The combination of estramustine and mitoxantrone in hormone-refractory prostate cancer: a phase II feasibility study conducted by the Hellenic Cooperative Oncology Group

Treatment Options in Hormone-refractory Metastatic Prostate Carcinoma

Prostate cancer represents one of the most important health problems in industrialized countries. It is the second leading cause of cancer-related death in the United States. Therapeutic options are different according to the stage of the disease at the diagnosis. Patients with localized disease may be treated with surgery or radiation, whereas the treatment for patients with a metastatic disease is purely palliative. Hormonal treatment represents the standard therapy for stage IV prostate cancer, but patients ultimately become unresponsive to androgen ablation and are classified as hormone-refractory prostate cancer patients. The molecular mechanisms involved in progression in hormone resistance are characterized by mutations, down and up-regulation in the androgen receptor gene, mutations in p53 and over-expression of Bcl2 and other alterations in genes and in gene expression. The important thing is that we understand these mechanisms to define potential therapeutic agents for the treatment of hormone-refractory prostate cancer patients. Conventional options for patients with hormone-refractory prostate cancer include secondary hormone therapy, radiotherapy and cytotoxic chemotherapy. The commonest antineoplastic agents are mitoxantrone, estramustine and taxanes. Despite an improvement In the palliative benefit, none of these agents has demonstrated a beneficial impact on the overall survival of patients. Therefore, there is no standard therapy for these patients, thus we need new approaches which should be studied in clinical trials. The evaluation and incorporation of new agents into current treatment regimens could have a role in the treatment of hormone-refractory prostate cancer, but their efficacy has not yet been demonstrated.

Assessing outcomes in prostate cancer clinical trials: a twenty-first century tower of Babel

BACKGROUND

Because of the osseous distribution of prostate cancer metastases, progression is more readily identified than response in prostate cancer clinical trials. As a result, there is an increased focus on progression-free survival (PFS) as a phase 2 endpoint. PFS, however, is vulnerable to inter-study design variability. The authors sought to identify and quantify this variability and the resultant error in PFS across prostate cancer clinical trials.

METHODS

The authors reviewed phase 2 clinical trials of cytotoxic agents in castration-resistant metastatic prostate cancer over 5 years to evaluate the policies determining extent of disease and the definitions of disease progression. A simulation model was created to define the degree of error in estimating PFS in 3 hypothetical cohorts (median PFS of 12, 24, and 36 weeks) when the frequency of outcome assessments varies.

RESULTS

Imaging policies for trial entry were heterogeneous, as were the type, timing, and indications for outcome assessments. In the simulation, error in the reported PFS varied according to the interval between assessments. The difference between the detected and the true PFS could vary as much as 6.4 weeks per cycle, strictly resulting from the variability of assessment schedules tested.

CONCLUSIONS

Outcome assessment policies are highly variable in phase 2 studies of castration-resistant prostate cancer patients, despite published guidelines designed to standardize authentication of disease progression. The estimated error in PFS can exceed 6 weeks per cycle, exclusively because of variations in the assessment schedules. Comparisons of PFS times from different studies must be made with circumspection.

Changing perspectives of the role of chemotherapy in advanced prostate cancer

The use of cytotoxic chemotherapy in advanced prostate adenocarcinoma has been validated by the recent demonstration of survival benefit in two large randomized phase III trials. Before publication of these landmark trials, SWOG 9916 and TAX 327, no chemotherapeutic regimen had shown survival benefit in the treatment of androgen independent prostate cancer (AIPC). These trials provide new encouragement for the use of chemotherapy in all stages of disease. Improved communication between medical and urologic oncologists and early patient referral for clinical trial participation remains essential for identifying new chemotherapeutic regimens with improved activity in AIPC and for defining the role of chemotherapy in earlier-stage disease. This article discusses the role of chemotherapy as the current standard of care for the treatment of AIPC and provides a historical perspective of the trials that preceded the development of current docetaxel-based regimens.

New standards in the chemotherapy of metastatic hormone-refractory prostate cancer

Hormone-refractory prostate cancer (HRPC) is a major issue in Western countries and the second leading cause of cancer death in North American men. In the prostate-specific antigen era, most HRPCs are currently diagnosed in asymptomatic patients based on biochemical failure, with increasing demand for active treatment. Until recently, chemotherapy for HRPC patients was not considered a standard of care due to the absence of clear data evidencing an overall survival benefit. In fact, few Phase III studies conducted in the 1980s and early 1990s had documented a superiority over corticosteroids alone in terms of biochemical response (declines in serum prostate-specific antigen levels) and quality of life, but not survival. Due to their impact on pain control, mitoxantrone and prednisone were long considered the best regimen for symptomatic HRPC patients. In recent years, more chemotherapeutic agents have been tested, among which the microtubule inhibitors (vinca alkaloids and taxanes) have obtained the most promising results in Phase II trials and have entered Phase III testing. Two well-designed randomized trials have changed this scenario. Both compared docetaxel (with or without estramustine) against mitoxantrone and prednisone, and demonstrated a significant advantage not only in terms of response, pain control and quality of life, but also in terms of overall survival. Which patients need to be treated, the regimen of choice and duration of chemotherapy will be the next questions to be answered in the coming years in the field of HRPC, along with the role of new signal transduction inhibitors and other targeted therapies.

The combination of estramustine, vinorelbine, and mitoxantrone in hormone-refractory prostate cancer: a Phase II feasibility study conducted by the Hellenic Cooperative Oncology Group

OBJECTIVES

To evaluate the safety profile and therapeutic value of the combination of estramustine, mitoxantrone, and vinorelbine in the treatment of hormone-refractory prostate cancer.

METHODS

Fifty-two patients with hormone-refractory prostate cancer were included in the study. Median age was 70 years (range, 49 to 100 years), World Health Organization performance status ranged from 0 to 2. The treatment schedule consisted of estramustine capsules (140 mg 3 times daily on days 1 to 3 and days 8 to 10 per os), intravenous mitoxantrone (12 mg/m2 on day 2), and intravenous vinorelbine (25 mg/m2 on day 2 and day 9), given in a 3-week cycle.

RESULTS

Thirty-one percent of patients with measurable soft-tissue disease demonstrated an objective response, which included six complete and ten partial responses in all involved organs (bone responses not included). Twenty-nine patients (56%) had a greater than 50% reduction in serum prostate-specific antigen level. The median duration of response was 6.9 months, and the median survival for all patients was 14.5 months.

CONCLUSIONS

The combination of estramustine, vinorelbine, and mitoxantrone is safe, well tolerated, and relatively active in patients with hormone-refractory prostate cancer.

The novel estrogen 17α-20Z-21-[(4-amino)phenyl]-19-norpregna-1,3,5(10),20-tetraene-3,17β-diol induces apoptosis in prostate cancer cell lines at nanomolar concentrations in vitro

Prostate cancer remains the number one cause of noncutaneous cancer, with 220,900 new cases predicted for the year 2003 alone. Of the more promising classes of compounds studied thus far for the treatment of prostate cancer, estrogens of various types have consistently exhibited antitumor activities both in vitro and in vivo. For this reason, we have synthesized and screened a library of unique 17α/11β modified 17β-estradiol (E2) analogues designed for estrogen receptor β (ER-β) specificity and a potential for cytotoxic activity directed toward prostate cancer cells. From this library, the novel compound 17α-20Z-21-[(4-amino)phenyl]-19-norpregna-1,3,5(10),20-tetraene-3,17β-diol (APVE2) was identified as the primary lead, found to induce a high level (>90%) of cell death through an apoptotic mechanism, with an EC50 of 1.4, 2.7, and 16 nm in the LNCaP, PC3, and DU145 cell lines, respectively. APVE2 was found to bind to ER-β, albeit weakly, with an EC50 of 250 nm and a binding activity of 6.2% relative to E2, nearly two orders of magnitude less than the concentration required to induce apoptosis. APVE2 bound preferentially to ER-β by 7-fold over ER-α, and did not induce growth in the MCF-7 cell line, thus indicating that it is not a classical ER agonist. Furthermore, the cytotoxic actions of APVE2 were not reversed by co-treatment with a 50-fold excess E2. In summary, a novel 17 modified estrogen APVE2 was identified as a lead compound, capable of inducing apoptosis in three prostate cancer cell lines at low nanomolar concentrations, through a mechanism inconsistent with an ER-mediated mechanism.

Update on hormone-refractory prostate cancer

PURPOSE OF REVIEW

Androgen deprivation therapy is the cornerstone treatment for men with de novo or recurrent metastatic prostate cancer. Unfortunately, androgen deprivation therapy is primarily palliative, with nearly all men progressing to an androgen-independent state. Hormone-refractory prostate cancer presents significant management challenges and is the focus of this review.

RECENT FINDINGS

Investigations into the pathophysiology of hormone-refractory prostate cancer, the exploration of chemotherapeutic combinations, novel biological targets, skeletal protectants, and radiopharmaceuticals, as well as new prognostic tools are expanding the clinician's armamentarium and improving patient outcomes.

SUMMARY

Bisphosphonates and chemotherapy are providing effective palliative approaches. Phase II trials of taxane-based regimens show higher response rates and longer survival than has typically been achieved with existing standards. Two completed randomized phase III studies to be reported in mid-2004 will more definitively answer the question of whether currently available chemotherapy can improve survival.