Tryptophan hydroxylase

The peripheral but not the brain of the mice is less serotonin-containing when telotristat ethyl (15, 50, 150, 300 mg/kg, po, qd) is administered. Telotristat ethyl (200 mg/kg po, qd) significantly protects against TNBS-induced elevation in blood neutrophil counts in a rat model of inflammatory bowel disease. The mouse IBD model is protected by telotristat ethyl (200 mg/kg po, qd), as shown by histopathological evaluation[1]. In the jejunum, telotristat ethyl (15, 50, 150, and 300 mg/kg) depletes 5-HT, but not in the brain. However, neither the constitutive gastrointestinal motility in mice nor the depletion of enteric neuronal serotonin (5-HT) are caused by telotristat ethyl (200 mg/kg, po). The severity of colitis caused by trinitrobenzene sulfonic acid (TNBS) is lessened by telotristat ethyl (200 mg/kg)[2].

In normal mice, telotristat etiprate (administered once daily for 4 days at doses of 15–300 mg/kg/day) was found to reduce serotonin levels throughout the gastrointestinal tract. These reductions occurred in a dose dependent fashion with maximal effects observed with doses of telotristat etiprate ≥150 mg/kg. No significant change in brain serotonin or 5-hydroxyindoleacetic acid (5-HIAA, a serotonin metabolite) was observed. Similar findings were seen in Sprague-Dawley rats. Gastrointestinal motility studies were conducted in rats using the charcoal meal test. There was a significant dose-related delay in both gastrointestinal transit and gastric emptying, associated with a reduction in blood serotonin levels and proximal colon serotonin. A quantitative whole-body autoradiography study was conducted to assess the absorption, distribution and excretion of radioactivity in rats following a single oral dose of telotristat etiprate labeled with carbon 14. Rats were administered either 30 mg/kg or 100 mg/kg of the compound. The distribution of radioactivity was limited to tissues of the hepatic and renal system and the contents of the GI tract. There was no measurable radioactivity in the brain at any dose tested.

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Dissolved in 15% cyclodextrin or 0.25% methylcellulose; 300 mg/kg; p.o.

Male C57BL/6 mice and male C57 albino mice.

Absorption, Distribution and Excretion
After a single oral dose of telotristat ethyl to healthy subjects, telotristat ethyl was absorbed and metabolized to its active metabolite, telotristat. Peak plasma concentrations of telotristat ethyl were achieved within 0.5 to 2 hours, and those of telotristat within 1 to 3 hours. Plasma concentrations thereafter declined in a biphasic manner. Following administration of a single 500 mg dose of telotristat ethyl (twice the recommended dosage) under fasted conditions in healthy subjects, the mean Cmax and AUC0-inf were 4.4 ng/mL and 6.23 ng•hr/mL, respectively for telotristat ethyl. The mean Cmax and AUC0-inf were 610 ng/mL and 2320 ng•hr/mL, respectively for telotristat. Peak plasma concentrations and AUC of telotristat ethyl and telotristat appeared to be dose proportional following administration of a single dose of telotristat ethyl in the range of 100 mg (0.4 times the lowest recommended dose to 1000 mg [4 times the highest recommended dose]) under fasted conditions. Following multiple-dose administration of telotristat ethyl 500 mg three times daily, there was negligible accumulation at steady state for both telotristat ethyl and telotristat. In patients with metastatic neuroendocrine tumors and carcinoid syndrome diarrhea treated with SSA therapy, the median Tmax for telotristat ethyl and telotristat was approximately 1 and 2 hours, respectively. Following administration of 500 mg telotristat ethyl three times daily, with meals in patients, the mean Cmax and AUC0-6hr were approximately 7 ng/mL and 22 ng•hr/mL, respectively, for telotristat ethyl. The mean Cmax and AUC0-6hr were approximately 900 ng/mL and 3000 ng•hr/mL, respectively for telotristat. The pharmacokinetic parameters for both telotristat ethyl and telotristat were highly variable with about 55% coefficient of variation.
Following a single 500 mg oral dose of ¹⁴C-telotristat ethyl, 93.2% of the dose was recovered over 240 hours: 92.8% was recovered in the feces, with less than 0.4% being recovered in the urine.
The estimated apparent total volume of distribution for the active metabolite from the Population PK model of 428.1 L in a typical healthy fasted subject and 348.7 L in patients with carcinoid syndrome.
The apparent total clearance at steady state (CL/F_ss) following oral dosing with telotristat ethyl 500 mg three times daily for 14 days (twice the recommended dosage) in healthy subjects was 2.7 and 152 L/hr for telotristat ethyl and telotristat, respectively.

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Metabolism / Metabolites
After oral administration, telotristat ethyl undergoes hydrolysis via carboxylesterases to telotristat, its active metabolite. Telotristat is further metabolized. Among the metabolites of telotristat, the systemic exposure to an acid metabolite of oxidative deaminated decarboxylated telotristat was about 35% of that of telotristat. In vitro data suggest that telotristat ethyl and telotristat are not substrates for CYP enzymes.

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Biological Half-Life
Following a single 500 mg oral dose of telotristat ethyl in healthy subjects, the apparent half-life was approximately 0.6 hours for telotristat ethyl and 5 hours for telotristat.

Protein Binding
Both telotristat ethyl and telotristat are greater than 99% bound to human plasma proteins.

[1]. LX1606 (aka LX1032), a Novel Inhibitor of Serotonin Synthesis, Alleviates Development of Inflammatory Bowel Disease in a Preclinical Model.

[2]. Pharmacological reduction of mucosal but not neuronal serotonin opposes inflammation in mouse intestine. Gut, 2013.

Telotristat ethyl is a prodrug of telotristat that was approved by the FDA in March 2017 as Xermelo. It was previously referred to as telotristat etiprate, the hippurate salt form; however, the FDA recommends the use of the name of the neutral form rather than that of the salt. Currently, telotristat ethyl is used to treat carcinoid syndrome diarrhea from neuroendocrine tumors that are inadequately controlled by short-acting somatostatin analog (SSA) treatment. Neuroendocrine cells are cells that secrete regulatory peptides and biogenic amines in response to chemical, neural, or other types of stimuli. Neuroendocrine tumors (NET) arising from these cells can therefore secrete chemical mediators into the bloodstream to cause side effects in distant sites, a phenomenon called carcinoid syndrome. The most common peptides and amines secreted by NET are histamines, tachykinins, kallikrein, and serotonin. Overexposure to serotonin can cause severe diarrhea, one of the main clinical symptoms of carcinoid syndrome. Serotonin is metabolized in the urinary metabolite 5-hydroxy indole acetic acid (u5-HIAA), and high levels of u5-HIAA is associated with poor survival outcome in patients with NET. The first line treatment of carcinoid syndrome diarrhea is SSA, but symptoms still reoccur over the course of the disease.
Telotristat Ethyl is the ethyl ester form of telotristat, a tryptophan hydroxylase (TPH) inhibitor, with potential anti-serotonergic activity. Upon administration, telotristat binds to and inhibits the activity of TPH. This may result in a reduction in peripheral serotonin (5-HT) production and improvement of serotonin-mediated gastrointestinal effects such as severe diarrhea. TPH, the rate-limiting enzyme in serotonin biosynthesis, is overexpressed in carcinoid tumor cells.
See also: Telotristat (has active moiety).

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Drug Indication
Xermelo is indicated for the treatment of carcinoid syndrome diarrhea in combination with somatostatin analog (SSA) therapy in adults inadequately controlled by SSA therapy.
Xermelo is indicated for the treatment of carcinoid syndrome diarrhoea in combination with somatostatin analogue (SSA) therapy in adults inadequately controlled by SSA therapy.

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Mechanism of Action
Telotristat, the active metabolite of telotristat ethyl, is an inhibitor of tryptophan hydroxylase, which mediates the rate-limiting step in serotonin biosynthesis. The in vitro inhibitory potency of telotristat towards tryptophan hydroxylase is 29 times higher than that of telotristat ethyl. Serotonin plays a role in mediating secretion, motility, inflammation, and sensation of the gastrointestinal tract, and is over-produced in patients with carcinoid syndrome. Through inhibition of tryptophan hydroxylase, telotristat and telotristat ethyl reduce the production of peripheral serotonin, and the frequency of carcinoid syndrome diarrhea.

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Pharmacodynamics
In normal mice, telotristat etiprate (administered once daily for 4 days at doses of 15–300 mg/kg/day) was found to reduce serotonin levels throughout the gastrointestinal tract. These reductions occurred in a dose dependent fashion with maximal effects observed with doses of telotristat etiprate ≥150 mg/kg. No significant change in brain serotonin or 5-hydroxyindoleacetic acid (5-HIAA, a serotonin metabolite) was observed. Similar findings were seen in Sprague-Dawley rats. Gastrointestinal motility studies were conducted in rats using the charcoal meal test. There was a significant dose-related delay in both gastrointestinal transit and gastric emptying, associated with a reduction in blood serotonin levels and proximal colon serotonin. A quantitative whole-body autoradiography study was conducted to assess the absorption, distribution and excretion of radioactivity in rats following a single oral dose of telotristat etiprate labeled with carbon 14. Rats were administered either 30 mg/kg or 100 mg/kg of the compound. The distribution of radioactivity was limited to tissues of the hepatic and renal system and the contents of the GI tract. There was no measurable radioactivity in the brain at any dose tested.

C27H26CLF3N6O3

574.99

574.17

C, 56.40; H, 4.56; Cl, 6.17; F, 9.91; N, 14.62; O, 8.35

1033805-22-9

Telotristat etiprate;1137608-69-5;Telotristat;1033805-28-5; 1033805-22-9 (ethyl); 1374745-52-4 (besilate)

25181577

Typically exists as Light yellow to yellow solids at room temperature

1.4±0.1 g/cm3

704.7±70.0 °C at 760 mmHg

380.0±35.7 °C

0.0±2.2 mmHg at 25°C

1.621

5.47

2

11

10

40

821

2

N[C@@H](CC1=CC=C(C2=NC(N)=NC(O[C@H](C3=CC=C(Cl)C=C3N4N=C(C)C=C4)C(F)(F)F)=C2)C=C1)C(OCC)=O

MDSQOJYHHZBZKA-GBXCKJPGSA-N

InChI=1S/C27H26ClF3N6O3/c1-3-39-25(38)20(32)12-16-4-6-17(7-5-16)21-14-23(35-26(33)34-21)40-24(27(29,30)31)19-9-8-18(28)13-22(19)37-11-10-15(2)36-37/h4-11,13-14,20,24H,3,12,32H2,1-2H3,(H2,33,34,35)/t20-,24+/m0/s1

ethyl (2S)-2-amino-3-[4-[2-amino-6-[(1R)-1-[4-chloro-2-(3-methylpyrazol-1-yl)phenyl]-2,2,2-trifluoroethoxy]pyrimidin-4-yl]phenyl]propanoate

LX 1032; LX 1606; LX-1032; LX1606; LX1032; LX-1606; LX1606; LX 1606; Xermelo; Telotristat ethyl [USAN]; trade name: Xermelo

2934.99.9001

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: ≥ 2.5 mg/mL (4.35 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 (4.35 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 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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