A new therapy paradigm for prostate cancer founded on clinical observations

Prediction of disease progression indicators in prostate cancer patients receiving HDR-brachytherapy using Raman spectroscopy and semi-supervised learning: a pilot study

This work combines Raman spectroscopy (RS) with supervised learning methods-group and basis restricted non-negative matrix factorisation (GBR-NMF) and linear discriminant analysis (LDA)-to aid in the prediction of clinical indicators of disease progression in a cohort of 9 patients receiving high dose rate brachytherapy (HDR-BT) as the primary treatment for intermediate risk (D'Amico) prostate adenocarcinoma. The combination of Raman spectroscopy and GBR-NMF-sparseLDA modelling allowed for the prediction of the following clinical information; Gleason score, cancer of the prostate risk assessment (CAPRA) score of pre-treatment biopsies and a Ki67 score of < 3.5% or > 3.5% in post treatment biopsies. The three clinical indicators of disease progression investigated in this study were predicted using a single set of Raman spectral data acquired from each individual biopsy, obtained pre HDR-BT treatment. This work highlights the potential of RS, combined with supervised learning, as a tool for the prediction of multiple types of clinically relevant information to be acquired simultaneously using pre-treatment biopsies, therefore opening up the potential for avoiding the need for multiple immunohistochemistry (IHC) staining procedures (H&E, Ki67) and blood sample analysis (PSA) to aid in CAPRA scoring.

A Phase 2 Trial of Abiraterone Followed by Randomization to Addition of Dasatinib or Sunitinib in Men With Metastatic Castration-Resistant Prostate Cancer

BACKGROUND

Resistance to novel androgen signaling inhibition and metastatic castration-resistant prostate cancer (mCRPC) progression is likely dependent on tumor microenvironment interactions. The Src pathway and neoangiogenesis have been implicated in prostate cancer progression. We studied the effect of adding the targeted agents dasatinib and sunitinib to abiraterone acetate (AA) in men with mCRPC.

PATIENTS AND METHODS

In this open-label randomized phase 2 study, mCRPC patients received AA. At resistance to AA, they were randomized 1:1 to combination with dasatinib or sunitinib. At second progression, patients crossed over. The primary end point was time to treatment failure (TTF), defined as time to progression or death. Secondary end points included overall survival and safety.

RESULTS

From March 2011 to February 2015, a total of 179 patients were enrolled and 132 subsequently randomized. Median TTF was 5.7 months in the dasatinib group and 5.5 months in the sunitinib group. There was no difference between the two groups in terms of TTF (hazard ratio, 0.85; 95% confidence interval, 0.59-1.22). Median overall survival from study entry was 26.3 months in the dasatinib group and 27.7 months in the sunitinib group (hazard ratio, 1.02; 95% confidence interval, 0.71-1.47). Grade 3 or higher adverse events related to study medication were more frequent with sunitinib (n = 44, 46%) compared to dasatinib (n = 26, 24%). At data cutoff, 7 patients were experiencing a continuous response to AA, with a median duration of treatment of 5.7 years.

CONCLUSION

There is no difference in overall survival and TTF between dasatinib and sunitinib combined with abiraterone in the treatment of patients with bone mCRPC.

IL-8 Secreted from M2 Macrophages Promoted Prostate Tumorigenesis via STAT3/MALAT1 Pathway

Prostate cancer (PCa) is a major health problem in males. Metastasis-associated with lung adenocarcinoma transcript-1 (MALAT1), which is overexpressed in PCa tissue, is associated with physiological and pathological conditions of PCa. M2 macrophages are major immune cells abundant in the tumor microenvironment. However, it remains unknown whether M2 macrophages are involved in the effects or not, and molecular mechanisms of MALAT1 on PCa progression have not yet been comprehensively explored. Here we reported that, M2 macrophages (PMA/IL-4 treated THP1) induced MALAT1 expression in PCa cell lines. Knockdown MALAT1 expression level in PCa cell lines inhibited cellular proliferation, invasion, and tumor formation. Further mechanistic dissection revealed that M2 macrophages secreted IL-8 was sufficient to drive up MALAT1 expression level via activating STAT3 signaling pathway. Additional chromatin immunoprecipitation (ChIP) and luciferase reporter assays displayed that STAT3 could bind to the MALAT1 promoter region and transcriptionally stimulate the MALAT1 expression. In summary, our present study identified the IL-8/STAT3/MALAT1 axis as key regulators during prostate tumorigenesis and therefore demonstrated a new mechanism for the MALAT1 transcriptional regulation.

Prognostic Impacts of Metastatic Site and Pain on Progression to Castrate Resistance and Mortality in Patients with Metastatic Prostate Cancer

PURPOSE

To investigate predictors of progression to castration-resistant prostate cancer (CRPC) and cancer-specific mortality (CSM) in patients with metastatic prostate cancer (mPCa).

MATERIALS AND METHODS

A retrospective analysis was performed on 440 consecutive treatment-naïve patients initially diagnosed with mPCa between August 2000 and June 2012. Patient age, body mass index (BMI), Gleason score, prostate-specific antigen (PSA), PSA nadir, American Joint Committee on Cancer stage, Visual Analogue Scale pain score, Eastern Cooperative Oncology Group performance score (ECOG PS), PSA response to hormone therapy, and metastatic sites were assessed. Cox-proportional hazards regression analyses were used to evaluate survivals and predictive variables of men with bone metastasis stratified according to the presence of pain, compared to men with visceral metastasis.

RESULTS

Metastases were most often found in bone (75.4%), followed by lung (16.3%) and liver (8.3%) tissues. Bone metastasis, pain, and high BMI were associated with increased risks of progression to CRPC, and bone metastasis, pain, PSA nadir, and ECOG PS≥1 were significant predictors of CSM. During the median follow-up of 32.0 (interquartile range 14.7-55.9) months, patients with bone metastasis with pain and patients with both bone and visceral metastases showed the worst median progression to CRPC-free and cancer-specific survivals, followed by men with bone metastasis without pain. Patients with visceral metastasis had the best median survivals.

CONCLUSION

Metastatic spread and pain patterns confer different prognosis in patients with mPCa. Bone may serve as a crucial microenvironment in the development of CRPC and disease progression.

Tumor-secreted Hsp90 subverts polycomb function to drive prostate tumor growth and invasion

Prostate cancer remains the second highest contributor to male cancer-related lethality. The transition of a subset of tumors from indolent to invasive disease is associated with a poor clinical outcome. Activation of the epithelial to mesenchymal transition (EMT) genetic program is a major risk factor for cancer progression. We recently reported that secreted extracellular Hsp90 (eHsp90) initiates EMT in prostate cancer cells, coincident with its enhanced expression in mesenchymal models. Our current work substantially extended these findings in defining a pathway linking eHsp90 signaling to EZH2 function, a methyltransferase of the Polycomb repressor complex. EZH2 is also implicated in EMT activation, and its up-regulation represents one of the most frequent epigenetic alterations during prostate cancer progression. We have now highlighted a novel epigenetic function for eHsp90 via its modulation of EZH2 expression and activity. Mechanistically, eHsp90 initiated sustained activation of MEK/ERK, a signal critical for facilitating EZH2 transcriptional up-regulation and recruitment to the E-cadherin promoter. We further demonstrated that an eHsp90-EZH2 pathway orchestrates an expanded repertoire of EMT-related events including Snail and Twist expression, tumor cell motility, and anoikis resistance. To evaluate the role of eHsp90 in vivo, eHsp90 secretion was stably enforced in a prostate cancer cell line resembling indolent disease. Remarkably, eHsp90 was sufficient to induce tumor growth, suppress E-cadherin, and initiate localized invasion, events that are exquisitely dependent upon EZH2 function. In summary, our findings illuminate a hitherto unknown epigenetic function for eHsp90 and support a model wherein tumor eHsp90 functions as a rheostat for EZH2 expression and activity to orchestrate mesenchymal properties and coincident aggressive behavior.

Molecular characterization of enzalutamide-treated bone metastatic castration-resistant prostate cancer

BACKGROUND

Enzalutamide is a novel antiandrogen with proven efficacy in metastatic castration-resistant prostate cancer (mCRPC).

OBJECTIVE

To evaluate enzalutamide's effects on cancer and on androgens in blood and bone marrow, and associate these with clinical observations.

DESIGN, SETTING, AND PARTICIPANTS

In this prospective phase 2 study, 60 patients with bone mCRPC received enzalutamide 160mg orally daily and had transilial bone marrow biopsies before treatment and at 8 wk of treatment.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Androgen signaling components (androgen receptor [AR], AR splice variant 7 (ARV7), v-ets avian erythroblastosis virus E26 oncogene homolog [ERG], cytochrome P450, family 17, subfamily A, polypeptide 1 [CYP17]) and molecules implicated in mCRPC progression (phospho-Met, phospho-Src, glucocorticoid receptor, Ki67) were assessed by immunohistochemistry; testosterone, cortisol, and androstenedione concentrations were assessed by liquid chromatography-tandem mass spectrometry; AR copy number was assessed by real-time polymerase chain reaction. Descriptive statistics were applied.

RESULTS AND LIMITATIONS

Median time to treatment discontinuation was 22 wk (95% confidence interval, 19.9-29.6). Twenty-two (37%) patients exhibited primary resistance to enzalutamide, discontinuing treatment within 4 mo. Maximal prostate-specific antigen (PSA) decline ≥ 50% and ≥ 90% occurred in 27 (45%) and 13 (22%) patients, respectively. Following 8 wk of treatment, bone marrow and circulating testosterone levels increased. Pretreatment tumor nuclear AR overexpression (> 75%) and CYP17 (> 10%) expression were associated with benefit (p = 0.018). AR subcellular localization shift from the nucleus was confirmed in eight paired samples (with PSA decline) of 23 evaluable paired samples. Presence of an ARV7 variant was associated with primary resistance to enzalutamide (p = 0.018). Limited patient numbers warrant further validation.

CONCLUSIONS

The observed subcellular shift of AR from the nucleus and increased testosterone concentration provide the first evidence in humans that enzalutamide suppresses AR signaling while inducing an adaptive feedback. Persistent androgen signaling in mCRPC was predictive of benefit and ARV7 was associated with primary resistance.

PATIENT SUMMARY

We report a first bone biopsy study in metastatic prostate cancer in humans that searched for predictors of outcome of enzalutamide therapy. Benefit is linked to a pretreatment androgen-signaling signature.

TRIAL REGISTRATION

ClinicalTrials.gov identifier NCT01091103.

Bone microenvironment-targeted manipulations for the treatment of osteoblastic metastasis in castration-resistant prostate cancer

INTRODUCTION

Most patients with advanced prostate cancer will develop incurable bone metastasis. Although prostate cancer is the quintessential androgen-dependent neoplastic disease in males, the tumor will ultimately become refractory to androgen ablation treatment. Understanding the complex dialog between prostate cancer and the bone microenvironment has allowed the development of promising treatment strategies.

AREAS COVERED

The present review summarizes the pathophysiology of prostate cancer bone metastasis and provides a concise update on bone microenvironment-targeted therapies for prostate cancer. The current and future prospects and challenges of these strategies are also discussed.

EXPERT OPINION

A wide variety of signaling pathways, bone turnover homeostatic mechanisms and immunoregulatory networks are potential targets for the treatment of metastatic castration-resistant prostate cancer (mCRPC). Anti-survival factor therapy can enhance the efficacy of existing treatment regimens for mCRPC by exploiting the interaction between the bone microenvironment and androgen signaling networks. In addition, many novel bone microenvironment-targeted strategies have produced promising objective clinical responses. Further elucidation of the complex interactions between prostate cancer cells and the bone stroma will open up new avenues for treatment interventions that can produce sustained cancer suppression.

Metabolic reprogramming and validation of hyperpolarized 13C lactate as a prostate cancer biomarker using a human prostate tissue slice culture bioreactor

BACKGROUND

The treatment of prostate cancer has been impeded by the lack of both clinically relevant disease models and metabolic markers that track tumor progression. Hyperpolarized (HP) (13) C MR spectroscopy has emerged as a new technology to investigate the metabolic shifts in prostate cancer. In this study, we investigate the glucose reprogramming using HP (13) C pyruvate MR in a patient-derived prostate tissue slice culture (TSC) model.

METHODS

The steady-state metabolite concentrations in freshly excised human prostate TSCs were assessed and compared to those from snap-frozen biopsy samples. The TSCs were then applied to a perfused cell (bioreactor) platform, and the bioenergetics and the dynamic pyruvate flux of the TSCs were investigated by (31) P and HP (13) C MR, respectively.

RESULTS

The prostate TSCs demonstrated steady-state glycolytic and phospholipid metabolism, and bioenergetics that recapitulate features of prostate cancer in vivo. (13) C spectra following injection of HP (13) C pyruvate showed significantly increased pyruvate to lactate flux in malignant as compared to the benign prostate TSCs. This increased flux in the malignant prostate TSCs correlated with both increased expression of monocarboxylate transporters (MCT) and activity of lactate dehydrogenase (LDH).

CONCLUSIONS

We provide the first mechanistic evidence for HP (13) C lactate as a prostate cancer biomarker in living human tissues, critical for the interpretation of in vivo studies. More broadly, the clinically relevant metabolic model system in combination with HP MR can facilitate the identification of clinically translatable biomarkers of prostate cancer presence, aggressiveness, and treatment response.

Molecular classification of prostate cancer progression: foundation for marker-driven treatment of prostate cancer

Recently, many therapeutic agents for prostate cancer have been approved that target the androgen receptor and/or the prostate tumor microenvironment. Each of these therapies has modestly increased patient survival. A better understanding of when in the course of prostate cancer progression specific therapies should be applied, and of what biomarkers would indicate when resistance arises, would almost certainly improve survival due to these therapies. Thus, applying the armamentarium of therapeutic agents in the right sequences in the right combination at the right time is a major goal in prostate cancer treatment. For this to occur, an understanding of prostate cancer evolution during progression is required. In this review, we discuss the current understanding of prostate cancer progression, but challenge the prevailing view by proposing a new model of prostate cancer progression, with the goal of improving biologic classification and treatment strategies. We use this model to discuss how integrating clinical and basic understanding of prostate cancer will lead to better implementation of molecularly targeted therapeutics and improve patient survival.

Integrated Hedgehog signaling is induced following castration in human and murine prostate cancers

BACKGROUND

The interplay between androgen and Hedgehog (Hh) signaling pathways may be associated with prostate cancer progression and resistance to therapy.

METHODS

Tissue microarrays from prostatectomy specimens were derived from 53 patients treated preoperatively with androgen ablation (AA) with or without chemotherapy, and from 26 stage- and grade-matched controls. A previously characterized androgen-regulated human prostate cancer xenograft was used to conduct parallel murine studies. Expression of markers of interest was determined on both untreated and castrated tumors.

RESULTS

Four-month exposure to AA or AA with chemotherapy led to a uniform increase in Hh signaling as compared to controls, paired with an inverse trend of androgen receptor (AR) and CYP17 expression in clinically derived specimens. Changes in the expression profiles of Hh signaling were observed in the epithelium and stroma, in response to genotoxic stress of androgen ablation and chemotherapy. A reduced expression of KI67 and increased bcl2 expression was observed in the malignant epithelial compartment.

CONCLUSION

To our knowledge, this is the first clinical evidence that Hh signaling is induced by AA or the combination of AA and chemotherapy and, by inference, contributes to castrate-resistant progression of prostate cancer as supported by parallel human and murine studies. These data are in agreement with previous reports that implicate Hh signaling in castrate-resistant progression of prostate cancer. Based on these findings, we are pursuing parallel clinical and murine investigations to determine if Hh signaling inhibition combined with AA will be more effective than AA alone.

Effect of abiraterone acetate on fatigue in patients with metastatic castration-resistant prostate cancer after docetaxel chemotherapy

BACKGROUND

Fatigue is a common, debilitating side-effect of prostate cancer and its treatment. Patient-reported fatigue was evaluated as part of COU-AA-301, a randomized, placebo-controlled, phase III trial of abiraterone acetate and prednisone versus placebo and prednisone in metastatic castration-resistant prostate cancer (mCRPC) patients after docetaxel chemotherapy. This is the first phase III study in advanced prostate cancer to evaluate fatigue outcomes using a validated fatigue-specific instrument.

PATIENTS AND METHODS

The Brief Fatigue Inventory (BFI) questionnaire was used to measure patient-reported fatigue intensity and fatigue interference with activities of daily life. All analyses were conducted using prespecified responder definitions of clinically meaningful changes.

RESULTS

A total of 797 patients were randomized to abiraterone acetate and prednisone, and 398 were randomized to placebo and prednisone. Compared with prednisone alone, in patients with clinically significant fatigue at baseline, abiraterone acetate and prednisone significantly increased the proportion of patients reporting improvement in fatigue intensity (58.1% versus 40.3%, P = 0.0001), improved fatigue interference (55.0% versus 38.0%, P = 0.0075), and accelerated improvement in fatigue intensity (median 59 days versus 194 days, P = 0.0155).

CONCLUSIONS

In patients with mCRPC progressing after docetaxel chemotherapy, abiraterone acetate and prednisone yielded clinically meaningful improvements in patient-reported fatigue compared with prednisone alone.

Secreted Hsp90 is a novel regulator of the epithelial to mesenchymal transition (EMT) in prostate cancer

Prostate cancer (PCa) is the most frequently diagnosed malignancy in men, and the second highest contributor of male cancer related lethality. Disease mortality is due primarily to metastatic spread, highlighting the urgent need to identify factors involved in this progression. Activation of the genetic epithelial to mesenchymal transition (EMT) program is implicated as a major contributor of PCa progression. Initiation of EMT confers invasive and metastatic behavior in preclinical models and is correlated with poor clinical prognosis. Extracellular Hsp90 (eHsp90) promotes cell motility and invasion in cancer cells and metastasis in preclinical models, however, the mechanistic basis for its widespread tumorigenic function remains unclear. We have identified a novel and pivotal role for eHsp90 in driving EMT events in PCa. In support of this notion, more metastatic PCa lines exhibited increased eHsp90 expression relative to their lineage-related nonmetastatic counterparts. We demonstrate that eHsp90 promoted cell motility in an ERK and matrix metalloproteinase-2/9-dependent manner, and shifted cellular morphology toward a mesenchymal phenotype. Conversely, inhibition of eHsp90 attenuated pro-motility signaling, blocked PCa migration, and shifted cell morphology toward an epithelial phenotype. Last, we report that surface eHsp90 was found in primary PCa tumor specimens, and elevated eHsp90 expression was associated with increased levels of matrix metalloproteinase-2/9 transcripts. We conclude that eHsp90 serves as a driver of EMT events, providing a mechanistic basis for its ability to promote cancer progression and metastasis in preclinical models. Furthermore, its newly identified expression in PCa specimens, and potential regulation of pro-metastatic genes, supports a putative clinical role for eHsp90 in PCa progression.

The role of enzalutamide in the treatment of castration-resistant prostate cancer

Prostate cancer is the most common solid organ cancer affecting the male population. Men with metastatic prostate cancer treated with androgen ablation therapy often respond rapidly, with improvement in bone pain and decreases in serum prostate-specific antigen. However, almost all patients progress to the castration-resistant state and abiraterone acetate was the last treatment available with proven survival benefit. Enzalutamide (formerly MDV3100) is an androgen receptor signaling inhibitor that has been shown to improve survival in men with metastatic castration-resistant prostate cancer previously treated with chemotherapy. In this article we discuss the characteristics of enzalutamide and provide a review of its clinical development.

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.

The role of abiraterone in the management of metastatic castration-resistant prostate cancer

Prostate cancer is the most common solid-organ cancer affecting the male population. Men with metastatic prostate cancer treated with androgen ablation therapy often respond rapidly, with improvement in bone pain and decreases in serum prostate-specific antigen. However, almost all patients progress to the castrate-resistant state and until recently chemotherapy was the only treatment available with proven survival benefit. Abiraterone is a new class of anti-androgen with proven survival benefit post-chemotherapy. In this review we discuss the characteristics of abiraterone and the clinical trials that led to its approval for the treatment of patients with prostate cancer.

Effects of abiraterone acetate on androgen signaling in castrate-resistant prostate cancer in bone

PURPOSE

Persistent androgen signaling is implicated in castrate-resistant prostate cancer (CRPC) progression. This study aimed to evaluate androgen signaling in bone marrow-infiltrating cancer and testosterone in blood and bone marrow and to correlate with clinical observations.

PATIENTS AND METHODS

This was an open-label, observational study of 57 patients with bone-metastatic CRPC who underwent transiliac bone marrow biopsy between October 2007 and March 2010. Patients received oral abiraterone acetate (1 g) once daily and prednisone (5 mg) twice daily. Androgen receptor (AR) and CYP17 expression were assessed by immunohistochemistry, testosterone concentration by mass spectrometry, AR copy number by polymerase chain reaction, and TMPRSS2-ERG status by fluorescent in situ hybridization in available tissues.

RESULTS

Median overall survival was 555 days (95% CI, 440 to 965+ days). Maximal prostate-specific antigen decline ≥ 50% occurred in 28 (50%) of 56 patients. Homogeneous, intense nuclear expression of AR, combined with ≥ 10% CYP17 tumor expression, was correlated with longer time to treatment discontinuation (> 4 months) in 25 patients with tumor-infiltrated bone marrow samples. Pretreatment CYP17 tumor expression ≥ 10% was correlated with increased bone marrow aspirate testosterone. Blood and bone marrow aspirate testosterone concentrations declined to less than picograms-per-milliliter levels and remained suppressed at progression.

CONCLUSION

The observed pretreatment androgen-signaling signature is consistent with persistent androgen signaling in CRPC bone metastases. This is the first evidence that abiraterone acetate achieves sustained suppression of testosterone in both blood and bone marrow aspirate to less than picograms-per-milliliter levels. Potential admixture of blood with bone marrow aspirate limits our ability to determine the origin of measured testosterone.

Expression of hedgehog pathway components in prostate carcinoma microenvironment: shifting the balance towards autocrine signalling

AIMS

The hedgehog (Hh) signalling pathway has been implicated in the pathogenesis and aggressiveness of prostate cancer through epithelial-mesenchymal interactions. The aim of this study was to elucidate the cell-type partitioned expression of the Hh pathway biomarkers in the non-neoplastic and tumour microenvironments and to correlate it with the grade and stage of prostate cancer.

METHODS AND RESULTS

Expression of the Hh pathway components (Shh, Smo, Ptch, Gli1) in the microenvironment of non-neoplastic peripheral zone (n = 119), hormone-naive primary prostate carcinoma (n = 141) and castrate-resistant bone marrow metastases (n = 53) was analysed using immunohistochemistry in tissue microarrays and bone marrow sections. Results showed that epithelial Shh, Smo and Ptch expression was up-regulated, whereas stromal Smo, Ptch, and Gli1 expression was down-regulated in prostate carcinomas compared to non-neoplastic peripheral zone tissue. Ptch expression was modulated further in high-grade and high-stage primary tumours and in bone marrow metastases. Hh signalling correlated with ki67 and vascular endothelial growth factor (VEGF) but not with CD31 expression.

CONCLUSION

Our results highlight the importance of Hh-mediated epithelial-mesenchymal interactions in the non-neoplastic prostate and imply that shifting the balance from paracrine towards autocrine signalling is important in the pathogenesis and progression of prostate carcinoma.

Novel therapies for metastatic castrate-resistant prostate cancer

Recent advances in tumor biology have made remarkable achievements in the development of therapy for metastatic castrate-resistant prostate cancer. These advances reflect a growing appreciation for the role of the tumor microenvironment in promoting prostate cancer progression. Prostate cancer is no longer viewed predominantly as a disease of abnormally proliferating epithelial cells but rather as a disease of complex interactions between prostate cancer epithelial cells (epithelial compartment) and the surrounding tissues (stromal compartment) in which they reside. For example, prostate cancers frequently metastasize to bone, an organ that contains a microenvironment rich in extracellular matrix proteins and stromal cells including hematopoietic cells, osteoblasts, osteoclasts fibroblasts, endothelial cells, adipocytes, immune cells, and mesenchymal stem cells. Multiple signaling pathways provide crosstalk between the epithelial and the stromal compartments to enhance tumor growth, including androgen receptor signaling, tyrosine kinase receptor signaling, and immune surveillance. The rationale to disrupt this "two-compartment" crosstalk has led to the development of drugs that target tumor stromal elements in addition to the cancer epithelial cell.

Correlation of phospholipid metabolites with prostate cancer pathologic grade, proliferative status and surgical stage - impact of tissue environment

This study investigates the relationship between phospholipid metabolite concentrations, Gleason score, rate of cellular proliferation and surgical stage in malignant prostatectomy samples by performing one- and two-dimensional, high-resolution magic angle spinning, total correlation spectroscopy, pathology and Ki-67 staining on the same surgical samples. At radical prostatectomy, surgical samples were obtained from 49 patients [41 with localized TNM stage T1 and T2, and eight with local cancer spread (TNM stage T3)]. Thirteen of the tissue samples were high-grade prostate cancer [Gleason score: 4 + 3 (n = 7); 4 + 4 (n = 6)], 22 low-grade prostate cancer [Gleason score: 3 + 3 (n = 17); 3 + 4 (n = 5)] and 14 benign prostate tissues. This study demonstrates that high-grade prostate cancer shows significantly higher Ki-67 staining and concentrations of phosphocholine (PC) and glycerophosphocholine (GPC) than does low-grade prostate cancer (2.4 ± 2.8% versus 7.6 ± 3.5%, p < 0.005, and 0.671 ± 0.461 versus 1.87 ± 2.15 mmolal, p < 0.005, respectively). In patients with local cancer spread, increases in [PC + GPC + PE + GPE] (PE, phosphoethanolamine; GPE, glycerophosphoethanolamine] and Ki-67 index approached significance (4.2 ± 2.5 versus 2.7 ± 2.4 mmolal, p = 0.07, and 5.3 ± 3.8% versus 2.9 ± 3.8%, p = 0.07, respectively). PC and Ki-67 were significantly lower and GPC higher in prostate tissues when compared with cell cultures, presumably because of a lack of important stromal-epithelial interactions in cell cultures. The findings of this study will need to be validated in a larger cohort of surgical patients with clinical outcome data, but support the role of in vivo (1)H MRSI in discriminating between low- and high-grade prostate cancer based on the magnitude of elevation of the in vivo total choline resonance.

Steps in prostate cancer progression that lead to bone metastasis

Prostate cancer is a complex disease in which metastasis to the bone is the main cause of death. Initial stages of metastasis are generally similar to those for most solid tumors; however, the mechanisms that underlie the homing of prostate tumor cells to the bone are not completely understood. Prostate cancer bone metastasis is also a microenvironment-driven disease, involving bidirectional interactions between the tumor and the bone microenvironment. In this review, we discuss the current understanding of the biologic processes and regulatory factors involved in the metastasis of prostate cancer cells, and their specific properties that promote growth in bone. Although many of these processes still need to be fully elucidated, a better understanding of the complex tumor/microenvironment interplay is slowly leading to more effective therapies for patients with prostate cancer bone metastases.

Current and emerging treatment modalities for metastatic castration-resistant prostate cancer

Docetaxel-based therapy is established as the standard first-line chemotherapy in patients with metastatic castration-resistant prostate cancer (mCRPC), based on results from two landmark Phase III studies. However, prognosis remains poor, with a median survival of less than 2 years. There is no standard of care for patients who progress during or after docetaxel treatment, which represents a real unmet medical need. Several small retrospective studies suggest that patients with mCRPC who responded to first-line docetaxel-based therapy are sensitive to re-treatment, but a survival benefit in prospective randomized trials has not been demonstrated. Epithelial-stromal interactions in the tumour microenvironment appear to play a central role in prostate cancer progression and response to therapy. Recent insights into the molecular mechanisms that underpin prostate cancer progression have allowed the identification of potential therapeutic targets. New agents, including angiogenesis inhibitors, hormone therapies, chemotherapies, bone targeting agents, vaccines and immunotherapies are currently undergoing clinical development in advanced prostate cancer using docetaxel as a backbone. Several Phase III studies have now been completed. Sipuleucel-T prolonged survival compared with placebo in asymptomatic or minimally symptomatic patients with mCRPC. Cabazitaxel plus prednisone prolonged survival in patients with mCRPC who progressed during or after docetaxel-based therapy compared with the active agent mitoxantrone, plus prednisone. Multidisciplinary management and optimization of the role and timing of new agents in this evolving treatment continuum will be critical to maximizing patient outcomes. Identification of predictive markers and better gene expression profiling will be critical to tailoring therapies to individual patients and disease states, whereas validated surrogate markers of overall survival will help accelerate drug approval.

Persistent, biologically meaningful prostate cancer after 1 year of androgen ablation and docetaxel treatment

PURPOSE

Clinicians are increasingly willing to treat prostate cancer within the primary site in the presence of regional lymph node or even limited distant metastases. However, no formal study on the merits of this approach has been reported. We used a preoperative clinical discovery platform to prioritize pathways for assessment as therapeutic targets and to test the hypothesis that the primary site harbors potentially lethal tumors after aggressive treatment.

PATIENTS AND METHODS

Patients with locally advanced or lymph node-metastatic prostate cancer underwent 1 year of androgen ablation and three cycles of docetaxel therapy, followed by prostatectomy. All specimens were characterized for stage by accepted criteria. Expression of select molecular markers implicated in disease progression and therapy resistance was determined immunohistochemically and compared with that in 30 archived specimens from untreated patients with high-grade prostate cancer. Marker expression was divided into three groups: intracellular signaling pathways, stromal-epithelial interaction pathways, and angiogenesis.

RESULTS

Forty patients were enrolled, 30 (75%) of whom underwent prostatectomy and two (5%) who underwent cystoprostatectomy. Twenty-nine specimens contained sufficient residual tumor for inclusion in a tissue microarray. Immunohistochemical analysis showed increased epithelial and stromal expression of CYP17, SRD5A1, and Hedgehog pathway components, and modulations of the insulin-like growth factor I pathway.

CONCLUSION

A network of molecular pathways reportedly linked to prostate cancer progression is activated after 1 year of therapy; biomarker expression suggests that potentially lethal cancers persist in the primary tumor and may contribute to progression.

Control of tumor and microenvironment cross-talk by miR-15a and miR-16 in prostate cancer

The interaction between cancer cells and microenvironment has a critical role in tumor development and progression. Although microRNAs regulate all the major biological mechanisms, their influence on tumor microenvironment is largely unexplored. Here, we investigate the role of microRNAs in the tumor-supportive capacity of stromal cells. We demonstrated that miR-15 and miR-16 are downregulated in fibroblasts surrounding the prostate tumors of the majority of 23 patients analyzed. Such downregulation of miR-15 and miR-16 in cancer-associated fibroblasts (CAFs) promoted tumor growth and progression through the reduced post-transcriptional repression of Fgf-2 and its receptor Fgfr1, which act on both stromal and tumor cells to enhance cancer cell survival, proliferation and migration. Moreover, reconstitution of miR-15 and miR-16 impaired considerably the tumor-supportive capability of stromal cells in vitro and in vivo. Our data suggest a molecular circuitry in which miR-15 and miR-16 and their correlated targets cooperate to promote tumor expansion and invasiveness through the concurrent activity on stromal and cancer cells, thus providing further support to the development of therapies aimed at reconstituting miR-15 and miR-16 in advanced prostate cancer.

Therapeutic targeting of the prostate cancer microenvironment

Solid tumors can be thought of as multicellular 'organs' that consist of a variety of cells as well as a scaffold of noncellular matrix. Stromal-epithelial crosstalk is integral to prostate cancer progression and metastasis, and androgen signaling is an important component of this crosstalk at both the primary and metastatic sites. Intratumoral production of androgen is an important mechanism of castration resistance and has been the focus of novel therapeutic approaches with promising results. Various other pathways are important for stromal-epithelial crosstalk and represent attractive candidate therapeutic targets. Hedgehog signaling has been associated with tumor progression, growth and survival, while Src family kinases have been implicated in tumor progression and in regulation of cancer cell migration. Fibroblast growth factors and transforming growth factor beta signaling regulate cell proliferation, apoptosis and angiogenesis in the prostate cancer microenvironment. Integrins mediate communication between the cell and the extracellular matrix, enhancing growth, migration, invasion and metastasis of cancer cells. The contribution of stromal-epithelial crosstalk to prostate cancer initiation and progression provides the impetus for combinatorial microenvironment-targeting strategies.

Intracellular adaptor molecules and AR signalling in the tumour microenvironment

Androgen deprivation therapy is the mainstay for treating advanced prostate cancer. A better understanding in the complexity of the androgen receptor (AR) signalling pathway has highlighted that this form of treatment is not sufficient. Since Huggins and Hodges made their crucial observations on the benefits of castration for prostate cancer, significant progress has been achieved in understanding the importance of the cross-talk between the hormone signalling pathway and the kinase signalling network. We now know that preventing androgen production or ligand binding to the AR does not necessarily mark the end of the road for prostate tumour growth. Emerging evidence suggests that there exists a complex set of compensatory mechanisms which allows growth factors to push the transformed cells into a 'survival adaptation mode' within the tumour microenvironment. An increase in autocrine and paracrine cascades of growth factor are the most commonly reported events to correlate with progression of androgen-dependent disease to a disseminated androgen independent state. The mechanism of how growth factors can sustain AR activation when cells are deprived of androgens is unknown. This is due to the lack of information about the critical factors linking the intracellular signalling molecules associated with the downstream AR signalling events triggered by growth factors. The aim of this mini review is to highlight a potentially new insight into how intracellular adaptor molecules activated by growth factors may influence and act as a molecular switch to allow the continuation of AR activity in the presence of therapeutic anti-androgens following chemical or surgical castration.