EPI-001 is the first inhibitor of the androgen receptor amino-terminal domain. The single stereoisomer of EPI-001, EPI-002, is a first-in-class drug that the USAN council assigned a new stem class "-aniten" and the generic name "ralaniten". This distinguishes the anitens novel molecular mechanism from anti androgens that bind the C-terminus ligand-binding domain and have the stem class "lutamide" (such as flutamide, nilutamide, bicalutamide, enzalutamide, etc.). EPI-001 and its stereoisomers and analogues were discovered by Marianne Sadar and Raymond Andersen, who co-founded the pharmaceutical company ESSA Pharma Inc (Vancouver, Canada) for the clinical development of anitens for the treatment of castration-resistant prostate cancer (CRPC).
EPI-001's successor, ralaniten acetate (EPI-506), a prodrug of ralaniten (EPI-002), one of the four stereoisomers of EPI-001, was under clinical investigation in a phase I study.[3] EPI-506 was the first drug that directly binds to an intrinsically disordered region to be tested in humans and marks a leap in drug development from folded drug targets.
Pharmacology
Pharmacodynamics
EPI-001 is a mixture of four stereoisomers. EPI-001 binds to the activation function-1 (AF-1) region in the NTD of the AR, as opposed to other AR antagonists, which bind to the C-terminal LBD.[4] A functional AF-1 is essential for the AR to have transcriptional activity. If AF-1 is deleted or mutated, the AR will still bind androgens, but will have no transcriptional activity.[5] Importantly, if the AR lacks an LBD, the receptor will be nuclear and constitutively-active.[5] Constitutively active splice variants of the AR that lack the C-terminal LBD are correlated to CRPC and poor survival.[6][7][8][9][10][11] EPI-001 is an inhibitor of constitutively active splice variant of ARs that lack the C-terminal LBD.[2] Conventional antiandrogens do not inhibit constitutively-active variants of AR that have a truncated or deleted C-terminal LBD.
In the absence of androgen, all known antiandrogens cause translocation of AR from the cytoplasm to the nucleus,[4][12][13] whereas EPI-001 does not cause the AR to become nuclear.[2] Binding of EPI-001 to the NTD of the AR blocks protein-protein interactions that are essential for its transcriptional activity. Specifically, EPI-001 blocks AR interactions with CREB-binding protein, RAP74, and between the NTD and C-terminal domain (termed N/C interaction) required for antiparallel dimer formation of AR.[2] Unlike antiandrogens such as bicalutamide,[12][14] EPI-001 does not cause the AR to bind to androgen response elements on the DNA of target genes.[2]
EPI-001 at extremely high concentrations of 50 to 200 uM has also been found to act as a selective PPARγ modulator (SPPARM), with both agonistic and antagonistic actions on the PPARγ.[15] Via PPARγ activation, EPI-001 has been found to inhibit AR expression and activity in prostate cancer cells, indicating at least one AR-independent action by which EPI-001 exhibits antiandrogen properties in the prostate.[15]
EPI-001 inhibits AR-dependent proliferation of human prostate cancer cells while having no significant effects on cells that do not require the AR for growth and survival.[2] EPI-001 has specificity to the AR (aside from the PPARγ) and has excellent anti-tumor activity in vivo with xenografts of CRPC.[2]
^Sadar MD (June 2012). "Advances in small molecule inhibitors of androgen receptor for the treatment of advanced prostate cancer". World Journal of Urology. 30 (3): 311–318. doi:10.1007/s00345-011-0745-5. PMID21833557. S2CID11956563.