Identification, purification, and molecular cloning of a putative plastidic glucose translocator.

During photosynthesis, part of the fixed carbon is directed into the synthesis of transitory starch, which serves as an intermediate carbon storage facility in chloroplasts. This transitory starch is mobilized during the night. Increasing evidence indicates that the main route of starch breakdown proceeds by way of hydrolytic enzymes and results in glucose formation. This pathway requires a glucose translocator to mediate the export of glucose from the chloroplasts. We have reexamined the kinetic properties of the plastidic glucose translocator and, using a differential labeling procedure, have identified the glucose translocator as a component of the inner envelope membrane. Peptide sequence information derived from this protein was used to isolate cDNA clones encoding a putative plastidic glucose translocator from spinach, potato, tobacco, Arabidopsis, and maize. We also present the molecular characterization of a candidate for a hexose transporter of the plastid envelope membrane. This transporter, initially characterized more than 20 years ago, is closely related to the mammalian glucose transporter GLUT family and differs from all other plant hexose transporters that have been characterized to date.

Efficacy of continuous sequential transdermal estradiol and norethindrone acetate in relieving vasomotor symptoms associated with menopause.

OBJECTIVE: This study was undertaken to evaluate the efficacy and tolerability of a combination estradiol plus norethindrone acetate transdermal delivery system given in a continuous sequential regimen with transdermal estradiol versus placebo in the treatment of vasomotor symptoms of menopause. STUDY DESIGN: This was a 12-week double-blind trial of 220 healthy postmenopausal women with > or = 8 moderate to severe hot flushes and sweating episodes per day. Women were randomly assigned to wear transdermal placebo patches or a transdermal patch releasing 50 microg/d 17beta-estradiol alone (Vivelle) for days 1 to 14 of each cycle and a combination patch releasing 50 microg/d 17beta-estradiol plus 1 of 3 dosage levels (140, 250, or 400 microg/d) of norethindrone acetate (CombiPatch) for days 15 through 28. RESULTS: There was a significant (P <.001) reduction by the second week in the mean number of daily hot flushes from baseline to end point with all 3 doses of estradiol plus norethindrone acetate compared with placebo. Significant (P <.001) reductions in the mean intensity of hot flushes and sweating were also noted with estradiol plus norethindrone acetate compared with placebo. The incidences of adverse events with all 3 doses of estradiol plus norethindrone acetate and with placebo were comparable. CONCLUSION: An estradiol plus norethindrone acetate transdermal delivery system administered in a continuous sequential regimen with transdermal estradiol was well tolerated and effective for the treatment of moderate to severe vasomotor symptoms in postmenopausal women.

Population pharmacokinetics/pharmacodynamics of docetaxel in phase II studies in patients with cancer.

PURPOSE: The population pharmacokinetic/pharmacodynamic (PK/PD) approach was prospectively integrated in the clinical development of docetaxel to assess the PK profile in a large population of patients and investigate systemic exposure as a prognostic factor for clinical outcome. PATIENTS AND METHODS: PK analysis was performed at first course in 24 phase II studies of docetaxel monotherapy using four randomized limited-sampling schedules. Bayesian estimates of clearance (CL), area under the concentration-time curve (AUC), and peak and duration of plasma levels greater than threshold levels were used as measures of exposure. PD data included for efficacy, response rate, time to first response, and time to progression (TTP) in breast cancer and non-small-cell lung cancer (NSCLC), and for toxicity, grade 4 neutropenia, and febrile neutropenia at first course and time to onset of fluid retention. PK/PD analysis was conducted using logistic and Cox multivariate regression models. RESULTS: PK protocol implementation was successful. Most of the patients registered (721 of 936, 77%) were sampled and 68% were assessable for PK (640 patients). First-course docetaxel AUC was a significant predictor (P = .0232) of TTP in NSCLC (n = 151). Docetaxel CL was a strong independent predictor (P < .0001) of both grade 4 neutropenia and febrile neutropenia (n = 582). Cumulative dose was the strongest predictor (P < .0001) of the time to onset of fluid retention (n = 631). However, the duration of exposure over 0.20 micromol/L (0.16 microg/mL) at first course was an independent predictor (P = .0029). Few patients (n = 25, 4%) received the recommended dexamethasone premedication. CONCLUSION: First-course docetaxel PK is a predictor of first-course hematologic toxicity, but also of fluid retention, which is cumulative in nature. Patients with elevated hepatic enzymes have a 27% reduction in docetaxel CL and are at a higher risk of toxicity. A starting dose of 75 mg/m2 is currently being evaluated in this population. Prospective implementation of large-scale population PK/PD evaluation is feasible in early drug development and this approach generates clinically relevant findings.

The pathophysiological mechanism of fluid retention in advanced cancer patients treated with docetaxel, but not receiving corticosteroid comedication.

AIMS: Fluid retention is a phenomenon associated with taxoids. The principal objective of this study was to investigate the pathophysiological mechanism of docetaxel-induced fluid retention in advanced cancer patients. METHODS: Docetaxel was administered as a 1 h intravenous infusion every 3 weeks, for at least 4-6 consecutive cycles, to patients with advanced breast (n = 21) or ovarian (n = 3) carcinoma, who had received previous chemotherapy, 21 for advanced disease. Phase II clinical trials have shown that 5 day corticosteroid comedication, starting 1 day before docetaxel infusion, significantly reduces the incidence and severity of fluid retention. This prophylactic corticosteroid regimen is currently recommended for patients receiving docetaxel but was not permitted in this study because of its possible interference with the underlying pathophysiology of the fluid retention. RESULTS: Fluid retention occurred in 21 of the 24 patients but was mainly mild to moderate, with only five patients experiencing severe fluid retention. Eighteen patients received symptomatic flavonoid treatment, commonly prescribed after the last cycle. Specific investigations for fluid retention confirmed a relationship between cumulative docetaxel dose and development of fluid retention. Capillary filtration test analysis showed a two-step process for fluid retention generation, with progressive congestion of the interstitial space by proteins and water starting between the second and the fourth cycle, followed by insufficient lymphatic drainage. CONCLUSIONS: A vascular protector such as micronized diosmine hesperidine with recommended corticosteroid premedication and benzopyrones may be useful in preventing and treating docetaxel-induced fluid retention.

Pharmacokinetic and pharmacodynamic properties of docetaxel: results of phase I and phase II trials.

The pharmacokinetics of docetaxel as investigated in Phase I and Phase II trials are discussed. Phase I trials have shown that docetaxel exhibits linear pharmacokinetics consistent with a three-compartment model. Population pharmacokinetic and pharmacodynamic analysis of the results of 22 nonrandomized Phase II trials with nonlinear mixed-effects modeling showed that the interpatient variability of docetaxel pharmacokinetics is mainly related to body surface area and hepatic function. The effect of body surface area on clearance does not present a problem, since the dose of docetaxel is adjusted for body size. However, patients with impaired liver function are at increased risk of serious adverse effects (febrile neutropenia, severe infections, severe stomatitis, and toxic death) during treatment with docetaxel 100 mg/ m2. Patients with impaired liver function should receive a reduced dose (75 mg/m2). The presence of liver metastases without impaired liver function had no effect on docetaxel's clearance or safety, suggesting that a dose of 100 mg/m2 is well tolerated in such patients. Docetaxel pharmacokinetics and pharmacodynamics determined in Phase I and Phase II trials indicate a need to adjust the dosage for body surface area and liver function.