Abstract :
[en] As the most common endocrine malignancy, thyroid cancer is increasingly diagnosed worldwide with an incidence that is growing steadily. The main challenge is to diagnose the patients who really need a surgery. Indeed, thyroid nodules are frequent and 90% of thyroid surgeries are made for benign lesions. Current diagnosis approaches imply painful and often useless thyroid surgeries. Thereby, this project aims to develop a new and non-invasive diagnosis approach of papillary carcinoma, which is the most frequent thyroid malignancy.
This work is based on the targeting of galectin-1 (gal-1) as a diagnostic tool for well-differentiated thyroid cancers. Gal-1 is a small adhesion protein expressed in muscles, neurons and some embryonic tissues in non-pathologic conditions. Mostly secreted in the extracellular compartment, this protein can also be found in cytoplasm and in nucleus. It is involved in cellular adhesion, aggregation, migration, cytoskeleton reorganisation, and cell cycle regulation phenomena. In addition, gal-1 is overexpressed in a large variety of cancers (head and neck, skin, lungs, bladder, prostate, ovaries, colorectal region) and also in thyroid cancers. In fact, gal-1 is implied in tumour-induced immunosuppression, angiogenesis, hypoxia and metastasis.
During this project, the phage display technique has been used to identify peptides targeting the gal-1. Six successive rounds have been performed by exposing the immobilized target to a phage library. Each phage clone wears on its capsid a different random peptide sequence. The pre-selection has been carried out on a control protein and after washing and elution steps, the phages bound to gal-1 have been collected and amplified to start a new round. The affinity of these 6 outputs has been evaluated by ELISA and showed an increase along the rounds. From the sixth output, 50 clones have been isolated and their affinity evaluated. Two clones over 50 showed a good specific affinity toward gal-1 (Peptide 1 and Peptide 8). The peptide sequence has been revealed after DNA extraction and the two peptides were synthesized.
The affinity of these two molecules has been evaluated by ELISA and the cellular localization has been demonstrated by immunohistochemistry on human papillary thyroid cancer slices. Once their binding is attested, these peptides will be conjugated to a contrast agent in order to visualize tumours in vivo by molecular imaging.
