Ostarine

Technical data

INN name

Ostarine

Development code

MK-2866

Identity and composition

Ostarine (also known as Ostarine, Enobosarm, MK-2866, GTx-024 o S-22) is a non-steroidal orally administered selective androgen receptor modulator (SARM), studied in research as a tissue-selective anabolic agent. It is not a peptide, but a synthetic small molecule. This is a product for research use.

Reference chemical identity data:

• Molecular formula: C19H14F3N3O3
• Molecular weight: 389.3 g/mol
• PubChem CID: 11326715
• IUPAC name: (2S)-3-(4-cyanophenoxy)-N-[4-cyano-3-(trifluoromethyl)phenyl]-2-hydroxy-2-methylpropanamide

As it is a small molecule and not a peptide, an amino acid sequence does not apply. The catalog presentation corresponds to 25 mg × 100 tablets.

Mechanism of action

Ostarine acts as androgen receptor (AR) ligand, producing tissue-selective anabolic activity. In the clinical trials reviewed, its documented measurable effect is the increase in lean body mass (lean body mass) (PMID 23499390).

The mechanistic premise of the SARM class is to achieve AR activation with a greater effect on muscle and bone tissue and less classic androgenic activity; however, that tissue selectivity separation has not been conclusively demonstrated in humans in the sources gathered. What direct clinical evidence documents is the effect on lean mass, not a fully established tissue separation.

In simple terms: it is a small synthetic molecule that binds to the androgen receptor and, in the available studies, was measurably associated with changes in lean mass.

Pharmacokinetics

Ostarine is a oral administration. In the open primary sources reviewed, no confirmed value was found for half-life; the phase 2 and phase 3 abstracts consulted do not report a half-life. Therefore, this datum is considered not verified and no numerical figure is offered to avoid unsupported information.

Scientific evidence

The available evidence is limited and of an investigational nature; ostarine (enobosarm) was never approved by the FDA or the EMA. The most advanced indication studied was the prevention/treatment of muscle wasting (cachexia) cancer-associated.

• In a phase 2 trial double-blind and randomized in cancer patients; in studies, increases were observed modest but statistically significant of lean mass with oral doses of 1 mg and 3 mg/day (PMID 23499390).
• El phase 3 program (POWER 1 and 2 trials, enobosarm 3 mg/day versus placebo in non-small-cell lung cancer) was designed with co-primary endpoints of lean mass and functional power (PMID 27138015; NCT01355484). According to the secondary literature, both phase 3 trials did not fully meet their co-primary endpoints; the exact result was not verified in the primary abstract.

The preliminary evidence suggests an effect on lean mass in oncology populations, but without conclusive clinical results that support an established therapeutic use.

Research applications

Product for research use.

Ideal for:

• Laboratory and research studies in vitro or preclinical on selective androgen receptor modulators (SARM).
• Chemical characterization and analytical reference work on the non-steroidal SARM class.
• Comparative research within the class (versus andarine, ligandrol, RAD-140).

Not applicable for:

• clinical use, supplementation, clinical use, or self-administration.
• Use in sport: ostarine is banned by WADA in the sports context.
• Any application that assumes clinical support for catalog doses (e.g. 25 mg), far higher than the studied doses (1-3 mg/day) and without clinical support at that order of magnitude.

Research protocols

The doses studied in clinical trials were administered oral, at 1 mg and 3 mg/day in phase 2 in oncology patients (PMID 23499390), and of 3 mg/day in the phase 3 POWER program in non-small-cell lung cancer (PMID 27138015; NCT01355484).

It is important to note that supplier catalog doses (e.g. 25 mg) are much higher at the clinical doses studied and do not have clinical support to that order of magnitude. No dosing protocol for clinical use is offered here, since the product is exclusively for research.

Reconstitution

The catalog ostarine is presented in 25 mg tablets, so it does not require reconstitution like an injectable lyophilizate.

As a general laboratory handling reference for compounds that are indeed supplied lyophilized: the usual reconstitution is carried out with bacteriostatic water (sterile water with approximately 0.9% benzyl alcohol as a preservative). The standard technique consists of letting the diluent run slowly down the wall of the vial onto the powder, without injecting directly onto the solid, and gently swirling the vial (without shaking forcefully) until complete dissolution. This guide is qualitative and standard laboratory practice; it does not apply directly to the tablet presentation.

Stability and storage

General standard laboratory handling guide:

• Solid product (tablets/powder): store in a cool, dry place protected from light. For prolonged storage, cold (refrigeration or freezing) favors stability; avoid moisture and temperature cycles.
• Reconstituted product (when applicable to lyophilizates): keep refrigerated and use within a brief window, protected from light.

These indications are for general laboratory handling and do not replace the specific conditions indicated by the batch certificate of analysis.

Safety profile

Ostarine is not approved for clinical use and its safety profile should be interpreted with caution.

• In the phase 2 trial in oncology patients, the most frequent serious adverse events were progression of the neoplasm (9-15%), pneumonia (4-6%) and febrile neutropenia (0-6%); the authors attributed them to the underlying disease and did not consider them related to the drug (PMID 23499390).
• Class safety note (general for SARMs, not specific to these abstracts): in unsupervised use, SARMs are generally associated with hepatotoxicity y suppression of endogenous testosterone.
• Ostarine is banned in sport by WADA.

As a research compound without regulatory approval, it must not be used in clinical use.

Comparative context

Ostarine belongs to the class of non-steroidal SARM, together with the andarine (S-4), the LGD-4033 (ligandrol) and the RAD-140.

The shared premise of the class is to seek muscle and bone anabolism with lower androgenic activity prostatic or virilizing than the classic anabolic-androgenic steroids. Within this group, enobosarm (ostarine) stands out as one of the SARMs most clinically advanced, since it reached phase 3, unlike most of the other compounds of the class, whose clinical development was more limited.

History and development

Ostarine (enobosarm / MK-2866 / GTx-024) is a research compound developed by GTx. Was never approved by the FDA or the EMA.

Its most advanced development line was oriented toward prevention and treatment of muscle wasting (cachexia) associated with cancer. After a phase 2 trial in oncology patients (PMID 23499390), it advanced to the phase 3 program POWER 1 and 2 in non-small-cell lung cancer (PMID 27138015; NCT01355484). It has also been investigated in AR-positive breast cancer. According to the secondary literature, the phase 3 trials did not fully meet their co-primary endpoints, which set the course of its subsequent clinical development.

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Scientific references (5)

Peer-reviewed literature on Ostarine, with its PubMed identifier when available:

• Ostarine blunts the effect of endurance training on submaximal endurance in rats (Vasilev V et al. · Naunyn-Schmiedeberg's archives of pharmacology · 2024) PMID 38451281.
• Sex-specific cytotoxicity of ostarine in cardiomyocytes (Leciejewska N et al. · Molecular and cellular endocrinology · 2023) PMID 37543162.
• Ostarine-Induced Myogenic Differentiation in C2C12, L6, and Rat Muscles (Leciejewska N et al. · International journal of molecular sciences · 2022) PMID 35457222.
• The selective androgen receptor modulator GTx-024 (enobosarm) improves lean body mass and physical function in healthy elderly men and postmenopausal women: results of a double-blind, placebo-controlled phase II trial (Dalton, et al. · Journal of Cachexia, Sarcopenia and Muscle · 2011) PMID 22031847.
• Effects of enobosarm on muscle wasting and physical function in patients with cancer: a double-blind, randomised controlled phase 2 trial (Dobs, et al. · The Lancet Oncology · 2013) PMID 23499390.

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