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Institute
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Sonstige beteiligte Institutionen
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- Pharmazie, Universität Mailand (1)
- Spectral Service AG (1)
The high failure rate of new drug candidates in preclinical or clinical studies due to hepatotoxicity represents a considerable problem in the drug development. Hence, there is an urgent need to develop new approaches for early and reliable prediction of drug-induced hepatotoxicity that enables a better identification of drug candidates with high potential for toxicity at early stages of drug development. Therefore, the aim of this work was to improve the prediction of drug-induced liver injury in preclinical studies through evaluation of more reliable and sensitive biomarkers of hepatotoxicity and a better understanding of the underlying mechanistic basis for drug-induced toxicity. First, the ability of a set of potential markers (NGAL, thiostatin, clusterin, PON1) to detect early signs of liver injury was assessed in rats treated with drug candidates that were dropped from further development, in part due to toxic adverse effects in the liver. In summary, PON1 and clusterin were not consistently altered in response to liver injury and thus provide no additive information to the traditional liver enzymes in detecting drug-induced hepatotoxicity. In contrast, thiostatin and NGAL were increased in serum and urine of treated animals in a time- and dose-dependent manner. These changes correlated well with mRNA expression in the target organ and generally reflected the onset and degree of drug-induced liver injury. Receiver-operating characteristics analyses supported serum thiostatin, but not NGAL, as a better indicator of drug-induced hepatobiliary injury than conventional clinical chemistry parameters, such as ALP, ALT and AST. Although thiostatin, an acute phase protein expressed in a range of tissues, may not be specific for liver injury, our results indicate that thiostatin may serve as a sensitive, minimally-invasive diagnostic marker of inflammation and tissue damage in preclinical safety assessment. In the second part of this work, combined application of genomics profiling technology and RNAi to inhibit the pharmacological target of a drug candidate BAY16, a glucagon receptor (GCGR) antagonist, was used to determine if interference with the pharmacological target plays a role in the toxic response to BAY16, and to narrow down those molecular changes that are associated with toxicity, and not the pharmacological action of BAY16. In contrast to Bay 16, which was found to be cytotoxic at concentrations of 75 µM, silencing of the glucagon receptor did not affect cell viability in primary rat hepatocytes. Thus, it can be concluded that hepatotoxicity of Bay 16 was not related to the drugs inhibitory effect on the glucagon receptor in vitro and in vivo. These findings were supported by the fact that most of BAY16-induced changes in gene expression occurred independently of the pharmacological modulation of GCGR. These off-target effects include altered xenobiotic metabolism, oxidative stress, increased fatty acid synthesis, and alterations in cholesterol and bile acid metabolic processes. Although it was not possible to draw a final conclusion about the mechanism of BAY16 hepatotoxicity, changes in these molecular mechanisms appear contribute to progression of hepatic injury. With regard to drug safety assessment in preclinical studies, the utilization of siRNA technology in vitro represents a new approach to improve mechanistic understanding of the nature of drug’s toxicity, being either chemically mediated or due to primary or secondary pharmacological mode of action.
The aim of the present study was to design different dosage forms as carrier systems to deliver sorafenib to the lung of BXB-23 transgenic mice using different routes of administration. Three dosage forms were used one of them was an oil-in-water emulsion and the oral route was chosen for this experiment. The other delivery system was a liposome preparation for intratracheal instillation. In this case the oral route was considered as a control experiment. The last dosage form was PLGA microspheres. Before sorafenib administration it was important to develop a HPLC method to assess sorafenib absorption after its administration and to determine its concentrations in mouse serum. The HPLC method allowed sorafenib quantification in small volumes (30 µl) of mouse serum and tissues. The developed HPLC method was validated resulting in satisfactory selectivity, good linearity, good accuracy and precision over the concentration range examined. Sorafenib was successfully incorporated in a fat emulsion (o/w) using a traditional method resulting in a white homogenous emulsion and no particle aggregation was observed. Sorafenib exhibited antitumor activity on the lung adenoma in BXB-23 transgenic mice when administered orally (2 mg sorafenib per mouse) in the emulsion preparation. The determined effect was an approximately 29 % reduction in the tumor area of the adenoma foci and a proliferation reduction. In order to improve the pharmacological effects of sorafenib on the lung adenoma in BXB-23 mice, the targeting of sorafenib directly to the site of action (the lung) was an attractive concept. For this purpose the intratracheal route was used. Since sorafenib administration by instillation required incorporation of sorafenib in a dosage form suitable for its lipophilic nature, a liposome suspension was the second dosage form used. A lyophilization method was employed for sorafenib liposome preparation utilizing dilauroylphosphatidylcholine (DLPC) which is safe and tolerable for the lung. Incorporation of sorafenib in the liposomes did not influence the particle size and its distribution. The sorafenib liposomes showed high encapsulation efficiency, good stability at 4 °C for one month and satisfactory in vitro release properties and inhibited Raf-1 mediated activation of ERK in cell culture assay. In a pharmacokinetic experiment sorafenib loaded liposomes were instilled directly into the lung. The results revealed that a significant level of sorafenib was achieved in the lung tissues after 2 hours and then reduced after 48 h and remained nearly constant for one week. On the other hand, only traces of sorafenib were found in the mice serum up to 48 h. Subsequently, the pharmacological activity of sorafenib (1 mg per mouse) was studied when delivered in a liposomal suspension intratracheally to treat the lung adenoma of BXB-23 mice. The data of this experiment demonstrated that sorafenib intratracheal instillation resulted in a reduction of tumor area of adenoma foci (67 %) and an elevation of the percent of apoptotic cells. In contrast, prolongation of the treatment period did not further enhance sorafenib activity on the lung adenoma. This previous finding suggested a development of multidrug resistance (MDR) by the adenoma foci cells against sorafenib instillation, which was examined by immunohistochemistry staining. The percent of MDR positive cells was higher after two and three weeks sorafenib liposome instillation treatment than that after one week treatment. The last dosage form used for sorafenib was microspheres, which were prepared by emulsion-diffusion-evaporation method using biodegradable PLGA 50:50 resulting in a white lyophilized powder. The system was characterized physicochemically and revealed a good microspheres yield, high encapsulation efficiency, a homogenous particle size distribution and slow in vitro release of sorafenib. The other strategy studied in the present research project was gene delivery to target the lung bearing tumor of BXB-23 mice using a non-viral vector (polyethylenimine). Polyethylenimine (PEI) was used to investigate its efficiency in transfecting lung bearing tumor of BXB-23 mice model and its ability to transfect the adenoma foci cells. LacZ, which encodes Beta-galactosidase was used in the present study as a reporter gene and was complexed with PEI before delivered intravenously. A high LacZ expression in the alveolar region with some expression in the adenoma foci was observed. On contrary, a low LacZ expression in the alveoli and in the adenoma foci was achieved after instillation of the same polyplex intratracheally.
The work presented in this thesis was mainly targeted at exploring the capabilities of evaporation based LC detectors as well as further alternatives for the control of impurities in substances not exhibiting a suitable chromophore for UV-detection. In the course of the work carried out, several new methods for the identification, impurities control and composition testing of APIs were elaborated. An evaporation based detector that entered into the field of pharmaceutical analysis in the recent years was the Evaporative Light Scattering Detector (ELSD). However, non-reproducible spikes were reported when injecting concentrated test solutions as they are usually required for the control of impurities. The reasons, for the appearance of these spikes as well as possibilities for their avoidance were explored in a systematic study. Moreover, the dependence of the detector sensitivity on different eluent composition, eluent flow-rate and ELSD settings was investigated. In the course of the revision of the Ph.Eur. monographs for aspartic acid and alanine, a C18 reversed phase ion-pair LC method using 1 mmol/L of perfluoroheptanoic acid as an ion-pair reagent and a charged aerosol detector (CAD) was developed and fully validated for the purity control of Asp. The method was capable of separating the organic acids and major amino acids known to occur as process related impurities. With a slight modification, the method was also applicable for the purity control of Ala. Based on the developed LC-CAD method for the impurity control of alanine, a comparative study of the performance characteristics of different evaporation based LC detectors, i.e. ELSD, CAD and the recently developed Nano Quantity Analyte Detector (NQAD) was carried out. Additionally, an MS detector and qNMR were included in this study. It was found that the control of impurities in Alanine at an ICH conform level could be ensured using LC coupled to CAD, MSD and NQAD detection as well as by the use of qNMR. In terms of performance, prize and ease of use CAD and NQAD were found to be the most suitable alternatives. In terms of repeatability and sensitivity, the CAD appeared slightly superior to the NQAD. The quality of streptomycin sulfate is not sufficiently controlled by the current Ph.Eur. monograph in that an appropriate test for the control of the related substances is missing. A study was carried out to develop a C18 reversed phase ion-pair LC method using pentafluoropropionic acid as an ion-pair reagent and a CAD for the identification and control of the related substances. The developed method allowed the separation of 21 impurities from streptomycin. Moreover, coupling of the method to MS allowed the identification of the separated impurities. The method was shown to be sufficiently sensitive to control the related substances with a disregard limit of 0.1% as it is normally applied in the Ph.Eur. for products derived from fermentation. Currently, the aescin content of horse-chestnut standardized dry extract is determined using a complex and laborious photometric determination. A more selective LC-UV assay determination for beta-aescin has been proposed for the Ph.Eur. draft monograph of horse-chestnut standardized dry extract. Possibilities were explored to further improve the LC-method using detection by CAD. It was demonstrated that by the use of a modified LC-CAD method several problems related to the differences in the UV-response of the various components contained in the active aescin fraction could be eliminated. Moreover the proposed reference standard strategy was reviewed. Eventually, it was demonstrated on the example of two different clusters of pharmacologically active peptides how low energy collision induced dissociation mass spectrometry (low energy CID-MS) can successfully be used for identification testing in pharmacopoeial monographs. In this respect, the combination of a direct confirmation of the molecular mass via the m/z-ratio of the molecule ions with structural sequence information obtained by low energy CID-MS experiments was found to deliver a higher degree of certainty of the identity of a given substance than the set of tests currently described in the monographs. A significant gain in efficiency and throughput and important reduction of the amount of sample consumed during testing were identified as being additional advantages of this approach. Taken together, it could be demonstrated on various examples how recent technological advancements in the field of analytical chemistry can contribute to improve the quality control of APIs.
Synthesis of (RS)-5-amino-3-aryl (methyl)-pentanoic acid hydrochlorides, 3 aminomethyl-5-chloro-benzoic acid hydrochloride and (RS)-4-amino-3-(4`-ethynyl(iodo)-phenyl)-butanoic acid hydrochlorides have been accomplished. The aim of their synthesis was to evaluate their GABABR agonist activity and to derive a model which will correlate their structure with the observed pEC50. The GABABR agonist activity of the prepared compounds has been determined in functional assay based on calcium measurement in vitro using tsA cells transfected with GABAB1b/GABAB2/Gαq-z5. Reviews on the neurotransmitter receptors (ligand-gated ion channel receptors and G protein-coupled receptors), their agonists and antagonists have been given in the general part of this work. A detailed discussion on the strategy followed for the synthesis of the designed compounds as well as the starting materials and intermediates has been described and illustrated in Schemes 2-6. The synthesized compounds were evaluated for their GABABR agonist activity. Furthermore, these compounds were docked in the available 3D homology model of GABABR using the program FlexiDock implemented in SYBYL software. Subsequently, we derived a predictive model which correlates the experimentally determined pEC50 with the calculated binding energy of certain baclofen analogues and homologues. In addition, we used the program DISCO (DIStance COmparisons) implemented in SYBYL software to find the pharmacophore features of GABAB agonists.
Starting in the late 1990s ionic liquids (ILs) gained momentum both in academia as well as industry. ILs are defined as organic salts with a melting point below 100 °C. Active pharmaceutical ingredients (APIs) may be transferred into ILs by creating salts with a bulky counterion with a soft electron density. ILs have demonstrated the potential to tune important pharmaceutical features such as the solubility and the dissolution rate, particularly addressing the challenge of poor water soluble drugs (PWSD). Due to the tunability of ILs, modification of physico-chemical properties of APIs may be envisioned without any modifications of the chemical structure.
In the first chapter the potential as well as the limitation of ILs are discussed. The chapter commences with an overview of preparation and characterization of API-ILs. Moreover, examples for pharmaceutical parameters are presented which may be affected by IL formation, including the dissolution rate, kinetic solubility or hygroscopicity as well as biopharmaceutical performance and toxicology. The impact of IL formation on those pharmaceutically relevant features is highlighted, resulting in a blueprint for a novel formulation concept to overcome PWSD challenges without the need for structural changes of the API.
Within the second chapter the IL concept is detailed for one specific API - counterion combination. A poorly water soluble acidic API against migraine attacks was transformed into an IL in an effort to minimize the time to maximum plasma concentration (tmax) and optimize the overall bioavailability. These studies were conducted in parallel to a prodrug of the API for comparison of the IL strategy versus a strategy involving modification of the API’s structure. A significantly longer duration of API supersaturation and a 700 fold faster dissolution rate of the IL in comparison to the free acid were obtained and the underlying mechanism was elucidated. The transepithelial absorption was determined using Caco-2 cell layers. For the IL about 3 times more substance was transported in comparison to the prodrug when substances were applied as suspensions, despite the higher permeability of the prodrug, as increased solubility of the IL exceeded this effect. Cytotoxicity of the counterion was assessed in hepatic, renal and macrophage cell lines, respectively, and IC50 values were in the upper µM / lower mM range. The outcome of the study suggested the IL approach instrumental for tuning biopharmaceutical properties, without structural changes of the API as required for preparation of prodrugs. Thus the toolbox for formulation strategies of poorly water soluble drugs could be extended by an efficient concept.
The third chapter focuses on the effect of different counterions on the physico-chemical properties of an API-IL, in particular to overcome the challenge of poor water solubility. Therefore, the same poorly water soluble acidic API against migraine attacks mentioned above was combined with 36 counterions resulting in ILs and low lattice enthalpy salts (LLES). Depending on the counterions, different dissolution rates, durations of supersaturation and hygroscopicities were obtained and release profiles could be tailored from immediate to sustained release. Besides, in vitro the cytotoxicity of the counterions was assessed in three cell lines. Using molecular descriptors such as the number of hydrophobic atoms, the graph theoretical diameter and the number of positive charges of the counterion, the dissolution rate, supersaturation and hygroscopicity as well as the cytotoxicity of counterions could be adequately modeled, rendering it possible to predict properties of new LLESs.
Within the forth chapter different poorly water soluble APIs were combined with the counterion tetrabutylphosphonium (TBP) studying the impact on the pharmaceutical and physical properties of the APIs. TBP-ILs and low lattice enthalpy salts were prepared of the acidic APIs Diclofenac, Ibuprofen, Ketoprofen, Naproxen, Sulfadiazine, Sulfamethoxazole and Tolbutamide. NMR and IR spectroscopy, DSC, XRPD, DVS and dissolution rate measurements, release profiles and saturation concentration measurements were used to characterize the free acids and TBP salts as compared to the corresponding sodium salts. The TBP salts as compared to the free acids displayed lower melting points and glass transition temperatures and up to 1000 times higher dissolution rates. The increase in the dissolution rate directly correlated with the salts’ hygroscopicity, an aspect which is critically discussed in terms of pharmaceutical translation challenges. In summary TBP ILs of solid salts were proved instrumental to approach the challenge of poor water solubility. The outcome profiled tailor-made counterions as a powerful formulation strategy to address poor water solubility, hence bioavailability and ultimately therapeutic potential of challenging APIs.
In summary, a plethora of ILs and LLESs were prepared by combination of different acidic APIs and counterions. The IL and LLESs concept was compared to conventional salt and prodrug strategies. By choice of the counterion, biopharmaceutical relevant parameters were deliberately modified and release profiles were tuned ranging from immediate to prolonged release. The impact of distinct structural counterion features controlling the dissolution, supersaturation, hygroscopicity and counterion cytotoxicity were identified, correlations were presented and predictive models were built. ILs and LLESs could be proven to be a powerful concept for the formulation of poorly water soluble acidic APIs.
Spectroscopic methods were established decades ago in a wide variety of fields. This also applies to the pharmaceutical field, although they initially were mostly used for identity testing or structure elucidation only. Technical developments, such as miniaturization (NMR benchtop devices), Fourier transformations (for NMR, MIR spectroscopy) or the combination with chemometric evaluation (e.g., in Process Analytical Technology, PAT), have further increased their importance and opened up new applications. The aim of this work was to investigate further new approaches and to find new applications for already established methods and to show their benefits.
By means of MIR, NIR and NMR data and their chemometric evaluation (principal component analysis, PCA; hierarchical cluster analysis, HCA; linear discriminant analysis, LDA), possibilities were presented to successfully determine the manufacturer or the pharmaceutical company of various paracetamol preparations. In the course of this, various similarities and correlations between the preparations of individual companies could also be identified. For this purpose, a suitable sample preparation was developed for each spectroscopic method, and suitable measurement parameters in order to obtain reproducible spectra for the chemometric evaluation were determined. Furthermore, the results of the two unsupervised methods (HCA, PCA) were compared with each other. The HCA was able to confirm those of the PCA for the very most part. Additionally, through these methods it was possible to characterize many of the preparations based on clusters formed by comparable tablet compositions.
In order to be able to measure unmortared, whole tablets using the NIR spectrometer, an attachment was developed and manufactured using 3D printing. Its functionality was demonstrated by measuring and analyzing the tablets of two different batches of nine paracetamol preparations. The batches were clearly distinguished on the basis of a PCA and a significant difference was also demonstrated by means of statistical tests.
For NMR spectroscopy, a method was developed to obtain optimized "fingerprint" spectra of drug formulations. For this purpose, a 1D DOSY measurement was elaborated, in which the signals of the active ingredient could be filtered out by the appropriate choice of measurement parameters. The chemometric evaluation can thus focus on the remaining signals of the excipients, on the basis of which the preparations of the same API can be distinguished. Especially in the case of formulations that consist largely of active ingredient, data pre processing of the spectra can thus be simplified and greater importance can be assigned to the originally very small excipient signals.
A quantitative 1H NMR method was developed for the comparison of a high field spectrometer (400 MHz) with a benchtop spectrometer (80 MHz) for two finished drugs. It was shown that it is possible to obtain comparable results with both instruments, but that the influence of the excipients on the signals and the lower resolution of the benchtop instrument must be taken into account. Therefore, it was not possible to obtain comparable results without further optimization of the method for one of the active ingredients.
In the investigation of various reactions between APIs and excipients using DOSY, its usefulness as a screening method in stability testing was demonstrated. For this purpose, three different APIs and excipients were stressed together and the reaction mixtures were subsequently measured using DOSY. Based on the translational diffusion coefficient, the reaction products could be identified and distinguished from the active ingredients and the excipients used. The importance of thoughtful processing could also be demonstrated. If all peak heights are selected when evaluating signals split by direct spin spin coupling, this allows the detection of hidden signals as long as not all signals have the same diffusion coefficient. The selective selection of individual peak heights in the case of split signals also enables the evaluation of signals that overlap slightly. However, the limitations of this method were also shown when two signals overlap too much and differ too little in their diffusion coefficients.
Hence, it has been successfully demonstrated in the various projects that the new chemometric approaches, as well as the new applications of already established methods, enable in depth findings and thus have a clear added value.
Development of Novel Quinolone Amides Against the African Sleeping Sickness - A Fluorine Walk
(2019)
In recent years the transmission of the Human African Trypanosomiasis could be significantly reduced. The reported cases in 2016 reached a historic low level of 2184 cases and these achievements can be ascribed to intense control and surveillance programmes.118 However, most of the reported cases (>1000 in 2015) occurred in the Democratic Republic of the Congo and thus, need to be treated adequately. In particular, when the parasites have traversed the blood-brain barrier (BBB), treatment proved to be even more difficult. In addition, the number of cases always came in waves due to many reasons, e.g., development of resistances. Thus, it can be expected from experiences of the past that the number of cases will increase again. Hence, novel chemical entities are desperately needed in order to overcome the drawbacks which are associated with the current treatment options.
Our drug discovery approach included an initial drug repurposing strategy combined with a phenotypic screening. S. Niedermeier found novel active compounds derived from commercial fluoroquinolones. The most promising hit compound was further developed by G. Hiltensperger resulting in the lead quinolone amide GHQ168 (IC50 = 0.047 µM).
This doctoral thesis is about new insights into the SAR of the quinolone amides and the enhancement of the lead compound. Special consideration was given to the fluorine atom in the quinolone amides and how certain fluorine substitution patterns influence the antitrypanosomal activity, physicochemical properties and pharmacokinetics (i.e. ‘fluorine walk’). Moreover, the ability of the compound class crossing the BBB should be investigated. This feature is inevitable necessary in order to potentially treat African sleeping sickness stage II.
The Gould-Jacobs protocol was predominantly used for the synthesis of the quinolone core. Since former SAR studies mainly concentrated on the variation in positions 1, 3 and 7, quinolone scaffolds (2a-i) with diverse substitution patterns regarding positions 5, 6, 7 and 8 were synthesised in this thesis. The resulting quinolone amides were evaluated for their antitrypanosomal activity.
Voluminous residues in position C-5 resulted in diminished activities (compounds 13, 16 and 18) and solely small-sized moieties were tolerated. In particular the fluorine atom in position 5 revealed beneficial trypanocidal effects as shown for compounds 6 (IC50 = 0.05 µM), 8 (IC50 = 0.04 µM), and 24 (IC50 = 0.02 µM). Furthermore, having fluorine only in position 5 of the quinolone core could considerably reduce the cytotoxic effects (CC50 >100 µM, SI = >2000 for 6). Hence, the 5-fluoro-substituted quinolone amides were considered superior to GHQ168.
Regarding the C-6 position all other moieties (e.g., H in 9, OCH3 in 10, CF3 in 12) except of a fluorine atom decreased the activity against Trypanosoma brucei brucei. A double fluorination in C-6 and C-8 was not beneficial (IC50 = 0.06 µM for 7) and a single fluorine atom in C-8 even showed a negative effect (IC50 = 0.79 µM for 5).
The logP value is considered a surrogate parameter for lipophlicity and thus, affecting permeability and solubility processes. In particular the fluorine atom influences the lipophilicity due to versatile effects: Lipophilicity is increased by additional fluorine atoms on aromatic rings (7, 23) and reduced by fluorine atoms at an alkyl chain (49), respectively. Additionally, the 5-fluoro-substituted quinolone amides (6, 8, and 24) could prove the contrary effect of decreasing lipophilicity when the aromatic fluorine substituent is in vicinity to a carbonyl group.
For the most promising drug candidates 6, 23, and 24 the respective metabolites and the metabolic turnover were investigated by C. Erk. In comparison to GHQ168 the hydroxylation of the benzylamide was prevented by the para-fluorine atom. Hence, half-life was extended for compound 23 (t1/2 = 6.4 h) and N-desalkylation was the predominant pathway. Moreover, the respective fluorine substitution pattern of the quinolone core affected the metabolism of compound 6. The 5-fluoro-substituted quinolone amide was less prone for biotransformation (t1/2 = 7.2 h) and half-life could even be further prolonged for compound 24 (t1/2 = 7.7 h).
Due to the most appropriate safety profile of compound 6, this particular drug candidate was considered for in vivo study. Its poor solubility made a direct intraperitoneal administration unfeasible. Thus, an amorphous solid dispersion of 6 was generated using the spray-drying method according to the previous protocol. Unfortunately, the required solubility for the predicted in vivo study was not achieved.
Furthermore, the compound class of the quinolone amide was evaluated for its ability for brain penetration. The methanesulfonyl precursor 48 was synthesised and subsequently radiofluorinated in the group of Prof. Dr. Samnick (Department of Nuclear Medicine, University Hospital of Würzburg). The labelled compound [18F]49 was administered to mice, and its distribution throughout the body was analysed using positron emission tomography and autoradiography, respectively. The autoradiography of the murine brains revealed medium to high concentrations of [18F]49. Therefore, the quinolone amides are generally suitable for treating Human African Trypanosomiasis stage II.
A scaffold hopping approach was performed starting from the quinolone amides and concluding with the compound class of pyrazoloquinolin-3-ones. The intramolecular hydrogen bond between the sec. amide and the C-4 carbonyl moiety was replaced by a covalent bond. The two compound classes were comparable regarding the antitrypanosomal activity to some degree (IC50 = 7.9 µM (EK02) vs. 6.37 µM (53a)). However, a final evaluation of 59 was not possible due to poor solubility.
Progressive loss of skeletal muscle mass, strength and function poses a major threat to independence and quality of life, particularly in the elderly. To date, sarcopenia therapy consists of resistance exercise training in combination with protein supplementation due to the limited efficacy of available pharmacological options in counteracting the effects of muscle wasting. Therapeutic intervention with growth factors including insulin-like growth factor I (IGF-I) or inhibitors of myostatin a potent suppressor of myogenesis hold potential to rebalance the altered activity of anabolic and catabolic cytokines. However, dosing limitations due to acute side effects and disruptions of the homeostasis have so far precluded clinical application.
Intending to provide a therapy with a superior safety and efficacy profile by directing drug release to inflamed tissue and minimizing off-target activity, we designed bioresponsive delivery systems for an anti-catabolic peptide and anabolic IGF-I responding to local flares of muscle wasting.
In Chapter I, current concepts for bioorthogonal conjugation methods are discussed and evaluated based on various drug delivery applications. With a focus on protein delivery, challenges and potential pitfalls of each chemical and enzymatic conjugation strategy are analyzed and opportunities regarding their use for coupling of biomolecules are given. Based on various studies conjugating proteins to polymers, particles and biomaterials using different site-directed approaches, the chapter summarizes available strategies and highlights certain aspects requiring particular consideration when applied to biomolecules. Finally, a decision process for selection of an optimum conjugation strategy is exemplarily presented.
Three of these bioorthogonal coupling reactions are applied in Chapter II detailing the potential of site-directed conjugation in the development of novel, homogenous drug delivery systems. The chapter describes the design of a delivery system of a myostatin inhibitor (MI) for controlled and local release counteracting myositis flares. MI release from the carrier is driven by increased matrix metalloproteinase (MMP) levels in compromised muscle tissues cleaving the interposed linker, thereby releasing the peptide inhibitor from the particulate carrier. Release experiments were performed to assess the response towards various MMP isoforms (MMP-1, -8, -9 and -13) – as upregulated during skeletal muscle myopathies – and the release pattern of the MI in case of disease progression was analyzed. By selection of the protease-sensitive linker (PSL) showing variable susceptibilities to proteases, release rates of the MI can be controlled and adapted. Immobilized MI as well as released MI as response to MMP upregulation was able to antagonize the effects of myostatin on cell signalling and myoblast differentiation.
The approach of designing bioresponsive protein delivery systems was also applied to the anabolic growth factor IGF-I, as described in Chapter III. Numerous studies of PEGylated proteins or peptides reveal, that successful therapy is challenged by safety and efficacy issues, as polymer attachment considerably alters the properties of the biologic, thereby jeopardizing clinical efficacy. To this end, a novel promising approach is presented, intending to exploit beneficial effects of PEGylation on pharmacokinetics, but addressing the pharmacodynamic challenges by releasing the protein upon entering the target tissue. This was realized by integration of a PSL between the PEG moiety and the protein. The soluble polymer conjugate was produced by site-directed, enzymatic conjugation of IGF-I to the PSL, followed by attachment of a 30 kDa-PEG using Strain-promoted azide-alkyne cycloaddition (SPAAC). This strategy illustrates the potential of bioorthogonal conjugation (as described in Chapter I) for generation of homogenous protein-polymer conjugates with reproducible outcome, but also emphasizes the altered protein properties resulting from permanent polymer conjugation. As compared to wild type IGF-I, the PEGylated protein showed considerable changes in pharmacologic effects – such as impaired insulin-like growth factor binding protein (IGFBPs) interactions, submaximal proliferative activity and altered endocytosis patterns. In contrast, IGF-I characteristics were fully restored upon local disintegration of the conjugate triggered by MMP upregulation and release of the natural growth factor.
For successful formulation development for the proteins and conjugates, the careful selection of suitable excipients is crucial for a safe and reliable therapy. Chapter IV addresses one aspect by highlighting the chemical heterogeneity of excipients and associated differences in performance. Polysorbate 80 (PS80) is a surfactant frequently used in protein formulations to prevent aggregation and surface adsorption. Despite being widely deployed as a standard excipient, heterogeneous composition and performance entails the risk of eliciting degradation and adverse effects on protein stability. Based on a comprehensive study using different batches of various suppliers, the PS80 products were characterized regarding chemical composition and physicochemical properties, facilitating the assessment of excipient performance in a formulation. Noticeable deviations were recorded between different suppliers as well as between batches of the same suppliers. Correlation of all parameters revealed, that functionality related characteristics (FRCs) could be reliably predicted based on chemical composition alone or by a combination of chemical and physicochemical properties, respectively.
In summary, this thesis describes and evaluates novel strategies for the targeted delivery and controlled release of biologics intended to counteract the imbalance of anabolic and catabolic proteins observed during aging and musculoskeletal diseases. Two delivery platforms were developed and characterized in vitro – (i) using anti-catabolic peptides immobilized on a carrier for local delivery and (ii) using soluble IGF-I polymer conjugates for systemic application. Both approaches were implemented by bioorthogonal coupling strategies, which were carefully selected in consideration of limitations, side reactions and efficiency aspects. Bioresponsive release of the active biomolecules following increased protease activity could be successfully realized. The therapeutic potential of these approaches was demonstrated using various cell-based potency assays. The systems allow targeted and controlled release of the growth factor IGF-I and anti-catabolic peptides thereby overcoming safety concerns of current growth factor therapy and thus positively impacting the benefit-risk profile of potent therapeutics. Taking potential heterogeneity and by-product concerns into account, comprehensive excipient characterization was performed and a predictive algorithm for FRCs developed, in order to facilitate formulation design and guarantee a safe and efficient therapy from start to finish.
Background: Population pharmacokinetic-pharmacodynamic (PKPD) modeling and simulations were applied to identify optimal dosage regimens for antibiotics. As the emergence of bacterial resistance is increasing and as only a few new antibiotics became available during the last decade, optimal use of established agents and preserving their effectiveness seems vital. Objectives: 1) To find the descriptor of body size and body composition which allows to achieve target concentrations and target effects in patients with cystic fibrosis (CF) most precisely. 2) To identify the mode of administration with the highest probability of successful treatment for intravenous beta-lactams. 3) To develop formulas for optimal dose selection for patients of various body size. General methods: Drug analysis in plasma and urine was performed by HPLC or LC-MS/MS in a single laboratory, at the IBMP. Drug analysis was not done by the author of this thesis. We used non-compartmental analysis and parametric population PK analysis for all studies. We used non-parametric bootstrapping to assess the uncertainty of PK parameters for our meta-analysis of the PK in CF-patients and healthy volunteers. Plasma concentration time profiles for several thousand virtual subjects were simulated by MCS which account for average PK parameters, their between subject variability (BSV), and patient specific demographic data. Convincing literature data show that the duration of non-protein bound concentration above MIC (fT>MIC) best predicts the microbiological and clinical success of beta-lactams and the area under the non-protein bound concentration curve divided by the MIC (fAUC/MIC) best predicts success for quinolones. We used PKPD targets from literature that were based on the fT>MIC or fAUC/MIC, respectively. Achieving a PKPD target was used as a surrogate measure for successful treatment. In our MCS, we calculated the fT>MIC or fAUC/MIC for all simulated concentration profiles and compared it to the value of the PKPD target. The fraction of subjects who achieved the target at the respective MIC approximates the probability of target attainment (PTA). The PTA can be interpreted as probability of successful treatment under certain assumptions. Studies in CF-patients Methods: We had data from ten studies (seven beta-lactams and three quinolones) in CF-patients which all included a healthy volunteer control group. Clinical procedures were very similar for all ten studies. Both subject groups had study conditions as similar as possible. We had data on 90 CF-patients (average +/- SD, age: 21+/-3.6 yrs) and on 111 healthy volunteers (age: 25+/-3.5 yrs). We compared the average clearance and volume of distribution between CF-patients and healthy volunteers for various body size descriptors including total body weight (WT), fat-free mass (FFM), and predicted normal weight (PNWT). We considered linear and allometric scaling of PK parameters by body size and used a meta-analysis based on population PK parameters for the comparison of CF-patients and healthy volunteers. Target concentrations can be achieved more precisely, if a size descriptor reduces the random, unexplained BSV. Therefore, we studied the reduction of unexplained BSV for each size descriptor relative to linear scaling by WT, since doses for CF-patients are commonly selected as mg/kg WT. Results: Without accounting for body size, average total clearance was 15% lower (p=0.005) and volume of distribution at steady-state was 17% lower (p=0.001) in CF-patients compared to healthy volunteers. For linear scaling by WT, average total clearance in CF-patients divided by total clearance in healthy volunteers was 1.15 (p=0.013). This ratio was 1.06 (p=0.191) for volume of distribution. A ratio of 1.0 indicates that CF-patients and healthy volunteers of the same body size have identical average clearances or volumes of distribution. For allometric scaling by FFM or PNWT, the ratio of total clearance and volume of distribution between CF-patients and healthy volunteers was within 0.80 and 1.25 for almost all drugs and the average ratio was close to 1. Allometric scaling by FFM or PNWT reduced the unexplained BSV in renal clearance by 24 to 27% (median of 10 drugs) relative to linear scaling by WT. The unexplained BSV was reduced for seven or eight of the ten drugs by more than 15% and the remaining two or three drugs had essentially unchanged (+/-15%) unexplained BSVs in renal clearance. Conclusions: The PK in CF-patients was comparable to the PK in healthy volunteers after accounting for body size and body composition by allometric scaling with FFM or PNWT. Target concentrations and target effects in CF-patients can be achieved most precisely by dose selection based on an allometric size model with FFM or PNWT. Future studies are warranted to study the clinical superiority of allometric dosing by FFM or PNWT compared to dose selection as mg/kg WT in CF-patients.
Estrogens, namely 17β-estradiol (E2) and estrone (E1) are considered to play an important role in the initiation and promotion of breast cancer (summarized in Raftogianis et al., 2000), a malignancy responsible for around 500,000 deaths per year (summarized in Ghislain et al., 2016). Two major mechanisms have been postulated to explain the carcinogenic effects of estrogens: (1) the estrogen receptor-mediated stimulation of breast cell proliferation with a concomitant enhanced rate of mutations and (2) the metabolism of hydroxylated estrogens to quinone derivatives which can react with the DNA (Russo and Russo, 2006, summarized in Yager and Davidson, 2006). Nevertheless, as a detoxifying mechanism, E1, E2, and their hydroxylated and methoxylated metabolites are reversibly conjugated into sulfates and glucuronides devoid of biological activity (summarized in Guillemette et al., 2004). Yet, despite the key detoxifying function of these conjugates, the study of their circulating levels face some significant problems: (1) analysis by techniques such as radioimmunoassay lack specificity and accuracy and requires enzymatic/chemical hydrolysis before analysis, being unable to differentiate between sulfates and glucuronides (summarized in Stanczyk et al., 2007, summarized in Wang et al., 2016), (2) very little knowledge in healthy women, which has been identified as a barrier to advance in breast cancer research (summarized in Liu, 2000), and (3) far fewer studies in pre- than in postmenopausal women (summarized in Samavat and Kurzer, 2015). Therefore, to get more insights into the research of breast cancer etiology and prevention, the analysis of circulating levels of estrogens (including metabolites and conjugates) in women without breast cancer through reliable analytical techniques, is required.