William B. Isaacs

AR-V7 and Resistance to Enzalutamide and Abiraterone in Prostate Cancer

BACKGROUND The androgen-receptor isoform encoded by splice variant 7 lacks the ligand-binding domain, which is the target of enzalutamide and abiraterone, but remains constitutively active as a transcription factor. We hypothesized that detection of androgen-receptor splice variant 7 messenger RNA (AR-V7) in circulating tumor cells from men with advanced prostate cancer would be associated with resistance to enzalutamide and abiraterone. METHODS We used a quantitative reverse-transcriptase-polymerase-chain-reaction assay to evaluate AR-V7 in circulating tumor cells from prospectively enrolled patients with metastatic castration-resistant prostate cancer who were initiating treatment with either enzalutamide or abiraterone. We examined associations between AR-V7 status (positive vs. negative) and prostate-specific antigen (PSA) response rates (the primary end point), freedom from PSA progression (PSA progression-free survival), clinical or radiographic progression-free survival, and overall survival. RESULTS A total of 31 enzalutamide-treated patients and 31 abiraterone-treated patients were enrolled, of whom 39% and 19%, respectively, had detectable AR-V7 in circulating tumor cells. Among men receiving enzalutamide, AR-V7-positive patients had lower PSA response rates than AR-V7-negative patients (0% vs. 53%, P=0.004) and shorter PSA progression-free survival (median, 1.4 months vs. 6.0 months; P<0.001), clinical or radiographic progression-free survival (median, 2.1 months vs. 6.1 months; P<0.001), and overall survival (median, 5.5 months vs. not reached; P=0.002). Similarly, among men receiving abiraterone, AR-V7-positive patients had lower PSA response rates than AR-V7-negative patients (0% vs. 68%, P=0.004) and shorter PSA progression-free survival (median, 1.3 months vs. not reached; P<0.001), clinical or radiographic progression-free survival (median, 2.3 months vs. not reached; P<0.001), and overall survival (median, 10.6 months vs. not reached, P=0.006). The association between AR-V7 detection and therapeutic resistance was maintained after adjustment for expression of full-length androgen receptor messenger RNA. CONCLUSIONS Detection of AR-V7 in circulating tumor cells from patients with castration-resistant prostate cancer may be associated with resistance to enzalutamide and abiraterone. These findings require large-scale prospective validation. (Funded by the Prostate Cancer Foundation and others.).

Genome-wide association study identifies a second prostate cancer susceptibility variant at 8q24

Prostate cancer is the most prevalent noncutaneous cancer in males in developed regions, with African American men having among the highest worldwide incidence and mortality rates. Here we report a second genetic variant in the 8q24 region that, in conjunction with another variant we recently discovered, accounts for about 11%–13% of prostate cancer cases in individuals of European descent and 31% of cases in African Americans. We made the current discovery through a genome-wide association scan of 1,453 affected Icelandic individuals and 3,064 controls using the Illumina HumanHap300 BeadChip followed by four replication studies. A key step in the discovery was the construction of a 14-SNP haplotype that efficiently tags a relatively uncommon (2%–4%) susceptibility variant in individuals of European descent that happens to be very common (∼42%) in African Americans. The newly identified variant shows a stronger association with affected individuals who have an earlier age at diagnosis.

Major susceptibility locus for prostate cancer on chromosome 1 suggested by a genome-wide search.

Despite its high prevalence, very little is known regarding genetic predisposition to prostate cancer. A genome-wide scan performed in 66 high-risk prostate cancer families has provided evidence of linkage to the long arm of chromosome 1 (1q24-25). Analysis of an additional set of 25 North American and Swedish families with markers in this region resulted in significant evidence of linkage in the combined set of 91 families. The data provide strong evidence of a major prostate cancer susceptibility locus on chromosome 1.

Evidence for a prostate cancer susceptibility locus on the X chromosome.

Over 200,000 new prostate cancer cases are diagnosed in the United States each year, accounting for more than 35% of all cancer cases affecting men, and resulting in 40,000 deaths annually1. Attempts to characterize genes predisposing to prostate cancer have been hampered by a high phenocopy rate, the late age of onset of the disease and, in the absence of distinguishing clinical features, the inability to stratify patients into subgroups relative to suspected genetic locus heterogeneity. We previously performed a genome-wide search for hereditary prostate cancer (HPC) genes, finding evidence of a prostate cancer susceptibility locus on chromosome 1 (termed HPC1; ref. 2). Here we present evidence for the location of a second prostate cancer susceptibility gene, which by heterogeneity estimates accounts for approximately 16% of HPC cases. This HPC locus resides on the X chromosome (Xq27-28), a finding consistent with results of previous population-based studies suggesting an X-linked mode of HPC inheritance. Linkage to Xq27-28 was observed in a combined study population of 360 prostate cancer families collected at four independent sites in North America, Finland and Sweden. A maximum two-point lod score of 4.60 was observed at DXS1113, θ=0.26, in the combined data set. Parametric multipoint and non-parametric analyses provided results consistent with the two-point analysis. evidence for genetic locus heterogeneity was observed, with similar estimates of the proportion of linked families in each separate family collection. Genetic mapping of the locus represents an important initial step in the identification of an X-linked gene implicated in the aetiology of HPC.

Cumulative Association of Five Genetic Variants with Prostate Cancer

BACKGROUND Single-nucleotide polymorphisms (SNPs) in five chromosomal regions--three at 8q24 and one each at 17q12 and 17q24.3--have been associated with prostate cancer. Each SNP has only a moderate association, but when SNPs are combined, the association may be stronger. METHODS We evaluated 16 SNPs from five chromosomal regions in a Swedish population (2893 subjects with prostate cancer and 1781 control subjects) and assessed the individual and combined association of the SNPs with prostate cancer. RESULTS Multiple SNPs in each of the five regions were associated with prostate cancer in single SNP analysis. When the most significant SNP from each of the five regions was selected and included in a multivariate analysis, each SNP remained significant after adjustment for other SNPs and family history. Together, the five SNPs and family history were estimated to account for 46% of the cases of prostate cancer in the Swedish men we studied. The five SNPs plus family history had a cumulative association with prostate cancer (P for trend, 3.93x10(-28)). In men who had any five or more of these factors associated with prostate cancer, the odds ratio for prostate cancer was 9.46 (P=1.29x10(-8)), as compared with men without any of the factors. The cumulative effect of these variants and family history was independent of serum levels of prostate-specific antigen at diagnosis. CONCLUSIONS SNPs in five chromosomal regions plus a family history of prostate cancer have a cumulative and significant association with prostate cancer.

Germline mutations in the ribonuclease L gene in families showing linkage with HPC1.

Although prostate cancer is the most common non-cutaneous malignancy diagnosed in men in the United States, little is known about inherited factors that influence its genetic predisposition. Here we report that germline mutations in the gene encoding 2′-5′-oligoadenylate(2-5A)–dependent RNase L (RNASEL) segregate in prostate cancer families that show linkage to the HPC1 (hereditary prostate cancer 1) region at 1q24–25 (ref. 9). We identified RNASEL by a positional cloning/candidate gene method, and show that a nonsense mutation and a mutation in an initiation codon of RNASEL segregate independently in two HPC1-linked families. Inactive RNASEL alleles are present at a low frequency in the general population. RNASEL regulates cell proliferation and apoptosis through the interferon-regulated 2-5A pathway and has been suggested to be a candidate tumor suppressor gene. We found that microdissected tumors with a germline mutation showed loss of heterozygosity and loss of RNase L protein, and that RNASEL activity was reduced in lymphoblasts from heterozyogous individuals compared with family members who were homozygous with respect to the wildtype allele. Thus, germline mutations in RNASEL may be of diagnostic value, and the 2-5A pathway might provide opportunities for developing therapies for those with prostate cancer.

Copy Number Analysis Indicates Monoclonal Origin of Lethal Metastatic Prostate Cancer

Many studies have shown that primary prostate cancers are multifocal and are composed of multiple genetically distinct cancer cell clones. Whether or not multiclonal primary prostate cancers typically give rise to multiclonal or monoclonal prostate cancer metastases is largely unknown, although studies at single chromosomal loci are consistent with the latter case. Here we show through a high-resolution genome-wide single nucleotide polymorphism and copy number survey that most, if not all, metastatic prostate cancers have monoclonal origins and maintain a unique signature copy number pattern of the parent cancer cell while also accumulating a variable number of separate subclonally sustained changes. We find no relationship between anatomic site of metastasis and genomic copy number change pattern. Taken together with past animal and cytogenetic studies of metastasis and recent single-locus genetic data in prostate and other metastatic cancers, these data indicate that despite common genomic heterogeneity in primary cancers, most metastatic cancers arise from a single precursor cancer cell. This study establishes that genomic archeology of multiple anatomically separate metastatic cancers in individuals can be used to define the salient genomic features of a parent cancer clone of proven lethal metastatic phenotype.

Hypermethylation of CpG Islands in Primary and Metastatic Human Prostate Cancer

Aberrant DNA methylation patterns may be the earliest somatic genome changes in prostate cancer. Using real-time methylation-specific PCR, we assessed the extent of hypermethylation at 16 CpG islands in DNA from seven prostate cancer cell lines (LNCaP, PC-3, DU-145, LAPC-4, CWR22Rv1, VCaP, and C42B), normal prostate epithelial cells, normal prostate stromal cells, 73 primary prostate cancers, 91 metastatic prostate cancers, and 25 noncancerous prostate tissues. We found that CpG islands at GSTP1, APC, RASSF1a, PTGS2, and MDR1 were hypermethylated in >85% of prostate cancers and cancer cell lines but not in normal prostate cells and tissues; CpG islands at EDNRB, ESR1, CDKN2a, and hMLH1 exhibited low to moderate rates of hypermethylation in prostate cancer tissues and cancer cell lines but were entirely unmethylated in normal tissues; and CpG islands at DAPK1, TIMP3, MGMT, CDKN2b, p14/ARF, and CDH1 were not abnormally hypermethylated in prostate cancers. Receiver operator characteristic curve analyses suggested that CpG island hypermethylation changes at GSTP1, APC, RASSF1a, PTGS2, and MDR1 in various combinations can distinguish primary prostate cancer from benign prostate tissues with sensitivities of 97.3–100% and specificities of 92–100%. Hypermethylation of the CpG island at EDNRB was correlated with the grade and stage of the primary prostate cancers. PTGS2 CpG island hypermethylation portended an increased risk of recurrence. Furthermore, CpG island hypermethylation patterns in prostate cancer metastases were very similar to the primary prostate cancers and tended to show greater differences between cases than between anatomical sites of metastasis.

Pathological and molecular aspects of prostate cancer

This review focuses on new findings and controversial issues in the the pathology and molecular biology of adenocarcinoma of the prostate. Since management of high-grade prostatic intraepithelial neoplasia on needle biopsy--the most common precursor lesion to prostate cancer--is the crucial issue with this lesion, we discuss the risk of cancer subsequent to this histological diagnosis and the issue of whether such neoplasia should be regarded as carcinoma-in-situ. We also look at prostate cancer itself, starting with its diagnosis, reporting on needle biopsy, and reviewing how the most frequently used grading system, the Gleason grading system, affects treatment. The molecular basis of prostate cancer includes inheritable and somatic genetic changes (tumour suppressor genes, loss of heterozygosity, gene targets and regions of chromosomal gain, CpG island promoter methylation, invasion and metastasis suppressor genes, telomere shortening, and genetic instability). Changed gene expression (eg, proliferation-related genes, changes in the androgen receptor, apoptosis and stress-response genes) have potential as biomarkers and therapeutic targets in prostate cancer.

Germline mutations and sequence variants of the macrophage scavenger receptor 1 gene are associated with prostate cancer risk

Deletions on human chromosome 8p22–23 in prostate cancer cells and linkage studies in families affected with hereditary prostate cancer (HPC) have implicated this region in the development of prostate cancer. The macrophage scavenger receptor 1 gene (MSR1, also known as SR-A) is located at 8p22 and functions in several processes proposed to be relevant to prostate carcinogenesis. Here we report the results of genetic analyses that indicate that mutations in MSR1 may be associated with risk of prostate cancer. Among families affected with HPC, we identified six rare missense mutations and one nonsense mutation in MSR1. A family-based linkage and association test indicated that these mutations co-segregate with prostate cancer (P = 0.0007). In addition, among men of European descent, MSR1 mutations were detected in 4.4% of individuals affected with non-HPC as compared with 0.8% of unaffected men (P = 0.009). Among African American men, these values were 12.5% and 1.8%, respectively (P = 0.01). These results show that MSR1 may be important in susceptibility to prostate cancer in men of both African American and European descent.