DENDRIMAGE · Luminescent lanthanide dendrimer imaging agents for detection of cancer cells and tumors in vivo

Luminescent lanthanide dendrimer imaging agents for detection of cancer cells and tumors in vivo

The global goal of this project was to create novel imaging agents based on luminescent lanthanide ions for optical detection in cancer research and medical diagnostic. Optical imaging techniques such as fluorescence microscopy are highly attractive as they allow sensitive detection using small amounts of reagents for the planned imaging, limiting the risks of interfering with the behavior of the biological system to be observed. Such techniques are also exciting for diagnostic as they permit to monitor biological events in whole organisms, blood and urine samples using a rather inexpensive equipment (CCD camera for detection and LEDs as illumination systems) that contrasts significantly with the costs associated with currently used techniques such as MRI and PET. Another advantage of such techniques is the high portability of the equipment that allows its placement close to an experiment to perform (it can be compared to a digital camera). It can also be easily installed in the office of a doctor for more rapid diagnostic. For these reasons, the use of optical imaging has the potential to significantly decrease the cost of diagnostics allowing for a better comfort of patients (earlier detection) and for the costs associated with cancer cure: an earlier detection is a key advantage for the prognostics of patients. The current bottlenecks are the reagents that are used and that are mostly based on organic molecules. These molecules tend to photo-decompose rapidly when exposed to light and possess emission that can often not be discriminated from the native fluorescence of biological systems (autofluorescence). A major originality of this work is based on the use of the luminescence of lanthanide ions as a source of light for such biological imaging. Lanthanide ions emit as sharp bands that can be discriminated easily from autofluorescence. Another specificity of lanthanides is their ability to emit near-infrared light which is not present in biological systems. Therefore the use of such light allows for accurate and unambiguous detection in biological systems due to the absence of interferences originating from tissues or blood. Another advantage of near-infrared light lies in its ability to deeper penetrate into tissues for non-invasive research investigations or diagnostics. The lanthanide imaging agents need to (1) emit a sufficient number of photons to ensure sensitive detection, (2) be sufficiently stable in biological conditions, (3) be soluble enough and (4) versatile to ensure the proper targeting and selectivity. This project aimed specifically at designing, synthesizing, characterizing and studying luminescent lanthanide-based imaging agents with ultimate properties for practical applications. The specificity of the proposed imaging agents is their ability to detect potassium channels in cancer cells that are hypothesized to be pertinent metastatic markers for both research and diagnostics. Several parallel and innovative routes were taken to achieve the planned goal in order to maximize chances of success: (i) the creation of small molecules that absorb in biologically compatible window of wavelengths, (ii) the creation of beads optimized for biological compatibility, the surface of which can be easily functionalized by different types of targeting units to ensure a specific location of these species in biological systems, and (iii) creation of polymetallic systems based on dendrimer complexes that possess a high number of chromophoric units. With this approach, a high number of photons is produced by densifying the number of lanthanide emitters and theirs sensitizers. Different types of sensitizers were tested here. The prototype lanthanide complexes incorporating RGD peptides as targeting moieties were synthesized. The synthetic strategy have been developed which should allow synthesis of non-symmetric dendrimers functionalized with both chromophoric and targeting moieties. A communication has been published in a top level journal (Angewandte Chemie) reporting the first example of a dendrimer complex that allows to perform lanthanide-based detection in living cells in the visible and in the near-infrared. This article was recognized by CNRS Institute of Chemistry and published as a highlight since it was only the second disclosure of imaging agents based on the NIR lanthanide luminescence. Several other manuscripts are in preparation. One of the achievements of this project: we have been able to demonstrate for the first time that a lanthanide complex can be used to perform non-invasive biological imaging in a mouse in the visible and in the near-infrared ranges. Another achievement is a design of NIR-to-NIR lanthanide-based imaging agent emission of which could be determined in a whole blood thus opening perspectives for bioanalytical applications. Several compounds have been identified as having a high commercial potential. We have therefore forwarded invention disclosures to the CNRS. It is worth noting that since only low quantities of compounds are required for optical imaging, no significant scale up for the synthesis is needed prior commercialization and therefore, a rapid valorization can be foreseen with these compounds. The first type of products that can be developed by an European startup company are lanthanide-based imaging agents to be used in living cells in vitro. The project has been interrupted before its end (24 months) by lasting 21 months as Dr. Eliseeva has been able to go through extremely competitive concourse and obtain a tenured permanent researcher position that she had to occupy prior to February 1, 2015. Dr. Eliseeva will continue to pursue her academic work at the same place (Centre of Molecular Biophysics CNRS UPR4301) where she has been doing her training and where she has developed the equipment required for her further experiments.

Data: CORDIS, © European Union