Friedemann Zengerling

Inhibition of Glycogen Synthase Kinase-3β Counteracts Ligand-Independent Activity of the Androgen Receptor in Castration Resistant Prostate Cancer

In order to generate genomic signals, the androgen receptor (AR) has to be transported into the nucleus upon androgenic stimuli. However, there is evidence from in vitro experiments that in castration-resistant prostate cancer (CRPC) cells the AR is able to translocate into the nucleus in a ligand-independent manner. The recent finding that inhibition of the glycogen-synthase-kinase 3β (GSK-3β) induces a rapid nuclear export of the AR in androgen-stimulated prostate cancer cells prompted us to analyze the effects of a GSK-3β inhibition in the castration-resistant LNCaP sublines C4-2 and LNCaP-SSR. Both cell lines exhibit high levels of nuclear AR in the absence of androgenic stimuli. Exposure of these cells to the maleimide SB216763, a potent GSK-3β inhibitor, resulted in a rapid nuclear export of the AR even under androgen-deprived conditions. Moreover, the ability of C4-2 and LNCaP-SSR cells to grow in the absence of androgens was diminished after pharmacological inhibition of GSK-3β in vitro. The ability of SB216763 to modulate AR signalling and function in CRPC in vivo was additionally demonstrated in a modified chick chorioallantoic membrane xenograft assay after systemic delivery of SB216763. Our data suggest that inhibition of GSK-3β helps target the AR for export from the nucleus thereby diminishing the effects of mislocated AR in CRPC cells. Therefore, inhibition of GSK-3β could be an interesting new strategy for the treatment of CRPC.

Circulating free testosterone is an independent predictor of advanced disease in patients with clinically localized prostate cancer

PurposeTo evaluate the clinical value of the pre-treatment calculated free testosterone (fT), total testosterone (tT), sexual hormone-binding globulin (SHBG) and estradiol (E2) levels as potential predictors of pathological stage and grade in patients with clinically localized prostate cancer.MethodsPreoperative sex hormone serum levels were prospectively measured in 137 patients who underwent radical prostatectomy at the University Hospital Ulm from February 2011 to February 2012. We related sex hormone levels to clinicopathologic data including tumour stage, Gleason score and prostate specific antigen (PSA). (Non)parametric statistical tests and receiver operating characteristics (ROC) analyses were performed.ResultsPreoperative serum fT levels were significantly associated with advanced disease (pT3–4 and/or pN+; pxa0=xa00.047) and lymph node involvement (pN+) (pxa0=xa00.027). Patients with low (<0.047xa0μg/l) vs. normal fT values (≥0.047xa0μg/l) were associated with higher tumour stage (pxa0=xa00.049), positive lymph node status (pN+xa0, pxa0=xa00.038) and advance disease (pxa0=xa00.016). Moreover, low tT values (≤0.193xa0μg/l; pxa0=xa00.018) and elevated SHBG levels (>48.4xa0nmol/l, pxa0=xa00.043) correlated with a higher Gleason score. Conversely, E2 levels were not associated with tumour stage or grade. Applying multivariate analysis, unlike tT, SHBG, and E2 levels, low fT levels were a significant independent predictor of advanced disease (relative hazard ratio 3.05, pxa0=xa00.028).ConclusionsLow pre-treatment fT levels were significantly associated with tumour stage and extraprostatic tumour spread and might—in addition or combination with PSA—serve as a useful prognostic parameter for prostate cancer patients prior to radical prostatectomy.

Effects of sorafenib on C-terminally truncated androgen receptor variants in human prostate cancer cells.

Recent evidence suggests that the development of castration resistant prostate cancer (CRPCa) is commonly associated with an aberrant, ligand-independent activation of the androgen receptor (AR). A putative mechanism allowing prostate cancer (PCa) cells to grow under low levels of androgens, is the expression of constitutively active, C-terminally truncated AR lacking the AR-ligand binding domain (LBD). Due to the absence of a LBD, these receptors, termed ARΔLBD, are unable to respond to any form of anti-hormonal therapies. In this study we demonstrate that the multikinase inhibitor sorafenib inhibits AR as well as ARΔLBD-signalling in CRPCa cells. This inhibition was paralleled by proteasomal degradation of the AR- and ARΔLBD-molecules. In line with these observations, maximal antiproliferative effects of sorafenib were achieved in AR and ARΔLBD-positive PCa cells. The present findings warrant further investigations on sorafenib as an option for the treatment of advanced AR-positive PCa.

AR-Q640X, a model to study the effects of constitutively active C-terminally truncated AR variants in prostate cancer cells

PurposeA recently identified mechanism allowing prostate cancer (PCa) cells to grow in the absence of androgens is the expression of constitutively active, C-terminally truncated androgen receptor (AR) variants lacking vast parts of the ligand-binding domain. These AR variants termed ARΔLBD are either products of alternative splicing, point mutations leading to premature stop codons or proteolytic cleavage of the AR. Some controversies exist about the requirement of additional full-length AR for the full transcriptional activity of the ARΔLBD. On basis of a mutated, C-terminally truncated AR termed Q640X, we developed an experimental model for the study of ARΔLBD in PCa cells.MethodsActivation of AR-dependent promoters was analyzed by reporter gene assays. Dimerization studies were conducted using a mammalian two-hybrid system.ResultsAlthough Q640X/Q640X homodimers were able to induce the expression of certain AR target genes, Q640X/AR heterodimers were necessary to activate the full panel of androgen-dependent genes under androgen-deprived conditions.ConclusionsThe following study supports the hypothesis that castration-resistant prostate cancer (CRPC) cells are able to activate specific androgen-dependent genes by selective modulation of the ratio between ARΔLBD and their putative dimerization partners like the full-length AR or other ARΔLBD in the absence of androgens. The present data suggest that AR-mutant Q640X is a powerful experimental tool for the functional analysis of ARΔLBD in CRPC.

Stilbene induced inhibition of androgen receptor dimerization: implications for AR and ARΔLBD-signalling in human prostate cancer cells.

Background Advanced castration resistant prostate cancer (CRPC) is often characterized by an increase of C-terminally truncated, constitutively active androgen receptor (AR) variants. Due to the absence of a ligand binding domain located in the AR-C-terminus, these receptor variants (also termed ARΔLBD) are unable to respond to all classical forms of endocrine treatments like surgical/chemical castration and/or application of anti-androgens. Methodology In this study we tested the effects of the naturally occurring stilbene resveratrol (RSV) and (E)-4-(2, 6-Difluorostyryl)-N, N-dimethylaniline, a fluorinated dialkylaminostilbene (FIDAS) on AR- and ARΔLBD in prostate cancer cells. The ability of the compounds to modulate transcriptional activity of AR and the ARΔLBD-variant Q640X was shown by reporter gene assays. Expression of endogenous AR and ARΔLBD mRNA and protein levels were determined by qRT-PCR and Western Blot. Nuclear translocation of AR-molecules was analyzed by fluorescence microscopy. AR and ARΔLBD/Q640X homo-/heterodimer formation was assessed by mammalian two hybrid assays. Biological activity of both compounds in vivo was demonstrated using a chick chorioallantoic membrane xenograft assay. Results The stilbenes RSV and FIDAS were able to significantly diminish AR and Q640X-signalling. Successful inhibition of the Q640X suggests that RSV and FIDAS are not interfering with the AR-ligand binding domain like all currently available anti-hormonal drugs. Repression of AR and Q640X-signalling by RSV and FIDAS in prostate cancer cells was caused by an inhibition of the AR and/or Q640X-dimerization. Although systemic bioavailability of both stilbenes is very low, both compounds were also able to downregulate tumor growth and AR-signalling in vivo. Conclusion RSV and FIDAS are able to inhibit the dimerization of AR and ARΔLBD molecules suggesting that stilbenes might serve as lead compounds for a novel generation of AR-inhibitors.

German second-opinion network for testicular cancer: Sealing the leaky pipe between evidence and clinical practice

In 2006, the German Testicular Cancer Study Group initiated an extensive evidence-based national second-opinion network to improve the care of testicular cancer patients. The primary aims were to reflect the current state of testicular cancer treatment in Germany and to analyze the project’s effect on the quality of care delivered to testicular cancer patients. A freely available internet-based platform was developed for the exchange of data between the urologists seeking advice and the 31 second-opinion givers. After providing all data relevant to the primary treatment decision, urologists received a second opinion on their therapy plan within <48 h. Endpoints were congruence between the first and second opinion, conformity of applied therapy with the corresponding recommendation and progression-free survival rate of the introduced patients. Significance was determined by two-sided Pearson’s χ2 test. A total of 1,284 second-opinion requests were submitted from November 2006 to October 2011, and 926 of these cases were eligible for further analysis. A discrepancy was found between first and second opinion in 39.5% of the cases. Discrepant second opinions led to less extensive treatment in 28.1% and to more extensive treatment in 15.6%. Patients treated within the framework of the second-opinion project had an overall 2-year progression-free survival rate of 90.4%. Approximately every 6th second opinion led to a relevant change in therapy. Despite the lack of financial incentives, data from every 8th testicular cancer patient in Germany were submitted to second-opinion centers. Second-opinion centers can help to improve the implementation of evidence into clinical practice.

Androgen receptor aberrations in the era of abiraterone and enzalutamide

Prostate cancer is the most prevalent non-skin cancer and the second leading cause of cancer death in men of the western world. As growth and differentiation of prostate cancer largely depend on androgens, inhibition of the androgen/androgen receptor signaling axis is the main treatment for locally advanced and/or metastatic tumors. Although first-line androgen deprivation therapies like chemical/surgical castration and/or administration of anti-androgens are able to control the disease for several years, prostate cancer almost invariably recurs as castration-resistant prostate cancer. This stage of the disease is characterized by a sustained AR-signaling despite castrate levels of circulating androgens. Various molecular mechanisms were shown to induce castration resistance. This review will discuss the most recent and relevant experimental findings on AR-signaling in castration-resistant prostate cancer in order to provide a comprehensive interpretation of the clinical behavior of this tumor entity following treatments with abiraterone, enzalutamide, ARN-509 or taxanes.

Inhibition of IGF-1R diminishes transcriptional activity of the androgen receptor and its constitutively active, C-terminally truncated counterparts Q640X and AR-V7

AbstractPurposeFailure of endocrine treatment in castration-resistant prostate cancer (CRPC) is often associated with the emergence of C-terminally truncated androgen receptor variants that function as constitutively active transcription factors (i.e., AR∆LBD). The mechanisms involved in the regulation of AR∆LBD signaling are largely unknown. Since the IGF-1 pathway was repeatedly shown to affect AR function, we studied whether an inhibition of IGF-1R could also affect AR∆LBD signaling.nMethodsRegulation of androgen receptor (AR) and AR∆LBD signaling was analyzed by reporter gene assays, immunoblotting, ELISA and quantitative RT-PCR.ResultsInhibition of IGF-1R with the small-molecule inhibitor NVP-AEW541 reduced the transcriptional activity of the AR and its truncated counterparts Q640X and AR-V7. As shown in Q640X, the inhibition of transcriptional activity was paralleled by a decreased receptor phosphorylation.ConclusionsInhibition of IGF-1R leads to a down-regulation of AR∆LBD signaling and provides a rationale for CRPC therapies targeting growth factor receptors.

The "Aging Males' Symptoms" Scale (AMS): predictive value for lowered circulating androgens.

Background: Symptoms of the “male climacteric” are often at least in part referred to an age-dependent decline of serum androgen levels. Therefore, we evaluated the relationship of climacteric symptoms as assessed by the “Aging Males’ Symptoms” (AMS) Questionnaire with circulating androgen levels. Methods: 146 ambulatory men (age, 27–85 years) were surveyed with the AMS Questionnaire and sampled for serum values of total testosterone (tT) and sexual hormone binding globulin (SHBG). Free testosterone (fT) was calculated from tT and SHBG. A total AMS score ≥37 was considered pathological; the lower limits for tT and fT were set to 8 nmol/l and 180 pmol/l, respectively. Results: A significant deficit in tT and fT was shown in 25 (17.1%) and 34 (24.5%) men, respectively; the AMS Questionnaire showed pathological results for 66 (45.2%) men. In predicting a tT deficit, the AMS Questionnaire rendered a sensitivity of 76% and a specificity of 61.6%, only. However, multiple regression analysis revealed a significant correlation of lowered tT with a pathological somatovegetative and psychological AMS subscore (p = 0.042 and p = 0.01) and a correlation of lowered fT with a pathological sexual subscore (p = 0.039). Conclusion: In predicting hypogonadism the AMS Questionnaire in total did not render a sufficient diagnostic efficiency.

Partial nephrectomy using porcine small intestinal submucosa

BackgroundWhenever technically feasible and oncologically justified, nephron-sparing surgery is the current standard of care for localized renal cell carcinomas (RCC). The main complications of partial nephrectomy, especially for large and centrally located tumors, are urinary leakage and parenchymal bleeding. We prospectively evaluated the pros and cons of using porcine small intestinal submucosa (SIS, Surgisis®) to close the renal defect after nephron-sparing surgery.MethodsWe used Surgisis® (Cook medical, Bloomington, IN, USA) to secure and compress the capsular defect after tumor resection in 123 patients submitted to 129 partial nephrectomies between August 2003 and February 2011.ResultsThe median tumor size was 3.7 cm (range 1.1-13.0 cm). Procedures were performed with cold ischemia in 24 cases (18.2%), with warm ischemia in 46 (35.6%), and without ischemia in 59 cases (44.8%). In the total group of patients, 4 (3.1%) developed urinary fistula, and only 2 (1.6%) required postoperative transfusions due to hemorrhage after the application of the small intestinal submucosa membrane.ConclusionSmall intestinal submucosa is an easy-to-use biomaterial for preventing complications such as postoperative bleeding and urinary fistula in nephron-sparing surgery, especially in cases where tumor excision causes significant renal capsular and/or renal pelvic defects.