Comparison of Linear and Hyperbranched Polyether Lipids for Liposome Shielding by 18F-Radiolabeling and Positron Emission Tomography.

Multifunctional and highly biocompatible polyether structures play a key role in shielding liposomes from degradation in the bloodstream, providing also multiple functional groups for further attachment of targeting moieties. In this work hyperbranched polyglycerol ( hbPG) bearing lipids with long alkyl chain anchor are evaluated with respect to steric stabilization of liposomes. The branched polyether lipids possess a hydrophobic bis(hexadecyl)glycerol membrane anchor for the liposomal membrane. hbPG was chosen as a multifunctional alternative to PEG, enabling the eventual linkage of multiple targeting vectors. Different hbPG lipids ( Mn = 2900 and 5200 g mol-1) were examined. A linear bis(hexadecyl)glycerol-PEG lipid ( Mn = 3000 g mol-1) was investigated as well, comparing hbPG and PEG with respect to shielding properties. Radiolabeling of the polymers was carried out using 1-azido-2-(2-(2-[18F]fluoroethoxy)ethoxy)ethane ([18F]F-TEG-N)3 via copper-catalyzed alkyne-azide cycloaddition with excellent radiochemical yields exceeding 95%. Liposomes were prepared by the thin-film hydration method followed by repeated extrusion. Use of a custom automatic extrusion device gave access to reproducible sizes of the liposomes (hydrodynamic radius of 60-94 nm). The in vivo fate of the bis(hexadecyl)glycerol polyethers and their corresponding assembled liposome structures were evaluated via noninvasive small animal positron emission tomography (PET) imaging and biodistribution studies (1 h after injection and 4 h after injection) in mice. Whereas the main uptake of the nonliposomal polyether lipids was observed in the kidneys and in the bladder after 1 h due to rapid renal clearance, in contrast, the corresponding liposomes showed uptake in the blood pool as well as in organs with good blood supply, that is, heart and lung over the whole observation period of 4 h. The in vivo behavior of all three liposomal formulations was comparable, albeit with remarkable differences in splenic uptake. Overall, liposomes shielded by the branched polyglycerol lipids show a favorable biodistribution with greatly prolonged blood circulation times, rendering them promising novel nanovesicles for drug transport and targeting.

Bone scintigraphy predicts bisphosphonate-induced osteonecrosis of the jaw (BRONJ) in patients with metastatic castration-resistant prostate cancer (mCRPC).

OBJECTIVES: The aim of this study was to evaluate the role of bone scintigraphy (BS) in early prediction of clinically asymptomatic bisphosphonate (BP)-related osteonecrosis of the jaws (BRONJ) in patients with metastatic castration-resistant prostate cancer (mCRPC). MATERIAL AND METHODS: BS of mCRPC patients treated with BP was evaluated for pathologic tracer uptake of the jaws in BS suspicious for BRONJ. Results were compared to development of clinically evident BRONJ. Sensitivity, specificity and predictive values of BS for the detection of BRONJ as well as time from beginning of BP therapy to pathologic tracer uptake in BS and time from pathologic tracer uptake in BS to clinically evident BRONJ were determined. RESULTS: Thirty BP-treated patients were included. Nine patients (30%) had pathologic BS lesions of the jaws. Six patients (20%) developed BRONJ. Sensitivity and specificity of BS for BRONJ prediction were 67 and 79%. Median time from the start of BP treatment to pathologic tracer uptake in BS was 28 months (range 10-33) and from pathologic tracer uptake in BS to clinically evident BRONJ 6.5 months (range 2-19). Pathologic tracer uptake in BS was significantly more often observed in patients who developed BRONJ compared to patients who did not (p = 0.049; OR 7.6). CONCLUSIONS: Patients with pathologic tracer uptake in the jaws in BS significantly more often develop BRONJ. An unsuspicious BS is predictive for absence of BRONJ in the future. CLINICAL RELEVANCE: We conclude that when BS has been performed, it should not only be used to assess tumour stage and treatment response but also to check for pathologic tracer uptake in the jaws in BS to detect BRONJ at an early stage in mCRPC patients receiving bisphosphonates.

Fate of linear and branched polyether-lipids in vivo in comparison to their liposomal formulations by 18F-radiolabeling and positron emission tomography.

In this study, linear poly(ethylene glycol) (PEG) and novel linear-hyperbranched, amphiphilic polyglycerol (hbPG) polymers with cholesterol (Ch) as a lipid anchor moiety were radiolabeled with fluorine-18 via copper-catalyzed click chemistry. In vivo investigations via positron emission tomography (PET) and ex vivo biodistribution in mice were conducted. A systematic comparison to the liposomal formulations with and without the polymers with respect to their initial pharmacokinetic properties during the first hour was carried out, revealing remarkable differences. Additionally, cholesterol was directly labeled with fluorine-18 and examined likewise. Both polymers, Ch-PEG27-CH2-triazole-TEG-(18)F and Ch-PEG30-hbPG24-CH2-triazole-TEG-(18)F (TEG: triethylene glycol), showed rapid renal excretion, whereas the (18)F-cholesten displayed retention in lung, liver, and spleen. Liposomes containing Ch-PEG27-CH2-triazole-TEG-(18)F revealed a hydrodynamic radius of 46 nm, liposomal Ch-PEG30-hbPG24-CH2-triazole-TEG-(18)F showed a radius of 84 nm and conventional liposomes with (18)F-cholesten 204 nm, respectively. The results revealed fast uptake of the conventional liposomes by liver, spleen, and lung. Most importantly, the novel hbPG-polymer stabilized liposomes showed similar behavior to the PEG-shielded vesicles. Thus, an advantage of multifunctionality is achieved with retained pharmacokinetic properties. The approach expands the scope of polymer tracking in vivo and liposome tracing in mice via PET.

Highly Loaded Semipermeable Nanocapsules for Magnetic Resonance Imaging.

Magnetic resonance imaging has become an essential tool in medicine for the investigation of physiological processes. The key issues related to contrast agents, i.e., substances that are injected in the body for imaging, are the efficient enhancement of contrast, their low toxicity, and their defined biodistribution. Polyurea nanocapsules containing the gadolinium complex Gadobutrol as a contrast agent in high local concentration and high relaxivity up to 40 s-1 mmol-1 L are described. A high concentration of the contrast agent inside the nanocapsules can be ensured by increasing the crystallinity in the shell of the nanocapsules. Nanocapsules from aliphatic polyurea are found to display higher crystallinity and higher relaxivity at an initial Gadobutrol concentration of 0.1 m than aromatic polyurea nanocapsules. The nanocapsules and the contrast agent are clearly identified in cells. After injection, the nanocarriers containing the contrast agent are mostly found in the liver and in the spleen, which allow for a significant contrast enhancement in magnetic resonance imaging.