Structures of cytochrome P450 17A1 with prostate cancer drugs abiraterone and TOK-001

Abstract

Cytochrome P450 17A1 (also known as CYP17A1 and cytochrome P450c17) catalyses the biosynthesis of androgens in humans. As prostate cancer cells proliferate in response to androgen steroids, CYP17A1 inhibition is a new strategy to prevent androgen synthesis and treat lethal metastatic castration-resistant prostate cancer, but drug development has been hampered by lack of information regarding the structure of CYP17A1. Here we report X-ray crystal structures of CYP17A1, which were obtained in the presence of either abiraterone, a first-in-class steroidal inhibitor recently approved by the US Food and Drug Administration for late-stage prostate cancer, or TOK-001, an inhibitor that is currently undergoing clinical trials. Both of these inhibitors bind the haem iron, forming a 60° angle above the haem plane and packing against the central I helix with the 3β-OH interacting with aspargine 202 in the F helix. Notably, this binding mode differs substantially from those that are predicted by homology models and from steroids in other cytochrome P450 enzymes with known structures, and some features of this binding mode are more similar to steroid receptors. Whereas the overall structure of CYP17A1 provides a rationale for understanding many mutations that are found in patients with steroidogenic diseases, the active site reveals multiple steric and hydrogen bonding features that will facilitate a better understanding of the enzyme's dual hydroxylase and lyase catalytic capabilities and assist in rational drug design. Specifically, structure-based design is expected to aid development of inhibitors that bind only CYP17A1 and solely inhibit its androgen-generating lyase activity to improve treatment of prostate and other hormone-responsive cancers.

Figure 1. Function of CYP17A1 and inhibition by clinical compounds

a, CYP17A1 titration with abiraterone (10–274 nM) yields progressive shifts in the UV/Vis difference spectrum typical of nitrogen binding to heme iron. b, Similar titration with progesterone (10–1535 nM) indicates water displacement from the heme iron. c, IC₅₀ of abiraterone (circles) and TOK-001 (squares) for progesterone 17 α–hydroxylation.

Figure 2. CYP17A1 ligand binding

Stick and sphere representations have non-carbon atoms indicated as: blue, N; red, O; rust, Fe; heme, black; abiraterone, grey; TOK-001, cyan. a, CYP17A1/abiraterone structure colored from N-terminus (blue) to C-terminus (red). b, Abiraterone binds (2|Fo|−|Fc| density at 1 σ, blue mesh) at ~60° from heme against helix I (yellow). c, Abiraterone cavity (grey mesh), ~180° rotation from 2b. d, TOK-001 binding (2|Fo|−|Fc| density at 1 σ, blue mesh). e, TOK-001 cavity (grey mesh). f, Overlay of abiraterone (yellow) and TOK-001 (purple) structures with respective voids (mesh). B′ helix removed from panels c-f to view ligands.

Figure 3. Hydrogen bond network with abiraterone

CYP17A1 has a hydrogen bonding network at the top of the active site that interacts with abiraterone. Molecule A/B (yellow) and C/D (green) have slightly different networks with the main difference being the involvement of Y201. Water molecules are indicated by small spheres. C17 and C16 are labeled. Hydrogen bonds indicated by dashed lines with distances indicated.

Figure 4. CYP17A1 compared to the androgen receptor and CYP11A1

a, The hydrogen bonding network near the abiraterone 3β-OH involves N202, R239, and conserved waters. b, The androgen receptor (PDB 3L3X) has a similar hydrogen bond network with R752, Q711, and several waters interacting with the dihydrotestosterone ketone. c, Overlay of CYP17A1 with abiraterone (yellow) and CYP11A1 with 20,22-dihydroxycholesterol (PDB 3NA0, pink) shows dramatically different steroid orientations.