A peripherally restricted P2Y receptor antagonist altered rat tumor incidences with no human relevance: Mode of action consistent with dopamine agonism.

Background: Ticagrelor is an orally available, direct acting and reversible P2Y receptor antagonist approved for treatment of acute coronary syndrome. The objectives of these studies were to (1) evaluate the Ticagrelor 2-year rat carcinogenicity bioassay data; (2) investigate potential mode of action (MOA) and (3) interpret human relevance.

Methods: The following studies were done (1) rat two-year carcinogenicity study in male and female rats, (2) and genotoxicity assays, (3) quantitative whole body autoradiography (QWBA; male and female rats), (4) pharmacological profiling for more than 300 assays, and (5) ovariectomized rat assay.

Results: The carcinogenicity study indicated Ticagrelor increased uterine tumor incidence while decreasing mammary and pituitary tumors/hyperplasia incidences in only high dose female rats. However, this altered tumor incidences were not P2Y target related since marketed non-reversible P2Y receptor antagonists were not associated with alter tumor incidences. MOA studies determined Ticagrelor exposure in the anterior pituitary and Ticagrelor was (1) non-genotoxic, (2) peripherally-restricted, (3) a dopamine transport (DAT) inhibitor with an IC lower than systemic free exposure in the rat carcinogenic study and more than a log higher than the free systemic exposure seen in clinical trials and (4) an inhibitor of estradiol-induced prolactin secretion.

Discussion: Similar to Ticagrelor, centrally active dopamine agonists induce the same altered tumor incidence patterns that according to literature do not translate into the clinical setting, with a MOA involving decreased prolactin secretion. The Ticagrelor MOA data and literature suggest that altered dopamine levels in the hypophyseal part of the hypothalamus-hypophyseal axis (by Ticagrelor) will result in similar altered tumor incidences in rat that do not translate into the clinical setting, based on qualitative species differences. In conclusion Ticagrelor increased uterine tumors in the rat carcinogenesis study by a MOA consistent with reduced dopamine inhibition of prolactin, which is not a patient safety risk.