Microbial Metabolite; HSV-1

Cytarabine (AraC) is phosphorylated into a triphosphate form (Ara-CTP) by deoxycytidine kinase (dCK), which inhibits the activity of DNA and RNA polymerases to prevent DNA synthesis by competing with dCTP for incorporation into DNA. With an IC50 of 16 nM, cytarabine exhibits a greater growth inhibitory activity against wild-type CCRF-CEM cells than against other acute myelogenous leukemia (AML) cells.[1] The metabolic activity of the sensitive rat leukemic cell line RO/1 decreases with increasing concentrations of cytarabine (IC50 of 0.69 μM). Transfection with human wt dCK (IC50 of 0.037 μM) can greatly increase the cell toxity, but not the inactive, alternatively spliced dCK forms.[2] Rat sympathetic neurons appear to undergo apoptosis when exposed to cytarabine at concentrations of up to 10 μM. The highest toxicity of cytarabine is at 100 μM, which results in the death of over 80% of the neurons in 84 hours through the activation of caspase-3 and the release of mitochondrial cytochrome-c. The toxicity can be mitigated by p53 knockdown and postponed by bax deletion.[3]

Cytarabine is highly effective against acute leukemias, which result in the characteristic G1/S blockage and synchronization. It also weakly dose-relatedly prolongs the survival time of leukaemic Brown Norway rats, suggesting that higher dosages of Cytarabine do not enhance its antileukaemic efficacy in humans.[4] In addition to causing placental growth retardation, cytarabine (250 mg/kg) also increases the apoptosis of placental trophoblastic cells in the placental labyrinth zone of pregnant Slc:Wistar rats. This apoptosis begins to increase three hours after the treatment, peaks at six hours, and returns to control levels at 48 hours. Notably, p53 protein and p53 transcriptional target genes, including p21, cyclin G1, fas, and caspase-3 activity, are markedly enhanced.[5]

Cytarabine is prepared in absolute ethanol as a stock solution, and Cytarabine is prepared in serial dilutions. The RPMI medium containing 10% FBS, 0.1% gentamicin, and 1% sodium pyruvate is supplemented with CCRF-CEM cells. To achieve a final density of 3-6 × 10⁴ cells/mL, the cells are suspended in their respective media to yield 10 mL volumes of cell suspension. After adding the appropriate amounts of cytarabine solution to the cell suspensions, the incubation process is extended for a full 72 hours. Final cell counts are obtained after the cells are spun down and resuspended in new Cytarabine-free medium. The results are expressed as the IC50, or the concentration of cytarabine that inhibits cell growth to 50% of the control value. The data are analyzed by fitting a sigmoidal curve to the relationship between the cell count and cytarabine concentration.

Different concentrations of cytarabine are incubated with cells for 24, 48, and 72 hours at 37 °C. 10 milliliters of the cell proliferation reagent WST-1 solution are added after the 20-, 44-, or 68-hour incubation period in the presence of cytarabine. Following a 2- or 4-hour incubation period with WST-1, colorimetric alterations are measured by calculating the absorbance at 450 nm in a spectrophotometer to determine the metabolic activity of the cells. Additionally, cell division times are determined by counting eosin in tandem with a viability test.

Absorption, Distribution and Excretion
Less than 20% of the orally administered dose is absorbed from the gastrointestinal tract.
The primary route of elimination of cytarabine is metabolism to the inactive compound ara-U, followed by urinary excretion of ara-U.
Less than 20% of a dose of conventional cytarabine is absorbed from the GI tract, and the drug is not effective when administered orally. Following subcutaneously or im injection of conventional cytarabine H 3, peak plasma concentrations of radioactivity occur within 20-60 min and are considerably lower than those attained after iv administration. Continuous iv infusions of conventional cytarabine produce relatively constant plasma concn of the drug in 8-24 hr.
Cytarabine is rapidly and widely distributed into tissues and fluids, including liver, plasma, and peripheral granulocytes. Following rapid IV injection of cytarabine in one study, approximately 13% of the drug was bound to plasma proteins.
Cytarabine crosses the blood-brain barrier to a limited extent. During a continuous IV or subcutaneous infusion, cytarabine concentrations in the CSF are higher than those attained after rapid IV injection and are about 40-60% of plasma concentrations. Most of an intrathecal dose of cytarabine diffuses into the systemic circulation but is rapidly metabolized and usually only low plasma concentrations of unchanged drug occur.
The drug apparently crosses the placenta. It is not known if cytarabine or ara-U is distributed into milk.
For more Absorption, Distribution and Excretion (Complete) data for CYTARABINE (7 total), please visit the HSDB record page.

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Metabolism / Metabolites
Hepatic.
Cytarabine is rapidly and extensively metabolized mainly in the liver but also in kidneys, GI mucosa, granulocytes, and to a lesser extent in other tissues by the enzyme cytidine deaminase, producing the inactive metabolite 1-ß-d-arabinofuranosyluracil (ara-U, uracil arabinoside). After the initial distribution phase, more than 80% of the drug in plasma is present as ara-U. In the CSF, only minimal amounts of cytarabine are converted to ara-U because of low CSF concentrations of cytidine deaminase. Intracellularly, cytarabine is metabolized by deoxycytidine kinase and other nucleotide kinases to cytarabine triphosphate, the active metabolite of the drug. Cytarabine triphosphate is inactivated by a pyrimidine nucleoside deaminase, which produces the uracil derivative.
The primary route of elimination of cytarabine is metabolism to the inactive compound ara-U (1-(beta)-D-arabinofuranosyluracil or uracilarabinoside), followed by urinary excretion of ara-U. In contrast to systemically administered cytarabine, which is rapidly metabolized to ara-U, conversion to ara-U in the CSF is negligible after intrathecal administration because of the significantly lower cytidine deaminase activity in the CNS tissues and CSF. The CSF clearance rate of cytarabine is similar to the CSF bulk flow rate of 0.24 mL/min. /Cytarabine liposome injection/
Cytarabine must be converted to the 5'-monophosphate nucleotide by deoxycytidine kinase to be active. Ara-cytidine diphosphate &/or ara-cytidine triphosphate are presumably the form that inhibit DNA polymerase & block ribonucleoside diphosphate reductase.
Hepatic.

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Biological Half-Life
10 minutes
After rapid IV injection of cytarabine, plasma drug concentrations appear to decline in a biphasic manner with a half-life of about 10 minutes in the initial phase and about 1-3 hours in the terminal phase. Cytarabine reportedly undergoes triphasic elimination in some patients. After intrathecal injection, cytarabine concentrations in the CSF reportedly decline with a half-life of about 2 hours.
Peak levels were followed by a biphasic elimination profile with a terminal phase half-life of 100 to 263 hours over a dose range of 12.5 mg to 75 mg. In contrast, intrathecal administration of 30 mg of free cytarabine showed a biphasic CSF concentration profile with a terminal phase half-life of 3.4 hours. /Cytarabine liposome injection/
After iv admin, there is a rapid phase of disappearance of AraC (half-life = 10 min), followed by a slower phase of elimination with a half-time of about 2.5 hr ... After intrathecal admin of the drug at a dose of 50 mg/sq m ... peak concn of 1 to 2 mM are achieved, which decline slowly with a terminal half-life of approx 3.4 hr.

Toxicity Summary
/HUMAN EXPOSURE STUDIES/ The principal toxicity of standard induction regimens for acute non-lymphocytic leukemia (ANLL) [including cytarabine (ARA-C) 100 mg/sq m for 7 days plus an anthracycline] is myelotoxicity, leading to death in at least 25% of cases during induction in non-selected patients. The complete remission rate is less than 35% in patients over 65 years of age, due in part to an age-related increase of myelotoxicity. The other important adverse effect of standard-dose cytarabine is gastrointestinal toxicity, especially oral mucositis, diarrhea, intestinal ulceration, ileus and subsequent Gram-negative septicaemia. Idiosyncratic reactions like exanthema, fever and elevation of hepatic enzymes are relatively frequent, but do not represent therapeutic problems. Intermittent high-dose cytarabine (3 g/sq m in 8 to 12 doses) is extremely myelosuppressive. Similarly, the gastrointestinal toxicity is formidable and dose-limiting. Severe, and sometimes irreversible, cerebellar/cerebral toxicity in 5 to 15% of courses of treatment limits the peak dose of cytarabine. The pathogenesis, prophylactic and therapeutic measures are unknown. These major toxicities are age-related and prohibitive to the use of high-dose cytarabine therapy in patients older than 55 to 60 years. Subacute noncardiogenic pulmonary edema occurs in some patients, with an incidence of about 20%, and seems to have an intriguing coincidence with precedent streptococcal septicaemia; high-dose systemic steroids may be beneficial. Corneal toxicity is very frequent in high-dose cytarabine therapy but is always reversible. It is largely preventable with prophylactic steroid or 2-deoxycytidine eyedrops. Fever, exanthema and hepatic toxicity have an incidence similar to that in standard dosage. The maximum tolerable cumulated dose of cytarabine is significantly lower when the agent is administered as a continuous infusion, due to myelosuppression and gastrointestinal toxicity. Conversely, continuous infusion may be less neurotoxic. The antileukemic effect of continuous infusion high-dose cytarabine is less well established. The only significant toxicity of low-dose cytarabine is myelosuppression. Given the generally poor condition of leukemia patients, low-dose cytarabine therapy is well tolerated, although occasional cases of diarrhoea, reversible cerebellar symptoms, peritoneal and pericardial reactions, and ocular toxicity have been reported. Continuous infusion may be more toxic than the usual intermittent dosage. It is concluded that the toxicity of the standard induction regimen for ANLL is acceptable in patients younger than 60 to 65 years with no concurrent disease. Low dose cytarabine is tolerable for virtually all ANLL patients, but the overall therapeutic efficacy still needs to be defined and compared to standard therapy in the relevant age groups.
Cytarabine acts through direct DNA damage and incorporation into DNA. Cytarabine is cytotoxic to a wide variety of proliferating mammalian cells in culture. It exhibits cell phase specificity, primarily killing cells undergoing DNA synthesis (S-phase) and under certain conditions blocking the progression of cells from the G1 phase to the S-phase. Although the mechanism of action is not completely understood, it appears that cytarabine acts through the inhibition of DNA polymerase. A limited, but significant, incorporation of cytarabine into both DNA and RNA has also been reported.

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Hepatotoxicity
Serum aminotransferase elevations occur in 5% to 10% of patients on conventional doses of cytarabine and a greater proportion (9% to 75%) at higher doses. However, the serum enzyme elevations are rarely associated with symptoms and are generally self-limited and resolve rapidly, rarely requiring dose modification. Cases of clinically apparent liver injury attributed to cytarabine have been reported but are uncommon. The time to onset was usually within the first few cycles of therapy, and the pattern of serum enzyme elevations ranged from cholestatic to hepatocellular. Immunoallergic and autoimmune features were generally not present. Antineoplastic regimens, including cytarabine, have been implicated in cases of sinusoidal obstruction syndrome and peliosis, but the role of cytarabine in these reactions was unclear. Many examples of liver injury attributed to cytarabine in the literature were typical of jaundice of sepsis rather than acute hepatocellular or cholestatic injury, although high doses of cytarabine may cause hyperbilirubinemia independent of hepatic injury.
Likelihood score: C (probable cause of clinically apparent liver injury).

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Effects During Pregnancy and Lactation
◉ Summary of Use during Lactation
No information is available on the excretion of cytarabine into breastmilk. However, the drug has a short half-life of 2 to 3 hours after intravenous administration, so it should be eliminated from milk a day after intravenous administration. Very little information is available on the use of cytarabine during breastfeeding. In one case, a mother began breastfeeding her infant 3 weeks after receiving cytarabine, mitoxantrone and etoposide intravenously, with no apparent harm to her infant. After intrathecal administration of the liposomal formulation of cytarabine, drugs levels in plasma are barely detectable, and are unlikely to appear in milk in clinically relevant amounts.
◉ Effects in Breastfed Infants
One mother received 3 daily doses of 6 mg/sq. m. of mitoxantrone intravenously along with 5 daily doses of etoposide 80 mg/sq. m. and cytarabine 170 mg/sq. m. intravenously. She resumed breastfeeding her infant 3 weeks after the third dose of mitoxantrone at a time when mitoxantrone was still detectable in milk. The infant had no apparent abnormalities at 16 months of age. However, after 3 weeks of abstinence from breastfeeding, it is unlikely that cytarabine was present in milk during breastfeeding.
◉ Effects on Lactation and Breastmilk
Relevant published information was not found as of the revision date.

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Protein Binding
13%

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Toxicity Data
Cytarabine syndrome may develop - it is characterized by fever, myalgia, bone pain, occasionally chest pain, maculopapular rash, conjunctivitis, and malaise.

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Interactions
GI absorption of oral digoxin tablets may be substantially reduced in patients receiving combination chemotherapy regimens (including regimens containing cytarabine), possibly as a result of temporary damage to intestinal mucosa caused by the cytotoxic agents. Plasma concentrations of digoxin should be carefully monitored in patients receiving such combination chemotherapy regimens. Use of digoxin oral elixir or liquid-filled capsules may minimize the potential interaction, since the drug is rapidly and extensively absorbed from these dosage forms. Limited data suggest that the extent of GI absorption of digitoxin (no longer commercially available in the US) is not substantially affected by concomitant administration of combination chemotherapy regimens known to decrease absorption of digoxin.
One in vitro study indicates that cytarabine may antagonize the activity of gentamicin against Klebsiella pneumoniae. Patients receiving concurrent cytarabine and aminoglycoside therapy for the treatment of infections caused by K. pneumoniae should be closely monitored; if therapeutic response is not achieved, reevaluation of anti-infective therapy may be necessary.
Limited data suggest that cytarabine may antagonize the anti-infective activity of flucytosine, possibly by competitive inhibition of the anti-infective's uptake by fungi.
The incidence of toxicity may be increased when liposomal cytarabine is used concurrently with systemic chemotherapy in patients withneoplastic meningitis. Increased neurotoxicity has been observed in patients recievingconcomitant intrathecal administration of conventionalcytarabine and other cytotoxic agents.
For more Interactions (Complete) data for CYTARABINE (15 total), please visit the HSDB record page.

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Non-Human Toxicity Values
LD50 Mouse ip 3779 mg/kg
LD50 Mouse oral 3150 mg/kg

[1]. Mol Pharm . 2004 Mar-Apr;1(2):112-6.

[2]. Blood . 2002 Feb 15;99(4):1373-80.

[3]. Cell Death Differ . 2003 Sep;10(9):1045-58./a >

[4]. Br J Cancer . 1988 Dec;58(6):730-3.

[5]. Biol Reprod . 2004 Jun;70(6):1762-7.

Therapeutic Uses
Antimetabolites, Antineoplastic; Antiviral Agents; Immunosuppressive Agents; Teratogens
DepoCyt (cytarabine liposome injection) is indicated for the intrathecal treatment of lymphomatous meningitis. This indication is based on demonstration of increased complete response rate compared to unencapsulated cytarabine. There are no controlled trials that demonstrate a clinical benefit resulting from this treatment, such as improvement in disease-related symptoms, or increased time to disease progression, or increased survival. /Cytarabine liposome injection/
Cytarabine is indicated, in combination with other antineoplastic agents, for treatment of acute nonlymphocytic leukemia in adults and children. /Included US product label/
Cytarabine is indicated for treatment of acute lymphocytic leukemia and chronic myelocytic leukemia (blast phase). /Included in US product label/
For more Therapeutic Uses (Complete) data for CYTARABINE (10 total), please visit the HSDB record page.

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Drug Warnings
The patient's hematologic status must be carefully monitored. Leukocyte and platelet counts should be performed frequently during cytarabine therapy. The manufacturers state that leukocyte and platelet counts should be determined daily during remission induction therapy of acute leukemia. The manufacturers also recommend frequent bone marrow examinations after blast cells have disappeared from the peripheral blood.
Patients who receive myelosuppressive drugs experience an increased frequency of infections (e.g., viral, bacterial, fungal) as well as possible hemorrhagic complications. Because these complications are potentially fatal, the patient should be instructed to notify the clinician if fever, sore throat, or unusual bleeding or bruising occurs. ...Treatment with cytarabine should be initiated only with extreme caution in patients with preexisting drug-induced bone marrow suppression.
The manufacturers recommend that periodic determinations of renal function be performed in patients receiving cytarabine. Periodic determinations of hepatic function should also be performed in patients receiving cytarabine, and the manufacturers state that the drug should be used with caution and in reduced dosage in patients with poor hepatic function.
Cytarabine is contraindicated in patients with known hypersensitivity to the drug.
For more Drug Warnings (Complete) data for CYTARABINE (30 total), please visit the HSDB record page.

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Pharmacodynamics
Cytarabine is an antineoplastic anti-metabolite used in the treatment of several forms of leukemia including acute myelogenous leukemia and meningeal leukemia. Anti-metabolites masquerade as purine or pyrimidine - which become the building blocks of DNA. They prevent these substances becoming incorporated in to DNA during the "S" phase (of the cell cycle), stopping normal development and division. Cytarabine is metabolized intracellularly into its active triphosphate form (cytosine arabinoside triphosphate). This metabolite then damages DNA by multiple mechanisms, including the inhibition of alpha-DNA polymerase, inhibition of DNA repair through an effect on beta-DNA polymerase, and incorporation into DNA. The latter mechanism is probably the most important. Cytotoxicity is highly specific for the S phase of the cell cycle.

C9H13N3O5

243.22

243.085

C, 44.45; H, 5.39; N, 17.28; O, 32.89

147-94-4

6253

White to off-white solid powder

1.9±0.1 g/cm3

529.7±60.0 °C at 760 mmHg

214 °C

274.1±32.9 °C

0.0±3.2 mmHg at 25°C

1.756

-1.78

4

5

2

17

383

4

O1[C@]([H])(C([H])([H])O[H])[C@]([H])([C@@]([H])([C@]1([H])N1C(N=C(C([H])=C1[H])N([H])[H])=O)O[H])O[H]

UHDGCWIWMRVCDJ-CCXZUQQUSA-N

InChI=1S/C9H13N3O5/c10-5-1-2-12(9(16)11-5)8-7(15)6(14)4(3-13)17-8/h1-2,4,6-8,13-15H,3H2,(H2,10,11,16)/t4-,6-,7+,8-/m1/s1

4-amino-1-[(2R,3S,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl)oxolan-2-yl]pyrimidin-2-one

2934.99.03.00

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Solubility in Formulation 1: ≥ 2.08 mg/mL (8.55 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.08 mg/mL (8.55 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 3: ≥ 2.08 mg/mL (8.55 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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Solubility in Formulation 4: Saline: 30 mg/mL

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Solubility in Formulation 5: 100 mg/mL (411.15 mM) in PBS (add these co-solvents sequentially from left to right, and one by one), clear solution; with ultrasonication (<60°C).

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 (Please use freshly prepared in vivo formulations for optimal results.)