Pharmacokinetics, Metabolism, and Oral Bioavailability of the DNA Methyltransferase Inhibitor 5-Fluoro-2′-Deoxycytidine in Mice

Abstract

Purpose: In vivo, 5-fluoro-2 ¶-deoxycytidine (FdCyd) is rapidly and sequentially converted to 5-fluoro-2 ¶-deoxyuridine, 5-fluorouracil, and 5-fluorouridine. The i.v. combination of FdCyd and 3,4,5,6-tetrahydrouridine (THU), a cytidine deaminase (CD) inhibitor that blocks the first metabolic step in FdCyd catabolism, is being investigated clinically for its ability to inhibit DNA methyltransferase. However, the full effects of THU on FdCyd metabolism and pharmacokinetics are unknown. We aimed to characterize the pharmacokinetics, metabolism, and bioavailability of FdCyd with and withoutTHU in mice. Conclusions: FdCyd is well absorbed but undergoes substantial first-pass catabolism by CD to potentially toxic metabolites that do not inhibit DNA methyltransferase. THU is sufficiently bioavailable to reduce the first-pass effect of CD on FdCyd. Oral coadministration of THU and FdCyd is a promising approach that warrants clinical testing because it may allow maintaining effective FdCyd concentrations on a chronic basis, which would be an advantage over other DNA methyltransferase inhibitors that are currently approved or in development.

Plasma pharmacokinetics and oral bioavailability of 3,4,5,6-tetrahydrouridine, a cytidine deaminase inhibitor, in mice

“…First, THU can improve the po absorption of a cytidine analogue into the systemic circulation by reducing the first-pass metabolism by intestinal and liver CD [34,35]. Second, THU can increase, and prolong, plasma concentrations of cytidine analogues by reducing systemic metabolism by CD [2,25]. Third, THU can make organs with high CD activity therapeutically accessible to cytidine analogues [17,27].…”

“…Uracil arabinoside is associated with Ara-C toxicity of the central nervous system [29,33], and 5-fluoro-2′-deoxyuridine and 5-fluorouracil are associated with undesirable cytotoxic effects related to 5-fluoro-2′-deoxycytidine [2].…”

“…The entire po THU dose is delivered to compartment 5, is transferred to compartment 4 (k 54 ), and from there is either eliminated (k 40 , never absorbed or pre-systemically metabolized) or taken up into the central compartment V 1 via a non-linear transfer rate (V max , K m ). Distribution takes place to compartments 2 and 3 by their respective rate constants (k 12 , k 21 , k 13 , k 31 ), and elimination from V 1 is determined by k 10 Table 1 Non-compartmental pharmacokinetic parameters of THU after iv or po administration to male CD 2 Vd volume of distribution, F oral bioavailability, i.e., the fraction/percentage of the administered dose that reaches the systemic circulation or plasma compartment, relative to when the drug is administered iv (for iv administration F is assumed to be unity/100%), Cl total body clearance a The half-lives were derived from the slope of the last points in the log concentration versus time curve. The last three time points were used, except for the 100 mg/kg po study where the last two points were used b The percentage of the AUC 0-inf that was extrapolated from the observed AUC ranged from 2.1-22% c The parameters calculated for the 100 mg/kg iv administration included the 2 min time point that was obtained later (see text) Table 2 Estimated values for the parameters of the compartmental model shown in Fig.…”

“…Historically, nucleoside analogues were developed as cytotoxic drugs. More recently, several cytidine analogues have been licensed (decitabine and 5-azacytidine), or are in development (5-fluoro-2′-deoxycytidine), based on their ability to inhibit methylation of DNA [2,12]. Cytidine analogues compete with endogenous cytidine and 2′-deoxycytidine and thereby have an impact on important biological processes such as DNA and RNA synthesis.…”

“…1) is a transition-state analogue of cytidine to uridine [6] that binds tightly to CD and thereby competitively inhibits deamination with a reported K i of 28-240 nM (7-60 ng/ml) [6,27,42]. By potently inhibiting CD, THU can prolong the half-life of i.v.-administered cytidine analogues, and, by decreasing first-pass metabolism in the gut and liver, THU can increase the bioavailability of cytidine analogues administered po [2,8,19,25,34]. This latter property may enable convenient, chronic po dosing of cytidine analogues.…”