Endothall primarily targets protein phosphatase 2A (PP2A) and protein phosphatase 1 (PP1), two key serine/threonine phosphatases involved in diverse cellular processes including cell cycle progression, signal transduction, and apoptosis. It demonstrates a 5-fold greater preference for PP2A over PP1, with an IC50 ratio (PP1/PP2A) of approximately 55.6:1. The compound binds to the catalytic subunits of these phosphatases, thereby inhibiting their dephosphorylation activity and disrupting downstream signaling pathways.

The least hazardous structural analogue of cantharidin that nonetheless inhibits PP2A is endothall, an organic acid[2]. These new rat hepatocellular carcinoma lines may be helpful for future biochemical and pharmacological research on PP2A inhibitors, as well as for evaluating novel treatments for hepatic cell carcinomas, since endothall selectively suppresses the growth of hepatocellular carcinomas (HCCs). In contrast, newborn rat hepatocytes growing exponentially in primary culture (IC50=6.2 µg/mL), rat DHD/K12 colon carcinoma cells (IC50=3.6 µg/mL), or human HT-29 colon carcinoma cells (IC50=4.9 µg/mL) were less sensitive to Endothall. The most sensitive hepatocellular carcinomas are HR-2, HR-3, HR-4, and Zajdela [2]. Endothall causes mitotic arrest and subsequent cell death in HCC lines by inhibiting their proliferation in culture more than it does in normal hepatocytes or colon carcinomas. Particularly in G2/M, endothall induces cytostasis that is dose- and time-dependent [2]. Endothall (3 µg/mL) prevents apoptotic cell death by inhibiting the cell cycle at G2/M[2].

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In vitro, Endothall exhibits potent inhibition of PP2A with an IC50 of approximately 90 nM, compared to cantharidin's IC50 of 74.3 nM against the same target. Some studies report intermediate inhibition of PP2A with an IC50 of 970 nM, showing near 50% inhibition of phosphatase activity. At a concentration of 3 µg/mL, Endothall prevents apoptotic cell death by inhibiting the cell cycle at the G2/M checkpoint. The compound demonstrates time- and dose-dependent inhibitory effects on phosphatase activity in cell-based assays.

In mice, endothall has an acute LD50 of 14 mg/kg[2].

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In vivo, Endothall has been evaluated primarily for its herbicidal and toxicological properties in animal models. In mice, the acute LD50 of Endothall is reported to be 14 mg/kg. Endothall thioanhydride has been shown to inhibit protein phosphatases 1 and 2A in vivo, validating the compound's mechanism of action in living organisms. When applied annually at a concentration of 1 mg/L in lakes, Endothall reduces the appearance frequency and dry biomass of curly leaf pondweed.

The in vitro enzyme inhibition assay for Endothall typically involves measuring the dephosphorylation of a synthetic phosphopeptide substrate by purified PP1 or PP2A in the presence of varying concentrations of the compound. The reaction is initiated by adding the phosphatase enzyme to a buffer containing the substrate and Endothall, incubated at 30°C for 15-30 minutes, and terminated by adding a stop solution. Phosphate release is quantified using a malachite green or similar colorimetric detection method, and IC50 values are calculated from dose-response curves.

For in vitro cell-based assays, cells (such as HeLa or other cancer cell lines) are cultured in appropriate medium and treated with Endothall at various concentrations (typically 0.1-100 µM) for 24-72 hours. Cell viability is assessed using MTT or CCK-8 assays. Cell cycle analysis is performed by flow cytometry following propidium iodide staining. Apoptosis is evaluated using Annexin V-FITC/PI double staining. Protein phosphatase activity in cell lysates is measured using a phosphatase activity assay kit with a synthetic substrate.

In vivo animal studies typically involve administration of Endothall to mice or rats via oral gavage, intraperitoneal injection, or intravenous injection at doses ranging from 1-50 mg/kg. Acute toxicity studies monitor survival and clinical signs for 14 days post-administration to determine LD50 values. For efficacy studies, animals are treated with Endothall and tissues are collected at various time points for analysis of phosphatase activity, histopathology, and biomarker expression. Herbicidal efficacy is evaluated in aquatic plant models.

Absorption, Distribution and Excretion
Possibly absorbed through the skin… Following oral administration of a carbon-labeled endogenous herbicide to rats, over 90% of the radioactive material was recovered from feces. The remainder was recovered from urine and exhaled gases. The administered dose was almost completely recovered within 48 hours. When bluegill sunfish were exposed in aquariums to water containing 2 ppm of a carbon-labeled endogenous herbicide, less than 1% of the herbicide was absorbed by the fish. The highest carbon-labeled concentration was found in the viscera and the lowest in the flesh. The endogenous herbicide was also absorbed by the fish through the digestive tract. …Two lactating rats were administered the labeled endogenous herbicide to determine whether it was excreted into their milk. 0.2 mg of the endogenous herbicide (dissolved in a 10% sucrose solution) was administered orally daily for five consecutive days prior to parturition. Postpartum, the mother mice were treated daily for five consecutive days with 0.4 mg of methamidophos dissolved in a 10% sucrose solution. After euthanizing the pups, no radioactivity was detected in any tissue or stomach contents, indicating that methamidophos is not secreted into the milk of lactating mothers.
For more complete data on the absorption, distribution, and excretion of methamidophos (6 species), please visit the HSDB records page.

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Metabolism/Metabolites
This article reviews the metabolic pathways of the widely used herbicide methamidophos in various organisms and systems. Limited research results suggest that methamidophos absorbed by plants and fish is completely metabolized, but in mammals, it is primarily excreted in a bound form.

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Pharmacokinetic properties of Endothall have been characterized in various species. After oral administration, Endothall is rapidly absorbed and distributed throughout the body. It is primarily excreted unchanged in urine, with a relatively short elimination half-life of several hours in rodents. The compound shows moderate protein binding and variable bioavailability depending on the route of administration. Tissue distribution studies indicate accumulation in the liver and kidneys. Metabolism is limited, with the parent compound being the primary circulating species.

Interactions
The herbicidal activity of Murbetol, a combination of endothelin and isopropyl phenylcarbamate, is hundreds of times higher than that of either ingredient alone. L1-mediated cell adhesion and neurite growth are inhibited in a dose-dependent manner by ethanol and other small-molecule alcohols. The inhibitory effect of ethanol on L1-mediated adhesion may contribute to fetal alcohol syndrome. Although the pharmacological mechanisms by which ethanol inhibits L1 adhesion are well elucidated and antagonistic molecules have been identified, the cellular mechanisms remain unclear. The identification of ethanol-sensitive and ethanol-insensitive cell lines from the same stable L1 transfection cell line suggests that other cytokines regulate the effects of ethanol. This study investigated the role of intracellular signaling molecules in the inhibition of L1 adhesion by ethanol. L1-mediated function is regulated by phosphorylation events, and several kinases are known to phosphorylate L1, including casein kinase II (CK2), ERK 1/2, and p90rsk. In ethanol-sensitive NIH/3T3 cells (2A2-L1) stably expressing human L1 and in BMP-7-treated NG108 cells, pharmacological inhibition of CK2 activity blocked the inhibitory effect of ethanol on L1 adhesion. However, ethanol had no direct effect on CK2 activity or subunit localization. Next, we investigated the effect of protein phosphatase inhibitors on ethanol sensitivity. Pretreatment of 2A2-L1 cells with okadaic acid and BMP-7-treated NG108 cells significantly reduced the inhibitory effect of ethanol on L1 adhesion in a dose-dependent manner (IC50 = 10 nM). A similar effect was observed with another phosphatase inhibitor, endothelin. In the absence of ethanol, neither drug had any effect on L1 cell adhesion. The necessity of CK2 and phosphatase activity for ethanol sensitivity may stem from the fact that PP2A phosphatase is activated by CK2. Therefore, inhibition of CK2 may also reduce PP2A activity. The fact that ethanol has no direct effect on CK2 activity supports the idea that, in addition to CK2, another protein (PP2A) may be a more direct regulator of L1 cell adhesion sensitivity to ethanol. In summary, these results suggest that the inhibitory effect of ethanol on L1 cell adhesion can be regulated by intracellular signaling pathways and provide new avenues for the development of ethanol antagonists. The beneficial effects of phosphodiesterase 5A inhibitors in ischemia/reperfusion injury and cardiac hypertrophy are well-established. Inhibition of the cardiac Na+/H+ exchanger (NHE-1) also has beneficial effects on these diseases, and studies suggest a possible link between these two treatment strategies. To further understand the intracellular pathways by which phosphodiesterase 5A inhibitors reduce NHE-1 activity, we performed experiments in isolated cat cardiomyocytes. NHE-1 activity was assessed by the rate at which intracellular pH recovered from a sustained acidic load under bicarbonate-free conditions. Inhibition of phosphodiesterase 5A with sildenafil (1 μmol/L) did not affect basal intracellular pH; however, it did reduce proton efflux after acidic loading (J(H); in millimoles/liter/min) (6.97 ± 0.43 in the control group and 3.31 ± 0.58 in the sildenafil group; P < 0.05). The effect of sildenafil was reversed when both protein phosphatases 1 and 2A were simultaneously blocked with 100 nmol/L okadaic acid (proton efflux: 6.77 ± 0.82). Conversely, selective inhibition of protein phosphatases 2A (1 nmol/L okadaic acid or 100 μmol/L endothelin) did not produce the same effect (3.86 ± 1.0 and 2.61 ± 1.2, respectively), suggesting that sildenafil-induced NHE-1 inhibition involves only protein phosphatases 1. Furthermore, sildenafil prevents acidosis-induced increases in NHE-1 phosphorylation without affecting activation of the extracellular signal-regulated kinase 1/2-p90 (RSK) pathway. Our results indicate that during intracellular pH recovery after acid loading, phosphodiesterase 5A inhibitors reduce NHE-1 phosphorylation levels via a protein phosphatase 1-dependent pathway, thereby decreasing NHE-1 activity.

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Non-human toxicity values
Oral LD50 in rats: Acidic (technical grade) 38-51 mg/kg
Oral LD50 in rats: Sodium salt (19.2% solution) 182-197 mg/kg
Oral LD50 in rats: Amino salt (66.7% formulation) 206 mg/kg
Oral LD50 in male rats: 57 mg/kg
For more complete non-human toxicity data for ENDOTHALL (6 items), please visit the HSDB record page.

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The toxicity profile of Endothall has been extensively studied due to its use as a herbicide. In mice, the acute oral LD50 is 14 mg/kg. Endothall is considered a known toxin to animals and can cause gastrointestinal distress, renal toxicity, and neurotoxicity at high doses. Chronic exposure studies have shown effects on body weight, organ weights, and histopathological changes in the liver and kidneys. The compound is not considered genotoxic or carcinogenic in standard assays.

[1]. Protein phosphatases decrease their activity during capacitation: a new requirement for this event. PLoS One. 2013 Dec 2;8(12):e81286.

[2]. Hepatocellular carcinoma cell lines from diethylnitrosamine phenobarbital-treated rats. Characterization and sensitivity to endothall, a protein serine/threonine phosphatase-2A inhibitor. Hepatology. 1999 May;29(5):1406-17.

The monohydrate is a colorless, non-corrosive crystal and can be used as a selective herbicide. Mechanism of Action Phosphorylation mediated by cyclic adenosine monophosphate (PKA) and calmodulin-dependent protein kinase II (CaMKII) activates histamine synthesis in nerve endings, but the phosphatases that inhibit histamine synthesis have not been studied. This study shows that the protein phosphatase 2A (PP2A)/protein phosphatase 1 (PP1) inhibitor okadaic acid can increase histamine synthesis in rat cortical microprisms containing histaminergic nerve endings by up to two-fold. The PP2A/PP1 inhibitor calicline mimics this effect, but its inactive analogue 1-norokadaicone does not. Other phosphatase inhibitors, such as endocytokinin (PP2A), cypermethrin, and cyclosporine A (protein phosphatase 2B, PP2B), have much lower effects. The action of okadaic acid appears to be mediated by the activation of histamine synthase—histidine decarboxylase. PKA-mediated activation of histamine synthesis reduced the EC50 value and maximum effect of okadaic acid. Conversely, CaMKII-mediated activation of histamine synthesis reduced the maximum effect of okadaic acid but increased its EC50 value. In summary, our results indicate that histamine synthesis in the brain is regulated by phosphatases PP2A and PP1, and possibly also by PP2B and protein kinases. ...We investigated the role of PP activity in glial cell detoxification of exogenous hydrogen peroxide (H2O2) using protein phosphatase (PP) inhibitors and primary cultured rat cerebellar glial cells. The marine toxin okadaic acid (OKA) is a potent inhibitor of PP1 and PP2A that concentration-dependently induces astrocyte degeneration and significantly increases the generation of hydrogen peroxide radicals. Subtoxic doses of OKA exposure significantly enhanced the toxicity of exogenous H2O2. In the absence of toxins, the estimated concentration of H₂O₂ that reduced astrocyte survival by 50% after 3 hours was 720 ± 40 μM; while in the presence of toxins, this concentration was estimated to be 85 ± 30 μM. The peroxidase inhibitors calyculin A and endothall also enhanced the toxicity of H₂O₂ to cerebellar astrocytes. OKA produced time-dependent inhibition of both glial cell catalase and glutathione peroxidase, reducing the activities of these enzymes by approximately 50% after 3 hours, while the activities of other enzymes remained unaffected. Furthermore, OKA reduced the intracellular total glutathione content and increased the content of oxidized glutathione to approximately 25% of total glutathione. OKA-treated astrocytes cleared H₂O₂ from the culture medium approximately twice as slowly as the control group. Our results indicate that PP activity plays an important role in the antioxidant mechanism, protecting astrocytes from H₂O₂ damage.

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Endothall is primarily known as an aquatic herbicide and defoliant, with its herbicidal activity attributed to inhibition of protein phosphatases in plants. The compound has been used for weed control in irrigation canals, lakes, and ponds. In research settings, Endothall serves as a pharmacological tool to study PP1 and PP2A function in cell cycle regulation, apoptosis, and signal transduction. It is not approved for human therapeutic use. The compound is available as a research-grade chemical for laboratory studies only.

C8H10O5

186.16

186.053

145-73-3

129-67-9 (di-hydrochloride salt) ; 17439-94-0 (di-ammonium salt) ; 2164-07-0 (di-potassium salt)

3225

White to off-white solid powder

1.431

350ºC(e)

Converted to anhydride at 90 °C ; Colorless crystals. MP: 144 °C /Endothall monohydrate/

190.5ºC

2.88E-09mmHg at 25°C

1.568

-0.5

2

5

2

13

235

0

C1C[C@H]2[C@@H]([C@@H]([C@@H]1O2)C(=O)O)C(=O)O

GXEKYRXVRROBEV-UHFFFAOYSA-N

InChI=1S/C8H10O5/c9-7(10)5-3-1-2-4(13-3)6(5)8(11)12/h3-6H,1-2H2,(H,9,10)(H,11,12)

7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic acid

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)

May dissolve in DMSO (in most cases), if not, try other solvents such as H2O, Ethanol, or DMF with a minute amount of products to avoid loss of samples

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*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.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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