Novel Agents and Targets in Managing Patients with Metastatic Prostate Cancer

Background

Docetaxel has recently been found to improve survival in patients with metastatic androgen-independent prostate cancer (AIPC). Chemotherapy as a first-line option leaves room for improvement, while second-line options are multiple and somewhat controversial.

Methods

Clinically relevant articles focusing on chemotherapy drugs for metastatic prostate cancer and their mechanism of action and efficacy were reviewed from January 2004 through April 2006.

Results

Docetaxel is the standard of care for AIPC. However, for doublets with docetaxel or second-line chemotherapy, multiple studies have shown interesting and promising results with calcitriol, thalidomide, bevacizumab, satraplatin, vaccines, ixabepilone, and atrasentan.

Conclusions

Docetaxel should be considered for first-line treatment of metastatic AIPC. Due to its progression-free survival of only 6 months, more effective drugs and drug combinations need to be developed to treat patients with AIPC. Combination treatments with docetaxel and other new agents are promising, but adequately powered phase III trials need to be conducted with survival as the principal endpoint for these promising drug combinations.

Early growth inhibition is followed by increased metastatic disease with vitamin D (calcitriol) treatment in the TRAMP model of prostate cancer

The active metabolite of vitamin D₃, 1,25-dihydroxyvitamin D₃ (calcitriol) has antiproliferative effects in non-aggressive prostate cancer, however, its effects in more aggressive model systems are still unclear. In these studies, effects of calcitriol and a less-calcemic vitamin D analog, QW-1624F₂-2 (QW), were tested in vivo, using the aggressive autochthonous transgenic adenocarcinoma of mouse prostate (TRAMP) model. To study prevention of androgen-stimulated prostate cancer, vehicle, calcitriol (20 µg/kg), or QW (50 µg/kg) were administered to 4 week-old TRAMP mice intraperitoneal (i.p.) 3×/week on a MWF schedule for 14 weeks. Calcitriol and QW slowed progression of prostate cancer as indicated by reduced urogenital tract (p = 0.0022, calcitriol; p = 0.0009, QW) and prostate weights (p = 0.0178, calcitriol; p = 0.0086, QW). However, only calcitriol increased expression of the pro-differentiation marker, cadherin 1 (p = 0.0086), and reduced tumor proliferation (p = 0.0467). By contrast, neither vitamin D analog had any effect on castration resistant prostate cancer in mice treated pre- or post-castration. Interestingly, although vitamin D showed inhibitory activity against primary tumors in hormone-intact mice, distant organ metastases seemed to be enhanced following treatment (p = 0.0823). Therefore, TRAMP mice were treated long-term with calcitriol to further examine effects on metastasis. Calcitriol significantly increased the number of distant organ metastases when mice were treated from 4 weeks-of-age until development of palpable tumors (20–25 weeks-of-age)(p = 0.0003). Overall, data suggest that early intervention with vitamin D in TRAMP slowed androgen-stimulated tumor progression, but prolonged treatment resulted in development of a resistant and more aggressive disease associated with increased distant organ metastasis.

Evolving treatment paradigms for locally advanced and metastatic prostate cancer

While men with early stage prostate cancer typically enjoy long-term survival after definitive management, for those who present with locally advanced or metastatic disease, survival is compromised. Multimodality therapy can prolong survival in these patients, with state-of-the-art options including intensity-modulated radiation or brachytherapy in conjunction with androgen ablation, adjuvant androgen ablation and/or chemotherapy with radical retropubic prostatectomy. In addition, novel biological therapies are being explored to target the unique molecular changes in prostate cancer cells and their interactions with the microenvironment. With these advances the outlook will undoubtedly improve, even for patients presenting with advanced disease. Careful application of these emerging therapies to a select group of prostate cancer patients most likely to obtain benefit from them is the challenge for urologists, medical oncologists and radiation oncologists for the future.

Prediction of survival following first-line chemotherapy in men with castration-resistant metastatic prostate cancer

PURPOSE

We sought to evaluate predictors of overall survival following progression after systemic chemotherapy in men with metastatic castration-resistant prostate cancer.

EXPERIMENTAL DESIGN

For our study population, we used the TAX327 multicenter randomized phase III trial comparing administration of docetaxel and prednisone every 3 weeks, weekly administration of docetaxel and prednisone, and administration of mitoxantrone and prednisone every 3 weeks. Progression was defined as the earliest of prostate-specific antigen (PSA), tumor, or pain progression. We analyzed predictors of postprogression survival according to both prechemotherapy and postchemotherapy variables with adjustment for potential confounders.

RESULTS

Among 1,006 men, 640 had evaluable information on protocol-defined progression leading to further therapy. Median postprogression survival was 14.5 months. In the multivariable analysis, several pretreatment factors were associated with postprogression survival: pain, performance status, alkaline phosphatase, number of sites of metastatic disease, liver metastases, hemoglobin, PSA, and time since diagnosis. In addition, we found that the number of progression factors (PSA, pain, and tumor size), the duration of first-line chemotherapy, and whether progression occurred during chemotherapy independently predicted postprogression survival. We found evidence for the benefit of continuation of chemotherapy beyond progression only for men who had isolated worsening of pain. A nomogram was constructed and internally validated with a concordance index of 0.70.

CONCLUSIONS

An internally validated model to predict postchemotherapy survival was developed. Evaluation of men in the postdocetaxel setting should consider the type of progression, duration of therapy, and known pretreatment prognostic factors. Definitions of progression in castration-resistant prostate cancer that include pain should also consider composite measures of tumor or PSA progression. External validation is planned.

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.

Calcitriol as a chemopreventive and therapeutic agent in prostate cancer: role of anti-inflammatory activity

Calcitriol, the hormonally active form of vitamin D, inhibits the growth and development of several cancers. Inflammation has been implicated in the development and progression of many cancers, including prostate cancer (PCa). Recent research from our laboratory suggests that calcitriol exhibits anti-inflammatory actions that may contribute to its inhibitory effects in PCa. We found that calcitriol inhibits the synthesis and actions of pro-inflammatory prostaglandins (PGs) by three mechanisms: (1) inhibition of the expression of cyclooxygenase-2 (COX-2), the enzyme that synthesizes PGs, (2) induction of the expression of 15-prostaglandin dehydrogenase (15-PGDH), the enzyme that inactivates PGs, and (3) decreasing the expression of prostaglandin E and prostaglandin F PG receptors, which are the mediators of PG signaling. The combination of calcitriol and nonsteroidal anti-inflammatory drugs (NSAIDs) result in a synergistic inhibition of PCa cell growth and offers a potential therapeutic strategy. Acting on a separate anti-inflammatory pathway, calcitriol induces the expression of mitogen-activated protein kinase phosphatase 5 (MKP5), a member of a family of phosphatases that are negative regulators of MAP kinases, causing the selective dephosphorylation and inactivation of the stress-activated protein kinase p38. Because p38 activation may be both procarcinogenic and promote inflammation, this calcitriol action, especially coupled with the inhibition of the PG pathway, may contribute to the chemopreventive activity of calcitriol. We conclude that calcitriol exerts several anti-inflammatory actions in prostate cells, which contribute to its potential as a chemopreventive and therapeutic agent in PCa.

A phase I pharmacokinetic and pharmacodynamic study of intravenous calcitriol in combination with oral gefitinib in patients with advanced solid tumors

PURPOSE

In preclinical models, calcitriol and the tyrosine kinase inhibitor gefitinib are synergistic and modulate extracellular signal-regulated kinase (Erk) and Akt pathways. Therefore, we conducted a phase I study of calcitriol and gefitinib to determine the maximum tolerated dose (MTD) of this combination.

EXPERIMENTAL DESIGN

Calcitriol was given i.v. over 1 h on weeks 1, 3, and weekly thereafter. Gefitinib was given at a fixed oral daily dose of 250 mg starting at week 2 (day 8). Escalation occurred in cohorts of three patients until the MTD was defined. Pharmacokinetic studies were done for calcitriol and gefitinib. Serial skin biopsies were done to investigate epidermal growth factor receptor (EGFR) pathway pharmacodynamic interactions.

RESULTS

Thirty-two patients were treated. Dose-limiting hypercalcemia was noted in two of four patients receiving 96 mug/wk of calcitriol. One of seven patients developed dose-limiting hypercalcemia at the MTD 74 mug/wk calcitriol dose level. The relationship between calcitriol dose and peak serum calcitriol (C(max)) and systemic exposure (AUC) was linear. Mean (+/-SD) serum calcitriol C(max) at the MTD was 6.68 +/- 1.42 ng/mL. Gefitinib treatment inhibited EGFR, Akt, and Erk phosphorylation in the skin. Calcitriol did not have consistent effects on skin EGFR or its downstream elements. The combination of gefitinib and calcitriol did not modulate tumor EGFR pathway in patients with serial tumor biopsies.

CONCLUSIONS

High doses of weekly i.v. calcitriol can be administered safely in combination with gefitinib. Calcitriol concentrations achieved at the MTD 74 mug calcitriol exceed in vivo concentrations associated with antitumor activity in preclinical models.

Phase I/II study of bortezomib plus docetaxel in patients with advanced androgen-independent prostate cancer

PURPOSE

To determine the dose-limiting toxicities and maximum tolerated dose, and evaluate the antitumor activity of bortezomib/docetaxel combination therapy in androgen-independent prostate cancer.

EXPERIMENTAL DESIGN

Two bortezomib doses (1.3 and 1.6 mg/m(2)/dose) in combination with four docetaxel doses (25-40 mg/m(2)/dose) were evaluated. Both drugs were administered weekly for 2 out of 3 weeks. Antitumor activity was evaluated using prostate-specific antigen (PSA) levels and Response Evaluation Criteria in Solid Tumors guidelines.

RESULTS

Eighty-three patients received at least one dose of study drug. No dose-limiting toxicities were observed despite escalation to the highest dose level. PSA response (>or=50% decline in PSA levels from the baseline) occurred in 19 (28%) of 67 evaluable patients and was maintained for >or=4 weeks in 14 patients (21%). According to Response Evaluation Criteria in Solid Tumors guidelines, 11% achieved a partial response, and an additional 67% had stable disease. The degree of proteasome inhibition was similar to that reported with single-agent bortezomib. Treatment was well tolerated; fatigue was the most common drug-related adverse event, whereas diarrhea was the most common drug-related grade 3/4 adverse event. No clinically significant febrile neutropenia or neuropathy occurred.

CONCLUSIONS

The maximum tolerated dose of this 21-day regimen has not been reached. The highest dose level (1.6 mg/m(2) bortezomib plus 40 mg/m(2) docetaxel) was feasible and tolerable; bortezomib plus docetaxel showed antitumor activity. Activity and tolerability results were consistent with previous studies of bortezomib alone or in combination with docetaxel. Further investigations are warranted to determine activity and optimize bortezomib/docetaxel therapy in androgen-independent prostate cancers.

Molecular Therapy in Urologic Oncology

During recent years, significant advances have been made in the field of molecular therapy in urologic oncology, mainly for advanced renal cell carcinoma. In this hitherto largely treatment-refractory disease, several agents have been developed targeting the von Hippel-Lindau metabolic pathway which is involved in carcinogenesis and progression of the majority of renal cell carcinomas. Although cure may not be expected, new drugs, such as the multikinase inhibitors sorafenib and sunitinib and the mammalian target of rapamycine inhibitor temsirolimus, frequently stabilize the disease course and may improve survival. Fewer data are available supporting molecular therapies in prostate, bladder, and testicular cancers. Preliminary data suggest a potential role of high-dose calcitriol and thalidomide in hormone-refractory prostate cancer, whereas targeted therapies in bladder and testicular cancers are still more or less limited to single-case experiences. The great theoretical potential and the multitude of possible targets and drug combinations, however, support further research into this exciting field of medical treatment of urologic malignancies.

Pre-clinical and clinical evaluation of estramustine, docetaxel and thalidomide combination in androgen-independent prostate cancer

OBJECTIVE

To evaluate the combination of docetaxel plus estramustine (which prolongs survival in patients with androgen-independent prostate cancer, AIPC), and thalidomide (that also adds to docetaxel activity), both pre-clinically and clinically in AIPC.

PATIENTS, MATERIALS AND METHODS

In the pre-clinical evaluation we injected PC3 cells subcutaneously into severely combined immunodeficient mice and started treatment after the tumour volume reached 50 mm3. We also evaluated the combination using luciferase-labelled PC3M-luc-C6 cells in nude mice. We enrolled 20 patients with metastatic progressive AIPC into a phase II clinical trial to evaluate this combination. Docetaxel (30 mg/m2) was administered every week, for 3 of 4 weeks. The dose of thalidomide was 200 mg/day and estramustine was given three times a day at 1, 2, 3, 8, 9, 10, 15, 16 and 17 days.

RESULTS

In the mice, thalidomide with docetaxel plus estramustine reduced tumour volume by 88% at 17 days vs the control treatment (p=0.001). The combination of docetaxel, estramustine and thalidomide nearly eradicated the signal from the luciferase-expressing PC3M cells in the metastasis model. Clinically, the progression-free time was 7.2 months with this combination; 18 of 20 patients had a decline of half or more in prostate-specific antigen level and two of 10 patients with soft-tissue lesions had a partial response on computed tomography. There were 24 grade 3 and two grade 4 complications associated with this combination. There was a statistically significant association between overall survival and the CYP1B1*3 genotype (P=0.013).

CONCLUSION

Docetaxel-based chemotherapy is now regarded as a standard regimen for metastatic AIPC. The combination of estramustine, docetaxel and thalidomide is an advantageous treatment in pre-clinical models of prostate cancer and is a safe, tolerable and active regimen in patients with AIPC.

Advances in the Treatment of Prostate Cancer

Several recent advances have been made in the management of prostate cancer. Active surveillance is an increasingly attractive and reasonable approach for those with low-volume, low-risk disease. For locally advanced or localized high-risk disease, neoadjuvant and adjuvant therapies are emerging as the standard of care. Innovative uses of traditional hormonal treatments can potentially limit common side effects. Recent data also support the utility of second-line hormonal therapy. For the first time, a survival advantage with the use of chemotherapy has been established. Much work is under way to augment its efficacy with novel agents such as targeted therapeutics and tumor vaccines. Recent scientific breakthroughs suggest additional strategies in treating prostate cancer.

Antitumor effects of two less-calcemic vitamin D analogs (Paricalcitol and QW-1624F2-2) in squamous cell carcinoma cells

The active metabolite of vitamin D(3) (1alpha,25-dihydroxyvitamin D(3), calcitriol) has potent antitumor activities in vitro and in vivo in multiple cancers. Concerns about induction of hypercalcemia by calcitriol and the desire for more potent agents have prompted development of less-calcemic vitamin D analogs. These studies demonstrate that two vitamin D analogs, 19-nor-1alpha,25-dihydroxyvitamin D(2) (paricalcitol) and 1alpha-hydroxymethyl-16-ene-24,24-difluoro-25-hydroxy-26,27-bis-homovitamin D(3) (QW-1624F(2)-2, QW), have anticancer effects in the calcitriol-responsive squamous cell carcinoma (SCC) cell line. Paricalcitol (GI50 = 0.7 nM) and QW (GI50 = 0.001 nM) inhibited SCC cell growth; however, QW was more potent. Paricalcitol (10 nM) and QW (10 nM) induced G0/G1 cell cycle arrest and inhibited DNA synthesis by approximately 95%. The vitamin D analogs modulated cell cycle regulators, including decreasing mRNA and protein levels of p21(Waf1/Cip1) (p21) and cyclin-dependent kinase 2 (cdk2), and increasing p27(Kip1) (p27) protein expression. Vitamin D analogs induced apoptosis, caspase-3 cleavage and increased expression of pro-apoptotic MEKK-1. Phosphorylation of Akt, MEK and ERK1/2 that promote cell growth and survival were inhibited by vitamin D analogs. The anticancer effects of paricalcitol and QW are comparable to the effect of calcitriol. These less-calcemic vitamin D analogs are as effective as calcitriol in vitro and are promising for prevention and treatment of cancer and other diseases.

Novel targets in prostate cancer

Despite recent advances in the understanding of the cellular and molecular biology of prostate cancer, new options for the treatment of prostate cancer remain elusive. Targeted therapies have shown promising activities in many solid tumours and the growing number of targets and targeted agents is creating numerous opportunities for clinical research in advanced prostate cancer. At ASCO 2006 in Atlanta, a clinical science symposium on novel targets in prostate cancer was presented. It consisted of three abstracts, each of which was followed by a discussant who reviewed the work and placed it in the overall context of current approaches to treating prostate cancer. The three abstracts were a discussion of a new method for quantification of the androgen receptor; the impact of high-dose vitamin D plus chemotherapy on hormone refractory disease and on the risk of thromboembolic disease; and the paradoxical effects seen with the raf-kinase and vascular endothelial growth factor inhibitor sorafenib, which produced improvement in bone scans in the absence of any prostate-specific antigen responses.

A phase II trial of dexamethasone, vitamin D, and carboplatin in patients with hormone-refractory prostate cancer

BACKGROUND

A Phase II prospective trial was performed to study the efficacy of combination therapy with dexamethasone, calcitriol (1,25-dihydroxyvitamin D3), and carboplatin in patients with hormone-refractory prostate cancer (HRPC). Preclinical data from prostate cancer cell lines suggested a synergistic effect of these therapies.

METHODS

All patients had pathologically confirmed prostate cancer with at least 2 consecutive increases in prostate-specific antigen (PSA). Treatment started with 1 mg of oral dexamethasone given daily with 0.5 mcg of daily calcitriol added at the start of Week 5. Carboplatin (area under the concentration time curve = 2) was started at the beginning of Week 7. Initially, carboplatin was given weekly; however, the protocol was changed later to give carboplatin for the first 4 weeks of a 6-week cycle. Of 40 patients who consented to participate, 6 patients were ineligible or declined to start therapy, leaving 34 treated patients. The median follow-up was 80.7 weeks (range, 11.5-260 weeks).

RESULTS

A formal PSA response was seen in 13 of 34 treated patients (38.2%; 95% confidence interval [95% CI], 22.2-56.4%). The median overall survival was 97.7 weeks (95% CI, 61-114 weeks). Significant adverse events that were observed during the trial period included 2 deaths (myocardial infarction and cardiogenic shock), 4 patients with Grade 3 neutropenia (according to the National Cancer Institute Common Toxicity Criteria, version 2.0), 2 patients with thrombosis, 2 patients with inflammatory bowel symptoms, and 2 patients with new-onset diabetes mellitus.

CONCLUSIONS

The novel combination of dexamethasone, calcitriol, and carboplatin for patients with HRPC produced a PSA response in 13 of 34 patients and had an acceptable side-effect profile.

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.

Phase II trial evaluating a docetaxel-capecitabine combination as treatment for hormone-refractory prostate cancer

BACKGROUND

Docetaxel is a well-recognized drug in patients with hormone-refractory prostate cancer (HRPC), either alone or combined with estramustine. In this indication, a Phase II trial was conducted investigating a docetaxel-capecitabine combination.

METHODS

Forty-six patients presenting with documented HRPC were enrolled in the study. The treatment regimen consisted of docetaxel (D) at a dose of 35 mg /m2/week (intravenously, 3 consecutive weeks) plus oral capecitabine (C) at a dose of 625 mg/m2 twice daily (Days 5-18) every 28 days for 4 cycles. The primary endpoint was the biological response defined as a reduction in prostate-specific antigen (PSA) level > or =50%. Secondary endpoints were overall survival, safety, and quality of life.

RESULTS

Thirty of 44 assessable patients (68.2%) achieved a biological response, 14 of whom (31.8%) normalized their PSA value. The median overall survival time was 17.7 months (95% confidence interval, 15.8 to not reached). Four treatment cycles were completed by 87% of the patients. Hematologic toxicity was mild. The main Grade 3-4 toxicities were cutaneous toxicity (13.1%) and changes in nails (6.5%). Physical functioning and role scales were higher before treatment (P = .02 and P = .003, respectively), fatigue and diarrhea were more frequent during and after treatment (P = .0003 and P = .03, respectively), and pain was lower during and after treatment.

CONCLUSIONS

The results of the current study demonstrated the high efficacy of the DC combination in patients with HRPC, and the associated good tolerability. This combination offers a new alternative to the docetaxel-estramustine combination. Further randomized trials are warranted.

Achieving Treatment Goals for Hormone‐Refractory Prostate Cancer with Chemotherapy

The belief that hormone-refractory prostate cancer (HRPC) is a chemotherapy-resistant disease has been effectively refuted by the results of two recent randomized phase III trials. The TAX327 trial compared weekly docetaxel, every-3-weeks (Q3W) docetaxel, and Q3W mitoxantrone plus prednisone in 1,006 patients with HRPC, and results demonstrated that survival was significantly longer with a docetaxel-based regimen than with mitoxantrone. That trial demonstrated that only Q3W docetaxel was significantly superior to mitoxantrone with respect to overall survival. Quality of life was also superior in the docetaxel groups. In the Southwest Oncology Group (SWOG) 9916 trial, 674 men with progressive HRPC were randomized to 3-week cycles of docetaxel plus estramustine or mitoxantrone plus prednisone. Overall and disease-free survival times were significantly longer in the docetaxel arm. Collectively, the results of these trials demonstrate that survival can be significantly improved with chemotherapy in patients with HRPC to an extent that is comparable with the survival benefits seen in other cancers considered sensitive to chemotherapy such as breast cancer. Among various research tasks in HRPC is the definition of potential surrogate end points for survival, which will facilitate the conduct of pivotal trials. Prostate-specific antigen (PSA) response rate and changes in PSA constructs (i.e., PSA doubling time and PSA velocity) are promising potential surrogate end points for future trials and are being actively evaluated at the present time. Until there is clear demonstration of a surrogate role for these alternative end points, survival remains the appropriate end point for phase III trials in HRPC. There is a need for safe and effective second- and third-line regimens for patients progressing after docetaxel, and these patients should enter clinical trials designed for this population. Mitoxantrone, vinorelbine, the platinum analogue satraplatin, and epothilone are among compounds that require careful testing in this setting. The addition of targeted therapies, such as the endothelin receptor antagonist, atrasentan, and angiogenesis inhibitors, such as thalidomide and bevacizumab, to docetaxel-based therapy is being evaluated. High-dose calcitriol may also be an effective addition to docetaxel. The extensive effort devoted to the evaluation of chemotherapy and other systemic modalities of treatment of HRPC is likely to yield additional clinical benefit for patients, making HRPC a more manageable, less lethal, and less debilitating disease.