Update on options for treatment of metastatic castration-resistant prostate cancer

Vaccine Therapies for Cancer: Then and Now

There are strong biologic and preclinical rationales for the development of therapeutic cancer vaccines; however, the clinical translation of this treatment strategy has been challenging. It is now understood that many previous clinical trials of cancer vaccines used target antigens or vaccine designs that inherently lacked sufficient immunogenicity to induce clinical responses. Despite the historical track record, breakthrough advances in cancer immunobiology and vaccine technologies have supported continued interest in therapeutic cancer vaccinations, with the hope that next-generation vaccine strategies will enable patients with cancer to develop long-lasting anti-tumor immunity. There has been substantial progress identifying antigens and vaccine vectors that lead to strong and broad T cell responses, tailoring vaccine designs to achieve optimal antigen presentation, and finding combination partners employing complementary mechanisms of action (e.g., checkpoint inhibitors) to overcome the diverse methods cancer cells use to evade and suppress the immune system. Results from randomized, phase 3 studies testing therapeutic cancer vaccines based on these advances are eagerly awaited. Here, we summarize the successes and failures in the clinical development of cancer vaccines, address how this historical experience and advances in science and technology have shaped efforts to improve vaccines, and offer a clinical perspective on the future role of vaccine therapies for cancer.

Green tea and quercetin sensitize PC-3 xenograft prostate tumors to docetaxel chemotherapy

Background

Chemotherapy with docetaxel (Doc) remains the standard treatment for metastatic and castration-resistance prostate cancer (CRPC). However, the clinical success of Doc is limited by its chemoresistance and side effects. This study investigated whether natural products green tea (GT) and quercetin (Q) enhance the therapeutic efficacy of Doc in CRPC in mouse models.

Methods

Male severe combined immunodeficiency (SCID) mice (n = 10 per group) were inoculated with androgen-independent prostate cancer PC-3 cells subcutaneously. When tumors were established the intervention started. Mice were administered with GT + Q, Doc 5 mg/kg (LD), GT + Q + LD Doc, Doc 10 mg/kg (HD) or control. The concentration of GT polyphenols in brewed tea administered as drinking water was 0.07 % and Q was supplemented in diet at 0.4 %. Doc was intravenously injected weekly for 4 weeks, GT and Q given throughout the study.

Results

GT + Q or LD Doc slightly inhibited tumor growth compared to control. However, the combination of GT and Q with LD Doc significantly enhanced the potency of Doc 2-fold and reduced tumor growth by 62 % compared to LD Doc in 7-weeks intervention. A decrease of Ki67 and increase of cleaved caspase 7 were observed in tumors by the mixture, along with lowered blood concentrations of growth factors like VEGF and EGF. The mixture significantly elevated the levels of tumor suppressor mir15a and mir330 in tumor tissues. An increased risk of liver toxicity was only observed with HD Doc treatment.

Conclusions

These results provide a promising regimen to enhance the therapeutic effect of Doc in a less toxic manner.

Active Holistic Surveillance: The Nutritional Aspect of Delayed Intervention in Prostate Cancer

Purpose. Active surveillance is an emergent strategy for management of indolent prostate cancer. Our institution's watchful waiting protocol, Active Holistic Surveillance (AHS), implements close monitoring for disease progression along with various chemopreventive agents and attempts to reduce unnecessary biopsies. Our objective is to report on the treatment rates of men on our AHS protocol as well as determine reasons for progression. Materials/Methods. Low risk and low-intermediate risk patients were enrolled in AHS at Winthrop University Hospital between February 2002 and August 2015. Our IRB-approved study analyzed survival rate, discontinuation rates, and definitive treatments for patients in our AHS cohort. Results. 235 patients met inclusion criteria. Median age and follow-up for the cohort were 66 (44-88) years and 42 (3-166) months, respectively. The overall survival for the cohort was 99.6% and the disease specific survival was 100%. A total of 27 (11.5%) patients discontinued AHS. Conclusion. The incorporation of chemopreventive agents in our AHS protocol has allowed patients to prolong definitive treatment for many years. Longer follow-up and additional studies are necessary to further validate the effectiveness of AHS.

Prostate cancer vaccines in combination with additional treatment modalities

Immunotherapy has been investigated in both preclinical studies and clinical trials as a new therapy for prostate cancer. Vaccines, including those that utilize dendritic cells, viruses, or DNA, immunize against prostate-specific antigen and prostatic acid phosphatase. The vaccines have long been studied as monotherapy for the cancer, but increasingly more trials have been initiated in combination with other modalities. These include radiation, chemotherapy, and androgen deprivation therapy. This review describes and discusses the various combinations of vaccine immunotherapies.

Sensitization to docetaxel in prostate cancer cells by green tea and quercetin

Chemotherapy with docetaxel (Doc) is a standard treatment for metastatic and castration-resistant prostate cancer. However, chemoresistance and side effects of Doc limit its clinical success. We investigated whether natural products green tea (GT) and quercetin (Q), a flavonoid from apples and onions, will enhance the efficacy of Doc in androgen-independent (AI) prostate cancer cells. Two cell lines including LAPC-4-AI and PC-3 were treated in vitro with 40 μM of (-)-epigallocatechin gallate (EGCG), 5 μM of Q, 2 or 5 nM of Doc alone or in combination. The mixture of EGCG+Q+Doc increased the antiproliferative effect by threefold in LAPC-4-AI cells and eightfold in PC-3 cells compared to Doc alone. EGCG, Q and Doc in combination significantly enhanced cell cycle arrest at G2/M phase and increased apoptosis in both LAPC-4-AI and PC-3 cells compared to Doc alone. The mixture increased the inhibition of PI3K/Akt and the signal transducer and activator of transcription (Stat) 3 signaling pathways compared to Doc alone, and decreased the protein expression of multidrug resistance-related protein. In addition, the combination with EGCG and Q increased the inhibition of tumor cell invasion and colony formation in both LAPC-4-AI and PC-3 cells compared to Doc alone, and decreased the percentage of CD44(+)/CD24(-) stem-like LAPC-4-AI cells. In summary, GT and Q enhanced the therapeutic effect of Doc in castration-resistant prostate cancer cells through multiple mechanisms including the down-regulation of chemoresistance-related proteins. This study provides a novel therapeutic modality to enhance the efficacy of Doc in a nontoxic manner.

NSK-01105, a novel sorafenib derivative, inhibits human prostate tumor growth via suppression of VEGFR2/EGFR-mediated angiogenesis

The purpose of this study is to investigate the anti-angiogenic activities of NSK-01105, a novel sorafenib derivative, in in vitro, ex vivo and in vivo models, and explore the potential mechanisms. NSK-01105 significantly inhibited vascular endothelial growth factor (VEGF)-induced migration and tube formation of human umbilical vein endothelial cells at non-cytotoxic concentrations as shown by wound-healing, transwell migration and endothelial cell tube formation assays, respectively. Cell viability and invasion of LNCaP and PC-3 cells were significantly inhibited by cytotoxicity assay and matrigel invasion assay. Furthermore, NSK-01105 also inhibited ex vivo angiogenesis in matrigel plug assay. Western blot analysis showed that NSK-01105 down-regulated VEGF-induced phosphorylation of VEGF receptor 2 (VEGFR2) and the activation of epidermal growth factor receptor (EGFR). Tumor volumes were significantly reduced by NSK-01105 at 60 mg/kg/day in both xenograft models. Immunohistochemical staining demonstrated a close association between inhibition of tumor growth and neovascularization. Collectively, our results suggest a role of NSK-01105 in treatment for human prostate tumors, and one of the potential mechanisms may be attributed to anti-angiogenic activities.

Activation of Wnt/β-catenin signaling in a subpopulation of murine prostate luminal epithelial cells induces high grade prostate intraepithelial neoplasia

BACKGROUND

Wnt/β-catenin signaling is important for prostate development and cancer in humans. Activation of this pathway in differentiated luminal cells of mice induces high-grade prostate intraepithelial neoplasia (HGPIN). Though the cell of origin of prostate cancer has yet to be conclusively identified, a castration-resistant Nkx3.1-expressing cell (CARN) may act as a cell of origin for prostate cancer.

METHODS

To activate Wnt/β-catenin signaling in CARNs, we crossed mice carrying tamoxifen-inducible Nkx3.1-driven Cre to mice containing loxP sites in order to either conditionally knock out adenomatous polyposis coli (Apc) or constitutively activate β-catenin directly. We then castrated and hormonally regenerated these mice to target the CARN population.

RESULTS

Loss of Apc in hormonally normal mice induced HGPIN; however, after one or more rounds of castration and hormonal regeneration, Apc-null CARNs disappeared. Alternatively, when β-catenin was constitutively activated under the same conditions, HGPIN was apparent.

CONCLUSION

Activation of Wnt/β-catenin signaling via Apc deletion is sufficient to produce HGPIN in hormonally normal mice. Loss of Apc may destabilize the CARN population under regeneration conditions. When β-catenin is constitutively activated, HGPIN occurs in hormonally regenerated mice. A second genetic hit is likely required to cause progression to carcinoma and metastasis.

Complete regression of advanced prostate cancer for ten years: A case report and review of the literature

Long-term complete regression of prostate cancer (PCa) is a rare phenomenon. The current report presents the case of an advanced PCa patient with rare clinical features. Following the generation of a definitive diagnosis, the patient was administered with flutamide treatment (0.25 g flutamide) 3 times a day, for 5 consecutive years, prior to surgical castration. Following surgery, 3.75 mg enantone was injected (i.h.) once per month for 3 months, without suspending the flutamide treatment. In addition, traditional Chinese herbal medicine was administrated immediately following surgery. Strontium-89 radiotherapy was performed for multiple bone metastases, and the multiple metastatic lesions (lung and bone) of the individual disappeared in <7 months. The patient has currently survived for >10 years with no development of castration resistance or signs of recurrence. Nadir prostate-specific antigen (PSA) levels had remained at <0.1 ng/ml following the initial treatment, and the erythrocyte sedimentation rate (ESR) value was high and had been observed to fluctuate during the treatment. The present case report considers the role of the androgen-receptor in PCa and indicates that careful interpretation of nadir PSA and ESR levels may aid in the prediction of patient prognosis.

Phase II study of first-line sagopilone plus prednisone in patients with castration-resistant prostate cancer: a phase II study of the Department of Defense Prostate Cancer Clinical Trials Consortium

BACKGROUND

Preclinical studies in prostate cancer (PC) models demonstrated the anti-tumour activity of the first fully synthetic epothilone, sagopilone. This is the first study to investigate the activity and safety of sagopilone in patients with metastatic castration-resistant PC (CRPC).

METHODS

Chemotherapy-naïve patients with metastatic CRPC received sagopilone (one cycle: 16 mg m(-2) intravenously over 3 h q3w) plus prednisone (5 mg twice daily). The primary efficacy evaluation was prostate-specific antigen (PSA) response rate (≥50% PSA reduction confirmed ≥28 days apart). According to the Simon two-stage design, ≥3 PSA responders were necessary within the first 13 evaluable patients for recruitment to continue until 46 evaluable patients were available.

RESULTS

In all, 53 patients received ≥2 study medication cycles, with high compliance. Mean individual dose was 15.1±1.4 mg m(-2) during initial six cycles, mean dose intensity 94±9%. The confirmed PSA response rate was 37%. Median overall progression-free survival was 6.4 months. The most commonly reported adverse events (>10% of patients) were peripheral neuropathy (94.3%), fatigue (54.7%) and pain in the extremities (47.2%). Sagopilone was associated with very little haematological toxicity.

CONCLUSION

This study shows that first-line sagopilone has noteworthy anti-tumour activity and a clinically significant level of neuropathy for patients with metastatic chemotherapy-naïve CRPC.

The tumor microenvironment in prostate cancer: elucidating molecular pathways for therapy development

Mechanisms leading to the development of virulent prostate cancer are not confined to the cancer epithelial cell, but also involve the tumor microenvironment. Multiple signaling pathways exist between epithelial cells, stromal cells, and the extracellular matrix to support tumor progression from the primary site to regional lymph nodes and distant metastases. Prostate cancers preferentially metastasize to the skeleton, prompting considerable research effort into understanding the unique interaction between prostate cancer epithelial cells and the bone microenvironment. This effort has led to the discovery that signaling pathways involved in normal prostate and bone development become dysregulated in cancer. These pathways stimulate excessive cell growth and neovascularization, impart more invasive properties to epithelial cells, weaken antitumor immune surveillance, and promote the emergence of castrate-resistant disease. An improved understanding of the complex relationship between cancer epithelial cells and the organ-specific microenvironments with which they interact has created a powerful opportunity to develop novel therapies.

Open-label, phase I, pharmacokinetic studies of abiraterone acetate in healthy men

Purpose

To evaluate pharmacokinetics, safety, and tolerability of abiraterone acetate (AA) in healthy men.

Methods

Two phase I studies (dose-escalation study and dose-proportionality study) were conducted in healthy men aged 18–55 years. All subjects received 4 consecutive single doses of AA (250, 500, 750 and 1,000 mg). The dose-escalation study subjects (N = 33) received AA doses in a sequential manner, starting with the lowest dose. The dose-proportionality study subjects (N = 32) were randomly allocated (1:1:1:1) to receive each of the 4 doses in a four-way crossover design.

Results

A dose-related increase in abiraterone exposure was observed in both studies. Over the evaluated dose range, the mean abiraterone maximum plasma concentrations increased from 26 to 112 ng/mL in dose-escalation study and from 40 to 125 ng/mL in dose-proportionality study; the mean area under the plasma concentration–time curve from 0 to the last measurable plasma concentration increased from 155 to 610 ng.h/mL in dose-escalation study, and from 195 to 607 ng.h/mL in dose-proportionality study. In the dose-proportionality study, abiraterone exposure was dose proportional between 1,000 and 750 mg doses; however, the exposure was slightly greater than dose proportional when exposures at 500 and 250 mg doses were compared with the exposure at 1,000 mg. Single doses of AA were well tolerated in healthy men, and safety profile was consistent with its known toxicities in CRPC patients.

Conclusion

Systemic exposure to abiraterone increased with increasing doses of AA (250–1,000 mg) in healthy men; AA was well tolerated in this population.

Castration-resistant prostate cancer: mechanisms, targets, and treatment

Patients with castration-resistant prostate cancer (CRPC), who progress after docetaxel therapy, had until very recently, only a few therapeutic options. Recent advances in this field brought about new perspectives in the treatment of this disease. Molecular, basic, and translational research has given us a better understanding on the mechanisms of CRPC. This great investment has turned into a more rational approach to the development of new drugs. Some of the new treatments are already available to our patients outside clinical trials and may include inhibitors of androgen biosynthesis; new chemotherapy agents; bone-targeted therapy; and immunotherapy. This paper aims to review the mechanisms of prostate cancer resistance, possible therapeutic targets, as well as new options to treat CRPC.

CXCR4 expression in prostate cancer progenitor cells

Tumor progenitor cells represent a population of drug-resistant cells that can survive conventional chemotherapy and lead to tumor relapse. However, little is known of the role of tumor progenitors in prostate cancer metastasis. The studies reported herein show that the CXCR4/CXCL12 axis, a key regulator of tumor dissemination, plays a role in the maintenance of prostate cancer stem-like cells. The CXCL4/CXCR12 pathway is activated in the CD44⁺/CD133⁺ prostate progenitor population and affects differentiation potential, cell adhesion, clonal growth and tumorigenicity. Furthermore, prostate tumor xenograft studies in mice showed that a combination of the CXCR4 receptor antagonist AMD3100, which targets prostate cancer stem-like cells, and the conventional chemotherapeutic drug Taxotere, which targets the bulk tumor, is significantly more effective in eradicating tumors as compared to monotherapy.

Prolonged remission of fulminant castrate-resistant prostate cancer: a case report

Castrate-resistant prostate cancer (CRPC) is the main cause of prostate cancer (PC) morbidity and mortality. Newer therapies have only modestly improved survival. CRPC patients’ various comorbidities mean one must treat them cautiously. Cyclophosphamide, vincristine, and dexamethasone (CVD) therapy has a favorable risk-benefit profile, and diethylstilbestrol (DES) was used widely in PC. The patient we describe responded remarkably to combination treatment with CVD plus DES. The 77-year-old man had fulminant CRPC with multiple comorbidities and bony metastases in March 2008. In May 2008, his prognosis was dismal: performance status score, 4; pancytopenia; 51 × 109/l platelets; abnormal coagulation profile consistent with disseminated intravascular coagulopathy; and cranial images consistent with dural metastases. We administered one dose of CVD (cyclophosphamide [300 mg/m2 IV], vincristine [1 mg IV], and dexamethasone [0.75 mg PO b.i.d.]) plus DES (1 mg PO b.i.d.). He responded quickly with no clinically significant toxicity. His performance status improved and platelet count increased to 89,000 × 109/l. We administered maintenance CVD (cyclophosphamide, 150 mg/day PO for 21 days every 28 days; vincristine, 1 mg IV weekly; dexamethasone, 0.5 mg PO b.i.d.) plus DES (1 mg PO b.i.d.) for 5 months. In January 2011, nearly 3 years after his initial treatment, he remained alive and well. CVD plus DES may help selected patients with advanced CRPC who are too ill to tolerate or benefit from other therapies.

[Second line therapy for castration-resistant prostate cancer (CRPC)]

Every year in Germany approximately 12,000 men die of castration-resistant prostate cancer even though early detection using PSA-based diagnostics allows more patients to be diagnosed with a curable cancer. An established first line therapy at this stadium is docetaxel chemotherapy, given in a 3-week regimen, providing an overall survival advantage of 2 months. In 6-9 months, the patients treated primarily with docetaxel will progress to a docetaxel-insensitive phase which requires a secondary systemic therapy. Increasing understanding of molecular signal transduction has permitted a growing variety of promising modern drugs, including cabazitaxel, sipuleucel-T and abiraterone. More prospective clinical data will provide a large variety of different therapy combinations, sequence therapies or other therapy regimens particularly for selected subgroups of patients with castration-resistant prostate cancer.

Progression of metastatic castrate-resistant prostate cancer: impact of therapeutic intervention in the post-docetaxel space

Despite the proven success of hormonal therapy for prostate cancer using chemical or surgical castration, most patients eventually will progress to a phase of the disease that is metastatic and shows resistance to further hormonal manipulation. This has been termed metastatic castrate-resistant prostate cancer (mCRPC). Despite this designation, however, there is evidence that androgen receptor (AR)-mediated signaling and gene expression can persist in mCRPC, even in the face of castrate levels of androgen. This may be due in part to the upregulation of enzymes involved in androgen synthesis, the overexpression of AR, or the emergence of mutant ARs with promiscuous recognition of various steroidal ligands. The therapeutic options were limited and palliative in nature until trials in 2004 demonstrated that docetaxel chemotherapy could significantly improve survival. These results established first-line docetaxel as the standard of care for mCRPC. After resistance to further docetaxel therapy develops, treatment options were once again limited. Recently reported results from phase 3 trials have shown that additional therapy with the novel taxane cabazitaxel (with prednisone), or treatment with the antiandrogen abiraterone (with prednisone) could improve survival for patients with mCRPC following docetaxel therapy. Compared with mitoxantrone/prednisone, cabazitaxel/prednisone significantly improved overall survival, with a 30% reduction in rate of death, in patients with progression of mCRPC after docetaxel therapy in the TROPIC trial. Similarly, abiraterone acetate (an inhibitor of androgen biosynthesis) plus prednisone significantly decreased the rate of death by 35% compared with placebo plus prednisone in mCRPC patients progressing after prior docetaxel therapy in the COU-AA-301 trial. Results of these trials have thus established two additional treatment options for mCRPC patients in the "post-docetaxel space." In view of the continued AR-mediated signaling on mCRPC, results from additional phase 3 studies with novel antiandrogens which are directed at inhibition of the AR (e.g., MDV3100), as well as other agents, are awaited with interest and may further expand the treatment choices for this difficult-to-manage population of patients.

Mouse models of prostate cancer

The development and optimization of high-throughput screening methods has identified a multitude of genetic changes associated with human disease. The use of immunodeficient and genetically engineered mouse models that mimic the human disease has been crucial in validating the importance of these genetic pathways in prostate cancer. These models provide a platform for finding novel therapies to treat human patients afflicted with prostate cancer as well as those who have debilitating bone metastases. In this paper, we focus on the historical development and phenotypic descriptions of mouse models used to study prostate cancer. We also comment on how closely each model recapitulates human prostate cancer.