Resistance Mechanisms in Enzalutamide Therapy

What resistance mechanisms emerge during enzalutamide therapy?

Enzalutamide resistance mechanisms include AR pathway alterations (amplifications, mutations, splice variants), bypass signaling pathways (JAK2-STAT5, glucocorticoid receptor), metabolic adaptations (AKR1C3, HMGCR), and lineage plasticity, primarily through clonal selection of pre-existing heterogeneity rather than newly acquired mutations.

Abstract

Resistance to enzalutamide in castration-resistant prostate cancer involves multiple mechanisms operating at both androgen receptor-dependent and AR-independent levels. AR pathway alterations represent the most extensively validated resistance mechanisms, with AR amplifications increasing from 53.9% at baseline to 64.7% at progression, specific AR mutations (H875Y, F877L, T878A/S) detected in approximately 15% of patients with progressive disease, and AR-V7 splice variants rising from 29% at baseline to 40% during treatment. However, a substantial proportion of resistance mechanisms are pre-existing rather than purely acquired, with 73.1% of baseline biopsies showing AR pathway alterations and 92.3% harboring tumor suppressor mutations (PTEN, RB1, TP53), indicating that clonal selection during treatment intensifies pre-existing heterogeneity...

Methods

We analyzed 10 sources from an initial pool of 200, using 7 screening criteria. Each paper was reviewed for 6 key aspects that mattered most to the research question.

Records from Elicit search

• n = 200
• Papers screened using: Enzalutamide Treatment, Resistance Mechanisms, Patient Population, Study Design, Acquired Resistance Focus, Enzalutamide-Specific Focus, Sample Size Adequacy

Papers screened out

• n = 190

Papers included for extraction

• n = 10

Screening

We screened in sources based on their abstracts that met these criteria:

• Enzalutamide Treatment: Does this study involve patients treated with enzalutamide?
• Resistance Mechanisms: Does this study investigate, describe, or analyze resistance mechanisms to enzalutamide?
• Patient Population: Does this study include patients with castration-resistant prostate cancer (CRPC) or metastatic castration-sensitive prostate cancer (mCSPC)?
• Study Design: Is this an original research study (clinical trial, cohort study, case-control study, cross-sectional study), systematic review, meta-analysis, or laboratory study (in vitro/in vivo) with clinical relevance?
• Acquired Resistance Focus: Does this study examine resistance that develops after treatment exposure (acquired resistance) rather than focusing exclusively on primary resistance without treatment exposure?
• Enzalutamide-Specific Focus: Does this study focus on enzalutamide resistance specifically, rather than solely examining other antiandrogen therapies without enzalutamide comparison?
• Sample Size Adequacy: If this is a case report or case series, does it include 5 or more patients? (Answer “Yes” if this is not a case report/case series)

Data extraction

We asked a large language model to extract each data column below from each paper.

Resistance Mechanisms:

• AR amplification
• AR mutations (H875Y, F877L, T878A/S)
• AR splice variants (AR-V7)
• JAK2-STAT5 activation
• Metabolic alterations including AKR1C3 and HMGCR

Evidence Type:

• Cell line studies
• Patient tissue samples
• Circulating tumor cells or cell-free DNA

Mechanistic Basis:

• AR amplification increases AR protein expression
• AR mutations may convert enzalutamide from an antagonist to an agonist
• Bypass mechanisms like glucocorticoid receptor upregulation

Clinical Validation:

• Detected in patient samples at baseline and progression
• Correlation with clinical outcomes

Emergence Timing:

• Pre-existing versus acquired mechanisms during treatment

Therapeutic Targeting:

• Combination approaches with inhibitors (e.g., PARP inhibitors)

Results

Characteristics of Included Studies

• Xinyi Wang et al., 2025: Review, cell line studies, patient tissue samples
• R. McKay et al., 2021: Primary study, patient tissue samples
• A. Wyatt et al., 2016: Primary study, circulating tumor cells or cell-free DNA

Resistance Mechanisms

Androgen Receptor-Dependent Mechanisms

• AR amplification (copy number gain): Detected in 53.9% at baseline, 64.7% at progression
• AR mutations: Observed in ~15% of progressive mCRPC patients
• AR splice variants (AR-V7): Detected in 29% at baseline, 40% at progression

Bypass Signaling Pathways

• Glucocorticoid Receptor Pathway: GR can activate AR target genes through an alternative pathway.
• JAK2-STAT5 Signaling: Drives patient adaptation during treatment, facilitating tumor growth.
• PI3K/Akt/mTOR Pathway: Maintains cell survival signals independent of AR.

Metabolic and Steroid Biosynthesis Alterations

• AKR1C3 and Cholesterol Biosynthesis: Enables intracrine androgen production.
• HMGCR and Mevalonate Pathway: Supports tumor viability and proliferation independent of AR.

Tumor Suppressor Loss and Lineage Plasticity

• PTEN loss: Present in 92.3% of baseline biopsies, associated with resistance.
• RB1 and TP53 loss: Drive lineage plasticity toward neural induction.

Tumor Microenvironment and Immune Mechanisms

• IL6 from the tumor microenvironment promotes resistance through immune evasion.

Conclusion

The landscape of enzalutamide resistance mechanisms highlights significant heterogeneity in molecular adaptations, influenced by the tumor's evolutionary pressures during treatment. Understanding these mechanisms is vital for guiding therapeutic strategies and improving patient outcomes.