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Frontiers in Bioscience (Elite Edition) Jan 2010We review the semiparametric approach previously proposed by Kong and Lee and extend it to a case in which the dose-effect curves follow the Emax model instead of the...
We review the semiparametric approach previously proposed by Kong and Lee and extend it to a case in which the dose-effect curves follow the Emax model instead of the median effect equation. When the maximum effects for the investigated drugs are different, we provide a procedure to obtain the additive effect based on the Loewe additivity model. Then, we apply a bivariate thin plate spline approach to estimate the effect beyond additivity along with its 95 per cent point-wise confidence interval as well as its 95 per cent simultaneous confidence interval for any combination dose. Thus, synergy, additivity, and antagonism can be identified. The advantages of the method are that it provides an overall assessment of the combination effect on the entire two-dimensional dose space spanned by the experimental doses, and it enables us to identify complex patterns of drug interaction in combination studies. In addition, this approach is robust to outliers. To illustrate this procedure, we analyzed data from two case studies.
Topics: Analysis of Variance; Cell Line, Tumor; Data Interpretation, Statistical; Dose-Response Relationship, Drug; Drug Interactions; Folic Acid; Glutamates; Humans; Models, Theoretical; Pyrimidines; Trimetrexate
PubMed: 20036878
DOI: 10.2741/e90 -
Frontiers in Bioscience (Elite Edition) Jan 2010In this paper we review the application of the Separate Ray Model to analyze drug combination experiments coming from a fixed ratio design. The idea is the joint fit of...
In this paper we review the application of the Separate Ray Model to analyze drug combination experiments coming from a fixed ratio design. The idea is the joint fit of separate concentration response curves to each ray under investigation leading to an interaction index for each together with a 95 percent Confidence Interval. The approach is a simple and easy to implement parametric modeling approach and allows estimation and testing of drug interactions based on regularly sampling in the entire space of all combinations going from pure compound A to pure compound B. The analysis is implemented using the SAS/STAT procedure NLMIXED. Two datasets were provided for the modeling exercise. One included different qualitative effects with some rays showing synergy, others antagonism and again others additivity. The second dataset involved the presence of very large synergy together with different observed background effects for the individual rays. The Separate Ray Model is able to handle these practical issues making it a flexible tool to investigate drug interaction experiments using a fixed ratio design.
Topics: Cell Line, Tumor; Data Interpretation, Statistical; Dose-Response Relationship, Drug; Drug Interactions; Drug Synergism; Folic Acid; Glutamates; Humans; Models, Theoretical; Pyrimidines; Research Design; Trimetrexate
PubMed: 20036877
DOI: 10.2741/e89 -
Frontiers in Bioscience (Elite Edition) Jan 2010The design and analysis of drug combination studies continue to be an area requiring further methodological developments. Faessel et al. (1998) studied the joint effects...
The design and analysis of drug combination studies continue to be an area requiring further methodological developments. Faessel et al. (1998) studied the joint effects of the combinations of trimetrexate (TMQ) and the GARFT inhibitor AG2034 to inhibit the growth of HCT-8 human ileocecal adenocarcinoma cells. Their experiments provide a rich data resource to validate the performance of new experimental design and analysis methods for future experiments. In this paper, we first re-analyze the same data with a nonparametric model and briefly review the experimental design used in the original paper. By comparing the analysis results, we found that the fixed ratio design and the usage of the parametric model for estimating the interaction index are based on an assumption not supported by the data. We then show how the efficiency of the experiments would be improved had the maximal power experimental design based on uniform measures been used. The usage of the proposed maximal power experimental design is further supported by simulation studies.
Topics: Cell Line, Tumor; Computer Simulation; Data Interpretation, Statistical; Drug Interactions; Glutamates; Humans; Models, Theoretical; Pyrimidines; Research Design; Statistics, Nonparametric; Trimetrexate
PubMed: 20036876
DOI: 10.2741/e88 -
Frontiers in Bioscience (Elite Edition) Jan 2010This paper is concerned with the statistical analysis of data obtained in studies of the joint action of drugs. The three methods that are compared are illustrated on... (Comparative Study)
Comparative Study
This paper is concerned with the statistical analysis of data obtained in studies of the joint action of drugs. The three methods that are compared are illustrated on real data (1), using the statistical package SAS. It is argued that while the results obtained using these methods do not differ substantially, the method allowing for estimating simultaneously all required parameters is to be preferred. It allows for a statistical test for the significance of the joint action of the drug combinations to be carried out.
Topics: Cell Line, Tumor; Data Interpretation, Statistical; Dose-Response Relationship, Drug; Drug Combinations; Drug Interactions; Drug Synergism; Folic Acid; Glutamates; Humans; Models, Theoretical; Pyrimidines; Trimetrexate
PubMed: 20036875
DOI: 10.2741/e87 -
Frontiers in Bioscience (Elite Edition) Jan 2010The goal of the present report is to compare several published methods of analyzing drug-drug interaction data. The compared methods are the curve-shift analysis,... (Comparative Study)
Comparative Study
The goal of the present report is to compare several published methods of analyzing drug-drug interaction data. The compared methods are the curve-shift analysis, isobologram, combination index, and universal surface response analysis, and the comparison was based on analysis of published cytotoxicity data of combinations of two anti-folate agents. Major findings are as follows. The curve shift analysis enabled the inspection of the experimental data and visual evaluation of the approximate parallelism between the dose response curves. Isobologram analysis provided the range of concentration ratios where maximal synergy was obtained. The combination index analysis readily provided quantitative estimation of the extent of synergy or antagonism. The universal surface response method summarized drug-drug interaction in a single parameter, facilitating comparison of larger arrays of combinations. Only the curve shift analysis and the universal surface response method yielded a statistical estimate of differentiation between synergy, additivity, and antagonism. In summary, curve shift analysis, isobolograms, combination index analysis, and the universal response surface method are useful methods for analyzing drug-drug interaction, and provide complementary information.
Topics: Cell Line, Tumor; Data Interpretation, Statistical; Dose-Response Relationship, Drug; Drug Combinations; Drug Interactions; Drug Synergism; Folic Acid; Glutamates; Humans; Models, Theoretical; Pyrimidines; Trimetrexate
PubMed: 20036874
DOI: 10.2741/e86 -
The Journal of Antimicrobial... Dec 2009First-line therapy for Pneumocystis jirovecii pneumonia (PCP) is trimethoprim/sulfamethoxazole. Few data exist to guide the choice of second-line therapy for patients...
OBJECTIVES
First-line therapy for Pneumocystis jirovecii pneumonia (PCP) is trimethoprim/sulfamethoxazole. Few data exist to guide the choice of second-line therapy for patients failing or developing toxicity to first-line therapy.
METHODS
A case note review of 1122 patients with 1188 episodes of HIV-associated PCP from three observational cohorts in Copenhagen, London and Milan, between 1989 and 2004, was conducted.
RESULTS
Trimethoprim/sulfamethoxazole (962 PCP episodes, 81%) was the most frequently used first-line therapy, followed by intravenous pentamidine (87 episodes, 7%), clindamycin/primaquine (72 episodes, 6%) and 'other' (atovaquone, dapsone/pyrimethamine, trimetrexate or inhaled pentamidine; 67 episodes, 6%). Rates of unchanged therapy were trimethoprim/sulfamethoxazole = 79%, clindamycin/primaquine = 65% and pentamidine = 60% (P < 0.001). First-line therapy was changed because of failure in 82 (7%) episodes and because of toxicity in 198 (17%) episodes. Three month survival rates were trimethoprim/sulfamethoxazole = 85%, clindamycin/primaquine = 81% and pentamidine = 76% (P = 0.09). After adjustment for possible confounders, pentamidine was associated with a significantly greater risk of death at 3 months [hazard ratio (HR) = 2.0, 95% confidence interval (CI) = 1.2-3.4]. Second-line therapy survival rates differed: trimethoprim/sulfamethoxazole = 85%; clindamycin/primaquine = 87%; and pentamidine = 60% (P = 0.01). Multivariable time-updated Cox regression analysis showed a greater risk of death associated with pentamidine (HR = 3.3, 95% CI = 2.2-5.0), but not for clindamycin/primaquine, when both were compared with trimethoprim/sulfamethoxazole.
CONCLUSIONS
Pentamidine was associated with a greater risk of death when used as first- and second-line therapy for HIV-associated PCP, and was associated with more treatment changes. Clindamycin/primaquine appeared superior to pentamidine as second-line therapy for PCP in patients failing or developing toxicity with trimethoprim/sulfamethoxazole. In patients failing first-line treatment with non-trimethoprim/sulfamethoxazole regimens, second-line therapy should be trimethoprim/sulfamethoxazole.
Topics: AIDS-Related Opportunistic Infections; Acquired Immunodeficiency Syndrome; Adolescent; Adult; Aged; Antifungal Agents; Clindamycin; Cohort Studies; Denmark; Female; Humans; Italy; London; Male; Middle Aged; Pentamidine; Pneumocystis carinii; Pneumonia, Pneumocystis; Primaquine; Survival Analysis; Treatment Outcome; Trimethoprim, Sulfamethoxazole Drug Combination; Young Adult
PubMed: 19858161
DOI: 10.1093/jac/dkp372 -
American Journal of Clinical Oncology Apr 2010The primary objective of this trial was to evaluate the response rate for trimetrexate in conjunction with 5-FU and leucovorin (LV) (= TFL) in the treatment of advanced...
OBJECTIVE
The primary objective of this trial was to evaluate the response rate for trimetrexate in conjunction with 5-FU and leucovorin (LV) (= TFL) in the treatment of advanced gastric cancer in a phase II, cooperative group setting.
METHODS
Patients with locally advanced, unresectable, or metastatic adenocarcinoma of the stomach received trimetrexate 110 mg/m IV over 60 minutes day 1, followed by 5-FU 500 mg/m IV bolus and LV 200 mg/m IV over 60 minutes day 2, followed by oral LV 15 mg every 6 hours x 7 doses, all weekly for 6 weeks followed by 2 weeks of rest, continued until progression.
RESULTS
Characteristics for 37 eligible patients: median age 63 (range: 23-83); male/female: 69% of 31%; performance status 0/1/2 15/20/1. The confirmed response rate was 19%, and median overall survival was 6 months. Two patients died as a result of therapy, 1 because of infection without significant neutropenia, and 1 due to perforation of a responding gastric lesion. Seventy-two percent experienced grades 3 and 4 toxicity, most commonly diarrhea, fatigue, and lymphopenia.
CONCLUSIONS
This regimen achieves response rates comparable to other 5-FU-based regimens, when used in treatment of incurable gastric cancer. Toxicity appears manageable.
Topics: Adenocarcinoma; Adult; Aged; Aged, 80 and over; Antineoplastic Combined Chemotherapy Protocols; Female; Fluorouracil; Humans; Leucovorin; Male; Middle Aged; Neoplasm Staging; Stomach Neoplasms; Survival Rate; Treatment Outcome; Trimetrexate; Young Adult
PubMed: 19770625
DOI: 10.1097/COC.0b013e318199fb84 -
Antimicrobial Agents and Chemotherapy Sep 2009We have analyzed the activities of the antifolates pyrimethamine (PM), chlorcycloguanil (CCG), WR99210, trimethoprim (TMP), methotrexate (MTX), and trimetrexate (TMX)...
In vitro activity of antifolate and polymorphism in dihydrofolate reductase of Plasmodium falciparum isolates from the Kenyan coast: emergence of parasites with Ile-164-Leu mutation.
We have analyzed the activities of the antifolates pyrimethamine (PM), chlorcycloguanil (CCG), WR99210, trimethoprim (TMP), methotrexate (MTX), and trimetrexate (TMX) against Kenyan Plasmodium falciparum isolates adapted in vitro for long-term culture. We have also assessed the relationship between these drug activities and mutations in dihydrofolate reductase (dhfr), a domain of the gene associated with antifolate resistance. As expected, WR99210 was the most potent drug, with a median 50% inhibitory concentration (IC50) of <0.075 nM, followed by TMX, with a median IC50 of 30 nM. The median IC50 of CCG was 37.80 nM, and that of MTX was 83.60 nM. PM and TMP were the least active drugs, with median IC50s of 733.26 nM and 29,656.04 nM, respectively. We analyzed parasite dhfr genotypes by the PCR-enzyme restriction technique. No wild-type dhfr parasite was found. Twenty-four of 33 parasites were triple mutants (mutations at codons 108, 51, and 59), and only 8/33 were double mutants (mutations at codons 108 and 51 or at codons 108 and 59). IC50s were 2.1-fold (PM) and 3.6-fold (TMP) higher in triple than in double mutants, though these differences were not statistically significant. Interestingly, we have identified a parasite harboring a mutation at codon 164 (Ile-164-Leu) in addition to mutations at codons 108, 51, and 59. This quadruple mutant parasite had the highest TMP IC50 and was in the upper 10th percentile against PM and CCG. We confirmed the presence of this mutation by sequencing. Thus, TMX and MTX are potent against P. falciparum, and quadruple mutants are now emerging in Africa.
Topics: Animals; Antimalarials; Folic Acid Antagonists; Genotype; Inhibitory Concentration 50; Kenya; Methotrexate; Mutation; Plasmodium falciparum; Polymerase Chain Reaction; Polymorphism, Genetic; Proguanil; Pyrimethamine; Tetrahydrofolate Dehydrogenase; Triazines; Trimethoprim; Trimetrexate
PubMed: 19528269
DOI: 10.1128/AAC.00308-09 -
Molecular Microbiology Jul 2008The phenotypes of single- (SKO) and double-knockout (DKO) lines of dihydrofolate reductase-thymidylate synthase (DHFR-TS) of bloodstream Trypanosoma brucei were...
The phenotypes of single- (SKO) and double-knockout (DKO) lines of dihydrofolate reductase-thymidylate synthase (DHFR-TS) of bloodstream Trypanosoma brucei were evaluated in vitro and in vivo. Growth of SKO in vitro is identical to wild-type (WT) cells, whereas DKO has an absolute requirement for thymidine. Removal of thymidine from the medium triggers growth arrest in S phase, associated with gross morphological changes, followed by cell death after 60 h. DKO is unable to infect mice, whereas the virulence of SKO is similar to WT. Normal growth and virulence could be restored by transfection of DKO with T. brucei DHFR-TS, but not with Escherichia coli TS. As pteridine reductase (PTR1) levels are unchanged in SKO and DKO cells, PTR1 is not able to compensate for loss of DHFR activity. Drugs such as raltitrexed or methotrexate with structural similarity to folic acid are up to 300-fold more potent inhibitors of WT cultured in a novel low-folate medium, unlike hydrophobic antifols such as trimetrexate or pyrimethamine. DKO trypanosomes show reduced sensitivity to these inhibitors ranging from twofold for trimetrexate to >10 000-fold for raltitrexed. These data demonstrate that DHFR-TS is essential for parasite survival and represents a promising target for drug discovery.
Topics: Animals; Antiprotozoal Agents; Biosynthetic Pathways; Cell Death; Cell Division; Flow Cytometry; Gene Deletion; Genetic Complementation Test; Genotype; Inhibitory Concentration 50; Mice; Microscopy, Electron, Transmission; Oxidoreductases; Protozoan Proteins; Survival Analysis; Tetrahydrofolate Dehydrogenase; Thymidine; Thymidylate Synthase; Trypanosoma brucei brucei; Trypanosomiasis, African; Virulence
PubMed: 18557814
DOI: 10.1111/j.1365-2958.2008.06305.x -
Parasitology Research May 2008The folate derivatives folic acid (FA) and folinic acid (FNA) decrease the in vivo and in vitro activities of antifolate drugs in Plasmodium falciparum. However, the...
The folate derivatives folic acid (FA) and folinic acid (FNA) decrease the in vivo and in vitro activities of antifolate drugs in Plasmodium falciparum. However, the effects of 5-methyl-tetrahydrofolate (5-Me-THF) and tetrahydrofolate (THF), the two dominant circulating folate forms in humans, have not been explored yet. We have investigated the effects of FA, FNA, 5-Me-THF, and THF on the in vitro activity of the antimalarial antifolates pyrimethamine and chlorcycloguanil and the anticancer antifolates methotrexate (MTX), aminopterin, and trimetrexate (TMX), against P. falciparum. The results indicate that these anticancers are potent against P. falciparum, with IC50 < 50 nM. 5-Me-THF does not significantly decrease the activity of all tested drugs, and none of the tested folate derivatives significantly decrease the activity of these anticancers. Thus, malaria folate metabolism has features different from those in human, and the exploitation of this difference could lead to the discovery of new drugs to treat malaria. For instance, the combination of 5-Me-THF with a low dose of TMX could be used to treat malaria. In addition, the safety of a low dose of MTX in the treatment of arthritis indicates that this drug could be used alone to treat malaria.
Topics: Aminopterin; Animals; Antimalarials; Antineoplastic Agents; Folic Acid; Folic Acid Antagonists; Inhibitory Concentration 50; Leucovorin; Methotrexate; Molecular Structure; Plasmodium falciparum; Proguanil; Pyrimethamine; Tetrahydrofolates; Triazines; Trimetrexate
PubMed: 18259776
DOI: 10.1007/s00436-008-0897-4