Design and synthesis of isoniazide mimetic conjugated with DTPA, potential ligand of novel radiopharmaceutical and contrast agent for medical imaging, bis (amide) of diethylenetriaminepentaacetic acid: DTPA-Bis(INH)

The structure of isonicotinic acid hydrazide (INH) was coupled to diethylenetriaminepentaacetic acid (DTPA) via amide linkage. The overall yield of three steps synthesis starting from DTPA is above 80%. In particular, complexation of DTPA moiety with 99mTc showed excellent results as the metallopharmaceutical for medical imaging. The main objective of the present research was to develop a novel INH derivative based on DTPA, which forms stable complexes with most of the lanthanides and transition metals in the periodic table. A second objective was to introduce a chelating group without compromising the biological activity of the anti-infective drug for the diagnosis of infection using nuclear medicine. The DTPA-Bis(INH) was synthesized in high yield using a simple synthetic procedure and was characterized using mass spectroscopy in ESI positive mode ([M+H+] was found to be 632.2). Moreover, the complex with the DTPA-Bis(INH) is reflected in increased kinetic ability of the stabilized 99mTc complex compared with the unmodified INH. The complex was successfully labelled with the 99mTc radionuclide with more than 95% labelling efficiency. Radiochemical purity was ascertained chromatographically (ITLC and C18 RP chromatography) using different solvent systems. Blood kinetics in rabbits and biodistribution in mice was studied. Blood kinetics showed rapid first pass clearance with a biological half-life, t1/2 (F), of 11 min. The ability of DTPA-Bis(INH) to target the infection site in vivo was assessed in gamma scintigraphic studies of normal rabbit and a rabbit with induced infections. From the present work it can be concluded that the radiolabelled DTPABis( INH) accumulates at the site of infection. (author)