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I am planning to conduct tissue distribution studies for a peptide containing 40 amino acids. 125 iodination was chosen as the method for peptide labeling. I have a couple of questions regarding how to conduct the studies.
1. In ICH Topic S 6, it's stated that "When using radiolabeled proteins, it is important to show that the radiolabeled test material maintains activity and biological properties equivalent to that of the unlabeled material". I am wondering practically, what techniques are people frequently used to fulfill the regulatory requirement that the 125I-peptide maintains activity and biological properties equivalent to that of the unlabeled peptide. I have searched literatures and hardly found anyone mentioned that they had done this before using 125I-biologics in animal tissue distribution studies.
2. The intended clinical administration route for this peptide is subcutaneous injection. However, the bioavailability of this peptide by SC is less than 10%. I am wondering, whether I can use IV injection of this peptide in the tissue distribution studies.
Any comments or suggestions are highly appreciated. Since I cannot receive emails from the PharmPK discussion list since this April, please cc my email address (yulan.qi.at.gmail.com) if you reply.
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