Linkages to Liberate Radiometabolites From Antibody Fragments by Renal Brush Border Enzymes

METABOLIZABLE LINKAGES TO LIBERATE RADIOMETABOLITES FROM ANTIBODY FRAGMENTS BY RENAL BRUSH BORDER ENZYMES. 

When the peptide bond between glycine and lysine is cleaved, meta-iodohippuric acid is released from the conjugate. For comparison, two additional radioiodinated Fab fragments were prepared. Meto-iodohippuric acid was conjugated to Fab fragments though an amide bond to prepare MPH-Fab by procedures similar to those employed for HML-Fab. 

Conjunction Chemistries to Reduce Renal Radioactivity Levels 

Fiffire 3. Conjugation of radioiodinated HML to Fab fragments using 2-iminothiolane. 

The radioactivity excreted in the urine for 6 hours postinjection of HML-Fab was then analyzed to assess the present chemical design of radiolabeled antibody fragments. On size-exclusion HPLC, more than 85 % of the radioactivity was eluted at the low molecular weight fractions and about 12 % of the radioactivity was eluted in fractions similar to those of the intact Fab fragment. On reversed-phase HPLC of the urine sample, over 93 % of the low molecular weight fractions had a retention time identical to that of ffjeto-iodohippuric acid. These findings indicated that the low renal radioactivity levels of HML-Fab were attributed to rapid and selective release of /weto-iodohippuric acid in the kidney. 

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