In our previous studies,
interleukin-8 (IL-8) was labeled with (99m)Tc using hydrazinonicotinamide (HYNIC) as bifunctional coupling agent and
tricine as coligand. This preparation showed excellent characteristics for imaging of
infection in a rabbit model of
soft-tissue infection. In the present study, the propylaldehyde
hydrazone formulation of HYNIC was introduced to stabilize HYNIC-IL-8. (99m)Tc-HYNIC-IL-8 was prepared using 5 different coligand formulations. The effect of these coligand formulations on the in vitro characteristics and in vivo behavior of (99m)Tc-HYNIC-IL-8 was investigated. HYNIC-conjugated
IL-8 was labeled with (99m)Tc in the presence of either (A)
tricine, (B) ethylenediaminediacetic
acid (
EDDA), (C)
tricine and trisodium triphenylphosphinetrisulfonate (TPPTS), (D)
tricine and
nicotinic acid (NIC), or (E)
tricine and
isonicotinic acid (ISONIC). These preparations were characterized in vitro by RP-HPLC, determination of the octanol/water partition coefficient, stability studies, and receptor binding assays. The in vivo biodistribution of the radiolabel in rabbits with E. coli-induced
soft-tissue infection was determined both by
gamma-camera imaging as well as by tissue counting at 6 h pi. Specific activity (MBq/microg) was highest for (ISO)NIC (up to 80) > TPPTS (40) >
tricine (15) >
EDDA (7). RP-HPLC and octanol/water partition coefficients showed a shift toward higher lipophilicity for the TPPTS preparation. The leukocyte receptor binding fractions were around 40-55% for all preparations except for TPPTS, which showed predominantly nonspecific binding. All preparations were stabilized in serum, but the stability in PBS was highest for NIC and TPPTS >
EDDA > ISONIC >
tricine. The in vivo biodistribution showed highest
abscess/muscle for NIC and ISONIC (>200) >
EDDA and
tricine (approximately 100) > TPPTS (<40).
Gamma camera imaging rapidly visualized the
abscess from 2 h pi onward for all formulations. The
abscess/background (A/B) at 6 h pi for ISONIC was significantly higher (P < 0.05) than that of
tricine and the A/B of TPPTS was significantly lower (P < 0.05).
IL-8 can be rapidly and easily labeled with (99m)Tc using HYNIC as a
chelator in combination with various coligands. The most optimal
infection imaging characteristics were found for formulations using
nicotinic acid/
tricine as coligand system combining a high specific activity and high in vitro stability with high
abscess/muscle ratios (>200) and high
abscess/background ratios (>20).
Protein doses to be administered were as low as 70 ng/kg bodyweight. At these low
protein doses, side effects are not to be expected in the human system. This paves the way for
infection imaging studies in patients.