Additivity of dilantin and vinblastine inhibitory effects on microtubule assembly.

Dilantin (phenytoin) is a commonly used antiepileptic agent that is known to decrease conductance of sodium and calcium ions and delay outward potassium currents. Separate from its antiseizure activity, dilantin interferes with microtubule protein polymerization. It induces metaphase arrest and potentiates the effects of the antimitotics vincristine and vinblastine in cell culture. We show here by fluorescence binding studies that dilantin interacts directly with tubulin at a low affinity site [Ka = 3.5 (+/- 2.5) x 10(3) M(-1); Kd = 286 microM]. We quantitatively examined the effect of dilantin on bulk microtubule formation and found that the drug raises the critical concentration for microtubule polymerization in 2 M glycerol identically in the presence or absence of vinblastine. The change in free energy for microtubule polymerization attributable to 400 microM dilantin [deltadelta G = 117 (+/- 28) cal/mol] is additive with vinblastine effects. Under the same conditions, mean microtubule lengths are 7.7 +/- 4.3 microm (n = 558) and 7.4 +/- 4.0 microm (n = 477) in the presence or absence of dilantin, respectively. Dilantin has no effect on vinblastine-induced tubulin spiral formation, as measured by sedimentation velocity. Our data suggest that the mechanism for the antimicrotubule effects of dilantin involves sequestration of tubulin heterodimers in 1:1 drug:tubulin complexes that do not participate in tubulin polymerization. The dilantin binding site is distinct from the Vinca binding site, and these independent binding modes account for the additive effects in vitro. The sequestration of tubulin heterodimers could explain the combined drug synergy in cell cultures if it disrupted interactions with proteins that regulate microtubule dynamics and/or cell cycle events.

A comparison of thermodynamic parameters for vinorelbine- and vinflunine-induced tubulin self-association by sedimentation velocity.

We present a comparison of the energetics of spiral formation for two vinca alkaloids: a novel difluorinated vinorelbine derivative 20',20'-difluoro-3',4'-dihydrovinorelbine (F12158, or vinflunine) and the parent compound, vinorelbine. Vinca alkaloids are antineoplastic agents that halt cell division at metaphase by inhibiting microtubule assembly and inducing tubulin self-association into spiral aggregates. The overall affinities for tubulin of vincristine, vinblastine, and vinorelbine seem to correlate with their clinical doses, where vincristine with the highest overall affinity is used at the lowest doses. Doses of chemotherapeutic agents, however, also are determined by toxicities. In the physicochemical study described here, we used sedimentation velocity to compare vinorelbine- and vinflunine-induced self-association of porcine brain tubulin in the presence of 50 micro M GDP or 50 micro M GTP. Vinflunine demonstrates 3-16-fold lower overall affinity for tubulin and induces smaller polymers compared with vinorelbine. Sedimentation velocity provides the only direct evidence to date that vinflunine is a tubulin-binding drug. Stopped-flow light scattering demonstrates the shortest relaxation times for polymer redistribution for vinflunine consistent with induction of the shortest spirals. Data collected at 5 degrees, 15 degrees, 25 degrees, and 37 degrees show increasing 20,w values with increasing temperature and are consistent with an entropically driven process. These data are entirely consistent with our hypothesis that vinflunine is likely to result in reduced clinical neurotoxicity relative to vinorelbine, vinblastine, and vincristine.

Personality/behavioral characteristics in children: differential effects of putative anterior versus posterior cerebral asymmetry.

The current study was carried out to examine the possible relationships among personality/behavioral characteristics and anterior/posterior (A/P) functional cerebral asymmetry in children referred for learning problems. Two hundred nineteen children between 7 and 12 years of age were administered a battery of neuropsychological measures, and their parents completed the Child Behavior Checklist (CBC) and the Personality Inventory for Children-Revised (PIC). Anterior and posterior composite scores were obtained for each subject using scores on the neuropsychological measures. Out of this subject pool, 33 children had sufficient anterior/posterior (A/P) score differences (i.e., greater than one standard deviation difference) to permit their categorization into either an A (n = 19) or P (n = 14) group. The MANOVA results showed that the A group scored significantly higher than the P group on the CBC scales of social withdrawal, aggressiveness, hyperactivity and externalizing, while the P group scored higher, though not significantly, on the (PIC) scale of anxiety. Thus, it appeared that, by using neuropsychological measures along the A/P dimension to classify children with learning problems, significant differences could also be identified on personality/ behavioral variables for some children. In addition, in the current study, children with A type functional cerebral asymmetry exhibited a relatively greater number of behavioral problems.

Immunochemical quantitation of an airborne proteolytic enzyme, Esperase, in a consumer products factory.

Occupational exposure of dry bleach factory workers to proteolytic enzymes poses a potential health hazard to susceptible workers. A sensitive immunochemical technique has been developed for quantitating exposure of factory workers to Esperase by sampling airborne particles on a fiberglass filter sheet followed by elution and assay for enzyme in a two-site immunoradiometric assay. By this method, 0.05 to 0.1 ng of enzyme (activity 50 KNPU/g) can be quantitated. With this sensitivity, as little as 2 to 4 ng/m3 airborne Esperase could be detected by personal monitors (flow rate of 0.002 m3/min; sampling time of 8 hr) and 0.05-0.1 ng/m3 of airborne Esperase with high volume samplers (flow rate of 1.13 m3/min;sampling time of 8 hr). There were significant day-to-day and site-to-site variations in the airborne Esperase content in the factory. Significant variations were also noted in the quantities of Esperase/m3 in the air inhaled by the workers in the same area on the same day. With this sensitive immunochemical technique and the use of personal monitors, the actual exposure of the worker as he moves about the factory could be measured.

A critical evaluation of the protection provided by common safety glasses from ultraviolet emissions in welding operations.

The purpose of this investigation was to evaluate critically several brands of safety spectacle lens and side shield combinations to determine their attenuation characteristics for ultraviolet (UV) radiation. By combining the information developed in this investigation with field data on UV from arc welding operations, it was possible to draw the conclusion that under the conditions stated, ordinary safety glasses with solid side shields provided adequate eye protection from UV.

A field study of near ultraviolet welding irradiance.

Spectral irradiance in the near U.V. was measured for several welding operations at a large steel fabrication shop. The variations of spectral irradiance with time were measured and a brief study of the effects of amperage welding rod, and distance was performed. At the measurement distance used in this study the proposed standard for near U.V. was not exceeded.