Endogenous Metabolite

L-5-HTP blocks PD-L1 induction in cancer cells. L-5-HTP transcriptionally suppresses inducible PD-L1 expression directly rather than via transformation to related metabolites. The inhibitory effects of L-5-HTP on IFN-γ stimulated PD-L1 induction are mediated by reduced expression of RTK ligands and suppression of the downstream RTK receptor/MEK/ERK/c-JUN signaling cascade.
Researchers discovered that L-5-HTP suppressed IFN-γ-induced PD-L1 expression in tumor cells transcriptionally, and this effect was directly due to itself. Mechanistically, L-5-HTP inhibited IFN-γ-induced expression of RTK ligands and thus suppressed phosphorylation-mediated activation of RTK receptors and the downstream MEK/ERK/c-JUN signaling cascade, leading to decreased PD-L1 induction [6].

Animal depression models can be created using L-5-hydroxytryptophan in animal modeling.

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THE depletion by reserpine of storage in the body of 5-hydroxytryptamine (‘Serotonin’) and of the catechol amines is now well established. In reserpinized animals the peripheral part of the adrenergic system does not function owing to lack of the transmitter. This is presumably true also of the central part of the adrenergic system. However, it remains to be proved to what extent the central action of reserpine may be attributed to changes in brain catechol amines and/or 5-hydroxytryptamine.[1]

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A double-blind, placebo-controlled study of the efficacy and tolerability of 5-hydroxytryptophan (5-HTP) was conducted in 50 patients with primary fibromyalgia syndrome. All the clinical parameters studied were significantly improved by treatment with 5-HTP and only mild and transient side-effects were reported. Further controlled studies are required to define properly the value of 5-HTP in patients with primary fibromyalgia syndrome.[2]

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Six patients with myoclonus of varying cause were treated with L-5-hydroxytryptophan (L-5-HTP) and carbidopa. While spontaneous myoclonus decreased in three of the patients and action myoclonus in four, only two patients had marked functional improvement. Side effects included gastrointestinal and affective disturbances. L-5-HTP therapy caused a diminished frequency of paroxysmal discharges in the electroencephalograms of three patients which did not always correlate with clinical improvement. Lumbar cerebrospinal fluid 5-hydroxyindoleacetic acid (5-HIAA) concentration after probenecid was decreased in all patients prior to therapy, but this reduction did not predict treatment response. Urinary excretion patterns for 5-HTP, serotonin, and 5-HIAA during treatment were similar in responders and nonresponders. It is concluded that while some patients with myoclonus do benefit from L-5-HTP therapy, biochemical and electrophysiological tests are not useful predictors of treatment response, and the high incidence of side effects limits the usefulness of this therapy.[3]

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The clinical effects of the protracted treatment with 5-OH Tryptophane (5-HTP) of some patients with chronic migraine are compared with other patients with acetylsalicylic acid. The pain threshold was neurophysiologically determined in migraneous on patients whose response to 5-HTP therapy was specially good. The results with 5-HTP can be accounted for by an action of the substance on the serotonin turnover with activation of the serotoninergic antinociceptive system.[4]

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Some features of cerebellar ataxia have been reported to regress partially with long-term administration of 5-hydroxytryptophan or levorotatory form of 5-hydroxytryptophan. To test this effect further, 30 patients with various inherited or acquired cerebellar ataxias underwent a randomized, double-blind trial of placebo, and the levorotatory form of 5-hydroxytryptophan taken orally for four months. The levorotatory form of 5-hydroxytryptophan significantly improved the ataxia score. It also significantly modified the time of standing upright, the spread of feet, the speed of walking, speaking, and writing. In five cases in which the levorotatory form of 5-hydroxytryptophan therapy was maintained for 12 months, the effect continued progressively.[5]

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L-5-HTP reduces PD-L1 expression and tumor growth in vivo [6]
We next investigated the potential immunotherapeutic effects of L-5-HTP. First, we determined that L-5-HTP does not have any significant deleterious effects on the proliferation of OVA-activated primary T cells isolated from an OT-Ⅰ mouse (online supplemental figure S4A). We then tested for any in vivo antitumor effects of L-5-HTP in immunocompetent mouse models. Two immunogenic mouse colon cancer cell lines (MC38 and CT26) were subcutaneously implanted into immunocompetent mice, which were given daily intraperitoneal injections of 100 mg/kg L-5-HTP. Compared with the vehicle control, L-5-HTP treatment significantly delayed the growth of both MC38 and CT26 tumors and reduced tumor weight (figure 4A, B). No significance in body weight were detected between the vehicle group and the treated group (figure 4C), suggesting that L-5-HTP was well tolerated. Moreover, the L-5-HTP treated group showed significantly better survival over the vehicle control group in both MC38 and CT26 tumor models (figure 4D). We also confirmed the antitumor therapeutic effects of L-5-HTP by showing that delaying the start of treatment until tumors reached 5 mm×5 mm (online supplemental figure S4B–D) resulted in similar suppression of tumor growth.

RNA sequencing and bioinformatic analysis [6]
BXPC3 cells were treated with one of four treatments—DMSO, IFN-γ, L-5-HTP (10 µM), and IFN-γ+L-5-HTP (10 µM)—for 24 hours. Three biological replicates were performed. Total RNA was extracted to prepare cDNA libraries, which were sequenced on the Illumina HiSeq 2000 platform using the paired-end approach. The sequencing reads were mapped to hg19 using STAR 2.5, and gene expression was quantified using the featureCounts software. Differential gene expression analysis was performed using the DESeq2 R package, and genes with significant changes in expression were identified as those with a p value <0.05 and a log2 (fold change) >2. Differentially expressed genes were subjected to enrichment analysis in KOBAS. An FDR value of 0.05 was used as a cut-off.

Mice and in vivo tumor model [6]
Female 6–8 week-old C57BL/6 mice, BALB/c mice, and BALB/c nude mice were fed a standard laboratory diet and provided with free access to water. The animals were housed under standard laboratory conditions (21°C±2°C, 12-hour light–dark cycle). CT26 (3×105), MC38 (3×105/1×106), and MC38 Pd-l1−/− (1×106) cells were subcutaneously inoculated into BALB/c mice or C57BL/6 mice. L-5-HTP (dissolved in 5% DMSO in PBS) was injected intraperitoneally (100 mg/kg) once per day. PD-1 monoclonal antibody (150 µg dissolved in PBS) (Bio X cell) was administered intraperitoneally at day 8, 12, and 16 alone or combined with L-5-HTP. Body weight and tumor volume were measured every 3 days. Tumor volume was calculated as 1/2×(length×width2). Mice were sacrificed at the endpoint.

Metabolism / Metabolites
5-Hydroxytryptophan is decarboxylated to serotonin (5-hydroxytryptamine or 5-HT) by the enzyme aromatic-L-amino-acid decarboxylase via a vitamin B6 dependent reaction in nervous tissue and in the liver.

rat LD50 oral 243 mg/kg BEHAVIORAL: SOMNOLENCE (GENERAL DEPRESSED ACTIVITY); BEHAVIORAL: EXCITEMENT; BEHAVIORAL: ATAXIA Nippon Yakurigaku Zasshi. Japanese Journal of Pharmacology., 69(523), 1973 [PMID:4546003]
rat LD50 intraperitoneal 91 mg/kg BEHAVIORAL: SOMNOLENCE (GENERAL DEPRESSED ACTIVITY); BEHAVIORAL: EXCITEMENT; BEHAVIORAL: ATAXIA Nippon Yakurigaku Zasshi. Japanese Journal of Pharmacology., 69(523), 1973 [PMID:4546003]
rat LD50 subcutaneous 149 mg/kg SENSE ORGANS AND SPECIAL SENSES: LACRIMATION: EYE; BEHAVIORAL: TREMOR; BEHAVIORAL: CONVULSIONS OR EFFECT ON SEIZURE THRESHOLD Iyakuhin Kenkyu. Study of Medical Supplies., 6(307), 1975
rat LD50 intravenous 27 mg/kg SENSE ORGANS AND SPECIAL SENSES: LACRIMATION: EYE; BEHAVIORAL: TREMOR; BEHAVIORAL: CONVULSIONS OR EFFECT ON SEIZURE THRESHOLD Iyakuhin Kenkyu. Study of Medical Supplies., 6(307), 1975
mouse LD50 oral 1708 mg/kg SENSE ORGANS AND SPECIAL SENSES: LACRIMATION: EYE; BEHAVIORAL: TREMOR; BEHAVIORAL: CONVULSIONS OR EFFECT ON SEIZURE THRESHOLD Iyakuhin Kenkyu. Study of Medical Supplies., 6(307), 1975

[1]. 3,4-Dihydroxyphenylalanine and 5-Hydroxytryptophan as Reserpine Antagonists. Nature 180, page1200 (1957).

[2]. Double-blind study of 5-hydroxytryptophan versus placebo in the treatment of primary fibromyalgia syndrome. J Int Med Res. 1990 May-Jun;18(3):201-9.

[3]. Treatment of myoclonus with L-5-hydroxytryptophan and carbidopa: clinical, electrophysiological, and biochemical observations. Ann Neurol. 1980 Jun;7(6):570-6.

[4]. 5-OH-Tryptophane in migraine: clinical and neurophysiological considerations. J Neurol. 1981;225(1):41-6.

[5]. Improvement of cerebellar ataxia with levorotatory form of 5-hydroxytryptophan. A double-blind study with quantified data processing. Arch Neurol. 1988 Nov;45(11):1217-22.

[6]. L-5-hydroxytryptophan promotes antitumor immunity by inhibiting PD-L1 inducible expression. J Immunother Cancer. 2022 Jun;10(6):e003957.

L-5-hydroxytryptophan appears as colorless to pale pink crystals. (NTP, 1992)
5-hydroxy-L-tryptophan is the L-enantiomer of 5-hydroxytryptophan. It has a role as a human metabolite, a plant metabolite and a mouse metabolite. It is a 5-hydroxytryptophan, a hydroxy-L-tryptophan and a non-proteinogenic L-alpha-amino acid. It is an enantiomer of a 5-hydroxy-D-tryptophan. It is a tautomer of a 5-hydroxy-L-tryptophan zwitterion.
5-Hydroxytryptophan (5-HTP), also known as oxitriptan (INN), is a naturally occurring amino acid and metabolic intermediate in the synthesis of serotonin and melatonin. 5-HTP is sold over-the-counter in the United Kingdom, United States and Canada as a dietary supplement for use as an antidepressant, appetite suppressant, and sleep aid, and is also marketed in many European countries for the indication of major depression under trade names like Cincofarm, Levothym, Levotonine, Oxyfan, Telesol, Tript-OH, and Triptum. Several double-blind placebo-controlled clinical trials have demonstrated the effectiveness of 5-HTP in the treatment of depression, though a lack of high quality studies has been noted. More study is needed to determine efficacy in treating depression.
5-hydroxy-L-tryptophan has been reported in Aspergillus fumigatus, Homo sapiens, and other organisms with data available.
Oxitriptan is an aromatic amino acid with antidepressant activity. In vivo, oxitriptan (or 5-hydroxytryptophan) is converted into 5-hydroxytryptamine (5-HT or serotonin) as well as other neurotransmitters. Oxitriptan may exert its antidepressant activity via conversion to serotonin or directly by binding to serotonin (5-HT) receptors within the central nervous system (CNS). Endogenous oxitriptan is produced from the essential amino acid L-tryptophan. The exogenous therapeutic form is isolated from the seeds of the African plant Griffonia simplicifolia.
5-Hydroxytryptophan, DL- is a racemic mixture of 5-hydroxytryptophan (5-HTP), a precursor to the neurotransmitter serotonin with anti-depressant, analgesic and appetite-suppressant activities. DL-5-HTP is decarboxylated to serotonin by aromatic-L-amino-acid decarboxylase, and results in increased serotonin levels within the brain. Mediated through serotonin receptors, elevated levels of serotonin causes increased serotonin neurotransmissions, hence leading to release of depression, pain and appetite.
The immediate precursor in the biosynthesis of SEROTONIN from tryptophan. It is used as an antiepileptic and antidepressant.
See also: ... View More ...

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Drug Indication
For use as an antidepressant, appetite suppressant, and sleep aid.

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Pharmacodynamics
The psychoactive action of 5-HTP is thought to be due to increased serotonin production in central nervous system tissue.

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Background: The repression or downregulation of programmed death-ligand 1 (PD-L1) can release its inhibition of T cells and activate antitumor immune responses. Although PD-1 and PD-L1 antibodies are promising treatments for diverse tumor types, their inherent disadvantages and immune-related adverse events remain significant issues. The development of small molecule inhibitors targeting the interaction surface of PD-1 and PD-L1 has been reviving, yet many challenges remain. To address these issues, we aimed to find small molecules with durable efficacy and favorable biosafety that alter PD-L1 surface expression and can be developed into a promising alternative and complementary therapy for existing anti-PD-1/PD-L1 therapies. Methods: Cell-based screen of 200 metabolic molecules using a high-throughput flow cytometry assay of PD-L1 surface expression was conducted, and L-5-hydroxytryptophan (L-5-HTP) was found to suppress PD-L1 expression induced by interferon gamma (IFN-γ). Inhibition of PD-L1 induction and antitumor effect of L-5-HTP were evaluated in two syngeneic mouse tumor models. Flow cytometry was performed to investigate the change in the tumor microenvironment caused by L-5-HTP treatment. Results: We discovered that L-5-HTP suppressed IFN-γ-induced PD-L1 expression in tumor cells transcriptionally, and this effect was directly due to itself. Mechanistically, L-5-HTP inhibited IFN-γ-induced expression of RTK ligands and thus suppressed phosphorylation-mediated activation of RTK receptors and the downstream MEK/ERK/c-JUN signaling cascade, leading to decreased PD-L1 induction. In syngeneic mouse tumor models, treatment with 100 mg/kg L-5-HTP (intraperitoneal) inhibited PD-L1 expression and exhibited antitumor effect. L-5-HTP upregulated the ratio of granzyme B+ CD8+ activated cytotoxic T cells. An intact immune system and PD-L1 expression was critical for L-5-HTP to exert its antitumor effects. Furthermore, L-5-HTP acted synergistically with PD-1 antibody to improve anticancer effect. Conclusion: Our study illustrated L-5-HTP's inhibitory effect on PD-L1 induction stimulated by IFN-γ in tumor cells and also provided insight into repurposing L-5-HTP for use in tumor immunotherapy.[6]

220.084

C, 59.99; H, 5.49; N, 12.72; O, 21.80

4350-09-8

L-5-Hydroxytryptophan-d3;1276197-29-5;L-5-Hydroxytryptophan-d3-1;L-5-Hydroxytryptophan-d4;1246818-91-6

439280

White to light brown solid powder

1.5±0.1 g/cm3

520.6±50.0 °C at 760 mmHg

270 °C (dec.)(lit.)

268.7±30.1 °C

0.0±1.4 mmHg at 25°C

1.737

-0.14

4

4

3

16

272

1

O([H])C1C([H])=C([H])C2=C(C=1[H])C(=C([H])N2[H])C([H])([H])[C@@]([H])(C(=O)O[H])N([H])[H]

LDCYZAJDBXYCGN-VIFPVBQESA-N

InChI=1S/C11H12N2O3/c12-9(11(15)16)3-6-5-13-10-2-1-7(14)4-8(6)10/h1-2,4-5,9,13-14H,3,12H2,(H,15,16)/t9-/m0/s1

(2S)-2-amino-3-(5-hydroxy-1H-indol-3-yl)propanoic acid

5 Hydroxytryptophan; Oxitriptan; 5-hydroxy-L-tryptophan; L-5-Hydroxytryptophan; oxitriptan; 4350-09-8; Levothym; Cincofarm; Pretonine; L-5-Htp; 5-hydroxy-L-tryptophan; Oxytryptophan5-HTP

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)

DMSO : ~12.5 mg/mL (~56.76 mM)

Solubility in Formulation 1: ≥ 1.25 mg/mL (5.68 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 12.5 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: ≥ 1.25 mg/mL (5.68 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 12.5 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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 (Please use freshly prepared in vivo formulations for optimal results.)