Kisspeptins (Kp) are a family of neuropeptides differing in their length (54, 14, 13 and 10 amino acids in human) but derived from a common precursor. Kp stimulate GnRH secretion through their cognate receptor (KISS1R). Endogenous Kp isoforms have short in vivo half-life. Hence, an infusion could be necessary to achieve the required level of stimulation to induce ovulation or to treat some pathological conditions. Single injection treatment, however, is preferable to infusion. To meet this need we designed Kp10 analogs with improved pharmacokinetics and pharmacodynamics.

Analogs were created on Kp10 scaffold by combing modifications improving resistance to degradation and reducing renal clearance. Analogs potency and efficacy were assessed using a calcium mobilization assay on hKISS1R transfected HEK293 cells. Combination of various modifications leads to analogs having the same efficacy and similar or better potency compared to Kp10. Compounds stability assessed in ewe blood serum confirmed a significant increase in half-life. In vivo efficacy was tested in anoestrus ewes by recording LH plasma concentration kinetic after bolus intravenous injection at doses ranging from 1 to 15 nmoles/ewe. Analogs with resistance to proteolytic degradation produced an increase of LH plasma concentration that lasted more than thrice that induced by Kp10, from 30 minutes to 100 minutes. Insertion into these analogs of an albumin binding tag, to slow down renal clearance, acted synergistically leading to a dramatic prolongation of the effect. At the end of the experiment, 9 hours after injection, LH level were still three-fold the basal. Furthermore also peak LH concentration as well as the total amount of LH secreted were significantly increased.

In conclusion we generate analogs with improved pharmacokinetics and pharmacodynamics that stimulate the reproductive system and hold potential to manage livestock reproduction and treat human reproductive disorders.

Financial support: Région Centre (Reprokiss project).