Enobosarm, also known as ostarine or MK-2866, is a selective androgen receptor modulator (SARM) developed by GTx, Inc. for the treatment of conditions such as muscle wasting, osteoporosis, and breast cancer, now under development by Veru, Inc.. Enobosarm is the most well-studied SARM. According to GTx, 25 studies have been carried out on more than 1,700 humans involving doses from 1 to 18 mg each day.
Chemistry
According to a 2009 paper authored by GTx, "Readers are cautioned to note that the name ostarine is often mistakenly linked to the chemical structure of [S-4], which is also known as andarine. The chemical structure of ostarine has not been publicly disclosed." A 2009 review stated "Recently, GTx disclosed that compound 5 had advanced into clinical trials. The patent application described detailed data in an initial proof-of-concept Phase IIa clinical trial. It is not explicitly stated that compound 5 is Ostarine (MK-2866).
History
GTx Incorporated was founded in Memphis in 1997 and licensed rights to enobosarm from the University of Tennessee Research Foundation; the SARM compounds were invented by James T. Dalton, Duane D. Miller, Karen A. Veverka and their research teams at Ohio State University, the University of Tennessee and GTx, respectively.
By 2007, enobosarm was in a Phase II trial, and that year GTx signed an exclusive license agreement for its SARM program with Merck & Co. The companies ended the deal in 2010.
In August 2011, there was a double-blind, placebo controlled phase II trial that focused on elderly men and postmenopausal women which concluded that Enobosarm showed statistically significant improvements in total lean body mass and physical function without the negative side effects that are normally present with steroids.
In August 2013, GTx announced that enobosarm had failed in two Phase III clinical trials to treat wasting in people with lung cancer. The company had invested around $35 million in the development of the drug. The company said at that time that it planned to pursue approval of enobosarm in Europe; the company was also still developing GTx-758 for castration-resistant prostate cancer.
In 2016, GTx began Phase II trials, to see if enosobarm might be effective to treat stress urinary incontinence in women.
In 2018, GTx announced the Phase II trials on Enobosarm's efficacy on stress urinary incontinence in women failed to achieve its primary endpoint in the ASTRID Trial.
In 2022, the FDA granted fast tract designation to ostarine in AR+, ER+, HER2- metastatic breast cancer.
Side effects
A common, negative effect of SARMs and other anabolic steroids is the reduction of HDL and LDL, this has been confirmed in human clinical trials when comparing Ostarine to a placebo. Additionally, in trials where 1 mg of Ostarine (or more) was administered, there was a statistically significant lowering of Sex Hormone-Binding Globulin (SHBG) and serum total testosterone levels. Alanine Transaminase (ALT), an enzyme present in the liver, has been shown to fluctuate abnormally while clinical patients were given no more than 3 mg per day. However, the elevated levels seem to be resolved after the discontinuation of the SARM. In women, ostarine reduces LH and FSH, but with no change in circulating estradiol.
The FDA has warned that SARMs could have serious side effects ranging from risk of heart attack to stroke and liver damage.
Society and culture
Doping
SARMs including Enobosarm may be and have been used by athletes to assist in training and increase physical stamina and fitness, potentially producing effects similar to anabolic steroids. For this reason, SARMs were banned by the World Anti-Doping Agency in January 2008, despite no drugs from this class yet being in clinical use, and blood tests for all known SARMs have been developed. There are a variety of known cases of doping in sports with enobosarm by professional athletes.
In May 2017, Dynamic Technical Formulations voluntarily recalled all lots of Tri-Ton, a dietary supplement that the USFDA tested and found to contain Enobosarm and andarine.
In October 2018, UFC fighter Sean O'Malley tested positive for Enobosarm and was suspended by the Nevada State Athletic Commission and USADA for six months. O'Malley tested positive again on May 25, 2019 and was suspended for nine months by the same agencies. USADA determined that none of O'Malley's positive tests were consistent with intentional use and he was allowed to compete at UFC 248 as long as he kept his levels below the threshold of 100 ng/ml.