First- and second-line chemotherapy with docetaxel or mitoxantrone in patients with hormone-refractory prostate cancer

A review of treatments targeting DNA-repair gene defects in metastatic castration resistant prostate cancer

Prostate cancer is the most common cancer in men. About 6% of those diagnosed will develop metastatic disease. Unfortunately, metastatic prostate cancer is fatal. Prostate cancer can be castration sensitive or castration resistant. Many treatments have been shown to improve progression free survival and overall survival in metastatic castration resistant prostate cancer (mCRPC). In recent years, studies have been exploring targeting mutations in the DNA Damage Repair (DDR) response that may amplify oncogenes. In this paper, we aim to discuss DDR, new approved targeted therapies, and the most recent clinical trials in the setting of metastatic CRPC.

Chinese Expert Consensus on the Diagnosis and Treatment of Castration-Resistant Prostate Cancer (2019 Update)

Currently, the basic treatment of advanced prostate cancer is still endocrine therapy, but almost all patients eventually progress to castration-resistant prostate cancer (CRPC). In 2016, the Chinese Expert Consensus on the Diagnosis and Treatment of CRPC which aimed to help Chinese clinicians formulate treatment plans for CRPC was published. In this 2019 update, the 2016 version was updated with the aim of providing a more appropriate reference for clinical practice, standardizing CRPC patient management, and facilitating decision-making. The consensus is evidence-based and reviews the optimal therapeutic recommendations for CRPC management in China by taking into consideration the clinical characteristics of Chinese patients; drug availability, efficacy and safety; and recent advancements and developments in the international medical arena.

Clusterin as a therapeutic target

INTRODUCTION

Clusterin (CLU) is a stress-activated, ATP-independent molecular chaperone, normally secreted from cells, that is up-regulated in Alzheimer disease and in many cancers. It plays important roles in protein homeostasis/proteostasis, inhibition of cell death pathways, and modulation of pro-survival signalling and transcriptional networks. Changes in the CLU gene locus are highly associated with Alzheimer disease, and many therapy-resistant cancers over-express CLU. The extensive post-translational processing and heterogeneous oligomerization of CLU have so far prevented any definitive structure determination. This in turn has meant that targeting CLU with small molecule inhibitors is challenging. Therefore, inhibiting CLU at the gene-expression level using siRNA or antisense is a valid approach to inhibit its function. Areas covered: This article reviews recent advances regarding the role of CLU in proteostasis, cellular trafficking, human diseases, and signalling pathways involved in oncogenesis. It addresses the rationale for CLU as a therapeutic target in cancer, and the current status of pre-clinical and clinical studies using CLU antisense inhibitor OGX011. Expert opinion: Discusses challenges facing the therapeutic targeting of CLU including rapid changes in the treatment landscape for prostate cancer with multiple new FDA approved drugs, selection of windows of intervention, and potential side effects when silencing CLU expression.

Improved efficacy of mitoxantrone in patients with castration-resistant prostate cancer after vaccination with GM-CSF-transduced allogeneic prostate cancer cells

Previous vaccination studies in patients with castration-resistant prostate cancer (CRPC) showed improved survival without prolongation of progression-free survival (PFS). This might be explained by enhanced efficacy of subsequent therapies because of heightened immune status. We therefore evaluated the efficacy of chemotherapy in CRPC patients after immunotherapy. We retrospectively analyzed 28 patients who were treated with ipilimumab and GVAX, an allogeneic vaccine, and 21 patients who were randomized to GVAX or no vaccination. To study whether immune status was related to the efficacy of chemotherapy, frequencies of myeloid and lymphocyte subsets were determined. Of 28 patients treated with GVAX and ipilimumab, 23 patients received docetaxel and 13 patients mitoxantrone. Median PFS after docetaxel was 6.4 mo (range 0.8-11.2), while median PFS after mitoxantrone was markedly longer than expected (4.8 mo; range 1.4-13.7). High CD8+ICOS+ Tcell/Treg and pDC/mMDSC ratios were associated with relatively long PFS after mitoxantrone, suggesting a correlation between activated immune status and benefit of mitoxantrone. Analysis of 21 patients, randomized to GVAX or not, revealed a median PFS after docetaxel of 9.9 mo for vaccinated patients and 7.1 mo for unvaccinated patients. Interestingly, PFS after mitoxantrone (n = 14) was significantly longer in vaccinated patients as compared to controls (5.9 vs. 1.6 mo, p = 0.0048). In conclusion, mitoxantrone seems more effective in CRPC patients after immunotherapy, which may be related to the immune-stimulating effect of mitoxantrone in patients with heightened antitumor immunity. As this was a retrospective study with limited sample size, prospective studies are warranted to definitively show proof of principle.

The 2015 CUA-CUOG Guidelines for the management of castration-resistant prostate cancer (CRPC)

Agents that have shown improvements in survival in mCRPC now include abiraterone, enzalutamide, docetaxel, cabazitaxel and radium-223. Bone supportive agents and palliative radiation continue to play an important role in the overall management of mCRPC. Given the complexity, variety and importance of optimizing the use of these agents, a multidisciplinary team approach is highly recommended.

Overview of the latest treatments for castration-resistant prostate cancer

Over the past few years, we have developed an increased understanding of the molecular mechanisms that underlie prostate cancer progression and castration resistance and expanded our repertoire of therapeutic options for castration-resistant prostate cancer (CRPC). Four new agents (cabazitaxel, abiraterone acetate, enzalutamide, and radium-233) have been shown to prolong overall survival in patients with CRPC in the postchemotherapy setting. Targeting the androgen receptor pathway continues to have an important role in the treatment of CRPC, with abiraterone acetate and enzalutamide being the most exciting developments. Cabazitaxel is now considered the standard-of-care second-line chemotherapy for men with metastatic CRPC (mCRPC). Bone-targeted therapy is an active area of research, with denosumab being the first bone-targeted agent able to significantly delay the appearance of bone metastases in patients with CRPC and radium-223 being the first radiopharmaceutical agent to improve survival in patients with mCRPC.

A multicenter phase 1 study of EMD 525797 (DI17E6), a novel humanized monoclonal antibody targeting αv integrins, in progressive castration-resistant prostate cancer with bone metastases after chemotherapy

BACKGROUND

EMD 525797 (DI17E6) is a deimmunized, humanized monoclonal immunoglobulin G2 antibody against the αv subunit of human integrins. Blocking αv integrins may be an effective strategy for inhibiting prostate cancer (PCa) metastasis.

OBJECTIVE

Evaluate EMD 525797 safety/tolerability and pharmacokinetics (PK) in castration-resistant PCa patients. Secondary objectives included antitumor activity assessments.

DESIGN, SETTING, AND PARTICIPANTS

A phase 1 open-label study in 26 patients (four European centers). Eligible patients (≥ 18 yr) had histologically proven PCa with bone metastases after prior chemotherapy and evidence of progressive disease (PD) based on prostate-specific antigen (PSA) values.

INTERVENTION

Patients received three intravenous EMD 525797 infusions (250, 500, 1000, or 1500 mg every 2 wk).

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Treatment-emergent adverse events (TEAEs) and dose-limiting toxicities (DLTs) were assessed. PK parameters were calculated according to noncompartmental standard methods. Antitumor activity measures were response after 6 wk, changes in PSA levels, and pain interference total score. Descriptive statistics were used.

RESULTS AND LIMITATIONS

Patients were treated for a mean of 16.8 ± 16.7 wk. No DLTs were reported in any of the cohorts. All patients experienced TEAEs, which were considered drug-related in 11 patients. Four deaths occurred during the trial and were considered not related to EMD 525797. EMD 525797 showed dose-dependent, nonlinear PK. Eighteen of 26 patients did not show PD for ≥ 18 wk. Two patients (500-mg cohort), treated for 42.4 and 76.3 wk, had clinically significant PSA reductions and pain relief, including one patient with confirmed partial response. This trial was not specifically designed to assess clinical activity, and further investigations are needed in randomized controlled trials.

CONCLUSIONS

No DLTs were reported in any of the evaluated cohorts. There was evidence of clinical activity. For the currently ongoing phase 2 trial, EMD 525797 doses of 750 and 1500 mg every 3 wk were chosen.

TRIAL REGISTRATION

NCT00958477 (EMR 62242-002).

A multi-peptide, dual-adjuvant telomerase vaccine (GX301) is highly immunogenic in patients with prostate and renal cancer

BACKGROUND

Anti-tumor vaccination is a new frontier in cancer treatment applicable to immunogenic neoplasms such as prostate and renal cancers. GX301 is a vaccine constituted by four telomerase peptides and two adjuvants, Montanide ISA-51 and Imiquimod.

OBJECTIVE

The aim of this study was to analyze safety and tolerability of GX301 in an open-label, phase I/II trial. Immunological and clinical responses were also evaluated as secondary endpoints.

EXPERIMENTAL DESIGN

GX301 was administered by intradermally injecting 500 μg of each peptide (dissolved in Montanide ISA-51) in the skin of the abdomen. Imiquimod was applied as a cream at the injection sites. The protocol included 8 administrations at days 1, 3, 5, 7, 14, 21, 35, 63. Eligible patients were affected with stage IV prostate or renal cancer resistant to conventional treatments. Patients were clinically and immunologically monitored up to 6 months from the first immunization.

RESULTS

No grade 3-4 adverse events were observed. Evidence of vaccine-specific immunological responses was detected in 100 % of patients. Disease stabilization occurred in 4 patients. Prolonged progression-free survival and overall survival were observed in patients showing a full pattern of vaccine-specific immunological responses.

CONCLUSION

GX301 demonstrated to be safe and highly immunogenic. Further studies are needed to determine its clinical efficacy.

Custirsen (OGX-011): a second-generation antisense inhibitor of clusterin in development for the treatment of prostate cancer

Clusterin is a stress-induced cytoprotective chaperone that confers broad-spectrum treatment resistance and is overexpressed across a number of cancers. custirsen (OGX-011) is a promising novel second-generation antisense inhibitor of clusterin in clinical development. This article describes the mechanism of action and safety profile of OGX-011 and details the Phase I and II results in human solid organ malignancies. Two Phase III registration trials are currently under recruitment evaluating OGX-011 in combination with chemotherapy in patients with metastatic castration-resistant prostate cancer. These studies not only have the potential to significantly alter the standard of care in prostate cancer, but would also endorse a new class of targets and targeted therapy approach for cancer.

Increased chemosensitivity via targeting testicular nuclear receptor 4 (TR4)-Oct4-interleukin 1 receptor antagonist (IL1Ra) axis in prostate cancer CD133+ stem/progenitor cells to battle prostate cancer

Prostate cancer (PCa) stem/progenitor cells are known to have higher chemoresistance than non-stem/progenitor cells, but the underlying molecular mechanism remains unclear. We found the expression of testicular nuclear receptor 4 (TR4) is significantly higher in PCa CD133(+) stem/progenitor cells compared with CD133(-) non-stem/progenitor cells. Knockdown of TR4 levels in the established PCa stem/progenitor cells and the CD133(+) population of the C4-2 PCa cell line with lentiviral TR4 siRNA led to increased drug sensitivity to the two commonly used chemotherapeutic drugs, docetaxel and etoposide, judging from significantly reduced IC50 values and increased apoptosis in the TR4 knockdown cells. Mechanism dissection studies found that suppression of TR4 in these stem/progenitor cells led to down-regulation of Oct4 expression, which, in turn, down-regulated the IL-1 receptor antagonist (IL1Ra) expression. Neutralization experiments via adding these molecules into the TR4 knockdown PCa stem/progenitor cells reversed the chemoresistance, suggesting that the TR4-Oct4-IL1Ra axis may play a critical role in the development of chemoresistance in the PCa stem/progenitor cells. Together, these studies suggest that targeting TR4 may alter chemoresistance of PCa stem/progenitor cells, and this finding provides the possibility of targeting TR4 as a new and better approach to overcome the chemoresistance problem in PCa therapeutics.

Management of castration-resistant prostate cancer: a global approach

Treatment options for castration-resistant prostate cancer (crpc) have evolved since the start of the 2000s, with most of the new effective therapies appearing since 2010. In 2004, docetaxel was the first chemotherapeutic agent to improve survival in crpc, but little else was available once patients recurred. Since 2010, four new options have been shown to improve survival in patients with refractory or recurring disease after docetaxel. In the management of bone metastases, two bone-targeted therapies have been shown to reduce the risk of bone complications, and they are part of the overall management strategy in crpc patients. Therapeutic options before chemotherapy have shown promising results and may soon become available in Canada. The present article reviews the treatment options that have shown to be effective in crpc and also some of the ongoing work in the field.

Multiple rechallenges for castration-resistant prostate cancer patients responding to first-line docetaxel: assessment of clinical outcomes and predictive factors

OBJECTIVE

To describe the feasibility and efficacy of multiple sequential rechallenges and analyze the predictive factors that may aid in selecting patients who are more likely to respond. Several studies have demonstrated the feasibility and activity of a single docetaxel rechallenge in patients with castration-resistant prostate cancer (CRPC), thus providing an additional opportunity for treatment in docetaxel-sensitive CRPC patients in clinical practice.

MATERIALS AND METHODS

CRPC patients who completed first-line docetaxel therapy without disease progression have been offered a docetaxel rechallenge, and the responders have undergone further rechallenges until the appearance of docetaxel resistance. We assessed their clinical outcomes and evaluated all the variables potentially capable of predicting the response to rechallenge by means of uni- and multivariate analysis.

RESULTS

Forty-six consecutive patients underwent 92 rechallenges. The overall biochemical response rate (prostate-specific antigen [PSA] reduction >50%) was 66%. Median overall survival was 32 months with a projected 2-year overall survival from the first docetaxel administration of 77.5%. Multivariate analysis showed that the time slope-log PSA, the time from the previous cycle, and the response to the previous cycle were predictive of the response to a rechallenge.

CONCLUSION

A docetaxel rechallenge may be safely repeated several times in CRPC patients and in selected patients could improve disease control. The predictive factors found in our analysis may help select the most appropriate strategy in the light of the availability of active second-line drugs.

[Strategy in advanced castration-resistant prostate cancer]

If androgen deprivation, chemical with LH-RH analogs or surgical with bilateral orchiectomy, still remains the stone edge of treatment of prostate cancer, in the metastatic setting, this hormonosensitivity, most of the time long, finally move on in hormonal-failure. If rare changes in the therapeutic strategy have been achieved in this setting since 2004 and the arrival of docetaxel, it is the global perception of the disease that has been modified and the definition of one specific entity: the castrate-resistant prostate cancer. This new definition and the changes of design and end-points of clinical trials testing new agents with strong recruitment during the past years have conducted to a real revolution in the management of castrate-refractory prostate cancer. The place of secondary hormonal manipulations, such as withdrawal of the anti-androgen, oestrogen or ketoconazole, still exists for a selected group of patients. In case of aggressive disease and symptoms, chemotherapy should be selected, docetaxel, in a three weeks schedule, and may be combined with Estracyt. It is time to consider the revolution of the post-chemotherapy setting with the arrival of two new drugs ; a cytotoxic one, the cabazitaxel and hormonal for the second one, the abiraterone acetate. The place of the immunotherapy with the sipuleucel-T may be more difficult to precise, especially in Europe, even if it has been finally indicated in the United States in the metastatic setting. Concerning bone metastasis, zoledronic acid was during a long time the only bone-targeted agent, effective in reducing the incidence of skeletal related events, and was recently exceeded by the denosumab, an anti-RANK ligand. Finally, let us hope that other changes will be achieved in the near future, with the cabazitaxel-docetaxel confrontation in the first-line setting, and the introduction of the abiraterone acetate before chemotherapy with docetaxel, already tested in ongoing trials.

Second-line therapy for castrate-resistant prostate cancer: a literature review

Despite a survival benefit in the first-line treatment of castrate-resistant prostate cancer (CRPC) with docetaxel, the prognosis remains limited. There are increasing options available for patients with CRPC in the second-line setting, but there is currently little consensus regarding the optimal treatment. There have been numerous phase II and retrospective studies examining second-line options in CRPC, including retreatment with docetaxel, mitoxantrone, cyclophosphamide and carboplatin, which can be associated with meaningful responses in a significant minority of patients. In 2010 three randomized trials were published or presented which demonstrated a survival benefit in the second-line setting. These included cabazitaxel compared with mitoxantrone, sipuleucel-T (immunotherapy) and abiraterone acetate versus placebo. Ongoing research in the second-line setting of CRPC to optimize treatment options, with the objectives of survival prolongation, improvement in quality of life and pain management, is still needed.

New and emerging agents for the treatment of castration-resistant prostate cancer

Most men with recurrent prostate cancer (CaP) initially respond to androgen deprivation therapy but eventually develop metastatic castration-resistant prostate cancer (CRPC). Over the last decade, new therapeutic targets have been identified in CRPC and several new drugs have reached advanced stages of clinical development. In 2010, the Food and Drug Administration (FDA) approved sipuleucel-T and cabazitaxel, and in 2011, abiraterone for patients with metastatic CRPC based on phase 3 trials showing improved survival. Although not yet available for clinical use, a press release in June 2011 announced that radium 223 also demonstrated a survival advantage in men with metastatic CRPC. Emerging therapies in advanced stages of clinical development in CRPC include the hormonal therapies MDV3100 and TAK 700, and the immunotherapy ipilimumab. Results are also pending on phase 3 studies comparing docetaxel plus prednisone with docetaxel given with the novel agents aflibercept, dasatinib, lenalidomide, and custirsen. In addition to these new and emerging therapeutic agents, denosumab was approved for the prevention of skeletal complications in patients with bone metastases due to solid tumor malignancies, providing an alternative to zoledronic acid. While the addition of these new treatment options is a great advance for men with metastatic CRPC, there are many new questions arising regarding sequencing of these treatments with each other, with previously existing therapies, and with the emerging agents now in clinical trials. Furthermore, there are concerns that on-going phase 3 trials may be contaminated if patients go off study treatment to start 1 of the newly approved agents or take the agent subsequently. These realities make clinical trial design more challenging than ever.

Pemetrexed as second-line chemotherapy for castration-resistant prostate cancer after docetaxel failure: results from a phase II study

OBJECTIVE

Although there is no standard treatment after docetaxel failure in patients with castration-resistant prostate cancer (CRPC), second-line chemotherapy is increasingly required. Its mechanism of action and toxicity profile make pemetrexed suitable for testing in this setting.

METHODS AND MATERIALS

Patients with docetaxel-resistant CRPC received pemetrexed 500 mg/m(2) every 3 weeks for 6 courses. The usual premedication with vitamin supplementation and dexamethasone prophylaxis was regularly administered. The primary objective was to quantify the biochemical response rate.

RESULTS

The biochemical response rate was 10.5% (95% CI 1.3-33.1), with 2 patients showing a reduction in prostate specific antigen (PSA) of ≥50%. The null hypothesis that the PSA response rate would be less than 20% was therefore accepted, and patient accrual was stopped after the evaluation of the 19th patient. The 1-year overall survival rate was 61.5%, with a median survival of 14 months. A considerable proportion of the patients (36%) were withdrawn from the study because of hematologic and nonhematologic toxicity.

CONCLUSIONS

Our experience with pemetrexed in CRPC patients appears discouraging in terms of activity and toxicity. No further studies of this drug should be performed in CRPC patients.

Randomized phase II trial of Custirsen (OGX-011) in combination with docetaxel or mitoxantrone as second-line therapy in patients with metastatic castrate-resistant prostate cancer progressing after first-line docetaxel: CUOG trial P-06c

PURPOSE

Clusterin (CLU) is an antiapoptotic, stress-induced protein conferring treatment resistance when overexpressed. This study tested custirsen, a CLU inhibitor, in patients with metastatic castration-resistant prostate cancer (mCRPC) progressing during or within 6 months of initial docetaxel therapy.

PATIENTS AND METHODS

Men were randomized to receive either docetaxel + prednisone + custirsen (DPC) or mitoxantrone + prednisone + custirsen (MPC).

RESULTS

Forty-two patients received study treatment. Toxicity was similar in both arms. Twenty patients treated with DPC received a median of 8 cycles; overall survival (OS) was 15.8 months. Median time to pain progression (TTPP) was 10.0 months; 10 of 13 (77%) evaluable patients had pain responses. Three of 13 (23%) evaluable patients had objective partial responses. Prostate-specific antigen (PSA) declines of 90% or more, 50% or more, and 30% or more occurred in 4 (20%), 8 (40%), and 11 (55%) patients, respectively. Twenty-two patients treated with MPC received a median of 6 cycles; OS was 11.5 months. The median TTPP was 5.2 months; 6 of 13 (46%) evaluable patients had pain responses. No objective responses were observed. PSA declines of 50% or more and 30% or more occurred in 6 (27%) and 7 (32%) patients, respectively. Low serum CLU levels during treatment showed superior survival for patients based on modeling with proportional hazard regression with a time-dependent covariate and different landmarks.

CONCLUSIONS

Custirsen plus either docetaxel or mitoxantrone was feasible in patients with progressive mCRPC following first-line docetaxel therapy. Pain relief was higher than expected, with interesting correlations between serum CLU and survival. A phase III trial evaluating the pain palliation benefit of custirsen with taxane therapy is ongoing.

Current management of castrate-resistant prostate cancer

Prostate cancer (PCa) is the most frequently diagnosed cancer in North America. Castrate-resistant PCa presents a spectrum of disease ranging from rising PSA levels in the absence of metastases or symptoms and despite androgen-deprivation therapy, to metastases and significant debilitation from cancer symptoms. Castrate-resistant PCa is usually suspected in patients with new symptoms on androgen deprivation therapy, with a rising PSA, or with new evidence of disease on bone scans or computed tomography scans. Institution of treatment and the choice of systemic or local therapy depend on a number of factors. This review discusses the various currently available treatments for patients with castrate-resistant PCa, from secondary hormonal manipulations to options for post-docetaxel systemic therapy.

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.

Current treatment strategies for castration-resistant prostate cancer

Prostate cancer is the most common cancer in men in United States and the fifth most common cancer in men in Korea. Although the majority of patients with metastatic prostate cancer initially respond to androgen deprivation therapy, almost all patients will eventually progress to develop castration-resistant prostate cancer (CRPC). Treatment options for CRPC remain limited. Prostate cancer was considered unresponsive to chemotherapy until the mid-1990s, when mitoxantrone combined with prednisone was shown to play a role in the palliative treatment of patients with CRPC. In 2004, two large randomized clinical trials demonstrated for the first time a small but significant survival advantage of docetaxel-based chemotherapy compared with mitoxantrone in patients with metastatic CRPC. Recently, cabazitaxel was shown to improve survival in patients with metastatic CRPC who progressed after docetaxel-based chemotherapy. Sipuleucel-T was also demonstrated to improve overall survival in patients with asymptomatic or minimally symptomatic metastatic CRPC. Along with mitoxantrone and docetaxel, cabazitaxel and sipuleucel-T are now approved for use in metastatic CRPC by the US Food and Drug Administration. There have been multiple early-phase clinical trials of various agents for the treatment of CRPC, and some are in phase III development. This review focuses on the key clinical trials of various treatment options of CRPC currently in use and under investigation.

Second-line chemotherapy in metastatic docetaxel-resistant prostate cancer: a review

The results of cytotoxic therapy in the second-line setting of metastatic castration-resistant prostate cancer have demonstrated that disease is poorly controlled after taxane resistance with a time to progression of 3 months or less. Many trials of second-line chemotherapy have been disappointing. However, most of patients with docetaxel-pretreated castration-resistant disease receive a second-line chemotherapy. Molecular mechanism of castration resistance and docetaxel resistance is resumed, and clinical trials of second-line chemotherapy after docetaxel progression are reviewed. Reintroduction of docetaxel after a drug-free interval is an active treatment in docetaxel-pretreated patients, and only recently a prospective study documented a survival benefit of 2.4 months after second-line taxane-based chemotherapy of metastatic docetaxel-resistant prostate cancer. Although a second-line chemotherapy with a taxane could improve overall survival, a change of biology of castration-resistant prostate cancer after docetaxel is suggested, as inferred by the renewed hormonal sensitivity, whose role on survival remains unknown, and from the activity of antiangiogenic drugs.

Novel targeted agents on the horizon for castration-resistant prostate cancer

Androgen deprivation treatment in prostate cancer patients is well established; however, resistance to such treatment manifests itself by progression to castration-resistant prostate cancer (CRPC). Despite significant advances in treatment options for patients with CRPC, their prognosis remains poor. Resistance results from multiple processes that facilitate cancer cell growth and survival. Mechanisms underlying the shift to castrate resistance have been attributed to a complex interplay of clonal selection, reactivation of the androgen receptor axis despite castrate levels of serum testosterone, stress-induced prosurvival genes and cytoprotective chaperone networks and alternative mitogenic growth factor pathways. This article discusses several pathways involved in the development of CRPC, with a particular focus on those mechanisms that have led to the development of new targeted therapies.

A phase II study of 2-methoxyestradiol (2ME2) NanoCrystal® dispersion (NCD) in patients with taxane-refractory, metastatic castrate-resistant prostate cancer (CRPC)

PURPOSE

2ME2 (Panzem®) is a non-estrogenic derivative of estradiol with antiproliferative and antiangiogenic activity. Preclinical data support antitumor activity in prostate cancer. This trial evaluated the efficacy of 2ME2 NCD in patients with taxane-refractory, metastatic CRPC.

EXPERIMENTAL DESIGN

Patients with metastatic CRPC who had progressed on only one prior taxane-based regimen were eligible. All patients received 2ME2 NCD at 1,500 mg orally four times daily, repeated in 28 day cycles. The primary endpoint was progression-free survival at month 6, with a secondary endpoint of PSA response. An exploratory endpoint was metabolic response on FDG-PET imaging.

RESULTS

A total of 50 pts was planned. The study was terminated after 21 pts when a futility analysis showed the primary endpoint was unlikely to be reached. The median number of cycles on study was 2 (range <1 to 12). Adverse events (AE) of grade ≥3 related to the study drug occurred in 7 unique patients (33%): elevations in liver function tests, fatigue or weakness, gastrointestinal hemorrhage, and hyponatremia. Paired FDG-PET scans were obtained for 11 pts. No metabolic responses were observed.

CONCLUSIONS

2ME2 NCD did not appear to have clinically significant activity in this study. 2ME2 NCD was well-tolerated and showed some evidence of biologic activity. Given the aggressive biology in this taxane-refractory population, the potential benefit from a cytostatic agent like 2ME2 might better be realized in the pre-chemotherapy (or rising PSA only) stage of CRPC.

Phase 1/2 study of preoperative docetaxel and mitoxantrone for high-risk prostate cancer

BACKGROUND

: A study was conducted to determine the 5-year recurrence-free survival in patients with high-risk prostate cancer after neoadjuvant combination chemotherapy followed by surgery. Secondary endpoints included safety, pathologic effects of chemotherapy, and predictors of disease recurrence.

METHODS

: Fifty-seven patients were enrolled in a phase 1/2 study of weekly docetaxel 35 mg/m(2) and escalating mitoxantrone to 4 mg/m(2) before prostatectomy. Patients were treated with 16 weeks of chemotherapy administered weekly on a 3 of every 4 week schedule. A tissue microarray, constructed from the prostatectomy specimens, served to facilitate the exploratory evaluation of biomarkers. The primary endpoint was recurrence-free survival. Disease recurrence was defined as a confirmed serum prostate-specific antigen (PSA) >0.4 ng/mL.

RESULTS

: Of the 57 patients, 54 received 4 cycles of docetaxel and mitoxantrone before radical prostatectomy. Grade 4 toxicities were limited to leukopenia, neutropenia, and hyperglycemia. Serum testosterone levels remained stable after chemotherapy. Negative surgical margins were attained in 67% of cases. Lymph node involvement was detected in 18.5% of cases. With a median follow-up of 63 months, 27 of 57 (47.4%) patients recurred. The Kaplan-Meier recurrence-free survival at 2 years was 65.5% (95% confidence interval [CI], 53.0%-78.0%) and was 49.8% at 5 years (95% CI, 35.5%-64.1%). Pretreatment serum PSA, lymph node involvement, and postchemotherapy tissue vascular endothelial growth factor expression were independent predictors of early recurrence.

CONCLUSIONS

: Preoperative chemotherapy with docetaxel and mitoxantrone is feasible. Approximately half of the high-risk patients remain free of disease recurrence at 5 years, and clinical and molecular predictors of early recurrence were identified. Cancer 2010. (c) 2010 American Cancer Society.

Carboplatin plus weekly docetaxel as salvage chemotherapy in docetaxel-resistant and castration-resistant prostate cancer

BACKGROUND

There is no proven, effective, standard second-line chemotherapy for castration- and docetaxel-resistant prostate cancer (DRPC). Recent data suggest that carboplatin may be effective in combination with docetaxel in this setting; however, the optimal docetaxel/carboplatin-based regimen is still unclear.

AIM OF THE STUDY

We identified 43 consecutive patients with DRPC treated with carboplatin (AUC5 d1) and docetaxel (35 mg/m(2) d1, 8, 15 q4w i.v.) as a second-line or subsequent salvage chemotherapy until discontinuation of therapy due to disease progression or unacceptable toxicity.

RESULTS

Decreased prostate-specific antigen (> or =50% PSA) was observed in 22/43 (51.2%, 95% CI, 35.5, 66.7%) patients, with > or =90% reduction in 12/43 patients (27.9%). At the time of analysis, the median follow-up time for all patients was 10.4 months. Median progression-free survival (PFS) for all patients was 6.5 months (95% CI 4.1, 8.9), and median overall survival (OS) was 15.8 months (95% CI 12.1, 18.5). In PSA responders, PFS was 9.5 (95% CI 8.2, 19.0) months versus 3.3 (95% CI 2.6, 4.0) months in PSA non-responders (P < 0.0001; hazard ratio (HR) 0.108) and OS was 24.4 months (95% CI 19.5, 29.4) versus 7.8 (95% CI 5.2, 10.3) months (P = 0.001; HR 0.232). Established prognostic factors were associated with survival. This regimen was reasonably well tolerated, with leukopenia/neutropenia as the most common reversible grade 3/4 toxicity (41.9/39.5%).

CONCLUSION

These data suggest that weekly docetaxel plus carboplatin may be an important therapeutic second-line treatment option for patients with DRPC.

Docetaxel reintroduction in patients with metastatic castration-resistant docetaxel-sensitive prostate cancer: a retrospective multicentre study

OBJECTIVE

To investigate the potential benefit of reintroducing docetaxel chemotherapy in patients with progressive metastatic castration-resistant prostate cancer (mCRPC) who had initially responded to first-line docetaxel-based regimen.

PATIENTS AND METHODS

Records were evaluated retrospectively from French patients with mCRPC who had been included in seven controlled clinical studies of docetaxel as first-line treatment. We identified patients who were confirmed as responders to first-line treatment, discontinued for reasons other than disease progression or unacceptable toxicity, and who received further docetaxel chemotherapy for disease progression. The primary objective was to assess efficacy in terms of the prostate-specific antigen (PSA) response after resuming a docetaxel-based chemotherapy. Secondary objectives were overall survival and tolerance.

RESULTS

Of the 148 patients who responded to first-line docetaxel, 50 received further therapy with docetaxel and were analysed. The median (range) response duration to first-line docetaxel was 10.3 (4.6-45.7) months and the median docetaxel-free interval was 18.4 (5.0-46.7) months. Docetaxel was reintroduced as second-line therapy in 52% of patients and as further lines in 48%. After docetaxel reintroduction, 24 patients (48%) had a 50% decrease in PSA level (95% confidence interval, CI, 34.1-61.8%). The median (95% CI) overall survival from docetaxel reintroduction was 16 (13-20) months. Re-treatment was well tolerated (6% of grade 3-4 haemotoxicity).

CONCLUSION

Docetaxel reintroduction appears to be effective, with favourable tolerance profiles, in patients with mCRPC having responded to first-line docetaxel, and should be prospectively assessed in clinical trials against alternative therapies or investigational agents given alone or in combination, to define further management.

Targeting the cytoprotective chaperone, clusterin, for treatment of advanced cancer

Many strategies used to kill cancer cells induce stress-responses that activate survival pathways to promote emergence of a treatment resistant phenotype. Secretory clusterin (sCLU) is a stress-activated cytoprotective chaperone up-regulated by many varied anticancer therapies to confer treatment resistance when overexpressed. sCLU levels are increased in several treatment recurrent cancers including castrate resistant prostate cancer, and therefore sCLU has become an attractive target in cancer therapy. sCLU is not druggable with small molecule inhibitors, therefore nucleotide-based strategies to inhibit sCLU at the RNA level are appealing. Preclinical studies have shown that antisense oligonucleotide (ASO) or siRNA knockdown of sCLU have preclinical activity in combination with hormone- and chemotherapy. Phase I and II clinical trial data indicate that the second generation ASO, custirsen (OGX-011), has biologic and clinical activity, suppressing sCLU expression in prostate cancer tissues by more than 90%. A randomized study comparing docetaxel-custirsen to docetaxel alone in men with castrate resistant prostate cancer reported improved survival by 7 months from 16.9 to 23.8 months. Strong preclinical and clinical proof-of-principle data provide rationale for further study of sCLU inhibitors in randomized phase III trials, which are planned to begin in 2010.

Emerging drugs for prostate cancer

Prostate cancer mortality usually occurs as a result of castrate resistant disease. Many approaches are currently being evaluated to improve the treatment of this condition. These include drugs that induce androgen deprivation, that is, LHRH antagonists; more active or less toxic chemotherapy agents; immunologic approaches, including passive and active immunization; drugs that target the androgen receptor and/or androgen synthesis; drugs that target specific pathways, including tyrosine kinase inhibitors, angiogenesis inhibitors, endothelin antagonists and matrix metalloproteinase inhibitors; and antioxidants and cell cycle inhibitors. Many of these agents seem promising. The rationale, biologic activity and therapeutic results of these emerging drugs are reviewed.

A phase II study of pemetrexed as second-line chemotherapy for the treatment of metastatic castrate-resistant prostate cancer (CRPC); Hoosier Oncology Group GU03-67

BACKGROUND

No standard therapy exists for post-docetaxel castrate-resistant prostate cancer (CRPC) patients. This trial aimed to determine the safety and efficacy of pemetrexed in post-docetaxel CRPC patients.

MATERIALS AND METHODS

CRPC patients with progression after docetaxel (Taxotere) therapy received pemetrexed (500 mg/m2) i.v. every 3 weeks. The primary end point was prostate-specific antigen (PSA) response. A pharmacogenetic analysis of the reduced folate carrier-1 gene (RFC1) G80A polymorphism was also carried out.

RESULTS

Forty-nine patients were enrolled: median age 68 years, median baseline PSA 72 ng/ml, and median Karnofsky performance status of 90. Grade 3 or 4 toxicity occurred in 20 (43%) and four patients (8%), respectively. Confirmed >50% PSA decline occurred in four patients (8%), stable PSA lasting at least 12 weeks in 10 patients (20%). A significant relationship was observed between time from prior docetaxel therapy and overall survival. Pharmacogenetic analyses of RFC1 G80A genotype frequencies showed no relationship between genotypes and clinical efficacy.

CONCLUSIONS

Pemetrexed treatment of CRPC patients after docetaxel therapy was associated with only modest clinical activity. Further investigation of pemetrexed as a single agent in a nonenriched CRPC population is unlikely to add significant clinical benefit over that seen with traditional second-line chemotherapy agents such as mitoxantrone.

Knockdown of p21-activated kinase 6 inhibits prostate cancer growth and enhances chemosensitivity to docetaxel

OBJECTIVES

To investigate whether silencing of p21-activated kinase 6 (PAK6) would inhibit prostate cancer growth and to assess the effect of PAK6 silencing when used in combination with docetaxel. PAK6 is a serine/threonine kinase belonging to the PAK family and has been implicated in cell motility, apoptosis, and transformation.

METHODS

Expression of PAK6 in PC-3, DU145, and LAPC4 prostate cancer cell lines was knocked down by small, interfering RNA (siRNA). Cellular proliferation, cell cycle distribution, the ability to undergo apoptosis, and the invasive capacity through matrigel were evaluated. Furthermore, in vivo growth of prostate cancer in nude mice treated with PAK6-siRNA alone or in combination with docetaxel was examined.

RESULTS

PAK6 was overexpressed in prostate cancer tissues. PAK6-siRNA efficiently and specifically downregulated the expression of PAK6 and inhibited cell growth of prostate cancer. It also suppressed invasive ability in matrigel and caused cell cycle arrest at the G(2)/M phase. Xenograft tumor growth in nude mice was inhibited significantly by PAK6-siRNA. The average weight of the harvested tumor was 46 +/- 8.5 mg in the PAK6-siRNA group, lower than the 451 +/- 22.3 mg in the control group (P < .05). Combined use of PAK6-siRNA and docetaxel produced a greater effect than docetaxel alone in both in vitro and in vivo models.

CONCLUSIONS

Knockdown of PAK6 expression produced an inhibitory effect on prostate cancer growth and enhanced chemosensitivity of docetaxel. PAK6 could be a valuable molecular target for the treatment of prostate cancer.

Custirsen (OGX-011): a second-generation antisense inhibitor of clusterin for the treatment of cancer

BACKGROUND

Clusterin is a stress-induced cytoprotective chaperone protein, regulated by HSF1, and functions similarly to a small heat-shock protein. Clusterin is expressed in a variety of cancers and associated with broad-spectrum treatment resistance. Custirsen (OGX-011) is a 2'-methoxyethyl modified phosphorothioate antisense oligonucleotide that is complementary to clusterin mRNA; it is currently in clinical trials for patients with cancer.

OBJECTIVE/METHODS

To review the literature on the role of clusterin in cancer progression and treatment resistance, and to summarize completed and ongoing clinical trials with custirsen.

RESULTS/CONCLUSIONS

Custirsen is well tolerated in humans and biologically active in inhibiting expression of clusterin in patients with cancer. Randomized trials of custirsen in combination with chemotherapy are planned in patients with castration-resistant prostate cancer.

Docetaxel chemotherapy of Korean patients with hormone- refractory prostate cancer:comparative analysis between 1st-line and 2nd-line docetaxel

PURPOSE

This study was undertaken to investigate the outcomes associated with docetaxel treatment of Korean patients with hormone-refractory prostate cancer (HRPC) and to compare its clinical efficacies in 1st and 2nd-line settings.

PATIENTS AND METHODS

This study was retrospectively performed and included 47 patients with HRPC. The 1st-line group consisted of 19 patients who had not undergone prior chemotherapy, and the 2nd-line group consisted of 28 patients who underwent prior chemotherapy. All patients were treated with 75mg/m2 IV docetaxel every 3 weeks and 5mg of prednisone twice daily with a continuous androgen blockade.

RESULTS

Of 47 study subjects, 14 patients (29.8%) had > or = 50% PSA decline from baseline. PSA response was more common in the 1st-line group, but this was not statistically different (42.1% vs. 21.4%, p = 0.114). After a median follow up of 11 months (range, 6-24 months), the 1st-line group showed a longer time to PSA progression (4 vs. 2 months, p = 0.015) and survival (17 vs. 10 months, p = 0.037) than the 2nd-line group. In terms of toxicities, no difference was apparent between the 2 groups.

CONCLUSION

In a 1st-line setting, docetaxel is an effective and tolerable agent for Korean HRPC patients, and that its efficacy is limited, although 2nd-line docetaxel is tolerable.

Systemic therapy after first-line docetaxel in metastatic castration-resistant prostate cancer

PURPOSE OF REVIEW

There is an urgent need for systemic treatment options for patients with castration-resistant prostate cancer who have progressed after receiving first-line docetaxel chemotherapy. The purpose of this article is to review recent developments in this area.

RECENT FINDINGS

Retreatment with docetaxel has been employed with evidence of activity in selected populations. Mitoxantrone, the previous first-line standard based on its palliative effect, has also been used with clinical responses observed; however, the symptom benefit in this setting has not been established. Several classes of cytotoxic agents have been tested including platinum agents (satraplatin), epothilones (ixabepilone and patupilone) and taxanes (XRP-6258). A number of targeted therapies have also been clinically evaluated including inhibitors of cytoprotective chaperones (OGX-011) and the vascular endothelial growth factor receptor (sorafenib, sunitinib, and cediranib). An area generating great interest has been the development of agents that target the androgen receptor axis more effectively (MDV3100 and abiraterone) with encouraging early phase trial results.

SUMMARY

There is no accepted standard systemic treatment for patients with castration resistant prostate cancer and progressive disease after docetaxel. Novel agents are in phase II and III clinical testing in this setting.

The Canadian Uro-Oncology Group multicentre phase II study of docetaxel administered every 3 weeks with prednisone in men with metastatic hormone-refractory prostate cancer progressing after mitoxantrone/prednisone

OBJECTIVE

To investigate the use of docetaxel 75 mg/m(2) intravenously every 3 weeks plus prednisone 5 mg orally twice daily in men with metastatic hormone-refractory prostate cancer (HRPC) progressing after first-line mitoxantrone/prednisone (MP), the primary outcome being progression-free survival with prostatic-specific antigen (PSA) and pain response, toxicity and quality of life (QoL) also assessed.

PATIENTS AND METHODS

Thirty patients from four centres were enrolled in the study; all had had previous MP for symptomatic, metastatic HRPC and all had castrate levels of testosterone maintained during therapy.

RESULTS

At enrolment, the median age was 69 years, the mean PSA level was 324 ng/dL, and 86% of patients reported pain. There was a PSA response in 57% of the men and a reduction in pain in >60%; the overall QoL was maintained. There were four cases of febrile neutropenia and two treatment-related deaths. The median progression-free and overall survival were 5 and 15 months, respectively.

CONCLUSION

Docetaxel was associated with high rates of PSA and pain response in this study. Non-haematological toxicity was similar to that during first-line treatment, but rates of febrile neutropenia and toxic death appeared to be slightly higher. In selected patients with progressive metastatic HRPC previously treated with mitoxantrone, docetaxel appears to be a beneficial therapeutic option.

Survival and PSA response of patients in the TAX 327 study who crossed over to receive docetaxel after mitoxantrone or vice versa

BACKGROUND

The TAX 327 study compared 3-weekly docetaxel, weekly docetaxel or 3-weekly mitoxantrone, each with prednisone, for 1006 patients with metastatic hormone-refractory prostate cancer. Survival and symptom control were superior following 3-weekly docetaxel as compared with mitoxantrone. At progression, many patients were treated with the other drug. Here, we provide a retrospective report of survival and prostate-specific antigen (PSA) response after second-line therapy.

METHODS

The TAX 327 database provided information about treatment after progression on first-line therapy, and survival has been updated. Investigators were asked to provide information about crossover treatment and serial PSA values.

RESULTS

We identified 232 crossover patients. Median survival after crossover was 10 months and did not depend on direction of crossover. Data on PSA response are available for 96 patients: PSA response (> or =50% reduction) occurred in 15% of 71 men receiving mitoxantrone after docetaxel and in 28% of 25 men receiving docetaxel after mitoxantrone. Median PSA progression-free survival was 3.4 months for mitoxantrone after docetaxel and 5.9 months for docetaxel after mitoxantrone.

CONCLUSIONS

One quarter of men received crossover therapy and survival was similar in the crossover groups. The PSA response rate to docetaxel after mitoxantrone was higher than that for mitoxantrone after docetaxel.

Biweekly doxorubicin/ketoconazole as second-line treatment in docetaxel-resistant, hormone-refractory prostate cancer

OBJECTIVES

Docetaxel is an effective first-line treatment for hormone-refractory prostate cancer. Nevertheless, the prognosis subsequent to progression after first-line therapy is poor and no second-line treatment has been established.

METHODS

A total of 34 patients with androgen-independent prostate cancer received doxorubicin, 30 mg/m(2), every 2 weeks and ketoconazole daily, 400 mg orally every 8 hours. All patients had been treated with docetaxel and had disease progression within 6 months after completion of first-line treatment.

RESULTS

Of the 32 evaluable patients, 13 (43.7%, 95% confidence interval [CI] 26.3% to 62.3%) had a prostate-specific antigen (PSA) response, and 4 (28%, 95% CI 8.4% to 58.1%) of 14 patients with measurable disease had a response to therapy. The median time to progression (TTP) was 3.9 months (95% CI 2.0 to 5.9), and the median overall survival (OS) was 13 months (95% CI 8.7 to 17.3). Toxicity was mild, with only 4 cases of nonhematologic grade 3 or 4 toxicity. The most frequent toxicity was nail changes (33 of 34 patients), which was mainly grade 1 (30 cases).

CONCLUSIONS

The combination of biweekly doxorubicin and ketoconazole is an effective, well-tolerated, second-line therapy for hormone-refractory prostate cancer.