Evaluation of radiolabelled hynic-salmon calcitonin analogues as imaging agents for multiple myeloma and characterisation of novel hynic derivatives as chelators for technetium

Abstract

Calcitonin is a peptide hormone produced by the C-cells of the thyroids. Calcitonin receptors (CTR) are expressed by osteoclasts in the normal bone and in many cancers such as multiple myeloma (MM), breast and prostate cancer. In this thesis we report on the synthesis and evaluation of Tc-99m labelled salmon calcitonin (sCT) derivatives, sCTLys18-hynic-TFA and sCT(8-32)Lys18-hynic-TFA as potential imaging agents for MM and other CTR+ malignancies and the characterisation of novel hydrazinonicotinate (hynic) chelators. Following chemical characterisation in vitro stabilities of the radiopeptides were assessed on incubation in human serum. In vitro uptake studies in CTR+ MCF-7 cells confirmed that the Tc-99m labelled sCTLys18-hynic-TFA and sCT(8-32)Lys18-hynic-TFA were both ligands for CTR with nanomolar affinity. These findings also confirmed that the evolutionarily conserved disulfide loop in calcitonin peptides is not vital for receptor binding. We evaluated the radiopeptides in vivo in the 5T33 murine MM model. By using In-111-oxine labelled enhanced green fluorescence protein transfected 5T33 cells (eGFP-5T33) we confirmed that MM cells have a very high affinity to haemopoietic organs i.e. the liver, spleen and bone marrow. When imaging eGFP-5T33 myeloma bearing mice with Tc-99m labelled sCTLys18-hynic-TFA and sCT(8-32)Lys’8-hynic-TFA we found increased radiopeptide uptake in the liver, spleen and femora when compared to healthy controls. We could not establish correlation between radiopeptide uptake and the size of eGFP+ or CTR+ cell population in target organs. Our results suggest that the Tc-99m labelled hynic-sCT peptides may be capable of detecting changes caused by MM in the biology of the liver, spleen and bone marrow. Studies with novel hynic derivatives confirmed that hynic was most likely a bidentate chelator rather than a monodentate ligand in technetium complexes.

Date of Award	1 Jan 2013
Original language	English
Awarding Institution	King's College London
Supervisor	Philip Blower (Supervisor) & Yolanda Calle (Supervisor)