Bipolar androgen therapy (BAT) — cyclic administration of supraphysiologic testosterone on a background of continued androgen deprivation — is an active but incompletely validated strategy for metastatic castration-resistant prostate cancer (mCRPC). The cellular and tissue-level mechanism by which BAT acts, the fidelity of the cell-line models used to study it, and its clinical translation (safety, cycling intervals, and the patient subgroups most likely to benefit) are incompletely resolved. The open questions that remain are: an integrated, tissue-level mechanistic account of how BAT reprograms androgen receptor (AR) signaling and the tumor microenvironment in disease resistant to androgen receptor pathway inhibitors (ARPIs); identification of the most responsive patient groups from existing response biomarkers; and optimal deployment of BAT (sequencing versus combination, cycling interval, safety and patient management).

Background

Prostate cancer is initially driven by androgen signaling, and androgen deprivation therapy (ADT) — surgical or chemical suppression of testosterone to near-castrate levels — is the backbone of treatment for advanced disease. Almost all tumors eventually progress despite castrate testosterone, a state called castration-resistant prostate cancer (CRPC). Most CRPCs still depend on the androgen receptor (AR), a steroid-activated transcription factor, so second-line hormonal agents that further block AR signaling — abiraterone (which blocks androgen synthesis) and enzalutamide (a direct AR antagonist), together called androgen receptor pathway inhibitors (ARPIs) or androgen receptor-targeted agents — extend survival, but resistance to them is nearly universal.

Paradoxically, prostate cancer cells adapted to a low-androgen environment can be killed by androgen at the opposite extreme. Bipolar androgen therapy (BAT) injects high-dose testosterone (typically 400 mg testosterone cypionate intramuscularly every 28 days, with ADT continued) so that serum testosterone cycles between supraphysiologic and near-castrate levels. Preclinical work showed that supraphysiologic androgen suppresses AR-overexpressing CRPC cells through several cooperating mechanisms: downregulation of the AR itself, blockade of DNA replication licensing (the AR acts as a replication licensing factor whose mitotic degradation is prevented by high androgen, blocking origin relicensing), induction of DNA damage and cellular senescence (a state of permanent cell-cycle arrest), and downregulation of the oncogenic transcription factor MYC.

Clinically, BAT is feasible and active in a minority of patients: a 2023 meta-analysis of ten studies found a PSA50 response (a ≥50% decline in prostate-specific antigen, PSA, the standard prostate cancer blood marker) in 27% of patients, an objective response rate (measurable tumor regression on imaging) of 34%, and grade ≥3 adverse events in 14%. The randomized phase 2 TRANSFORMER trial (Denmeade et al., 2021) compared BAT with enzalutamide in abiraterone-pretreated metastatic CRPC (mCRPC) and found equal progression-free survival (5.7 months in both arms) and PSA50 rates of 28.2% versus 25.3%; strikingly, after crossover, enzalutamide's PSA-progression-free survival rose from 3.8 to 10.9 months when given after BAT, and the sequence BAT→enzalutamide yielded longer progression-free survival on second therapy (28.2 versus 19.6 months). The RESTORE trial (Markowski et al., 2021) showed PSA50 responses to BAT of 30% in a post-enzalutamide cohort versus 17% in a post-abiraterone cohort (not significant), with frequent responses on ARPI rechallenge after BAT. Mechanistically, Sena et al. (2022) showed that high pretreatment AR activity predicts response to BAT through MYC downregulation, that the AR downregulation BAT induces is itself the mechanism of acquired resistance, and that alternating supraphysiologic androgen with enzalutamide can resensitize tumors. The COMBAT phase 2 trial (Markowski et al., 2024, BAT plus nivolumab, an antibody that blocks the immune-checkpoint receptor PD-1 (programmed cell death protein 1, which restrains antitumor T cells)) demonstrated in paired metastatic biopsies that BAT induces pro-inflammatory gene-expression changes restricted to responding patients, implicating tumor microenvironment (the immune and stromal cells surrounding the tumor) remodeling in BAT action. Candidate response biomarkers — a high AR-activity transcriptional state and baseline serum testosterone ≥ 20 ng/dL (Kanayama et al., 2025) — exist only as retrospective or post-hoc analyses. No phase 3 trial of BAT has been completed or is registered; ongoing trials are phase 1–2 combinations (with carboplatin, radium-223, sipuleucel-T, darolutamide, olaparib, and in tumors with alterations in DDR (DNA damage response) genes).

Preclinical in vitro and in vivo work (Yu, Lim and Song, 2024) quantified AR downregulation in androgen-deprived, bicalutamide-adapted cell lines (LNCaP, VCaP, 22Rv1) and xenografts (tumors grown from human cancer cells in mice). That work did not test BAT in CRPC already exposed to ARPIs, did not directly measure AR localization, downstream signaling or microenvironment effects, and relied on dextran-coated-charcoal (DCC)-stripped-serum cell-line models (charcoal stripping removes not only androgens but also other serum factors); the clinical-translational questions of safety, cycling intervals, and benefiting subgroups remain open.

Problem Statement

In metastatic castration-resistant prostate cancer that has been exposed to androgen receptor pathway inhibitors, produce a written mechanistic analysis and translational validation plan for bipolar androgen therapy (BAT) as a mechanistically grounded, biomarker-guided treatment. The overarching objective combines three scientifically linked questions that remain open: (1) Mechanism — determine whether and how BAT alters androgen receptor (AR) abundance, localization, and downstream signaling (including the MYC oncogene, DNA replication licensing, DNA damage, and senescence pathways) and the tumor microenvironment (immune and stromal compartments) in ARPI-exposed/resistant disease, and whether these changes are causally linked to response and acquired resistance; (2) Patient selection — determine how the existing retrospective or post-hoc response biomarkers (high pretreatment AR activity and baseline serum testosterone) can be developed into a strategy that identifies which patients benefit; (3) Deployment — determine the optimal use of BAT relative to standard agents, i.e. sequencing versus combination (e.g. with enzalutamide alternation, PD-1 immune-checkpoint blockade, PARP (poly(ADP-ribose) polymerase, a DNA-repair enzyme) inhibition, or cytotoxic chemotherapy), the cycling interval, and side-effect management. Components (1)-(3) are all mandatory and jointly serve this single objective of turning BAT from an experimentally active strategy into a routinely deployable, mechanistically rational therapy. The resolution is analytical rather than empirical: prospective cohorts and clinical trials lie outside the scope of the question, which is addressed by reasoning over the existing evidence.

References

  1. Yu J, Lim JE, Song W. Therapeutic Potential of Bipolar Androgen Therapy for Castration-Resistant Prostate Cancer: In Vitro and In Vivo Studies. Biomedicines 2024;12(1):181. DOI: 10.3390/biomedicines12010181. https://doi.org/10.3390/biomedicines12010181
  2. Denmeade SR, Wang H, Agarwal N, Smith DC, Schweizer MT, Stein MN, Assikis V, Twardowski PW, Flaig TW, Szmulewitz RZ, Holzbeierlein JM, Hauke RJ, Sonpavde G, Garcia JA, Hussain A, Sartor O, Mao S, Cao H, Fu W, Wang T, Abdallah R, Lim SJ, Bolejack V, Paller CJ, Carducci MA, Markowski MC, Eisenberger MA, Antonarakis ES. TRANSFORMER: A Randomized Phase II Study Comparing Bipolar Androgen Therapy Versus Enzalutamide in Asymptomatic Men With Castration-Resistant Metastatic Prostate Cancer. Journal of Clinical Oncology 2021;39(12):1371-1382. DOI: 10.1200/JCO.20.02759. https://doi.org/10.1200/JCO.20.02759
  3. Markowski MC, Wang H, Sullivan R, Rifkind I, Sinibaldi V, Schweizer MT, Teply BA, Ngomba N, Fu W, Carducci MA, Paller CJ, Marshall CH, Eisenberger MA, Luo J, Antonarakis ES, Denmeade SR. A Multicohort Open-label Phase II Trial of Bipolar Androgen Therapy in Men with Metastatic Castration-resistant Prostate Cancer (RESTORE): A Comparison of Post-abiraterone Versus Post-enzalutamide Cohorts. European Urology 2021;79(5):692-699. DOI: 10.1016/j.eururo.2020.06.042. https://doi.org/10.1016/j.eururo.2020.06.042
  4. Teply BA, Wang H, Luber B, Sullivan R, Rifkind I, Bruns A, Spitz A, DeCarli M, Sinibaldi V, Pratz CF, Lu C, Silberstein JL, Luo J, Schweizer MT, Drake CG, Carducci MA, Paller CJ, Antonarakis ES, Eisenberger MA, Denmeade SR. Bipolar androgen therapy in men with metastatic castration-resistant prostate cancer after progression on enzalutamide: an open-label, phase 2, multicohort study. The Lancet Oncology 2018;19(1):76-86. DOI: 10.1016/S1470-2045(17)30906-3. https://doi.org/10.1016/S1470-2045(17)30906-3
  5. Sena LA, Wang H, Lim SJ, Rifkind I, Ngomba N, Isaacs JT, Luo J, Pratz C, Sinibaldi V, Carducci MA, Paller CJ, Eisenberger MA, Markowski MC, Antonarakis ES, Denmeade SR. Bipolar androgen therapy sensitizes castration-resistant prostate cancer to subsequent androgen receptor ablative therapy. European Journal of Cancer 2021;144:302-309. DOI: 10.1016/j.ejca.2020.11.043. https://doi.org/10.1016/j.ejca.2020.11.043
  6. Sena LA, Kumar R, Sanin DE, Thompson EA, Rosen DM, Dalrymple SL, Antony L, Yang Y, Gomes-Alexandre C, Hicks JL, Jones T, Bowers KA, Eskra JN, Meyers J, Gupta A, Skaist A, Yegnasubramanian S, Luo J, Brennen WN, Kachhap SK, Antonarakis ES, De Marzo AM, Isaacs JT, Markowski MC, Denmeade SR. Androgen receptor activity in prostate cancer dictates efficacy of bipolar androgen therapy through MYC. Journal of Clinical Investigation 2022;132(23):e162396. DOI: 10.1172/jci162396. https://doi.org/10.1172/jci162396
  7. Markowski MC, Taplin ME, Aggarwal R, Sena LA, Wang H, Qi H, Lalji A, Sinibaldi V, Carducci MA, Paller CJ, Marshall CH, Eisenberger MA, Sanin DE, Yegnasubramanian S, Gomes-Alexandre C, Ozbek B, Jones T, De Marzo AM, Denmeade SR, Antonarakis ES. Bipolar androgen therapy plus nivolumab for patients with metastatic castration-resistant prostate cancer: the COMBAT phase II trial. Nature Communications 2024;15:14. DOI: 10.1038/s41467-023-44514-2. https://doi.org/10.1038/s41467-023-44514-2
  8. Kanayama M, Tsai HL, Wang H, Antonarakis ES, Denmeade SR, Luo J. Baseline serum testosterone and differential efficacy of bipolar androgen therapy and enzalutamide in the randomized TRANSFORMER trial. Prostate Cancer and Prostatic Diseases 2025;28(2):509-512. DOI: 10.1038/s41391-024-00844-w. https://doi.org/10.1038/s41391-024-00844-w
  9. Kumar R, Sena LA, Denmeade SR, Kachhap S. The testosterone paradox of advanced prostate cancer: mechanistic insights and clinical implications. Nature Reviews Urology 2023;20(5):265-278. DOI: 10.1038/s41585-022-00686-y. https://doi.org/10.1038/s41585-022-00686-y
  10. You X, Huang S, Wang X, Yi C, Gong N, Yu J, Xu C, Xiang Z. Efficacy and safety of bipolar androgen therapy in castration-resistant prostate cancer following abiraterone or enzalutamide resistance: A systematic review. Frontiers in Endocrinology 2023;13:1125838. DOI: 10.3389/fendo.2022.1125838. https://doi.org/10.3389/fendo.2022.1125838
  11. Denmeade SR, Sena LA, Wang H, Antonarakis ES, Markowski MC. Bipolar Androgen Therapy Followed by Androgen Receptor Inhibition as Sequential Therapy for Prostate Cancer. The Oncologist 2023;28(6):465-473. DOI: 10.1093/oncolo/oyad055. https://doi.org/10.1093/oncolo/oyad055