Radiolabeling and preclinical evaluation of technetium-99m labeled colistin.

Introduction: Antibiotic resistance is a burden on the healthcare system. In present study, we have labeled an antibiotic named Colistimethate sodium (CMS) with technetium-99m (Tc) to develop a SPECT based imaging tracer.

Methods: We standardised the labeling using 0.5-2 mg of CMS (in water) using stannous chloride dihydrate as a reducing agent followed by addition of 370 ± 74 MBq of Tc. A group of mice were injected intravenously (in tail vein) with 4-6 MBq of [Tc]Tc-CMS diluted with saline and euthanized at various time intervals. microSPECT Imaging (ϒ-eye) was acquired to study the biodistribution in the healthy mice.

Results: We standardised the labeling using 0.5 mg of colistin in 0.5 ml of saline with addition of 30 μg stannous chloride dihydrate. The retention factor value was 0.1-0.3 as compared to 0.9-1.0 for free Tc by TLC and retention time was found to be 14.2 ± 1.3 min as evaluated by HPLC. The biodistribution data showed uptake in lungs, spleen, and liver at 30 min but the uptake decreased in lung at 60 min. The imaging data corroborated with the biodistribution data.

Conclusions: We could successfully label [Tc]Tc-CMS Tc and we could study its biodistribution in healthy mice.