Toxicity and DNA binding of dextran-doxorubicin conjugates in multidrug-resistant KB-V1 cells: optimization of dextran size

We previously showed that conjugating doxorubicin to very large 70-500 kDa dextran decreased its removal rate from P-glycoprotein (P-gp) over-expressing, multidrug-resistant KB-V1 cells. Furthermore these conjugates could act synergistically with other cancer drugs. In the drug-sensitive 3-1 clone, but not in the V1 subclone which was 300-fold more resistant to free doxorubicin, conjugation led to a size-related decrease in toxicity. Here we identified the optimal size of dextran for avoiding P-gp-mediated efflux and yet preserving as much as possible doxorubicin toxicity. Chemically reduced, intracellularly stable 3.4-10 kDa conjugates were prepared. Confocal microscopy and fluorescence quenching experiments showed that these conjugates entered nuclei and interacted with DNA. In 3-1 cells, but not in V1 cells, cytotoxicity of conjugates decreased 14- to 45-fold linearly related to log size of the carrier (r=0.95). In V1 cells toxicity of the 10 kDa conjugate exceeded that of free doxorubicin. After conjugation the equilibrium binding constant of the DNA-drug complex (KA) decreased only by up to 3-fold. In 3-1 cells, but not in VI cells, DNA binding kinetics was an important factor and toxicity could be linearly correlated to 1/KA of conjugate (r=0.94). Drug accumulation decreased with an increase in dextran size but drug removal was decreased only in V1 cells. It appeared that drug uptake was also sensitive to dextran conjugation. In Vl cells drug removal was sensitive to the P-gp inhibitor verapamil or energy starvation. Ratios of V1/3-1 toxicity, drug accumulation and drug removal correlated linearly with log dextran size. When these ratios equaled 1, dextran sizes were estimated to be 32, 103 and 21 kDa, respectively.

Rapid detection of the mecA gene in methicillin resistant staphylococci using a colorimetric cycling probe technology

A Cycling Probe Technology (CPT) assay was developed for the detection of the mecA gene from methicillin resistant staphylococcal cultures. The assay is based on a colorimetric enzyme-immuno-assay (EIA) and uses a mecA probe (DNA-RNA-DNA) labeled with fluorescein at the 5'-terminus and biotin at the 3'-terminus. The reaction occurs at a constant temperature that allows the target DNA to anneal to the probe. RNase H cuts the RNA portion, allowing the cut fragments to dissociate from the target, making it available for further cycling. CPT-EIA uses streptavidin-coated microplate wells to capture uncut probe followed by detection with horseradish-peroxidase conjugated anti-fluorescein antibody. The assay was compared to PCR and shown to accurately detect the presence or absence of the mecA gene in 159 staphylococcal clinical isolates. The CPT-EIA assay takes two hours starting from cultured cells compared with the 24-48 h required for detection of methicillin resistance by conventional susceptibility tests.

Functional evidence for divergent receptor activation mechanisms of luteotrophic and luteolytic events in the human corpus luteum

Using a dispersed human luteal cell culture model, progesterone synthesis following treatment by incremental doses of human chorionic gonadotrophin (HCG) and the stable prostaglandin F2alpha (PGF2alpha) analogue cloprostenol, alone or in combination, was related to corpora lutea (CL) mRNA transcript abundance coding for the luteinizing hormone (LH)/HCG receptor (LH-R) and PGF2alpha-receptor (FP) by semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) in 33 otherwise healthy women, scheduled for surgery due to benign conditions. CL were grouped according to age, based on the occurrence of a preovulatory LH surge where post-LH days 2-5 were designated as early luteal phase, days 6-10 as mid-luteal phase and days 11-14 as late luteal phase. When exposed to HCG, maximal progesterone output was raised 2.2-fold (P = 0.08, n = 5) compared with untreated controls in the early CL, while it increased 5.7- and 4.6-fold in the mid- and late groups respectively (P<0.05, n = 4 mid-luteal phase, n = 3 late luteal phase). This stimulation pattern was found to be concordant with the value of mRNA coding for LH-R in all groups (n = 6 early luteal phase, n = 5 mid-luteal phase, n = 6 late luteal phase). The integrated response to HCG and cloprostenol showed a dose-dependent 60% inhibition of progesterone production; but only in late luteal phase luteal cells (P<0.01, n = 3). FP mRNA values were lowest in early luteal phase, and increased with the age of the CL. Interestingly, lowest CL tissue concentrations of the natural FP agonist PGF2alpha were found during mid-luteal phase while it increased again 1.6-fold during late luteal phase (P<0.05, n = 8 versus mid-luteal phase, n = 6). Collectively, these data demonstrate that (i) the extrinsic functional control (or rescue of CL in the event of pregnancy) occurs when the sensitivity towards LH/HCG is maximal; and (ii) the demise of CL function is mediated via an acquisition of sensitivity towards the intrinsic luteolytic signal, PGF2alpha in the ageing CL.

Characterization and regulation of a mRNA encoding the prostaglandin F2alpha receptor in the rat ovary

The recent cloning of several cDNAs encoding prostaglandin (PG) receptors has paved the way for a more detailed investigation of the postulated regulatory role of prostaglandins in corpus luteum function. We have utilized the reverse transcription-polymerase chain reaction (RT-PCR) to isolate a mRNA encoding the ovarian PGF(2alpha) (FP) receptor, using oligonucleotides based on the recently cloned mouse cDNA as primers. The 5'-untranslated region of the rat ovarian mRNA was isolated following 5'-RACE (rapid amplification of cDNA ends). The isolated 1526 base-pair sequence, which spans the entire open reading frame, was found 100% identical in the protein coding region to a similar sequence isolated from a rat astrocyte cDNA library, but different in the first 32 nucleotides of the 5'-untranslated region, possibly due to tissue-specific splicing heterogeneity. Using ribonuclease protection assay, a quantitative analysis of FP receptor mRNA levels was performed in corpora lutea excised from adult pseudopregnant rats (Day 8) at different timepoints (0.5-48 h) following the in vivo s.c. regimen of a luteolytic dose of the FP receptor agonist cloprostenol (5 microg). Already 3 h after cloprostenol injection, FP receptor mRNA levels exhibited a pronounced increase to values 4.0-fold higher (P < 0.01) than before injection. At 7 h through 24 h, the amount of luteal FP receptor mRNA decreased, approaching preinjection levels, whereafter they were again 3.0-fold higher (P < 0.01) at 48 h than before injection. We conclude that following homologous stimulation of the FP receptor, abundance of this mRNA is tissue-specifically regulated in a dynamic pattern, suggestive of an important role for FP receptor-mediated action on gene expression during the demise of corpus luteum function.

Dynamic computed tomography through interpolation

A method is proposed to reduce the requirement on the scanning speed for dynamic computed tomography of relatively fast moving objects such as the heart. From the projections measured at different times, a set of optimal projections is computed for reconstructing the image at any specified time within a permissible interval. In the method, the corresponding characteristic features of the measured projections at the same viewing angle are matched optimally by a nonlinear transformation. The matched projections are then used in an interpolation procedure to compute the projections required at the specified time. The method has been tested with mathematical phantoms that undergo partial expansion, contraction, and translational motion. The results show that the proposed method can provide acceptable images from data collected at scanning speeds that would otherwise produce severely blurred images by conventional methods.