Use of receptor-binding domain derived from bovine leukemia virus for the diagnosis or treatment of cationic l-amino acid transporter-related diseases

1. A method for detecting and/or quantifying the cationic amino acid transporter-1 (CAT1) in a cell, wherein said method comprises:

(a) contacting said cell with one and only one ligand comprising a bovine leukemia virus-RBD ligand (BLV-RBD ligand), a variant and/or a fragment thereof, and

(b) determining and/or quantifying the binding of said BLV-RBD ligand, a variant and/or fragment thereof to CAT1 by detecting and/or quantifying a complex formed between CAT1 and said BLV-RBD ligand, variant or fragment thereof,

wherein said BLV-RBD ligand comprises the sequence of SEQ ID NO: 21, a variant and/or fragment thereof,

wherein said variant of a BLV-RBD ligand comprises a sequence presenting a sequence identity of at least 85% with SEQ ID NO: 21 and

wherein said fragment of a BLV-RBD ligand comprises or consists of amino acids 34 to 149 of SEQ ID NO: 21.

2. The method according to claim 1 , wherein said method further comprises comparing the binding level determined and/or quantified at step (b) with a reference value.

3. A method for diagnosing or monitoring a CAT1-related disease in a subject, wherein said method comprises:

(a) contacting a cell with one and only one ligand comprising a bovine leukemia virus-RBD ligand (BLV-RBD ligand), a variant and/or a fragment thereof,

(b) determining and/or quantifying the binding of said BLV-RBD ligand, variant and/or fragment thereof to CAT1 by detecting and/or quantifying a complex formed between CAT1 and said BLV-RBD ligand, variant or fragment thereof,

(c) comparing the binding level determined and/or quantified at step (b) with a reference binding value, wherein an equivalence or a binding level greater than the reference binding level is indicative of the presence of a CAT1-related disease,

wherein said BLV-RBD ligand comprises the sequence of SEQ ID NO: 21, a variant and/or fragment thereof,

wherein said variant of a BLV-RBD ligand comprises a sequence presenting a sequence identity of at least 85% with SEQ ID NO: 21,

wherein said fragment of a BLV-RBD ligand comprises or consists of amino acids 34 to 149 of SEQ ID NO: 21, and

wherein said CAT1-related disease is selected from arginine-related cancers, argininosuccinate lyase-related diseases, argininosuccinate synthetase-related cancers or diseases, cardiac fibrosis, muscle fibrosis, hyperlysinemia, glutaric aciduria type I, L-2 hydroxyglutaric aciduria, D-2 hydroxyglutaric aciduria, herpes simplex infection, histidinemia, histidine ammonia-lyase deficiency, ornithine transcarbamylase deficiency, cirrhosis, carcinogenesis, chronic renal failure, chronic heart failure, congestive heart failure, hypertension, atherosclerosis, stroke, thrombosis, polyarthritis, rheumatoid arthritis, asthma, inflammatory bowel diseases, celiac diseases, autoimmune diseases, multiple sclerosis, obesity, diabetes, cardiovascular mortality, renal damage and ischemia.

4. The method according to claim 1 , being an in vitro method.

5. The method according to claim 3 , being an in vivo method, wherein the method comprises administering to a subject in need thereof the BLV-RBD ligand, a variant and/or a fragment thereof.

6. The method according to claim 5 , being an in vivo method for diagnosing or monitoring a CAT1-related disease in a subject by medical imaging, wherein the ligand is coupled with at least one contrast agent.

7. The method according to claim 1 , wherein said variant of the BLV-RBD ligand comprises a sequence selected from the list consisting of SEQ ID NO: 4, 28 and 29.

8. The method according to claim 3 , being an in vitro method.

9. The method according to claim 3 , wherein said variant of the BLV-RBD ligand comprises a sequence selected from the list consisting of SEQ ID NO: 4, 28 and 29.