Abstract
19F-magnetic resonance imaging (MRI) is a promising technique that may allow us to measure the concentration of exogenous fluorinated imaging probes quantitatively in vivo. Here, we describe the synthesis and characterisation of a novel geminal bisphosphonate (19F-BP) that contains chemically-equivalent fluorine atoms that show a single and narrow 19F resonance and a bisphosphonate group that may be used for labelling inorganic materials based in calcium phosphates and metal oxides. The potential of 19F-BP to provide contrast was analysed in vitro and in vivo using 19F-MRI. In vitro studies demonstrated the potential of 19F-BP as an MRI contrast agent in the millimolar concentration range with signal-to-noise ratios (SNR) comparable to previously reported fluorinated probes. The preliminary in vivo MRI study reported here allowed us to visualise the biodistribution of 19F-BP, showing uptake in the liver and in the bladder/urinary system areas. However, bone uptake was not observed. In addition, 19F-BP showed undesirable toxicity effects in mice that prevent further studies with this compound at the required concentrations for MRI contrast. This study highlights the importance of developing 19F MRI probes with the highest signal intensity achievable.
Highlights
magnetic resonance imaging (MRI) is a medical imaging technique that offers high-resolution images of soft tissues without the need for ionising radiation
One area that MRI currently lags behind other imaging modalities, positron emission tomography (PET) and single photon emission computed tomography (SPECT), is the quantitative measurement of the signal provided by these contrast agents
More recently attempts have been made to image smaller compounds by modulating the 19F signal using lanthanide metals [12,13] and used for the detection of gene expression [14]. Despite these early promising results and clear advantages for molecular imaging compared to 1H-MRI, 19F-MRI remains underused in clinical practice
Summary
MRI is a medical imaging technique that offers high-resolution images of soft tissues without the need for ionising radiation. We hypothesised that a fluorinated BP molecule could be an useful tool in the development of 19F-MRI probes, that would allow to combine of the amplification properties of nanoparticle-based platforms (high numbers of equivalent fluorine atoms) with the relaxation-enhancement properties of lanthanide-based materials (short acquisition times) without affecting their water solubility. In this way we could potentially achieve 19F-MRI probes with high signal intensity and sensitivity that could be imaged in a short time. We report our first attempts at achieving this aim by synthesizing and characterising a new fluorinated BP (19F-BP,Scheme 1) and evaluate for the first time its properties as a single molecule for 19F-MRI in vitro and in vivo
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