転移性去勢抵抗性前立腺癌の男性に対する治療としてのウンデカン酸テストステロン経口投与に続くエンザルタミドの安全性と有効性

Metastatic prostate cancer is a highly significant disease that claims the lives of approximately 30,000 American men each year. Androgen Deprivation Therapy (ADT) is initially very effective but is never curative as all men eventually develop castrate resistant prostate cancer (CRPC). A major factor driving resistance is the ability of prostate cancer (PCa) cells to adapt to the chronic low androgen conditions by upregulating androgen receptor (AR) activity through overexpression, gene amplification and expression of truncated, transcriptionally active AR variants that lack the ligand-binding domain. Persistent signaling through AR makes CRPC sensitive to more potent inhibition of AR by abiraterone acetate or second generation anti-androgens such as enzalutamide. Yet these therapies have a limited duration of benefit prior to development of resistance, often through further increase in AR levels.

While this marked upregulation of AR can drive resistance, the investigators have demonstrated that it also creates a therapeutic vulnerability to exposure to high levels of androgen. However, the investigators have also found that sustained exposure of CRPC to supraphysiological levels of androgens results in downregulation of AR and acquired resistance to this therapy. Therefore the investigators have developed a therapy called Bipolar Androgen Therapy (BAT) in which testosteronecypionate 400 mg IM is administered every 28 days to result in cycling from supraphysiological (>1500 ng/dL) to near-castrate levels. The rationale for cycling was that high serum T would kill high AR expressing CRPC while low serum T would prevent adaptation to high T and kill low AR expressing CRPC.

To date the investigators have treated approximately 250 men with BAT across four completed studies in asymptomatic men with CRPC. The key findings have been that BAT: (a) could be safely administered; (b) did not produce symptomatic disease progression; (c) produced sustained PSA and objective responses in approximately 30-40% of patients; (d) re-sensitized and prolonged response of patients to subsequent antiandrogen therapy. While ADT for advanced PCa often produces debilitating sexual and metabolic side effects, another highly significant feature of this approach is that BAT can make men feel remarkably better by decreasing fatigue, increasing physical activity and restoring libido and sexual function. BAT also produced favorable effects on body composition by increasing skeletal muscle mass and decreasing subcutaneous and visceral fat. Thus, incorporation of BAT into the treatment paradigm has the potential to improve the quality of life and well-being of PCa patients and minimize the morbidity from the metabolic sequelae produced by androgen ablative therapies.

The studies performed to date demonstrate the safety and efficacy of high dose T in men with metastatic CRPC who are progressing on androgen ablative therapy. The investigators' limited data suggests that high serum levels of T may be required for clinical response. This high level has is achieved through intramuscular (IM) administration of testosterone cypionate at the highest FDA-approved dose of 400 mg every 28 days. This regimen initially produces high serum T levels but these levels drop to a varying degrees approaching near castrate levels in some men over a 28-day cycle. To date, the investigators have not tested whether more rapid cycling of serum T would produce similar or improved therapeutic response in this patient population. Additional issues with IM testosterone are (1) it requires patients to come to hospital every 28 days for injection, (2) has highly variable pharmacokinetics, (3) can cause physical discomfort from IM injections.

Recently two novel oral testosterone (OT) agents were developed for the treatment of male hypogonadism. Historically, an oral option for testosterone replacement therapy was unavailable because of risks of liver toxicity, including cholestasis and jaundice, associated with earlier developed 17-alpha-alkylated oral analogs. These novel oral agents feature specialized formulations that avoid adverse hepatic effects. In clinical trials, both oral agents produced no significant adverse effects on liver function tests. The investigators have formed a collaborative partnership with Clarus Therapeutics, the makers of Jatenzo, an oral lipoprotein-coated testosterone undecanoate (OT) formulation that was FDA-approved in December 2019 as T-replacement therapy. Published pharmacokinetic data demonstrate that OT can produce supraphysiologic serum T levels when administered at the highest FDA-approved dose. Therefore, the investigators' hypothesis is that OT, given at the highest FDA approved dose, will achieve more homogeneous and sustained supraphysiologic levels of serum T that will produce similar or enhanced therapeutic response. To avoid adaptation of CRPC to this sustained level of T, the investigators will utilize a dosing schedule of 1 week-on, 1 week-off.