Antitumor agents-CLXXV. Anti-tubulin action of (+)-thiocolchicine prepared by partial synthesis

(+)-Thiocolchicine (2b) was prepared from (±)-colchicine (1) in a five-step reaction sequence that included chromatographic separation of appropriate camphanylated diastereomers. Acid hydrolysis of the (+)-diastereomer, followed by acetylation, yielded the desired product 2b. (+)-Thiocolchicine has 15-fold lower inhibitory activity against tubulin polymerization than (−)-thiocolchicine, and is 29-fold less potent for inhibiting growth of human Burkitt lymphoma cells. The enantiomer 2a, prepared from the (−)-camphanylated diastereomer, had potent activity in all assays comparable to that of (−)-thiocolchicine prepared by other methods. These results support the hypothesis that the proper configuration of colchicine-related compounds is an important requirement for their anti-tubulin action.     

Purification and Characterization of a Human Brain Galectin-1 Ligand

Abstract: Our previous studies have characterized an endogenous lectin from human brain identified as galectin-1. A soluble ligand of galectin-1 was purified from human brain by affinity chromatography and preparative electrophoresis. The purified ligand (termed HBGp82, for human brain galectin-1-binding polypeptide of 82,000 daltons) has an apparent molecular mass of 82 kDa and is glycosylated by N -linked biantennary complex structures. HBGp82 was partially characterized by microsequencing of peptide fragments. Similar peptides were found in a heat shock of protein of 90,000 daltons, hsp90. However, comparison of apparent molecular weights and matrix-assisted laser desorption mass spectrometry clearly showed that HBGp82 differs to some degree from hsp90.     

Crystals of an antibody FV fragment against an integral membrane protein diffracting to 1.28 Å resolution

The F_v fragment of a monoclonal antibody, 7E2 (IgG₁, κ, murine), which is directed against the integral membrane protein cytochrome c oxidase (EC 1.9.3.1) from Paracoccus denitrificans, was cloned and produced in Escherichia coli. Crystals suitable for highresolution X-ray analysis were obtained by microdialysis under low salt conditions. The crystals belong to the orthorhombic space group P2₁2₁2₁ with unit cell dimensions of a = 51.51 Å, b = 56.15 Å, c = 99.86 Å (1 Å = 0.1 nm) and contain one F _v fragment per asymmetric unit. Using synchrotron radiation diffraction data were collected up to 1.28 Å resolution. This high resolution is very unusual for a heterodimeric protein. The crystals should open the way for refining not only the atomic positions, but also for obtaining information about internal dynamics. © 1995 Wiley-Liss, Inc.     

Sequence of ionophore conformational changes induced by a simulated membrane/water interface

We demonstrate how the progressive passage through an interface simulated by a linear increase in dielectric constant may mediate a reversible transconformation of Na⁺/X337A (lasalocid A) from a cyclic to an extended structure, During the passage through the interface, the complex adopts progressively a more extended conformation favorable to the Na⁺ complexation or decomplexation at the interface.     

Fetal mortality at the time of chorionic villi sampling

Summary To estimate the background fetal loss rates among women who might be candidates for chorionic villi sampling (CVS) for prenatal diagnosis, we examined the frequency of spontaneous abortion and of non-viable fetuses in two groups of women thought to be pregnant at 8–12 weeks' gestation. Among 1519 women over 35 years given an appointment for amniocentesis 1978–1981, 9.8% had a spontaneous abortion prior to 16 weeks' gestation. For those under observation before week 12, the loss rate by 16 weeks was 15.3%. Among all 190 candidates for elective termination of pregnancy between 6 and 12 weeks' gestation, 12.6% were found to have a non-viable fetus at the scheduled date of abortion. The frequency of non-viability was 14% among those seen before week 12. The data suggest that the background loss rate between the time of CVS and the time of amniocentesis is approximately 1–2% and is unlikely to be higher than 9%. Until randomized clinical trials of the procedure are completed we will not know how much, if at all, the loss rate associated with CVS is increased above this background. Nevertheless, knowledge of these background risk estimates may be useful in counseling women considering participating in trials of CVS.     

The use of acridine orange for testing blood platelet integrity

Two processes are involved in the accumulation of acridine orange in human blood platelets. One follows a diffusion like kinetics and is independent of the ATP level whereas the second one can be completely abolished by ATP depletion. The acridine orange incorporation rate seems to be a suitable parameter for testing platelet integrity. It reflects very sensitively the influence of the preparation method as well as of anticoagulating substances used on the stability of platelet suspensions. The rates of acridine orange incorporation and of aggregation were measured in platelet-rich plasma and in saline suspended platelets after gel filtration, respectively, over a period of 120 min storage. Both rates are influenced to a different degree by anticoagulating agents such as citrate, heparin and EDTA. When contact with anticoagulating agents during platelet preparation is avoided, platelets show a constant acridine orange incorporation and aggregation during storage and the smallest morphological alteration.     

Dependence of the early steps of chlorophyll(ide) synthesis on respiration in dark-grown Euglena gracilis

Protochlorophyll(ide) disappearance and chlorophyll(ide) accumulation, in dark-grown Euglena, promoted by series of actinic light flashes, have been followed by in vivo fluorescence measurements. The data show that chlorophyll(ide) accumulation is biphasic, i.e., there is an initial rapid phase followed by a slower linear phase. The linear phase is highly dependent on flash frequency and on cell respiration whereas the initial phase is much less affected by these factors. It is concluded that dark-grown cells contain a limited pool of phototransformable protochlorophyll(ide); once this pool is exhausted, its reformation and/or the synthesis of some unknown metabolite necessary for the photoreduction appears to be dependent on respiration.     

A Specific Transduction Mechanism for the Glutamate Action on Phosphoinositide Metabolism via the Quisqualate Metabotropic Receptor in Rat Brain Synaptoneurosomes: II. Calcium Dependency, Cadmium Inhibition

In this article, we demonstrate that an increase in intracellular Ca2+ concentration may represent a specific common step(s) in the mechanism(s) of action of glutamate (Glu) and depolarizing agents on formation of inositol phosphates (IPs) in 8-day-old rat forebrain synaptoneurosomes. In fact, A23187, a Ca2+ ionophore, induces a dose-dependent accumulation of IPs, which is not additive with that evoked by Glu and K+ but is slightly synergistic with that induced by carbachol. In addition, Glu and K+ augment the intracellular Ca2+ concentration in synaptoneurosome preparations as measured by the fura-2 assay. The absence of external Ca2+ decreases basal and Glu-, and K(+)-stimulated formation of IPs. Cd2+ (100 microM) fully inhibits both Glu- and K(+)-evoked formation of IPs without affecting the carbachol-elicited response of IPs. Zn2+ inhibits Glu- and K(+)-stimulated accumulation of IPs (IC50 approximately 0.4 mM) but with a lower affinity than Cd2+ (IC50 approximately 0.035 mM). The organic Ca2+ channel blockers verapamil (10 microM), nifedipine (10 microM), omega-conotoxin (2 microM), and amiloride (10 microM) as well as the inorganic blockers Co2+ (100 microM) and La3+ (100 microM) block neither Glu- nor K(+)-evoked formation of IPs, a result suggesting that the opening of the L-, T-, N-, or P-type Ca2+ channels does not participate in these responses. All these data suggest that an increase in intracellular Ca2+ concentration resulting from an influx of Ca2+, sensitive to Cd2+ but not to other classical Ca2+ antagonists, may play a key role in the transduction mechanism activated by Glu or depolarizing agents.