Synthesis of ¹²³I‐ and ¹³¹I‐labelled derivatives of low‐density lipoprotein for radiopharmaceutical use

The syntheses of two analogues of low‐density lipoprotein (LDL) labelled with ¹²³I or ¹³¹I was optimized for radiopharmaceutical application. Rabbit LDL was employed due to its usefulness in pre‐clinical experimentation, although the parameters which were optimized also pertain to human LDL. LDL was iodinated directly with exchange‐labelled [¹²³I]ICI to produce injectable [¹²³I]LDL in 40% radiochemical yield within 30 min. A derivatized version of LDL, [¹²³I]TC‐LDL, was produced in about 30% radiochemical yield within 75 min by radioiodination of tyramine‐cellobiose (TC) via in situ oxidation of ¹²³I⁻ followed by cross‐linking to LDL using cyanuric chloride. Quality control tests indicated that both radioiodinated LDL and TC‐LDL were very similar in character to the native LDL molecule.