99mTc-labeled annexin V fragments: a potential SPECT radiopharmaceutical for imaging cell death.
BACKGROUND
Annexin V is a protein that binds to phosphatidylserine exposed on dying cells. The phosphatidylserine-specific sequence is attributed to a chain on the N-terminal of annexin consisting of 13 amino acid sequence. Radiolabeled annexin V is used for imaging apoptosis.


METHODS
With an aim to synthesize a probe that can detect cell death akin to annexin V but smaller in size, annexin-13 fragments were derivatized to contain cysteine, cysteine-cysteine and histidine in their sequence at N terminal and were labeled with (99m)Tc via nitrido and carbonyl precursors. The (99m)Tc-labeled annexin-13 derivatives were characterized by HPLC and studied for their stability. In vitro and in vivo studies were carried out in apoptotic HL-60 cells and fibrosarcoma tumor-bearing Swiss mice, respectively.


RESULTS
The (99m)Tc complexes were formed in high yields and were found to be stable. HPLC pattern of (99m)Tc nitrido complex of cysteine-cysteine-annexine 13 (CC-Anx13) and (99m)Tc carbonyl complex of histdine-annexin 13 (H-Anx13) revealed the formation of single species. In vitro cell uptake studies with (99m)Tc nitrido complex of cysteine-cysteine-annexin 13 fragment showed 6.5% uptake in apoptotic HL-60 cells. The uptake was found to be specific on testing with apoptotic HL-60 cells. Biodistribution studies of (99m)Tc nitrido complex with CC-Anx13 in fibrosarcoma tumor-bearing Swiss mice revealed optimum tumor uptake of 0.52 (0.17) %ID/g at 1 h pi.


CONCLUSIONS
(99m)Tc(N)-CC-anx13 showed specific uptake in apoptotic tumor cells and warrants further evaluation.
Mukherjee
Archana
A
Radiopharmaceuticals Division, Radiochemistry and Isotope Group, Bhabha Atomic Research Centre, Mumbai-400085, India.
Kothari
Kanchan
K
Tóth
Géza
G
Szemenyei
Erzsébet
E
Sarma
Hal Dhar
HD
Környei
József
J
Venkatesh
Meera
M
D000818:Animals; D017304:Annexin A5 / Q000737:chemistry / Q000493:pharmacokinetics*; D017209:Apoptosis; D005240:Feasibility Studies; D005354:Fibrosarcoma / Q000000981:diagnostic imaging* / Q000378:metabolism* / Q000473:pathology; D018922:HL-60 Cells; D006801:Humans; D007553:Isotope Labeling / Q000379:methods; D008657:Metabolic Clearance Rate; D051379:Mice; D009928:Organ Specificity; D015609:Organotechnetium Compounds / Q000737:chemistry / Q000493:pharmacokinetics*; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*
D017304:Annexin A5; D015609:Organotechnetium Compounds; D019275:Radiopharmaceuticals; C417036:technetium Tc 99m annexin V