The epothilones: new therapeutic agents for castration-resistant prostate cancer

The management of castration-resistant prostate cancer (CRPC) presents a clinical challenge because of limitations in efficacy and durability with currently available therapeutics. The epothilones represent a novel class of anticancer therapy that stabilizes microtubules, causing cell death and tumor regression in preclinical models. The structure of the tubulin-binding site for epothilones is distinct from that of the taxanes. Moreover, preclinical studies suggest nonoverlapping mechanisms of resistance between epothilones and taxanes. In early-phase studies in patients with CRPC, treatment with ixabepilone, a semisynthetic analog of epothilone B, induced objective responses and prostate-specific antigen declines in men previously progressing on docetaxel-based regimens. Clinical activity has been observed in nonrandomized trials for patients with CRPC using ixabepilone in the first- and second-line settings as a single agent and in combination with estramustine. Patupilone and sagopilone were also shown to have promising efficacy in phase II clinical trials of patients with CRPC. All three epothilones appear to be well tolerated, with modest rates of neutropenia and peripheral neuropathy. The lack of crossresistance between epothilones and taxanes may allow sequencing of these agents. Evaluating epothilones in phase III comparative trials would provide much-needed insight into their potential place in the management of patients with CRPC.

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.

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.

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.