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Biomedical subjects

F Chu

Publications and source records attributed to F Chu.

At least 19 recordsLinked to original sources
PubMed1994

Developing multianalyte assays.

Multianalyte 'binding' assays represent a major advance in microanalytical technology for the measurement of substances of biological importance. Their further development should facilitate sensitive and reproducible quantification of analytes in many areas that are currently problematic, including diagnostic medicine and the standardization of biologicals.

Forecasting↗
PubMed1994

Expression of the plasmodial pfmdr1 gene in mammalian cells is associated with increased susceptibility to chloroquine.

Chloroquine (CQ)-resistant (CQR) Plasmodium falciparum malaria parasites show a strong decrease in CQ accumulation in comparison with chloroquine-sensitive parasites. Controversy exists over the role of the plasmodial pfmdr1 gene in the CQR phenotype. pfmdr1 is a member of the superfamily of ATP-binding cassette transporters. Other members of this family are the mammalian multidrug resistance genes and the CFTR gene. We have expressed the pfmdr1-encoded protein, Pgh1, in CHO cells and Xenopus oocytes. CHO cells expressing the Pgh1 protein demonstrated an increased, verapamil-insensitive susceptibility to CQ. Conversely, no increase in drug susceptibility to primaquine, quinine, adriamycin, or colchicine was observed in Pgh1-expressing cells. CQ uptake experiments revealed an increased, ATP-dependent accumulation of CQ in Pgh1-expressing cells over the level in nonexpressing control cells. The increased CQ accumulation in Pgh1-expressing cells coincided with an enhanced in vivo inhibition of lysosomal alpha-galactosidase by CQ. CHO cells expressing Pgh1 carrying two of the CQR-associated Pgh1 amino acid changes (S1034C and N1042D) did not display an increased CQ sensitivity. Immunofluorescence experiments revealed an intracellular localization of both mutant and wild-type forms of Pgh1. We conclude from our results that wild-type Pgh1 protein can mediate an increased intracellular accumulation of CQ and that this function is impaired in CQR-associated mutant forms of the protein. We speculate that the Pgh1 protein plays an important role in CQ import in CQ-sensitive malaria parasites.

ATP-Binding Cassette Transporters↗
PubMed1994

Lung cancer: evaluation with MR imaging during and after irradiation.

We used magnetic resonance (MR) imaging to evaluate treatment response of 10 consecutive lung cancer patients while they were receiving radiation therapy. Patients were scanned before treatment, during treatment, at completion of treatment, and if possible, at 3-month intervals thereafter. The initial tumor response to radiation was increasing signal intensity and increasing heterogeneity, best seen on T2-weighted images. Small tumors virtually disappeared, whereas larger masses remained as complex cystic structures or developed cavities. The adjacent irradiated lung parenchyma had increased signal on both the T1- and T2-weighted images as early as 17 days after start of treatment. The signal intensity continued to increase for several months after treatment, but subsequently decreased.

Adult↗
PubMed1993

Radioimmunoassay of ganirelix in plasma or serum.

A procedure for the radioimmunoassay (RIA) of ganirelix in plasma or serum at concentrations as low as 0.050 ng/ml is described. Antiserum was produced by coupling the N-terminus glycyl analog of ganirelix to BSA by a carbodiimide reaction and immunizing rabbits with this conjugate. The antiserum did not crossreact with LHRH or with various ganirelix peptide fragments. For RIA, 125I labeled ganirelix was used as the tracer and a double antibody procedure was used to separate the free and bound fractions. No purification of the analyte was required prior to RIA. Accuracy of the method was assessed by adding known quantities of ganirelix to ganirelix-free plasma and determining the ratio of measured to added analyte. Linear regression analysis for the concentration range 0.050-50.0 ng/ml yielded a regression equation of y = 0.97x + 0.18, r = 0.999, where x is the amount added and y is the amount measured. Additional validation was obtained from an in vivo study in which [3H]-ganirelix was administered to monkeys and plasma clearance profiles were determined by RIA and an HPLC-radiochemical method. The results were in agreement within experimental error of the two methods. Linear regression analysis of the comparative data gave the equation y = 0.92x + 33.7, r = 0.980, where x is the amount measured by RIA and y is the amount measured by HPLC-radiochemical analysis.

Amino Acid Sequence↗
PubMed1993

Sonographic heat generation in vivo in the gravid long-tailed macaque (Macaca fascicularis).

Temperature elevations that occur during diagnostic ultrasonic exposure were assessed in vivo in gravid macaques after 10, 20, or 30 min (scan mode; N = 30) or 5, 10, or 15 min (pulsed Doppler; N = 32). Five time points were assessed during the second and third trimesters (gestational days 70 to 150 +/- 2; term, approximately 165 days) using a transient thermocouple technique. Measurements were obtained intracranially or at the muscle-bone interface using a commercial sector scanner (ATL MK 600, 7.5 MHz scanhead; scan mode, ISPTA) = 27 mW/cm2, ISPPA = 85 W/cm2, pulse repetition frequency (PRF) = 1 kHz; pulsed Doppler - ISPTA = 54 mW/cm2, ISPPA = 1.5 W/cm2, PRF = 18.5 kHz). Overall, the greatest temperature elevation achieved with either modality or location was 0.6 degrees C.

Animals↗
PubMed1992

Multianalyte microspot immunoassay. The microanalytical 'compact disk' of the future.

Throughout the 1970s, controversy centered both on immunoassay 'sensitivity' per se and on the relative sensitivities of labelled antibody and labelled analyte methods. Our own theoretical studies in this period revealed that radioimmunoassay (RIA) sensitivities could be surpassed only by the use of very high specific activity non-isotopic labels in 'non-competitive' designs, preferably based on the use of monoclonal antibodies. The time-resolved fluorescence methodology known as Delfia - developed in collaboration with the instrument manufacturer LKB/Wallac - represented the first commercial 'ultra-sensitive' non-isotopic technique based on these theoretical insights, the same concepts being subsequently adopted in comparable methodologies relying on the use of chemiluminescent and enzyme labels. However, a second advantage of high specific activity labels is that they permit the development of 'multi-analyte' immunoassay systems combining ultra-sensitivity with the simultaneous measurement of tens, hundreds or thousands of analytes in a small biological sample. This possibility relies on simple, albeit hitherto unexploited, physicochemical concepts. The first is that all immunoassays rely on measurement of Ab occupancy by analyte. The second is that, provided the Ab concentration used is 'vanishingly small', fractional Ab occupancy is independent of both Ab concentration and sample volume. This leads to the notion of 'ratiometric' immunoassay, involving measurement of the ratio of signals (eg fluorescent signals) emitted by two labelled Ab's, the first ('sensor' Ab) deposited as a microspot on a solid support, the second a 'developing' Ab directed against either occupied or unoccupied sensor Ab binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding, Competitive↗
PubMed1991

Studies on antipeptic ulcer agents: the quantitative structure-activity relationship analysis of heterocyclic aldehyde N4-substituted phenyl (thio) semicarbazones.

Forty-five condensation products of furan-, pyrrole- and N-methyl pyrrole-alpha-carboaldehyde with N4-3- or N4-4-substituted phenyl semicarbazones and thiosemicarbazones were designed to optimize the antiulcer activity of a previously derived lead structure, formula II. Quantitative structure-activity relationships revealed that among the series of semicarbazones, increasing hydrophobicity and the introduction of electron-donating groups into the phenyl ring raise the antiulcer activity. Generally, semicarbazones are more active than the corresponding thiosemicarbazones. The wide gulf between the activity and toxicity of two derivatives (Compounds III and IV) necessitates further investigation of their pharmacological effects.

Anti-Ulcer Agents↗
PubMed1990

Studies on antipeptic ulcer agents: a structure-activity relationship analysis of aldehyde semicarbazones and aryl hydrazones.

Twenty-eight condensation products of heterocyclic-a-carboaldehydes with N-aminooxazolidones, semicarbazides, thiosemicarbazides and benzoxycarbonyl hydrazide were synthesized so as to deduce the antiulcer pharmacophore or fragment of furazolidone (I), a prototype which has shown therapeutic efficacy in patients with gastric and duodenal ulcers. SAR analysis of the compounds indicated that the substitution of furan, thiophene, pyrrole or N-methyl pyrrole rings for 5-nitrofuran and the cleavage of the oxazolidone ring did not fully destroy the activity. The electron density of the carbonyl group was found to be of importance. A lead structure, therefore, was derived for further optimization.

Animals↗
PubMed1990

Multispot, multianalyte, immunoassay.

Consideration of the basic principles of immunoassay design reveals that highly sensitive assays can, in principle, be developed using amounts of "sensor" antibody far smaller than are currently conventional in this field. Furthermore, when using such amounts, the fractional occupancy of antibody binding sites by analyte is independent of both sample volume and antibody concentration. Labelling of both the sensor-antibody and a developing antibody (designed to recognize either occupied or unoccupied sensor-antibody binding sites) permits the development of "ratiometric" immunoassays relying on measurement of the ratio of signals emitted by the two labelled antibodies. Furthermore, the sensor-antibody can be located within a "microspot" a few microns 2 in area. By labelling both sensor and developing antibodies with fluorescent labels, and scanning the microspot using a highly focussed laser beam, microspot immunoassays at least comparable in sensitivity with conventional "macroscopic" immunoassays are made possible. This in turn permits the development of immunoassay "arrays" capable in principle of measuring very large numbers of different substances within small samples (such as a drop of blood). The general principles and theory underlying these concepts are discussed, and preliminary experimental data using currently available instrumentation reported.

Fluorescent Antibody Technique↗
PubMed1989

High specific activity chemiluminescent and fluorescent markers: their potential application to high sensitivity and 'multi-analyte' immunoassays.

The sensitivities of immunoassays relying on conventional radioisotopic labels (i.e. radioimmunoassay (RIA) and immunoradiometric assay (IRMA) permit the measurement of analyte concentrations above ca 10(7) molecules/ml. This limitation primarily derives, in the case of 'competitive' or 'limited reagent' assays, from the 'manipulation errors arising in the system combined with the physicochemical characteristics of the particular antibody used; however, in the case of 'non-competitive' systems, the specific activity of the label may play a more important constraining role. It is theoretically demonstrable that the development of assay techniques yielding detection limits significantly lower than 10(7) molecules/ml depends on: (1) the adoption of 'non-competitive' assays designs; (2) the use of labels of higher specific activity than radioisotopes; (3) highly efficient discrimination between the products of the immunological reactions involved. Chemiluminescent and fluorescent substances are capable of yielding higher specific activities than commonly used radioisotopes when used as direct reagent labels in this context, and both thus provide a basis for the development of 'ultra-sensitive', non-competitive, immunoassay methodologies. Enzymes catalysing chemiluminescent reactions or yielding fluorescent reaction products can likewise be used as labels yielding high effective specific activities and hence enhanced assay sensitivities. A particular advantage of fluorescent labels (albeit one not necessarily confined to them) lies in the possibility they offer of revealing immunological reactions localized in 'microspots' distributed on an inert solid support. This opens the way to the development of an entirely new generation of 'ambient analyte' microspot immunoassays permitting the simultaneous measurement of tens or even hundreds of different analytes in the same small sample, using (for example) laser scanning techniques. Early experience suggests that microspot assays with sensitivities surpassing that of isotopically based methodologies can readily be developed.

Antibody Affinity↗
PubMed1988

Combination chemotherapy with mastectomy or radiotherapy for stage III breast carcinoma: a Cancer and Leukemia Group B study.

One hundred thirteen evaluable patients with previously untreated stage III breast carcinoma were treated with three monthly cycles of cyclophosphamide (CYC), doxorubicin (DOX), 5-fluorouracil (5-FU), vincristine (VCR), and prednisone (PRED) (CAFVP). Subsequently, 91 (81%) were deemed operable. Patients were then randomized to receive surgery or radiotherapy (RT) to determine which of these modalities afforded better local tumor control. All patients also received 2 additional years of CAFVP in a further attempt to eradicate local disease and systemic micrometastases. Forty-one of the randomized patients have relapsed. Approximately half of the initial relapses in each arm were local. The overall duration of disease control was similar following either modality, with a median of 29.2 months for surgery patients and 24.4 months for RT patients. Similarly, there was no major difference in survival related to randomized treatment with an overall median of 39 months (median follow-up 37 months). Pre- or perimenopausal status and inflammatory disease were associated with shorter disease control and survival. Treatment was generally well tolerated and toxicity was acceptable. This study demonstrates that prolonged control of stage III breast carcinoma can be achieved with combined modality therapy in which cytotoxic chemotherapy precedes and follows treatment directly primarily at the breast tumor, using either surgery or RT. Nevertheless, new regimens must be designed if significant advances that may lead to the cure of this disease are to be achieved.

Adult↗
PubMed1987

Two domains for splicing in the intron of the phage T4 thymidylate synthase (td) gene established by nondirected mutagenesis.

Of 97 nondirected T4 thymidylate synthase-defective (td) mutations, 27 were mapped to the intron of the split td gene. Clustering of these intron mutations defined two domains that are functional in splicing, each within approximately 220 residues of the respective splice sites. Two selected mutations, tdN57 and tdN47, fell within phylogenetically conserved pairings, with tdN57 disrupting the exon I-internal guide pairing (P1) in the 5' domain and tdN47 destabilizing the P9 helix in the 3' domain. A splicing assay with synthetic oligonucleotides complementary to RNA junction sequences revealed processing defects for T4tdN57 and T4tdN47, both of which are impaired in cleavage at the 5' and 3' splice sites. Thus prokaryotic genetics facilitates association of specific residue changes with their consequences to splicing.

Base Sequence↗