Abiraterone acetate in metastatic castration-resistant prostate cancer: A retrospective review of the Princess Margaret experience of (I) low dose abiraterone and (II) prior ketoconazole

Real-world outcomes for first line next-generation hormonal agents in metastatic prostate cancer: a systematic review

Aim: This review aims to summarize published evidence on the real-world (RW) outcomes of abiraterone or enzalutamide in first-line metastatic castration-resistant prostate cancer. Materials & methods: Studies reporting on RW effectiveness, safety, economic and/or health-related quality of life outcomes were identified by systematic literature review (2011-2021, incl. Embase®, MEDLINE®) and presented in a qualitative synthesis. Risk of bias was assessed using ROBINS-I or the Molinier checklist. Results: 88 studies (n = 83,427 patients) were included. Median progression-free (40 studies) and overall survival (38 studies) ranged from 3.7 to 20.9 months and 9.8 to 45 months, respectively. Survival, safety and economic outcomes were similar across individual treatments, while limited health-related quality of life evidence suggested improvements with abiraterone. Risk of bias was moderate to high. Conclusion: RW outcomes in first-line metastatic castration-resistant prostate cancer remain poor despite treatment, highlighting an unmet need for new regimens. This review was supported by AstraZeneca and Merck Sharp & Dohme.

Is Low-Dose Abiraterone for Prostate Cancer An Attractive Strategy for Limited Resource Settings?

Abiraterone acetate in combination with prednisone is approved for locally advanced as well as metastatic (hormone-sensitive and castrate-resistant) prostate cancer, with overall or disease-free survival gains in suitable patients. Long-term use poses a significant financial strain on the self-paying patients as well as the national health insurance schemes. Abiraterone is known to be a drug with a high “food effect” with increased bioavailability following high fat diet. Some retrospective series and phase 1 and 2 clinical studies have explored the use of low-dose abiraterone (at 25% of standard dose) with high fat meal with similar bioavailability and biochemical response to the standard drug dose. We review and report the available literature for this approach and discuss the financial and scientific implications of the same.

Time on treatment with abiraterone and enzalutamide in the Patient-overview Prostate Cancer in The National Prostate Cancer Register of Sweden

BACKGROUND

There are little and inconsistent data from clinical practice on time on treatment with the androgen receptor-targeted drugs (ART) abiraterone and enzalutamide in men with metastatic castration-resistant prostate cancer (mCRPC). We assessed time on treatment with ART and investigated predictors of time on treatment.

MATERIAL AND METHODS

Time on treatment with ART in men with mCRPC in the patient-overview prostate cancer (PPC), a subregister of the National Prostate Cancer Register (NPCR) of Sweden, was assessed by use of Kaplan-Meier plots and Cox regression. To assess the representativity of PPC for time on treatment, a comparison was made with all men in NPCR who had a filling for ART in the Prescribed Drug Registry.

RESULTS

2038 men in PPC received ART between 2015 and 2019. Median time on treatment in chemo-naïve men was 10.8 (95% confidence interval 9.1-13.1) months for abiraterone and 14.1 (13.5-15.5) for enzalutamide. After the use of docetaxel, time on treatment was 8.2 (6.5-12.4) months for abiraterone and 11.1 (9.8-12.6) for enzalutamide. Predictors of a long time on treatment with ART were long duration of ADT prior to ART, low serum levels of PSA at start of ART, absence of visceral metastasis, good performance status, and no prior use of docetaxel. PPC captured 2522/6337 (40%) of all men in NPCR who had filled a prescription for ART. Based on fillings in the Prescribed Drug Registry, men in PPC had a slightly longer median time on treatment with ART compared to all men in NPCR, 9.6 (9.1-10.3) vs. 8.6 (6.3-9.1) months.

CONCLUSIONS

Time on treatment in clinical practice was similar or shorter than that in published RCTs, due to older age, poorer performance status and more comorbidities.

Observational study on time on treatment with abiraterone and enzalutamide

Introduction

The aim of this study was to assess time on treatment with abiraterone and enzalutamide, two androgen receptor targeted (ART) drugs, the impact on time on treatment of time interval without drug supply between prescription fillings, and adherence to treatment.

Material and methods

By use of data from The National Prostate Cancer Register, The Prescribed Drug Registry and the Patient Registry, time on treatment with the abiraterone and enzalutamide was analyzed in all men with castration resistant prostate cancer (CRPC) in Sweden 2015–2019. Three time intervals between consecutive fillings, i.e. time without drug supply, were assessed. Adherence to the treatment was evaluated by use of the Medication Possession Ratio. Kaplan Meier analysis and multivariable Cox regression model were used to assess factors affecting time on treatment.

Results

Between January 2015 and October 2019, 1803 men filled a prescription for abiraterone and 4 534 men filled a prescription for enzalutamide. With a time interval of 30 days or less between two fillings, median time on treatment was 4.9 months (IQR 2.6–11.7) for abiraterone and 8.0 months (IQR 3.6–16.4) for enzalutamide. In sensitivity analyses, allowing for no more than 14 days without drug supply between fillings, median time on treatment was 3.9 months (IQR 2.1–9.0) for abiraterone and 5.9 months (IQR 2.8–12.1) for enzalutamide. Allowing for any time period without drug between fillings, median time on treatment was 5.7 months (IQR 2.7–14.0) for abiraterone and 9.8 months (IQR 4.4–21.0) for enzalutamide. Adherence to treatment was above 90% for both drugs.

Conclusion

Time on treatment with abiraterone and enzalutamide was shorter in clinical practice than in randomized controlled trials and varied almost two-fold with time interval without drug. Adherence to treatment was high. The main limitation of our study was the lack of data on use of chemotherapy.

Prior switching to a second-line nonsteroidal antiandrogen does not impact the therapeutic efficacy of abiraterone acetate in patients with metastatic castration-resistant prostate cancer: a real-world retrospective study

Even in the era of novel targeted agents, switching to a second-line nonsteroidal antiandrogen (NSAA) is still widely used in treating metastatic castration-resistant prostate cancer (mCRPC), especially in undeveloped countries. However, whether prior treatment with a second-line NSAA would impact the efficacy of abiraterone acetate (Abi) remains uncertain. In the current study, 87 mCRPC patients treated with Abi were analyzed. Among them, 21 were treated with a second-line NSAA (from bicalutamide to flutamide) before receiving abiraterone, while the remaining 66 received Abi directly. Therapeutic efficacy of Abi was compared between those with and without prior second-line NSAA using Kaplan-Meier curves, log-rank test, and Cox regression models. The therapeutic efficacy of Abi was similar between those with or without the prior switching treatment of flutamide, in terms of either prostate-specific antigen progression-free survival (PSA-PFS, 5.5 vs 5.6 months, P = 0.967), radiographic progression-free survival (rPFS, 12.8 vs 13.4 months, P = 0.508), overall survival (OS, not reached vs 30.6 months, P = 0.606), or PSA-response rate (71.4% [15/21] vs 60.6% [40/66], P = 0.370). This is the first time that the impact of prior switching of treatment to a second-line NSAA on the efficacy of Abi in mCRPC patients has been addressed. Our data support that, use of prior sequential bicalutamide and flutamide does not seem to preclude response to abiraterone, although larger cohort studies and, ideally, a randomized controlled trial are needed. These findings will facilitate doctors' decision-making in the treatment of mCRPC patients, especially for those with previous experience of switching NSAA second-line treatments in the clinic.

The role of ketoconazole in current prostate cancer care

Ketoconazole is a nonselective steroid 17α-hydroxylase/17,20 lyase (CYP17A1) inhibitor that has been used, off-label, as a second-line therapy for castration-resistant prostate cancer (CRPC). The drug has shown clinical efficacy without survival benefit. Despite not improving survival, ketoconazole has beneficial characteristics, such as its low cost, a relatively favourable toxicity profile compared with chemotherapy, and its efficacy both before and after chemotherapy. The approval of several new, highly effective treatments, including abiraterone acetate, enzalutamide, and apalutamide, warrants re-evaluation of the role of ketoconazole and other classic agents in achieving the optimal timing and sequencing of available agents to prolong survival and maintain patients' quality of life. In the current CRPC treatment landscape, we believe that ketoconazole can be considered in patients with nonmetastatic CRPC and in those with metastatic CRPC who do not respond to, tolerate, or have access to chemotherapy and other standard therapeutic options.

Which Factors Predict Overall Survival in Patients With Metastatic Castration-Resistant Prostate Cancer Treated With Abiraterone Acetate Post-Docetaxel?

BACKGROUND

Abiraterone acetate (AA) increases overall survival (OS) in patients with metastatic castration-resistant prostate cancer (mCRPC) previously treated with docetaxel. However, survival time varies substantially between individuals. Our goal was to identify prognostic factors that better estimate OS.

MATERIALS AND METHODS

This is a retrospective multicentric analysis of 368 patients with mCRPC starting AA with prednisone after docetaxel. Cox proportional hazards statistics were applied. A multivariate model was constructed based on significant univariate predictors by using a manual stepwise forward and backward selection strategy. Model performance was determined by using receiver operating characteristic (ROC) curves.

RESULTS

Univariate analysis identified 20 significant OS predictors. A multivariate model was constructed, based on 220 patients, incorporating 5 independent risk factors for decreased OS at the time of AA initiation: hemoglobin < 12 g/dL (hazard ratio [HR] 2.02), > 10 metastases (HR 1.80), ECOG performance status ≥ 2 (HR 1.88), radiographic progression (HR 1.50), and time since diagnosis < 90 months (HR 1.66, all P < .05). Patients were stratified into 3 groups: good (0-2 risk factors, median OS 22.6 months), intermediate (3 risk factors, median OS 13.9 months), and poor prognosis (4-5 risk factors, median OS 6.2 months). The area under the ROC curve based on the event "death by the time of median OS (13.3 months)" was 0.736 (95% confidence interval 0.670-0.803).

CONCLUSION

We identified 5 readily available risk factors independently associated with decreased OS. The resulting model may be used for patient counseling in daily clinical practice, as well as patient stratification in clinical trials.

The hunt for a selective 17,20 lyase inhibitor; learning lessons from nature

Given prostate cancer is driven, in part, by its responsiveness to androgens, treatments historically employ methods for their removal from circulation. Approaches as crude as castration, and more recently blockade of androgen synthesis or receptor binding, are still of limited use long term, since other steroids of adrenal origin or tumor origin can supersede that role as the 'castration resistant' tumor re-emerges. Broader inhibition of steroidogenesis using relatively nonselective P450 inhibitors such as ketoconazole is not an alternative since a general disruption of steroid biosynthesis is neither safe nor effective. The recent emergence of drugs more selectively targeting CYP17 have been more effective, and yet extension of life has been on the scale of months rather than years. It is now becoming clear this shortcoming arises from the adaptive capabilities of many tumors to initiate local steroid synthesis and/or become responsive to novel early pathway adrenal steroids that are synthesized when lyase activity is not selectively blocked, and ACTH rises in the face of declining cortisol feedback. Abiraterone has been described as a lyase selective inhibitor, yet its use still requires co-administration of prednisone to suppress such a rise of ACTH and fall in cortisol. So is creation of a selective lyase inhibitor even possible? Can C19 steroid production be achieved without a prominent decline in cortisol and corresponding rise in ACTH? Decades of scientific study of CYP17 in humans and nonhuman primates, as well as nature's own experiments of gene mutations in humans, reveal 'true' or 'isolated' 17,20 lyase deficiency does quite selectively prevent C19 steroid biosynthesis whereas simple 17 hydroxylase deficiency also suppresses cortisol. We propose these known outcomes of natural mutations should be used to guide analysis of clinical trials and long term outcomes of CYP17 targeted drugs. In this review, we use that framework to re-evaluate the basic and clinical outcomes of many compounds being used or in development for treatment of castration resistant prostate cancer. Specifically, we include the nonselective drug ketoconazole, and then the CYP17 targeted drugs abiraterone, orteronel (TAK-700), galaterone (TOK-001), and seviteronel (VT-464). Using this framework, we can fully discriminate the clinical outcomes for ketoconazole, a drug with broad specificity, yet clinically ineffective, from that of abiraterone, the first CYP17 targeted therapy that is limited by its need for prednisone co-therapy. We also can identify potential next generation CYP17 targeted drugs now emerging that show signs of being far more 17,20 lyase selective. We conclude that a future for improved therapy without substantial cortisol decline, thus avoiding prednisone co-administration, seems possible at long last.

Dihydrotestosterone synthesis pathways from inactive androgen 5α-androstane-3β,17β-diol in prostate cancer cells: Inhibition of intratumoural 3β-hydroxysteroid dehydrogenase activities by abiraterone

Intratumoural dihydrotestosterone (DHT) synthesis could be an explanation for castration resistance in prostate cancer (PC). By using liquid chromatography-mass spectrometry, we evaluated the intratumoral DHT synthesis from 5α-androstane-3β,17β-diol (3β-diol), which is inactive androgen metabolized from DHT. 3β-diol had biochemical potential to be converted to DHT via three metabolic pathways and could stimulate PC cell growth. Especially, 3β-diol was not only converted back to upstream androgens such as dehydroepiandrosterone (DHEA) or Δ5-androstenediol but also converted directly to DHT which is the main pathway from 3β-diol to DHT. Abiraterone had a significant influence on the metabolism of DHEA, epiandrosterone and 3β-diol, by the inhibition of the intratumoural 3β-hydroxysteroid dehydrogenase (3β-HSD) activities which is one of key catalysts in androgen metabolic pathway. The direct-conversion of 3β-diol to DHT was catalysed by 3β-HSD and abiraterone could inhibit this activity of 3β-HSD. These results suggest that PC had a mechanism of intratumoural androgen metabolism to return inactive androgen to active androgen and intratumoural DHT synthesis from 3β-diol is important as one of the mechanisms of castration resistance in PC. Additionally, the inhibition of intratumoural 3β-HSD activity could be a new approach to castration-resistant prostate cancer treatment.

CYP17A1 Polymorphisms and Clinical Outcome of Castration-Resistant Prostate Cancer Patients Treated with Abiraterone

Background

We evaluated the role of single nucleotide polymorphisms in the CYP17A1 gene for predicting clinical outcome in castration-resistant prostate cancer (CRPC) patients treated with abiraterone.

Methods

Sixty-four patients were genotyped for the selected polymorphisms (rs743572, rs10883783, rs17115100 and rs284849) in CYP17A1. We hypothesized that different genotypes could be associated with progression-free survival (PFS) and overall survival (OS).

Results

Statistical analyses highlighted no significant associations between these polymorphisms and clinical outcome. However, individuals with the most common TT genotype for rs10883783 had a 3 months’ longer PFS than individuals with the TA + AA genotype.

Conclusions

With the limitation of the retrospective study design and the small sample size, the analyzed polymorphisms do not seem to be correlated with clinical outcome of CRPC patients treated with abiraterone.