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Building confidence & reliability

Custom radiolabelling

The use of radioactive probes remains the gold standard labelling technique for ADME/PK purposes in drug development (small and large molecules).

If the labelling strategy has to be carefully tailored depending on the considered application, it is also essential, before any in vivo investigation, to insure that the label preserves biological properties of large molecules.


Radioiodination may be performed by two alternative methods, namely by targeting iodine-accepting groups present on the sequence or by the conjugation of a small radioiodinated molecule to the protein.

Direct radioiodination

Iodogen, Chloramine-T or Lactoperoxidase lead to the in situ preparation of an electrophilic radioiodine species, which reacts mostly with tyrosine groups.

Indirect radioiodination (conjugation method)

This labelling method provides an alternative way to label proteins via Lysine amino acid using a prosthetic group.
- The 125I-Bolton-Hunter reagent (N-succinimidyl-3-(4-hydroxy-3-[125I]iodophenyl) propionate)
- The 125I-SIB reagent (N-succinimidyl-3-[125I]iodobenzoate)

Besides custom radioiodination, Chelatec also proposes freshly prepared radioligands
(download our catalogue)

Protein labelling with 3H-NSP

N-succinimidyl-[2,3-3H]propionate is a labelling reagent that allows to prepare tritiated proteins by a method similar to the one using 125I-SIB or 125I-Bolton Hunter reagent. It labels free amino functions.

Due to its smaller size, it can minimize interaction with protein structure but it will lower the specific activity:



Iodine-125, 125I-SIB, 125I-BH

Specific Activity

~ 80 Ci/mmol
~ 3000 GBq/mmol

~ 2200 Ci/mmol
~ 84100 GBq/mmol



Using the appropriate bifunctionnal chelating agent, radioactive metal ions (Indium-111, Lutetium-177,...) will be attached on biologic molecules (antibodies, proteins,...). The labelled immunoconjugateobtained can be used in DMPK investigations or as a radiopharmaceutical.

The use of such residualizing radionuclides in DMPK studies can provide very usefull information regarding the cumulative uptake in tumors/tissues (in case of internalization).

Please contact us to discuss the best labelling strategy for your scientific goals