RELATIVE REACTIVITY OF DTPA, IMMUNOREACTIVE ANTIBODY-DTPA CONJUGATES, AND NONIMMUNOREACTIVE ANTIBODY-DTPA CONJUGATES TOWARD IN-111

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  • 1 January 1985
    • journal article
    • research article
    • Vol. 26  (5) , 482-487
Abstract
Anti-human serum albumin antibody (Ab) was reacted with cyclic DTPA [diethylenetriaminepentaacetic acid] dianhydride (cDTPAA) at various cDTPAA/Ab molar ratios between 1 and 40. Using a carrier in titration method for DTPA and DTPA-antibody conjugate (Ab-DTPA), determined that the above reactions produced between 0.1 and 11 DTPA molecules per either immunoreactive antibody (sAb) or nonimmunoreactive antibody (nAb). The percentage of sAb remaining after the above reactions was between 88 and 62%. The reaction of no-carrier-added 111In with the reaction mixture from cDTPAA/Ab molar ratios of 1-40 gave radiochemical yields .ltoreq. 25% for the respective Ab-DTPA. The rest of the 111In activity was associated with free DTPA. Apparently, Ab-DTPA containing > 1 DTPA molecule per Ab is more reactive than that containing < 1 DTPA and consequently prevent colloid formation. The percentage of 111In activity incorporated into sAb-DTPA from the reactions at these molar ratios was similar to that found from the UV analysis. Evidently the reactivity of sAb-DTPA and nAB-DTPA from the same conjugation reaction is similar. About one DTPA molecule was conjugated to the Ab without causing deactivation of the Ab and labeled it with 111In in the presence of excess DTPA. A specific activity of 6 .mu.Ci 111In/Umg of Ab was obtained using research grade 111In without further purification.

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