Ionizable calixarene-crown ethers with high selectivity for radium over light alkaline earth metal ions

α particle emitters are of increasing interest as the radionuclide attached to monoclonal antibodies of other targeting mechanisms for applications in cell-directed therapy of cancer. α particles are more effective than β- particles for cell-killing and promise a more effective treatment of cancer than other forms of radiation. This is because α particles have high initial energy (4--8 MeV), short path lengths (40--80 microm, or several cell diameters), and consequently greater energy dissipation per unit length. Cell-directed immunotherapy can help improve irradiation of tumor cells while sparing normal tissues. The success of this approach will require effective chemistry for attaching the radionuclide to the antibody. Therefore, a concerted effort has been directed toward the design of chelating agents capable of holding the desired α-emitting radionuclide, both selectively and with high stability, to the antibody