Enzalutamide is an orally bioavailable diarylthiohydantoin compound that is rapidly absorbed after oral dosing, reaching peak plasma concentrations within one to two hours. It is highly protein-bound and primarily eliminated by hepatic metabolism, with CYP3A4 as the dominant enzyme generating the pharmacologically active metabolite N-desmethyl enzalutamide. The drug distributes broadly to peripheral tissues, including prostatic tissue and bone, consistent with the lipophilic nature of its diarylthiohydantoin scaffold. Renal excretion contributes minimally to clearance, and dose adjustment is generally unnecessary in mild-to-moderate hepatic impairment.

The central pharmacological event is high-affinity, competitive binding of enzalutamide to the ligand-binding domain (LBD) of the androgen receptor (AR). Enzalutamide binds the AR with approximately five- to eight-fold greater affinity than bicalutamide, displacing dihydrotestosterone and other androgens from the hydrophobic binding pocket formed by helices 3, 4, 5, and 12 of the LBD. Crucially, and unlike first-generation antiandrogens such as bicalutamide, the bound enzalutamide–AR complex adopts a conformation that is unfavorable for the conformational switch required to activate the receptor — it lacks AR agonistic activity even in cells with AR overexpression, a cellular context that converts bicalutamide into a partial agonist.

Blockade of AR nuclear translocation. After androgen binding, the unliganded AR is held in the cytoplasm in a chaperone complex with heat shock proteins HSP90 and HSP70, and accessory co-chaperones including p23. Agonist binding triggers dissociation of this complex, exposing a nuclear localization signal on the AR hinge region that engages importin-α/β and enables microtubule-dependent translocation through the nuclear pore complex. Enzalutamide impairs this process: the drug-bound AR remains disproportionately sequestered in the cytoplasm, and agonist-induced AR nuclear translocation is inhibited more effectively than by bicalutamide in AR-YFP reporter cell systems. This retention in the cytoplasm prevents the receptor from accessing target gene chromatin entirely.

Inhibition of AR–DNA interaction and coactivator recruitment. For the fraction of drug-bound AR that does enter the nucleus, enzalutamide imposes two further layers of transcriptional blockade. First, the LBD conformation induced by enzalutamide is incompatible with stable AR dimerization at androgen-response elements (AREs), reducing productive chromatin occupancy. Second, coactivator recruitment — including that of the p160 family members SRC-1 and SRC-2 — is inhibited because the activation function 2 (AF-2) surface on helix 12 is not correctly assembled in the antagonist-bound conformation. Together, these events shut down transcription of AR-regulated genes, including PSA (KLK3), TMPRSS2, and the network of genes governing cell-cycle progression.

Downstream transcriptional and antiproliferative consequences. Microarray profiling of LNCaP cells treated with enzalutamide reveals a reversal of androgen-stimulated gene expression patterns, including suppression of genes involved in cell adhesion, angiogenesis, and anti-apoptotic signaling. The net effect is G1 cell-cycle arrest followed by apoptosis in AR-dependent cells. In xenograft models with AR overexpression — the preclinical surrogate of the clinical CRPC setting — enzalutamide induces tumor regression rather than mere stasis, a property that distinguishes it from earlier-generation antiandrogens.

Autophagy as a parallel adaptive survival response. In addition to the pro-apoptotic program, AR blockade triggers a parallel cytoprotective response in CRPC cells. Enzalutamide-induced androgen deprivation activates the AMPK pathway and suppresses mTOR through Raptor phosphorylation, inducing macro-autophagy — a mechanism that sustains cell viability under metabolic stress. Pharmacological or genetic inhibition of autophagy increases apoptosis and impairs clonogenic survival in enzalutamide-treated castration-resistant prostate cancer cells in vitro and in orthotopic xenograft models, identifying autophagy as a key resistance-promoting parallel pathway activated downstream of AR blockade.

AR splice variants and the limits of LBD-directed antagonism. Because enzalutamide functions exclusively through LBD engagement, it cannot suppress constitutively active AR variants that lack this domain. Truncated splice variants — most prominently AR-V7, which retains the DNA-binding domain but not the LBD — translocate constitutively to the nucleus and drive AR target-gene expression independently of androgen or enzalutamide. Selective knockdown of AR splice variant expression inhibits androgen-independent growth and restores antiandrogen responsiveness, establishing AR-Vs as mechanistically sufficient drivers of resistance. This structural limitation motivates the development of N-terminal domain inhibitors and other next-generation approaches that target AR isoforms regardless of LBD integrity.

Clinically, the multi-step suppression of AR signaling translates into durable disease control in metastatic castration-resistant prostate cancer. In the pivotal phase III AFFIRM trial, enzalutamide improved median overall survival from 13.6 to 18.4 months versus placebo in men who had received prior docetaxel, with concordant improvements in PSA response, radiographic progression-free survival, and skeletal event timing — outcomes directly reflecting suppression of the AR transcriptional program that drives prostate cancer cell proliferation, survival, and bone-metastatic behavior.