Pharmacokinetic/ pharmacodynamic studies of a copper-64 labelled Kv1.3-blocking peptide targeting autoimmune diseases

Objectives
The voltage-gated potassium channel Kv1.3 is an attractive therapeutic target to treat autoimmune disorders such as multiple sclerosis, rheumatoid arthritis, systemic lupus erythematosus and type-1 diabetes mellitus [1, 2]. This channel is highly expressed in T
effector memory lymphocytes and plays an important role in their activation. A scorpion toxin derived peptide analogue, HsTX1[R14A], blocks Kv1.3 with an affinity in the picomolar range [3].Moreover, this peptide is stabilized by four disulfide bridges, conferring high in vivo stability.
Methods
The peptide was synthesised by SPPS using Fmoc-tBu strategy [3]. The N-terminus of HsTX1[R14A] has been coupled to NOTA (1,4,7-triazacyclononane-triacetic acid) to permit labelling with the positron emitter copper-64. Biodistribution studies and metabolite analysis were carried out in healthy male Wistar rats using Positron Emission Tomography and Radioluminography.
Results
The distribution studies demonstrated a rapid blood clearance after intravenous injection and a fast renal elimination. The highest accumulation was found in the kidney and urine. As a consequence, a long in vivo half-life has been observed. Furthermore, there were no indications of lymphatic cell binding in direct measurements with unfractionated human Tcells.
Conclusion
The promising pharmacological profile of the radiotracer enhances the potential of this peptide to be developed as a therapeutic. Its extraordinary stability and high selectivity for the target channel Kv1.3 make it an attractive candidate for autoimmune disorders.
References
[1] V. Chi, M. W. Pennington, R. S. Norton, E. Tarcha, L. Londono, B. Sims-Fahey, S. K. Upadhyay, J. T. Lakey, S. Iadonato, H. Wulff, C. Beeton, K. G. Chandy, Toxicon 2012, 59, 529-546.
[2] C. Beeton, et al. Proc. Natl. Acad. Sci. U. S. A. 2006, 103, 17414-17419.
[3] M. H. Rashid, R. Huq, M. R. Tanner, S. Chhabra, K. K. Khoo, R. Estrada, V. Dhawan, S. Chauhan, M. W. Pennington, C. Beeton, S. Kuyucak, and R. S. Norton, Sci. Rep. 2014, 4, 1-9.