A Bio-Chemosynthetic Approach to Superparamagnetic Iron Oxide-Ansamitocin Conjugates for Use in Magnetic Drug Targeting.

A combination of mutasynthesis using a mutant strain of A. pretiosum blocked in the biosynthesis of amino-hydroxybenzoic acid (AHBA) and semisynthesis relying on a Stille cross-coupling step provided access to new ansamitocin derivatives of which one was attached by a thermolabile linker to nanostructured iron oxide particles. When exposed to an oscillating electromagnetic field the resulting iron oxide/ansamitocin conjugate 19 heats up in an aqueous suspension and the ansamitocin derivative 16 is released by means of a retro-Diels-Alder reaction. It exerts strong antiproliferative activity (IC =4.8 ng mg ) in mouse fibroblasts. These new types of conjugates have the potential for combating cancer through hyperthermia and chemotherapy using an electromagnetic external trigger.