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Purpose We have recently demonstrated the brain-delivery of an Amyloid-ß oligomer (Aßo)-binding peptide-therapeutic fused to the BBB-crossing single domain antibody FC5. The bi-functional fusion protein, FC5-mFc-ABP (KG207-M) lowered both CSF and brain Aß levels after systemic dosing in transgenic mouse and rat models of Alzheimer’s disease (AD). For development as a human therapeutic, we have humanized and further engineered the fusion protein named KG207-H. The purpose of the present study was to carry out comparative PK/PD studies of KG207-H in wild type rat and beagle dogs (middle-aged and older) to determine comparability of systemic PK and CSF exposure between rodent species and larger animals with more complex brain structure such as dogs. Method Beagle dogs were used in this study as they accumulate cerebral Aß with age, as seen in human AD patients, and can serve as a model of sporadic AD. KG207-H (5 to 50 mg/kg) was administered intravenously and serum and CSF samples were serially collected for PK studies and to assess target engagement. KG207-H and Aβ levels were quantified using multiplexed selected reaction monitoring mass spectrometry. Results After systemic dosing, KG207-H demonstrated similar serum pharmacokinetics in rats and dogs. KG207-H appeared in the CSF in a time- and dose-dependent manner with similar kinetics, indicating CNS exposure. Further analyses revealed a dose-dependent inverse relationship between CSF KG207-H and Aß levels in both species indicating target engagement. Conclusion This study demonstrates translational attributes of BBB-crossing Aβ-targeting biotherapeutic KG207-H in eliciting a pharmacodynamic response, from rodents to larger animal species.

In vivo biomarker abnormalities provide measures to monitor therapeutic interventions targeting amyloid-β pathology as well as its effects on downstream processes associated with Alzheimer’s disease pathophysiology. Here, we applied an in vivo longitudinal study design combined with imaging and cerebrospinal fluid biomarkers, mirroring those used in human clinical trials to assess the efficacy of a novel brain-penetrating anti-amyloid fusion protein treatment in the McGill-R-Thy1-APP transgenic rat model. The bi-functional fusion protein consisted of a blood-brain barrier crossing single domain antibody (FC5) fused to an amyloid-β oligomer-binding peptide (ABP) via Fc fragment of mouse IgG (FC5-mFc2a-ABP). A five-week treatment with FC5-mFc2a-ABP (loading dose of 30 mg/Kg/iv followed by 15 mg/Kg/week/iv for four weeks) substantially reduced brain amyloid-β levels as measured by positron emission tomography and increased the cerebrospinal fluid amyloid-β42/40 ratio. In addition, the 5-week treatment rectified the cerebrospinal fluid neurofilament light chain concentrations, resting-state functional connectivity, and hippocampal atrophy measured using magnetic resonance imaging. Finally, FC5-mFc2a-ABP (referred to as KG207-M) treatment did not induce amyloid-related imaging abnormalities such as microhemorrhage. Together, this study demonstrates the translational values of the designed preclinical studies for the assessment of novel therapies based on the clinical biomarkers providing tangible metrics for designing early-stage clinical trials.

The maintenance of therapeutic glycoproteins within the circulatory system is associated, in large part, with the integrity of sialic acids as terminal sugars on the glycans. Glycoprotein desialylation, either by spontaneous cleavage or through host sialidases, leads to protein clearance, mainly through the liver. Thus, the installation of minimally modified sialic acids that are hydrolysis-resistant yet biologically equivalent should lead to increased circulatory half-lives and improved pharmacokinetic profiles. Here we describe the chemoenzymatic synthesis of CMP–sialic acid sugar donors bearing fluorine atoms at the 7-position, starting from the corresponding 4-deoxy-4-fluoro-N-acetylhexosamine precursors. For the derivative with natural stereochemistry we observe efficient glycosyl transfer by sialyltransferases, along with improved stability of the resultant 7-fluorosialosides toward spontaneous hydrolysis (3- to 5-fold) and toward cleavage by GH33 sialidases (40- to 250-fold). Taking advantage of the rapid transfer of 7-fluorosialic acid by sialyltransferases, we engineered the O-glycan of Interferon α-2b and the N-glycans of the therapeutic glycoprotein α1-antitrypsin. Studies of the uptake of the glyco-engineered α1-antitrypsin by HepG2 liver cells demonstrated the bioequivalence of 7-fluorosialic acid to sialic acid in suppressing interaction with liver cell lectins. In vivo pharmacokinetic studies reveal enhanced half-life of the protein decorated with 7-fluorosialic acid relative to unmodified sialic acid in the murine circulatory system. 7-Fluorosialylation therefore offers considerable promise as a means of prolonging circulatory half-lives of glycoproteins and may pave the way toward biobetters for therapeutic use., 7-Fluorosialylation offers considerable promise as a means of prolonging circulatory half-lives of glycoproteins and may pave the way toward biobetters for therapeutic use.

The blood-brain barrier (BBB) is a formidable obstacle for brain delivery of therapeutic antibodies. However, antibodies against the transferrin receptor (TfR), enriched in brain endothelial cells, have been developed as delivery carriers of therapeutic cargos into the brain via a receptor-mediated transcytosis pathway. In vitro and in vivo studies demonstrated that either a low-affinity or mono-valent binding of these antibodies to the TfR improves their release on the abluminal side of the BBB and target engagement in brain parenchyma. However, these studies have been performed with mouse-selective TfR antibodies that recognize different TfR epitopes and have varied binding characteristics. In this study, we evaluated serum pharmacokinetics, brain and CSF exposure of the rat TfR-binding antibody OX26 affinity variants, having Kds of 5 nM, 76 nM, 108 nM and 174 nM; all binding the same epitope in bi-valent format. Pharmacodynamic responses were tested in Hargreaves chronic pain model after conjugation of OX26 affinity variants with the analgesic and anti-epileptic peptide, galanin. OX26 variants with affinities of 76 nM and 108 nM showed enhanced brain and CSF exposure and higher potency in Hargreaves model, compared to a 5 nM affinity variant; lowering affinity to 174 nM resulted in prolonged serum pharmacokinetics, but reduced brain and CSF exposure. The study demonstrates that binding affinity optimization of TfR-binding antibodies could improve their brain and CSF exposure even in the absence of mono-valent TfR engagement.

The purpose of this study was to evaluate the performance of a commercially available CyberKnife system with a multileaf collimator (CK-MLC) for stereotactic body radiotherapy (SBRT) and standard fractionated intensity-modulated radiotherapy (IMRT) applications. Ten prostate and ten intracranial cases were planned for the CK-MLC. Half of these cases were compared with clinically approved SBRT plans generated for the CyberKnife with circular collimators, and the other half were compared with clinically approved standard fractionated IMRT plans generated for conventional linacs. The plans were compared on target coverage, conformity, homogeneity, dose to organs at risk (OAR), low dose to the surrounding tissue, total monitor units (MU), and treatment time. CK-MLC plans generated for the SBRT cases achieved more homogeneous dose to the target than the CK plans with the circular collimators, for equivalent coverage, conformity, and dose to OARs. Total monitor units were reduced by 40% to 70% and treatment time was reduced by half. The CK-MLC plans generated for the standard fractionated cases achieved prescription isodose lines between 86% and 93%, which was 2%-3% below the plans generated for conventional linacs. Compared to standard IMRT plans, the total MU were up to three times greater for the prostate (whole pelvis) plans and up to 1.4 times greater for the intracranial plans. Average treatment time was 25 min for the whole pelvis plans and 19 min for the intracranial cases. The CK-MLC system provides significant improvements in treatment time and target homogeneity compared to the CK system with circular collimators, while maintaining high conformity and dose sparing to critical organs. Standard fractionated plans for large target volumes (>100 cm3) were generated that achieved high prescription isodose levels. The CK-MLC system provides more efficient SRS and SBRT treatments and, in select clinical cases, might be a potential alternative for standard fractionated treatments. PACS numbers: 87.56.nk, 87.56.bd.

Purpose This study investigates the potential application of image-based motion tracking and real-time motion correction to a helical tomotherapy system. Methods A kV x-ray imaging system was added to a helical tomotherapy system, mounted 90 degrees offset from the MV treatment beam, and an optical camera system was mounted above the foot of the couch. This experimental system tracks target motion by acquiring an x-ray image every few seconds during gantry rotation. For respiratory (periodic) motion, software correlates internal target positions visible in the x-ray images with marker positions detected continuously by the camera, and generates an internal-external correlation model to continuously determine the target position in three-dimensions (3D). Motion correction is performed by continuously updating jaw positions and MLC leaf patterns to reshape (effectively re-pointing) the treatment beam to follow the 3D target motion. For motion due to processes other than respiration (e.g., digestion), no correlation model is used - instead, target tracking is achieved with the periodically acquired x-ray images, without correlating with a continuous camera signal. Results The system's ability to correct for respiratory motion was demonstrated using a helical treatment plan delivered to a small (10 mm diameter) target. The phantom was moved following a breathing trace with an amplitude of 15 mm. Film measurements of delivered dose without motion, with motion, and with motion correction were acquired. Without motion correction, dose differences within the target of up to 30% were observed. With motion correction enabled, dose differences in the moving target were less than 2%. Nonrespiratory system performance was demonstrated using a helical treatment plan for a 55 mm diameter target following a prostate motion trace with up to 14 mm of motion. Without motion correction, dose differences up to 16% and shifts of greater than 5 mm were observed. Motion correction reduced these to less than a 6% dose difference and shifts of less than 2 mm. Conclusions Real-time motion tracking and correction is technically feasible on a helical tomotherapy system. In one experiment, dose differences due to respiratory motion were greatly reduced. Dose differences due to nonrespiratory motion were also reduced, although not as much as in the respiratory case due to less frequent tracking updates. In both cases, beam-on time was not increased by motion correction, since the system tracks and corrects for motion simultaneously with treatment delivery.

An oral, peripherally restricted CB1/CB2 agonist could provide an interesting approach to treat chronic pain by harnessing the analgesic properties of cannabinoids but without the well-known central side effects. γ-Carbolines are a novel class of potent mixed CB1/CB2 agonists characterized by attractive physicochemical properties including high aqueous solubility. Optimization of the series has led to the discovery of 29, which has oral activity in a rat inflammatory pain model and limited brain exposure at analgesic doses, consistent with a lower risk of CNS-mediated tolerability issues.

To establish an inverse planning set of parameters (class solution) to boost dominant intra-prostatic lesion (DIL) defined by MRI/MRSI.For 15 patients, DIL were contoured on CT or MR images and a class solution was developed to boost the DIL under the dosimetric requirements of the RTOG-0321 protocol. To determine the maximum attainable level of boost for each patient, 5 different levels were considered, at least 110%, 120%, 130%, 140% and 150% of the prescribed dose. The maximum attainable level was compared to the plan without boost using cumulative dose volume histogram (DVH).DIL dose escalation was feasible for 11/15 patients under the requirements. The planning target volume (PTV) dose was slightly increased, while the DIL dose was significantly increased without any violation of requirements. With slight adjustments of the dose constraint parameters, the dose escalation was feasible for 13/15 patients under requirements.Using a class solution, a dose escalation of the MRI/MRSI defined DIL up to 150% while complying with RTOG dosimetric requirements is feasible. This HDR brachytherapy approach to dose escalation allows a significant dose increase to the tumor while maintaining an acceptable risk of complications.

The robustness of treatment planning to prostatic edema for three different isotopes ({sup 125}I, {sup 103}Pd, and {sup 131}Cs) is explored using dynamical dose calculations on 25 different clinical prostate cases. The treatment plans were made using the inverse planning by simulated annealing (IPSA) algorithm. The prescription was 144, 127, and 125 Gy for {sup 125}I, {sup 131}Cs, and {sup 103}Pd, respectively. For each isotope, three dose distribution schemes were used to impose different protection levels to the urethra: V{sub 120}=0%, V{sub 150}=0%, and V{sub 150}=30%. Eleven initial edema values were considered ranging from 1.0 (no edema) to 2.0 (100%). The edema was assumed to resolve exponentially with time. The prostate volume, seed positions, and seed activity were dynamically tracked to produce the final dose distribution. Edema decay half-lives of 10, 30, and 50 days were used. A total of 675 dynamical calculations were performed for each initial edema value. For the {sup 125}I isotope, limiting the urethra V{sub 120} to 0% leads to a prostate D{sub 90} under 140 Gy for initial edema values above 1.5. Planning with urethra V{sub 150} at 0% provides a good response to the edema; the prostate D{sub 90} remains higher than 140 Gymore » for edema values up to 1.8 and a half-life of 30 days or less. For {sup 103}Pd, the prostate D{sub 90} is under 97% of the prescription dose for approximately 66%, 40%, and 30% of edema values for urethra V{sub 120}=0%, V{sub 150}=0%, and V{sub 150}=30%, respectively. Similar behavior is seen for {sup 131}Cs and the center of the prostate becomes 'cold' for almost all edema scenarios. The magnitude of the edema following prostate brachytherapy, as well as the half-life of the isotope used and that of the edema resorption, all have important impacts on the dose distribution. The {sup 125}I isotope with its longer half-life is more robust to prostatic edema. Setting up good planning objectives can provide an adequate compromise between organ doses and robustness. This is even more important since seed misplacements will contribute to further degrade dose coverage.« less

Prostate cancer is increasingly treated with high-dose-rate (HDR) brachytherapy, a type of radiotherapy in which a radioactive source is guided through catheters temporarily implanted in the prostate. Clinicians must set dwell times for the source inside the catheters so the resulting dose distribution minimizes deviation from dose prescriptions that conform to patient-specific anatomy. The primary contribution of this paper is to take the well-established dwell times optimization problem defined by Inverse Planning by Simulated Annealing (IPSA) developed at UCSF and exactly formulate it as a linear programming (LP) problem. Because LP problems can be solved exactly and deterministically, this formulation provides strong performance guarantees: one can rapidly find the dwell times solution that globally minimizes IPSA's objective function for any patient case and clinical criteria parameters. For a sample of 20 prostates with volume ranging from 23 to 103 cc, the new LP method optimized dwell times in less than 15 s per case on a standard PC. The dwell times solutions currently being obtained clinically using simulated annealing (SA), a probabilistic method, were quantitatively compared to the mathematically optimal solutions obtained using the LP method. The LP method resulted in significantly improved objective function values compared to SA (P = 1.54 x 10(-7)), but none of the dosimetric indices indicated a statistically significant difference (P < 0.01). The results indicate that solutions generated by the current version of IPSA are clinically equivalent to the mathematically optimal solutions.

The purpose of this paper is to present a method for the selection of inverse planning parameters and to establish a set of inverse planning parameters (class solution) for the inverse planning included in a commercial permanent prostate implant treatment planning system. The manual planning of more than 750 patients since 1996 led to the establishment of general treatment planning rules. A class solution is tuned to fulfill the treatment planning rules and generate equivalent implants. For ten patients, the inverse planning is compared with manual planning performed by our experienced physicist. The prostate volumes ranged from 17 to 51 cc and are implanted with low activity 1-125 seeds. Dosimetric indices are calculated for comparison. The inverse planning needed about 15 s for each optimization (400 000 iterations on a 2.5 GHz PC). In comparison, the physicist needed about 20 min to perform each manual plan. A class solution is found that consistently produces dosimetric indices equivalent or better than the manual planning. Moreover, even with strict seed placement rules, the inverse planning can produce adequate prostate dose coverage and organ at risk protection. The inverse planning avoids implant with seeds outside of the prostate and too close to the urethra. It also avoids needles with only one seed and needles with three consecutive seeds. This reduces the risk of complication due to seed misplacement and edema. The inverse planning also uses a smaller number of needles, reducing the cause of trauma. The quality of the treatment plans is independent of the gland size and shape. A class solution is established that consistently and rapidly produces equivalent dosimetric indices as manual planning while respecting severe seed placement rules. The class solution can be used as a starting point for every patient, dramatically reducing the time needed to plan individual patient treatments. The class solution works with inverse preplanning, intraoperative inverse preplanning, and intraoperative real-time planning. This technology is not intended to replace the physicist but to accelerate the planning process, making intraoperative treatment planning more effective.

Background and purpose: The aim of this study is to evaluate the acute and late complications in patients who have received HDR implant boost using inverse planning, and to determine dose volume correlations. Patients and methods: Between September 1999 and October 2002, 44 patients with locally advanced prostate cancer (PSA R10 ng/ml, and/or Gleason score R7, and/or Stage T2c or higher) were treated with 40–45 Gy external pelvic field followed by 2–3 fraction of inverse-planned HDR implant boost (6–9.5 Gy /fraction). Median follow-up time was 1.7 years with 81.8% of patients who had at least 12 months of follow up (range 8.6–42.5. Acute and late morbidity data were collected and graded according to RTOG criteria. Questionnaires were used to collect prostate related measures of quality of life, and international prostate symptom score (IPSS) before and after treatment. Dose–volume histograms for prostate, urethra, bladder, penis bulb and rectum were analyzed. Results: The median patient age was 64 years. Of these, 32% were in the high risk group, and 61% in the intermediate risk group. 3 patients (7%) had no adverse prognostic factors. A single grade 3 GU acute toxicity was reported but no grade 3–4 acute GI toxicity. No grade 3–4 late GU or GI toxicity was reported. Acute (late) grade 2 urinary and rectal symptoms were reported in 31.8 (11.4%) and 4.6% (4.6%) of patients, respectively. A trend for predicting acute GU toxicity is seen for total HDR dose of more than 18 Gy (ORZ3.6, 95%CIZ[0.96–13.5], PZ0.058). The evolution of toxicity is presented for acute and late GU/GI toxicity. Erectile dysfunction occurs in approximately 27% of patients who were not on hormonal deprivation, but may be taking sildenafil. The IPSS peaked on averaged 6 weeks post-implant and returned to the baseline at a median of 6 months. Conclusions: Inverse-planned HDR brachytherapy is a viable option to deliver higher dose to the prostate as a boost without increasing GU or rectal complication. Further HDR dose escalation to the prostate is feasible. q 2005 Published by Elsevier Ireland Ltd. Radiotherapy and Oncology 75 (2005) 318–324.

Purpose: To develop and optimize a technique for inverse treatment planning based solely on magnetic resonance imaging (MRI) during high-dose-rate brachytherapy for prostate cancer. Methods and Materials: Phantom studies were performed to verify the spatial integrity of treatment planning based on MRI. Data were evaluated from 10 patients with clinically localized prostate cancer who had undergone two high-dose-rate prostate brachytherapy boosts under MRI guidance before and after pelvic radiotherapy. Treatment planning MRI scans were systematically evaluated to derive a class solution for inverse planning constraints that would reproducibly result in acceptable target and normal tissue dosimetry. Results: We verified the spatial integrity of MRI for treatment planning. MRI anatomic evaluation revealed no significant displacement of the prostate in the left lateral decubitus position, a mean distance of 14.47 mm from the prostatic apex to the penile bulb, and clear demarcation of the neurovascular bundles on postcontrast imaging. Derivation of a class solution for inverse planning constraints resulted in a mean target volume receiving 100% of the prescribed dose of 95.69%, while maintaining a rectal volume receiving 75% of the prescribed dose of

Purpose To dose escalate selected regions inside the prostate without compromising the dose coverage of the prostate and the protection to the urethra, rectum, and bladder for prostate cancer patients treated with high-dose-rate brachytherapy. Methods and materials Magnetic resonance imaging combined with magnetic resonance spectroscopy imaging was used to differentiate between normal and malignant prostate and define cancer-validated dominant intraprostatic lesions (DIL) on 10 patients. The DILs were then contoured on the planning scans (CT or MRI based, 5 patients each), and our inverse planning dose optimization algorithm (called IPSA) was used to generate dose distributions for 3 different boost levels. Dose–volume histograms of the target and each organ at risk were compared with optimized plans without DIL boost. Results Combined MRI/magnetic resonance spectroscopic imaging identified 2 DILs in 8/10 of the 10 patients studied and a single DIL in the remaining 2 patients. The average prostate dose coverage V100 was 97% (σ = 1.0%). When the minimum DIL dose requested was 120% of the prescribed dose, the average DIL V120 was 97.1% (σ = 1.8%). For a boost value of 150%, the average V150 ranged from 77.8% to 86.1%, depending on the upper limit of the dose constraints. The bladder V50 increased by 1%, independently of the boost levels. The absolute increases in V50 for the rectum varied from 1% to 3%, depending on the boost level. The urethra V120 were increased by 13.4% and 32.5% for the lowest and highest boost levels, respectively. Conclusion The DIL dose can be escalated to a minimum of 120% while the entire prostate is treated simultaneously, without increasing the dose to surrounding normal tissues. Higher boost levels between 150% and 170% are feasible, but with slightly larger doses delivered to the rectum and urethra.

Purpose: The objective is to evaluate the prostate volume change and its dosimetric consequences after the insertion of catheters for high-dose-rate brachytherapy. Methods and Materials: For 13 consecutive patients, a spiral CT scan was acquired before each of the 2 fractions, separated on average by 20 hours. The coordinates of the catheters were obtained on 3 axial CT slices corresponding to apex, mid portion, and base portion of the prostate. A mathematical expansion model was used to evaluate the change of prostate volumes between the 2 fractions. It is based on the difference in the cube of the average distance between the centroid and catheter positions. The variation of implant dose–volume histograms between fractions was computed for plans produced by either inverse planning based on simulated annealing or geometric optimization. Results: The average magnitude of either increase or reduction in prostate volume was 7.8% (range, 2–17%). This volume change corresponds to an average prostate radius change of only 2.5% (range, 0.7–5.4%). For 5 patients, the prostate volume increased on average by 9% (range, 2–17%), whereas a reduction was observed for 8 patients by an average of 7% (range, 2–13%). More variation was observed at the prostate base than at mid or apex gland. The comparison of implant dose–volume histograms showed a small reduction of V100 receiving the prescription dose, with an average of 3.5% (range, 0.5–12%) and 2.2% (range, 1–6%) for inverse planning based on our simulated annealing and geometric optimization plans, respectively. Conclusion: Small volume change was observed between treatment fractions. This translates into small changes in dose delivered to the prostate volume.

PURPOSE: An inverse planning simulated annealing (IPSA) algorithm for optimization of high- dose-rate (HDR) brachytherapy has been previously described. In this study, IPSA is compared with geometrical optimization (GO) for prostate brachytherapy. METHODS AND MATERIALS: Using CT data collected from 10 patients, treatment plans were prepared using GO and IPSA. The clinical target volume (CTV) and critical organs (CO) including bladder, rectum, and urethra were contoured using Plato Version 14.2.1 (Nucletron Corp., Veenendaal, The Netherlands). Implant catheters were digitized using the CT planning system. All dwell positions outside of the CTV were turned off. Two optimized plans were generated for each implant using GO and IPSA. The same set of dose constraints were used for all inverse planning calculations and no manual adjustment of the dwell weight was used. Two prescription methods were used. Using the first method, coverage was prioritized: the prescription dose was normalized to the isodose volume that covers 98% of the CTV (V100 98% of CTV). The dose volume histograms (DVH) of CO were generated for comparison. Using the second method, sparing was prioritized: the prescription dose was normalized such that no urethra volume received 150% of the prescription dose (V150-urethra 0 cc). The DVH of CTV and CO were generated, and the homogeneity index (HI) and conformal index (COIN) were calculated for comparison and compared using the Wilcoxon matched-pairs test. RESULTS: Using the coverage-prioritized method, the difference in V80-bladder dose was not statistically significant (p 0.09; median: IPSA 0.62 cc, GO 1.05 cc). The V80-rectum ranged from 0.20-4.8 cc, and 0.05-1.4 cc using GO and IPSA, respectively. IPSA's V80-rectum was significantly lower (p 0.005; median: IPSA 0.38 cc, GO 1.31 cc). V150-urethra ranged from 0.02-0.75 cc and 0.0-0.01 cc using GO and IPSA, respectively. The V150-urethra was significantly lower using IPSA (p 0.005; median: IPSA 0.00 cc, GO 0.33 cc). Using the sparing prioritized method, the V100-prostate ranged from 30-97% and 95-100% using GO and IPSA, respectively. This difference was statistically significant (p 0.008). The HI and COIN were statistically higher using IPSA (p 0.005). CONCLUSION: Anatomy-based inverse optimization using IPSA is superior to dwell-position- based optimization using GO as it: (1) Improves target coverage and conformality while sparing normal structures, (2) Improves dose homogeneity within the target, and (3) Minimizes volume of non-contoured normal tissue irradiated. Routine application of three-dimensional brachytherapy planning and anatomy-based inverse dwell time optimization is recommended. 2004 American Brachytherapy Society. All rights reserved.

1. Mexiletine is extensively metabolized in man by C- and N-oxidation and the aim of the present study was to characterize major cytochrome P450 enzyme(s) involved in the formation of N-hydroxymexiletine. 2. Incubations with genetically engineered microsomes indicated that the formation rate of N-hydroxymexiletine was highest in the presence of microsomes expressing high levels of either CYP1A2 or CYP2E1 and the formation of N-hydroxymexiletine by human liver microsomes was inhibited about 40% by antibodies directed against CYP1A1/1A2 or CYP2E1. Additional incubations demonstrated that formation of N-hydroxymexiletine was decreased 47 and 51% by furafylline, 40 microm and 120 microm, respectively, and decreased 55 and 67% by alpha-naphthoflavone, 1 microm and 3 microm, respectively (all p < 0.05 versus control). 3. The formation rate of N-hydroxymexiletine in human liver microsomes was highly correlated with CYP2B6 (RS-mexiletine, r = 0.7827; R-(-)-enantiomer, r = 0.7034; S-(+)-enantiomer, r = 0.7495), CYP2E1 (S-(+)-enantiomer, r = 0.7057) and CYP1A2 (RS-mexiletine, r = 0.5334; S-(+)-enantiomer, r = 0.6035). 4. In conclusion, we have demonstrated that CYP1A2 is a major human cytochrome P450 enzyme involved in the formation of N-hydroxymexiletine. However, other cytochrome P450 enzymes (CYP2E1 and CYP2B6) also appear to play a role in the N-oxidation of this drug.

CYP2D6 is involved in the O-demethylation metabolic pathway of venlafaxine in humans. In this study, we investigated whether this isozyme is stereoselective. Plasma samples from seven CYP2D6 extensive metabolizers (EMs) and five CYP2D6 poor metabolizers (PMs), collected during a period without and w

Purpose: Commercially available optimization schemes generally result in an undesirable dose distribution, because of the particular shapes of tumors extending laterally from the tandem. Dose distribution is therefore manually obtained by adjusting relative dwell time values until an acceptable solution is found. The objective of this work is to present the clinical application of an inverse planning dose optimization tool for the automatic determination of source dwell time values in the treatment of interstitial gynecologic templates. Methods and Materials: In cases where the tumor extends beyond the range of the tandem-ovoid applicator, catheters as well as the tandem are inserted into the paravaginal and parametrial region in an attempt to cover the tumor volume. CT scans of these patients are then used for CT-based dose planning. Dose distribution is obtained manually by varying the relative dwell times until adequate dose coverage is achieved. This manual planning is performed by an experienced physician. In parallel, our in-house inverse planning based on simulated annealing is used to automatically determine which of all possible dwell positions will become active and to calculate the dwell time values needed to fulfill dose constraints applied to the tumor volume and to each organ at risk. To compare the results of these planning methods, dose‐volume histograms and isodose distributions were generated for the target and each organ at risk. Results: This procedure has been applied for the dose planning of 12 consecutive interstitial gynecologic templates cases. For all cases, once the anatomy was contoured, the routine of inverse planning based on simulated annealing found the solution to the dose constraints within 1 min of CPU time. In comparison, manual planning took more than 45 min. The inverse planning‐ generated plans showed improved protection to organs at risk for the same coverage compared to manual planning. Conclusion: This inverse planning tool reduced the planning time significantly and produced improved plans with reduced dose to the organs at risk. Furthermore, the inverse planning approach improves the physician’s control over treatment. The focus becomes the physician’s prescription to the target and his or her compromise due to dose to normal structures. © 2002 Elsevier Science Inc. Brachytherapy, Gynecologic, Inverse planning, Simulated annealing, IPSA.

~Received 7 August 2000; accepted for publication 26 February 2001!An anatomy-based dose optimization algorithm is developed to automatically and rapidly producea highly conformal dose coverage of the target volume while minimizing urethra, bladder, andrectal doses in the delivery of an high dose-rate~HDR! brachytherapy boost for the treatment ofprostate cancer. The dwell times are optimized using an inverse planning simulated annealingalgorithm ~IPSA! governed entirely from the anatomy extracted from a CT and by a dedicatedobjective function ~cost function! reflecting clinical prescription and constraints. With this inverseplanning approach, the focus is on the physician’s prescription and constraint instead of on thetechnical limitations. Consequently, the physician’s control on the treatment is improved. Thecapacity of this algorithm to represent the physician’s prescription is presented for a clinical pros-tate case. The computation time ~CPU! for IPSA optimization is less than 1 min ~41 s for 142915iterations! for a typical clinical case, allowing fast and practical dose optimization. The achieve-ment of highly conformal dose coverage to the target volume opens the possibility to deliver ahigher dose to the prostate without inducing overdosage of urethra and normal tissues surroundingthe prostate. Moreover, using the same concept, it will be possible to deliver a boost dose to adelimited tumor volume within the prostate. Finally, this method can be easily extended to otheranatomical sites. © 2001 American Association of Physicists in Medicine.@DOI: 10.1118/1.1368127#Key words: inverse planning, brachytherapy, HDR, prostate, simulated annealingI. INTRODUCTIONThe last decade has seen major changes in the way radiationtreatments are delivered. The century-old objective of radia-tion therapy, i.e., to deliver a curative dose to the target whilepreserving normal tissues, can now be aimed at with a highdegree of sophistication. However, in spite of major im-provements achieved with 3D imaging modalities that allowthe anatomy to be properly defined, brachytherapy treat-ments have not yet fully benefit from these important newpieces of information. The positioning of the seeds for per-manent implant or of catheters for after-loading treatment isnow image guided, greatly improving the localization of theapplicators. At the planning stage, however, the anatomy isusually only indirectly taken into account. For high dose-rate~HDR! brachytherapy, catheters are placed in the target vol-ume and it is assumed that if the dose distribution covers thecatheters, it should also cover the anatomy. Imaging is com-monly used to set the treatment margins, but optimized dosedistributions are based on considerations such as catheter po-sitions and desired dose to a few defined points. This neces-sarily results in an approximation of the shape of theanatomy. For the case of treatment of the prostate, volumeoptimization results in a dose distribution that is essentiallycylindrical in shape. This may represent an ‘‘average’’ pros-tate, but each prostate has a very specific shape. Any ap-proximation of its shape to a geometrical representation willresult in an overdosage of normal tissues surrounding theprostate. The organs at risk in the vicinity of the prostatemay be included in this unnecessarily overdosed region.Recent studies

CYP2D6 is the major enzyme involved in the metabolism of venlafaxine. Subjects with a low CYP2D6 activity have increased plasma concentrations of venlafaxine that may predispose them to cardiovascular side effects. In vitro and in vivo studies showed that diphenhydramine, a nonprescription antihistamine, can inhibit CYP2D6 activity. Therefore, the authors investigated in this study a potential drug interaction between diphenhydramine and venlafaxine. Fifteen male volunteers, nine with the extensive metabolizer (EM) and six with the poor metabolizer (PM) phenotype of CYP2D6, received venlafaxine hydrochloride 18.75 mg orally every 12 hours for 48 hours on two occasions (1 week apart): once alone and once during the concomitant administration of diphenhydramine hydrochloride (50 mg every 12 hours). Blood and urine samples were collected for 12 hours under steady-state conditions. In EMs, diphenhydramine decreased venlafaxine oral clearance from 104+/-60 L/hr to 43+/-23 L/hr (mean +/- SD; p < 0.05) without any effect on renal clearance (4+/-1 L/hr during venlafaxine alone and 4+/-2 L/hr during venlafaxine plus diphenhydramine). In PMs, coadministration of diphenhydramine did not cause significant changes in oral clearance and partial metabolic clearances of venlafaxine to its various metabolites. Diphenhydramine disposition was only slightly affected by genetically determined low CYP2D6 activity or concomitant administration of venlafaxine. In conclusion, diphenhydramine, at therapeutic doses, inhibits CYP2D6-mediated metabolism of venlafaxine in humans. Clinically significant interactions could be encountered during the concomitant administration of diphenhydramine and other antidepressant or antipsychotic drugs that are substrates of CYP2D6.

Background and objective Mexiletine and propafenone are often used concomitantly and are metabolized by the same cytochrome P450 isozymes, namely CYP2D6, CYP1A2, and probably CYP3A4. Our objective was to study the potential pharmacokinetic and electrophysiological interactions between mexiletine and propafenone. Methods Fifteen healthy volunteers, 8 extensive metabolizers and 7 poor metabolizers of CYP2D6, received oral doses of mexiletine 100 mg two times daily from day 1 to day 8 and oral doses of propafenone 150 mg two times daily from day 5 to day 12. Interdose studies were performed at steady-state on mexiletine alone (day 4), mexiletine plus propafenone (day 8), and propafenone alone (day 12). Results In subjects in the extensive metabolizer group, coadministration of propafenone decreased oral clearances of R-(−)-mexiletine (from 41 ± 11 L/h to 28 ± 7 L/h) and S-(+)-mexiletine (from 43 ± 15 L/h to 29 ± 11 L/h) to an extent such that these values were no longer different between the extensive and the poor metabolizer groups. Propafenone coadministration also decreased partial metabolic clearances of mexiletine to hydroxymethylmexiletine, p-hydroxymexiletine, and m-hydroxymexiletine in extensive metabolizers by 71%, 67%, and 73%, respectively. In contrast, propafenone did not alter the kinetics of mexiletine enantiomers in subjects in the poor metabolizer group except for a slight decrease in the formation of hydroxymethylmexiletine. Pharmacokinetic parameters of propafenone were not changed during concomitant administration of mexiletine in subjects of either phenotype. Finally, electrocardiographic parameters (QRS duration, QTc, RR, and PR intervals) were not modified during the combined administration of the drugs. Conclusion Propafenone is a potent CYP2D6 inhibitor that may cause an increase in plasma concentrations of coadministered CYP2D6 substrates. Clinical Pharmacology & Therapeutics (2000) 68, 44–57; doi: 10.1067/mcp.2000.108023

Occurrence of a lupus-like syndrome in a significant number of patients treated with procainamide has limited the clinical use of this antiarrhythmic drug. In-vitro studies conducted in our laboratory have demonstrated that CYP2D6 is the major cytochrome P450 isozyme involved in the formation of N-hydroxyprocainamide, a metabolite potentially involved in the drug-induced lupus erythematosus syndrome observed with procainamide. In the current study, we evaluated the role of CYP2D6 activity in the in-vivo oxidation of procainamide in man. Nineteen healthy individuals, 13 with high (extensive metabolizers) and six with low (poor metabolizers) CYP2D6 activity, received a single 500 mg oral dose of procainamide hydrochloride on two occasions, once alone (period 1) and once during the concomitant administration of the selective inhibitor quinidine (50 mg four times daily; period 2). Blood and urine samples were collected over 36 h after drug administration of procainamide and analysed for procainamide and its major metabolites (N-acetylprocainamide, desethylprocainamide, N-acetyl-desethylprocainamide, p-aminobenzoic acid and its N-acetylated derivative, and nitroprocainamide). No differences were observed in the oral and renal clearances of procainamide between extensive metabolizers and poor metabolizers during either study period. However, partial metabolic clearance of procainamide to desethylprocainamide was significantly greater in extensive metabolizers than in poor metabolizers during both periods. Most importantly, the urinary excretion of nitroprocainamide during period 1 was measurable in 7/13 extensive metabolizers but in none of the poor metabolizers. During the concomitant administration of quinidine, nitroprocainamide could not be detected in the urine of any individuals tested. Therefore, our results suggest that CYP2D6 is involved in the in-vivo aliphatic amine deethylation and N-oxidation of procainamide at its arylamine function in man. Further studies are needed to demonstrate whether a low CYP2D6 activity, either genetically determined or pharmacologically modulated, could prevent drug-induced lupus erythematosus syndrome observed during chronic therapy with procainamide.

An improved high-performance liquid chromatographic assay for the determination of procainamide and N-acetylprocainamide (NAPA) at concentrations observed up to 32 h after a single oral dose administration of procainamide to human subjects is reported. Following liquid-liquid extraction of plasma samples, procainamide, NAPA, and the internal standard (N-propionylprocainamide) are separated on a reversed-phase C8 column with retention times of 4.0, 6.7, and 13.2 min, respectively. The ultraviolet detection limit (wavelength, 280 nm) of procainamide and NAPA is 2 ng/mL (signal-to-noise ratio, 3:1), and the quantitation limit is 4 ng/mL (signal-to-noise ratio, 5:1). Intra- and interday coefficients of variation are less than 8% in the range of 20-500 ng/mL.

Sequential oxidations at the arylamine moiety of the procainamide molecule leading to the formation of N-hydroxyprocainamide and its nitroso derivative may be responsible for lupus erythematosus observed in patients treated with the drug. The objective of the present study was to characterize major cytochrome P450 isozyme(s) involved in the N-hydroxylation of procainamide. Firstly, incubations were performed with microsomes from either lymphoblastoid cells or yeast transfected with cDNA encoding for specific human cytochrome P450 isozymes. Experiments performed with these enzyme expression systems indicated that the highest formation rate of N-hydroxyprocainamide was observed in the presence of CYP2D6 enriched microsomes. Additional experiments demonstrated that the formation rate of N-hydroxyprocainamide by CYP2D6 enriched microsomes was decreased from 45 +/- 4% to 93 +/- 1% by quinidine at concentrations ranging from 30 nM to 100 microM (all p < 0.05 vs control) and by approximately 75% by antibodies directed against CYP2D6. Secondly, incubations were performed with microsomes prepared from 15 human liver samples. Using this approach, an excellent correlation was observed between the formation rate of N-hydroxyprocainamide and dextromethorphan O-demethylase activity (CYP2D6; r = 0.9305; p < 0.0001). In contrast, no correlation could be established between N-hydroxyprocainamide formation rate and caffeine N3-demethylase (CYP1A2), coumarin 7-hydroxylase (CYP2A6), S-mephenytoin N-demethylase (CYP2B6), tolbutamide methlhydroxylase (CYP2C9), S-mephenytoin 4'-hydroxylase (CYP2C19), chlorzoxazone 6-hydroxylase (CYP2E1), dextromethorphan N-demethylase (CYP3A4), testosterone 6 beta-hydroxylase (CYP3A4/5) or lauric acid 12-hydroxylase (CYP4A11) activities. Furthermore, formation rate of N-hydroxyprocainamide was decreased in a concentration-dependent manner by quinidine (300 nM to 100 microM) and by antibodies directed against CYP2D6 but not by furafylline 20 microM (CYP1A2), ketoconazole 1 microM (CYP3A4), sulfaphenazole 10 microM (CYP2C9) or antibodies directed against CYP1A1/1A2, CYP2C, CYP2A6, CYP2E1 or CYP3A4/3A5. In conclusion, the results obtained in the present study demonstrate that CYP2D6 is the major human cytochrome P450 isozyme involved in the formation of the reactive metabolite of procainamide, namely N-hydroxyprocainamide.

Cannabinoid CB1 receptor agonists exhibit potent analgesic effects in rodents and humans, but their clinical utility as analgesic drugs is often limited by centrally mediated side effects. We report herein the preparation of N-methyl-3-(tetrahydro-2H-pyran-4-yl)-2,3,4,9-tetrahydro-1H-carbazole-6-carboxamides as a novel class of hCB1/hCB2 dual agonists with attractive physicochemical properties. More specifically, (R)-N,9-dimethyl-N-(4-(methylamino)-4-oxobutyl)-3-(tetrahydro-2H-pyran-4-yl)-2,3,4,9-tetrahydro-1H-carbazole-6-carboxamide, displayed an extremely low level of CNS penetration (Rat Cbr/Cplasma = 0.005 or 0.5%) and was devoid of CNS side effects during pharmaco-dynamic testing.

Pre-clinical behavioral pharmacology studies supporting indications like analgesia typically consist of at least three different studies; dose-finding, duration of effect, and tolerance-development studies. Pharmacokinetic (PK) plasma samples are generally taken from a parallel group of animals to avoid disruption of the behavioral pharmacodynamic (PD) endpoint. Our objective was to investigate if pre-clinical behavioral pharmacology studies in rats could be performed effectively by combining three studies into a single experimental design and using sparse PK sampling in the same animals as for PD. A refined dosing strategy was applied for a muscarinic agonist, AZD6088, using the rat spinal nerve ligation heat hyperalgesia model. PD measurements were performed on day 1, 3, 5 and 8. Two PK samples per day were taken day 2 and 4. In a separate control group, PD measurements were performed on rats without PK sampling. Data was analyzed using a population approach in NONMEM. The animals produced a consistent and reproducible response irrespective of day of testing suggesting that blood sampling on alternate days did not interfere with the PD responses. A direct concentration–effect relationship with good precision was established and no tolerance development was observed. The new design combining three studies into one and eliminating a satellite PK group realized substantial savings compared to the old design; animal use was reduced by 58% and time required to generate results was reduced by 55%. The design described here delivers substantial savings in animal lives, time, and money whilst still delivering a good quality and precise description of the PKPD relationship.

Cannabinoids are analgesic in man, but their use is limited by their psychoactive properties. One way to avoid cannabinoid receptor subtype 1 (CB1R)-mediated central side-effects is to develop CB1R agonists with limited CNS penetration. Activation of peripheral CB1Rs has been proposed to be analgesic, but the relative contribution of peripheral CB1Rs to the analgesic effects of systemic cannabinoids remains unclear. Here we addressed this by exploring the analgesic properties and site of action of AZ11713908, a peripherally restricted CB1R agonist, in rodent pain models. Systemic administration of AZ11713908 produced robust efficacy in rat pain models, comparable to that produced by WIN 55, 212-2, a CNS-penetrant, mixed CB1R and CB2R agonist, but AZ11713908 generated fewer CNS side-effects than WIN 55, 212-in a rat Irwin test. Since AZ11713908 is also a CB2R inverse agonist in rat and a partial CB2R agonist in mouse, we tested the specificity of the effects in CB1R and CB2R knock-out (KO) mice. Analgesic effects produced by AZ11713908 in wild-type mice with Freund’s complete adjuvant-induced inflammation of the tail were completely absent in CB1R KO mice, but fully preserved in CB2R KO mice. An in vivo electrophysiological assay showed that the major site of action of AZ11713908 was peripheral. Similarly, intraplantar AZ11713908 was also sufficient to induce robust analgesia. These results demonstrate that systemic administration of AZ11713908, produced robust analgesia in rodent pain models via peripheral CB1R. Peripherally restricted CB1R agonists provide an interesting novel approach to analgesic therapy for chronic pain.

This study was initiated to characterize the metabolism and pharmacokinetics of SNC80 in rats and to evaluate the impact of Freund's complete adjuvant (FCA)-induced inflammation on its body disposition. In vitro, the disappearance and intrinsic clearance (CL(int)) of SNC80 were measured following incubations in recombinant rat CYPs and in phenotyped liver microsomes from naive and 24-h FCA-treated rats. The unbound fraction (f(u)) was assessed by ultrafiltration. Based on the Clint values, in vivo blood clearance of 3.35 and 2.48 L/h/kg were predicted in naive and FCA-treated rats. In vivo, SNC80 was administered to naive and 24-h FCA-treated rats at 10 micromol/kg i.v. and 50 micromol/kg p.o. The naive animals showed high plasma clearance (3.1 L/h/kg), low renal clearance (

The purpose of this paper is to report the clinical benefits of our in house inverse planning routine (IPSA) for the treatment planning of permanent prostate implant (PPI). IPSA has been designed for 3D image guided brachytherapy treatment planning. The optimization process is guided by dose objectives define for each organ extracted from medical imaging. IPSA takes into account multiple targets (prostate, boost) and multiple organs at risk (urethra, rectum, bladder, etc.). IPSA is setup to maximize the prostate dose coverage while taking into account other clinical objectives like the dose homogeneity and the organs at risk protection. A simulated annealing algorithm optimizes the source and needle positions to fulfill the dose objectives and few source placement rules in less than 1 minute. For ten patients IPSA is compared to conventional manual planning. IPSA is also tested to optimize with different maximum number of needles and different source activity. IPSA needs about 15 seconds for each optimization. In comparison an experienced physicist needs about 20 minutes to perform a manual planning. The prostate volumes range from 17 to 51cc. IPSA consistently and rapidly produces equivalent dosimetric indices as manual planning while respecting severe restrictions on source placement rules. IPSA produces implant without seeds outside of the prostate, without needles with only one seed and without needles with 3 consecutive seeds. This reduces the risk of complication due to seed misplacement and edema. IPSA also uses a smaller number of needles reducing the cause of trauma. IPSA is appropriate for pre-planning, intra-operative pre-planning and intra-operative real-time planning taking into account the implanted sources and needles. This technology is not intended to replace the physicist but to accelerate the planning process making intra-operative treatment planning more effective.

The purpose of this paper is to report the clinical benefits of our in house inverse planning routine (IPSA) for the treatment planning of prostate high dose rate brachytherapy (HDR). IPSA has been designed for 3D image guided brachytherapy treatment planning. The optimization process is guided by dose objectives define for each organ extracted from medical imaging. IPSA takes into account multiple targets (prostate, boost) and multiple organs at risk (urethra, rectum, bladder, etc.). IPSA is setup to maximize the prostate dose coverage while taking into account other clinical objectives like the dose homogeneity and the organs at risk protection. A simulated annealing algorithm optimizes the dwell times to fulfill the dose objectives in less than 1 minute. The dose volume histograms of 30 consecutive prostate cancer patients were computed and analyzed for this study. The prostate volumes range from small to large and the number of implanted catheters vary accordingly. The dosimetric indices are excellent independently of the gland size and shape. IPSA reduced significantly the treatment planning time and produced improved treatment plans with reduced dose to the organs at risk compare to conventional treatment planning methods. This anatomy based optimization achieved conformal dose coverage to the prostate opening the possibility to deliver higher dose to the prostate while reducing the dose deliver to the urethra and normal tissues. Wide adaptation of this technology should improve quality of patient care.

Purpose To develop a technique using exclusively magnetic resonance imaging (MRI) to perform dwell position identification, targets and organs at risk delineation, and to apply inverse planning dose optimization to high-dose-rate brachytherapy for cervical cancer. Methods and materials We included 15 consecutive women treated with high-dose-rate (HDR) brachytherapy for cervical cancer. All patients underwent MRI after placement of tandem and ring applicator containing a gadodiamide-filled dummy marker. This technique allowed direct visualization of the source pathway and precise definition of the intra-applicator source positions. For each patient, we delineated gross target volume (GTV), high-risk clinical target volume (HR-CTV), and organs at risk on MRI, according to the European Gynecological GEC-ESTRO Working Group definitions. We performed inverse planning simulated annealing (IPSA) and analyzed the dose–volume histograms with the following endpoints: D90, D100, and V100 for GTV and HR-CTV; D0.1 cc, D1 cc, D2 cc for bladder, rectum, and bowel; and dose at Point A. Results The intra-applicator source pathway was easily visualized on MRI using the gadodiamide-filled marker. IPSA provided excellent target coverage. The mean D90 and V100 for HR-CTV were 103 ± 5% and 92 ± 3%, respectively. IPSA provided excellent bladder sparing. D1 cc and D2 cc of bladder were 73 ± 10% and 67 ± 10%, respectively. Conclusions We developed a novel technique that allows direct visualization of the intra-applicator source pathway on MRI. Using this technique, we successfully performed inverse planning directly from MRI.

The purpose of this paper is to present a method for the selection of inverse planning parameters and to establish a set of inverse planning parameters (class solution) for the inverse planning included in a commercial permanent prostate implant treatment planning system. The manual planning of more than 750 patients since 1996 led to the establishment of general treatment planning rules. A class solution is tuned to fulfill the treatment planning rules and generate equivalent implants. For ten patients, the inverse planning is compared with manual planning performed by our experienced physicist. The prostate volumes ranged from 17 to 51 cc and are implanted with low activity 1-125 seeds. Dosimetric indices are calculated for comparison. The inverse planning needed about 15 s for each optimization (400 000 iterations on a 2.5 GHz PC). In comparison, the physicist needed about 20 min to perform each manual plan. A class solution is found that consistently produces dosimetric indices equivalent or better than the manual planning. Moreover, even with strict seed placement rules, the inverse planning can produce adequate prostate dose coverage and organ at risk protection. The inverse planning avoids implant with seeds outside of the prostate and too close to the urethra. It also avoids needles with only one seed and needles with three consecutive seeds. This reduces the risk of complication due to seed misplacement and edema. The inverse planning also uses a smaller number of needles, reducing the cause of trauma. The quality of the treatment plans is independent of the gland size and shape. A class solution is established that consistently and rapidly produces equivalent dosimetric indices as manual planning while respecting severe seed placement rules. The class solution can be used as a starting point for every patient, dramatically reducing the time needed to plan individual patient treatments. The class solution works with inverse preplanning, intraoperative inverse preplanning, and intraoperative real-time planning. This technology is not intended to replace the physicist but to accelerate the planning process, making intraoperative treatment planning more effective.

The objective was to identify the major cytochrome P450 enzyme(s) involved in the metabolism of domperidone. Experiments were performed using human liver microsomes (HLMs), recombinant human cytochrome P450 enzymes, cytochrome P450 chemical inhibitors and monoclonal antibodies directed against cytochrome P450 enzymes. Four metabolites were identified from incubations performed with HLMs and excellent correlations were observed between the formation of domperidone hydroxylated metabolites (M1, M3 and M4), N-desalkylated domperidone metabolite (M2) and enzymatic markers of CYP3A4/5 (r2 = 0.9427, 0.951, 0.9497 and 0.8304, respectively). Ketoconazole (1 microM) decreased the formation rate of M1, M2, M3 and M4 by 83, 78, 75 and 88%, respectively, whereas the effect of other inhibitors (quinidine, furafylline and sulfaphenazole) was minimal. Important decreases in the formation rate of M1 (68%), M2 (64%) and M3 (54%) were observed with anti-CYP3A4 antibodies. Formation of M1, M2 and M3 in HLMs exhibited Michaelis-Menten kinetics (Km: 166, 248 and 36 microM, respectively). Similar Km values were observed for M1, M2 and M3 when incubations were performed with recombinant human CYP3A4 (Km: 107, 273 and 34 microM, respectively). The data suggest that CYP3As are the major enzymes involved in the metabolism of domperidone.

Purpose: To optimize dose distribution for high-dose-rate brachytherapy for prostate cancer, we have developed a new algorithm named Attraction-Repulsion Model (ARM). In this study, we compared the ARM with geometric optimization (GO). Methods and Materials: The ARM was used to optimize the dose distribution by finding the best dwell time combination. ARM requires grids inside the clinical target volume (CTV) and critical organs. These grids generate attraction or repulsion based on specific dose constraints. After calculations were performed repeatedly until the attraction and repulsion forces reached equilibrium, the optimal dwell time distribution was established. We compared the ARM with GO for 10 patients using dose-volume histograms. Results: The CTV ranged from 23 to 48 cc, and the CTV V150 ranged from 52% to 79%, and 23% to 44% for GO and ARM, respectively. This indicates that the dose homogeneity indices, as well as the conformal indices, were higher for ARM than for GO. The urethra V150 was 0-99% and 0-1% for GO and ARM, respectively. Conclusion: The ARM proved to be superior to GO in minimizing the dose to normal structures and in improving dose homogeneity for the target while reducing the dose to normal tissues.

Purpose: Three-dimensional treatment planning systems and inverse planning optimization for brachytherapy are becoming commercially available. Guidelines for target delineation and dose constrictions have not been established using this new software. In this study we describe a method of target delineation for the tandem and ovoids applicator. We then compare inverse planning dose distributions with the traditional methods of prescribing dose. Methods and Materials: Target and organ-at-risk volumes were defined using systematic guidelines on 15 patients treated in our department with high-dose-rate brachytherapy for cervical cancer using tandem and ovoids. High-dose-rate distributions were created according to three different dose optimization protocols: inverse planning simulated annealing (IPSA), point A, and point A with a normalization of 2 cc of the bladder receiving 80% of the dose (bladder-sparing method). An uniform cost function for dose constraints was applied to all IPSA generated plans, and no manual optimization was allowed for any planning method. Results: Guidelines for target and structure-at-risk volumes, as well as dose constraint cost functions, were established. Dose–volume histogram analysis showed that the IPSA algorithm indicated no difference in tumor coverage compared with point A optimization while decreasing dose to the bladder and rectum. The IPSA algorithm provided better target volume coverage compared with bladder-sparing method with equivalent doses to the bladder and rectum. Conclusion: This study uses a systematic approach for delineating target and organ-at-risk volumes and a uniform cost function for generating IPSA plans for cervical cancer using tandem and ovoids. Compared with conventional dose prescription methods, IPSA provides a consistent method of optimization that maintains or improves target coverage while decreasing dose to normal structures. Image-guided brachytherapy and inverse planning improve brachytherapy dosimetry.

Purpose Magnetic resonance imaging (MRI) provides superior visualization of the prostate and surrounding anatomy, making it the modality of choice for imaging the prostate gland. This pilot study was performed to determine the feasibility and dosimetric quality achieved when placing high-dose-rate prostate brachytherapy catheters under MRI guidance in a standard "closed-bore" 1.5T scanner. Methods and materials Patients with intermediate-risk and high-risk localized prostate cancer received MRI-guided high-dose-rate brachytherapy boosts before and after a course of external beam radiotherapy. Using a custom visualization and targeting program, the brachytherapy catheters were placed and adjusted under MRI guidance until satisfactory implant geometry was achieved. Inverse treatment planning was performed using high-resolution T 2 -weighted MRI. Results Ten brachytherapy procedures were performed on 5 patients. The median percentage of volume receiving 100% of prescribed minimal peripheral dose (V 100 ) achieved was 94% (mean, 92%; 95% confidence interval, 89–95%). The urethral V 125 ranged from 0% to 18% (median, 5%), and the rectal V 75 ranged from 0% to 3.1% (median, 0.3%). In all cases, lesions highly suspicious for malignancy could be visualized on the procedural MRI, and extracapsular disease was identified in 2 patients. Conclusion High-dose-rate prostate brachytherapy in a standard 1.5T MRI scanner is feasible and achieves favorable dosimetry within a reasonable period with high-quality image guidance. Although the procedure was well tolerated in the acute setting, additional follow-up is required to determine the long-term safety and efficacy of this approach.

CYP2D6 is involved in the O-demethylation metabolic pathway of venlafaxine in humans. In this study, we investigated whether this isozyme is stereoselective. Plasma samples from seven CYP2D6 extensive metabolizers (EMs) and five CYP2D6 poor metabolizers (PMs), collected during a period without and with coadministration of quinidine, were analysed. Subjects were administered venlafaxine hydrochloride 18.75 mg orally every 12 h for 48 h on two occasions (1 week apart); once alone and once during the concomitant administration of quinidine sulphate every 12 h. Blood and urine samples were collected under steady-state conditions over one dosing interval (12 h). The present results show that, although CYP2D6 catalyses the O-demethylation of both enantiomers of venlafaxine, it displays a marked stereoselectivity towards the (R)-enantiomer. The oral clearance of (R)-venlafaxine was found to be nine-fold higher in EMs compared to PMs [median (range) 173 (29-611) l/h versus 20 (16-24) l/h, P0.005], while it was two-fold higher for (S)-venlafaxine [73 (32-130) l/h versus 37 (21-44) l/h, P0.05]. In EMs, quinidine decreased (R)- and (S)-venlafaxine oral clearance by 12-fold ( 0.05) and four-fold ( 0.05), respectively. In contrast, quinidine did not have any effects on renal clearance of (R)-venlafaxine [4 (2-10) l/h for venlafaxine alone versus 5 (0.6-7) l/h for venlafaxine + quinidine] and of (S)-venlafaxine [4 (1-7) l/h for venlafaxine alone versus 3 (0.4-6) l/h for venlafaxine + quinidine]. The coadministration of quinidine to EMs resulted in an almost complete inhibition of the partial metabolic clearance of (R)-venlafaxine to O-demethylated metabolites [127 (10-493) l/h down to 1 (0.1-3) l/h, 0.05], while a seven-fold reduction was measured for (S)-venlafaxine [47 (14-94) l/h versus 7 (1-19) l/h, 0.05]. In PMs, coadministration of quinidine did not significantly change oral clearance and partial metabolic clearance of (R)- and (S)-venlafaxine to its various metabolites. In contrast, data obtained on the partial metabolic clearance of (R)- and (S)-venlafaxine to N-demethylated metabolites, a reaction which is mediated by CYP3A4, suggest a lack of stereoselectivity of this enzyme.

Purpose: To present an exhaustive dosimetric comparison between three geometric optimization methods and our inverse-planning simulated annealing (IPSA) algorithm, with two different prescriptions for high-dose-rate (HDR) boost of the prostate. The objective of this analysis was to quantify the dosimetric advantages of the IPSA algorithm compared with more standard geometric optimizations. Methods and Materials: Between September 1999 and June 2001, 34 patients were treated to a dose of 40 – 44 Gy by external pelvic fields, followed by an HDR boost of 18 Gy in 3 fractions. The first 4 patients were treated with HDR using geometric optimization, and anatomy-based inverse-planning dose optimization was used for the remaining 30 patients. We retrospectively used the data from these 30 patients to create HDR dose distributions according to five different dose optimization protocols, including our IPSA algorithm. The various geometric optimization procedures differed in the way the dwell positions were activated and plan normalization was performed. Dose–volume histograms from all these plans were analyzed and multiple implant quality indexes extracted. Results: The IPSA algorithm provided better clinical tumor volume prescription dose coverage than did the geometric optimizations. The average prostate volume receiving 100% of the prescribed dose (V100) was 96.3% and 94.5% for IPSA with two different prescriptions compared with 92.1%, 92.6%, and 88.8% for the three geometric optimization schemes. The average urethra V150 value was 0.0% and 0.7% for IPSA with two different prescriptions, and the three geometric optimization protocols generated average values of 22.9%, 33.9%, and 38.8%. The bladder and rectal dose–volume histograms were similar, although the latest version of the IPSA algorithm slightly decreases the dose to these organs at risk because of organ-specific dose constraints included in the objective function. Conclusion: We found that planning an HDR prostate boost could be performed in a fast, secure, and effective manner with the IPSA algorithm. We demonstrated that our inverse-planning algorithm produces superior HDR plans than more conventional geometric optimizations for adenocarcinoma of the prostate. The organs at risk protection included in the objective function is a major feature of the algorithm and should allow us to escalate the HDR dose to the prostate without increasing undesirable side effects. © 2002 Elsevier Science Inc. Brachytherapy, Inverse planning, HDR, Prostate, Dosimetric study.

Background: The delayed rectifier potassium current, which comprises both a rapid (I Kr) and a slow (IKs) component, is a major outward current involved in repolarization of cardiac myocytes. IKr is the target of most drugs that prolong repolarization, whereas electrophysio logical effects resulting from combined block of IKr and IKs still need to be characterized. Methods and Results: Studies in isolated, buffer-perfused guinea pig hearts were under taken to compare lengthening of cardiac repolarization under conditions of IKr block alone, I Ks block alone, or combined block of IKr and IKs. In protocol A, isolated perfusion with N-acetylprocainamide (NAPA) (I Kr block), indapamide (IKs block), or combined NAPA/ indapamide was performed at a pacing cycle length of 250 msec. Increases in monophasic action potential duration measured at 90% polarization (MAPD90) from baseline after per fusion with NAPA 100 μmol/L (IC50 for block of IKr) was 19 ± 6 msec (P < .05), after indap amide 100 μmol/L (EC50 for block of IKs) 13 ± 2 msec (P < .05), but 42 ± 5 msec after combined NAPA 100 μmol/L and indapamide 100 μmol/L (P < .05 vs. baseline and isolated administrations), suggesting the possibility of excessive lengthening of cardiac repolariza tion by blocking both IKr and IKs. As well, in protocol B where sequential perfusions with dofetilide (IKr blocker), dofetilide/indapamide, and indapamide in the same hearts were used, combined dofetilide/indapamide infusion showed a greater increase in MAPD90 dur ing all pacing cycles studied (250 to 150 msec). Conclusions: Combined IKr and IKs block may lead to excessive lengthening of cardiac repo larization. This may predispose patients to proarrhythmia during coadministration of drugs.