Assessment of human abuse potential of dasotraline compared to methylphenidate and placebo in recreational stimulant users.

AIMS: The aim of this study was to evaluate the abuse potential of dasotraline, a novel dopamine and norepinephrine reuptake inhibitor with slow absorption (tmax, 10-12h) and elimination (t1/2=47-77 h) that is in development for the treatment of attention deficit hyperactivity disorder (ADHD). METHODS: Recreational stimulant users (N=48) who had specific experience with cocaine, and who were able to distinguish methylphenidate (60 mg) versus placebo in a qualification session, were randomized, in a 6-period, double-blind, crossover design, to receive single doses of dasotraline 8 mg, 16 mg, and 36 mg, methylphenidate (MPH) 40 mg and 80 mg, and placebo. The primary endpoint was the Drug Liking Visual Analog Scale (VAS) score at the time of peak effect (Emax). RESULTS: There were no significant differences between the 3 doses of dasotraline and placebo on the drug liking VAS at Emax, and on most secondary endpoints. Both doses of MPH had significantly higher VAS-drug liking scores at Emax relative to both placebo (P<0.001 for all comparisons) and dasotraline 8 mg (P<0.001), 16 mg (P<0.001) and 36 mg (P<0.01). The increase in heart rate for MPH and dasotraline 36 mg showed a time-course that closely matched subject-rated measures such as Any Effects VAS. CONCLUSIONS: In this study, dasotraline was found to have low potential for abuse, which may be, in part, related to its established pharmacokinetics (PK) profile, which is characterized by slow absorption and gradual elimination.

A maximum entropy analysis of protein orientations using fluorescence polarization data from multiple probes.

Techniques have recently become available to label protein subunits with fluorescent probes at predetermined orientation relative to the protein coordinates. The known local orientation enables quantitative interpretation of fluorescence polarization experiments in terms of orientation and motions of the protein within a larger macromolecular assembly. Combining data obtained from probes placed at several distinct orientations relative to the protein structure reveals functionally relevant information about the axial and azimuthal orientation of the labeled protein segment relative to its surroundings. Here we present an analytical method to determine the protein orientational distribution from such data. The method produces the broadest distribution compatible with the data by maximizing its informational entropy. The key advantages of this approach are that no a priori assumptions are required about the shape of the distribution and that a unique, exact fit to the data is obtained. The relative orientations of the probes used for the experiments have great influence on information content of the maximum entropy distribution. Therefore, the choice of probe orientations is crucial. In particular, the probes must access independent aspects of the protein orientation, and two-fold rotational symmetries must be avoided. For a set of probes, a "figure of merit" is proposed, based on the independence among the probe orientations. With simulated fluorescence polarization data, we tested the capacity of maximum entropy analysis to recover specific protein orientational distributions and found that it is capable of recovering orientational distributions with one and two peaks. The similarity between the maximum entropy distribution and the test distribution improves gradually as the number of independent probe orientations increases. As a practical example, ME distributions were determined with experimental data from muscle fibers labeled with bifunctional rhodamine at known orientations with respect to the myosin regulatory light chain (RLC). These distributions show a complex relationship between the axial orientation of the RLC relative to the fiber axis and the azimuthal orientation of the RLC about its own axis. Maximum entropy analysis reveals limitations in available experimental data and supports the design of further probe angles to resolve details of the orientational distribution.

Inhibitors of kinesin activity from structure-based computer screening.

Kinesin motor proteins use ATP hydrolysis for transport along microtubules in the cell. We sought to identify small organic ligands to inhibit kinesin's activity. Candidate molecules were identified by computational docking of commercially available compounds using the computer program DOCK. Compounds were docked at either of two sites, and a selection was tested for inhibition of microtubule-stimulated ATPase activity. Twenty-two submillimolar inhibitors were identified. Several inhibitors appeared to be competitive for microtubule binding and not for ATP binding, and three compounds showed 50% inhibition down to single-digit micromolar levels. Most inhibitors grouped into four distinct classes (fluoresceins, phenolphthaleins, anthraquinones, and naphthylene sulfonates). We measured the binding of one inhibitor, rose bengal lactone (RBL), to kinesin (dissociation constant 2.5 microM) by its increase in steady-state fluorescence anisotropy. The RBL binding site on kinesin was localized by fluorescent resonance energy transfer (FRET) using a donor fluorophore (coumarin) covalently attached at unique, surface-exposed cysteine residues engineered at positions 28, 149, 103, 220, or 330. RBL was found to bind in its original docked site: the pocket cradled by loop 8 and beta-strand 5 in kinesin's three-dimensional structure. These results confirm this region's role in microtubule binding and identify this pocket as a novel binding site for kinesin inhibition.

Dynamic measurement of myosin light-chain-domain tilt and twist in muscle contraction.

A new method is described for measuring motions of protein domains in their native environment on the physiological timescale. Pairs of cysteines are introduced into the domain at sites chosen from its static structure and are crosslinked by a bifunctional rhodamine. Domain orientation in a reconstituted macromolecular complex is determined by combining fluorescence polarization data from a small number of such labelled cysteine pairs. This approach bridges the gap between in vitro studies of protein structure and cellular studies of protein function and is used here to measure the tilt and twist of the myosin light-chain domain with respect to actin filaments in single muscle cells. The results reveal the structural basis for the lever-arm action of the light-chain domain of the myosin motor during force generation in muscle.

Model-independent analysis of the orientation of fluorescent probes with restricted mobility in muscle fibers.

The orientation of proteins in ordered biological samples can be investigated using steady-state polarized fluorescence from probes conjugated to the protein. A general limitation of this approach is that the probes typically exhibit rapid orientational motion ("wobble") with respect to the protein backbone. Here we present a method for characterizing the extent of this wobble and for removing its effects from the available information about the static orientational distribution of the probes. The analysis depends on four assumptions: 1) the probe wobble is fast compared with the nanosecond time scale of its excited-state decay; 2) the orientational distributions of the absorption and emission transition dipole moments are cylindrically symmetrical about a common axis c fixed in the protein; 3) protein motions are negligible during the excited-state decay; 4) the distribution of c is cylindrically symmetrical about the director of the experimental sample. In a muscle fiber, the director is the fiber axis, F. All of the information on the orientational order of the probe that is available from measurements of linearly polarized fluorescence is contained in five independent polarized fluorescence intensities measured with excitation and emission polarizers parallel or perpendicular to F and with the propagation axis of the detected fluorescence parallel or perpendicular to that of the excitation. The analysis then yields the average second-rank and fourth-rank order parameters ( and ) of the angular distribution of c relative to F, and and , the average second-rank order parameters of the angular distribution for wobble of the absorption and emission transition dipole moments relative to c. The method can also be applied to other cylindrically ordered systems such as oriented lipid bilayer membranes and to processes slower than fluorescence that may be observed using longer-lived optically excited states.

Orientation changes of fluorescent probes at five sites on the myosin regulatory light chain during contraction of single skeletal muscle fibres.

Changes in the orientation of the myosin regulatory light chain (RLC) in single muscle fibres were measured using polarised fluorescence from acetamidotetramethylrhodamine (ATR). Mutants of chicken skeletal RLC containing single cysteine residues at positions 2, 73, 94, 126 and 155 were labelled with either the 5 or 6-isomer of iodo-ATR, giving ten different probes. The labelled RLCs were exchanged into demembranated fibres from rabbit psoas muscle without significant effect on active force generation. Fluorescence polarisation measurements showed that nine out of the ten probe dipoles were more perpendicular to the fibre axis in the absence of ATP (in rigor) than in either relaxation or active contraction. The orientational distribution of the RLC region of the myosin head in active contraction is closer to the relaxed than to the rigor orientation, and is not equivalent to a linear combination of the relaxed and rigor orientations. Rapid length steps were applied to the fibres to synchronise the motions of myosin heads attached to actin. In active contraction the fluorescence polarisation changed both during the step, indicating elastic distortion of the RLC region of the myosin head, and during the subsequent rapid force recovery that is thought to signal the working stroke. The peak change in fluorescence polarisation produced by an active release of 5 nm per half sarcomere indicates an axial tilt of less than 5 degrees for all ten probes, if all the myosin heads in the fibre respond to the length step. This tilting was towards the rigor orientation for all ten probes, and could be explained by 14% of the heads moving to the rigor orientation. An active stretch tilted the heads away from the rigor conformation by a similar extent.

Fluorescence polarization transients from rhodamine isomers on the myosin regulatory light chain in skeletal muscle fibers.

Fluorescence polarization was used to examine orientation changes of two rhodamine probes bound to myosin heads in skeletal muscle fibers. Chicken gizzard myosin regulatory light chain (RLC) was labeled at Cys108 with either the 5- or the 6-isomer of iodoacetamidotetramethylrhodamine (IATR). Labeled RLC (termed Cys108-5 or Cys108-6) was exchanged for the endogenous RLC in single, skinned fibers from rabbit psoas muscle. Three independent fluorescence polarization ratios were used to determine the static angular distribution of the probe dipoles with respect to the fiber axis and the extent of probe motions on the nanosecond time scale of the fluorescence lifetime. We used step changes in fiber length to partially synchronize the transitions between biochemical, structural, and mechanical states of the myosin cross-bridges. Releases during active contraction tilted the Cys108-6 dipoles away from the fiber axis. This response saturated for releases beyond 3 nm/half-sarcomere (h.s.). Stretches in active contraction caused the dipoles to tilt toward the fiber axis, with no evidence of saturation for stretches up to 7 nm/h.s. These nonlinearities of the response to length changes are consistent with a partition of approximately 90% of the probes that did not tilt when length changes were applied and 10% of the probes that tilted. The responding fraction tilted approximately 30 degrees for a 7.5 nm/h.s. release and traversed the plane perpendicular to the fiber axis for larger releases. Stretches in rigor tilted Cys108-6 dipoles away from the fiber axis, which was the opposite of the response in active contraction. The transition from the rigor-type to the active-type response to stretch preceded the main force development when fibers were activated from rigor by photolysis of caged ATP in the presence of Ca2+. Polarization ratios for Cys108-6 in low ionic strength (20 mM) relaxing solution were compatible with a combination of the relaxed (200 mM ionic strength) and rigor intensities, but the response to length changes was of the active type. The nanosecond motions of the Cys108-6 dipole were restricted to a cone of approximately 20 degrees half-angle, and those of Cys108-5 dipole to a cone of approximately 25 degrees half-angle. These values changed little between relaxation, active contraction, and rigor. Cys108-5 showed very small-amplitude tilting toward the fiber axis for both stretches and releases in active contraction, but much larger amplitude tilting in rigor. The marked differences in these responses to length steps between the two probe isomers and between active contraction and rigor suggest that the RLC undergoes a large angle change (approximately 60 degrees) between these two states. This motion is likely to be a combination of tilting of the RLC relative to the fiber axis and twisting of the RLC about its own axis.

Electric field and conformational effects of cytochrome c and solvent on cytochrome c peroxidase studied by high-resolution fluorescence spectroscopy.

Electronic spectra of mesoporphyrin-substituted yeast cytochrome c peroxidase (MP-CcP) were measured as a function of pH, ionic strength, and binding of cytochrome c (cyt c) by fluorescence line narrowing (FLN) spectroscopy at 5 K. The FLN spectra provided information about the vibrational structure of the first excited singlet state of MP-CcP, the various tautomeric forms of mesoporphyrin, and the positions and widths of their 0,0 bands. The composite 0,0 band of MP-CcP at pH 6 could be resolved into three components with peak positions at 16,046, 16,103, and 16,203 cm-1. MP-CcP at pH 8 could be analyzed using two components with peak positions at 16,048 and 16,193 cm-1. The disappearance of the 16,103-cm-1 component at alkaline pH suggests that it is due to a "chemical substate" arising from protonation of His52 in the distal side of the porphyrin. Computer simulations of the electrostatic field that CcP imposes on its porphyrin show that, in the presence of charged axial histidines His52 and His175, the electrostatic field at porphyrin nitrogens increases, especially along the normal to the heme by about 200 mV/A. Electric field effects may account for pH-dependent spectral shifts of the 0,0 positions of the resolved components, although hydrogen bonding may also affect these positions. On the other hand, the peak position of the components was not affected by ionic strength or binding of cyt c, implying that the electrostatic field of the heme pocket of MP-CcP remains unchanged. Indeed, computed changes in ionic strength of the solvent show no modification of the electrostatic field at the porphyrin. The only detectable effect of ionic strength and binding of cyt c to MP-CcP is on the relative contributions of the components, suggesting some rearrangements in the vicinity of the heme. Finally, shifts in the position of the vibrational lines for MP-CcP components indicate either that the tautomers have different vibrational frequencies due to the nonsymmetry of the porphyrin and/or that tautomers experience various distortions. Comparison of the vibrational spectrum of the first excited singlet state of mesoporphyrin in CcP and horseradish peroxidase also suggests that the heme pocket in the two peroxidases provides different steric restrictions.

Postoperative complication from hemostatic clips.

Hemostatic clips were found in a patient's bladder four months after radical retropubic prostatectomy. A calculus, which had formed on one clip, caused acute urinary retention. Inadvertent enclosure of the hemoclips within the bladder intraoperatively and early intraurethral migration of the hemoclips are possible causes of this complication. Although this problem is rarely reported, hemoclips should be used sparingly, if at all, around the vesicourethral anastomosis.

The stability and antitumor activity of recycled (intravesical) mitomycin C.

Although intravesical mitomycin C (MMC) is effective in the treatment of superficial bladder cancer, its expense is a major factor limiting its use. These authors have analyzed the antitumor activity and stability of MMC following 2-hour intravesical instillation in consideration of recycling the drug or using a smaller dose over a longer retention time. The first voided urine samples from 11 patients who received 40 mg MMC intravesically were measured for MMC content by high performance liquid chromatography (HPLC). An average of 50% of the parent drug was recovered. MMC from the urine samples inhibited the growth of a transplantable murine transitional cell carcinoma as effectively as stock drug. Moreover, MMC is relatively stable in human urine at body temperature. These findings suggest that recovery and reuse of the intravesically administered drug is possible and if sterility and appropriate concentrations can be established for the initial and subsequent doses, the drug may be able to be recycled.

Primary carcinoma of male urethra.

Carcinoma of the male urethra is infrequent. To date approximately 600 cases have been reported. We reviewed 16 cases of carcinoma of the male urethra seen at the University of Tennessee and the Memphis Veterans Administration Hospital. The mean patient age was sixty-three years (range 38 to 84). The most common presentation was a palpable mass followed by symptoms of urinary obstruction. Five urethral carcinomas arose distal to the suspensory ligament of the penis while 11 were of bulbar or bulbomembranous origin. The histology was squamous cell carcinoma in 8 patients (50%), mixed squamous and transitional cell carcinoma in 5 (31%), transitional cell carcinoma in 2 (13%), and adenocarcinoma in 1 (6%). The mean patient survival was fifteen months following diagnosis of a proximal urethral tumor and seventy-seven months for tumors arising distally. Neoplasms of the distal urethra can be surgically managed successfully even if regional lymph nodes are involved. The prognosis for proximal urethra tumors remains poor and is best treated by a combination of surgery and radiotherapy.

Total and nondialyzable hydroxyproline excretion in Stage D2 prostate cancer.

Hydroxyproline is excreted in urine as a breakdown product of normal bone turnover: A dialyzable (D) fraction (90% of total) reflects active bone destruction and a nondialyzable (ND) fraction reflects bone growth/regrowth. In metastatic prostate cancer where blastic osseous metastases predominate, disease progression on bone scan correlated with elevation of both total hydroxyproline excretion (7.84 + 1.28, P less than 0.001) and the ND urinary level (0.94 +/- 0.20, P less than 0.01). In patients with a serially stable/improving scan, urinary excretion of each fraction (2.18 + 0.27 and 0.27 +/- 0.01) was similar to that of men with no evidence of disease. For Stage D2 prostate cancer, these two markers satisfactorily monitor osseous activity in the intervals between serial bone scintigraphy.

Total, dialyzable, and nondialyzable postabsorptive hydroxyproline. Values in patients with cancer.

The postabsorptive urinary total (T), dialyzable (D), and nondialyzable (ND) hydroxyproline (HYPRO) tests were evaluated to determine whether the patterns of excretion varied according to the predominance of osteoblastic v osteolytic bone involvement in 58 patients with neoplastic disease. In patients with osteolytic lesions from multiple myeloma, elevated T and D levels with normal ND HYPRO values were observed, along with elevated D/ND ratios. In prostate cancer, the T, D, and ND values were all elevated and the D/ND ratio was normal. Patients with Hodgkin's disease had elevated T, D, and ND HYPRO levels, and the D/ND ratio was in the range of patients with prostate cancer. The data suggest that these collagen markers may be useful in the long-term evaluation of these neoplasms in patients.

Invasive bladder cancer: support for screening.

Of 297 patients with bladder cancer treated between 1975 and 1981, 90 (30 per cent) had histologic documentation of muscle invasion, 82 of whom (91 per cent) had invasion into the muscle at the time of presentation. Of these 82 patients 51 (62 per cent) had tumor localized to the bladder after clinical staging. Of 36 patients undergoing radical cystectomy 9 (25 per cent) had microscopic pelvic lymph node involvement. Nine patients underwent urinary diversion alone and 31 presented with perivesical or pelvic nodal tumor extension, or distant metastases. Only 8 of the 90 patients (9 per cent) had prior superficial bladder cancer. The mean survival for patients with stage B to C disease at diagnosis was 23 months and for those with stage D tumor it was 11 months. This experience indicates that the majority of patients with advanced bladder cancer are not identified at a stage when definitive therapy offers an excellent prognosis. More resources must be devoted to earlier detection.

Carcinoma of the female urethra: reassessment of modes of therapy.

Of 15 women with primary urethral carcinoma 2 had tumors confined to the urethra and were managed successfully by an operation. Of the 9 patients with tumor extending to the surrounding structures 6 (67 per cent) died of complications related to inadequate control of the primary tumor. The last 4 patients had stage D1 disease or greater at initial diagnosis and died of distant metastases. Our current approach for patients with locally advanced disease is combined brachytherapy and operation in an effort to eradicate the primary tumor, since morbidity and mortality result from failure to control the local tumor.

Serial spot hydroxyproline/creatinine ratios in metastatic prostatic cancer.

Analysis of urinary hydroxyproline levels offers a marker to monitor osseous involvement in patients with metastatic malignancies. Such a marker is needed in patients with prostatic cancer when bone metastases predominate. Thirty-two men with stage D2 prostatic cancer were monitored by bone scan, acid and alkaline phosphatase values, and urinary hydroxyproline, beginning from 4 to 36 months after initiation of hormonal manipulation and/or systemic chemotherapy. In patients with disease progression determined by bone scan serial urinary hydroxyproline values progressively increased and were significantly elevated compared to urinary values obtained from patients with a stable or improving scan (p less than 0.001). Simultaneous alkaline phosphatase determinations showed less significant differences between patient groups. Acid phosphatase did not reliably indicate osseous response to therapy. These data suggest that urinary hydroxyproline values are predictive as an early objective sign of osseous response in patients receiving therapy for stage D2 prostatic cancer.