Knocking out radiotracers for molecular imaging with PET.
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Animals↗
Biomedical subjects
Terry Jones
Publications and source records attributed to Terry Jones.
Assessment of pharmacodynamic vascular response in a phase I trial of combretastatin A4 phosphate.
PURPOSE: Clinical evaluation of novel agents that target tumor blood vessels requires pharmacodynamic end points that measure vascular damage. Positron emission tomography (PET) was used to measure the effects of the vascular targeting agent combretastatin A4 phosphate (CA4P) on tumor and normal tissue perfusion and blood volume. PATIENTS AND METHODS: Patients with advanced solid tumors were enrolled onto part of a phase I, accelerated-titration, dose-escalation study. The effects of 5 to 114 mg/m2 CA4P on tumor, spleen, and kidney were investigated. Tissue perfusion was measured using oxygen-15 (15O)-labeled water and blood volume was measured using 15O-labeled carbon monoxide (C15O). Scans were performed immediately before, and 30 minutes and 24 hours after the first infusion of each dose level of CA4P. All statistical tests were two sided. RESULTS: PET data were obtained for 13 patients with intrapatient dose escalation. Significant dose-dependent reductions were seen in tumor perfusion 30 minutes after CA4P administration (mean change, -49% at >or= 52 mg/m2; P =.0010). Significant reductions were also seen in tumor blood volume (mean change, -15% at >or= 52 mg/m2; P =.0070). Although by 24 hours there was tumor vascular recovery, for doses >or= 52 mg/m2 the reduction in perfusion remained significant (P =.013). Thirty minutes after CA4P administration borderline significant changes were seen in spleen perfusion (mean change, -35%; P =.018), spleen blood volume (mean change, -18%; P =.022), kidney perfusion (mean change, -6%; P =.026), and kidney blood volume (mean change, -6%; P =.014). No significant changes were seen at 24 hours in spleen or kidney. CONCLUSION: CA4P produces rapid changes in the vasculature of human tumors that can be assessed using PET measurements of tumor perfusion.
Adult↗
Metabolic activation of temozolomide measured in vivo using positron emission tomography.
The purpose of this research was to quantitate and confirm the mechanism of in vivo metabolic activation of temozolomide. The secondary aims were to evaluate the tumor, normal tissue, and plasma pharmacokinetics of temozolomide in vivo, and to determine whether such pharmacokinetics resulted in tumor targeting. [(11)C]temozolomide kinetics were studied in men using positron emission tomography (PET). It has been postulated that temozolomide undergoes decarboxylation and ring opening in the 3-4 position to produce the highly reactive methyldiazonium ion that alkylates DNA. To investigate this, a dual radiolabeling strategy, with [(11)C]temozolomide separately radiolabelled in the 3-N-methyl and 4-carbonyl positions, was used. We hypothesized that (11)C in the C-4 position of [4-(11)C-carbonyl]temozolomide would be converted to [(11)C]CO(2) if the postulated mechanism of metabolic conversion was true resulting in lower [(11)C]temozolomide tumor exposure. Paired studies were performed with both forms of [(11)C]temozolomide in 6 patients with gliomas. Another PET scan with (11)C-radiolabelled bicarbonate was performed and used to account for the metabolites of temozolomide using a data-led analytical approach. Plasma was analyzed for [(11)C]temozolomide and [(11)C]metabolites throughout the scan duration. Exhaled air was also sampled throughout the scan for [(11)C]CO(2). The percentage ring opening of temozolomide over 90 min was also calculated to evaluate whether there was a differential in metabolic breakdown among plasma, normal tissue, and tumor. There was rapid systemic clearance of both radiolabelled forms of [(11)C]temozolomide over 90 min (0.2 liter/min/m(2)), with [(11)C]CO(2) being the primary elimination product. Plasma [(11)C]CO(2) was present in all of the studies with [4-(11)C-carbonyl]temozolomide and in half the studies with [3-N-(11)C-methyl]temozolomide. The mean contributions to total plasma activity by [(11)C]CO(2) at 10 and 90 min were 12% and 28% with [4-(11)C-carbonyl]temozolomide, and 1% and 4% with [3-N-(11)C-methyl]temozolomide, respectively. There was a 5-fold increase in exhaled [(11)C]CO(2) sampled with [4-(11)C-carbonyl]temozolomide compared with [3-N-(11)C-methyl]temozolomide (P < 0.05). A decrease in tissue exposure [area under the curve between 0 and 90 min (AUC(0-90 min))] to [(11)C]temozolomide was also observed with [4-(11)C-carbonyl] temozolomide compared with [3-N-(11)C-methyl]temozolomide. Of potential therapeutic advantage was the higher [(11)C]radiotracer and [(11)C]temozolomide exposure (AUC(0-90 min)) in tumors compared with normal tissue. [(11)C]temozolomide ring opening over 90 min was less in plasma (20.9%; P < 0.05) compared with tumor (26.8%), gray matter (29.7%), and white matter (30.1%), with no differences (P > 0.05) between tumor and normal tissues. The significantly higher amounts of [(11)C]CO(2) sampled in plasma and exhaled air, in addition to the lower normal tissue and tumor [(11)C]temozolomide AUC(0-90 min) observed with [4-(11)C-carbonyl]temozolomide, confirmed the postulated mechanism of metabolic activation of temozolomide. A higher tumor [(11)C]temozolomide AUC(0-90 min) in tumors compared with normal tissue and the tissue-directed metabolic activation of temozolomide may confer potential therapeutic advantage in the activity of this agent. This is the first report of a clinical PET study used to quantify and confirm the in vivo mechanism of metabolic activation of a drug.
Adult↗
The design and implementation of a motion correction scheme for neurological PET.
A method is described to monitor the motion of the head during neurological positron emission tomography (PET) acquisitions and to correct the data post acquisition for the recorded motion prior to image reconstruction. The technique uses an optical tracking system, Polaris, to accurately monitor the position of the head during the PET acquisition. The PET data are acquired in list mode where the events are written directly to disk during acquisition. The motion tracking information is aligned to the PET data using a sequence of pseudo-random numbers, which are inserted into the time tags in the list mode event stream through the gating input interface on the tomograph. The position of the head is monitored during the transmission acquisition, and it is assumed that there is minimal head motion during this measurement. Each event, prompt and delayed, in the list mode event stream is corrected for motion and transformed into the transmission space. For a given line of response, normalization, including corrections for detector efficiency, geometry and crystal interference and dead time are applied prior to motion correction and rebinning in the sinogram. A series of phantom experiments were performed to confirm the accuracy of the method: (a) a point source located in three discrete axial positions in the tomograph field of view, 0 mm, 10 mm and 20 mm from a reference point, (b) a multi-line source phantom rotated in both discrete and gradual rotations through +/- 5 degrees and +/- 15 degrees, including a vertical and horizontal movement in the plane. For both phantom experiments images were reconstructed for both the fixed and motion corrected data. Measurements for resolution, full width at half maximum (FWHM) and full width at tenth maximum (FWTM), were calculated from these images and a comparison made between the fixedand motion corrected datasets. From the point source measurements, the FWHM at each axial position was 7.1 mm in the horizontal direction, and increasing from 4.7 mm at the 0 mm position, to 4.8 mm, 20 mm offset, in the vertical direction. The results from the multi-line source phantom with +/- 5 degrees rotations showed a maximum degradation in FWHM, when compared with the stationary phantom, of 0.6 mm, in the horizontal direction, and 0.3 mm in the vertical direction. The corresponding values for the larger rotation, +/- 15 degrees, were 0.7 mm and 1.1 mm, respectively. The performance of the method was confirmed with a Hoffman brain phantom moved continuously, and a clinical acquisition using [11C]raclopride (normal volunteer). A visual comparison of both the motion and non-motion corrected images of the Hoffman brain phantom clearly demonstrated the efficacy of the method. A sample time-activity curve extracted from the clinical study showed irregularities prior to motion correction, which were removed after correction. A method has been developed to accurately monitor the motion of the head during a neurological PET acquisition, and correct for this motion prior to image reconstruction. The method has been demonstrated to be accurate and does not add significantly to either the acquisition or the subsequent data processing.
Algorithms↗
Techniques for imaging neuroscience.
In the last 20 years, a number of non-invasive spatial mapping techniques have been demonstrated to provide powerful insights into the operation of the brain during task performance. These are, in order of their emergence as robust technologies: positron emission tomography, source localization with EEG and MEG, and functional magnetic resonance imaging. The imaging neuroscience study areas represented in this volume use the first or last of these - PET and fMRI. The physical principles underlying both of these techniques are outlined, and the important assumptions and limitations are made explicit. The range of applications for each is briefly indicated.
Brain↗
Efficacy and safety of a new triple-combination agent for the treatment of facial melasma.
Treatment of melasma, a hyperpigmentation disorder, remains a challenge. The primary objective of two 8-week, multicenter, randomized, investigator-blind studies was to compare the efficacy and safety of a hydrophilic cream formulation containing tretinoin 0.05%, hydroquinone 4.0%, and fluocinolone acetonide 0.01% (RA+HQ+FA) with the dual-combination agents tretinoin plus hydroquinone (RA+HQ), tretinoin plus fluocinolone acetonide (RA+FA), and hydroquinone plus fluocinolone acetonide (HQ+FA). All agents had the same drug concentration and vehicle. A total of 641 adult patients, predominantly female, with moderate to severe melasma and Fitzpatrick skin types I through IV, were randomized to the various treatment groups. Due to the similarity of the study designs, the results of the 2 studies were combined and are reported here. The primary efficacy analysis involved the proportion of intent-to-treat patients in each treatment group whose condition had completely cleared by week 8. The results of the combined clinical trials demonstrated that significantly more of the patients treated with RA+HQ+FA (26.1%) experienced complete clearing compared with the other treatment groups (4.6%) at the end of week 8 (P<.0001). In addition, at week 8, a 75% reduction in melasma/pigmentation was observed in more than 70% of patients treated with RA+HQ+FA compared with 30% in patients treated with the dual-combination agents. The most common adverse reactions seen with all treatment groups were erythema, skin peeling, burning, and/or stinging sensation. The majority of treatment-related adverse events were of mild severity.
Administration, Topical↗
Assessment of proliferation in vivo using 2-[(11)C]thymidine positron emission tomography in advanced intra-abdominal malignancies.
The purpose of this study was to determine the relationship between 2-[(11)C]thymidine positron emission tomography (PET) in vivo-derived parameters and the ex vivo Ki-67 index of proliferation in human tumors. The study comprised 17 treatment-naïve patients with advanced intra-abdominal malignancies. Tumor thymidine kinetics were measured using 2-[(11)C]thymidine PET. Tissue data were analyzed to give the standardized uptake value, the area under the time activity curve, and the fractional retention of thymidine (FRT) obtained by kinetic modeling. For the latter, the contribution of labeled metabolites was accounted for by measuring thymidine metabolites in arterial plasma. To examine the influence of tumor blood flow on the thymidine PET data, a perfusion scan using inhaled [(15)O]CO(2) was carried out in a subset of 11 patients. Biopsies were stained with a MIB1 antibody to obtain a Ki-67 index, and correlations with the PET-derived parameters were investigated. There was no relationship between tumor blood flow and the thymidine PET data, showing that the retention of 2-[(11)C]thymidine in tumors was independent of tumor perfusion. There was no correlation between the Ki-67 index and either standard uptake value or area under the curve. There was a correlation between the Ki-67 index and FRT (r = 0.58; P = 0.01). The correlation between the Ki-67 index and FRT in this dataset was not influenced by the interval between biopsy and imaging (0.1-126 weeks), the origin of the biopsy for Ki-67 staining (primary tumor or metastasis), or whether the biopsy was from an imaged or a nonimaged tumor. This is the first report in human tumors showing that 2-[(11)C]thymidine PET-derived parameters correlate with the level of tumor proliferation measured using Ki-67 immunohistochemistry. The study shows that the in vivo measurement of 2-[(11)C]thymidine in tumors using PET can provide a surrogate marker of proliferation and supports the potential use of the technique in the early assessment of response to antiproliferative cancer treatment.
Abdominal Neoplasms↗
Molecular imaging: what picture does it paint for future oncology?
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Antineoplastic Agents↗
Effective treatment of actinic keratosis with 0.5% fluorouracil cream for 1, 2, or 4 weeks.
New therapeutic options would benefit patients with actinic keratosis (AK), a precancerous condition that is a significant health concern. The efficacy and safety of a microsphere-based formulation of 0.5% fluorouracil cream were evaluated in a randomized, double-blind, multicenter, parallel-group study. Patients (N= 177) were randomized to receive 0.5% fluorouracil or vehicle once daily for 1, 2, or 4 weeks. Efficacy was assessed by lesion counts and clearance. Safety was evaluated by monitoring adverse events, including facial irritation. Significant improvements were seen from baseline to posttreatment follow-up in all efficacy variables for all fluorouracil regimens compared with vehicle. Patients treated for one week experienced significant improvements compared with vehicle, although efficacy increased with increasing treatment duration. Most patients experienced mild to moderate facial irritation of predictable onset and duration. Once-daily administration of 0.5% fluorouracil cream for 1, 2, or 4 weeks is safe and effective for the treatment of AKs.
Administration, Topical↗
A new treatment for acne vulgaris combining benzoyl peroxide with clindamycin.
Topical acne therapies are widely used for the treatment of mild to moderately severe acne vulgaris. However, many available treatments have limitations associated with their use, including lengthy time to response, cosmetic acceptability, and photosensitivity. Combinations of topical antibiotics and comedolytics are especially useful, but some formulations have stability challenges. A new combination formulation that contains 1% clindamycin and 5% benzoyl peroxide (BenzaClin Topical Gel) is currently available. In clinical trials, clinical improvement occurred at the first two follow-up visits and continued throughout treatment. In addition, combination therapy with clindamycin/benzoyl peroxide gel rapidly reduces Propionibacteria acnes counts and suppresses the emergence of clindamycin-resistant P. acnes. This formulation is stable at room temperature for up to 2 months after compounding. The aqueous gel vehicle is less drying, and there is no photosensitivity associated with its use. This study compares the combination treatment of 1% clindamycin and 5% benzoyl peroxide topical gel with other therapeutic options for mild to moderately severe acne vulgaris.
Acne Vulgaris↗
Evaluating nurse competency: evidence of validity for a skills recredentialing program.
A multitrait, multimethod approach was used to evaluate the validity of a hospital-based nurse competency assessment program as a mechanism for assuring compliance with the three standards for competence established by the National Council of State Boards of Nursing, Inc. For selected competencies, both knowledge and skill performance were evaluated under simulated conditions and under routine patient care conditions. Under simulated conditions, pass rates on first attempts among the 368 participating nurses were high as expected (82 per cent to 94 per cent on knowledge and 75 per cent to 99 per cent on performance). Offering immediate educational feedback followed by second attempts yielded a 97 per cent overall pass rate. Competencies assessed under both simulated and patient care conditions (35 sets of observations) revealed no differences in assessed competence. The equivalence of assessments made under simulated and patient care conditions supports the validity of competency assessment programs currently in use in many large health care settings.
Clinical Competence↗