Conformation of Pyroglutamated Amyloid ß (3-40) and (11-40) Fibrils - Extended or Hairpin?

Amyloid ß (Aß) is a hallmark protein of Alzheimer's disease. One physiologically important Aß variant is formed by initial N-terminal truncation at a glutamic acid position (either E3 or E11), which is subsequently cyclized to a pyroglutamate (either pE3 or pE11). Both forms have been found in high concentrations in the core of amyloid plaques and are likely of high importance in the pathology of Alzheimer's disease. However, the molecular structure of the fibrils of these variants is not entirely clear. Solid-state NMR spectroscopy studies have reported a molecular contact between Gly25 and Ile31, which would disagree with the conventional hairpin model of wildtype (WT-)Aß1-40 fibrils, most often described in the literature. We investigated the conformation of the monomeric unit of pE3-Aß3-40 and pE11-Aß11-40 (and for comparison also wildtype (WT)-Aß1-40) fibrils to find out whether the hairpin or a newly suggested extended structure dominates the structure of the Aß monomers in these fibrils. To this end, solid-state NMR spectroscopy was applied probing the inter-residual contacts between Phe19/Leu34, Ala21/Leu34, and especially Gly25/Ile31 using suitable isotopic labeling schemes. In the second part, the flexible turn of the Aß40 peptides was replaced by a (3-(3-aminomethyl)phenylazo)phenylacetic acid (AMPP)-based photoswitch, which can predefine the peptide conformation to either an extended (trans) or hairpin (cis) conformation. This enables simultaneous spectroscopic assessment of the conformation of the AMPP-photoswitch, allowing in situ structural investigations during fibrillation in contrast to structural techniques such as NMR spectroscopy or cryo-EM, which can only be applied to stable conformers. Both methods confirm an extended structure for the peptidic monomers in fibrils of all investigated Aß variants. Especially the Gly25/Ile31 contact is a decisive indicator for the extended structure along with the characteristic absorption spectra of trans-AMPP-Aß.

Peptide backbone modifications of amyloid ß (1-40) impact fibrillation behavior and neuronal toxicity.

Fibril formation of amyloid ß (Aß) peptides is one of the key molecular events connected to Alzheimer's disease. The pathway of formation and mechanism of action of Aß aggregates in biological systems is still object of very active research. To this end, systematic modifications of the Phe19-Leu34 hydrophobic contact, which has been reported in almost all structural studies of Aß40 fibrils, helps understanding Aß folding pathways and the underlying free energy landscape of the amyloid formation process. In our approach, a series of Aß40 peptide variants with two types of backbone modifications, namely incorporation of (i) a methylene or an ethylene spacer group and (ii) a N-methylation at the amide functional group, of the amino acids at positions 19 or 34 was applied. These mutations are expected to challenge the inter-ß-strand side chain contacts as well as intermolecular backbone ß-sheet hydrogen bridges. Using a multitude of biophysical methods, it is shown that these backbone modifications lead, in most of the cases, to alterations in the fibril formation kinetics, a higher local structural heterogeneity, and a somewhat modified fibril morphology without generally impairing the fibril formation capacity of the peptides. The toxicological profile found for the variants depend on the type and extent of the modification.

Probing the Influence of Single-Site Mutations in the Central Cross-ß Region of Amyloid ß (1-40) Peptides.

Amyloid ß (Aß) is a peptide known to form amyloid fibrils in the brain of patients suffering from Alzheimer's disease. A complete mechanistic understanding how Aß peptides form neurotoxic assemblies and how they kill neurons has not yet been achieved. Previous analysis of various Aß40 mutants could reveal the significant importance of the hydrophobic contact between the residues Phe19 and Leu34 for cell toxicity. For some mutations at Phe19, toxicity was completely abolished. In the current study, we assessed if perturbations introduced by mutations in the direct proximity of the Phe19/Leu34 contact would have similar relevance for the fibrillation kinetics, structure, dynamics and toxicity of the Aß assemblies. To this end, we rationally modified positions Phe20 or Gly33. A small library of Aß40 peptides with Phe20 mutated to Lys, Tyr or the non-proteinogenic cyclohexylalanine (Cha) or Gly33 mutated to Ala was synthesized. We used electron microscopy, circular dichroism, X-ray diffraction, solid-state NMR spectroscopy, ThT fluorescence and MTT cell toxicity assays to comprehensively investigate the physicochemical properties of the Aß fibrils formed by the modified peptides as well as toxicity to a neuronal cell line. Single mutations of either Phe20 or Gly33 led to relatively drastic alterations in the Aß fibrillation kinetics but left the global, as well as the local structure, of the fibrils largely unchanged. Furthermore, the introduced perturbations caused a severe decrease or loss of cell toxicity compared to wildtype Aß40. We suggest that perturbations at position Phe20 and Gly33 affect the fibrillation pathway of Aß40 and, thereby, influence the especially toxic oligomeric species manifesting so that the region around the Phe19/Leu34 hydrophobic contact provides a promising site for the design of small molecules interfering with the Aß fibrillation pathway.

Application of the Double-Mutant Cycle Strategy to Protein Aggregation Reveals Transient Interactions in Amyloid-ß Oligomers.

Transient oligomeric intermediates in the peptide or protein aggregation pathway are suspected to be the key toxic species in many amyloid diseases, but deciphering their molecular nature has remained a challenge. Here we show that the strategy of "double-mutant cycles", used effectively in probing protein-folding intermediates, can reveal transient interactions during protein aggregation. It does so by comparing the changes in thermodynamic parameters between the wild type, and single and double mutants. We demonstrate the strategy by probing the possible transient salt bridge partner of lysine 28 (K28) in the oligomeric states of amyloid ß-40 (Aß40), the putative toxic species in Alzheimer's disease. In mature fibrils, the binding partner is aspartate 23. This interaction differentiates Aß40 from the more toxic Aß42, where K28's binding partner is the C-terminal carboxylate. We selectively acetylated K28 and amidated the C-terminus of Aß40, creating four distinct variants. Spectroscopic measurements of the kinetics and thermodynamics of aggregation show that K28 and the C-terminus interact transiently in the early phases of the Aß40 aggregation pathway. Hydrogen-deuterium exchange mass spectrometry (using a simple analysis method that we introduce here that takes into account the isotopic mass distribution) supports this interpretation. It is also supported by cellular toxicity measurements, suggesting possible similarities in the mechanisms of toxicity of Aß40 oligomers (which are more toxic than Aß40 fibrils) and Aß42. Our results show that double-mutant cycles can be a powerful tool for probing transient interactions during protein aggregation.

Structural characteristics of oligomers formed by pyroglutamate-modified amyloid ß peptides studied by solid-state NMR.

Neuronal plaques of amyloid ß (Aß) peptides of varying length carrying different posttranslational modifications represent a molecular hallmark of Alzheimer's disease. It is believed that transient oligomeric Aß assemblies associating in early fibrillation events represent particularly cytotoxic peptide aggregates. Also, N-terminally truncated (in position 3 or 11) and pyroglutamate modified peptides exhibited an increased toxicity compared to the wildtype. In the current study, the molecular structure of oligomeric species of pGlu3-Aß(3-40) and pGlu11-Aß(11-40) was investigated using solid-state NMR spectroscopy. On the secondary structure level, for both modified peptides a large similarity between oligomers and mature fibrils of the modified peptides was found mainly based on 13C NMR chemical shift data. Some smaller structural differences were detected in the vicinity of the respective modification site. Also, the crucial early folding molecular contact between residues Phe19 and Leu34 could be observed for the oligomers of both modified peptide species. Therefore, it has to be concluded that the major secondary structure elements of Aß are already present in oligomers of pGlu3-Aß(3-40) and pGlu11-Aß(11-40). These posttranslationally modified peptides arrange in a similar fashion as observed for wild type Aß(1-40).

Incorporation of the Nonproteinogenic Amino Acid ß-Methylamino-alanine Affects Amyloid ß Fibril Properties and Toxicity.

The nonproteinogenic amino acid ß-methylamino alarelevant example for environmental hazards are nonnine (BMAA) is a neurotoxin and represents a potential risk factor for neurodegenerative diseases. Despite intense research over the last years, the pathological mechanism of BMAA is still unclear. One of the main open questions is whether BMAA can be misincorporated into proteins, especially as a substitute for serine, and whether this has structural and functional consequences for the afflicted proteins leading to early onset neurodegeneration. In this study, we hypothesize that BMAA was indeed incorporated into Aß40 molecules and study the structural and dynamical consequences of such misincorporation along with the effect such mutated Aß40 peptides have on neuronal cells. We used the synthetic ß-amyloid peptide (Aß40), a known key player in the development of Alzheimer's disease, to incorporate BMAA substitutions at three different positions in the peptide sequence: Ser8BMAA at the peptide's N-terminus, Phe19BMAA in the hydrophobic core region, and S26BMAA in the flexible turn region of Aß40 fibrils. We performed a set of biophysical experiments including fluorescence, circular dichroism, solid-state NMR spectroscopy, transmission electron microscopy, and X-ray diffraction to investigate structural and functional aspects of the mutated peptides compared to wildtype Aß40. All variants showed high structural tolerance to BMAA misincorporation. In contrast, the cellular response and neuronal survival were affected in a mutation site-specific manner. As a consequence, we can state from the physicochemical point of view that, if BMAA was misincorporated into proteins, it could indeed represent a risk factor that could potentially play a role in neurodegeneration. Further research addressing the role of BMAA, especially its protein-associated form, should be performed to obtain a better understanding of neurodegenerative diseases and to develop new therapeutic strategies.

Ring structure modifications of phenylalanine 19 increase fibrillation kinetics and reduce toxicity of amyloid ß (1-40).

We investigated the influence of the chemical structure of the phenylalanine side chain in position 19 of the 40 residue amyloid ß peptide. Side chain modifications in this position yielded fibrils of essentially unaltered morphology, structure, and dynamics, but significantly increased fibrillation kinetics and diminished the toxicity of the peptides.

Amyloid ß (1-40) Toxicity Depends on the Molecular Contact between Phenylalanine 19 and Leucine 34.

The formation of the hydrophobic contact between phenylalanine 19 (F19) and leucine 34 (L34) of amyloid ß (1-40) (Aß(1-40)) is known to be an important step in the fibrillation of Aß(1-40) peptides. Mutations of this putatively early molecular contact were shown to strongly influence the toxicity of Aß(1-40) ( Das et al. ( 2015 ) ACS Chem. Neurosci. 6 , 1290 - 1295 ). Any mutation of residue F19 completely abolished the toxicity of Aß(1-40), suggesting that a proper F19-L34 contact is crucial also for the formation of transient oligomers. In this work, we investigate a series of isomeric substitutions of L34, namely, d-leucine, isoleucine, and valine, to study further details of this molecular contact. These replacements represent very minor alterations in the Aß(1-40) structure posing the question how these alterations challenge the fibrillation kinetics, structure, dynamics, and toxicity of the Aß(1-40) aggregates. Our work involves kinetic studies using thioflavin T, transmission electron microscopy, X-ray diffraction for the analysis of the fibril morphology, and nuclear magnetic resonance experiments for local structure and molecular dynamics investigations. Combined with cell toxicity assays of the mutated Aß(1-40) peptides, the physicochemical and biological importance of the early folding contact between F19 and L34 in Aß(1-40) is underlined. This implies that the F19-L34 contact influences a broad range of different processes including the initiation of fibrillation, oligomer stability, fibril elongation, local fibril structure, and dynamics and cellular toxicity. These processes do not only cover a broad range of diverse mechanisms, but also proved to be highly sensitive to minor modulations of this crucial contact. Furthermore, our work shows that the contact is not simply mediated by general hydrophobic interactions, but also depends on stereospecific mechanisms.

Pyroglutamate-Modified Amyloid ß (11- 40) Fibrils Are More Toxic than Wildtype Fibrils but Structurally Very Similar.

The morphology, structure, and dynamics of mature amyloid ß (Aß) fibrils formed by the Aß variant, which is truncated at residue 11 and chemically modified by enzymatic pyroglutamate formation (pGlu11 -Aß(11-40)), was studied along with the investigation of the toxicity of these Aß variants to neurons and astrocytes. The fibrils of pGlu11 -Aß (11-40) were more toxic than wildtype Aß (1-40) and the longer pGlu3-Aß (3-40) especially at higher concentration, whereas the overall morphology was quite similar. The secondary structure of pGlu11 -Aß (11-40) fibrils shows the typical two ß-strands connected by a short turn as known for mature fibrils of Aß (1-40) and also pGlu3 -Aß (3-40). Further insights into tertiary contacts exhibit some similarities of pGlu11 -Aß (11-40) fibrils with wildtype Aß (1-40), but also a so far not described contact between Gly25 and Ile31 . This highlights the biological importance of chemical modifications on the molecular structure of Aß.

Stereoisomers Probe Steric Zippers in Amyloid-ß.

Shape complementarity between close-packed residues plays a critical role in the amyloid aggregation process. Here, we probe such "steric zipper" interactions in amyloid-ß (Aß40), whose aggregation is linked to Alzheimer's disease, by replacing natural residues by their stereoisomers. Such mutations are expected to specifically destabilize the shape sensitive "packing" interactions, which may potentially increase their solubility and change other properties. We study the stereomutants DF19 and DL34 and also the DA2/DF4/DH6/DS8 mutant of Aß40. F19-L34 is a critical contact in a tightly packed region of Aß, while residues 1-9 are known to be disordered. While both DF19 and DL34 slow down the kinetics of aggregation and form amyloid fibrils efficiently, only DL34 increases the final solubility. DF19 gives rise to additional off-pathway aggregation which results in large, kinetically stable aggregates, and has lower net solubility. DA2/DF4/DH6/DS8 does not have an effect on the kinetics or the solubility. Notably, both DF19 and DL34 oligomers have a significantly lower level of interactions with lipid vesicles and live cells. We conclude that stereoisomers can cause complex site dependent changes in amyloid properties, and provide an effective tool to determine the role of individual residues in shaping the packed interiors of amyloid aggregates.

Myofibroblasts have an impact on expression, dimerization and signaling of different ErbB receptors in OSCC cells.

INTRODUCTION: Receptors of the ErbB family belong to the key players in cancer development and are targets of several therapeutic approaches. Their functional dependency on the tumor microenvironment, especially on CAFs is albeit still poorly understood. Our objective was to investigate the impact of CAF secretome on ErbB receptor expression and signaling behavior in OSCC. METHODS: Stimulation of PE/CA-PJ15 OSCC cells with conditioned media of TGF-ß1-activated fibroblasts was used as model system for CAF to cancer cell communication. Thereby costimulation with inhibitors against matrix metalloproteinases (MMPs), epidermal growth factor receptor (EGFR), MAPK/ERK kinase (MEK), phosphoinositide-3 kinase (PI3-K), signal transducer and activator of transcription 3 (Stat3) or knockdown of Her3 by siRNA was utilized for detailed investigation of the expression, dimerization and signaling pattern of ErbB in western blot and coimmunoprecipitation. RESULTS: Our results show that soluble factors in activated fibroblast secretome stimulate metalloproteinase activity in the membrane of cancer cells. Thereby ligands are released that activate EGFR and subsequently upregulates EGFR expression via the STAT3 pathway. Simultaneously, the expression of PKCɛ was enhanced via a PI3-kinase/Akt-mediated pathway and a negative feedback regulation loop on EGFR downstream signaling generated. Furthermore, the activated fibroblasts secretome stimulated the highly oncogenic hetero-dimerization between HER3 and p95HER2. That protein association is inversely dependent on the expression level of HER3. CONCLUSIONS: Our results demonstrate that the activated fibroblasts secretome can induce a counterbalanced regulation of protein expression, downstream signaling and the dimerization patterns of different ErbB receptor subtypes in the cancer cell. Thus, the combinatorial targeting of CAFs and selective ErbB receptor subtype inhibitors may provide a useful approach in cancer therapy.

Transcriptome changes in renal allograft protocol biopsies at 3 months precede the onset of interstitial fibrosis/tubular atrophy (IF/TA) at 6 months.

BACKGROUND: Interstitial fibrosis and tubular atrophy (IF/TA) in renal transplants are the major morphological correlates of progressive graft deterioration. Early diagnosis of IF/TA is a pre-requisite for a timely therapeutic intervention in patients at risk. To evaluate events occurring before the overt onset of IF/TA, gene expression profiling of 3-month protocol biopsies from patients with IF/TA was performed in a patient group (n = 8) who developed mild IF/TA [chronic allograft nephropathy (CAN) grade I, by the Banff scoring system] in the subsequent 6-month protocol biopsy ('progressors'), and in 12 patients without IF/TA at 6 months ('non-progressors'). METHODS: RNA was extracted, labelled and hybridized to human specific genome wide DNA microarrays. Normalized data were subjected to gene-centric and pathway-centric statistical methods. RESULTS: Compared to the non-progressors, the 3-month biopsies of the progressor group showed overexpression of several genes that are important in the T- and B-cell activation and immune response. Genes involved in pro-fibrotic processes were identified in the biopsies of the progressors that preceded the observed IF/TA at 6 months. Furthermore, several genes with transporter and metabolic functions were underrepresented in the progressors in the 3-month biopsies. CONCLUSION: Gene expression profiling of early protocol biopsies identified changes in the transcriptome of grafts, which may be important for the development of IF/TA. Such early detection of transcriptome changes can facilitate the identification of patients at risk shifting the intervention time point well before the histological diagnosis of irreversible IF/TA.

Oral fingolimod (FTY720) for relapsing multiple sclerosis.

BACKGROUND: Fingolimod (FTY720) is a new oral immunomodulating agent under evaluation for the treatment of relapsing multiple sclerosis. METHODS: We randomly assigned 281 patients to receive oral fingolimod, at a dose of 1.25 mg or 5.0 mg, or a placebo once daily, and we followed these patients for 6 months with magnetic resonance imaging (MRI) and clinical evaluations (core study, months 0 to 6). The primary end point was the total number of gadolinium-enhanced lesions recorded on T(1)-weighted MRI at monthly intervals for 6 months. In an extension study in which the investigators and patients remained unaware of the dose assignments (months 7 to 12), patients who received placebo underwent randomization again to one of the fingolimod doses. RESULTS: A total of 255 patients completed the core study. The median total number of gadolinium-enhanced lesions on MRI was lower with 1.25 mg of fingolimod (1 lesion, P<0.001) and 5.0 mg of fingolimod (3 lesions, P=0.006) than with placebo (5 lesions). The annualized relapse rate was 0.77 in the placebo group, as compared with 0.35 in the group given 1.25 mg of fingolimod (P=0.009) and 0.36 in the group given 5.0 mg of fingolimod (P=0.01). For the 227 patients who completed the extension study, the number of gadolinium-enhanced lesions and relapse rates remained low in the groups that received continuous fingolimod, and both measures decreased in patients who switched from placebo to fingolimod. Adverse events included nasopharyngitis, dyspnea, headache, diarrhea, and nausea. Clinically asymptomatic elevations of alanine aminotransferase levels were more frequent with fingolimod (10 to 12%, vs. 1% in the placebo group). One case of the posterior reversible encephalopathy syndrome occurred in the 5.0-mg group. Fingolimod was also associated with an initial reduction in the heart rate and a modest decrease in the forced expiratory volume in 1 second. CONCLUSIONS: In this proof-of-concept study, fingolimod reduced the number of lesions detected on MRI and clinical disease activity in patients with multiple sclerosis. Evaluation in larger, longer-term studies is warranted. (Clinicaltrials.gov numbers, NCT00333138 [core study] and NCT00235430 [ClinicalTrials.gov] [extension].).

Early prognosis of the development of renal chronic allograft rejection by gene expression profiling of human protocol biopsies.

BACKGROUND: Chronic allograft rejection (CR) is the major cause of failure of long-term graft survival and is so far irreversible. Early prognosis of CR by molecular markers before overt histologic manifestation would be a valuable aid for the optimization of treatment regimens and the design of clinical CR trials. Oligonucleotide microarray-based approaches have proven to be useful for the diagnosis and prognosis of a variety of diseases and were chosen for the unbiased identification of prognostic biomarkers. METHODS: Renal allograft biopsies were taken at month 6 posttransplantation (PT) from two groups who were, at that time, healthy recipients: one group developed CR at month-12 PT, the other group remained healthy. Gene expression profiles from the two groups at month-6 PT biopsies were analyzed to identify differentially expressed genes with prognostic value for CR development at month 12. RESULTS: A set of 10 genes was identified that showed differential expression profiles between the two patient groups and had a complete separation of the 15% to 85% quantile range for each individual gene. This set of genes was sufficient to allow the correct prediction of the occurrence or nonoccurrence of CR in 15 of 17 (88%) patients using cross-validation (occurrence for a patient was predicted on the basis of the other patients' data only). In addition, a correct prediction could be made that a recipient with a normal biopsy 12 months PT developed CR within the following 6 months. CONCLUSIONS: Identified expression patterns seem to be highly prognostic of the development of renal CR.

Randomized double-blind study of immunoprophylaxis with basiliximab, a chimeric anti-interleukin-2 receptor monoclonal antibody, in combination with mycophenolate mofetil-containing triple therapy in renal transplantation.

BACKGROUND: Acute rejection remains a major problem in renal transplantation. Immunoprophylaxis with basiliximab (Simulect) has achieved significant reductions in acute rejection episodes in renal allograft recipients receiving dual immunosuppression. This study explored the tolerability and cumulative benefit of combining basiliximab with triple-drug therapy-cyclosporine (USP Modified, Neoral), mycophenolate mofetil, and steroids. METHODS: In a randomized, double-blind, placebo-controlled, multicenter study, 123 kidney transplant recipients received either basiliximab at 20 mg before transplantation (day 0) and 20 mg on day 4 (n=59), or placebo (n=64). All received triple-drug immunosuppression and were followed for 6 months. RESULTS: Tolerability of basiliximab was equivalent to placebo, with no increase in serious adverse events, infection, malignancy, or posttransplant lymphoproliferative disorder. At 6 months, there were trends in favor of basiliximab over placebo in the incidences of first biopsy-confirmed acute rejection (15.3% vs. 26.6%, P=NS) and of acute rejection treated with antibody (5.1% vs. 15.6%, P=NS). Kaplan-Meier estimates at 4 weeks and 6 months were significantly in favor of basiliximab treatment for first acute rejection, biopsy-confirmed rejection, rejection episodes treated with antibody therapy, and treatment failure. Renal function improved more rapidly in the basiliximab group, with mean creatinine clearance at week 2 being 54.7 mL/min versus 43.2 mL/min for placebo (P=0.034). At 12 months, patient survival was 100% in both groups; graft survival was 94.9% with basiliximab and 92.2% with placebo. CONCLUSIONS: Basiliximab immunoprophylaxis is safe, well tolerated, and shows a trend toward reduction in number of acute rejection episodes in renal transplant patients receiving cyclosporine, mycophenolate mofetil, and steroids.

Safety and efficacy of an alternative basiliximab (Simulect) regimen after renal transplantation: administration of a single 40-mg dose on the first postoperative day in patients receiving triple therapy with azathioprine.

This was a multi-center, open-label, randomized, dose-comparative study on 202 renal transplantation patients. We evaluated for the first time an alternative dosing regimen for basiliximab, consisting of a single 40-mg intravenous dose on day 1 post-transplantation plus triple therapy, in comparison with the conventional two-dose regimen (2 h before transplantation and on day 4) plus triple therapy. At 6 months, the incidence of acute rejection was low: 22.5% of patients in the basiliximab 2 x 20-mg group and 20.0% of patients in the basiliximab 1 x 40-mg group experienced an acute rejection episode ( P = 0.628) (biopsy-proven rejection: 19.6% and 17.0%, P = 0.585). There was no statistically significant difference in any of the secondary efficacy parameters. The incidence of graft loss by 12 months was 4.9% and 6.0% in the 2 x 20-mg and 1 x 40-mg group, respectively ( P = 0.73). No differences were observed between the dosage groups with regards to safety assessments (adverse events (AEs), infections, vital signs, laboratory safety evaluations, and physical examinations). The data reveal that basiliximab can be safely and effectively administered as a single 40-mg dose on day 1 after renal transplantation as a therapeutic option to the established 2 x 20-mg dosing regimen. This alternative dosing regimen may be of significant convenience under circumstances when a first dose of basiliximab was not given prior to transplantation. Both regimens can conveniently be used during the initial hospitalization of the patient.

A rational dosing algorithm for basiliximab (Simulect) in pediatric renal transplantation based on pharmacokinetic-dynamic evaluations.

BACKGROUND: The pharmacokinetics and immunodynamics of basiliximab were assessed in 39 pediatric de novo kidney allograft recipients to rationally chose a dose regimen for this age group. METHODS: In study part 1, patients were given 12 mg/m(2) of basiliximab by bolus intravenous injection before surgery and on day 4. An interim pharmacokinetic evaluation supported a fixed-dose approach for study part 2 in which infants and children received two 10-mg doses and adolescents received two 20-mg doses. Blood samples were collected over a 12-week period for analysis of basiliximab and soluble interleukin-2 receptor concentrations, flow cytometry, and screening for anti-idiotype antibodies. RESULTS: Basiliximab clearance in infants and children (n=25) was reduced by approximately half compared with adults from a previous study and was independent of age (1-11 years), weight (9-37 kg), and body surface area (0.44-1.20 m(2) ). Clearance in adolescents (12-16 years, n=14) approached or reached adult values. CD25-saturating basiliximab concentrations were maintained for 31+/-12 days in study part 1 with mg/m(2) dosing and for 36+/-14 days in study part 2 based on the fixed-dose regimen ( P=0.31). A single patient experienced a rejection episode during CD25 saturation. The duration of CD25 saturation in patients who experienced a rejection episode after desaturation did not differ from those who remained rejection-free for the full 6-month period: 34+/-6 days (n=6) vs. 35+/-14 days (n=33 patients); P=0.74. Anti-idiotype antibodies were detected in two patients; however, this did not influence the clearance of basiliximab or the duration of CD25 saturation. CONCLUSIONS: To achieve similar basiliximab exposure as is efficacious in adults, pediatric patients <35 kg should receive two 10-mg doses and those > or =35 kg should receive two 20-mg doses of basiliximab by intravenous infusion or bolus injection. The first dose is given before surgery and the second on day 4 after transplantation.

A multicenter, open-label, pharmacokinetic/pharmacodynamic safety, and tolerability study of basiliximab (Simulect) in pediatric de novo renal transplant recipients.

BACKGROUND: Basiliximab (Simulect) has been shown to be safe and effective in adult renal transplant recipients, when used in combination with cyclosporine (Neoral) and corticosteroids. We report on the safety and preliminary efficacy of basiliximab in pediatric de novo renal transplant recipients. METHODS: This was an open-label, 12-month study of basiliximab in 41 patients (2 cohorts: <9 and 9 to <16 years). In phase 1, two intravenous (IV) bolus injections of basiliximab (12 mg/m ) were administered (before and 4 days postsurgery). In phase 2, two injections (<40 kg, 10 mg and > or =40 kg, 20 mg) were administered at the same time points. Most patients (26/41 [63%]) received cadaveric kidneys. Almost half of the patients had three human leukocyte antigen mismatches with the organ donors. Concurrent immunosuppression included Neoral and corticosteroids. Azathioprine was allowed after 28 days. RESULTS: All patients completed the 1-year study. The acute tolerability of basiliximab via IV bolus injection was good, without evidence of cytokine-release syndrome or acute local reactions. All patients experienced adverse events, but most (71%) were mild or asymptomatic. No deaths or malignancies occurred. The incidence and types of serious adverse events (59%) and serious infections (44%) were as expected in this patient population, and few were drug-related (7% and 5%, respectively). Thirty-eight patients (93%) had infections, mostly urinary tract infections, as expected for renal transplant patients. Six patients (15%) had drug-related adverse events. Biopsy-confirmed acute rejection episodes occurred in 6/41 (15%) of patients during the first 6 months posttransplantation and in 9/41 (22%) patients during the first 12 months. Five patients (12%) experienced graft loss, none of which were preceded by acute rejection episodes. CONCLUSIONS: Basiliximab is safe and well tolerated when administered by IV bolus injection in de novo pediatric renal transplant recipients. These preliminary data suggest that basiliximab, given in combination with cyclosporine and corticosteroids, is an effective immunosuppressive regimen for the prevention of acute rejection in pediatric renal transplantation.

Basiliximab in pediatric liver transplantation: a pharmacokinetic-derived dosing algorithm.

The pharmacokinetics and immunodynamics of basiliximab were assessed in 37 pediatric de novo liver allograft recipients to rationally design a dose regimen for this age-group. In part one of the study, patients were given 12 mg/m2 basiliximab by bolus intravenous injection after organ perfusion and on day 4 after transplant. An interim pharmacokinetic evaluation supported a fixed-dose approach for part two of the study in which infants and children received two 10-mg doses of basiliximab and adolescents received two 20-mg doses. Blood samples were collected over a 12-week period for screening for anti-idiotype antibodies and analysis of basiliximab and soluble interleukin-2 receptor (IL-2R) concentrations. Basiliximab clearance in infants and children < 9 yr of age (n = 30) was reduced by approximately 50% compared with adults from a previous study and was independent of age to 9 yr, weight to 30 kg, and body surface area to 1.0 m2. Clearance in children and adolescents 9-14 yr of age (n = 7) approached or reached adult values. An average of 15% of the dose was eliminated via drained ascites fluid, and drug clearance via this route averaged 29% of total body clearance. Patients with > 5 L of ascites fluid drainage tended to have lower systemic exposure to basiliximab. CD25-saturating basiliximab concentrations were maintained for 27 +/- 9 days in part one of the study (mg/m2 dosing) with infants exhibiting the lowest durations. CD25 saturation lasted 37 +/- 11 days in part two of the study, based on the fixed-dose regimen (p = 0.004 vs. mg/mg2 dosing), but did not show the age-related bias observed in part one of the study. Anti-idiotype antibodies were detected in four patients, but this did not influence the clearance of basiliximab or duration of CD25 saturation. All 40 enrolled patients were included in the intent-to-treat clinical analysis. Episodes of acute rejection occurred in 22 patients (55%) during the first 12 months post-transplant. Three patients experienced loss of their graft as a result of technical complications, and six patients died during the 12-month study. Basiliximab was well tolerated by intravenous bolus injection, with no cytokine-release syndrome or other infusion-related adverse events. Hence, basiliximab was safe and well tolerated in pediatric patients undergoing orthotopic liver transplantation. To achieve similar basiliximab exposure as is efficacious in adults, pediatric patients < 35 kg in weight should receive two 10-mg doses and those > or = 35 kg should receive two 20-mg doses of basiliximab by intravenous infusion or bolus injection. The first dose should be given within 6 h after organ perfusion and the second on day 4 after transplantation. A supplemental dose may be considered for patients with a large volume of drained ascites fluid relative to body size.

Improved treatment response with basiliximab immunoprophylaxis after liver transplantation: results from a double-blind randomized placebo-controlled trial.

Basiliximab, a high-affinity chimeric monoclonal antibody, is effective in reducing acute rejection episodes in renal allograft recipients. We assessed the ability of this antibody to similarly improve the outcome in liver transplant recipients. Adult recipients of a primary cadaveric liver transplant were randomized to treatment, stratified by hepatitis C virus (HCV) seropositivity. Patients were administered 40 mg of basiliximab (n = 188) or placebo (n = 193) as two 20-mg bolus injections days 0 and 4, plus cyclosporine and steroids. Primary efficacy variables were biopsy-confirmed acute rejection and its composite end point, including death or graft loss, and were assessed at 6 and 12 months and by HCV cohort. Because of differential efficacy responses between HCV-positive and HCV-negative cohorts, an additional analysis incorporating HCV recurrence as a component of treatment failure, termed problem-free transplant, was introduced. Safety and tolerability were monitored over the 12 months of the study. All 381 patients were assessable, and no meaningful differences in background characteristics were apparent between treatment groups. Biopsy-confirmed acute rejection rates 6 months after transplantation were 35.1% in the basiliximab group versus 43.5% in the placebo group. For death, graft loss, or first biopsy-confirmed acute rejection, rates were 44.1% versus 52.8%, respectively. The reduction in rejection episodes was concentrated in the HCV-negative cohort (14.5% relative to placebo; P =.034), with a much smaller difference (2.9%) in the HCV-positive cohort. For HCV-positive patients, problem-free transplant was shown at 12 months in 26.6% of the basiliximab group versus 11.6% in the placebo group (P =.020) and for all patients at 12 months in 39.7% of the basiliximab group versus 30.1% in the placebo group (P =.035). The incidence of infection and other adverse events was similar across the two treatment groups. There were 56 deaths (25 deaths, basiliximab group; 31 deaths, placebo group) over the 12-month study. The intravenous bolus injection was well tolerated. Immunoprophylaxis with 40 mg of basiliximab, in combination with cyclosporine and steroids, reduces the incidence of acute rejection episodes with no clinically relevant safety or tolerability concerns. The influence of HCV recurrence on efficacy results can be accounted for in future trials by using the concept of problem-free transplant, incorporating recurrence as a component of treatment failure.