Chromatofocusing Studies Involving a Monoclonal Fab

Isoelectricfocusing(IEF)of the Fab' derivativeof murine monoclonal antibodyZCE-025 is knownto detectat leastsix bands having isoelectric points (pI) ranging from 5.4 to 7.8. Chromatofocusing wasemployedto separatethesebands. Electrophoresisof the starting materials under nonreducing conditions indicated all of the materialsto migrate as Fab'. The electrophoresisof unne samples obtained from Balb/c and nude mice 8 hr after the i.v. injectionof the various 1251 bandsrevealedthe low p1bandsto migrateapproximatelyas a 125l-Fab' . The higherp1band activitywas located in lower molecular weight regions. Serum samples taken at 8 hr postinjectionfrom the above mice revealeda series of what appeared to be highmolecular weightcomplexes andsome lowmolecular weightspecies.Biodistnbution studiesincom panson BaIb/c mice and nude mice revealedthat the low p1 1251-Fab' bandsgave an organ and tumor uptake at 8 hr very similarto Fab', while the high p1 @l-Fab' bandswere rapidly excretedintothe urineandfecesanddid not concentrate in the tumor. The data suggestthat the populationof molecules makingup the Fab' of this antibodyis heterogeneous and variably stable. Theoretically,some of the entities observed could be counter productive to successful radioimmunoim aging. It is also possible that some of the labeled molecules areassociating in vivowithendogenous proteinsthat might, in some Mabs, affect the biodistnbutionof the radiopharma ceutical. J NucIMed 1992;33:2148-2153