Topoisomerase I

Irinotecan (CPT-11, 5 mg/kg) significantly reduces the growth of tumors when injected intratumorally into rats for five days straight over the course of two weeks. In mice, the same effect is achieved by continuously infusing osmotic minipump fluid intraperitoneally. However, Irinotecan (10 mg/kg) shows no effect on the growth of tumor by i.p[1]. By day 21, it appears that irinotecan (CPT-11, 100–300 mg/kg, i.p.) inhibits the growth of HT-29 xenograft tumors in athymic female mice. Both the Irinotecan (125 mg/kg) plus TSP-1 (10 mg/kg per day) and the Irinotecan (150 mg/kg) plus TSP-1 (20 mg/kg per day) groups are almost as effective as Irinotecan alone, inhibiting tumor growth by 84% and 89%, respectively, at doses of 250 and 300 mg/kg[3].

In 20 cm² dishes, exponentially growing cells are seeded with the ideal number of cells for each cell line (20,000 for LoVo cells, 100,000 for HT-29 cells). They receive treatment with irinotecan or SN-38 at increasing concentrations for a single cell doubling period (24 hours for LoVo cells and 40 hours for HT-29 cells) after two days. Following a 0.15 M NaCl wash, the cells are cultured in normal medium for two more doubling times before being separated from the support using trypsin-EDTA and counted using a hemocytometer. Subsequently, the drug concentrations that cause a 50% inhibition of growth in cells treated with the drug are estimated as the IC50 values[2].

Absorption
The maximum plasma concentration (Cmax) when a dose of 125 mg/m^2 is given to patients with solid tumours is 1660 ng/mL. The AUC (0-24) is 10,200 ng·h/mL. The Cmax when a dose of 340 mg/m^2 is given to patients with solid tumours is 3392 ng/mL. The AUC (0-24) is 20,604 ng·h/mL.

Route of Elimination
The cumulative biliary and urinary excretion of irinotecan and its metabolites (SN-38 and SN-38 glucuronide) over a period of 48 hours following administration of irinotecan in two patients ranged from approximately 25% (100 mg/m2) to 50% (300 mg/m2).

Volume of Distribution
The volume of distribution of terminal elimination phase is 110 L/m^2 when a dose of 125 mg/m^2 is given to patients with solid tumours. The volume of distribution of terminal elimination phase is 234 L/m^2 when a dose of 340 mg/m^2 is given to patients with solid tumours.

Clearance
13.3 L/h/m^2 [Dose of 125 mg/m^2, patients with solid tumours]
13.9 L/h/m^2 [Dose of 340 mg/m^2, patients with solid tumours]

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Pharmacokinetic parameters for irinotecan and SN-38 were determined in 2 pediatric solid-tumor trials at dose levels of 50 mg/sq m (60-min infusion, n=48) and 125 mg/sq m (90-min infusion, n=6). Irinotecan clearance (mean + or - S.D.) was 17.3 + or - 6.7 L/h/sq m for the 50 mg/sq m dose and 16.2 + or - 4.6 L/h/sq m for the 125 mg/sq m dose, which is comparable to that in adults. Dose-normalized SN-38 AUC values were comparable between adults and children. Minimal accumulation of irinotecan and SN-38 was observed in children on daily dosing regimens (daily X 5 every 3 weeks or (daily X 5) X 2 weeks every 3 weeks).

The clinical pharmacokinetics of irinotecan (CPT11) can be described by a 2 or 3 compartment model, a mean terminal half-life of 12 hours, a volume of distribution at steady state of 168 L/sq m and a total body clearance of 15 L/sq m/hr. Irinotecan is 65% bound to plasma proteins. The areas under the plasma concentration-time curve (AUC) of both irinotecan and active metabolite SN38 increase proportionally to the administered dose, although interpatient variability is important. ... The mean 24 hr irinotecan urinary excretion represents 17-25% of the administered dose, whereas SN38 and its glucuronide recovery in urine is minimal (0.5 and 6%, respectively). Irinotecan and SN38 pharmacokinetics are not influenced by prior exposure to the parent drug. Irinotecan and SN38 AUCs correlate significantly with leuko-neutropenia and sometimes with the intensity of diarrhea. Increased bilirubin levels appear to influence irinotecan total body clearance. PMID:9932079 Bull Cancer (12): 11-20 (1998)

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Metabolism / Metabolites
Hepatic. The metabolic conversion of irinotecan to the active metabolite SN-38 is mediated by carboxylesterase enzymes and primarily occurs in the liver. SN-38 is subsequently conjugated predominantly by the enzyme UDP-glucuronosyl transferase 1A1 (UGT1A1) to form a glucuronide metabolite.

... SN38 levels achieved in humans are about 100-fold lower than corresponding irinotecan levels, but these concentrations are important since SN38 is 100- to 1,000-fold more cytotoxic than the parent compound. SN38 is 95% bound to plasma proteins. SN38 plasma decay follows closely that of the parent compound. Irinotecan is extensively metabolized in the liver. The bipiperidinocarbonyloxy group of irinotecan is first removed by a carboxyesterase to yield the corresponding carboxylic acid and SN38. This metabolite can be converted into SN38 glucuronide by UDP-glucuronyltransferase (1.1 isoform). A recently identified metabolite is the 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino]-carbonyloxy-camptothecin (APC), which is formed by the action of cytochrome P450 3A4. Numerous other unidentified metabolites are detected in bile and urine. ... PMID:9932079 Bull Cancer (12): 11-20 (1998)

Irinotecan, a camptothecin analogue, is a prodrug which requires bioactivation to form the active metabolite SN-38. SN-38 acts as a DNA topoisomerase I poison. ... Irinotecan is subjected to be shunted between CYP3A4 mediated oxidative metabolism to form two inactive metabolites APC or NPC and tissue carboxylesterase mediated hydrolysis to form SN-38 which is eventually detoxified via glucuronidation by UGT1A1 to form SN-38G. The pharmacology of this compound is further complicated by the existence of genetic inter-individual differences in activation and deactivation enzymes of irinotecan (e.g., CYP3A4, CYP3A5, UGT1A1) and sharing competitive elimination pathways with many concomitant medications, such as anticonvulsants, St. John's Wort, and ketoconazole. Efflux of the parent compound and metabolites out of cells by several drug transporters (e.g., Pgp, BCRP, MRP1, MRP2) also occurs. This review highlights the latest findings in drug activation, transport mechanisms, glucuronidation, and CYP3A-mediated drug-drug interactions of irinotecan in order to unlock some of its complicated pharmacology and to provide ideas for relevant future studies into optimization of this promising agent. PMID:12570720 Ma MK, McLeod HL; Curr Med Chem 10 (1): 41-9 (2003)

Irinotecan serves as a water-soluble precursor of the lipophilic metabolite SN-38. SN-38 is formed from irinotecan by carboxylesterase-mediated cleavage of the carbamate bond between the camptothecin moiety and the dipiperidino side chain. SN-38 is approximately 1000 times as potent as irinotecan as an inhibitor of topoisomerase I purified from human and rodent tumor cell lines. In vitro cytotoxicity assays show that the potency of SN-38 relative to irinotecan varies from 2- to 2000-fold. However, the plasma area under the concentration versus time curve (AUC) values for SN-38 are 2% to 8% of irinotecan and SN-38 is 95% bound to plasma proteins compared to approximately 50% bound to plasma proteins for irinotecan. The precise contribution of SN-38 to the activity of Camptosar is thus unknown. Both irinotecan and SN-38 exist in an active lactone form and an inactive hydroxy acid anion form. A pH-dependent equilibrium exists between the two forms such that an acid pH promotes the formation of the lactone, while a more basic pH favors the hydroxy acid anion form. Thomson Health Care Inc.; Physicians' Desk Reference 62 ed., Montvale, NJ 2008, p. 2594

The metabolic conversion of irinotecan to the active metabolite SN-38 is mediated by carboxylesterase enzymes and primarily occurs in the liver. SN-38 is subsequently conjugated predominantly by the enzyme UDP-glucuronosyl transferase 1A1 (UGT1A1) to form a glucuronide metabolite. UGT1A1 activity is reduced in individuals with genetic polymorphisms that lead to reduced enzyme activity such as the UGT1A1*28 polymorphism. Approximately 10% of the North American population is homozygous for the UGT1A1*28 allele. In a prospective study, in which irinotecan was administered as a single-agent on a once-every-3-week schedule, patients who were homozygous for UGT1A1*28 had a higher exposure to SN-38 than patients with the wild-type UGT1A1 allele. SN-38 glucuronide had 1/50 to 1/100 the activity of SN-38 in cytotoxicity assays using two cell lines in vitro. The disposition of irinotecan has not been fully elucidated in humans. The urinary excretion of irinotecan is 11% to 20%; SN-38, <1%; and SN-38 glucuronide, 3%. The cumulative biliary and urinary excretion of irinotecan and its metabolites (SN-38 and SN-38 glucuronide) over a period of 48 hours following administration of irinotecan in two patients ranged from approximately 25% (100 mg/sq m) to 50% (300 mg/sq m). Thomson Health Care Inc.; Physicians' Desk Reference 62 ed., Montvale, NJ 2008, p. 2594

Irinotecan has known human metabolites that include 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino] carbonyloxycamptothecin and (2S,3S,4S,5R)-6-[[(19S)-10,19-diethyl-14,18-dioxo-7-(4-piperidin-1-ylpiperidine-1-carbonyl)oxy-17-oxa-3,13-diazapentacyclo[11.8.0.02,11.04,9.015,20]henicosa-1(21),2,4(9),5,7,10,15(20)-heptaen-19-yl]oxy]-3,4,5-trihydroxyoxane-2-carboxylic acid. S73 | METXBIODB | Metabolite Reaction Database from BioTransformer | DOI:10.5281/zenodo.4056560

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Biological Half-Life
The half life of irinotecan is about 6 - 12 hours. The terminal elimination half-life of the active metabolite, SN-38 is 10 - 20 hours.

After intravenous infusion of irinotecan in humans, irinotecan plasma concentrations decline in a multiexponential manner, with a mean terminal elimination half-life of about 6 to 12 hours. The mean terminal elimination half-life of the active metabolite SN-38 is about 10 to 20 hours. The half-lives of the lactone (active) forms of irinotecan and SN-38 are similar to those of total irinotecan and SN-38, as the lactone and hydroxy acid forms are in equilibrium.

Protein Binding: 30%-68% protein bound, mainly to albumin.

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Rat LD50 oral 867 mg/kg

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Interactions
A total of 190 patients (49 smokers, 141 nonsmokers) treated with irinotecan (90-minute intravenous administration on a 3-week schedule) were evaluated for pharmacokinetics. Complete toxicity data were available in a subset of 134 patients receiving 350 mg/sq m or 600 mg flat-fixed dose irinotecan. In smokers, the dose-normalized area under the plasma concentration-time curve of irinotecan was significantly lower (median, 28.7 v 33.9 ng x hr/mL/mg; P = .001) compared with nonsmokers. In addition, smokers showed an almost 40% lower exposure to SN-38 (median, 0.54 v 0.87 ng x h/mL/mg; P < .001) and a higher relative extent of glucuronidation of SN-38 into SN-38G (median, 6.6 v 4.5; P = .006). Smokers experienced considerably less hematologic toxicity. In particular, the incidence of grade 3 to 4 neutropenia was 6% in smokers versus 38% in nonsmokers (odds ratio [OR], 0.10; 95% CI, 0.02 to 0.43; P < .001). There was no significant difference in incidence of delayed-onset diarrhea (6% v 15%; OR, 0.34; 95% CI, 0.07 to 1.57; P = .149). This study indicates that smoking significantly lowers both the exposure to irinotecan and treatment-induced neutropenia, indicating a potential risk of treatment failure. Although the underlying mechanism is not entirely clear, modulation of CYP3A and uridine diphosphate glucuronosyltransferase isoform 1A1 may be part of the explanation. The data suggest that additional investigation is warranted to determine whether smokers are at increased risk for treatment failure. PMID:17563393 van der Bol JM et al; J Clin Oncol 25 (19): 2719-26 (2007)

The coadministration of protease inhibitors with anticancer drugs in the management of human immunodeficiency virus-related malignancies can cause potential drug-drug interactions. The effect of lopinavir/ritonavir (LPV/RTV) on the pharmacokinetics of irinotecan (CPT11) has been investigated in seven patients with Kaposi's sarcoma. Coadministration of LPV/RTV reduces the clearance of CPT11 by 47% (11.3+/-3.5 vs 21.3+/-6.3 l/h/m(2), P=0.0008). This effect was associated with an 81% reduction (P=0.02) of the AUC (area under the curve) of the oxidized metabolite APC (7-ethyl-10-[4-N-(5-aminopentanoic-acid)-1-piperidino]-carbonyloxycamptothecin). The LPV/RTV treatment also inhibited the formation of SN38 glucuronide (SN38G), as shown by the 36% decrease in the SN38G/SN38 AUCs ratio (5.9+/-1.6 vs 9.2+/-2.6, P=0.002) consistent with UGT1A1 inhibition by LPV/RTV. This dual effect resulted in increased availability of CPT11 for SN38 conversion and reduced inactivation on SN38, leading to a 204% increase (P=0.0001) in SN38 AUC in the presence of LPV/RTV. The clinical consequences of these substantial pharmacokinetic changes should be investigated. PMID:17713471

[1]. Antitumoral effect of irinotecan (CPT-11) on an experimental model of malignant neuroectodermal tumor. J Neurooncol. 2002 Feb;56(3):219-26.

[2]. Determinants of the cytotoxicity of irinotecan in two human colorectal tumor cell lines. Cancer Chemother Pharmacol. 2002 Apr;49(4):329-35. Epub 2002 Jan 30.

[3]. Thrombospondin-1 plus irinotecan: a novel antiangiogenic-chemotherapeutic combination that inhibits the growth of advanced human colon tumor xenografts in mice. Cancer Chemother Pharmacol. 2004 Mar;53(3):261-6. Epub 2003 Dec 5.

Irinotecan hydrochloride hydrate is a hydrate that is the trihydrate form of irinotecan hydrochloride. Onivyde is used in combination with fluorouracil and leucovorin, for the treatment of patients with metastatic adenocarcinoma of the pancreas after disease progression following gemcitabine-based therapy. It is converted via hydrolysis of the carbamate linkage to its active metabolite, SN-38, which is ~1000 times more active. It has a role as an EC 5.99.1.2 (DNA topoisomerase) inhibitor, an antineoplastic agent, an apoptosis inducer and a prodrug. It contains an irinotecan hydrochloride (anhydrous).
Irinotecan Hydrochloride is the hydrochloride salt of a semisynthetic derivative of camptothecin, a cytotoxic, quinoline-based alkaloid extracted from the Asian tree Camptotheca acuminata. Irinotecan, a prodrug, is converted to a biologically active metabolite 7-ethyl-10-hydroxy-camptothecin (SN-38) by a carboxylesterase-converting enzyme. One thousand-fold more potent than its parent compound irinotecan, SN-38 inhibits topoisomerase I activity by stabilizing the cleavable complex between topoisomerase I and DNA, resulting in DNA breaks that inhibit DNA replication and trigger apoptotic cell death. Because ongoing DNA synthesis is necessary for irinotecan to exert its cytotoxic effects, it is classified as an S-phase-specific agent.
A semisynthetic camptothecin derivative that inhibits DNA TOPOISOMERASE I to prevent nucleic acid synthesis during S PHASE. It is used as an antineoplastic agent for the treatment of COLORECTAL NEOPLASMS and PANCREATIC NEOPLASMS.

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Drug Indication
Treatment of metastatic adenocarcinoma of the pancreas, in combination with 5 fluorouracil (5 FU) and leucovorin (LV), in adult patients who have progressed following gemcitabine based therapy.

C33H45CLN4O9

677.18

676.287

C, 58.53; H, 6.70; Cl, 5.23; N, 8.27; O, 21.26

136572-09-3

136572-09-3(HCl trihydrate); 100286-90-6 (HCl); 143490-53-3 (Lactone Impurity) ; 97682-44-5; 1329502-92-2 (Carboxylate Sodium Salt)

60837

Yellow solid powder

873.4ºC at 760 mmHg

250-256ºC (dec.)

482ºC

4.576

5

11

5

47

1200

1

Cl[H].O(C1C([H])=C([H])C2=C(C=1[H])C(C([H])([H])C([H])([H])[H])=C1C(C3=C([H])C4=C(C([H])([H])OC([C@@]4(C([H])([H])C([H])([H])[H])O[H])=O)C(N3C1([H])[H])=O)=N2)C(N1C([H])([H])C([H])([H])C([H])(C([H])([H])C1([H])[H])N1C([H])([H])C([H])([H])C([H])([H])C([H])([H])C1([H])[H])=O.O([H])[H].O([H])[H].O([H])[H]

KLEAIHJJLUAXIQ-JDRGBKBRSA-N

InChI=1S/C33H38N4O6.ClH.3H2O/c1-3-22-23-16-21(43-32(40)36-14-10-20(11-15-36)35-12-6-5-7-13-35)8-9-27(23)34-29-24(22)18-37-28(29)17-26-25(30(37)38)19-42-31(39)33(26,41)4-2;;;;/h8-9,16-17,20,41H,3-7,10-15,18-19H2,1-2H3;1H;3*1H2/t33-;;;;/m0..../s1

[(19S)-10,19-diethyl-19-hydroxy-14,18-dioxo-17-oxa-3,13-diazapentacyclo[11.8.0.02,11.04,9.015,20]henicosa-1(21),2,4(9),5,7,10,15(20)-heptaen-7-yl] 4-piperidin-1-ylpiperidine-1-carboxylate;trihydrate;hydrochloride

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: Please store this product in a sealed and protected environment, avoid exposure to moisture.

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: ≥ 2.5 mg/mL (3.69 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 25.0 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: ≥ 2.5 mg/mL (3.69 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 25.0 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: 2.5 mg/mL (3.69 mM) 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 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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Solubility in Formulation 4: 30% Propylene glycol , 5% Tween 80 , 65% D5W: 30 mg/mL

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