Innovations in the systemic therapy of prostate cancer

Systemic therapy has become an increasingly important component of treatment of advanced prostate cancer. In the past decade, important innovations have been achieved in the development of novel systemic hormonal therapies for the salvage treatment of metastatic castrate-resistant disease. These improvements have been accompanied by the broadening of potential indications for chemotherapy in castrate-resistant metastatic disease and the use of chemotherapy as an adjunct to the treatment of locally extensive tumors. These changes have begun to lead to improved outcomes, but at the expense of novel patterns of late toxic effects. We review the key steps in the recent evolution of systemic therapy of prostate cancer.

Epothilones: a novel class of microtubule-stabilizing drugs for the treatment of cancer

Microtubule-targeted anticancer drugs are effective in treating various cancers but are limited in use due to development of resistance and unacceptable toxicities. The epothilones are a novel class of microtubule-stabilizing anticancer drugs and may have a role in treating taxane-resistant cancers. Revised and updated data from several clinical studies for ixabepilone were recently published and subsequently resulted in ixabepilone becoming the first epothilone approved as monotherapy or in combination for treatment of locally advanced or metastatic breast cancer. BMS-310705, patupilone, KOS-862, KOS-1584 and ZK-EPO are epothilones that have been developed. Although peripheral sensory neuropathy and neutropenia are the dose-limiting toxicities for ixabepilone, these dose-limiting toxicities are ixabepilone specific. This review will discuss the current preclinical, clinical pharmacokinetic and pharmacodynamic, efficacy and toxicity data of the epothilones.

Systemic nonhormonal management of advanced prostate cancer and its likely impact on patients' survival and quality of life

Prostate cancer is a hormonal sensitive disease with a response rate ranging from 80 to 90%; however, the majority of patients develop hormone resistance resulting in poor long term survival. Chemotherapy has demonstrated a benefit over steroids in improving the quality of life in the hormone refractory phase. Furthermore, the introduction of docetaxel succeeded in improving the survival of these patients in first-line therapy. Second-line treatment following docetaxel is challenging with no agent classified as standard in this setting. In the last 5 years, several drugs have shown promising results in initial evaluation. However, randomized phase III trials would be needed to answer this question. The majority of patients develop bone metastasis and the use of bisphosphonates has yielded encouraging results. Our understanding of the biology of hormone refractory prostate cancer has improved dramatically over the past few years and has translated into the developments of new therapeutic targets for this disease. Agents affecting several targets, including calcitriol, endotheline-1, bcl-2, and angiogenesis, are being studied currently and have the potential to change the treatment paradigms of this otherwise fatal disease. This review focuses on current and potential treatment options, including cytotoxic agents, bisphosphonates, and targeted agents, for patients with hormone refractory prostate cancer and the impact of these options on survival and quality of life.

Therapeutic options for hormone-refractory prostate cancer in 2007

Prostate cancer is the most commonly diagnosed cancer in American men and a major health problem. While localized disease has an excellent chance for cure, metastatic disease leads to androgen-independent progression and death within a few years. Although docetaxel represents an important therapeutic milestone and is the current standard of care for metastatic hormone-refractory prostate cancer (HRPC), most patients eventually progress because of clonal selection of therapy-resistant cells or the development of cells with a drug-resistant phenotype. By understanding the molecular basis of resistance to androgen withdrawal and chemotherapy, the rational design of targeted therapeutics is possible. Over the last few years, many gene targets that regulate apoptosis, proliferation, and cell signalling have been identified, and numerous novel compounds have entered clinical trials either as single agents or in combination with cytotoxic chemotherapy. Neoadjuvant trials in particular must be further encouraged since they allow detection of biological activity in the prostatectomy specimen. This article reviews new treatment options available for men with advanced prostate cancer. Even though HRPC remains incurable, it is not untreatable. Recent findings are very promising, but challenges remain in demonstrating effective anti-tumor activity and showing a clinically relevant survival benefit in Phase III trials.

Efficacy and Safety of Ixabepilone (BMS-247550) in a Phase II Study of Patients With Advanced Breast Cancer Resistant to an Anthracycline, a Taxane, and Capecitabine

Purpose

To evaluate the efficacy and safety of ixabepilone in patients with metastatic breast cancer (MBC) resistant to anthracycline, taxane, and capecitabine, in this multicenter, phase II study.

Patients and Methods

Patients with measurable disease who had tumor progression while receiving prior anthracycline, taxane, and capecitabine were enrolled. Ixabepilone 40 mg/m2monotherapy was administered as a 3-hour intravenous infusion on day 1 of a 21-day cycle. The primary end point was objective response rate (ORR), assessed by an independent radiology facility (IRF).

Results

A total of 126 patients were treated and 113 were assessable for response. Patients were heavily pretreated: 88% had received at least two lines of prior chemotherapy in the metastatic setting. IRF-assessed ORR was 11.5% (95% CI, 6.3% to 18.9%) for response-assessable patients. Investigator-assessed ORR for all treated patients was 18.3% (95% CI, 11.9% to 26.1%). Fifty percent of patients achieved stable disease (SD); 14.3% achieved SD ≥ 6 months. Median duration of response and progression-free survival were 5.7 and 3.1 months, respectively. Median overall survival was 8.6 months. Patients received a median of 4.0 treatment cycles (range, one to 16 cycles), and 25% of patients received ≥ eight cycles. Grade 3/4 treatment-related events included peripheral sensory neuropathy (14%), fatigue/asthenia (13%), myalgia (8%), and stomatitis/mucositis (6%). Resolution of grade 3/4 peripheral sensory neuropathy occurred after a median period of 5.4 weeks.

Conclusion

Ixabepilone demonstrated clear activity and a manageable safety profile in patients with MBC resistant to anthracycline, taxane, and capecitabine. Responses were durable and notable in patients who had not previously responded to multiple prior therapies.

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.