Monoclonal antibodies directed toward metal chelating agents or metal-chelate complexes have many potential uses both in medicine and in environmental analysis. In medicine, chelator-linked antibodies have been used in vivo to transport and deliver radioisotopes to specific target sites, such as tumors (1-3). The availability of monoclonal antibodies to the chelating agent has permitted researchers to investigate the biodistribution of these "magic bullets" in cancer chemotherapy (4). In environmental analysis, the availability of monoclonal antibodies that can distinguish among different metals provides a basis for rapid, sensitive immunoassays that can be used onsite to assess heavy metal contamination (5, 6). Monoclonal antibodies that bind to chelators such as diethylenetriaminepentaacetic acid and 1,4,7,10-tetraazacyclododecane-N, NЈ, NЉ, Nٞ-tetraacetic acid have been reported (7, 8); however, these antibodies were directed primarily toward the chelate portion of the molecule and did not demonstrate the ability to differentiate among various metals bound in the chelate complex. Two hybridomas that synthesized monoclonal antibodies showing metal ion specificity have also been reported. The first, CHA255, was the result of immunization with a derivative of In(III)-EDTA coupled to a carrier protein by a thioureido-L-benzyl group (4). The monoclonal antibody synthesized by CHA255 bound to a variety of chelate complexes but bound to indium-chelate complexes more tightly than it did to other chelated metals (4, 9). Monoclonal antibodies directed toward mercuric ions have also been elicited by immunization of animals with a glutathione-Hg derivative (10). These antibodies, which bind to mercury with high affinity, have been used to detect mercuric ions in aqueous samples (6) and are the basis for a commercially available immunoassay to monitor mercury contamination in environmental samples.The molecular features responsible for an antibody's ability to differentiate among metals have been explored in some detail with CHA255 (11). Binding studies have shown that CHA255 was highly specific for the indium chelate; the antibody's affinity decreased from 24-to 20,000-fold when other metals were substituted for In(III) in the chelate complex. The structural basis for this fine discrimination was investigated by x-ray crystallographic analyses of the antigen-binding fragment complexed with either In(III) or Fe(III) chelates of thioureido-L-benzyl-EDTA. A notable feature of the antibodyIn(III)-EDTA complex was the additional coordination of the chelated metal by a histidine residue from the heavy chain's third complementarity determining region. This histidine coordination did not occur in the corresponding Fe(III) complex, due to a slightly different hapten coordination that reduced access to the metal. It was concluded that the absence of the histidine ligation was largely responsible for the 24-fold lower binding of the iron hapten to CHA255 relative to that of the indium hapten. The larger differences in the binding a...

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The purpose of this study was to investigate the role that tributyltin (TBT)-induced decreases in ATP levels may play in TBT-induced decreases in the tumor lysing (lytic) function of natural killer (NK) cells. NK cells are a subset of lymphocytes that act as an initial immune defense against tumor cells and virally infected cells. TBT is an environmental contaminant that has been detected in human blood, which has been shown to interfere with ATP synthesis. Previous studies have shown that TBT is able to decrease very significantly the lytic function of NK cells. In this study NK cells were exposed to various concentrations of TBT and to two other compounds that interfere with ATP synthesis (rotenone a complex I inhibitor and oligomycin an ATP synthase inhibitor) for various lengths of time before determining the levels of ATP and lytic function. Exposures of NK cells to 10, 25, 50 and 100 nm TBT did not significantly reduce ATP levels after 24 h. However, these same exposures caused significant decreases in cytotoxic function. Studies of brief 1 h exposures to a range of TBT, rotenone and oligomycin concentrations followed by 24 h, 48 h and 6 day periods in compound-free media prior to assaying for ATP levels or cytotoxic function showed that each of the compounds caused persistent decreases in ATP levels and lytic function of NK cells. Exposures to 0.05-5 microm rotenone or oligomycin for 1 h reduced ATP levels by 20-25% but did not have any measurable effect on the ability of NK cells to lyse tumor cells. ATP levels were also decreased by about 20-25% after 24 h or 48 h exposures to rotenone or oligomycin (0.5 microm ), and the lytic function was decreased by about 50%. The results suggest that TBT-induced decreases in ATP levels were not responsible for the loss of cytotoxic function seen at 1 h and 24 h. However, TBT-induced decreases of NK-ATP levels may be at least in part responsible for losses of NK-cytotoxic function seen after 48 h and 6 day exposures.

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