Liver effects of cyclin-dependent kinase inhibitor seliciclib. Relations with circadian pharmacokinetics and liver clock disruption. Free

A106

Background: The therapeutic activity of Seliciclib, a cyclin-dependent kinase (CDK) inhibitor, involves the induction of tumor molecular circadian clock in mice (Iurisci et al. Cancer Res 2006). Here we studied the relations between seliciclib pharmacokinetics (PK) and pharmacodynamic effects (PD) on liver toxicity (serum alanine aminotransferase, ALAT; and lactate dehydrogenase, LDH) and molecular clock genes expression patterns (Per2, Rev-erbα, Bmal1) in liver. PK-PD were assessed after seliciclib delivery at the time of best or poorest antitumor efficacy (Zeitgeber Time, ZT 3 or ZT19, respectively) in male B6D2F1mice.
 Methods: In experiment (Exp) 1, seliciclib (300 mg/kg p.o. single dose) was administered at ZT 3 or ZT19 Blood was sampled on heparin at 10, 20, 30 min, 1, 2, 4, 6, 8, 12 and 24 hours after dosing (3 mice per sampling time and dosing ZT). Seliciclib concentrations were analyzed using high performance liquid chromatography (HPLC) and UV-detectionand PK parameters were computed using WinNonlin Version 5.01 (Pharsight, Mountain View, CA, USA) and compared with Mann Whitney T-test. In Exp 2, serum ALAT and LDH were determined in 50 mice 24-h after seliciclib (300 mg/kg/d x 5d) or vehicle administration. In Exp 3, Seliciclib (same schedule) was administered at ZT3 or ZT19 to 132 mice. Livers were sampled at ZT 5, 11, 17 or 23, starting 24-h after the 5th dose. The 24-h mRNA expression patterns of Per2, Bmal1 and Rev-erbα were determined with q-RT-PCR. 
 Results:Seliciclib PK revealed higher drug exposure in mice dosed at ZT3 as compared to ZT19. Seliciclib dosing at ZT3 resulted in higher Cmax (21.9 vs 14.7 μg/ml, P= 0.02), higher AUC (114 vs 91 µg/ml x h, P = 0.001). Treatment at ZT3 resulted in a lower volume of distribution compared to ZT19 (160 mL vs 328 mL, P = 0.03). Mean serum ALAT selectively increased by 80% following seliciclib at ZT3 as compared to controls (P = 0.036), while no effect was found following treatment at ZT19 (P = 0.77). Mean serum LDH also increased following seliciclib at at ZT3 as compared to ZT19 (P =0.042). In the liver of control mice, mean mRNA expression of Rev-erbα varied 57-fold as a function of circadian time of sampling, with a maximum at Circadian Time 6 (CT6; P =0.001), The mRNA rhythms of Per2 and Bmal1 varied 5- and 8- fold respectively along the 24 hour time scale, with corresponding maxima occurring at CT14 (P =0.001) and at CT 19 (P =0.003). Seliciclib disrupted the liver clock according to drug dosing time: all three clock genes were markedly altered in the mice given Seliciclib at ZT3, the rhythm in Rev-erbα was phase advanced by nearly 6-h , while Per2 and Bmal1 rhythms were suppressed. Mice treated at ZT19 maintained near normal rhythms in Rev-erbα and Per2, with ablated Bmal1 rhythm. These results support a link between clock disruption and toxicity.
 Conclusion: PK-PD of seliciclib are controlled by the circadian timing system that regulate drug absorption, metabolism, distribution and elimination as well as cellular susceptibility. In turn, seliciclib can also modify the liver circadian clock, whose disruption likely contributes to toxicity. Circadian scheduling is an important determinant of seliciclib therapeutic index.
 Support by: ARTBC, hôp. P Brousse, Villejuif, F, Universita’ “G.D’Annunzio”,Chieti, It and the European Union (TEMPO and BioSim (Contracts LSHG-CT-2006-037543 & LSHB-CT-2004-005137).