Galeterone (developmental code names TOK-001, VN/124-1) is a

steroidal antiandrogen A steroidal antiandrogen (SAA) is an antiandrogen with a steroidal chemical structure. They are typically antagonists of the androgen receptor (AR) and act both by blocking the effects of androgens like testosterone and dihydrotestosterone (DHT) ...

which was under development by Tokai Pharmaceuticals for the treatment of

prostate cancer Prostate cancer is cancer of the prostate. Prostate cancer is the second most common cancerous tumor worldwide and is the fifth leading cause of cancer-related mortality among men. The prostate is a gland in the male reproductive system that sur ...

. It possesses a unique triple

mechanism of action In pharmacology, the term mechanism of action (MOA) refers to the specific biochemical interaction through which a drug substance produces its pharmacological effect. A mechanism of action usually includes mention of the specific molecular targe ...

, acting as an

androgen receptor The androgen receptor (AR), also known as NR3C4 (nuclear receptor subfamily 3, group C, member 4), is a type of nuclear receptor that is activated by binding any of the androgenic hormones, including testosterone and dihydrotestosterone in th ...

antagonist An antagonist is a character in a story who is presented as the chief foe of the protagonist. Etymology The English word antagonist comes from the Greek ἀνταγωνιστής – ''antagonistēs'', "opponent, competitor, villain, enemy, riv ...

, androgen receptor down regulator, and

CYP17A1 inhibitor A CYP17A1 inhibitor is a type of drug which enzyme inhibitor, inhibits the enzyme CYP17A1. It may inhibit both of the functions of the enzyme, 17α-hydroxylase and 17,20-lyase, or may be selective for inhibition of one of these two functions (gener ...

, the latter of which prevents the

biosynthesis Biosynthesis is a multi-step, enzyme-catalyzed process where substrates are converted into more complex products in living organisms. In biosynthesis, simple compounds are modified, converted into other compounds, or joined to form macromolecules. ...

androgen An androgen (from Greek ''andr-'', the stem of the word meaning "man") is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This inc ...

s. As a CYP17A1 inhibitor, galeterone shows selectivity for 17,20-lyase over

17α-hydroxylase Cytochrome P450 17A1 (steroid 17α-monooxygenase, 17α-hydroxylase, 17-alpha-hydroxylase, 17,20-lyase, 17,20-desmolase) is an enzyme of the hydroxylase type that in humans is encoded by the ''CYP17A1'' gene on chromosome 10. It is ubiquitously expr ...

. Galeterone was being compared to

enzalutamide Enzalutamide, sold under the brand name Xtandi, is a nonsteroidal antiandrogen (NSAA) medication which is used in the treatment of prostate cancer. It is indicated for use in conjunction with castration in the treatment of metastatic castrat ...

in a phase III

clinical trial Clinical trials are prospective biomedical or behavioral research studies on human participants designed to answer specific questions about biomedical or behavioral interventions, including new treatments (such as novel vaccines, drugs, dietar ...

(ARMOR3-SV) for AR-V7-expressing metastatic

castration-resistant prostate cancer Prostate cancer is cancer of the prostate. Prostate cancer is the second most common cancerous tumor worldwide and is the fifth leading cause of cancer-related mortality among men. The prostate is a gland in the male reproductive system that surr ...

. Tokai announced the discontinuation of ARMOR3-SV on July 26, 2016, after a data monitoring committee determined that the trial was unlikely to meet its endpoint. On August 22, 2016, the company announced the discontinuation of their phase II expansion (ARMOR2) as well. In the week following cancellation of the ARMOR3-SV clinical trial, Tokai announced a reduction of its workforce by around 60% to a total of 10 "full-time equivalent employees." On December 22, 2016, a definitive share purchase agreement was announced, under which shareholders of Otic Pharma Ltd. would become the majority owners of Tokai Pharmaceuticals Inc., resulting in a NASDAQ-listed company (OticPharma, Inc.) focused on the development and commercialization of products for ear, nose, and throat disorders. In August 2017, Tokai Pharmaceuticals discontinued the development of galeterone. On December 17, 2018, it was announced that Educational & Scientific, LLC (ESL), in conjunction with

University of Maryland The University of Maryland, College Park (University of Maryland, UMD, or simply Maryland) is a public land-grant research university in College Park, Maryland. Founded in 1856, UMD is the flagship institution of the University System of M ...

ventures, would develop the drug. Prostate cancer drug abiraterone and its analog Galeterone are Δ5,3β-hydroxy steroids. Structures of these two agents are identical to endogenous steroid substrates (cholesterole, dehydroepiandorosterone and pregnenolone) for the 3β-hydroxysteroid dehydrogenase (3βHSD) of endocrine system. It has been reported that both of these agents are metabolized to 3-oxo-Δ4-steroids by 3βHSD in short period on oral administration. First metabolite 3-oxo-Δ4-abiraterone has more potent anti-prostate cancer properties than abiraterone where galeterone metabolite (3-oxo-Δ4-galaterone) has activity comparable to parent. Further these two metabolites undergo metabolism by 5α-reductase (5α-SRD) of endocrine system which leads to five more biologically inactive metabolites (Ref: Cell Chem. Biol. 2017, 24(7), 825; DOI: 10.1016/j.chembiol.2017.05.020). It is known that galeterone has poor oral bioavailability in rodents. Poor pharmacokinetic properties (oral absorption and metabolic half-life) of galeterone may be the reason for its clinical compromise. Galeterone, along with

abiraterone acetate Abiraterone acetate, sold under the brand name Zytiga among others, is a medication used to treat prostate cancer. Specifically it is used together with a corticosteroid for metastatic castration-resistant prostate cancer (mCRPC) and metastatic ...

, has been identified as an inhibitor of

sulfotransferase Sulfotransferases (SULTs) are transferase enzymes that catalyze the transfer of a sulfo group from a donor molecule to an acceptor alcohol or amine. The most common sulfo group donor is 3'-phosphoadenosine-5'-phosphosulfate (PAPS). In the case o ...

s (

SULT2A1 Bile salt sulfotransferase also known as hydroxysteroid sulfotransferase (HST) or sulfotransferase 2A1 (ST2A1) is an enzyme that in humans is encoded by the ''SULT2A1'' gene. Function Sulfotransferase enzymes catalyze the sulfate conjugation ...

, SULT2B1b,

SULT1E1 Estrogen sulfotransferase is an enzyme that in humans is encoded by the ''SULT1E1'' gene. Sulfotransferase enzymes catalyze the sulfate conjugation of many hormones, neurotransmitters, drugs, and xenobiotic compounds. These cytosolic enzymes are ...

), which are involved in the

sulfation Sulfation is the chemical reaction that entails the addition of SO3 group. In principle, many sulfations would involve reactions of sulfur trioxide (SO3). In practice, most sulfations are effected less directly. Regardless of the mechanism, the ...

dehydroepiandrosterone Dehydroepiandrosterone (DHEA), also known as androstenolone, is an endogenous steroid hormone precursor. It is one of the most abundant circulating steroids in humans. DHEA is produced in the adrenal glands, the gonads, and the brain. It functio ...

and other

steroid A steroid is a biologically active organic compound with four rings arranged in a specific molecular configuration. Steroids have two principal biological functions: as important components of cell membranes that alter membrane fluidity; and a ...

s and compounds, with K_i values in the sub-micromolar range.

References

{{Androgen receptor modulators Abandoned drugs Sterols Androstanes Benzimidazoles CYP17A1 inhibitors Steroid sulfotransferase inhibitors Steroidal antiandrogens