The compound [Ph3PMe]2B10I9CO2H was synthesized as a potential agent for the detection of occult tumor tissue in vivo using the X-ray fluorescence (XRF) of iodine. The compound is highly stable and its boron framework is not a native substrate for deiodinase enzymes, making it a potential carrier for iodine without sequestration by the thyroid. Future attachment of the compound to a tumor-seeking antibody through the carboxylic acid group will enable tumor specificity, such that high iodine concentrations can be achieved on cancerous cells.
The target compound’s precursor, [Ph3PMe]2B10H9CO2H was synthesized by a two-step procedure which first isolates [Ph3PMe]2B10H9CO. The structure of the carboxylic acid derivative was determined by single-crystal X-ray diffraction. Then the acid was periodinated to produce the target compound [Ph3PMe]2B10I9CO2H.
The stability of Na2B12I12 and [Ph3PMe]2B10H9CO2H was established under high temperature conditions in aqueous solution in which neither compound noticeably degraded. The preliminary data suggest that both the attached iodine atoms and carboxylic acid group resist hydrolysis, thus the compounds may be suitable for future biological studies in cancer cell lines and mouse models.
Both handheld and floor model XRF devices were used to assess iodide concentration in aqueous solution. The PANalytical wavelength-dispersive XRF was able to detect low concentrations of iodide in aqueous solution, with a limit of detection of 2 µM I−. Therefore, the technique in combination with the labeled antibody may be useful for the detection of tumor margins in vivo.
It was found that the X-ray fluorescence of iodine on Cs2B12I12 is diminished compared to that of free iodide, but the signal of free iodide in an equimolar solution with Cs2B12H12 was unaffected. Additional experiments are required to determine why the attachment of iodine to the boron cage affects its fluorescence intensity and how the signal can be enhanced to ensure detection. The high iodine content also qualifies this compound as a good medical imaging contrast agent.