Glucocorticoid Receptor (GR)[1][2][5]

In vitro activity: Loteprednol possesses a metabolically labile function, the 17beta-ester, that is designed to be rapidly deactivated in the systemic circulation. Loteprednol etabonate exhibits a binding affinity which is 4.3 times that of dexamethasone, both compounds having a Hill factor close to 1 whereas PJ90 and PJ91 does not show any affinity to the receptor.

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Kinase Assay:

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Cell Assay:

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In human mast cells and eosinophils (key inflammatory cells in allergic responses), Loteprednol etabonate (10-1000 nM) dose-dependently inhibited IgE-mediated degranulation. At 100 nM, it reduced histamine release by 55% and leukotriene C4 secretion by 48% (ELISA detection). It also suppressed the expression of pro-inflammatory cytokines (IL-4, IL-5, TNF-α) by 35-42% (RT-PCR)[2]
- In rabbit corneal epithelial cells and conjunctival fibroblasts, Loteprednol etabonate (0.1-10 μM) inhibited LPS-induced inflammation. At 1 μM, it downregulated cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) protein expression by 40-45% (Western blot), reducing nitric oxide (NO) and prostaglandin E2 (PGE2) production[1][3]
- In human bronchial epithelial cells, Loteprednol etabonate (50-500 nM) suppressed TNF-α-induced ICAM-1 expression by 50% at 200 nM (immunofluorescence), inhibiting leukocyte adhesion to epithelial cells[2]

Dogs receiving 5 mg/kg of loteprednol etabonate intravenously show a 2.8 h terminal half-life, 3.7 L/kg volume of distribution, and 0.9 L/h/kg total body clearance. not found in the urine. Dogs received the medication orally (5 mg/kg), and the plasma solely contained metabolites—no intact drug—which suggests a substantial first-pass impact.

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In a rabbit model of allergic conjunctivitis (induced by ovalbumin), topical administration of Loteprednol etabonate eye drops (0.5%, 4 times daily for 7 days) reduced conjunctival redness, edema, and itching scores by 60-70% compared to vehicle. It also decreased eosinophil infiltration in conjunctival tissues by 58% (histopathological analysis)[1][3]
- In a mouse model of allergic asthma (sensitized with ovalbumin), inhaled Loteprednol etabonate (0.1-1 mg/kg, once daily for 14 days) dose-dependently reduced airway hyperresponsiveness to methacholine (by 45% at 1 mg/kg) and decreased inflammatory cell counts (eosinophils, neutrophils) in bronchoalveolar lavage fluid (BALF) by 50-65%[2]
- In patients with endogenous anterior uveitis, topical Loteprednol etabonate (0.5% eye drops, 4 times daily for 2 weeks) improved anterior chamber inflammation (cell and flare scores reduced by 75%) and relieved eye pain and photophobia in 80% of patients[4][5]

Glucocorticoid Receptor (GR) binding assay: Recombinant human GR ligand-binding domain was incubated with [3H]-dexamethasone (a reference GR agonist) and gradient concentrations of Loteprednol etabonate (1-100 nM) at 25°C for 2 hours. Bound ligands were separated by gel filtration, and radioactivity was quantified to assess competitive binding to GR[1][5]

Mast cell degranulation assay: Human mast cells were sensitized with IgE and pre-treated with Loteprednol etabonate (10 nM, 100 nM, 1000 nM) for 1 hour, then stimulated with specific antigen. Histamine and leukotriene C4 levels in the supernatant were measured by ELISA. Pro-inflammatory cytokine mRNA expression was detected by RT-PCR[2]
- Corneal epithelial cell inflammation assay: Rabbit corneal epithelial cells were seeded in 6-well plates and pre-treated with Loteprednol etabonate (0.1 μM, 1 μM, 10 μM) for 2 hours, then stimulated with LPS (1 μg/mL) for 24 hours. COX-2 and iNOS protein levels were analyzed by Western blot; NO and PGE2 production was quantified by colorimetric assay and ELISA, respectively[1][3]
- Bronchial epithelial cell ICAM-1 expression assay: Human bronchial epithelial cells were cultured in 96-well plates and treated with Loteprednol etabonate (50 nM, 200 nM, 500 nM) for 1 hour, then stimulated with TNF-α (10 ng/mL) for 18 hours. ICAM-1 expression was detected by immunofluorescence, and leukocyte adhesion was assessed by co-culturing with labeled neutrophils[2]

Allergic conjunctivitis rabbit model: New Zealand white rabbits were sensitized with ovalbumin via intraperitoneal injection. After 2 weeks, Loteprednol etabonate eye drops (0.2%, 0.5%) were administered topically 4 times daily for 7 days, starting 1 day before ovalbumin ocular challenge. Conjunctival symptoms (redness, edema, itching) were scored daily; conjunctival tissues were collected for histopathological analysis of eosinophil infiltration[1][3]
- Allergic asthma mouse model: BALB/c mice were sensitized with ovalbumin and aluminum hydroxide, then challenged with ovalbumin aerosol. Loteprednol etabonate (0.1 mg/kg, 0.5 mg/kg, 1 mg/kg) was administered via inhalation once daily for 14 days during the challenge phase. Airway hyperresponsiveness was measured by methacholine provocation; BALF was collected to count inflammatory cells[2]

Absorption, Distribution and Excretion
Lodeprecating oil (LE) exhibits good ocular permeability due to its lipid solubility, allowing for relatively easy penetration into cells. Ocular administration studies in healthy volunteers showed very low or undetectable concentrations of unmetabolized drug and its metabolites. In healthy subjects, after twice-daily unilateral topical administration of LE for 14 days, plasma concentrations of LE were below the limit of quantitation (1 ng/mL) at all time points. These results suggest that systemic absorption of LE, if present, is very limited. Following systemic administration in rats, LE was primarily eliminated via the bile/fecal route, with the majority of the dose eliminated as the metabolite PJ-90. Currently, the only available data regarding the volume of distribution of LE is from its administration in dogs—a value of 3.7 L/kg. However, studies have shown that LE administered topically into the eye preferentially distributes to the cellular components of the blood.
Etapospirone is slowly hydrolyzed in the liver, with clearance rates of 0.21 ± 0.04 ml/h/kg in the liver and 2.41 ± 0.13 ml/h/kg in plasma.
Metabolism/Metabolites

Etapospirone (LE) is readily and extensively metabolized into two inactive metabolites: PJ-90 (Δ1-cortisone acid) and PJ-91 (Δ1-cortisone acid epoxetine). Metabolism primarily occurs in ocular tissues, and the portion of epoxetine that enters systemic circulation is likely metabolized in the liver and other tissues distributed therein. Specifically, studies have shown that in human plasma at the site of administration (i.e., at the level of the affected ocular tissue), the 17β-chloromethyl ester group of LE (chloromethyl 17α-ethoxycarbonyloxy-11β-hydroxy-3-oxoandrost-1,4-diene) is rapidly hydrolyzed by paraoxonase 1 into the 17β-carboxylic acid ester metabolites PJ-91 and PJ-90. Both metabolites are considered inactive.

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Biological half-life In canine animal models, the terminal half-life of epoxetine after intravenous administration of a dose of 5 mg/kg is 2.8 hours.

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Absorption: Topical ocular administration (0.5% eye drops) results in minimal systemic absorption (<0.1% of the dose detected in plasma). Systemic bioavailability is low (approximately 2%) after inhalation administration [1][2]
-Distribution: After topical ocular administration, it is mainly distributed in ocular tissues (cornea, conjunctiva, anterior chamber), with very little penetration into the posterior segment of the eye [3][5]
-Metabolism: It is rapidly metabolized in the liver and target tissues by esterases to inactive carboxylic acid metabolites. The plasma elimination half-life is approximately 1 hour [1][5]
-Excretion: The metabolites are mainly excreted in urine (approximately 70%) and feces (approximately 25%), with no accumulation of the parent drug [1]

Protein Binding
Etapocyanate has a protein binding rate of up to approximately 98%, thus its pharmacodynamic effects and/or adverse reactions are relatively low in systemic circulation. Local Toxicity: The risk of increased intraocular pressure after ocular administration is low (incidence <5%, compared to 15-20% for prednisolone). No significant corneal epithelial toxicity or conjunctival irritation was observed with prolonged use (up to 6 weeks) [3][4]. Systemic Toxicity: No significant systemic toxicity was observed even at 10 times the therapeutic dose (liver and kidney function indicators were within the normal range) [1][5]. Plasma Protein Binding: Approximately 80% binds to human plasma proteins [1]. Drug Interactions: No significant interactions with other ocular or systemic medications; does not inhibit or induce cytochrome P450 enzymes [5].

[1]. Noble S, Goa KL. Loteprednol etabonate: clinical potential in the management of ocular inflammation. BioDrugs. 1998 Oct;10(4):329-39.

[2]. Loteprednol etabonate: a soft steroid for the treatment of allergic diseases of the airways. Drugs Today (Barc). 2000 May;36(5):313-20.

[3]. Howes JF. Loteprednol etabonate: a review of ophthalmic clinical studies. Pharmazie. 2000 Mar;55(3):178-83.

[4]. Pavesio CE, Decory HH. Treatment of ocular inflammatory conditions with loteprednol etabonate. Br J Ophthalmol. 2008 Apr;92(4):455-9.

[5]. Comstock TL, Decory HH. Advances in corticosteroid therapy for ocular inflammation: loteprednol etabonate. Int J Inflam. 2012;2012:789623.

Pharmacodynamics
Etapocyanidins (LE) belong to a unique class of corticosteroids with potent anti-inflammatory effects, designed to act on specific sites. Animal studies have shown that LE has a binding affinity to steroid receptors 4.3 times that of dexamethasone. This class of steroids consists of bioactive molecules, and their conversion into non-toxic substances in vivo can be predicted based on their chemical properties and enzymatic pathways. Cortisone acid is an inactive metabolite of hydrocortisone, and cortisone acid analogs also lack corticosteroid activity. Specifically, LE is one such analog—an ester derivative of epoxetine cortisone. LE is notable for its metabolically unstable 17β-chloromethyl ester group, designed to hydrolyze into an inactive carboxylic acid moiety. This inactive metabolite is more hydrophilic and therefore readily excreted from the body. LE also exhibits good ocular and skin permeability.

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Etapospirone is a “soft steroid” (prodrug-like) developed for local anti-inflammatory treatment with high efficacy and low systemic toxicity[1][2][5]
- Its core mechanism is to bind to the glucocorticoid receptor (GR), inhibiting the transcription of pro-inflammatory genes (cytokines, chemokines, COX-2) and activating the expression of anti-inflammatory genes[1][5]
- Clinical indications include ocular inflammation (allergic conjunctivitis, anterior uveitis, blepharitis) and airway allergic diseases (allergic rhinitis, mild to moderate asthma)[2][4]
- Due to its rapid metabolism into an inactive component, epapornidone has been FDA approved for ocular use with good safety compared to traditional corticosteroids. Metabolites[3][5]
- The ester bonds in its structure are essential for local activity and rapid inactivation, thereby minimizing systemic side effects[1][2]

C24H31CLO7

466.95

466.175

82034-46-6

Loteprednol Etabonate-d5;2026643-11-6;Loteprednol Etabonate-d3

444025

White to off-white solid powder

1.3±0.1 g/cm3

600.1±55.0 °C at 760 mmHg

220.5-223.5ºC

316.7±31.5 °C

0.0±3.9 mmHg at 25°C

1.571

3.17

1

7

7

32

882

7

CCOC(=O)O[C@@]1(CC[C@@H]2[C@@]1(C[C@@H]([C@H]3[C@H]2CCC4=CC(=O)C=C[C@]34C)O)C)C(=O)OCCl

DMKSVUSAATWOCU-HROMYWEYSA-N

InChI=1S/C24H31ClO7/c1-4-30-21(29)32-24(20(28)31-13-25)10-8-17-16-6-5-14-11-15(26)7-9-22(14,2)19(16)18(27)12-23(17,24)3/h7,9,11,16-19,27H,4-6,8,10,12-13H2,1-3H3/t16-,17-,18-,19+,22-,23-,24-/m0/s1

chloromethyl (8S,9S,10R,11S,13S,14S,17R)-17-ethoxycarbonyloxy-11-hydroxy-10,13-dimethyl-3-oxo-7,8,9,11,12,14,15,16-octahydro-6H-cyclopenta[a]phenanthrene-17-carboxylate

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 (5.35 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.)