Purpose: The aim of this study was to demonstrate the potential of Ga-68-labeled macrocycle (DOTA-en-pba) conjugated with phenylboronic vector for tumor recognition by positron emission tomography (PET), based on targeting of the overexpressed sialic acid (Sia). Procedures: The imaging reporter DOTA-en-pba was synthesized and labeled with Ga-68 at high efficiency. Cell binding assay on Mel-C and B16-F10 melanoma cells was used to evaluate melanin production and Sia overexpression to determine the best model for demonstrating the capability of [68Ga]DOTA-en-pba to recognize tumors. The in vivo PET imaging was done with B16-F10 tumor-bearing SCID mice injected with [68Ga]DOTA-en-pba intravenously. Tumor, blood, and urine metabolites were assessed to evaluate the presence of a targeting agent. Results: The affinity of [68Ga]DOTA-en-pba to Sia was demonstrated on B16-F10 melanoma cells, after the production of melanin as well as Sia overexpression was proved to be up to four times higher in this cell line compared to that in Mel-C cells. Biodistribution studies in B16-F10 tumor-bearing SCID mice showed blood clearance at the time points studied, while uptake in the tumor peaked at 60 min post-injection (6.36 ± 2.41 % ID/g). The acquired PET images were in accordance with the ex vivo biodistribution results. Metabolite assessment on tumor, blood, and urine samples showed that [68Ga]DOTA-en-pba remains unmetabolized up to at least 60 min post-injection. Conclusions: Our work is the first attempt for in vivo imaging of cancer by targeting overexpression of sialic acid on cancer cells with a radiotracer in PET.@en

It is known that phenylboronic acid (PBA) can target tumor tissues by binding to sialic acid, a substrate overexpressed by cancer cells. This capability has previously been explored in the design of targeting diagnostic probes such as Gd- and 68Ga-DOTA-EN-PBA, two contrast agents for magnetic resonance imaging (MRI) and positron emission tomography (PET), respectively, whose potential has already been demonstrated through in vivo experiments. In addition to its high resolution, the intrinsic low sensitivity of MRI stimulates the search for more effective contrast agents, which, in the case of small-molecular probes, basically narrows down to either increased tumbling time of the entire molecule or elevated local concentration of the paramagnetic ions, both strategies resulting in enhanced relaxivity, and consequently, a higher MRI contrast. The latter strategy can be achieved by the design of multimeric GdIII complexes. Based on the monomeric PBA-containing probes described recently, herein, we report the synthesis and characterization of the dimeric analogues (GdIII-DOTA-EN)2-PBA and (GdIII-DOTA-EN)2F2PBA. The presence of two Gd ions in one molecule clearly contributes to the improved biological performance, as demonstrated by the relaxometric study and cell-binding investigations.@en

Paramagnetic macrocycles functionalized with phenylboronic moieties have proven to be interesting for MRI applications based on their ability to recognize cancer cells and generate local contrast. However, full use of the potential of this class of compounds is hampered by laborious and inefficient synthetic and, especially, purification procedures. The amphiphilic character of water-soluble phenylboronates renders them difficult compounds to be prepared through conventional solution synthesis due to the tendency to aggregate and form adducts with other nucleophiles. The new strategy described herein exploits the advantage of solid-phase synthesis with the application of DEAM-PS resin for anchorage and the subsequent simplified derivatization of boronates. GdDOTA-EN-PBA and its fluorinated analogue GdDOTA-EN-F2PBA were synthesized in a much easier, faster and economically convenient way to achieve good yields and purity. Furthermore, the effect of electron-withdrawing fluorine atoms on the aromatic ring of the latter compound was investigated by comparing the physico-chemical properties of both compounds as well as their binding affinity towards melanoma cancer cells.@en