A retrospective evaluation of second-line chemotherapy response in hormone-refractory prostate carcinoma

Novel non-AR therapeutic targets in castrate resistant prostate cancer

Castrate resistant prostate cancer (CRPC) remains a disease with significant morbidity and mortality. The recent approval of abiraterone and enzalutamide highlight the improvements which can be made targeting the androgen receptor (AR) axis. Nonetheless, resistance inevitably develops and there is continued interest in targeting alternate pathways which cause disease resistance and progression. Here, we review non-AR targets in CRPC, with an emphasis on novel agents now in development. This includes therapeutics which target the tumour microenvironment, the bone metastatic environment, microtubules, cellular energetics, angiogenesis, the stress response, survival proteins, intracellular signal transduction, DNA damage repair and dendritic cells. Understanding the hallmarks of prostate cancer resistance in CRPC has led to the identification and development of these new targets. We review the molecular rationale, as well at the clinical experience for each of these different classes of agents which are in clinical development.

Neurotoxicity as a prognostic factor in patients with metastatic breast cancer treated with ixabepilone as a first-line therapy

OBJECTIVE

This study is a longitudinal follow-up of metastatic breast cancer patients treated with ixabepilone as first-line chemotherapy, with the aim to evaluate the association between a mechanism-based neurotoxicity and the efficacy of ixabepilone.

PATIENTS AND METHODS

At the 2 main investigational sites of a phase II clinical trial, 50 patients previously treated with anthracycline received ixabepilone. A chart review was performed to evaluate overall survival (OS) and time to progression (TTP) and to describe the subsequent treatments.

RESULTS

The severe neurotoxicity induced by ixabepilone (38%) is correlated with a higher overall response rate to ixabepilone (79 vs. 48%; p = 0.042), a longer TTP (11.4 vs. 6.8 months; p = 0.023) and a longer OS (36.6 vs. 19.9 months; p = 0.05). After ixabepilone discontinuation, patients received a median of 4 subsequent chemotherapy lines (range 1-12). Among the 31 patients who received taxanes, neither the neurotoxicity incidence under treatment with taxanes nor the response was affected by a previous occurrence under ixabepilone treatment.

CONCLUSION

These findings suggest that neurotoxicity development under ixabepilone treatment is a predictor of treatment outcomes as well as a favorable prognostic factor. It highlights the risk-to-benefit ratio issue of ixabepilone. We noticed the possibility to treat patients with taxanes after ixabepilone without systematic recurrent neurotoxicity.

Evolving landscape and novel treatments in metastatic castrate-resistant prostate cancer

Treatment options for castrate-resistant prostate cancer (CRPC) have advanced in recent years and significantly improved the outlook for patients with this aggressive and lethal disease. Further understanding of the biology of CRPC has led to several new targeted therapies and continues to emphasize the importance of androgen receptor (AR) directed therapy. The treatment landscape is rapidly changing and further biologically rationale, biomarker-based ongoing clinical trials are needed. We review the recent results of major clinical trials in CRPC. New and investigational agents now in clinical evaluation are reviewed including inhibitors of angiogenesis, microtubules, chaperones, AR and intracellular kinases, as well as immunotherapy, radiopharmaceuticals and bone-targeted agents. The recent improvement in prognosis for CRPC brings continued optimism for further improvements. Thoughtful planning of clinical trials and further understanding of the mechanisms of resistance to therapies will allow for continued progress in patient care.

Novel therapeutics for the management of castration-resistant prostate cancer (CRPC)

Androgen-deprivation therapy is the initial treatment for metastatic prostate cancer. Although highly effective, all men who live long enough will eventually experience disease progression and develop castration resistance. Patients who have castration-resistant prostate cancer (CRPC) have a median survival of ≈1-3 years. When evaluating novel therapies for CRPC, one must consider the endpoints measured for determination of response. We will discuss PSA, circulating tumour cells, progression-free survival, overall survival, and other endpoints used in clinical trials. Docetaxel and sipuleucel-T are currently the preferred first-line treatment options for patients with CRPC; cabazitaxel is a new option for patients after docetaxel failure. Patients with CRPC historically have very poor survival, underscoring the unmet need for novel therapeutics. Although many agents appear promising, well-designed randomized phase III trials are necessary to establish their impact on survival and health-related quality of life. Promising new therapies include hormonal agents, such as abiraterone and MDV3100, as well as other novel immunotherapeutics and anti-prostate-specific membrane antigen therapies. In the future, we anticipate therapies tailored to individual patients' malignancies using various molecular analyses.

[Chemotherapy of hormonorefractory and hormonoresistant metastatic prostate cancer]

Since 2004 and the first improvement in overall survival in hormone refractory prostate cancer patients (HRPC) brought about by docetaxel, numerous phase II and III studies have been initiated. Considering the lack of efficacy in terms of overall survival, hormonal manipulations such as antiandrogen withdrawal, di-ethylstilbesterol or dexamethason are only indicated in "rising PSA" patients without clinical or radiological evidence of metastases. As first line treatment, the optimal chemotherapy regimen is docetaxel (75 mg/m(2) every 3 weeks) in association with prednisone (5 mg twice daily). Second line chemotherapies (mitoxantron, ixabepilon, docetaxel as a re-treatment, vinorelbin, doxorubicin...) provide modest results only in terms of progression-free survival. A phase III study of Straplatin has been prematurely interrupted. Targeted anti-angiogenic therapies have shown encouraging results in patients with metastatic localizations, and underline the need to identify target patients early through cellular markers (mTOR or EGFR overexpression) as well as the uselessness of PSA dosage to monitor efficacy. An ongoing phase III study is evaluating bevacizumab in association with docetaxel to improve overall survival. Both the Provenge vaccine and DN 101 (calcitriol) showed a survival gain of a few months in phase III studies. An ongoing EORTC phase II trial is evaluating antisense oligonucleotids in HRPC. Early introduction of docetaxel raises the issue of when to start chemotherapy as it may be relevant to initiate this treatment before the onset of hormone independence. GETUG 15 trial will try to answer this question.

Microtubule active agents: beyond the taxane frontier

Microtubules are essential to cell transport, signaling, and mitosis. An increasing range of anticancer drugs interferes with the normal formation and function of microtubules. Vinca alkaloids act as microtubule destabilizers and the taxanes act as microtubule stabilizers. Taxanes are widely used cytotoxic agents that are active in a range of solid tumor malignancies and are routinely used in a variety of settings. Significant limitations with the taxanes exist, including acquired and intrinsic tumor resistance through the expression of multidrug resistance proteins such as P-glycoprotein, risk of hypersensitivity reactions, dose-limiting hematopoietic toxicity, and cumulative neurotoxicity. Hence, there is a need to develop novel agents that act on the microtubules. Epothilones are macrolide antibiotics that bind near the taxane-binding site on microtubules and have been extensively studied in recent and ongoing clinical trials. A variety of other agents that act on the microtubules at different sites with a variety of structures are at varying stages of development.

Ixabepilone: a new antimitotic for the treatment of metastatic breast cancer

OBJECTIVE

To evaluate the safety and efficacy of ixabepilone as a new antimitotic chemotherapeutic agent for the treatment of breast cancer.

DATA SOURCES

Data were identified by searches of MEDLINE, PubMed, and American Society of Clinical Oncology abstracts from 1966 to March 2008, using the primary search terms ixabepilone, epothilones, BMS-247550, and breast cancer.

STUDY SELECTION AND DATA EXTRACTION

Phase 1, Phase 2, and Phase 3 clinical trials examining the safety and efficacy of ixabepilone and its place in cancer treatment were reviewed. Preference was given to large Phase 2 and 3 clinical trials in the breast cancer population. Manufacturer product information was used to supplement data lacking in published trials.

DATA SYNTHESIS

Ixabepilone belongs to a novel class of drugs, the epothilones, which are nontaxane microtubule-stabilizing agents. Ixabepilone, in combination with capecitabine, has been approved by the Food and Drug Administration for treatment in patients with metastatic or locally advanced breast cancer that progresses after anthracycline and taxane therapy, or in patients with taxane-resistant cancer with contraindication to further anthracycline therapy. Ixabepilone has also been approved as monotherapy in patients with metastatic and locally advanced breast cancer refractory to taxanes, anthracyclines, and capecitabine. The most common adverse reactions reported by 20% or more of the patients receiving ixabepilone were peripheral sensory neuropathy, fatigue/asthenia, myalgia/arthralgia, alopecia, nausea, vomiting, stomatitis/mucositis, diarrhea, and musculoskeletal pain. The most common hematologic abnormalities seen in more than 40% of the patients include neutropenia, leukopenia, anemia, and thrombocytopenia. Premedication with histamine H(1) and H(2) antagonists is recommended to prevent hypersensitivity reactions.

CONCLUSIONS

Based on the clinical trials reviewed here and the current information available, ixabepilone is a welcome addition to the options available for the treatment of patients with metastatic breast cancer refractory to standard therapy.

Epothilones and new analogues of the microtubule modulators in taxane-resistant disease

BACKGROUND

Microtubule-stabilising agents typified by the epothilone class of drug have demonstrated promising activity in Phase II and III clinical trials.

OBJECTIVE

Data supporting the efficacy of these agents are reviewed and their potential use in taxane-refractory disease assessed.

METHODS

Preclinical evidence assessing the role of the spindle assembly checkpoint in determining the cellular response to microtubule stabilization are presented together with clinical data documenting the efficacy of non-taxane microtubule modulators.

RESULTS/CONCLUSIONS

Evidence suggests that microtubule-stabilising agents prolong activation of the spindle assembly checkpoint which may promote cancer cell death in mitosis or following mitotic exit. A weakened spindle assembly checkpoint is associated with altered sensitivity to agents targeting the microtubule and therefore pathways of drug resistance may be shared by these cytotoxic therapies. Preliminary clinical trial data do suggest modest activity of epothilones in truly taxane-resistant patient cohorts, indicating the potential niche for these agents in a molecularly undefined patient group, potentially implicating the role of P-glycoprotein in the acquisition of taxane-resistant disease. Trial data of these antimitotic agents will be presented together with their potential role in taxane-resistant disease and the implications for future clinical trial design.

Taxane refractory prostate cancer

PURPOSE

Although docetaxel based therapy has become established as a front line therapy choice based on large, randomized studies, published studies of second line therapy for taxane refractory disease are limited.

MATERIAL AND METHODS

The literature on the biology of taxane resistance and studies applied to prostate cancer were reviewed using a PubMed(R) search and proceedings from recent symposia.

RESULTS

Although taxane resistance invariably emerges in the treatment of prostate cancer, a consensus working definition or classification does not exist. Although there is a body of knowledge on the mechanisms of action of taxanes and resistance pathways, there are few clinical or translational studies in prostate cancer adequately assessing the modulation of these mechanisms. Results of additional clinical trials are needed to define and improve the standard of care in the second line setting for castration resistant prostate cancer after docetaxel failure.

CONCLUSIONS

The validation of the microtubule as a target in prostate cancer implies that a finer understanding of specific mechanisms of efficacy and resistance may yield novel strategies. Taxane analogues that have greater antitumor activity and/or are less susceptible to drug resistance mechanisms than their prototypes are in development, as are nontaxane microtubule targeting agents and other agents directed against the mitotic spindle. Combinations of such agents may yield added efficacy but potentially added neurotoxicity. In contrast, combinations with drugs that inhibit cellular mechanisms of taxane resistance and vascular endothelial or tumor-stromal prosurvival interactions may have lower neurotoxic profiles. Although alternate classes of cytotoxic agents, eg satraplatin, are being studied, there is a strong imperative for translational studies in this setting.

Epothilones in prostate cancer: review of clinical experience

BACKGROUND

Hormone-refractory prostate cancer (HRPC) is a progressive chemotherapy-resistant disease that remains a challenge to manage. Despite the recent approval of docetaxel (Taxotere) for the treatment of HRPC, the need exists for additional novel agents that can further improve patient outcomes. The epothilones are potent antimicrotubule agents that have demonstrated activity in the setting of taxane resistance. They are structurally distinct compounds that appear to lack cross-resistance with the taxanes.

DESIGN

This review summarizes current preclinical and clinical data on the safety and efficacy of the epothilones ixabepilone (BMS-247550) and patupilone (EPO906) for the treatment of prostate cancer. Data were identified by searches of PubMed and the Proceedings of the American Society of Clinical Oncology annual meetings from 2000 to 2006.

RESULTS

The epothilones have demonstrated potent antitumor activity in vitro and in experimental animal models of prostate cancer. In clinical studies, the epothilones have demonstrated potent activity in HRPC, including no cross-resistance with the taxanes and a manageable toxicity profile. Phase II studies of single-agent ixabepilone in patients with HRPC have reported a confirmed prostate-specific antigen (PSA) response rate of 33%. Higher PSA response rates have been reported in studies that assessed the combination of ixabepilone and estramustine in patients with HRPC.

CONCLUSIONS

The epothilones are promising new chemotherapeutic agents that have demonstrated single-agent antitumor activity in HRPC in the phase II setting. Phase III trials are needed to confirm the activity of the epothilones in tandem with docetaxel, given the experience to date.

Anticancer drugs from nature--natural products as a unique source of new microtubule-stabilizing agents

This review article provides an overview on the current state of research in the area of microtubule-stabilizing agents from natural sources, with a primary focus on the biochemistry, biology, and pharmacology associated with these compounds. A variety of natural products have been discovered over the last decade to inhibit human cancer cell proliferation through a taxol-like mechanism. These compounds represent a whole new range of structurally diverse lead structures for anticancer drug discovery.

Effective chemotherapy for hormone-refractory prostate cancer (HRPC): Present status and perspectives with taxane-based treatments

Prostate cancer is a significant health concern for men worldwide. It continues to be the most common lethal malignancy diagnosed in American men and the second leading cause of male cancer mortality. Hormone-refractory prostate cancer (HRPC) remains clinically challenging. Two large phase III studies have demonstrated a survival advantage in HRPC patients utilizing docetaxel chemotherapy, setting a new standard of care for this disease. This paper examines the progress that has been made in HRPC with the Taxanes (Docetaxel, Paclitaxel, and Epothilones) with a glimpse on mechanisms of resistance and on combinations able to overcome it. In addition, new targeted therapies under development in combination with taxanes are reviewed with an explanation of their molecular mechanisms of action.

Advances in Prostate Cancer Immunotherapies

Prostate cancer is a major cause of mortality in men in the Western world. Although treatment of early stage prostate cancer with radiation therapy or prostatectomy is efficient in most cases, some patients develop a fatal hormone-refractory disease. Treatments in this case are limited to aggressive chemotherapies, which can reduce serum prostate-specific antigen (PSA) levels in some patients. Taxane- and platinum-compound-based chemotherapies produce a survival benefit of only a few months. Therefore, it is crucial to develop novel, well tolerated treatment strategies. Over the past years, immunotherapy of hormone-refractory prostate cancer has been studied in numerous clinical trials. The fact that the prostate is a non-essential organ makes prostate cancer an excellent target for immunotherapy. Administration of antibodies targeting the human epidermal growth factor receptor-2 or the prostate-specific membrane antigen led to stabilisation of PSA levels in several patients. Vaccination of prostate cancer patients with irradiated allogeneic prostate cell lines has demonstrated that whole cell-based vaccines can significantly attenuate increases in PSA. Two different recombinant viral expression vectors have been applied in prostate cancer treatment: poxvirus and adenovirus vectors. Both vaccines have the advantages of using a natural method to induce immune responses and achieving high levels of transgene expression. Vaccinia viruses in combination with recombinant fowlpox or canarypox virus have been used to express recombinant PSA. Several studies demonstrated that this approach is safe and can lead to stabilisation of PSA values. A very promising approach in prostate cancer immunotherapy is vaccination of patients with dendritic cells. Thereby, peptides, recombinant proteins, tumour lysates or messenger RNA have been used to deliver antigens to autologous dendritic cells. Loading of dendritic cells with up to five different peptides derived from multiple proteins expressed in prostate cancer demonstrated that cytotoxic T-cell responses could be elicited in prostate cancer patients. Sipuleucel-T (APC8015), an immunotherapy product consisting of antigen-presenting cells, loaded ex vivo with a recombinant fusion protein consisting of prostatic acid phosphatase linked to granulocyte-macrophage colony-stimulating factor, demonstrated in a phase III, placebo-controlled trial an improvement in median time to disease progression. The improvement in overall survival was 4.5 months for sipuleucel-T-treated patients compared with the placebo group. Although there is a minor increase in overall survival of metastatic prostate cancer patients with some approaches, more effective therapeutic strategies need to be developed.

Activity of second-line chemotherapy in docetaxel-refractory hormone-refractory prostate cancer patients

BACKGROUND

This randomized, noncomparative, multicenter, clinical trial evaluated ixabepilone or mitoxantrone/prednisone (MP) as second-line chemotherapy for taxane-refractory, hormone-refractory, prostate cancer (HRPC).

METHODS

Patients with HRPC that progressed during or within 60 days of cessation of taxane chemotherapy were randomly selected with equal probability to ixabepilone 35 mg/m(2) intravenously every 3 weeks, or mitoxantrone 14 mg/m(2) intravenously every 3 weeks and prednisone 5 mg orally twice daily. Treatment continued until progression or toxicity; crossover was allowed.

RESULTS

Forty-one patients were accrued to each arm of the study. The median number of cycles administered for each arm was 3. Median survival from protocol entry was 10.4 months with ixabepilone and 9.8 months with MP. Prostate-specific antigen (PSA) declines of >or=50% were observed in 17% of ixabepilone (95% CI, 7-32) and 20% of second-line MP patients (95% CI, 9-35). Partial responses were observed in 1 of 24 ixabepilone and in 2 of 21 MP patients with evaluable measurable disease. Median duration of second-line ixabepilone and MP treatment was 2.2 months and 2.3 months, respectively. For third-line crossover treatment, PSA declines of >or=50% were observed in 3 of 27 ixabepilone-treated and 4 of 15 MP-treated patients. Prior taxane response was associated with an increased likelihood of second-line ixabepilone or MP response. Low baseline lactate dehydrogenase and absence of visceral metastases independently predicted improved survival. The most common grade 3/4 toxicity associated with second-line treatment was neutropenia (54% of ixabepilone patients and 63% of MP patients).

CONCLUSIONS

Ixabepilone and MP had modest activity as second-line chemotherapy for docetaxel-refractory HRPC. The median survival for the entire cohort treated in this study was 9.8 months.