Efficacy and immunogenicity of novel erythropoietic agents and conventional rhEPO in rats with renal insufficiency

Analytical chromatography approaches during the synthesis and conjugation of methoxypolyethylene glycol-succinimidyl butanoate (mPEG-SBA) to epoetin beta

Conjugation of epoetin beta (EPO) with methoxypolyethylene glycol-succinimidyl butanoate (mPEG-SBA) was studied. The compound mPEG-SBA was synthesized from mPEG, and the obtained intermediates and final product were analyzed by a reversed-phase chromatographic system equipped with an evaporative light scattering detector. Labeling the hydroxyl group in PEGs with benzoyl chloride and succinimide with benzylamine was applied to resolve and characterize different PEGs. The synthesized mPEG-SBA was used for the PEGylation of EPO. A size-exclusion chromatographic method monitored the reaction, simultaneously determining the PEGylated and unreacted EPO and protein aggregates. A borate buffer (0.1 M, pH 7.8) and PEG/protein molar ratio of 3:1 produced a maximum amount of monoPEGylated EPO with the minimum amount of polyPEGylated EPO variants. Although EPO is considered a stable glycoprotein hormone that remains monomeric when refrigerated, PEGylation of EPO with mPEG-SBA resulted in the significant formation of EPO dimer. The formation of EPO dimer and polyPEGylated EPO was pH-dependent, showing higher amounts of aggregates and lower amounts of polyPEGylated forms in lower pH values. Accordingly, aggregated EPO should be considered a major PEGylation-related impurity. In conclusion, the present study highlighted the importance of having suitable analytical approaches in controlling mPEG-SBA synthesis and conjugation to EPO.

Biological properties of adrenomedullin conjugated with polyethylene glycol

Adrenomedullin (AM) is a vasodilator peptide with pleiotropic effects, including cardiovascular protection and anti-inflammation. Because of these beneficial effects, AM appears to be a promising therapeutic tool for human diseases, while intravenous injection of AM stimulates sympathetic nerve activity due to short-acting potent vasodilation, resulting in increased heart rate and renin secretion. To lessen these acute reactions, we conjugated the N-terminal of human AM peptide with polyethylene glycol (PEG), and examined the biological properties of PEGylated AM in the present study. PEGylated AM stimulated cAMP production, an intracellular second messenger of AM, in cultured human embryonic kidney cells expressing a specific AM receptor in a dose-dependent manner, as did native human AM. The pEC50 value of PEGylated AM was lower than human AM, but no difference was noted in maximum response (Emax) between the PEGylated and native peptides. Intravenous bolus injection of 10nmol/kg PEGylated AM lowered blood pressure in anesthetized rats, but the acute reduction became significantly smaller by PEGylation as compared with native AM. Plasma half-life of PEGylated AM was significantly longer than native AM both in the first and second phases in rats. In summary, N-terminal PEGylated AM stimulated cAMP production in vitro, showing lessened acute hypotensive action and a prolonged plasma half-life in comparison with native AM peptide in vivo.

Pharmacokinetics of PEGylated Recombinant Human Erythropoietin in Rats

rHuEPO plays a central role as chemicals for the treatment of many diseases. Due to its short half-life, the main aim for this pharmacokinetic study is to investigate a newly developed PEG-rHuEPO with large molecular weight in SD rats. After a single intramuscular administration of different doses of 125I-PEG-rHuEPO, pharmacokinetic parameters, tissue distribution, and excretion were analyzed. In in vivo half-life time measured after 125I-PEG-rHuEPO administration at the doses of 1, 2, and 3 μg/kg, t1/2α was 1.90, 1.19, and 2.50 hours, respectively, whereas t1/2β was 22.37, 26.21, and 20.92 hours, respectively; at 8, 24, and 48 hours after intramuscular administration, PEG-rHuEPO was distributed to all of the examined tissues, however, with high concentrations of radioactivity, only in plasma, blood, muscle at the administration site, and bone marrow. Following a 2 μg/kg single intramuscular administration, approximately 21% of the radiolabeled dose was recovered after almost seven days of study. Urine was the major route of excretion; 20% of the administered dose was recovered in the urine, while excretion in the feces was less than 1.4%. Therefore, this PEG-rHuEPO has potential to be clinically used and could reduce frequency of injection.

Simultaneous measurement of kidney function by dynamic contrast enhanced MRI and FITC-sinistrin clearance in rats at 3 tesla: initial results

Glomerular filtration rate (GFR) is an essential parameter of kidney function which can be measured by dynamic contrast enhanced magnetic resonance imaging (MRI-GFR) and transcutaneous approaches based on fluorescent tracer molecules (optical-GFR). In an initial study comparing both techniques in separate measurements on the same animal, the correlation of the obtained GFR was poor. The goal of this study was to investigate if a simultaneous measurement was feasible and if thereby, the discrepancies in MRI-GFR and optical-GFR could be reduced. For the experiments healthy and unilateral nephrectomised (UNX) Sprague Dawley (SD) rats were used. The miniaturized fluorescent sensor was fixed on the depilated back of an anesthetized rat. A bolus of 5 mg/100 g b.w. of FITC-sinistrin was intravenously injected. For dynamic contrast enhanced perfusion imaging (DCE-MRI) a 3D time-resolved angiography with stochastic trajectories (TWIST) sequence was used. By means of a one compartment model the excretion half-life (t1/2) of FITC-sinistrin was calculated and converted into GFR. GFR from DCE-MRI was calculated by fitting pixel-wise a two compartment renal filtration model. Mean cortical GFR and GFR by FITC-sinistrin were compared by Bland-Altman plots and pair-wise t-test. Results show that a simultaneous GFR measurement using both techniques is feasible. Mean optical-GFR was 4.34 ± 2.22 ml/min (healthy SD rats) and 2.34 ± 0.90 ml/min (UNX rats) whereas MRI-GFR was 2.10 ± 0.64 ml/min (SD rats) and 1.17 ± 0.38 ml/min (UNX rats). Differences between healthy and UNX rats were significant (p<0.05) and almost equal percentage difference (46.1% and 44.3%) in mean GFR were assessed with both techniques. Overall mean optical-GFR values were approximately twice as high compared to MRI-GFR values. However, compared to a previous study, our results showed a higher agreement. In conclusion, the possibility to use the transcutaneous method in MRI may have a huge impact in improving and validating MRI methods for GFR assessment in animal models.

High Hematocrit Resulting from Administration of Erythropoiesis-stimulating Agents Is Not Fully Predictive of Mortality or Toxicities in Preclinical Species

We conducted a retrospective analysis of publicly available preclinical toxicology studies with erythropoiesis-stimulating agents (ESAs) to examine common adverse events in rats, Beagle dogs, and cynomolgus monkeys. Mortality and/or thrombotic events were reported sporadically in a subset of studies and attributed to the high hematocrit (HCT) achieved in the animals. However, similarly high HCT was achieved in both high-dose and low-dose groups, but there were no reported adverse events in the low-dose group suggesting HCT was not the sole contributing factor leading to toxicity. Our analysis indicated that increased dose, dose frequency, and dosing duration in addition to high HCT contributed to mortality and thrombosis. To further evaluate this relationship, the incidence of toxicities was compared in rats administered an experimental hyperglycosylated analog of recombinant human erythropoietin (AMG 114) at varying dosing schedules in 1-month toxicity studies. The incidence of mortality and thrombotic events increased in higher dose groups and when dosed more frequently, despite a similarly high HCT in all animals. The results from the investigative study and retrospective analysis demonstrate that ESA-related toxicities in preclinical species are associated with dose level, dose frequency, and dosing duration, and not solely dependent upon a high HCT.

Models for evaluation of relative immunogenic potential of protein particles in biopharmaceutical protein formulations

An immune response to a therapeutic protein that compromises the biopharmaceutical activity or cross-reacts with an endogenous protein is a serious clinical event. The role of protein aggregates and particles in biopharmaceutical formulations in mediating this immune response has gained considerable attention over the recent past. Model systems that could consistently and reliably predict the relative immunogenicity of biopharmaceutical protein formulations would be extremely valuable. Several approaches have been developed in an attempt to provide this insight, including in silico algorithms, in vitro tests utilizing human leukocytes and in vivo animal models. This commentary provides an update of these various approaches as well as the author's perspectives on the pros and cons of these different methods.

Design, modeling, expression, and chemoselective PEGylation of a new nanosize cysteine analog of erythropoietin

Background:

Recombinant human erythropoietin (rhEPO) is considered to be one of the most pivotal pharmaceutical drugs in the market because of its clinical application in the treatment of anemia-associated disorders worldwide. However, like other therapeutic proteins, it does not have suitable pharmacokinetic properties for it to be administrated at least two to three times per week. Chemoselective cysteine PEGylation, employing molecular dynamics and graphics in in silico studies, can be considered to overcome such a problem.

Methods:

A special kind of EPO analog was elicited based on a literature review, homology modeling, molecular dynamic simulation, and factors affecting the PEGylation reaction. Then, cDNA of the selected analog was generated by site-directed mutagenesis and subsequently cloned into the expression vector. The construct was transfected to Chinese hamster ovary/dhfr⁻ cells, and highly expressed clones were selected via methotrexate amplification. Ion-immobilized affinity and size exclusion (SE) chromatography techniques were used to purify the expressed analog. Thereafter, chemoselective PEGylation was performed and a nanosize PEGylated EPO was obtained through dialysis. The in vitro biologic assay and in vivo pharmacokinetic parameters were studied. Finally, E31C analog Fourier transform infrared, analytical SE-high-performance liquid chromatography, zeta potential, and size before and after PEGylation were characterized.

Results:

The findings indicate that a novel nanosize EPO31-PEG has a five-fold longer terminal half-life in rats with similar biologic activity compared with unmodified rhEPO in proliferation cell assay. The results also show that EPO31-PEG size and charge versus unmodified protein was increased in a nanospectrum, and this may be one criterion of EPO biologic potency enhancement.

Discussion:

This kind of novel engineered nanosize PEGylated EPO has remarkable advantages over rhEPO.

Time-dependent clearance and hematological pharmacodynamics upon erythropoietin multiple dosing in rats

The pharmacokinetics (PK) and pharmacodynamics (PD) of recombinant human erythropoietin (rHuEPO) upon its repeated administrations were investigated. Two groups (A and B) of normal Wistar rats received rHuEPO intravenously at 450 or 1350 IU/kg thrice weekly for 2 and 6 weeks. PK studies were conducted following days 0 and 4 for group (A) and days 0, 17 and 28 for group (B), then, washout PK were assessed on days 11 and 36 for both groups. Reticulocytes (RET), red blood cells (RBC) and hemoglobin (Hb) were evaluated daily until day 14, then every 2 days until day 30 for group (A) and 59 for group (B). The total clearance CL(Total) increased with the dose but decreased over time. Its decay reached 20% and 55% between the first and last full PK in both treatment arms. RET peaked on day 5 and were 77.6% and 87.3% higher than baselines for the two dosing regimen. Their nadirs occurred on days 22 and 55 and were 37.9% and 47.3% below normal values. Hb peaked on days 10 and 34 and was 28.9% and 38.6% above the baseline level, its nadirs occurred on days 25 and 57 and were 13.1% and 16% below baselines. Control animals showed stable baselines over the study but with moderate variability. In conclusion, rHuEPO exhibits a nonlinear PK with a time-dependent decrease of its CL(Total). During exposure, RET, RBC and Hb showed a tolerance effect. After exposure, the rebound was characterized for RET, RBC, but not Hb.

Simultaneous pharmacokinetics/pharmacodynamics modeling of recombinant human erythropoietin upon multiple intravenous dosing in rats

A pharmacokinetics (PK)/pharmacodynamics (PD) model was developed to describe the tolerance and rebound for reticulocyte (RET) and red blood cell (RBC) counts and the hemoglobin (Hb) concentrations in blood after repeated intravenous administrations of 1350 IU/kg of recombinant human erythropoietin (rHuEPO) in rats thrice weekly for 6 weeks. Drug concentrations were described by using a quasi-equilibrium model. The PD model consisted of a lifespan-based indirect response model (LIDR) with progenitor cells [burst colony-forming unit erythroblasts and colony-forming unit erythroblasts (CFUs)], normoblasts (NOR), RETs, and RBCs. Drug-receptor complex stimulatory effects on progenitor cells differentiation and RBC lifespan were expressed by using the E(max) model (S(max-epo) and SC(50-epo), E(max) and EC(50)). The Hb profile was indirectly modeled through a LIDR model for mean corpuscular hemoglobin (with a lifespan T(mch)) including a linear (S(max-mch)) drug stimulatory effect. The negative feedback from RBCs accounted for the time-dependent rHuEPO clearance decline. A simultaneous PK/PD fitting was performed by using MATLAB-based software. PK parameters such as equilibrium dissociation, erythropoietin receptor degradation, production, and internalization rate constants were 0.18 nM (fixed), 0.08 h(-1), 0.03 nM/h, and 2.51 h(-1), respectively. The elimination rate constant and central volume of distribution were 0.57 h(-1) and 40.63 ml/kg, respectively. CFU and NOR, RET, and RBC lifespans were 37.26 h, 17.25 h, and 30.15 days, respectively. S(max-epo) and SC(50-epo) were 7.3 and 0.47 10(-2) nM, respectively. E(max) was fixed to 1. EC(50) and SC(50-epo) were equal. S(max-mch) and T(mch) were 168.1 nM(-1) and 35.15 days, respectively. The proposed PK/PD model effectively described rHuEPO nonstationary PK and allowed physiological estimates of cell lifespans.

PEGylated polymers for medicine: from conjugation to self-assembled systems

Synthetic polymers have transformed society in many areas of science and technology, including recent breakthroughs in medicine. Synthetic polymers now offer unique and versatile platforms for drug delivery, as they can be "bio-tailored" for applications as implants, medical devices, and injectable polymer-drug conjugates. However, while several currently used therapeutic proteins and small molecule drugs have benefited from synthetic polymers, the full potential of polymer-based drug delivery platforms has not yet been realized. This review examines both general advantages and specific cases of synthetic polymers in drug delivery, focusing on PEGylation in the context of polymer architecture, self-assembly, and conjugation techniques that show considerable effectiveness and/or potential in therapeutics.

Chronic erythropoietin treatment affects different molecular pathways of diabetic cardiomyopathy in mouse

BACKGROUND

Recent studies in mice experimental models with acute ischaemic injury revealed that erythropoietin (EPO) has numerous tissue-protective effects in the heart, brain and kidneys. We therefore explored the tissue-protective properties of chronic EPO treatment in an experimental model of the db/db mouse with diabetic heart injury.

MATERIAL AND METHODS

We randomly treated 11 db/db mice with placebo (saline), 0.4 microg of the continuous erythropoietin receptor activator (CERA) per week (n = 11) or 1.2 microg CERA per week (n = 11) for 14 weeks, and analysed cardiac tissue. The lower CERA dose was a non-haematologically effective dose, whereas the second increased the haematocrit.

RESULTS

Compared with mice in the placebo group, CERA-treated mice had a reduction in TGF-beta(1) and collagen I expression in cardiac tissue (P < 0.01 vs. higher dose CERA). In addition, an increased expression of the pro-survival intracellular pathway p-AKT was observed (P < 0.05 vs. higher dose CERA). The values for the lower C.E.R.A had an intermediate nonsignificant effect. Furthermore, we were able to show that atrial natriuretic peptide (ANP) expression was increased in both CERA groups.

CONCLUSIONS

Chronic treatment with CERA protects cardiac tissue in diabetic animals, i.e. it inhibits molecular pathways of cardiac fibrosis, and the effects are dose-dependent.

Transcutaneous measurement of glomerular filtration rate using FITC-sinistrin in rats

BACKGROUND

Inulin/sinistrin (I/S) clearance is a gold standard for an accurate assessment of glomerular filtration rate (GFR). Here we describe and validate an approach for a transcutaneous determination of GFR by using fluorescein-isothiocyanate-labelled sinistrin (FITC-S) in rats.

METHODS

Using a small animal imager, fluorescence is measured over the depilated ear of a rat after the injection of FITC-S. The decay curve of fluorescence is used for the calculation of half-life and GFR. The thus obtained transcutaneous data were validated by simultaneously performed enzymatic and fluorometric measurements in plasma of both FITC-S and sinistrin.

RESULTS

The results of enzymatic sinistrin determination versus transcutaneous half-life of FITC-S or plasma fluorescence correlated well with each other (R(2) > 0.90). Furthermore, Bland-Altman analyses proved a good degree of agreement of the three methods used. The measurements performed in healthy animals as well as different models of renal failure demonstrate its appropriateness in a wide range of renal function.

CONCLUSIONS

The transcutaneous method described offers a precise assessment of GFR in small animals. As neither blood and/or urine sampling nor time-consuming lab work is required, GFR can be determined immediately after the clearance procedure is finished. This method, therefore, simplifies and fastens GFR determinations in small lab animals compared to conventional bolus clearance techniques based on blood sampling. A low-cost device for the measurement of transcutaneous fluorescence intensity over time is under construction.

Polymer-based sustained-release dosage forms for protein drugs, challenges, and recent advances

While the concept of using polymer-based sustained-release delivery systems to maintain therapeutic concentration of protein drugs for extended periods of time has been well accepted for decades, there has not been a single product in this category successfully commercialized to date despite clinical and market demands. To achieve successful systems, technical difficulties ranging from protein denaturing during formulation process and the course of prolonged in vivo release, burst release, and incomplete release, to low encapsulation efficiency and formulation complexity have to be simultaneously resolved. Based on this updated understanding, formulation strategies attempting to address these aspects comprehensively were reported in recent years. This review article (with 134 citations) aims to summarize recent studies addressing the issues above, especially those targeting practical industrial solutions. Formulation strategies representative of three areas, microsphere technology using degradable hydrophobic polymers, microspheres made of water soluble polymers, and hydrophilic in vivo gelling systems will be selected and introduced. To better understand the observations and conclusions from different studies for different systems and proteins, physicochemical basis of the technical challenges and the pros and cons of the corresponding formulation methods will be discussed.

Methoxy polyethylene glycol-epoetin beta: a review of its use in the management of anaemia associated with chronic kidney disease

Methoxy polyethylene glycol-epoetin beta (Mircera) is a continuous erythropoietin receptor activator, with a long half-life (approximately 130 hours). In patients with anaemia associated with chronic kidney disease (CKD), both on and not on dialysis, who had not previously received an erythropoiesis-stimulating agent (ESA), methoxy polyethylene glycol-epoetin beta administered intravenously or subcutaneously once every 2 weeks resulted in a smooth and steady rise in haemoglobin levels. The response rates were high (up to 97.5%) in these patients at the end of the correction period; response rates with the comparator ESAs (epoetin alfa or beta, or darbepoetin alfa) were up to 96.3%. Moreover, patients with CKD on dialysis who had previously been treated with an ESA maintained stable haemoglobin levels (within +/-1 g/dL of baseline and within a range of 10-13.5 g/dL) when directly converted to methoxy polyethylene glycol-epoetin beta administered intravenously or subcutaneously once every 2 or 4 weeks. Methoxy polyethylene glycol-epoetin beta is generally well tolerated, with most adverse events being of mild to moderate severity, consistent with the co-morbidities known to occur in this patient group and those reported with other ESAs. In conclusion, in patients with anaemia associated with CKD, subcutaneous or intravenous methoxy polyethylene glycol-epoetin beta achieved a high haemoglobin response rate (ESA-naive patients) when administered once every 2 weeks and maintained stable haemoglobin levels (patients previously treated with ESAs) when administered once monthly.

Cisplatin-induced peripheral neuropathy: Neuroprotection by erythropoietin without affecting tumour growth

This study examined the dose-dependent efficacy of erythropoietin (EPO) for preventing and/or treating cisplatin (CDDP) induced peripheral neurotoxicity (CINP), and its influence on tumour treatment and growth. Rats received eight intraperitoneal (ip) injections of 2 mg/kg CDDP twice weekly. EPO co-administered (50 or 10 microg/kg ip, three times/week) had a dose-dependent effect, partially preventing CINP, but 0.5 microg/kg ip was not effective. The neuroprotective effect lasted at least 5 weeks after the last dose of EPO and CDDP. In addition, EPO (50 microg/kg ip three times/week) after the last injection of CDDP still induced a significant recovery of CINP. In a separate experiment in rats bearing mammary carcinoma EPO treatment (50 microg/kg ip) given concurrently with CDDP (1.0 and 1.5 mg/kg twice a week for four weeks) was neuroprotective without influencing the effectiveness of the treatment or tumour growth. EPO thus appears to be an effective neuroprotectant that does not interfere with tumour treatment.

Angiogenesis and endothelial cell repair in renal disease and allograft rejection

This review discusses the concept that the turnover and replacement of endothelial cells is a major mechanism in the maintenance of vascular integrity within the kidney. CD133+CD34+KDR+ endothelial cell progenitor cells emigrate from the bone marrow and differentiate into CD34+KDR+ expressing cells, which are present in high numbers within the circulation. These progenitor cells are available for recruitment into normal or inflamed tissues to facilitate endothelial cell repair. In several forms of renal disease, proinflammatory insults mediate oxidative stress, senescence, and sloughing of endothelial cells. A lack of growth factors or an inefficient recruitment of endothelial cell progenitors results in hypoxic tissue injury and accelerates the process of chronic renal failure. Augmentation of vascular repair by the provision of growth factors such as vascular endothelial growth factor or by the transfer of progenitor cells directly into the kidney can be protective and prevent ongoing interstitial damage. In allografts, persistent injury results in excessive turnover of graft vascular endothelial cells. Moreover, chronic damage elicits a response that is associated with the recruitment of both leukocytes and endothelial cell progenitors, facilitating an overlapping process of inflammation and angiogenesis. Because the angiogenesis reaction itself is proinflammatory, this process becomes self-sustaining. Collectively, these data indicate that angiogenesis and endothelial cell turnover are important in renal inflammatory processes and allograft rejection. Manipulation of the response may have therapeutic implications to protect against injury and chronic disease processes.