C-terminal modification of monoclonal antibody drugs: amidated species as a general product-related substance.

Twelve therapeutic mAbs, comprising 10 IgG1s and 2 IgG4s, were analyzed by a peptide mapping technique to detect and quantify C-terminal modifications. C-terminal amidated structures were found in 8 out of the 12 mAbs. An in vitro study using a commercially available peptidylglycine alpha-amidating monooxygenase (PAM) revealed that both IgG1 and IgG4 can be substrates for PAM. This study showed that C-terminal amidation is a general C-terminal modification on the heavy chains of therapeutic mAbs and that C-terminal amidation of mAbs can be catalyzed by a certain PAM(s) in the Chinese hamster ovary (CHO) cells that are widely used for manufacturing therapeutic mAbs.

Identification of deamidation and isomerization sites on pharmaceutical recombinant antibody using H(2)(18)O.

Asparagine (Asn) deamidation and aspartic acid (Asp) isomerization are spontaneous and common alterations occurring in pharmaceutical protein drugs in solution. Because those reactions may cause functional changes, it is important to identify the product-related substances, especially when biopharmaceuticals are under development. In this study, we used H(2)(18)O to identify Asn deamidation and Asp isomerization sites on a recombinant humanized monoclonal antibody (mAb) by using high-performance liquid chromatography-mass spectrometry (HPLC-MS). This strategy takes advantage of reactions whereby (18)O is incorporated into the protein molecule. The mAb was lyophilized and reconstituted in H(2)O or H(2)(18)O, followed by incubation at 50 degrees C for 1 month. Samples were reduced/carboxymethylated and digested by trypsin and then subjected to HPLC-MS and HPLC-tandem mass spectrometry (MS/MS) analysis. Among all of the peptide fragments analyzed, there were two in which deamidation and/or isomerization was observed. In one peptide fragment, an obvious mass shift ( approximately 3Da) at Asn was observed in the newly produced peptide when the mAb was incubated in H(2)(18)O, whereas it was barely feasible to identify this mass shift in H(2)O. In the other peptide fragment, isomerization of Asp was identified after incubation in H(2)(18)O, although it was impossible to distinguish when using H(2)O. By means of this procedure, identification of deamidation and isomerization sites can be accomplished easily even when they are difficult or impossible to detect by the usual peptide mapping.

32P-Postlabeling/polyacrylamide gel electrophoresis analysis: application to the detection of DNA adducts.

32P-Postlabeling analysis is a powerful technique to detect DNA adducts. Polyethylenimine-cellulose TLC plates are generally used to separate (32)P-labeled adducts using several different buffers. However, separation by TLC is time-consuming and labor-intensive for a large number of DNA samples. To expedite analyses, nondenaturing 30% polyacrylamide gel electrophoresis (PAGE) has been adapted for the (32)P-postlabeling analysis. The major advantages of this technique are as follows: (a) many DNA samples can be loaded concomitantly on the PAGE with standard markers; (b) DNA adducts can be resolved in only a few hours; and (c) exposure to (32)P during handing can be minimized. To show the usefulness of (32)P-postlabeling/PAGE analysis, the formation of a tamoxifen (TAM)-DNA adduct resulting from O-sulfonation of alpha-hydroxytamoxifen was demonstrated. In addition, to quantify TAM adducts, oligodeoxynucleotides containing diastereoisomers of alpha-(N(2)-deoxyguanosinyl)tamoxifen can be used as standards. The detection limit of this assay for 5 microg of DNA was approximately 7 adducts/10(9) nucleotides. The (32)P-postlabeling/PAGE analysis can also be used to detect DNA adducts derived from benzo[a]pyrene diol epoxide, 2-acetylaminofluorene, and 4-hydroxyequilenin.