Natascha Drude

A nondestructive, statistical method for determination of initiation efficiency: dipentaerythritol-aided synthesis of ternary ABC3 miktoarm stars using a combined “arm-first” and “core-first” approach

The preparation of miktoarm stars, based on poly(ethylene oxide) (PEO), poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) and either poly(propylene oxide) (PPO) or poly(ethyl glycidyl ether) (PEGE), is described. Hereby, partly protected dipentaerythritol (dipentaerythritoldiacetonide) is used as a bifunctional alcohol in a polymer-based Williamson ether synthesis to become the core of the star. Mesylated PEO is reacted first with excess dipentaerythritoldiketal. This ensures full modification of the PEO with one telechelic dipentaerythritol moiety. This telechelic PEO with one hydroxyl function is then converted to a diblock copolymer with the dipentaerythritol unit at the junction point between the blocks. To achieve this, two pathways have been developed: (a) by reaction with ready-prepared, mesylated PPO and (b) by ring-opening, anionic polymerization of ethyl glycidyl ether, leading to a narrow dispersed block copolymer. The advantages and disadvantages of both routes are discussed, though both provide perfect scaffolds for further polymer grafting. This is achieved by mild deprotection of both diblocks in order to yield 4 hydroxyl functions at the core of the future star. After attachment of an initiator, atom transfer radical polymerization (ATRP) is used to grow up to 4 arms of PDMAEMA from the center of each diblock copolymer. Thus, (PEO)–(PDMAEMA)k–(PPO) or (PEO)–(PDMAEMA)k–(PEGE) heteroarm stars are prepared by a combined “arm-first” and “core-first” method. The molecular characterization is accompanied by NMR, size exclusion chromatography (SEC), osmometry and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI ToF MS). The latter method even allows an estimation of the initiation site efficiency during ATRP. In turn, the final molecular formula of the stars can be derived. We illustrate that a decreased initiation site efficiency generates a specific footprint in the molecular weight distribution, which could be partly reproduced by MALDI ToF MS. By comparing the simulated spectra with the real ones, one can draw conclusions on the initiation site efficiency. The obtained initiation site efficiency is found to be comparable to the one obtained by the standard destructive method: determination of molecular weight of cleaved arms, which is tedious and polymer-consuming. Therefore, it is anticipated that both the synthetic procedures as well as the analytics can be easily adapted to other polymers.

Synthesis, radiosynthesis and in vitro evaluation of 18F-Bodipy-C16/triglyceride as a dual modal imaging agent for brown adipose tissue

Background Brown adipose tissue research is in the focus in the field of endocrinology. We designed a dual-modal fluorescent/PET fatty acid based tracer on commercially available Bodipy-C16, which can be synthesized to its corresponding triglyceride and which combines the benefits of fluorescent and PET imaging. Methods Bodipy-C16 was coupled to 1,3-diolein resulting in Bodipy-triglyceride. Bodipy-C16 and Bodipy-triglyceride compounds were radiolabeled with 18F using an 18F/19F exchange reaction to yield a dual-modal imaging molecule. Uptake of radiolabeled and non-labeled Bodipy-C16 and Bodipy-triglyceride was analyzed by fluorescence imaging and radioactive uptake in cultured adipocytes derived from human brown adipose tissue and white adipose tissue. Results Bodipy-C16 and Bodipy-triglyceride were successfully radiolabeled and Bodipy-C16 showed high shelf life and blood plasma stability (99% from 0–4 h). The uptake of Bodipy-C16 increased over time in cultured adipocytes, which was further enhanced after beta-adrenergic stimulation with norepinephrine. The uptake of Bodipy-C16 was inhibited by oleic acid and CD36 inhibitor sulfosuccinimidyl-oleate. The poor solubility of Bodipy-triglyceride did not allow stability or in vitro experiments. Conclusion The new developed dual modal fatty acid based tracers Bodipy-C16 and Bodipy-triglyceride showed promising results to stimulate further in vivo evaluation and will help to understand brown adipose tissues role in whole body energy expenditure.

Theranostic and nanotheranostic probes in nuclear medicine

In nuclear medicine, a theranostic probe describes a substance that combines diagnostic and therapeutic capabilities by radiolabeling it with different radionuclides. Next to a brief description of the different emitters (α, β+, β-, γ) used for imaging and/or therapy, the aim of this review is to summarize the most commonly used theranostic probes in nuclear medicine. Another goal is to give an idea which chemical requirements need to be fulfilled for radiolabeling with either therapeutic and/or diagnostic relevant nuclides. Furthermore, a perspective is given into the field of nanotheranostics which is gaining more and more attention in nuclear medicine. The combination has been called radionanomedicine and is a very proliferative field with an enormous potential.

Multistage Passive and Active Delivery of Radiolabeled Nanogels for Superior Tumor Penetration Efficiency

Development of nanosized drug delivery systems in cancer therapy is directed toward improving tumor selectivity and minimizing damages of healthy tissue. We introduce a delivery system with synergistic optimization and combination of passive and active targeting strategies. The approach is based on radiopeptide labeled redox sensitive hydrophilic nanogels, which exploit passive targeting by the enhanced permeability and retention effect while avoiding elimination by the mononuclear phagocyte system and fast hepatic and renal clearance. The targeting peptide promotes endocytotic uptake of the nanogels by cancer cells. Specific to this delivery system, tumor-specific degradation by the antioxidant glutathione enhances penetration and retention within the tumor tissue. Using in vivo molecular imaging we demonstrate the superiority of combined passive and active targeting with down-sizable nanogels over exclusive passive targeting. Furthermore, the homogeneous tumor distribution of functionalized nanogels compared to the clinically used mere radiopeptide supports the potentially high impact of our targeting concept.

PSA levels, PSA doubling time, Gleason score and prior therapy cannot predict measured uptake of [68Ga]PSMA-HBED-CC lesion uptake in recurrent/metastatic prostate cancer

AIM To assess whether clinical prostate cancer (PCA) related factors and therapy status can predict the degree of tracer uptake on [68Ga]PSMA-HBED-CC PET/CT. MATERIALS & METHODS We retrospectively studied 124 patients with recurrent an/or metastatic PCA who underwent [68Ga]PSMAHBED-CC PET/CT. The maximum standardized uptake value (SUVmax) was determined in the prostate bed as well as in three size categories (≤ 5 mm, > 5-15 mm, > 15 mm) in pelvic lymph node, extrapelvic lymph node, bone and visceral metastases. RESULTS Significant positive correlations between lesion size and SUVmax were found in pelvic lymph node metastases > 5 -≤15 mm (Spearmans rho = 0.502, p = 0.002) as well as in extrapelvic lymph node metastases5 mm (rho = 0.314, p = 0.033) and > 5 ≤-15 mm (rho = 0.614, p < 0.001). SUVmax tended to be higher in the largest diameter category in each anatomic station than in the middle and lower categories. We were unable to find evidence for a relationship between SUVmax and PSA, PSAdt, Gleason score, androgen deprivation therapy, radiation therapy or chemotherapy status. CONCLUSION Measured tracer uptake in [68Ga]PSMA-HBED-CC PET/CT in patients with recurrent/metastasized prostate cancer is significantly influenced by lesion size as a result of partial volume effects in the very small lesions. Clinical indicators of aggressive prostate cancer behaviour such as PSA levels, PSA doubling time or the Gleason score of the primary tumour, as well as the androgen deprivation therapy, radiation therapy or chemotherapy status are not related to measured tracer uptake. ZIEL:: Beantwortung der Frage ob klinisch bestimmbare Faktoren und Therapiestatus bei Prostatakarzinom (PCA) eine Vorhersage zur Traceranreicherung in [68Ga]PSMA-HBED-CC PET/CT liefern können.Material & Methoden: 124 Patienten mit rezidiviertem und/oder metastasiertem PCA die [68Ga]PSMA-HBED-CC PET/CT untergingen, wurden retrospektiv untersucht. Der maximum Standardized Uptake Value (SUVmax) wurde in der Prostataloge gemessen sowie in drei Größen-Kategorien ( 5 mm, > 5-15 mm, > 15 mm) in Metastasen in den pelvinen Lymphknoten-, extrapelvinen Lymphknoten-, Knochen- und viszeralen Metastasen. ERGEBNISSE Signifikant positive Korrelationen zwischen Läsionsgröße und SUVmax wurden in pelvinen Lymphknotenmetastasen > 5 -≤15 mm (Spearmans rho = 0.502, p = 0.002), extrapelvinen Lymphknotenmetastasen5 mm (rho = 0.314, p = 0.033) und > 5 -≤15 mm (rho = 0.614, p < 0.001) gefunden. Für jede anatomische Lokalisation wurde ein höherer Wert SUVmax innerhalb der größten Kategorie verglichen zu mittleren und kleinsten Kategorie gefunden.

The reconstruction algorithm used for [68Ga]PSMA-HBED-CC PET/CT reconstruction significantly influences the number of detected lymph node metastases and coeliac ganglia

PurposeTo investigate whether the numbers of lymph node metastases and coeliac ganglia delineated on [68Ga]PSMA-HBED-CC PET/CT scans differ among datasets generated using different reconstruction algorithms.MethodsData were constructed using the BLOB-OS-TF, BLOB-OS and 3D-RAMLA algorithms. All reconstructions were assessed by two nuclear medicine physicians for the number of pelvic/paraaortal lymph node metastases as well the number of coeliac ganglia. Standardized uptake values (SUV) were also calculated in different regions.ResultsAt least one [68Ga]PSMA-HBED-CC PET/CT-positive pelvic or paraaortal lymph node metastasis was found in 49 and 35 patients using the BLOB-OS-TF algorithm, in 42 and 33 patients using the BLOB-OS algorithm, and in 41 and 31 patients using the 3D-RAMLA algorithm, respectively, and a positive ganglion was found in 92, 59 and 24 of 100 patients using the three algorithms, respectively. Quantitatively, the SUVmean and SUVmax were significantly higher with the BLOB-OS algorithm than with either the BLOB-OS-TF or the 3D-RAMLA algorithm in all measured regions (p < 0.001 for all comparisons). The differences between the SUVs with the BLOB-OS-TF- and 3D-RAMLA algorithms were not significant in the aorta (SUVmean, p = 0.93; SUVmax, p = 0.97) but were significant in all other regions (p < 0.001 in all cases). The SUVmean ganglion/gluteus ratio was significantly higher with the BLOB-OS-TF algorithm than with either the BLOB-OS or the 3D-RAMLA algorithm and was significantly higher with the BLOB-OS than with the 3D-RAMLA algorithm (p < 0.001 in all cases).ConclusionThe results of [68Ga]PSMA-HBED-CC PET/CT are affected by the reconstruction algorithm used. The highest number of lesions and physiological structures will be visualized using a modern algorithm employing time-of-flight information.

Dual addressing of thymidine synthesis pathways for effective targeting of proliferating melanoma

Here, we examined the potential of blocking the thymidine de novo synthesis pathways for sensitizing melanoma cells to the nucleoside salvage pathway targeting endogenous DNA irradiation. Expression of key nucleotide synthesis and proliferation enzymes thymidylate synthase (TS) and thymidine kinase 1 (TK1) was evaluated in differentiated (MITFhigh [microphthalmia‐associated transcription factor] IGR1) and invasive (MITFmedium IGR37) melanoma cells. For inhibition of de novo pathways cells were incubated either with an irreversible TS inhibitor 5‐fluoro‐2′‐deoxyuridine (FdUrd) or with a competitive dihydrofolate‐reductase (DHFR) inhibitor methotrexate (MTX). Salvage pathway was addressed by irradiation‐emitting thymidine analog [123/125I]‐5‐iodo‐4′‐thio‐2′‐deoxyuridine (123/125I‐ITdU). The in vivo targeting efficiency was visualized by single‐photon emission computed tomography. Pretreatment with FdUrd strongly increased the cellular uptake and the DNA incorporation of 125I‐ITdU into the mitotically active IGR37 cells. This effect was less pronounced in the differentiated IGR1 cells. In vivo, inhibition of TS led to a high and preferential accumulation of 123I‐ITdU in tumor tissue. This preclinical study presents profound rationale for development of therapeutic approach by highly efficient and selective radioactive targeting one of the crucial salvage pathways in melanomas.

Impact of Glutathione Modulation on Stability and Pharmacokinetic Profile of Redox‐Sensitive Nanogels

Nanoparticles degradable upon external stimuli combine pharmacokinetic features of both small molecules as well as large nanoparticles. However, despite promising preclinical results, several redox responsive disulphide-linked nanoparticles failed in clinical translation, mainly due to their unexpected in vivo behavior. Glutathione (GSH) is one of the most evaluated antioxidants responsible for disulfide degradation. Herein, the impact of GSH on the in vivo behavior of redox-sensitive nanogels under physiological and modulated conditions is investigated. Labelling of nanogels with a DNA-intercalating dye and a radioisotope allows visualization of the redox responsiveness at the cellular and the systemic levels, respectively. In vitro, efficient cleavage of disulphide bonds of nanogels is achieved by manipulation of intracellular GSH concentration. While in vivo, the redox-sensitive nanogels undergo, to a certain extent, premature degradation in circulation leading to rapid renal elimination. This instability is modulated by transient inhibition of GSH synthesis with buthioninsulfoximin. Altered GSH concentration significantly changes the in vivo pharmacokinetics. Lower GSH results in higher elimination half-life and altered biodistribution of the nanogels with a different metabolite profile. These data provide strong evidence that decreased nanogel degradation in blood circulation can limit the risk of premature drug release and enhance circulation half-life of the nanogel.

Evaluation of a Pretargeting Strategy for Molecular Imaging of the Prostate Stem Cell Antigen with a Single Chain Antibody

In pretargeted radio-immunotherapy, the gradual administration of a non-radioactive tumor antigen-addressing antibody-construct and the subsequent application of a radioactive labeled, low molecular weight substance enable a highly effective and selective targeting of tumor tissue. We evaluated this concept in prostate stem cell antigen (PSCA)-positive cancers using the antigen-specific, biotinylated single chain antibody scFv(AM1)-P-BAP conjugated with tetrameric neutravidin. To visualize the systemic biodistribution, a radiolabeled biotin was injected to interact with scFv(AM1)-P-BAP/neutravidin conjugate. Biotin derivatives conjugated with different chelators for complexation of radioactive metal ions and a polyethylene glycol linker (n = 45) were successfully synthesized and evaluated in vitro and in a mouse xenograft model. In vivo, the scFv(AM1)-P-BAP showed highly PSCA-specific tumor retention with a PSCA+ tumor/PSCA- tumor accumulation ratio of ten. PEGylation of radiolabeled biotin resulted in lower liver uptake improving the tumor to background ratio.

Tumor targeting via EPR: Strategies to enhance patient responses

The tumor accumulation of nanomedicines relies on the enhanced permeability and retention (EPR) effect. In the last 5-10 years, it has been increasingly recognized that there is a large inter- and intra-individual heterogeneity in EPR-mediated tumor targeting, explaining the heterogeneous outcomes of clinical trials in which nanomedicine formulations have been evaluated. To address this heterogeneity, as in other areas of oncology drug development, we have to move away from a one-size-fits-all tumor targeting approach, towards methods that can be employed to individualize and improve nanomedicine treatments. To this end, efforts have to be invested in better understanding the nature, the complexity and the heterogeneity of the EPR effect, and in establishing systems and strategies to enhance, combine, bypass and image EPR-based tumor targeting. In the present manuscript, we summarize key studies in which these strategies are explored, and we discuss how these approaches can be employed to enhance patient responses.