Liquid chromatography tandem mass spectrometry with triple stage fragmentation for highly selective analysis and pharmacokinetics of alarelin in rat plasma.

Alarelin, a gonadotropin-releasing hormone analogue, is widely used in China for the treatment of endometriosis and uterine leiomyoma. In order to investigate its pharmacokinetic behavior and support the preclinical application of new formulations, we have developed a novel and highly selective bioanalytical method to determine alarelin in rat plasma based on liquid chromatography tandem mass spectrometry with triple stage fragmentation. After sample preparation by protein precipitation followed by reversed phase solid phase extraction, alarelin and triptorelin (internal standard) were chromatographed on an Ascentis® Express C18 column (50 mm × 4.6 mm, 2.7 µm) using gradient elution with 0.1% formic acid in water and acetonitrile at a flow rate of 1 mL/min. Detection was by positive mode electrospray ionization followed by triple stage fragmentation using the transitions at m/z 584.6→249.1→221.0 for alarelin and 656.5→249.1→176.0 for triptorelin, The assay was linear in the concentration range 0.3-10 ng/mL with excellent precision and accuracy. It was successfully applied to a pharmacokinetic study in rats administered a dose of 13.5 µg/kg alarelin by intramuscular injection. The results show that the triple stage fragmentation strategy allows highly selective analysis of alarelin and has the potential to be widely applied to the bioassay of other peptidic drugs.

Micro-solid phase extraction and LC-MS3 for the determination of triptorelin in rat plasma and application to a pharmacokinetic study.

Triptorelin is a synthetic decapeptide used for the treatment of prostate cancer. Attempts to determine triptorelin in clinical use by liquid chromatography-tandem mass spectrometry with multiple reaction monitoring have encountered problems due to its low concentration in plasma (pg/mL) and interference from endogenous peptides. We have overcome these issues using micro-solid phase extraction (µ-SPE) on Oasis® HLB 96-well µElution plates followed by LC-MS3. Sample preparation by µ-SPE achieved sample concentration without the need for evaporation and reconstitution steps. Detection by LC-MS3 showed no significant matrix interference at the retention time of analyte and achieved high sensitivity (lower limit of quantitation 10 pg/mL) and good linearity in the range 10-3000 pg/mL. The method was successfully applied to a pharmacokinetic study in rat involving a single intramuscular injection of a formulation of triptorelin acetate biodegradable microspheres.

Investigation of adhesive interactions in the specific targeting of Triptorelin-conjugated PEG-coated magnetite nanoparticles to breast cancer cells.

The understanding of adhesive interaction at the nanoscale between functionalized nanoparticles and biological cells is of great importance to develop effective theranostic nanocarriers for targeted cancer therapy. Here, we report a combination of experimental and computational approaches to evaluate the adhesion between Triptorelin (a Luteinizing Hormone-Releasing Hormone (LHRH) agonist)-conjugated poly-(ethylene glycol) (PEG)-coated magnetite nanoparticles (Triptorelin-MNPs) and breast cells. The adhesion forces between Triptorelin-MNPs and normal/cancerous breast cells are obtained using atomic force microscopy. The corresponding work of adhesion is then estimated using Johnson-Kendall-Roberts model. Our results demonstrate that Triptorelin-MNPs have a fourteen-fold greater work of adhesion to breast cancer cells than to normal breast cells. In addition, the work of adhesion between Triptorelin-MNPs and breast cancer cells is found to be three times more than that between unmodified MNPs and breast cancer cells. Hence, the experimental observation indicates that Triptorelin ligands facilitate the specific targeting of breast cancer cells. Furthermore, molecular dynamics simulations are performed to investigate the molecular origins of the adhesive interactions. The simulations reveal that the interactions between molecules (e.g. Triptorelin and PEG) and LHRH receptors are dominated by van der Waals energies, while the interactions of these molecules with cell membrane are dominated by electrostatic interactions. Moreover, both experimental and computational results reveal that PEG serves as an effective coating that enhances adhesive interactions to breast cancer cells that over-express LHRH receptors, while reduces the adhesion to normal breast cells. Our results highlight the potential to develop Triptorelin-MNPs into tumor-specific MRI contrast agents and drug carriers. STATEMENT OF SIGNIFICANCE: Systematic investigation of adhesive interactions between functionalized nanoparticles and cancer cells is of great importance in developing effective theranostic nanocarriers for targeted cancer therapy. Herein, we use a combination of atomic force microscopy technique and molecular dynamics simulations approach to explore the adhesive interactions at the nanoscale between Triptorelin-conjugated polyethylene glycol (PEG)-coated magnetite nanoparticles and normal/cancerous breast cells. This study characterizes and quantifies the work of adhesion, as well as adhesion forces, at the nanocarrier/cell interfaces, unravels the molecular origins of adhesive interactions and highlights the effectiveness of PEG coatings and Triptorelin ligands in the specific targeting of breast cancer cells. Our findings expand the fundamental understanding of nanoparticle/cell adhesion and provide guidelines for the design of more rational nanocarriers.

Meta-Analysis of Paediatric Patients with Central Precocious Puberty Treated with Intramuscular Triptorelin 11.25 mg 3-Month Prolonged-Release Formulation
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BACKGROUND/AIMS: A meta-analysis was undertaken to assess the effect of triptorelin 11.25 mg 3-month prolonged-release formulation in central precocious puberty (CPP). METHODS: All available clinical studies with triptorelin 11.25 mg were included. The primary outcome was the proportion of children with suppressed luteinising hormone (LH) response (peak LH ≤3 IU/L) to the gonadotrophin-releasing hormone (GnRH) test 3 months after triptorelin 11.25 mg injection. Secondary outcomes included: the proportion with suppressed peak LH response at 6 months and the proportion with suppressed peak follicle-stimulating hormone (FSH) response (≤3 IU/L), suppressed oestradiol (≤20 pmol/L) in girls or suppressed testosterone (≤30 ng/dL) in boys at 3 months. RESULTS: 153 children (13 boys, 140 girls) were included. The proportion with a suppressed peak LH response to the GnRH test was 87.6% (95% CI: 81.3-92.4, p < 0.0001, for a proportion >70%) and 92.8% (95% CI: 87.5-96.4, p < 0.0001, for a proportion >70%) at 3 and 6 months, respectively. FSH peak, oestradiol, and testosterone were suppressed in 86.7% (95% CI: 79.1-92.4), 97.1% (95% CI: 91.6-99.4), and 72.7% (95% CI: 39.0-94.0) of children at 3 months, respectively. CONCLUSION: Triptorelin 11.25 mg 3-month formulation is efficacious in suppressing LH peak and other gonadal hormones and in slowing the progression of CPP in children.
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Development of a (68)Ga-peptide tracer for PET GnRH1-imaging.

OBJECTIVE: Total synthesis, quality control and preclinical evaluation of [(68)Ga]-DOTA-triptorelin ([(68)Ga]-DOTA-TRP) is reported as a possible PET radiotracer for GnRH receptor imaging. METHODS: DOTA-TRP was totally synthesized in two steps and after characterization went through radiolabelling optimization studies followed by tracer stability. The biodistribution of the tracer in normal male rats and 4T1 tumour-bearing mice was performed in 120 min after i.v. injection. RESULTS: The peptide and the conjugates were synthesized with >95 % chemical purity. [(68)Ga]-DOTA-TRP complex was prepared in high radiochemical purity (>99 %, ITLC, HPLC) and specific activity of 1400-2100 MBq/nM at 95 °C using 40-60 µg of the peptide in 5-7 min followed by solid phase purification. The IC50 [nM] DOTA-TRP was comparable to the intact peptide, 0.11 ± 0.01 and 0.22 ± 0.05, respectively. The biodistribution of the tracer demonstrated kidney, stomach, and testes significant uptake, all in accordance with GnRH receptor ligands. Significant tumour uptake was observed in 4T1 tumour-bearing female mice 30-120 min post-injection with tumour:blood and tumour:muscle ratios of 28 and >50 in 60 min, respectively. Kidney is rapidly washed from the tracer. [(68)Ga]-DOTA-TRP can be proposed as a possible tracer for GnRH-R imaging studies.

Determination of a deuterohemin-peptide conjugate in rat plasma by liquid chromatography-tandem mass spectrometry and application to a preclinical pharmacokinetic study.

The deuterohemin-peptide conjugate (DhHP-6) is a microperoxidase mimetic, which has demonstrated substantial benefits in vivo as a scavenger of reactive oxygen species. This paper reports the development of a sensitive and rapid liquid chromatography tandem mass spectrometry (LC-MS/MS) method for the determination of DhHP-6 in rat plasma using triptorelin as an internal standard (IS). 50µL plasma was used in sample preparation, and a simple protein precipitation procedure with acetonitrile was involved. Satisfactory peak shapes of analyte and IS were obtained on an Agilent HC-C18 column by using a gradient elution with 10mM ammonium acetate-0.5% formic acid (v:v) and acetonitrile, there was no significant interference impacting the determination. A calibration curve obtained from this method was linear within the concentration range 10-3000ng/mL with intra- and inter-day precisions of 4.2-6.8% and 3.2-8.9%, respectively and accuracy of -1.3% to 2.1%. The recovery was above 80% with low matrix effects. The method was successfully applied to support a preclinical pharmacokinetic study in rat.

Triptorelin for the treatment of endometriosis.

INTRODUCTION: Over the past 30 years, gonadotropin-releasing hormone agonists (GnRH-a) have been used to induce a hypoestrogenic status in women with endometriosis with the aim to cause an improvement in pain symptoms similar to that observed after menopause. Triptorelin is one of the most commonly used GnRH-a. AREAS COVERED: This review offers an explanation of the mechanism of action, of the pharmacokinetics and pharmacodynamics of triptorelin and gives the readers a complete overview of the studies on the clinical efficacy, tolerability and safety of this agent in patients with endometriosis. EXPERT OPINION: The studies reviewed in the current manuscript demonstrate the efficacy of triptorelin in improving pain symptoms caused by endometriosis. Further, this effect is confirmed by the reduction in the volume of the endometriotic nodules during treatment. Future research should evaluate whether the pre-operative administration of triptorelin prior to surgical excision of endometriomas may be useful in preserving the ovarian reserve.

An analytical strategy to characterize the pharmacokinetics and pharmacodynamics of triptorelin in rats based on simultaneous LC-MS/MS analysis of triptorelin and endogenous testosterone in rat plasma.

Triptorelin, a gonadotropin-releasing hormone agonist, has been used in the treatment of hormone-responsive prostate cancer by inducing testosterone suppression. Research on the relationship between the time courses of triptorelin and testosterone is very important, but accurate quantification of triptorelin and testosterone simultaneously in biological specimens is a challenging analytical problem. In the present study, a rapid, sensitive, and selective method for simultaneous determination of triptorelin and testosterone in rat plasma by solid-phase extraction and liquid chromatography-tandem mass spectrometry was developed using a ZORBAX RRHD Eclipse Plus C8 column (2.1 × 50 mm, 1.8 µm) with a 0.05% propionic acid/methanol gradient. In view of the polarity difference between the two analytes, two internal standards, i.e., leuprolide and testosterone-(13)C3, were used for individual quantitation of triptorelin and testosterone. Endogenous testosterone was determined by reference to a calibration curve prepared using testosterone-D3 as a surrogate analyte. The method exhibits excellent linearity over three orders of magnitude for each analyte. The lower limit of quantification was 0.01 ng/mL for triptorelin and 0.05 ng/mL for testosterone, with consumption of 100 µL of plasma. The method was successfully applied to characterize the pharmacokinetics and pharmacodynamics of slow-release 28-day form triptorelin acetate biodegradable microspheres in rats after intramuscular injections of three consecutive doses of 0.6 mg/kg per 28 days. The results revealed that the pharmacokinetic profile of triptorelin produced an initial flare-up in testosterone levels, rapid castration within 5 days after injection, and long-term castration until the next dose.

In vivo biocompatibility, sustained-release and stability of triptorelin formulations based on a liquid, degradable polymer.

Hexylsubstituted poly(lactic acid) (hexPLA) is a viscous polymer, which degrades in the presence of water similar to the structure related poly(lactic acid). With hydrophilic active compounds, like Triptorelin acetate, the lipophilic polymer was formulated in form of parenterally injectable suspensions. This first in vivo study toward the biocompatibility of hexPLA implants in rats over 3 months in comparison to in situ forming poly(lactic-co-glycolic acid) (PLGA) formulations is presented here. The hexPLA implants showed only a mild acute inflammation at the injection site after application, which continuously regressed. In contrast to the PLGA formulations, hexPLA did not provoke an encapsulation of the implant with extracellular matrix. Prior to the formulation application, the stability of Triptorelin inside the hexPLA matrix was assessed under different storage conditions and in the presence of buffer to simulate a peptide degrading environment. At 5°C Triptorelin showed a stability of 98% inside the polymer for at least 6 months. The stability was still 78% at an elevated temperature of 40°C. HexPLA protected the incorporated peptide from the surrounding aqueous environment, which resulted in 20% less degradation inside the polymer compared to the solution. This protection effect supports the use of Triptorelin-hexPLA formulations for parenteral sustained-release formulations. In a second in vivo evaluation in Wistar Hannover rats, formulations containing 5% and 10% Triptorelin in the polymeric matrix released the active compound continuously for 6 months. The formulations showed a higher release during the initial 7 days, which is necessary for the clinical use to down-regulate all GnRH-receptors. Afterwards, a zero order drug release was observed over the first 3 months. After 3 months, the plasma levels decreased slowly but remained at effective concentrations for the total of 6 months. Furthermore, a qualitative in vitro-in vivo correlation was observed, possibly facilitating future optimization of the Triptorelin-hexPLA sustained-release formulations.

Pharmacokinetic/pharmacodynamic model of the testosterone effects of triptorelin administered in sustained release formulations in patients with prostate cancer.

The objectives of the current work were to develop a predictive population pharmacokinetic (PK)/pharmacodynamic (PD) model for the testosterone (TST) effects of triptorelin (TRP) administered in sustained-release (SR) formulations to patients with prostate cancer and determine the minimal required triptorelin serum concentration (C(TRP_min)) to keep the testosterone levels of the patients below or equal to the level of castration (TST ≤ 0.5 ng/ml). A total of eight healthy male volunteers and 74 patients with prostate cancer received one or two doses of triptorelin injected subcutaneously or intramuscularly. Five different triptorelin formulations were tested. Pharmacokinetic (serum concentration of triptorelin) and pharmacodynamic (TST levels in serum) data were analyzed by using the population approach with NONMEM software (http://www.iconplc.com/technology/products/nonmem/). The PK/PD model was constructed by assembling the agonist nature of triptorelin with the competitive reversible receptor binding interaction with the endogenous agonist, a process responsible for the initial and transient TST flare-up, and triggering down-regulation mechanisms described as a decrease in receptor synthesis. The typical population values of K(D), the receptor equilibrium dissociation constant of triptorelin, and C(TRP_min) to keep 95% of the patients castrated were 0.931 and 0.0609 ng/ml, respectively. The semimechanistic nature of the model renders the predictions of the effect of triptorelin on TST possible regardless the type of SR formulation administered, while exploring different designs during the development of new delivery systems.

Quantitation of slow release triptorelin in beagle dog plasma by liquid chromatography-tandem mass spectrometry.

A sensitive method based on liquid chromatography-tandem mass spectrometry has been developed for the determination of triptorelin levels in beagle dog plasma. Plasma samples were applied to Oasis(®) HLB solid-phase extraction (SPE) cartridges. Extracted samples were evaporated under a stream of nitrogen and then reconstituted with 100 µl methanol:water:formic acid (60:40:0.08, v/v/v). The separation was achieved on a Venusil MP-C18 column (2.1 mm × 50 mm, 3 µm, Agela) with a gradient elution. Detection utilized a Qtrap5500 system operated in the positive ion mode with multiple reaction monitoring of the analyte at m/z 656.5→249.1 and of the I.S. at m/z 510.8→120.1. The proposed method was validated by assessing the specificity, linearity, precision and accuracy, recovery, matrix effects, and stability. Linear calibration curves were obtained in the concentration range of 0.01-10 ng/ml (the correlation coefficients were above 0.995). The lower limit of quantification (LLOQ) of the method was 0.01 ng/ml. The method was successfully applied to a pharmacokinetic study of a slow release triptorelin formulation in beagle dogs following a single intramuscular injection.

Formulation and evaluation of an in situ gel forming system for controlled delivery of triptorelin acetate.

The novel physical hydrogels composed of chitosan or its water soluble derivatives such as carboxymethyl chitosan (CMCh) and sodium carboxymethyl chitosan (NaCMCh) and opened ring polyvinyl pyrrolidone (OP-PVP) were used as a controlled delivery system for triptorelin acetate, a luteinizing-releasing hormone agonist. The in situ gel forming system designed according to physical interactions such as chains entanglements and hydrophilic attractions especially h-bonds of chitosan and/or NaCMCh and OR-PVP. In order to increase in situ gel forming rate the chitosan microspheres prepared through spray drying technique. The chitosan or NaCMCh/OR-PVP blends prepared at different ratios (0.05, 0.10, 0.12, 0.16, 0.20 and 0.24) and suspended in sesame oil as non-aqueous vehicle at different solid content (10-30%). The suitable ratio of polymers with faster in situ gel forming rate was selected for in vivo studies. The gel formation and drug release from the system was evaluated both in vitro and in vivo. In vitro and in vivo results were compared with Diphereline SR 3.75mg, a commercially available controlled delivery system of triptorelin. In vitro release studies showed a sustained release profile for about 192h with first order kinetics. In vivo studies on male rats by determination of serum testosterone were confirmed the acceptable performance of in situ gel forming system compared with Diphereline SR in decreasing the serum testosterone level for 35days, demonstrating the potential of the novel in situ gel forming system for controlled delivery of peptides.

Triptorelin embonate (6-month formulation).

A 6-month formulation of the gonadotropin-releasing hormone agonist triptorelin embonate (designed to deliver 22.5 mg of triptorelin over a 6-month period) has been developed for use in the treatment of advanced prostate cancer. Following intramuscular administration of the 6-month formulation of triptorelin embonate 22.5 mg to men with advanced prostate cancer (subset of 15 patients from the pivotal clinical trial), serum testosterone levels initially increased, followed by a rapid, sustained decrease. Castrate serum testosterone levels (i.e. < or =1.735 nmol/L) were achieved in a geometric mean time of 18.8 days. The 6-month formulation of triptorelin embonate achieved and maintained castrate serum testosterone levels in patients with advanced prostate cancer (n = 120), according to the results of the pivotal, noncomparative, multicentre trial (patients received intramuscular triptorelin embonate 22.5 mg on day 1 and at month 6 [week 24]). By day 29, 97.5% of patients had castrate serum testosterone levels. Castrate serum testosterone levels were maintained from months 2 to 12 in 93.0% of patients. Prior to the second injection at month 6, 98.3% of patients had castrate serum testosterone levels, and 98.3% of patients had castrate serum testosterone levels at study completion. The 6-month formulation of triptorelin embonate 22.5 mg was generally well tolerated in patients with advanced prostate cancer; adverse events were of mild severity in the majority of patients. Drug-related adverse events (e.g. hot flushes) were consistent with the pharmacological action of triptorelin. Injection-site reactions occurred in 6.7% of triptorelin embonate recipients.

Triptorelin 6-month formulation in the management of patients with locally advanced and metastatic prostate cancer: an open-label, non-comparative, multicentre, phase III study.

BACKGROUND AND OBJECTIVES: Triptorelin 6-month formulation was developed to offer greater convenience to both patients and physicians by reducing the injection frequency. The efficacy, pharmacokinetics and safety of a new 6-month formulation of triptorelin were investigated over 12 months (48 weeks). The primary objective was to evaluate the formulation in achieving castrate serum testosterone levels (< or = 1.735 nmol/L or < or = 50 ng/dL) on day 29 and in maintaining castration at months 2-12. Absence of luteinizing hormone (LH) stimulation and change in prostate-specific antigen (PSA) level were also assessed. METHODS: An open-label, non-comparative, phase III study in 120 patients with advanced prostate cancer was conducted from July 2006 to August 2007 in private and public institutions in South Africa. Each patient received two consecutive intramuscular injections of triptorelin embonate (pamoate) 22.5 mg at an interval of 24 weeks. In all patients, testosterone (primary outcome measurement) was measured at baseline and then every 4 weeks; LH was measured before and 2 hours after the two injections. PSA was measured on day 1 and at weeks 12, 24, 36 and 48. Adverse events were recorded at each visit. RESULTS: In the intent-to-treat population, 97.5% (95% CI 92.9, 99.5) of patients achieved castrate serum testosterone levels by day 29, and 93.0% (95% CI 86.8, 97.0) maintained castration at months 2-12. After the second injection, 98.3% of patients showed absence of LH stimulation. The most frequent drug-related adverse events were hot flushes (71.7% of patients). No patient withdrew from the study as a result of an adverse event. CONCLUSIONS: The triptorelin 6-month formulation was well tolerated and was able to achieve and maintain castration for the treatment of locally advanced and metastatic prostate cancer. By reducing the frequency of required injections, this new formulation offers a more convenient treatment regimen. (Clinical Trial Registration,NCT00751790 at www.clinicaltrials.gov).

Development of novel 68Ga- and 18F-labeled GnRH-I analogues with high GnRHR-targeting efficiency.

A large majority of tumors of the reproductive system express the gonadotropin releasing hormone receptor (GnRHR). Blockade and activation of this receptor with various antagonistic and agonistic analogues of native GnRH-I (pGlu(1)-His(2)-Trp(3)-Ser(4)-Tyr(5)-Gly (6)-Leu(7)-Arg(8)-Pro(9)-Gly(10)-NH2), respectively, has shown efficient suppression of tumor growth. In this study, the GnRH-receptor system has been evaluated with respect to its suitability as a target for in vivo peptide receptor targeting using radiolabeled GnRH-analogues, and in parallel, new (18)F- and (68Ga)-labeled GnRH analogues have been developed. In vitro radioligand binding assays performed with various GnRHR-expressing human cell lines using [(125)I]Triptorelin (D-Trp(6)-GnRH-I) as the standard radioligand revealed a very low level of GnRH receptor expression on the cell surface. Generally, total cellular activity was very low (approximately 3% of the applied activity), and only a small fraction (max. 40%) of cell-associated activity could be attributed to receptor-specific radioligand binding/internalization. However, substitution of fetal calf serum by NU serum in the culture medium led to increased and stable GnRHR-expression, especially in the ovarian cancer cell line EFO-27, thus allowing for a stable experimental setup for the evaluation of the new radiolabeled GnRH-I analogues. The new radiolabeled GnRH-I analogues developed in this study were all based on the D-Lys(6)-GnRH-I-scaffold. For (68)Ga-labeling, the latter was coupled with DOTA at D-Lys(6). To allow (18)F-labeling via chemoselective oxime formation, D-Lys(6)-GnRH-I was also conjugated with Ahx (aminohexanoic acid) or beta-Ala, which in turn was coupled with Boc-aminooxyacetic acid. (18)F-labeling via oxime formation with 4-[(18)F]fluorobenzaldehyde was performed using the Boc-protected precursors. Receptor affinities of [(68)Ga]DOTA-GnRH-I, D-Lys(6)-Ahx([(18)F]FBOA)-GnRH-I, and D-Lys(6)-betaAla([(18)F]FBOA)-GnRH-I (FBOA = fluorobenzyloxime acetyl) were determined using GnRHR-membrane preparations, and internalization efficiency of the new radioligands was determined in EFO-27 cells. Both quantities were highest for D-Lys(6)-Ahx([(18)F]FBOA)-GnRH-I (IC 50 = 0.50 +/- 0.08 nM vs 0.13 +/- 0.08 nM for Triptorelin; internalization: 86 +/- 16% of the internal reference [(125)I]Triptorelin), already substantially reduced in the case of the -betaAla([(18)F]FBOA)-derivative (IC 50 = 0.86 +/- 0.13 nM; internalization: 42 +/- 3% of [(125)I]Triptorelin), while the [(68)Ga]DOTA-analogue showed almost complete loss of binding affinity and ligand internalization (IC50 = 13.3 +/- 1.0 nM; internalization: 2.6 +/- 1.0% of [(125)I]Triptorelin). Generally, the lipophilic residue [(18)F]FBOA is much better tolerated as a modification of the D-Lys(6)-side chain, with receptor affinity of the respective analogues strongly depending upon spacer length between the D-Lys(6)-side chain and the [(18)F]FBOA-moiety. In summary, D-Lys(6)(Ahx-[(18)F]FBOA)-GnRH-I shows the highest potential for efficient GnRHR-targeting in vivo of the compounds investigated. Unfortunately, however, the very low cell surface expression of GnRH-receptors and thus very low radioligand uptake by GnRHR-positive tumor cells found in vitro was also confirmed by a preliminary biodistribution study in OVCAR-3 xenografted nude mice using the standard GnRHR radioligand [(125)I]Triptorelin. Tumor uptake was lower than blood activity concentration at 1 h p.i. (0.49 +/- 0.05 vs 0.96 +/- 0.13 for tumor and blood, respectively). These data seriously challenge the suitability of the GnRHR-system as a suitable target for in vivo peptide receptor imaging using radiolabeled GnRH-I derivatives, despite the availability of high-affinity radiolabeled receptor-ligands such as D-Lys(6)(Ahx-[(18)F]FBOA)-GnRH-I.

Population pharmacokinetic/pharmacodynamic (PK/PD) modelling of the hypothalamic-pituitary-gonadal axis following treatment with GnRH analogues.

AIMS: To develop a population pharmacokinetic/pharmacodynamic (PK/PD) model of the hypothalamic-pituitary-gonadal (HPG) axis describing the changes in luteinizing hormone (LH) and testosterone concentrations following treatment with the gonadotropin-releasing hormone (GnRH) agonist triptorelin and the GnRH receptor blocker degarelix. METHODS: Fifty-eight healthy subjects received single subcutaneous or intramuscular injections of 3.75 mg of triptorelin and 170 prostate cancer patients received multiple subcutaneous doses of degarelix of between 120 and 320 mg. All subjects were pooled for the population PK/PD data analysis. A systematic population PK/PD model-building framework using stochastic differential equations was applied to the data to identify nonlinear dynamic dependencies and to deconvolve the functional feedback interactions of the HPG axis. RESULTS: In our final PK/PD model of the HPG axis, the half-life of LH was estimated to be 1.3 h and that of testosterone 7.69 h, which corresponds well with literature values. The estimated potency of LH with respect to testosterone secretion was 5.18 IU l(-1), with a maximal stimulation of 77.5 times basal testosterone production. The estimated maximal triptorelin stimulation of the basal LH pool release was 1330 times above basal concentrations, with a potency of 0.047 ng ml(-1). The LH pool release was decreased by a maximum of 94.2% by degarelix with an estimated potency of 1.49 ng ml(-1). CONCLUSIONS: Our model of the HPG axis was able to account for the different dynamic responses observed after administration of both GnRH agonists and GnRH receptor blockers, suggesting that the model adequately characterizes the underlying physiology of the endocrine system.

Endocrine, morphological, and cytological effects of a depot GnRH agonist in bovine.

The present study was conducted to assess effects of the gonadotropin-releasing hormone agonist (GnRHa) triptorelin in dairy heifers. The peptide was released from a commercial 4-week depot formulation (Decapeptyl Depot) administered at animals' estrus (day 0). First experiment (EXP I, n=5), which was aimed to explore the availability of peptide, detected a maximum of triptorelin concentration between day 2 and 5 after depot injection, and the peptide remained detectable by RIA in peripheral blood for about 3 weeks. In further experiments, the peptide release was terminated on day 9 (EXP II, n=16) or day 21 (EXP III, n=47). Treatment effects were studied on follicular development, the characteristics of cumulus-oocyte complexes (COCs) (EXP II; EXP IIIa) and secretions of LH and progesterone (EXP IIIb). Results showed that the occurrence of the pre-ovulatory LH surge was more uniform in treated heifers than that in controls. The duration of ovulation periods was similar amongst the heifers of EXP II, but more compact amongst those of EXP III each compared with the respective controls. Post-ovulatory, the number of LH pulses was significantly reduced by treatment, whereas both basal LH and progesterone concentrations were elevated on a few days. Follicular growth was reduced only by the prolonged influence of the GnRHa. There were increased proportions of both degenerated COCs and immature oocytes from small follicles (<3mm in diameter), and meiotic configuration and quality of oocytes isolated from follicles 3-5mm were changed after the prolonged, 21-day treatment. These results indicate that a continuous influence of a GnRHa over more than 1 week may increasingly impair the development of bovine follicles and oocytes. This may have some significance for the development of novel GnRH-based techniques in regulating the reproductive function in cattle.

[Pharmacokinetics and pharmacodynamics of triptorelin]. / Pharmacocinétique et pharmacodynamique de la triptoréline.

GnRH agonists are derived from the native molecule by substitution of a D-amino acid in position 6 which increases their resistance to enzymatic breakdown and their affinity for LH-RH receptors in comparison with the native hormone. Because of this improved resistance which increases their half-life they have a super-agonistic effect. In 1973, two years only after he characterized LH-RH, A.V. Schally synthesized several GnRH analogs, including D-TRP6-LHRH obtained by substituting the glycine-6 with a D-tryptophan. The biological half life of this agonist injected by the subcutaneous route is 10 times greater than that observed after intravenous injection because of the progressive release of the peptide from the injection site. Pharmaceutical research has led to the development of delayed-release formulations allowing doses to be spaced by intervals of several weeks, or even three months when needed in some indications (Decapeptyl slow release). Triptorelin, as the other GnRH agonists, strongly reduces LH secretion, by preventing the production of the LH-beta subunit. On the opposite, the production of LH-alpha subunit is markedly increased and remains responsive to exogenous GnRH injection, demonstrating that the agonist does not induce actual pituitary desensitization. Compared with LH-RH antagonists which inhibit both LH-alpha and LH-beta subunit secretion, agonists offer the advantage of a sustained efficacy even after one or two days of withdrawal, while the effect of the agonist disappeared as soon as the administration is stopped. On the other hand, GnRH antagonists do not induce the initial hyperstimulation of the gonadotrophs, the so-called flare up, characteristic of the superagonistic effect.

[Treatment of precocious puberty by GnRH agonists]. / Le traitement des pubertés précoces par agonistes de la GnRH.

The objective of GnRH agonist treatment in precocious puberty is to block pubertal development, and to reduce the action of sex steroids on bone maturation in order to restore normal long-term growth of the skeleton. Currently available studies show a positive benefit-risk ratio of GnRH analogs in the treatment of precocious puberty. Adult heights obtained are in average greater than those predicted in the absence of treatment and close to the normal target height. The side effects observed during treatment such as headaches, asthenia or hot flushes, are related to sex steroid deprivation and are observed in 20 to 30% of cases. Questions remain concerning the impact of these treatments on intellectual development and body composition. Finally, to assess the impact on fertility, IPSEN laboratories decided to organize a prospective study on patients treated in the 1980-1990s. In pediatrics, a reduction in the number of injections is an important objective to improve compliance. "Depot" formulations with prolonged release over three months, already used in adult indications, represent a useful progress in pediatrics and have recently been assessed. The efficacy and safety of triptorelin acetate (Decapeptyl) administered at a dose of 11.25 mg every trimester for one year were evaluated in a European multicentre open trial including 54 girls and 10 boys. The LH peak during the GnRH test at three months was used as primary end-point. This slow release triptorelin was shown to be effective, similarly to delayed-acting leuprorelin. The auxological effects, in particular on adult height, were not evaluated in this study.

Pharmacodynamic equivalence of a decapeptyl 3-month SR formulation with the 28-day SR formulation in patients with advanced prostate cancer.

AIMS: The objective of the study was to assess the pharmacodynamic equivalence of LHRH analogue triptorelin 3-month and 28-day SR formulations. METHODS: Patients with documented locally advanced or metastatic prostate cancer were randomized to receive one injection of the 3-month formulation (n = 63) or three injections at 28-day intervals of the 28-day formulation (n = 68). Group-chemical castration rates defined as the percentage of patients reaching a testosterone plasma level