drug by virtue of, (1) amplified activity in its target enzyme, (2) impaired function of drug transport protein, e.g. reduced folate carrier (RFC), (3) induction of mutated target enzyme with low affinity for antifolate(s), and (4) defective polyglutamation of drug(s) in the cells. Recent studies have elucidated in part the molecular events involved in the resistance to antifolates. These include amplification and/or mutation of the gene encoding a target enzyme, reduced or altered gene expression of the RFC, and mutated expression of the FPGS gene. To overcome or circumvent the resistance mechanisms, new antifolates with diverse structures and different biological properties have been designed and developed for clinical use. Trimetrexate (TMQ), a lipophilic DHFR inhibitor which is not a substrate for RFC and FPGS, could overcome the MTX-resistance through impaired RFC and diminished polyglutamation, and partially through amplified DHFR. Selective inhibitors of TS with a folate structure such as raltitrexed could circumvent the resistance by virtue of DHFR overproduction, and this class of compounds which have higher substrate activities for FPGS than MTX may be of value for the treatment of myeloid leukemias in addition to lymphocytic malignancies resistant to conventional chemotherapy. Several strategies to overcome antifolate resistance by using gene therapy are currently under investigation.

Antimetabolites, Antineoplastic↗
PubMed2005

The pharmacogenetics of methotrexate in inflammatory bowel disease.

OBJECTIVES: Methotrexate (MTX) is an effective immunosuppressive treatment in inflammatory bowel disease (IBD) but its use is limited by unpredictable toxicity and efficacy. MTX metabolism is complex involving a number of enzymes. An individual's response to MTX may in part be genetically determined by functional genetic variation in genes encoding these enzymes. We report a pharmacogenetic evaluation of MTX therapy in IBD. METHODS: We studied 102 IBD patients treated with MTX, and 202 patients with Crohn's disease (CD), 205 patients with ulcerative colitis (UC) and 189 healthy volunteers served as controls to assess allele frequencies in the disease and healthy populations. All subjects were genotyped for four polymorphisms: G80A in the reduced folate carrier (RFC1) gene, G452T in the gamma-glutamyl hydrolase (GGH) gene and C677T and A1298C in the methylenetetrahydrofolate reductase (MTHFR) gene. Three non-conservative SNPs in the RFC1 and the MTHFR gene could not be detected in our patient cohort. Genotype-phenotype associations were evaluated with respect to efficacy and toxicity of MTX therapy. RESULTS: No significant differences in the allele frequencies between CD, UC and healthy controls were detected. Overall 21% of patients experienced MTX side effects. Patients homozygous for the MTHFR 1298C allele were more likely to experience one or more side effects compared to patients with the wild-type 1298AA genotype (21.0 vs. 6.3%, P < 0.05). None of the genotyped SNPs or haplotypes, either alone or in combination, was associated with short-term efficacy or sustained response. CONCLUSIONS: Side effects of MTX in IBD are associated with a SNP in the MTHFR gene but response cannot be predicted by any of the investigated SNPs.

Adolescent↗
PubMed2005

Cerebral folate deficiency with developmental delay, autism, and response to folinic acid.

The authors describe a 6-year-old girl with developmental delay, psychomotor regression, seizures, mental retardation, and autistic features associated with low CSF levels of 5-methyltetrahydrofolate, the biologically active form of folates in CSF and blood. Folate and B12 levels were normal in peripheral tissues, suggesting cerebral folate deficiency. Treatment with folinic acid corrected CSF abnormalities and improved motor skills.

Adaptation, Physiological↗
PubMed2006

Pacific Craniofacial Team and Cleft Prevention Program.

There is no doubt modern genetics have greatly influenced our professional and personal lives during the last decade. Uncovering genetic causes of many medical and dental pathologies is helping to narrow the diagnosis and select a treatment plan that would provide the best outcome. Importantly, having an understanding of multifactorial etiology helps direct our attention toward prevention. We now understand much better our own health problems. In some cases, we can modify our lifestyle and diet in order to prevent "environmental factors" from triggering the mutated genes inherited from our parents. Good examples are diabetes and cardiovascular diseases. If we realize we might have inherited genes for cardiovascular problems from several ancestors who had heart attacks, we already know that these genes will make us only "susceptible" for disease. Those who exercise, watch one's weight, diet, and carefully monitor one's lifestyle will very likely--though possessing "susceptibility genes"--stay healthier and, maybe, will never experience any cardiovascular problems. In principle, the same applies for craniofacial anomalies, especially for nonsyndromic cleft lip and palate. One needs to understand genetic and environmental causes of nonsyndromic orofacial clefts in order to prevent them. With all this in mind, the Pacific Craniofacial Team and Cleft Prevention Program have been established at the Department of Orthodontics, University of the Pacific Arthur A. Dugoni School of Dentistry in San Francisco. A partnership with Rotaplast International, Inc., has made it possible for the faculty, orthodontic residents, and students to participate in 27 multidisciplinary cleft medical missions in underdeveloped and developing countries by donating professional and educational services, and, last but not least, by collecting valuable data and specimens to further research. A significant number of research studies, including 15 master of science theses, have been accomplished in UOP's Craniofacial Genetics Laboratory, with contributions by faculty, undergraduate and graduate students. It has been leading to a better understanding of etiology of nonsyndromic orofacial clefts. It has been learned that genetic factors and environmental factors are ethnicity-specific and, in many places throughout the world, location-specific. Thus, a specific protocol for cleft prevention has to be worked out based on genetic and nutritional studies of each specific population group in order to be effective. This is our ultimate goal.

California↗
PubMed1993

Mutations leading to antifolate resistance in Chinese hamster ovary cells after exposure to the alkylating agent ethylmethanesulfonate.

Chinese hamster ovary cells with a single allele for dihydrofolate reductase were used as a model system to study the effect of exposure to an alkylating agent, ethylmethanesulfonate, on rates and types of mutations at the dihydrofolate reductase locus leading to antifolate resistance. After overnight exposure to 400 micrograms/ml ethylmethanesulfonate, cells were allowed to recover for 3 days, and resistant colonies were selected in 8 x 10(-8) M trimetrexate. Trimetrexate, rather than methotrexate, was used as the selecting agent to increase the probability of obtaining mutations in dihydrofolate reductase, rather than in the reduced folate transport carrier protein. Seven of several hundred surviving colonies were selected at random, and cell lines were established. Cell lines 1-3 were maintained in culture in the presence of 8 x 10(-8) M trimetrexate and were 66-170-fold resistant to the drug. Cell lines 4-7 were initially expanded in 8 x 10(-8) M trimetrexate but were then maintained in the absence of the drug. These cell lines were 4.4-26-fold resistant to the drug, compared with the parental cell line. Cell line 1 was found to have an increase in dihydrofolate reductase activity, a corresponding increase in mRNA for dihydrofolate reductase, and amplification of this gene. Cell lines 2 and 6 had a mutated dihydrofolate reductase with altered trimetrexate- and methotrexate-binding properties. Cell line 3 had a 3-fold increase in dihydrofolate reductase activity. In cell lines 4, 5, and 7 the mechanisms of resistance to trimetrexate remain unknown.

Alkylating Agents↗
PubMed1996

Thymidylate synthase inhibitors.

Folate analogues that inhibit thymidylate synthase (TS) selectively were developed based on TS and folate molecular structures and properties. The structure-activity relationship, preclinical and clinical development, and issues of potential importance in the future success of these TS inhibitors are reviewed herein. Properties of these new compounds depend mainly on the use of the reduced folate carrier (RFC) proteins for cellular entry and on intracellular polyglutamation, which augments TS inhibitory function and cellular retention. CB3717 [Zeneca (formerly ICI Pharmaceuticals), Macclesfield, United Kingdom], the first selective TS inhibitor developed, demonstrated antineoplastic activity in Phase I trials, but its development was abandoned due to nephrotoxicity. ZD1694 (Tomudex; Zeneca), a water-soluble, nonnephrotoxic quinazoline, demonstrated activity in colorectal, breast, and pancreatic cancer. Phase III trials of Tomudex in advanced colorectal cancer were completed recently. LY231514 (Eli Lilly Research Labs, Indianapolis, IN) uses the RFC and polyglutamation to exert its selective TS inhibitory action. Phase I trials of this compound have been completed. ZD9331 (Zeneca), currently in preclinical studies, was designed to obviate the use of the RFC for cellular entry. 1843U89 (Glaxo-Wellcome, Research Triangle Park, NC), currently in Phase I trial, does not require the RFC; polyglutamation of this potent TS inhibitor leads to its higher cellular retention without augmenting its TS inhibitory activity. Currently in clinical trials, AG337 (p.o. and i.v. forms) and AG331 (both by Agouron, La Jolla, CA) are lipophilic potent TS inhibitors with action independent of the RFC and polyglutamation. Multiple mechanisms through which cells may overcome TS inhibition have been described. Combining TS inhibitors with other agents that affect TS, interfere with TS gene and mRNA regulation, or inhibit salvage mechanisms of thymidylate depletion may potentially enable greater clinical utility of this class of compounds.

Animals↗