Hypoxia drives prostate tumour progression and impairs the effectiveness of therapy, but can also promote cell death and serve as a therapeutic target

Different predictive values of microvessel density for biochemical recurrence among different PCa populations: A systematic review and meta-analysis

BACKGROUND

Several studies have explored the relationship between intratumoral microvessel density (MVD) and the risk of postoperative biochemical recurrence (BCR) in prostate cancer (PCa), although the results are contradictory. Therefore, we conducted a meta-analysis to investigate the effect of MVD on BCR in PCa.

METHOD

We searched PubMed, MEDLINE, Science Direct/Elsevier, the Cochrane Library, CNKI, and EMBase databases from inception through January 2022, with no year or language restrictions, and used NOS guidelines to evaluate the quality of the 19 eligible studies. The derived hazard ratio (HR) and 95% confidence interval (95%CI) were used to assess each endpoint. Data synthesis was performed with RevMan to assess the prognostic value of MVD in PCa and its heterogeneity, while the publication bias was examined using STATA 16.0.

RESULTS

Our meta-analysis included 19 articles (4 for T1-2, 6 for T1-3, and 9 for T1-4) on postoperative biochemical recurrence of PCa, among which, 3933 patients were pooled. The predictive ability of intratumoral MVD for different stages of PCa on BCR was T1-2 (HR, 2.46; 95% CI, 1.08-5.58; p = 0.03; I²  = 83%), T1-3 (HR, 2.38, 95% CI, 1.41-4.01; p = 0.001; I²  = 82%), T1-4 (HR, 1.61; 95% CI, 1.19-2.19; p = 0.002; I²  = 61%).The subgroup analyses based on European and immunohistochemical antibody none-factor VII were consistent with primary one. Sensitivity analysis excluding those studies judged to be at high risk of bias in T1-2 showed a HR of 2.99[1.70,5.27] (I²  = 38%, p = 0.0001), demonstrating the robustness of risk estimates of MVD for the assessment of biochemical recurrence.

CONCLUSION

Microvessel density is a predictor of BCR among patients with PCa, and earlier T stage PCa with a stronger MVD is associated with BCR. Further studies are needed to investigate neoangiogenesis in different T stages of PCa and whether MVD will be of benefit to the EAU-recommended tool for biochemical recurrence risk assessment.

Role of opiorphin genes in prostate cancer growth and progression

Background: We describe the first studies investigating a role for opiorphin genes (PROL1, SMR3A and SMR3B) in prostate cancer (PrCa). Materials & methods: Databases and PrCa tissue arrays were screened for opiorphin expression. Xenografted tumor growth of human PrCa cells overexpressing PROL1 was compared with controls in nude mice. Modulated gene expression by overexpression of PROL1 was determined by RNA sequencing. Results: PrCa is associated with overexpression of opiorphin genes. Xenografted androgen-sensitive PrCa cells overexpressing PROL1 developed into tumors in castrated male mice (in contrast to parental cells). PROL1 overexpression modulates expression of genes in angiogenesis, steroid and hypoxic response pathways. Conclusions: Opiorphins promote the development of androgen-insensitive PrCa and activate pathways that potentially overcome the hypoxic barrier generated during tumor growth.

Aspartate β-hydroxylase targeting in castration-resistant prostate cancer modulates the NOTCH/HIF1α/GSK3β crosstalk

Castration-resistant prostate cancer (CRPC) is an incurable stage of the disease. A multivariate principal component analysis on CRPC in vitro models identified aspartyl (asparaginyl) β hydrolase (ASPH) as the most relevant molecule associated with the CRPC phenotype. ASPH is overexpressed in various malignant neoplasms and catalyzes the hydroxylation of aspartyl and asparaginyl residues in the epidermal growth factor (EGF)-like domains of proteins like NOTCH receptors and ligands, enhancing cell motility, invasion and metastatic spread. Bioinformatics analyses of ASPH in prostate cancer (PCa) and CRPC datasets indicate that ASPH gene alterations have prognostic value both in PCa and CRPC patients. In CRPC cells, inhibition of ASPH expression obtained through specific small interfering RNA or culturing cells in hypoxic conditions, reduced cell proliferation, invasion and cyclin D1 expression through modulation of the NOTCH signaling. ASPH and HIF1α crosstalk, within a hydroxylation-regulated signaling pathway, might be transiently driven by the oxidative stress evidenced inside CRPC cells. In addition, increased phosphorylation of GSK3β by ASPH silencing demonstrates that ASPH regulates GSK3β activity inhibiting its interactions with upstream kinases. These findings demonstrate the critical involvement of ASPH in CRPC development and may represent an attractive molecular target for therapy.

Aquaglyceroporin-3's Expression and Cellular Localization Is Differentially Modulated by Hypoxia in Prostate Cancer Cell Lines

Aquaporins are required by cells to enable fast adaptation to volume and osmotic changes, as well as microenvironmental metabolic stimuli. Aquaglyceroporins play a crucial role in supplying cancer cells with glycerol for metabolic needs. Here, we show that AQP3 is differentially expressed in cells of a prostate cancer panel. AQP3 is located at the cell membrane and cytoplasm of LNCaP cell while being exclusively expressed in the cytoplasm of Du145 and PC3 cells. LNCaP cells show enhanced hypoxia growth; Du145 and PC3 cells display stress factors, indicating a crucial role for AQP3 at the plasma membrane in adaptation to hypoxia. Hypoxia, both acute and chronic affected AQP3′s cellular localization. These outcomes were validated using a machine learning classification approach of the three cell lines and of the six normoxic or hypoxic conditions. Classifiers trained on morphological features derived from cytoskeletal and nuclear labeling alongside corresponding texture features could uniquely identify each individual cell line and the corresponding hypoxia exposure. Cytoskeletal features were 70–90% accurate, while nuclear features allowed for 55–70% accuracy. Cellular texture features (73.9% accuracy) were a stronger predictor of the hypoxic load than the AQP3 distribution (60.3%).

miR-210 is induced by hypoxia and regulates neural cell adhesion molecule in prostate cells

Hypoxia in prostate tumours has been associated with disease progression and metastasis. MicroRNAs are short noncoding RNA molecules that are important in several cell processes, but their role in hypoxic signalling is still poorly understood. miR-210 has been linked with hypoxic mechanisms, but this relationship has been poorly characterised in prostate cancer. In this report, the link between hypoxia and miR-210 in prostate cancer cells is investigated. Polymerase chain reaction analysis demonstrates that miR-210 is induced by hypoxia in prostate cancer cells using in vitro cell models and an in vivo prostate tumour xenograft model. Analysis of The Cancer Genome Atlas prostate biopsy datasets shows that miR-210 is significantly correlated with Gleason grade and other clinical markers of prostate cancer progression. Neural cell adhesion molecule (NCAM) is identified as a target of miR-210, providing a biological mechanism whereby hypoxia-induced miR-210 expression can contribute to prostate cancer. This study provides evidence that miR-210 is an important regulator of cell response to hypoxic stress and proposes that its regulation of NCAM may play an important role in the pathogenesis of prostate cancer.

Aurora B Kinase Promotes CHIP-Dependent Degradation of HIF1α in Prostate Cancer Cells

Hypoxia is a major factor in tumor progression and resistance to therapies, which involves elevated levels of the transcription factor HIF1α. Here, we report that prostate tumor xenografts express high levels of HIF1α and show greatly enhanced growth in response to knockdown of the E3 ligase CHIP (C-terminus of Hsp70-interacting protein). In multiple human prostate cancer cell lines under hypoxia, taxol treatment induces the degradation of HIF1α, and this response is abrogated by knockdown of CHIP, but not by E3 ligase VHL or RACK1. HIF1α degradation is accompanied by loss of function, evidenced by reduced expression of HIF1α-dependent genes. CHIP-dependent HIF1α degradation also occurs in cells arrested in mitosis by nocodazole instead of taxol. Mitotic kinase Aurora B activity is required for taxol-induced HIF1α degradation. Purified Aurora B directly phosphorylates HIF1α at multiple sites, and these modifications enhance its polyubiquitination by CHIP in a purified reconstituted system. Our results show how activation of Aurora B promotes CHIP-dependent degradation of HIF1α in prostate cancer cells. This new knowledge may affect the use of mitotic kinase inhibitors and open new approaches for treatment of hypoxic prostate tumors.

REST reduction is essential for hypoxia-induced neuroendocrine differentiation of prostate cancer cells by activating autophagy signaling

Prostate cancer (PCa) with neuroendocrine differentiation (NED) is tightly associated with hormone refractory PCa (HRPC), an aggressive form of cancer that is nearly impossible to treat. Determining the mechanism of the development of NED may yield novel therapeutic strategies for HRPC. Here, we first demonstrate that repressor element-1 silencing transcription factor (REST), a transcriptional repressor of neuronal genes that has been implicated in androgen-deprivation and IL-6 induced NED, is essential for hypoxia-induced NED of PCa cells. Bioinformatics analysis of transcriptome profiles of REST knockdown during hypoxia treatment demonstrated that REST is a master regulator of hypoxia-induced genes. Gene set enrichment analysis (GSEA) of hypoxia and REST knockdown co-upregulated genes revealed their correlation with HRPC. Consistently, gene ontology (GO) analysis showed that REST reduction potential associated with hypoxia-induced tumorigenesis, NE development, and AMPK pathway activation. Emerging reports have revealed that AMPK activation is a potential mechanism for hypoxia-induced autophagy. In line with this, we demonstrate that REST knockdown alone is capable of activating AMPK and autophagy activation is essential for hypoxia-induced NED of PCa cells. Here, making using of in vitro cell-based assay for NED, we reveal a new role for the transcriptional repressor REST in hypoxia-induced NED and characterized a sequential molecular mechanism downstream of REST resulting in AMPK phosphorylation and autophagy activation, which may be a common signaling pathway leading to NED of PCa.

Targeting Hypoxic Prostate Tumors Using the Novel Hypoxia-Activated Prodrug OCT1002 Inhibits Expression of Genes Associated with Malignant Progression

Purpose: To understand the role of hypoxia in prostate tumor progression and to evaluate the ability of the novel unidirectional hypoxia-activated prodrug OCT1002 to enhance the antitumor effect of bicalutamide.Experimental Design: The effect of OCT1002 on prostate cancer cells (LNCaP, 22Rv1, and PC3) was measured in normoxia and hypoxia in vitroIn vivo, tumor growth and lung metastases were measured in mice treated with bicalutamide, OCT1002, or a combination. Dorsal skin fold chambers were used to image tumor vasculature in vivo Longitudinal gene expression changes in tumors were analyzed using PCR.Results: Reduction of OCT1002 to its active form (OCT1001) decreased prostate cancer cell viability. In LNCaP-luc spheroids, OCT1002 caused increased apoptosis and decreased clonogenicity. In vivo, treatment with OCT1002 alone, or with bicalutamide, showed significantly greater tumor growth control and reduced lung metastases compared with controls. Reestablishment of the tumor microvasculature following bicalutamide-induced vascular collapse is inhibited by OCT1002. Significantly, the upregulation of RUNX2 and its targets caused by bicalutamide alone was blocked by OCT1002.Conclusions: OCT1002 selectively targets hypoxic tumor cells and enhances the antitumor efficacy of bicalutamide. Furthermore, bicalutamide caused changes in gene expression, which indicated progression to a more malignant genotype; OCT1002 blocked these effects, emphasizing that more attention should be attached to understanding genetic changes that may occur during treatment. Early targeting of hypoxic cells with OCT1002 can provide a means of inhibiting prostate tumor growth and malignant progression. This is of importance for the design and refinement of existing androgen-deprivation regimens in the clinic. Clin Cancer Res; 23(7); 1797-808. ©2016 AACR.

Lymphatic endothelial cells actively regulate prostate cancer cell invasion

Lymphatic vessels serve as the primary route for metastatic spread to lymph nodes. However, it is not clear how interactions between cancer cells and lymphatic endothelial cells (LECs), especially within hypoxic microenvironments, affect the invasion of cancer cells. Here, using an MR compatible cell perfusion assay, we investigated the role of LEC-prostate cancer (PCa) cell interaction in the invasion and degradation of the extracellular matrix (ECM) by two human PCa cell lines, PC-3 and DU-145, under normoxia and hypoxia, and determined the metabolic changes that occurred under these conditions. We observed a significant increase in the invasion of ECM by invasive PC-3 cells, but not poorly invasive DU-145 cells when human dermal lymphatic microvascular endothelial cells (HMVEC-dlys) were present. Enhanced degradation of ECM by PC-3 cells in the presence of HMVEC-dlys identified interactions between HMVEC-dlys and PCa cells influencing cancer cell invasion. The enhanced ECM degradation was partly attributed to increased MMP-9 enzymatic activity in PC-3 cells when HMVEC-dlys were in close proximity. Significantly higher uPAR and MMP-9 expression levels observed in PC-3 cells compared to DU-145 cells may be one mechanism for increased invasion and degradation of matrigel by these cells irrespective of the presence of HMVEC-dlys. Hypoxia significantly decreased invasion by PC-3 cells, but this decrease was significantly attenuated when HMVEC-dlys were present. Significantly higher phosphocholine was observed in invasive PC-3 cells, while higher glycerophosphocholine was observed in DU-145 cells. These metabolites were not altered in the presence of HMVEC-dlys. Significantly increased lipid levels and lipid droplets were observed in PC-3 and DU-145 cells under hypoxia reflecting an adaptive survival response to oxidative stress. These results suggest that in vivo, invasive cells in or near lymphatic endothelial cells are likely to be more invasive and degrade the ECM to influence the metastatic cascade. Copyright © 2016 John Wiley & Sons, Ltd.

Androgen deprivation in LNCaP prostate tumour xenografts induces vascular changes and hypoxic stress, resulting in promotion of epithelial-to-mesenchymal transition

Background:

When single-agent androgen deprivation therapy (ADT) is administered for locally advanced prostate cancer, men usually relapse within 1–2 years with more malignant castrate-resistant disease. The reason for this is currently unknown. We now hypothesise that an initial treatment response that increases tumour hypoxia drives selection of more malignant tumours.

Methods:

The LNCaP prostate tumour xenografts were analysed for physiological (oxygen and vasculature) and genetic (PCR array) changes during longitudinal treatment with ADT (bicalutamide, 6 or 2 mg kg⁻¹ daily for 28 days).

Results:

Bicalutamide caused an immediate (within 24 h) dose-dependent fall in oxygenation in LNCaP-luc prostate tumours with a nadir of ≤0.1% oxygen within 3–7 days; this was attributed to a significant loss of tumour microvessels (window chamber study). The hypoxic nadir persisted for 10–14 days. During the next 7 days, tumours regrew, oxygenation improved and the vasculature recovered; this was inhibited by the VEGF inhibitor B20.4.1.1. Gene expression over 28 days showed marked fluctuations consistent with the physiological changes. Accompanying the angiogenic burst (day 21) was a particularly striking increase in expression of genes associated with epithelial-to-mesenchymal transition (EMT). In particular, insulin-like growth factor 1 (IGF-1) showed increases in mRNA and protein expression.

Conclusions:

Hypoxic stress caused by ADT promotes EMT, providing a mechanism for the cause of malignant progression in prostate cancer.

Rat Prostate Tumor Cells Progress in the Bone Microenvironment to a Highly Aggressive Phenotype

Prostate cancer generally metastasizes to bone, and most patients have tumor cells in their bone marrow already at diagnosis. Tumor cells at the metastatic site may therefore progress in parallel with those in the primary tumor. Androgen deprivation therapy is often the first-line treatment for clinically detectable prostate cancer bone metastases. Although the treatment is effective, most metastases progress to a castration-resistant and lethal state. To examine metastatic progression in the bone microenvironment, we implanted androgen-sensitive, androgen receptor-positive, and relatively slow-growing Dunning G (G) rat prostate tumor cells into the tibial bone marrow of fully immune-competent Copenhagen rats. We show that tumor establishment in the bone marrow was reduced compared with the prostate, and whereas androgen deprivation did not affect tumor establishment or growth in the bone, this was markedly reduced in the prostate. Moreover, we found that, with time, G tumor cells in the bone microenvironment progress to a more aggressive phenotype with increased growth rate, reduced androgen sensitivity, and increased metastatic capacity. Tumor cells in the bone marrow encounter lower androgen levels and a higher degree of hypoxia than at the primary site, which may cause high selective pressures and eventually contribute to the development of a new and highly aggressive tumor cell phenotype. It is therefore important to specifically study progression in bone metastases. This tumor model could be used to increase our understanding of how tumor cells adapt in the bone microenvironment and may subsequently improve therapy strategies for prostate metastases in bone.

Oxygen supply maps for hypoxic microenvironment visualization in prostate cancer

Background:

Intratumoral hypoxia plays an important role with regard to tumor biology and susceptibility to radio- and chemotherapy. For further investigation of hypoxia-related changes, areas of certain hypoxia must be reliably detected within cancer tissues. Pimonidazole, a 2-nitroimindazole, accumulates in hypoxic tissue and can be easily visualized using immunohistochemistry.

Materials and Methods:

To improve detection of highly hypoxic versus normoxic areas in prostate cancer, immunoreactivity of pimonidazole and a combination of known hypoxia-related proteins was used to create computational oxygen supply maps of prostate cancer. Pimonidazole was intravenously administered before radical prostatectomy in n = 15 patients, using the da Vinci robot-assisted surgical system. Prostatectomy specimens were immediately transferred into buffered formaldehyde, fixed overnight, and completely embedded in paraffin. Pimonidazole accumulation and hypoxia-related protein expression were visualized by immunohistochemistry. Oxygen supply maps were created using the normalized information from pimonidazole and hypoxia-related proteins.

Results:

Based on pimonidazole staining and other hypoxia.related proteins (osteopontin, hypoxia-inducible factor 1-alpha, and glucose transporter member 1) oxygen supply maps in prostate cancer were created. Overall, oxygen supply maps consisting of information from all hypoxia-related proteins showed high correlation and mutual information to the golden standard of pimonidazole. Here, we describe an improved computer-based ex vivo model for an accurate detection of oxygen supply in human prostate cancer tissue.

Conclusions:

This platform can be used for precise colocalization of novel candidate hypoxia-related proteins in a representative number of prostate cancer cases, and improve issues of single marker correlations. Furthermore, this study provides a source for further in situ tests and biochemical investigations

High Lysyl Oxidase (LOX) in the Non-Malignant Prostate Epithelium Predicts a Poor Outcome in Prostate Cancer Patient Managed by Watchful Waiting

Lysyl oxidase (LOX) has been shown to both promote and suppress tumor progression, but its role in prostate cancer is largely unknown. LOX immunoreactivity was scored in prostate tumor epithelium, tumor stroma and in the tumor-adjacent non-malignant prostate epithelium and stroma. LOX scores in tumor and non-malignant prostate tissues were then examined for possible associations with clinical characteristics and survival in a historical cohort of men that were diagnosed with prostate cancer at transurethral resection and followed by watchful waiting. Men with a low LOX score in the non-malignant prostate epithelium had significantly longer cancer specific survival than men with a high score. Furthermore, LOX score in non-malignant prostate epithelium remained prognostic in a multivariable analysis including Gleason score. LOX score in prostate tumor epithelium positively correlated to Gleason score and metastases but was not associated with cancer survival. LOX score in tumor and non-malignant prostate stroma appeared unrelated to these tumor characteristics. In radical prostatectomy specimens, LOX immune-staining corresponded to LOX in-situ hybridization and LOX mRNA levels were found to be similar between tumor and adjacent non-malignant areas, but significantly increased in bone metastases samples. LOX levels both in tumors and in the surrounding tumor-bearing organ are apparently related to prostate cancer aggressiveness.

Incidence rate of prostate cancer in men treated for erectile dysfunction with phosphodiesterase type 5 inhibitors: retrospective analysis

The purpose of this study was to determine the incidence rate of prostate cancer among men with erectile dysfunction (ED) treated with phosphodiesterase type 5 inhibitors (PDE-5i) over a 7-year period vs. men with ED of the same age and with similar risk factors who were not treated with PDE-5i. In a retrospective review of electronic medical records and billing databases between the years 2000 and 2006, men with ED between the ages of 50 and 69 years and no history of prostate cancer prior to 2000 were identified. These individuals were divided into two groups: 2362 men who had treatment with PDE-5i, and 2612 men who did not have treatment. Demographic data in each group were compared. During the study period, 97 (4.1%) men with ED treated with PDE-5i were diagnosed with prostate cancer compared with 258 (9.9%) men with ED in the non-treated group (P<00001). A higher percentage of African Americans were treated with PDE-5i vs. those who were not (10.5% vs. 7.1%; P<0.0001). The PDE-5i group had lower documented diagnosis of elevated prostate-specific antigen (10.0% vs. 13.1%; P=0.0008) and higher percentage of benign prostatic hyperplasia (38.4% vs. 35.1%; P=0.0149). Men with ED treated with PDE-5i tended to have less chance (adjusted odds ratio: 0.4; 95% confidence intervals: 0.3-0.5; P<0.0001) of having prostate cancer. Our data suggest that men with ED treated with PDE-5i tended to have less of a chance of being diagnosed with prostate cancer. Further research is warranted.

Does changing androgen receptor status during prostate cancer development impact upon cholesterol homeostasis?

BACKGROUND

Recent evidence associates prostate cancer with high cholesterol levels, with cholesterol being an important raw material for cell-growth. Within the cell, cholesterol homeostasis is maintained by two master transcription factors: sterol-regulatory element-binding protein 2 (SREBP-2) and liver X receptor (LXR). We previously showed that the androgen receptor, a major player in prostate cell physiology, toggles these transcription factors to promote cholesterol accumulation. Given that prostate cancer therapy targets the androgen receptor, selecting for cells with altered androgen receptor activity, how would this affect SREBP-2 and LXR activity? Using a novel prostate cancer progression model, we explored how this crosstalk between the androgen receptor and cholesterol homeostasis changes during prostate cancer development.

METHODOLOGY/PRINCIPAL FINDINGS

Firstly, we characterised our progression model, which involved 1) culturing LNCaP cells at physiological testosterone levels to generate androgen-tolerant LNCaP-305 cells, and 2) culturing LNCaP-305 with the anti-androgen casodex to generate castration-resistant LNCaP-364 cells. This progression was accompanied by upregulated androgen receptor expression, typically seen clinically, and a reduction in androgen receptor activity. Although this influenced how SREBP-2 and LXR target genes responded to androgen treatment, cellular cholesterol levels and their response to changing sterol status was similar in all LNCaP sub-lines.

CONCLUSION/SIGNIFICANCE

Overall cholesterol homeostasis is unaffected by changing androgen receptor activity in prostate cancer cells. This does not negate the relationship between androgens and cholesterol homeostasis, but rather suggests that other factors compensate for altered androgen receptor activity. Given that cholesterol regulation is maintained during progression, this supports the growing idea that cholesterol metabolism is a suitable target for prostate cancer.

Androgen deprivation results in time-dependent hypoxia in LNCaP prostate tumours: informed scheduling of the bioreductive drug AQ4N improves treatment response

Androgen withdrawal induces hypoxia in androgen-sensitive tissue; this is important as in the tumour microenvironment, hypoxia is known to drive malignant progression. Our study examined the time-dependent effect of androgen deprivation therapy (ADT) on tumour oxygenation and investigated the role of ADT-induced hypoxia on malignant progression in prostate tumours. LNCaP xenografted tumours were treated with anti-androgens and tumour oxygenation measured. Dorsal skin fold (DSF) chambers were used to image tumour vasculature in vivo. Quantitative PCR (QPCR) identified differential gene expression following treatment with bicalutamide. Bicalutamide-treated and vehicle-only-treated tumours were re-established in vitro, and invasion and sensitivity to docetaxel were measured. Tumour growth delay was calculated following treatment with bicalutamide combined with the bioreductive drug AQ4N. Tumour oxygenation measurements showed a precipitate decrease following initiation of ADT. A clinically relevant dose of bicalutamide (2 mg/kg/day) decreased tumour oxygenation by 45% within 24 hr, reaching a nadir of 0.09% oxygen (0.67 ± 0.06 mmHg) by Day 7; this persisted until Day 14 when it increased up to Day 28. Using DSF chambers, LNCaP tumours treated with bicalutamide showed loss of small vessels at Days 7 and 14 with revascularisation occurring by Day 21. QPCR showed changes in gene expression consistent with the vascular changes and malignant progression. Cells from bicalutamide-treated tumours were more malignant than vehicle-treated controls. Combining bicalutamide with AQ4N (50 mg/kg, single dose) caused greater tumour growth delay than bicalutamide alone. Our study shows that bicalutamide-induced hypoxia selects for cells that show malignant progression; targeting hypoxic cells may provide greater clinical benefit.

Hypoxia increases CX3CR1 expression via HIF-1 and NF‑κB in androgen-independent prostate cancer cells

The unique CX3C chemokine CX3CL1 and its cognate receptor CX3CR1 have been implicated in organ-specific metastasis of various types of tumors. Hypoxia, a common phenomenon in solid tumors, is associated with a malignant cancer phenotype. Previous studies have proved that hypoxia facilitates cancer cell metastasis through upregulation of specific chemokine receptors. We hypothesized that hypoxia could upregulate CX3CR1 expression and lead to an increased chemotactic response to CX3CL1 in prostate cancer cells. In the present study, we found that CX3CR1 expression was significantly increased in androgen-independent prostate cancer cells, including DU145, PC-3 and PC-3M, following exposure to hypoxia. This upregulation of CX3CR1 corresponded to a significant increase in migration and invasion of prostate cancer cells under hypoxic conditions, which was attenuated after knocking down CX3CR1 expression. In addition, we examined the possible role of HIF-1 and NF-κB in the process of hypoxia-induced CX3CR1 expression and hypoxia-mediated metastasis. Attenuation of HIF-1 and NF-κB transcriptional activity by siRNAs or pharmacological inhibitors, abrogated hypoxia-induced upregulation of CX3CR1, and also prevented the migration and invasion of DU145 cells under a hypoxic environment. In summary, our study demonstrated that HIF-1 and NF-κB are essential for hypoxia-regulated CX3CR1 expression, which is associated with increased migratory and invasive potential of prostate cancer cells. CX3CR1 signaling is a potential therapeutic target in the adjuvant treatment of prostate cancer.

Liposomal doxorubicin improves radiotherapy response in hypoxic prostate cancer xenografts

Background

Tumor vasculature frequently fails to supply sufficient levels of oxygen to tumor tissue resulting in radioresistant hypoxic tumors. To improve therapeutic outcome radiotherapy (RT) may be combined with cytotoxic agents.

Methods

In this study we have investigated the combination of RT with the cytotoxic agent doxorubicin (DXR) encapsulated in pegylated liposomes (PL-DXR). The PL-DXR formulation Caelyx^® was administered to male mice bearing human, androgen-sensitive CWR22 prostate carcinoma xenografts in a dose of 3.5 mg DXR/kg, in combination with RT (2 Gy/day × 5 days) performed under normoxic and hypoxic conditions. Hypoxic RT was achieved by experimentally inducing tumor hypoxia by clamping the tumor-bearing leg five minutes prior to and during RT. Treatment response evaluation consisted of tumor volume measurements and dynamic contrast-enhanced magnetic resonance imaging (DCE MRI) with subsequent pharmacokinetic analysis using the Brix model. Imaging was performed pre-treatment (baseline) and 8 days later. Further, hypoxic fractions were determined by pimonidazole immunohistochemistry of excised tumor tissue.

Results

As expected, the therapeutic effect of RT was significantly less effective under hypoxic than normoxic conditions. However, concomitant administration of PL-DXR significantly improved the therapeutic outcome following RT in hypoxic tumors. Further, the pharmacokinetic DCE MRI parameters and hypoxic fractions suggest PL-DXR to induce growth-inhibitory effects without interfering with tumor vascular functions.

Conclusions

We found that DXR encapsulated in liposomes improved the therapeutic effect of RT under hypoxic conditions without affecting vascular functions. Thus, we propose that for cytotoxic agents affecting tumor vascular functions liposomes may be a promising drug delivery technology for use in chemoradiotherapy.

Prostate cancer increases hyaluronan in surrounding nonmalignant stroma, and this response is associated with tumor growth and an unfavorable outcome

Our objective was to investigate whether the presence of a tumor increases hyaluronan (HA) levels in surrounding prostate tissues and whether this extratumoral HA influences tumor growth and outcome. From a series of 287 men diagnosed with prostate cancer at transurethral resection and followed up with watchful waiting, tissue microarrays were constructed, stained, and scored for HA. A high HA staining score in the tumor stroma or in nonmalignant prostate tissue stroma were both associated positively with higher Gleason score and larger tumor volume, and was associated with a poor outcome. HA staining score was not an independent marker for outcome (multivariate Cox, with Gleason score, tumor volume, stage, and HA variables). In an orthotopic rat prostate cancer model, hyaluronic acid synthase-1 mRNA levels and HA staining were increased in normal prostate tissue surrounding prostate cancer. Orthotopic prostate cancer growth was increased by intraprostatic injection of HA. In conclusion, cancer in the prostate apparently stimulates HA synthesis both in tumor stroma and in the surrounding normal tissue. This promoted tumor growth and was associated with an unfavorable outcome.

Targeting castration-induced tumour hypoxia enhances the acute effects of castration therapy in a rat prostate cancer model

What's known on the subject? and What does the study add? Castration therapy has rather modest effects on cell death in tumours but can be enhanced by other treatments targeting tumour stroma and vasculature. This study shows that the prostate becomes hypoxic following castration and that targeting hypoxic cells during castration therapy potently enhances the effects of castration.

OBJECTIVE

To explore the effects of castration therapy, the standard treatment for advanced prostate cancer, in relation to tumour hypoxia and to elicit its importance for the short- and long-term therapeutic response.

MATERIAL AND METHODS

We used the androgen-sensitive rat Dunning H prostate tumour model that transiently responds to castration treatment followed by a subsequent relapse, much like the scenario in human patients. Tumour tissues were analysed using stereological methods in intact, 1 and 7 days after castration therapy.

RESULTS

Hypoxia was transiently up-regulated after castration therapy and correlated with the induction of tumour cell apoptosis. When castration therapy was combined with tirapazamine (TPZ), a drug that targets hypoxic cells and the vasculature, the effects on tumour cell apoptosis and tumour volume were enhanced in comparison to either castration or TPZ alone.

CONCLUSION

The present study suggests that castration-induced tumour hypoxia is a novel target for therapy.

Thrombospondin-1 regulates the normal prostate in vivo through angiogenesis and TGF-beta activation

Castration experiments in rodents show that the stromal vasculature is critical to the androgen-mediated prostate growth regulation. However, the role of angiogenesis inhibitors, such as thrombospondin-1 (TSP-1), in this process is unclear. TSP-1 is a multifunctional glycoprotein that can function as a potent angiogenesis inhibitor and an in vivo activator of latent transforming growth factor-beta (TGF-beta) in some tissues. On the basis of these observations, we hypothesized that TSP-1 regulated androgen withdrawal-induced prostate regression and that this process was mediated not only through antiangiogenic activity but also through TGF-beta activation. To test this, we evaluated angiogenic activity in human prostate epithelial and stromal cells treated with androgens and hypoxia in vitro. TSP-1 knockout mice were characterized to investigate the in vivo functions of TSP-1. In vitro, we found that androgens and hypoxia differentially regulated TSP-1 and angiogenic activity. Androgens stimulated normal epithelial cell, but inhibited normal stromal cell, angiogenic activity. Conversely, hypoxia stimulated stromal while inhibiting epithelial activity. Thus, in vivo, net angiogenic activity must reflect cellular interactions. And, we found that media conditioned by epithelial cells grown under normoxic conditions stimulated stromal cell angiogenic activity, and if epithelial cells were grown under hypoxic conditions, stromal activity was further increased. TSP-1 levels, however, were unchanged. In vivo, TSP-1 loss in a mouse model led to prostate epithelial hyperplasia by 3 months of age with only a modest stromal effect. Androgens suppressed TSP-1 as expression increased after castration both in normal mouse prostate and in human prostate cancer tissues. In addition, TSP-1 expression corresponded to increased TGF-beta activation in mouse tissues, specifically in the stromal compartment. These data show a critical role for TSP-1 in prostate epithelial and stromal growth regulation through angiogenic inhibition and activation of latent TGF-beta. Therefore, loss of TSP-1 during tumorigenesis would eliminate two barriers to cancer progression.