Synthesis and Biological Evaluation of Isonicotinic Acid Hydrazide Conjugated with Diethyelenetriaminepentaacetic Acid for Infection Imaging

Introduction: Isonicotinic acid hydrazide (INH) was coupled to diethylenetriaminepentaacetic acid (DTPA) via amide linkage. Primary object of the present invention was to propose a novel INH derivative based on DTPA, which form stable complexes with most of lanthanides and transition metals in periodic table. Another object of the present invention was to introduce a chelating group in INH without compromising its biological activity for early diagnosis of infection using nuclear medicine and MR techniques. Methods: The DTPA-bis(INH) was synthesized in high yield using simple synthetic procedure. Radiochemical purity was ascertained chromatographically using different solvent system. Blood kinetics in rabbits and biodistribution in mice were studied. The ability of DTPA-bis(INH) to target infection site in vivo was assessed by gamma scintigraphic studies of normal rabbit and rabbit with induced tuberculosis. Preliminary clinical studies were done in patients with known tuberculoses lesions. Results: DTPA-bis(INH) was characterized using spectroscopic techniques. The complex was successfully labeled with 99m Tc radionuclide with more than 95% labeling efficiency. It was found stable up to 24h. Blood kinetics showed rapid first pass clearance with biological half life t1/2 (F) of 11 min. Biodistribution in tuberculose induced Balb/c mice showed target to muscle ratio 4.53 ± 0.89 after 4h post injection. Gamma scintigraphy of normal as well as rabbits with induced tuberculosis was carried out. An appreciable activity was visualized in liver and kidneys. In infection induced rabbit similar pattern was observed with the accumulation of activity at the tuberculose site at 4 h post injection. Clinical scintigraphy with 99m Tc-DTPA-bis(INH) clearly indicated the accumulation of the tracer at the tuberculose region in six patients (median age 46 years, range 28-69 years, females; n=2 and males; n=4) which were found positive for Mycobacterium tuberculosis in bacterial culture analysis. Conclusions: From the present work it can be concluded that the radiolabeled DTPA-bis(INH) accumulates at the site of