In vitro drug-drug interactions of decitabine and tetrahydrouridine involving drug transporters and drug metabolising enzymes.

1. NDec is a novel, oral, fixed-dose formulation of decitabine and tetrahydrouridine that is currently being developed for the treatment of patients with sickle cell disease. Here, we examine the potential for both components of NDec to interact with key drug metabolising enzymes (tetrahydrouridine only) and drug transporters (decitabine and tetrahydrouridine).2. This study assessed the inhibition and induction of cytochrome P450 (CYP) enzymes by tetrahydrouridine, as well as the involvement of specific drug metabolising enzymes in tetrahydrouridine metabolism. Inhibition of efflux and uptake transporters by both decitabine and tetrahydrouridine was also studied.3. Tetrahydrouridine did not inhibit or induce relevant CYP enzymes at concentrations ranging from 0.1 to 100 µM. Metabolism of tetrahydrouridine did not occur in the presence of the human drug metabolising enzymes tested. Tetrahydrouridine showed weak inhibition towards the MATE2-K transporter (∼30% inhibition at 5 and 50 µM), which was not deemed clinically relevant. Tetrahydrouridine did not inhibit any of the remaining uptake or efflux transporters. Decitabine (0.5 and 5 µM) did not inhibit any of the evaluated uptake or efflux drug transporters.4. Data presented confirm that tetrahydrouridine and decitabine are unlikely to be involved in metabolism- or transporter-based drug-drug interactions.

Plasma pharmacokinetics and oral bioavailability of the 3,4,5,6-tetrahydrouridine (THU) prodrug, triacetyl-THU (taTHU), in mice.

PURPOSE: Cytidine drugs, such as gemcitabine, undergo rapid catabolism and inactivation by cytidine deaminase (CD). 3,4,5,6-tetrahydrouridine (THU), a potent CD inhibitor, has been applied preclinically and clinically as a modulator of cytidine analogue metabolism. However, THU is only 20% orally bioavailable, which limits its preclinical evaluation and clinical use. Therefore, we characterized THU pharmacokinetics after the administration to mice of the more lipophilic pro-drug triacetyl-THU (taTHU). METHODS: Mice were dosed with 150 mg/kg taTHU i.v. or p.o. Plasma and urine THU concentrations were quantitated with a validated LC-MS/MS assay. Plasma and urine pharmacokinetic parameters were calculated non-compartmentally and compartmentally. RESULTS: taTHU did not inhibit CD. THU, after 150 mg/kg taTHU i.v., had a 235-min terminal half-life and produced plasma THU concentrations >1 µg/mL, the concentration shown to inhibit CD, for 10 h. Renal excretion accounted for 40-55% of the i.v. taTHU dose, 6-12% of the p.o. taTHU dose. A two-compartment model of taTHU generating THU fitted the i.v. taTHU data best. taTHU, at 150 mg/kg p.o., produced a concentration versus time profile with a plateau of approximately 10 µg/mL from 0.5-2 h, followed by a decline with a 122-min half-life. Approximately 68% of i.v. taTHU is converted to THU. Approximately 30% of p.o. taTHU reaches the systemic circulation as THU. CONCLUSIONS: The availability of THU after p.o. taTHU is 30%, when compared to the 20% achieved with p.o. THU. These data will support the clinical studies of taTHU.

Stability of 5-fluoro-2'-deoxycytidine and tetrahydrouridine in combination.

In vivo, the DNA methyltransferase inhibitor, 5-fluoro-2'-deoxycytidine (FdCyd, NSC-48006), is rapidly converted to its unwanted metabolites. Tetrahydrouridine (THU, NSC-112907), a cytidine deaminase inhibitor can block the first metabolic step in FdCyd catabolism. Clinical studies have shown that co-administration with THU can inhibit the metabolism of FdCyd. The National Cancer Institute is particularly interested in a 1:5 FdCyd/THU formulation. The purpose of this study was to investigate the in vitro pH stability of FdCyd and THU individually and in combination. A stability-indicating high-performance liquid chromatography method for the quantification of both compounds and their degradants was developed using a ZIC(R)-HILIC column. The effect of THU and FdCyd on the in vitro degradation of each other was studied as a function of pH from 1.0 to 7.4 in aqueous solutions at 37 degrees C. The degradation of FdCyd appears to be first-order and acid-catalyzed. THU equilibrates with at least one of its degradants. The combination of FdCyd and THU in solution does not affect the stability of either compound. The stability and compatibility of FdCyd and THU in the solid state at increased relative humidity and at various temperatures are also evaluated.

Concentrations of the DNA methyltransferase inhibitor 5-fluoro-2'-deoxycytidine (FdCyd) and its cytotoxic metabolites in plasma of patients treated with FdCyd and tetrahydrouridine (THU).

PURPOSE: Although the DNA methyltransferase inhibitor 5-fluoro-2'-deoxycytidine (FdCyd), is being evaluated clinically, it must be combined with the cytidine deaminase inhibitor tetrahydrouridine (THU) to prevent rapid metabolism of FdCyd to the pharmacologically active, yet unwanted, metabolites 5-fluoro-2'-deoxyuridine (FdUrd), 5-fluorouracil (FU), and 5-fluorouridine (FUrd). We assessed plasma concentrations of FdCyd and metabolites in patients receiving FdCyd and THU. METHODS: We validated an LC-MS/MS assay, developed for a preclinical study, to quantitate FdCyd and metabolites in human plasma. Patients were treated with five daily, 3-h infusions of FdCyd at doses of 5-80 mg/m(2) with 350 mg/m(2) THU. Plasma was obtained during, and before the end of infusions on days 1 and 5. RESULTS: The lower limits of quantitation for FU, FdUrd, FUrd, FC and FdCyd were 1, 1.5, 10, 3, and 10 ng/ml, respectively. Plasma FdCyd increased with dose, from 19-96 ng/ml at 5 mg/m(2) to 1,600-1,728 ng/ml at 80 mg/m(2). FdUrd was undetectable in patients treated with FdCyd doses <20 mg/m(2), and increased from 2.3 ng/ml at 20 mg/m(2) to 3.5-5.7 ng/ml at 80 mg/m(2). FU increased from 1.2-5.5 ng/ml at 5 mg/m(2) to 6.0-12 ng/ml at 80 mg/m(2). CONCLUSIONS: By co-administering FdCyd with THU, FdCyd plasma concentrations were achieved that are known to inhibit DNA methylation in vitro. The accompanying plasma FU and FdUrd concentrations are <10% those observed after therapeutic infusions of FU or FdUrd, while FdCyd levels are well above those required to inhibit methylation in vitro. Therefore, inhibition of DNA methylation with FdCyd and THU appears feasible.

Biochemical mechanisms by which reutilization of DNA 5-methylcytosine is prevented in human cells.

The salvage metabolism of 5-methyldeoxycytidine 5'-monophosphate (5MedCMP) was studied in human promyelocytic leukemia (HL-60) cells and in PHA-stimulated human lymphocytes. To this end [5'-32P]5MedCMP was synthesized by a novel postlabeling procedure. At low substrate concentrations (less than 100 microM), the enzyme(s) present in crude HL-60 whole-cell extract deaminated 5MedCMP faster than they did dCMP. Although the phosphorylation of dCMP to dCDP was easily demonstrable with both kinds of cell extracts, no phosphorylation of 5MedCMP to 5MedCDP (5-methyldeoxycytidine 5'-diphosphate) was observed. This phenomenon was confirmed using HL-60 cells made permeable to nucleotides with Tween 80. In view of the substantial 5MeCyt (5-methylcytosine) content of DNA and the degradation of DNA that occurs in cells, it is conceivable that 5MedCyd (5-methyl-2'-deoxycytidine) and 5MedCMP are available for reutilization in DNA synthesis. This would have devastating effects on cellular control and gene expression. The results of the present investigation indicate that rapid deamination at the monophosphate level and, in particular, stringent discrimination of 5MedCMP by cellular monophosphokinase(s) are the key mechanisms by which reutilization of DNA 5MeCyt is prevented in human hematopoietic cells.

Tumor-selective metabolism of 5-fluoro-2'-deoxycytidine coadministered with tetrahydrouridine compared to 5-fluorouracil in mice bearing Lewis lung carcinoma.

The metabolic products formed and incorporated into the nucleic acids (RNA and DNA) of mice bearing Lewis lung carcinoma (LLC) following optimal doses of 5-fluorouracil (FUra), 5-fluoro-2'-deoxyuridine (FdUrd), and 5-fluoro-2'-deoxycytidine (FdCyd) coadministered with tetrahydrouridine (H4Urd), a potent inhibitor of cytidine deaminase, were examined. Treatment with FdCyd plus H4Urd resulted in a tumor-selective incorporation and formation of antimetabolites compared to either FUra or FdUrd treatments. Between 45- and greater than 5400-fold higher levels of the potent thymidylate synthetase inhibitor, 5-fluoro-2'-deoxyuridylate (FdUMP), were formed in tumor than in any of the normal tissues analyzed. RNA-level antimetabolites (FUra, 5-fluorouridine, and 5-fluorouridylate) were also between 3 and greater than 990-fold higher in tumor compared to normal tissue following FdCyd plus H4Urd administration. DNA-level antimetabolites (FdCyd, 5-fluorodeoxycytidylate, FdUrd, and FdUMP) were from 2- to 6-fold higher in tumor compared to normal tissue. FUra and FdUrd treatments resulted in between 3 and greater than 1300-fold higher RNA-level antimetabolites and from 4 to greater than 1020-fold higher FdUMP pools in normal tissues than FdCyd plus H4Urd treatment. DNA-level antimetabolites were also from 4- to 32-fold higher in normal tissues following optimal doses of FUra or FdUrd. In tumor tissue, optimal doses of FUra or FdUrd resulted in lower (a) FdUMP levels (5- to 2-fold), (b) RNA-level antimetabolites (6- to 3-fold), and (c) DNA-level antimetabolites (10- to 4-fold) compared to an optimal dosage of FdCyd plus H4Urd. In serum, the administration of H4Urd resulted in the protection of FdCyd from systemic catabolism, unlike that found with FUra or FdUrd. Substantial levels of FdUMP, FUrd, and FUMP were noted in serum following FUra or FdUrd treatment. The formation of di- and triphosphate antimetabolite pools and the incorporation of antimetabolites into the RNA and DNA of normal and tumor tissues demonstrated trends similar to those mentioned above with nucleoside, mononucleotide, and free base pools. H4Urd treatment of 25 mg/kg did not affect the elevated levels of deoxycytidine kinase or deoxycytidylate deaminase in LLC tumor tissue or the low levels found in normal tissue. A critical feature of this chemotherapeutic strategy using FdCyd plus H4Urd was that the elevated level of cytidine deaminase in LLC tumor tissue was inhibited less than 10% by the administration of 25 mg/kg H4Urd, whereas deoxycytidine deaminase activities in normal tissues (including bone marrow and intestine) were inhibited greater than 93%.(ABSTRACT TRUNCATED AT 400 WORDS)

Pharmacokinetic considerations in evaluating the effects of tetrahydrouridine on 5-azacytidine chemotherapy in L1210 leukemic mice.

The pharmacokinetics of 5-azacytidine (5-azaCR) and tetrahydrouridine (THU) were considered in evaluating the effect of THU on chemotherapy with 5-azaCR in L1210 leukemia mice. The administration of three different dose levels of THU and 5-azaCR ip in either a 6- or 72-hour infusion gave minimal increases in therapeutic effect. At the high-dose combinations (except in the 72-hour infusion), THU appeared to enhance toxicity. Toxicity, however, occurred only after exceeding a theoretic plasma concentration for 5-azaCR of 61 microgram/ml. THU was effective in increasing the excretion of 5-azaCR by sixfold and in altering its urinary metabolites when given simultaneously with or up to 1 hour prior to 5-azaCR.

Tetrahydrouridine: Physiologic disposition and effect upon deamination of cytosine arabinoside in man.

[14C]-tetrahydrouridine (THU), a strong inhibitor of cytidine (CR) deaminase, was, after iv administration, rapidly and quantitatively cleared from the blood with a plasma half-life of about 1 hour. The main pathway of excretion was through the kidneys: most of a dose of 50 mg/kg was excreted within 12 hours and excretion was essentially complete within 48 hours. Oral administration of the same dose revealed absorption of about 10% from the gastrointestinal tract. THU at 10, 25, and 50 mg/kg given 15 minutes before [3H]-cytosine arabinoside (ara-C) at a dose of 0.003 mg/kg produced about a two fold increase in ara-C blood levels at all times measured from 5 minutes to 4 hours, with only slight increases in the half-life of ara-C. A dose-related effect of THU upon the deamination of ara-C was obvious only during the time from 15 minutes to 1 hour after the injection of 3H-ara-C. The inhibitory effect of THU upon CR deaminase was also reflected in a considerably increased ratio of ara-C/uracil arabinoside in the urine.

Combinations of tetrahydrouridine and cytosine arabinoside in mouse tumors.

Thirteen experimental mouse neoplasms were tested by cytidine (CR)-deaminase and deoxycytidine (dCR)-kinase levels. Four neoplasms, Sarcoma T241, Adenocarcinoma E0771, Lewis lung carcinoma (LL), and Sarcoma 180 Japan (S180J), considered to have high deaminase and sufficient dCR-kinase activities, were tested in vivo for combination chemotherapy with cytosine arabinoside (ara-C) and the CR-deaminase inhibitor, tetrahydrouridine (THU). THU did not significantly improve the growth inhibition of ara-C in a wide range of combinations in T241, E0771, LL, and the solid form of S180J, but more than doubled the survival time of the S180J ascites-bearing animals. Toxicity in the form of weight loss and toxic deaths was observed in some but not all groups, especially at high dosages of ara-C and THU. Tissue distribution of [3H]-ara-C and [14C]-THU in T241-bearing mice revealed an accelerated clearance of ara-C-derived radioactivity under the influence of THU in the tumor and five host tissues, but not in the small intestines. With the exception of the small intestines, clearance of THU-derived radioactivity was faster in all tissues studied compared to the clearance of [3H]-ara-C-derived radioactivity. Intracellular CR-deaminase levels were inhibited significantly, ie, dose dependent, in tumor and host kidney after a single ip injection of THU to E0771--bearing mice. In the solid S180J, with or without simultaneous ip administration of THU, [3H]-ara-C was not converted to 5'-di- and tri-phosphates at all. In mice bearing the ascites form of S180J, [3H]-ara-C was extensively converted to ara-C 5'-di- and tri-phosphates. THU increased both overall ara-C-derived radioactivity and the relative amounts of ara-C 5'-di- and tri-phosphates.

Distribution of tetrahydrouridine in experimental animals.

2-14C-tetrahydrouridine was prepared and used to determine the serum levels and excretion of tetrahydrouridine by varous experimental animals. In mice injected ip with the agent (50 mg/kg), the serum level of tetrahydrouridine was maximum (76 mug/ml) at 15 minutes. For rats injected with the same dose, the tetrahydrouridine content of serum was greatest (58 mug/ml) at 30 minutes. Within 3 hours, the serum content of the drug in both mice and rats fell to less than 10% of the maximum. The kidneys of mice selectively accumulated tetrahydrouridine; the concentration rose to 275 mug/g at 1 hour after injection. Nearly all of the dose was excreted unchanged in the urine of mice and rats in 24 hours. For a dog and a monkey given an iv dose (50 mg/kg) of tetrahydrouridine, serum levels of the agent were 210 and 200 mug/ml, respectively, at 5 minutes. The apparent half-lives for the initial phase of disappearance were 18 and 20 minutes and those for the later phase were 65 and 70 minutes, respectively. In 24 hours the dog and monkey excreted most of the dose as unchanged tetrahydrouridine. No metabolites were detected in the biologic samples from either species.