Androgen receptor mutations
CRPC patients could be resistant to Enz because of AR mutations. The majority of mutations occur in the LBD (Snow, Lallous et al., 2019). Molecular dynamics simulations and molecular mechanics based on generalized Born surface area calculations have validated that helix 12 (H12) functions as a cover at the top of AR LBD. Under normal circumstances, the C-ring of Enz is near H12, leading to the closing of H12 and the distortion of the coactivator-binding site. When the C-ring of Enz is located near helix H11 or loop 11-12, H12 tends to serve as an auxiliary activator-binding site to promote transcription. Interestingly, in this case, Enz switches to become an AR agonist (Liu, Wang et al., 2017). For instance, the AR F876L mutation was previously found to convert the AR antagonist Enz to an AR agonist (Korpal, Korn et al., 2013). In this respect, the AR degradation enhancer ASC-J9® directly targets AR F876L, mediating the degradation of this mutant (Wang, Lin et al., 2016). In addition, a novel AR antagonist, JJ-450, inhibited the translocation and function of the AR F876L mutant, which suggests a new potential strategy for Enz-resistant CRPC treatment (Wu, Wang et al., 2020). Other studies incorporating the detection of circulating cell-free DNA showed that the F877L, H875Y, T878A/D891H, and T878A/S889G AR mutations can lead to altered Enz functions. In particular, the double mutant F877L/T878A converted Enz into a fully functional agonist. The AR antagonist darolutamide (ODM-201), which is focused on AR mutants, significantly suppressed the transcriptional activity of the F877L, H875Y/T878A, F877L/T878A, and T878G mutants (Prekovic, Van et al., 2016 , Borgmann, Lallous et al., 2018 , Lallous, Volik et al., 2016).
Glucocorticoid receptor overexpression
The glucocorticoid receptor (GR) is one of the members of a class of nuclear steroid receptors. The expression of GR is upregulated after Enz treatment, which contributes to the re-expression of approximately 50% of the AR-responsive genes. Several canonical AR target genes have not been shown to be regulated by GR, including KLK3 and TMPRSS2. AR and GR have highly homologous DBDs and overlapping transcriptomes and cistromes. AR directly represses GR expression via a negative androgen response element (ARE) in the GR promoter. Consequently, upon exposure to the AR inhibitor Enz, the inhibition of GR expression is abrogated. The GR agonist dexamethasone is sufficient to make patients resistant to Enz, while GR antagonists can restore sensitivity (Arora, Schenkein et al., 2013).
GR plays a critical role in humans, and completely blocking GR is incompatible with life. Li et al. (Li, Alyamani et al., 2017) focused on the tumour metabolic switch associated with GR activation. They demonstrated that Enz-resistant prostate cancer cells sustained cortisol concentrations due to the loss of 11β-hydroxysteroid dehydrogenase-2 (11β-HSD2) and the impaired conversion to cortisone. As a result, GR was inhibited, and glucocorticoid-dependent signalling was activated. Moreover, ubiquitin E3-ligase autocrine mobility factor receptor (AMFR) mediated the loss of 11β-HSD2, leading to Enz resistance. In a genome-wide CRISPR-Cas9 screening study (Palit, Vis et al., 2019), researchers found that the loss of transducin-like enhancer of split 3 (TLE3) in conjunction with AR inhibition by the GR enhancer resulted in GR upregulation, which led to Enz resistance in LNCaP cells. Hence, TLE3 was involved in the regulation of GR expression and drug resistance, providing a novel target for Enz-resistant CRPC treatment. Considering the increase in GR upon AR inhibition, Remi M et al. (Adelaiye-Ogala, Gryder et al., 2020) demonstrated that inhibiting the phosphatidylinositol 3-kinase/ protein kinase B (PI3K/AKT) pathway can block GR expression and activity after AR inhibition, overcoming GR-mediated resistance to Enz.
It was reported that BET bromodomain inhibition, pyrrole-imidazole polyamide, and selective glucocorticoid receptor modulators could inhibit GR expression and GR-regulated proliferation-associated genes for Enz-resistant CRPC treatment (Shah, Wang et al., 2017 , Kurmis, Yang et al., 2017 , Kach, Long et al., 2017). Recently, Wu et al. (Wu, Xie et al., 2019) utilized a rational drug design method to analyse the chemical structures of the anti-androgen and crystal structure of GR. They developed GR/AR dual antagonists by virtual screening and biological evaluation. After performing a bioassay, they found that the dual antagonist Z19 inhibited the transcriptional activity of both AR and GR, reducing the protein and mRNA levels of the downstream proteins of GR and AR signalling (PSA for AR and KLF9 for GR). This rational drug design provides an efficient strategy for the development of novel agents for Enz-resistant CRPC