The peptide HsTX1[R14A] is a potent and selective blocker of the voltage-gated potassium channel K_V1.3, which is a highly promising target for the treatment of autoimmune diseases and other conditions.^1,2 However, there is limited information on its pharmacokinetics and biodistribution in mice, both of which are important given that many preclinical efficacy studies are conducted in mice.

A bioanalytical method for the quantitative determination of HsTX1[R14A] in C57BL/6J mouse plasma was developed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The validated method was linear over the concentration range 6.7-66.7 nM for HsTX1[R14A]; and the lower limit of quantitation was 6.7 nM. The average precision and accuracy were <5.4% and <13.5%, respectively.  The entire analysis time was only 5 min per sample. The currently developed LC-MS/MS assay will be applied to assess the pharmacokinetics of HsTX1[R14A] in mice following intravenous administration.

In addition, a radiotracer was developed to enable positron emission tomography (PET) studies of peptide distribution in mice over a period of days. HsTX1[R14A] was synthesised¹ with a DOTA tag coupled to the N-terminus via a mini PEG, aminoethyloxyethyloxyacetyl (AeeA) linker and radiolabelled with copper-64. The radiochemical purity and in vitro stability of [⁶⁴Cu]Cu-DOTA-HsTX1[R14A] will be determined by radio-HPLC, prior to administration to mice and PET will be employed to monitor biodistribution.

These analytical methods (LC-MS/MS and PET) can now be applied to evaluate the plasma pharmacokinetics and biodistribution of HsTX1[R14A] in mice in both healthy and diseased states.