Polymorphisms of the drug transporter gene ABCB1 predict side effects of treatment with cabergoline in patients with PRL adenomas. 
Treatment with dopamine agonists in patients with prolactin (PRL) adenomas and Parkinson's disease is associated with central side effects.  Central side effects may depend on a substance's ability to pass the blood-brain barrier, which can be actively controlled by transporter molecules such as the P-glycoprotein (P-gp) encoded by the ABCB1 gene.  We aimed to determine whether cabergoline is transported by the P-gp and whether polymorphisms of its encoding ABCB1 gene predict central side effects of cabergoline therapy in patients with PRL adenomas.  i) In an experimental mouse model lacking the homologues of the human ABCB1 gene (Abcb1ab double knockout mouse model), we examined whether cabergoline is a substrate of the P-gp using eight mutant and eight wild-type mice.  ii) In a human case-control study including 79 patients with PRL adenomas treated with cabergoline at the Max Planck Institute of Psychiatry in Munich, we investigated the association of four selected ABCB1 gene single nucleotide polymorphisms (SNPs) (rs1045642, rs2032582, rs2032583 and rs2235015), with the occurrence of central side effects under cabergoline therapy.  i) In the experimental mouse model, we observed that brain concentrations of cabergoline were tenfold higher in the mutant mice compared with their wild-type littermates, implying that cabergoline is indeed a substrate of the transporter P-gp at the blood-brain barrier level.  ii) In the human study, we observed significant negative associations under cabergoline for the C-carriers and heterozygous CT individuals of SNP rs1045642 with two central side effects (frequency of fatigue and sleep disorders) and for the G-carriers of SNP rs2032582 with the enhancement of dizziness.  For the SNPs rs2235015 and rs2032583, no associations with central side effects under cabergoline were found.  This is the first study demonstrating that individual ABCB1 gene polymorphisms, reflecting a different expression and function of the P-gp, could predict the occurrence of central side effects under cabergoline.  Our findings can be viewed as a step into personalised therapy in PRL adenoma patients.