Manuel Luedeke

Detecting predictive androgen receptor modifications in circulating prostate cancer cells

Molecular modifications of the androgen receptor (AR) can cause resistance to androgen deprivation therapy (ADT) in prostate cancer patients. Since lack of representative tumor samples hinders therapy adjustments according to emerging AR-modifications, we evaluated simultaneous detection of the two most common AR modifications (AR-V7 splice variant and AR point mutations) in circulating tumor cells (CTCs). We devised a single-tube assay to detect AR-V7 splice variants and AR point mutations in CTCs using immunomagnetic cell isolation, followed by quantitative real-time PCR and DNA pyrosequencing. We prospectively investigated 47 patients with PSA progression awaiting therapy switch. Comparison of response to newly administered therapy and CTC-AR-status allowed effect size estimation. Nineteen (51%) of 37 patients with detectable CTCs carried AR-modifications. Seventeen patients carried the AR-V7 splice variant, one harbored a p.T878A point mutation and one harbored both AR-V7 and a p.H875Y mutation. We estimated a positive predictive value for response and non-response to therapy by AR status in CTCs of ~94%. Based on a conservative calculation, we estimated the effect size for molecularly-informed therapy switches for prospective clinical trial planning to ~27%. In summary, the ability to determine key resistance-mediating AR modifications in CTCs has the potential to considerably improve prostate cancer treatment.

Expression of AR-V7 in Circulating Tumour Cells Does Not Preclude Response to Next Generation Androgen Deprivation Therapy in Patients with Castration Resistant Prostate Cancer

The androgen receptor splice variant AR-V7 has recently been discussed as a predictive biomarker for nonresponse to next-generation androgen deprivation therapy (ADT) in patients with castration-resistant prostate cancer. However, we recently identified one patient showing a response from abiraterone despite expression of AR-V7 in his circulating tumour cells (CTC). Therefore, we precisely assessed the response in a cohort of 21 AR-V7 positive castration-resistant prostate cancer patients who had received therapy with abiraterone or enzalutamide. We detected a subgroup of six AR-V7 positive patients showing benefit from either abiraterone or enzalutamide. Their progression free survival was 26 d (censored) to 188 d. Four patients displayed a prostate-specific antigen decrease of >50%. When analysing prior therapies, we noticed that only one of the six patients had received next-generation ADT prior to CTC collection. As a result, we conclude that AR-V7 status in CTC cannot entirely predict nonresponse to next generation ADT and AR-V7-positive patients should not be systematically denied abiraterone or enzalutamide treatment, especially as effective alternative treatment options are still limited. PATIENT SUMMARY A subgroup of patients can benefit from abiraterone and/or enzalutamide despite detection of AR-V7 splice variants in their circulating tumour cells.

POU5F1P1, a putative cancer susceptibility gene, is overexpressed in prostatic carcinoma.

Association between genetic variants located on human chromosome 8q24.21 with an increased risk for prostatic carcinoma has been well established. POU5F1P1, a processed pseudogene homologous to the pluripotency factor OCT4, is the only sequence with coding capacity in this region. The objective of this study was to investigate the POU5F1P1 expression in prostatic carcinoma and carcinoma surrounding prostatic tissue.

Multiple novel prostate cancer susceptibility signals identified by fine-mapping of known risk loci among Europeans

Genome-wide association studies (GWAS) have identified numerous common prostate cancer (PrCa) susceptibility loci. We have fine-mapped 64 GWAS regions known at the conclusion of the iCOGS study using large-scale genotyping and imputation in 25 723 PrCa cases and 26 274 controls of European ancestry. We detected evidence for multiple independent signals at 16 regions, 12 of which contained additional newly identified significant associations. A single signal comprising a spectrum of correlated variation was observed at 39 regions; 35 of which are now described by a novel more significantly associated lead SNP, while the originally reported variant remained as the lead SNP only in 4 regions. We also confirmed two association signals in Europeans that had been previously reported only in East-Asian GWAS. Based on statistical evidence and linkage disequilibrium (LD) structure, we have curated and narrowed down the list of the most likely candidate causal variants for each region. Functional annotation using data from ENCODE filtered for PrCa cell lines and eQTL analysis demonstrated significant enrichment for overlap with bio-features within this set. By incorporating the novel risk variants identified here alongside the refined data for existing association signals, we estimate that these loci now explain ∼38.9% of the familial relative risk of PrCa, an 8.9% improvement over the previously reported GWAS tag SNPs. This suggests that a significant fraction of the heritability of PrCa may have been hidden during the discovery phase of GWAS, in particular due to the presence of multiple independent signals within the same region.

Predisposition for TMPRSS2-ERG Fusion in Prostate Cancer by Variants in DNA Repair Genes

The somatic fusion of TMPRSS2 to ETS oncogenes is a common event in prostate cancer (PCa). We hypothesized that defects in DNA repair may lead to an increase of chromosomal rearrangements and thus to the occurrence of ETS oncogene fusion. We have previously conducted a genome-wide linkage analysis in TMPRSS2-ERG fusion-positive PCa families, revealing potential susceptibility loci on chromosomes 5q14, 9q21, 10q26, 11q24, 12q15, 13q12, 18q, and Xq27. In the present study, nine candidate genes from these regions were selected from the context of DNA repair and screened for mutations in TMPRSS2-ERG fusion-positive families. Thirteen nonsynonymous variants, 5 of which had a minor allele frequency of <0.05, were genotyped in 210 familial cases, 47 of which with a known TMPRSS2-ERG status, 329 sporadic cases, and 512 controls. Significant association of TMPRSS2-ERG fusion-positive PCa was found with rare variants in the genes for POLI [variant F532S: P = 0.0011; odds ratios (OR), 4.62; 95% confidence interval (95% CI), 1.84-11.56] and ESCO1 (variant N191S: P = 0.0034; OR, 4.27; 95% CI, 1.62-11.28). Additional findings, regardless of TMPRSS2-ERG status, were the overrepresentation of a rare BRCA2 variant (V2728I: P = 0.03; OR, 6.16; 95% CI, 1.19-32.00) in familial PCa and of a common allele of RMI1 (variant N455S: P = 0.02; OR, 1.33; 95% CI, 1.04-1.70) in unselected PCa cases. The DNA repair genes POLI and ESCO1 are proposed as susceptibility genes for TMPRSS2-ERG fusion-positive PCa that warrant further investigation. (Cancer Epidemiol Biomarkers Prev 2009;18(11):3030–5)

Heritability of baseline and induced micronucleus frequencies

The scoring of micronuclei (MN) is widely used in biomonitoring and mutagenicity testing as a surrogate marker of chromosomal damage inflicted by clastogenic agents or by aneugens. Individual differences in the response to a mutagenic challenge are known from studies on cancer patients and carriers of mutations in DNA repair genes. However, it has not been studied to which extent genetic factors contribute to the observed variability of individual MN frequencies. Our aim was to quantify this heritable genetic component of both baseline and radiation-induced MN frequencies. We performed a twin study comprising 39 monozygotic (MZ) and 10 dizygotic (DZ) twin pairs. Due to the small number of DZ pairs, we had to recruit controls from which 38 age- and gender-matched random control pairs (CPs) were generated. For heritability estimates, we used biometrical modelling of additive genetic, common environmental, and unique environmental components (ACE model) of variance and direct comparison of variance between the sample groups. While heritability estimates from MZ to DZ comparisons produced inconclusive results, both estimation methods revealed a high degree of heritability (h(2)) for baseline MN frequency (h(2) = 0.68 and h(2) = 0.72) as well as for the induced frequency (h(2) = 0.68 and h(2) = 0.57) when MZ were compared to CP. The result was supported by the different intraclass correlation coefficients of MZ, DZ and CP for baseline (r = 0.63, r = 0.31 and r = 0.0, respectively) as well as for induced MN frequencies (r = 0.79, r = 0.74 and r = 0.0, respectively). This study clearly demonstrates that MN frequencies are determined by genetic factors to a major part. The strong reflection of the genetic background supports the idea that MN frequencies represent an intermediate phenotype between molecular DNA repair mechanisms and the cancer phenotype and affirms the approaches that are made to utilise them as predictors of, for example, cancer risk.

Expression changes of CAV1 and EZH2, located on 7q31∼q36, are rarely related to genomic alterations in primary prostate carcinoma

The chromosomal region 7q was repeatedly found to be rearranged in prostate carcinoma. It harbors several well described candidate tumor suppressor and oncogenes. We addressed two genes with opposite roles in cancer; CAV1, a putative tumor suppressor gene at 7q31, and EZH2 at 7q36, which is believed to promote tumor progression. Our primary aim was to assess their expression changes in primary tumors, and then to elucidate the underlying mechanism, assuming that genomic alterations of either locus could affect the other gene as well. In 35 prostate tumor samples, compared with adjacent tissues, CAV1 was overall downregulated (P < 10(-06)), whereas EZH2 was significantly overexpressed (P < 10(-06)). The observed dysregulations were coincident in nearly 70% of the cases. Copy number changes occurred in few tumors. Loss of CAV1 DNA was only marginally associated with reduced expression (P = 0.07), however, and genomic amplification of EZH2 could not explain its upregulation. Through bisulfite sequencing of four tumor samples, CpG-hypermethylation was verified as an alternative mechanism for CAV1 silencing, as reported previously. Moreover, it could also be involved in the reactivation of EZH2.

Prediction of individual genetic risk to prostate cancer using a polygenic score.

Polygenic risk scores comprising established susceptibility variants have shown to be informative classifiers for several complex diseases including prostate cancer. For prostate cancer it is unknown if inclusion of genetic markers that have so far not been associated with prostate cancer risk at a genome‐wide significant level will improve disease prediction.

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.

Genome-Wide Association Study of Prostate Cancer–Specific Survival

Background: Unnecessary intervention and overtreatment of indolent disease are common challenges in clinical management of prostate cancer. Improved tools to distinguish lethal from indolent disease are critical. Methods: We performed a genome-wide survival analysis of cause-specific death in 24,023 prostate cancer patients (3,513 disease-specific deaths) from the PRACTICAL and BPC3 consortia. Top findings were assessed for replication in a Norwegian cohort (CONOR). Results: We observed no significant association between genetic variants and prostate cancer survival. Conclusions: Common genetic variants with large impact on prostate cancer survival were not observed in this study. Impact: Future studies should be designed for identification of rare variants with large effect sizes or common variants with small effect sizes. Cancer Epidemiol Biomarkers Prev; 24(11); 1796–800. ©2015 AACR.