The Efficacy of Ketoconazole Containing Regimens in Castration-Resistant Prostate Cancer: A Systematic Review and Meta-Analysis

Castration resistant prostate cancer (CRPC) is a challenging subset of prostate cancer associated with an extensive metastatic profile and high mortality. Ketoconazole is a nonselective steroid 17α-hydroxylase/17,20 lyase (CYP17A1) inhibitor and is employed as a second line treatment option for CRPC with an established efficacy profile in patients. The aim of this study is to assess the efficacy of ketoconazole containing regimens for CRPC in terms of prostate specific antigen (PSA) decline rate using a systematic review and meta-analysis. In this review, an electronic search was carried out on PubMed, Cochrane CENTRAL, Scopus, and Google Scholar to find relevant literature. Random effects model was used to assess pooled PSA decline rate and 95% CIs. Publication bias was assessed using the funnel plot symmetry and one-tailed Egger's and Begg's test. In all cases, P-value <.05 was indicative of significant results. The review is registered with PROSPERO: CRD42023466536. A total of 483 articles were retrieved after database searching, out of which 23 studies (having a total of 1315 patients) were included in the review based on prespecified criteria. The PSA decline rate was reported in the 14 observational studies (having 964 patients) and 9 experimental studies (having 351 patients). Pooled results revealed that 48.6% (95% CI 43.1-54.2; P-value <.001; I2 = 73.24%) of participants achieved more than 50% decline in PSA (602/1315 participants). Sensitivity analysis using the leave-one-out method revealed no substantial change in pooled effect estimates; (Risk Ratio) RR 47.2% to RR 49.8% demonstrating the robustness of our results. There was no evidence of publication bias as assessed from the funnel plot symmetry. Ketoconazole containing regimens have shown moderate efficacy in high risk CRPC patients as demonstrated by the pooled results. Hence, a ketoconazole based chemotherapy can be added to patients' regimen if there is a persistent rise in PSA levels after androgen deprivation therapy.

Prospective evaluation of low-dose ketoconazole plus hydrocortisone in docetaxel pre-treated castration-resistant prostate cancer patients

Background

Ketoconazole is a well-known CYP-17-targeted systemic treatment for castration-resistant prostate cancer (CRPC). However, most of the published data has been in the pre-chemotherapy setting; its efficacy in the post-chemotherapy setting has not been as widely described. Chemotherapy-naïve patients treated with attenuated doses of ketoconazole (200-300 mg three times daily) had prostate specific antigen (PSA) response rate (greater than 50% decline) of 21% to 62%. We hypothesized that low-dose ketoconazole would likewise possess efficacy and tolerability in the CRPC post-chemotherapy state.

Methods

Men with CRPC and performance status (PS) 0-3, adequate organ function and who had received prior docetaxel were treated with low-dose ketoconazole (200 mg PO three times daily) and hydrocortisone (20 mg PO qAM and 10 mg PO qPM) until disease progression. Primary endpoint was PSA response rate (greater than 50% reduction from baseline) where a PSA response rate of 25% was to be considered promising for further study (versus a null rate of less than 5%); 25 patients were required. Secondary endpoints included PSA response greater than 30% from baseline, progression-free survival (PFS), duration of stable disease, and evaluation of adverse events (AEs).

Results

Thirty patients were accrued with median age of 72 years (range 55-86) and median pre-treatment PSA of 73 ng/ml (range 7-11,420). Twenty-nine patients were evaluable for response and toxicity. PSA response (>50% reduction) was seen in 48% of patients; PSA response (>30% reduction) was seen in 59%. Median PFS was 138 days; median duration of stable disease was 123 days. Twelve patients experienced grade 3 or 4 AEs. Of the 17 grade 3 AEs, only 3 were attributed to treatment. None of the 2 grade 4 AEs was considered related to treatment.

Conclusions

In docetaxel pre-treated CRPC patients, low-dose ketoconazole and hydrocortisone is a well-tolerated, relatively inexpensive and clinically active treatment option. PSA response to low-dose ketoconazole appears historically comparable to that of abiraterone in this patient context. A prospective, randomized study of available post-chemotherapy options is warranted to assess comparative efficacy.

Cabazitaxel for the treatment of castration-resistant prostate cancer

Treatment with docetaxel-based chemotherapy results in improved survival in patients with metastatic castration-resistant prostate cancer. However, all patients eventually develop progressive disease associated with poor outcomes. In this article, we discuss the available second-line therapeutic options following docetaxel, with a special focus on cabazitaxel, which is the first agent to yield extended survival as second-line therapy following docetaxel. Cabazitaxel, a novel semi-synthetic taxane, is effective even in docetaxel-resistant model systems. Recently, results of the Phase III TROPIC trial demonstrated improved survival with cabazitaxel plus prednisone compared with mitoxantrone and prednisone in patients with progressive metastatic castration-resistant prostate cancer, following prior docetaxel, which led to approval by the US FDA.

Evolving standards in the treatment of docetaxel-refractory castration-resistant prostate cancer

The management of men with metastatic castration-resistant prostate cancer (CRPC) has taken several leaps forward in the past year, with the demonstration of improved overall survival with three novel agents (sipuleucel-T, cabazitaxel with prednisone and abiraterone acetate with prednisone), and a significant delay in skeletal-related events observed with denosumab. The pipeline of systemic therapies in prostate cancer remains strong, as multiple agents with a diverse array of mechanisms of action are showing preliminary signs of clinical benefit, leading to more definitive phase III confirmatory trials. In this review, which represents part 1 of a two-part series on metastatic CRPC, we will summarize the mechanisms of resistance to hormonal and chemotherapies and discuss the evolving landscape of treatment options for men with CRPC, with a particular focus on currently approved and emerging treatment options following docetaxel administration, as well as prognostic factors in this post-docetaxel state. As docetaxel remains the standard initial systemic therapy for men with metastatic CRPC for both palliative and life-prolonging purposes, knowledge of these evolving standards will help to optimize delivery of care and long-term outcomes.

Contemporary management of metastatic castration-resistant prostate cancer

PURPOSE OF REVIEW

This review will describe the contemporary management of castration-resistant prostate cancer in the context of multiple recent advances.

RECENT FINDINGS

Two novel agents have been added to the therapeutic armamentarium including cabazitaxel and sipuleucel-T. Cabazitaxel, a novel taxane extended survival in men with progressive metastatic CRPC following conventional docetaxel-based chemotherapy. Sipuleucel-T, an autologous dendritic cell based vaccine extended survival in men with relatively asymptomatic metastatic CRPC without visceral metastasis. A third agent, abiraterone acetate, an orally administered CYP17 inhibitor, which suppresses androgen synthesis has been preliminarily reported to significantly prolong survival following prior docetaxel and approval by regulatory agencies is anticipated. Baseline and early changes in circulating tumor cells appear useful as a prognostic factor. Additionally, data demonstrated the superiority of denosumab, a RANK-ligand antagonist, compared to zoledronic acid in the prevention of skeletal related events in men with bone metastases.

SUMMARY

Cabazitaxel, sipuleucel-T and denosumab were approved in 2010 by regulatory agencies in the USA for men with metastatic CRPC, and approval of abiraterone acetate is anticipated based on the results of a phase III trial. The evaluation of circulating tumor cells assists in determining prognosis, although its utility for clinical decision-making entails validation.

Management of metastatic castration-resistant prostate cancer after first-line docetaxel

Although chemotherapy, based on docetaxel, is now established in the management of metastatic castration-resistant prostate cancer (mCRPC), until recently, there has been no treatment licensed for use in the second line in men whose disease progresses during or after docetaxel therapy. This article reviews the classes of agents that have shown potential in this setting, notably chemotherapy drugs, hormonal therapies, immunotherapies, anti-angiogenic drugs, and clusterin-targeted therapy.

New strategies for medical management of castration-resistant prostate cancer

Although advanced prostate cancer patients respond very well to front-line androgen deprivation, failure to hormonal therapy most often occurs after a median time of 18-24 months. The care of castration-resistant prostate cancer (CRPC) has significantly evolved over the past decade, with the onset of first-line therapy with docetaxel. Although numerous therapy schedules have been investigated alongside docetaxel, in either first-line or salvage therapy, results were dismal. However, CRPC chemotherapy is currently evolving, with, on the one hand, new agents targeting androgen metabolism and, on the other hand, significant progress in chemotherapy drugs, particularly for second-line therapy. The aim of the present review is to describe the current treatments for CRPC chemotherapy alongside their challengers that might shortly become new standards. In this article, we discuss the most recent data from clinical trials to provide the reader with a comprehensive, state-of-the-art overview of CRPC chemotherapy and hormonal therapy.

The role of abiraterone acetate in the management of prostate cancer: a critical analysis of the literature

CONTEXT

The development of agents targeting androgen signalling holds promise for men with castration-resistant prostate cancer (CRPC).

OBJECTIVE

The emerging role of abiraterone acetate (AA), a novel, orally administered androgen synthesis inhibitor, is critically analysed.

EVIDENCE ACQUISITION

Data were acquired from critically important original research published in peer-reviewed literature or presented at conferences conducted by the American Society of Clinical Oncology and the European Society of Medical Oncology.

EVIDENCE SYNTHESIS

The major findings are addressed in an evidence-based, objective, and balanced fashion.

CONCLUSIONS

AA specifically inhibits CYP17 and substantially reduces serum androgen levels without inducing significant adrenal insufficiency. A phase 3 trial reported a significant extension of survival in metastatic CRPC with AA plus prednisone compared to prednisone alone following docetaxel. The primary toxicity of mineralocorticoid excess is manageable. The addition of low-dose corticosteroids to AA may be necessary for controlling symptoms of mineralocorticoid excess.

Progression of metastatic castrate-resistant prostate cancer: impact of therapeutic intervention in the post-docetaxel space

Despite the proven success of hormonal therapy for prostate cancer using chemical or surgical castration, most patients eventually will progress to a phase of the disease that is metastatic and shows resistance to further hormonal manipulation. This has been termed metastatic castrate-resistant prostate cancer (mCRPC). Despite this designation, however, there is evidence that androgen receptor (AR)-mediated signaling and gene expression can persist in mCRPC, even in the face of castrate levels of androgen. This may be due in part to the upregulation of enzymes involved in androgen synthesis, the overexpression of AR, or the emergence of mutant ARs with promiscuous recognition of various steroidal ligands. The therapeutic options were limited and palliative in nature until trials in 2004 demonstrated that docetaxel chemotherapy could significantly improve survival. These results established first-line docetaxel as the standard of care for mCRPC. After resistance to further docetaxel therapy develops, treatment options were once again limited. Recently reported results from phase 3 trials have shown that additional therapy with the novel taxane cabazitaxel (with prednisone), or treatment with the antiandrogen abiraterone (with prednisone) could improve survival for patients with mCRPC following docetaxel therapy. Compared with mitoxantrone/prednisone, cabazitaxel/prednisone significantly improved overall survival, with a 30% reduction in rate of death, in patients with progression of mCRPC after docetaxel therapy in the TROPIC trial. Similarly, abiraterone acetate (an inhibitor of androgen biosynthesis) plus prednisone significantly decreased the rate of death by 35% compared with placebo plus prednisone in mCRPC patients progressing after prior docetaxel therapy in the COU-AA-301 trial. Results of these trials have thus established two additional treatment options for mCRPC patients in the "post-docetaxel space." In view of the continued AR-mediated signaling on mCRPC, results from additional phase 3 studies with novel antiandrogens which are directed at inhibition of the AR (e.g., MDV3100), as well as other agents, are awaited with interest and may further expand the treatment choices for this difficult-to-manage population of patients.

Low dose of ketoconazole in patients with prostate adenocarcinoma resistant to pharmacological castration

OBJECTIVE

• To assess the efficacy of ketoconazole in patients with castration-resistant prostate cancer (CRPC).

PATIENTS AND METHODS

• From April 2008 to November 2009, 37 patients with CRPC have been treated with ketoconazole. The primary endpoint was the prostate-specific antigen (PSA) response; the secondary endpoints were progression-free survival and safety profile. • Ketoconazole was administered by oral route at a dose of 200 mg every 8 h continuous dosing until the onset of serious adverse events or disease progression. • The study was based on a two-step design with an interim efficacy analysis carried out on the first 12 patients accrued.

RESULTS

• Main characteristics of population were: median age 75 years (range 60-88); baseline mean PSA 28.8 ng/mL (4.3-1000); 30 patients previously challenged with at least two lines of hormone therapy; 15 patients previously treated with chemotherapy. • Biochemical responses accounted for: two complete responses (5%), six partial responses (16%), 13 patients with stable disease (35%), and 14 with progressive disease (38%). Of 15 patients resistant to chemotherapy, overall disease control (complete plus partial responses plus stable disease) was recorded in seven of them. • Treatment was feasible without inducing grade 3-4 adverse events. The most common grade 1-2 adverse events were asthenia (27%), vomiting (8%) and abdominal pain (8%).

CONCLUSION

• Treatment with low-dose ketoconazole is feasible and well tolerated. The efficacy was satisfactory in patients previously treated with chemotherapy.

Evolution of Docetaxel-Based Therapy for Metastatic Castrate-Resistant Prostate Cancer

Until the publication of the SWOG 99–16 [1] and TAX 327 [2] trials in 2004, urologists understood that only purely palliative treatment was available for men with prostate cancer that was progressive despite androgen deprivation. However, following the establishment of docetaxel-based chemotherapy as an active treatment option for most men with metastatic disease, researchers have focused their questions on the optimal timing of treatment. Should docetaxel be considered after one or two lines of hormone manipulation? Is it necessary to wait until the patient has bone pain? In latter years, the research focus has widened to embrace second-line and even third-line chemotherapy for this patient group, raising the possibility of advanced prostate cancer being managed as a chronic condition. This article looks at the evolution of docetaxel-based chemotherapy in advanced prostate cancer, and considers the next likely developments.

Abiraterone acetate: a promising drug for the treatment of castration-resistant prostate cancer

Abiraterone acetate (CB7630), a pregnenolone analog, is an orally administered small molecule that irreversibly inhibits a rate-limiting enzyme in androgen biosynthesis, CYP17, and blocks the synthesis of androgens in the testes, adrenal glands and prostate without causing adrenal insufficiency. In clinical studies, abiraterone acetate is well tolerated and shows promising clinical activity in castration-resistant prostate cancer. The recommended Phase II dose of abiraterone acetate is 1000 mg orally daily in combination with prednisone 5 mg twice daily. Side effects are minimal and mostly associated with secondary mineralocorticoid excess, owing to a compensatory increase in upstream steroids, such as deoxycorticosterone and corticosterone. These include hypertension, hypokalemia and edema and are easily manageable with a selective mineralocorticoid antagonist, such as eplerenone, or low-dose corticosteroids. Currently, abiraterone acetate is being tested in a Phase III trial for men with progressive castration-resistant prostate cancer who are chemotherapy naive. A Phase III trial for patients following prior chemotherapy has been completed and is awaiting analysis.

A changing world for DCvax: a PSMA loaded autologous dendritic cell vaccine for prostate cancer

BACKGROUND

Northwest Therapeutics' DCvax-prostate consists of autologous dendritic cells (DCs) loaded with prostate-specific membrane antigen (PSMA) peptides, administered intravenously. Phase I-II testing, a decade ago, showed clinical benefit and immunological response in some patients. More recently DCvax brain, a product using a similar DC platform showed encouraging Phase I-II results and sipleucel-T, a prostatic acid phosphatase (PAP)-directed DC immunotherapy had positive Phase III results.

OBJECTIVE

Features of the clinical setting into which a new immunotherapy could be introduced are discussed, to refine a perspective on DCvax-prostate in the context of evolving prostate cancer therapeutics. PSMA-directed therapeutics and immune anticancer technologies are reviewed, and the clinical and immunological correlative testing of DCvax-prostate is discussed.

METHODS

Clinical and preclinical data from peer-reviewed literature, meetings proceedings and manufacturer-provided information are considered.

CONCLUSION

DCvax-prostate had encouraging early-phase trial results, but development and testing had stalled. As a more detailed understanding of patient-selection for capacity for anticancer immune response, the quantitation of immunological correlates, and the changing marketplace develop, it is appealing to consider a well tolerated, PSMA-directed autologous dendritic cell therapeutic product. Further clinical trial development of DCvax-prostate is warranted, and required if it is to find a relevant clinical application.

Leptomeningeal metastases from prostate cancer: an emerging clinical conundrum

Leptomeningeal metastases from solid tumors are relatively uncommon events with dismal prognosis. They can be seen mainly in patients with breast and lung cancer, and malignant melanoma, but have also been described in a variety of other tumor types. Leptomeningeal carcinomatosis from prostate cancer is an extremely rare complication, but as patients' survival is prolonged due to more effective treatments, it is expected that more patients will present with leptomeningeal involvement in advanced stages of the disease. In these cases high levels of prostate-specific antigen can be found in the cerebrospinal fluid. This comprehensive review presents the recent findings from the literature.

Activity of ketoconazole after taxane-based chemotherapy in castration-resistant prostate cancer

OBJECTIVE

To assess the efficacy of the androgen-synthesis inhibitor ketoconazole as a secondary hormonal therapy in patients with castration-resistant prostate cancer (CRPC) previously treated with chemotherapy, as persistent androgens appear to play a role in the development and maintenance of CRPC.

PATIENTS AND METHODS

We retrospectively identified 34 patients with CRPC who were treated with ketoconazole as a secondary hormonal therapy after paclitaxel- or docetaxel-based chemotherapy for CRPC. They were treated with ketoconazole 200-400 mg three times daily with or without hydrocortisone. Patients with previous use of ketoconazole were excluded. Half the patients had received estramustine as part of their chemotherapy regimen. The primary endpoint was the proportion of patients with a decline of > or =50% in their prostate-specific antigen (PSA) level. PSA progression was defined by the PSA Working Group 1 Criteria.

RESULTS

Eight of the 32 evaluable patients (25%) had a PSA decline of > or =50%. The median time to progression (TTP) was 3 months (95% confidence interval, 1.2-5.4). A history of previous response to taxane-based chemotherapy was not associated with the response to ketoconazole. However, previous use of oestrogens for CRPC was significantly associated with a shorter TTP on ketoconazole (1.5 vs 10.2 months; P = 0.03).

CONCLUSIONS

Ketoconazole has moderate activity as secondary hormonal therapy in patients with CRPC previously treated with taxane-based chemotherapy, although the TTP was short. Previous treatment with oestrogenic therapy is associated with a shorter TTP.