Marco Rupprich

68Ga- and 111In-labelled DOTA-RGD peptides for imaging of αvβ3 integrin expression

Purposeαvβ3 integrins are important cell adhesion receptors involved in angiogenic processes. Recently, we demonstrated using [18F]Galacto-RGD that monitoring of αvβ3 expression is feasible. Here, we introduce 68Ga- and 111In-labelled derivatives and compare them with [18F]Galacto-RGD.MethodsFor radiolabelling, cyclo(RGDfK(DOTA)) was synthesised using SPPS. For in vitro characterisation determination of partition coefficients, protein binding, metabolic stability, αvβ3 affinity and cell uptake and for in vivo characterization, biodistribution studies and micro positron emission tomography (PET) imaging were carried out. For in vivo and in vitro studies, human melanoma M21 (αvβ3 positive) and M21-L (αvβ3 negative) cells were used.ResultsBoth tracers can be synthesised straightforward. The compounds showed hydrophilic properties and high metabolic stability. Up to 23% protein-bound activity for [68Ga]DOTA-RGD and only up to 1.4% for [111In]DOTA-RGD was found. Cell uptake studies indicate receptor-specific accumulation. This is confirmed by the biodistribution data. One hour p.i. accumulation in αvβ3-positive tumours was 2.9 ± 0.3%ID/g and in αvβ3-negative tumours 0.8 ± 0.1%ID/g for [68Ga]DOTA-RGD ([111In]DOTA-RGD: 1.9 ± 0.3%ID/g and 0.5 ± 0.2%ID/g; [18F]Galacto-RGD: 1.6 ± 0.2%ID/g and 0.4 ± 0.1%ID/g). Thus, tumour uptake ratios were comparable. Due to approx. 3-fold higher blood pool activities for [68Ga]DOTA-RGD, tumour/blood ratios were higher for [111In]DOTA-RGD and [18F]Galacto-RGD. However, microPET studies demonstrated that visualisation of αvβ3-positive tumours using [68Ga]DOTA-RGD is possible.ConclusionsOur data indicate that [68Ga]DOTA-RGD allows monitoring of αvβ3 expression. Especially, the much easier radiosynthesis compared to [18F]Galacto-RGD would make it an attractive alternative. However, due to higher blood pool activity, [18F]Galacto-RGD remains superior for imaging αvβ3 expression. Introduction of alternative chelator systems may overcome the disadvantages.

A fully automated synthesis for the preparation of 68Ga-labelled peptides.

BackgroundGenerator-produced 68Ga has attracted increasing interest for radiolabelling peptides used in PET applications. So far, the synthesis of 68Ga-peptide radiopharmaceuticals is mainly based on semi-automated systems. Here we describe a fully automated approach for the synthesis of 68Ga-labelled peptides. MethodA commercially available 68Ga generator was eluted with 0.1 mol · l−1 HCl. Reaction parameters such as buffer conditions, pH range, reaction temperature and time, volume of reaction solution and generator fraction were optimized for labelling DOTA-Tyr3-octreotide (DOTATOC). Reaction yields, pH, radiochemical purity, sterility, endotoxins, breakthrough of 68Ge and final 68Ge content were determined. A fully automated radiopharmaceutical synthesis device based on a modular concept for remote-controlled processing was developed and evaluated for a number of DOTA-derivatized peptides. ResultsDOTATOC could be labelled in almost quantitative yields by heating 10–50 nmol peptide at pH 3.5–4.0 for 5 min at 95°C in 1.5 ml. Purification using a reversed-phase cartridge was required to avoid any potential 68Ge breakthrough: final activities of 68Ge were below 100 Bq · ml−1. Automated synthesis resulted in overall decay-corrected reaction yields of about 60% within 10 min. Even after 1 year using a 1110 MBq generator more than 130 MBq 68Ga-DOTATOC could be obtained. Moreover, it was demonstrated that a variety of DOTA-derivatized peptides can be labelled using identical reaction conditions with high yields. ConclusionThe system described allows the fully automated, efficient and rapid preparation of 68Ga-DOTA-derivatized peptides. It has been used successfully and reliably for routine preparations in clinical studies.

Poly(piperazine-amide)/PES Composite Multi-Channel Capillary Membranes for Low-Pressure Nanofiltration

The mechanical stability of conventional single-channel capillary fibres can be improved in a multi-channel geometry, which has previously found application in ultrafiltration. In this work, multi-channel polyethersulfone (PES) capillary membranes comprising seven feed channels were successfully fabricated in an enhanced steam–dry–wet spinning process and coated on the inner surface with a thin polyamide (PA) layer via interfacial polymerization (IP). The coating procedure consisted of impregnating the support multi-channel capillary membranes (MCM) with an aqueous piperazine solution, flushing with nitrogen gas to remove excess droplets, and pumping an organic trimesoylchloride solution through the channels. Insights into the interfacial polymerization process were gained through the investigation of various parameters, including monomer ratio, contact time, and drying time. Membranes were characterised via scanning electron microscopy (SEM), atomic force microscopy (AFM), and filtration experiments. The optimisation of both the PES support membrane and IP process parameters allowed for the fabrication of composite MCM with an MgSO4 rejection of 91.4% and a solute flux of 68.8 L m−2 h−1 at an applied pressure of 3 bar. The fabricated composite MCM demonstrates that a favourable multi-channel arrangement can be upgraded with a PA layer for application in low-pressure nanofiltration.