p53 Alteration and chromosomal instability in prostatic high-grade intraepithelial neoplasia and concurrent carcinoma: analysis by immunohistochemistry, interphase in situ hybridization, and sequencing of laser-captured microdissected specimens

Experimental challenges to modeling prostate cancer heterogeneity

Tumor heterogeneity plays a key role in prostate cancer prognosis, therapy selection, relapse, and acquisition of treatment resistance. Prostate cancer presents a heterogeneous diversity at inter- and intra-tumor and inter-patient levels which are influenced by multiple intrinsic and/or extrinsic factors. Recent studies have started to characterize the complexity of prostate tumors and these different tiers of heterogeneity. In this review, we discuss the most common factors that contribute to tumoral diversity. Moreover, we focus on the description of the in vitro and in vivo approaches, as well as high-throughput technologies, that help to model intra-tumoral diversity. Further understanding tumor heterogeneities and the challenges they present will guide enhanced patient risk stratification, aid the design of more precise therapies, and ultimately help beat this chameleon-like disease.

The Role of Chromosomal Instability in Cancer and Therapeutic Responses

Cancer is one of the leading causes of death, and despite increased research in recent years, control of advanced-stage disease and optimal therapeutic responses remain elusive. Recent technological improvements have increased our understanding of human cancer as a heterogeneous disease. For instance, four hallmarks of cancer have recently been included, which in addition to being involved in cancer development, could be involved in therapeutic responses and resistance. One of these hallmarks is chromosome instability (CIN), a source of genetic variation in either altered chromosome number or structure. CIN has become a hot topic in recent years, not only for its implications in cancer diagnostics and prognostics, but also for its role in therapeutic responses. Chromosomal alterations are mainly used to determine genetic heterogeneity in tumors, but CIN could also reveal treatment efficacy, as many therapies are based on increasing CIN, which causes aberrant cells to undergo apoptosis. However, it should be noted that contradictory findings on the implications of CIN for the therapeutic response have been reported, with some studies associating high CIN with a better therapeutic response and others associating it with therapeutic resistance. Considering these observations, it is necessary to increase our understanding of the role CIN plays not only in tumor development, but also in therapeutic responses. This review focuses on recent studies that suggest possible mechanisms and consequences of CIN in different disease types, with a primary focus on cancer outcomes and therapeutic responses.

The mammalian target of rapamycin pathway is widely activated without PTEN deletion in renal cell carcinoma metastases

BACKGROUND

Inhibitors of the mammalian target of rapamycin (mTOR) are emerging as promising therapies for metastatic renal cell carcinoma (RCC). Because rational treatment strategies require understanding the activation status of the underlying signaling pathway being targeted at the desired stage of disease, the authors examined the activation status of different components of the mTOR pathway in RCC metastases and matched primary tumors.

METHODS

The authors immunostained metastatic RCC samples from 132 patients and a subset of 25 matched primary RCCs with antibodies against phosphatidylinositol 3'-kinase, PTEN, phospho-Akt, phospho-mTOR, and p70S6. PTEN genomic status was assessed by fluorescent in situ hybridization. Marker expression was correlated to clinicopathologic variables and to survival.

RESULTS

The mTOR pathway showed widespread activation in RCC metastases of various sites with strong correlation between different components of this signaling cascade (P<.0001), but without significant PTEN genomic deletion. Only cytoplasmic phospho-mTOR showed independent prognostic significance (P = .029) and fidelity between primary RCCs and their matched metastases (P = .004).

CONCLUSIONS

Activation of various components of the mTOR signaling pathway in metastatic RCC lesions across various tumor histologies, nuclear grades, and metastatic sites suggests the potential for vertical blockade of multiple steps of this pathway. Patient selection may be improved by mTOR immunostaining of primary RCC.

PTEN genomic deletion is associated with p-Akt and AR signalling in poorer outcome, hormone refractory prostate cancer

PTEN haploinsufficiency is common in hormone-sensitive prostate cancer, though the incidence of genomic deletion and its downstream effects have not been elucidated in clinical samples of hormone refractory prostate cancer (HRPC). Progression to androgen independence is pivotal in prostate cancer and mediated largely by the androgen receptor (AR). Since this process is distinct from metastatic progression, we examined alterations of the PTEN gene in locally advanced recurrent, non-metastatic human HRPC tissues. Retrospective analyses of PTEN deletion status were correlated with activated downstream phospho-Akt (p-Akt) pathway proteins and with the androgen receptor. The prevalence of PTEN genomic deletions in transurethral resection samples of 59 HRPC patients with known clinical outcome was assessed by four-colour FISH analyses. FISH was performed using six BAC clones spanning both flanking PTEN genomic regions and the PTEN gene locus, and a chromosome 10 centromeric probe. PTEN copy number was also evaluated in a subset of cases using single nucleotide polymorphism (SNP) arrays. In addition, the samples were immunostained with antibodies against p-Akt, p-mTOR, p-70S6, and AR. The PTEN gene was deleted in 77% of cases, with 25% showing homozygous deletions, 18% homozygous and hemizygous deletions, and 34% hemizygous deletions only. In a subset of the study group, SNP array analysis confirmed the FISH findings. PTEN genomic deletion was significantly correlated to the expression of downstream p-Akt (p < 0.0001), AR (p = 0.025), and to cancer-specific mortality (p = 0.039). PTEN deletion is common in HRPC, with bi-allelic loss correlating to disease-specific mortality and associated with Akt and AR deregulation.

Gene expression profiling identifies lobe-specific and common disruptions of multiple gene networks in testosterone-supported, 17beta-estradiol- or diethylstilbestrol-induced prostate dysplasia in Noble rats

The xenoestrogen diethylstilbestrol (DES) is commonly believed to mimic the action of the natural estrogen 17beta-estradiol (E2). To determine if these two estrogens exert similar actions in prostate carcinogenesis, we elevated circulating levels of estrogen in Noble (NBL) rats with E(2/DES-filled implants, while maintaining physiological levels of testosterone (T) in the animals with T-filled implants. The two estrogens induced dysplasia in a lobe-specific manner, with E2 targeting only the lateral prostate (LP) and DES impacting only the ventral prostate (VP). Gene expression profiling identified distinct and common E2-disrupted versus DES-disrupted gene networks in each lobe. More importantly, hierarchical clustering analyses revealed that T + E2 treatment primarily affected the gene expression pattern in the LP, whereas T + DES treatment primarily affected the gene expression profile in the VP. Gene ontology analyses and pathway mapping suggest that the two hormone treatments disrupt unique and/or common cellular processes, including cell development, proliferation, motility, apoptosis, and estrogen signaling, which may be linked to dysplasia development in the rat prostate. These findings suggest that the effects of xenoestrogens and natural estrogens on the rat prostate are more divergent than previously suspected and that these differences may explain the lobe-specific carcinogenic actions of the hormones.

Interphase FISH analysis of PTEN in histologic sections shows genomic deletions in 68% of primary prostate cancer and 23% of high-grade prostatic intra-epithelial neoplasias

Prostate cancer (CaP) is characterized by the accumulation of both genetic and epigenetic alterations that transform premalignant lesions to invasive carcinoma. However, the molecular events underlying this critical transition are poorly understood. One of the important genes that might play a role in CaP development is the PTEN gene. At the present time, there has been no systematic analysis of the incidence of genomic PTEN deletion by fluorescence in situ hybridization (FISH) in CaP and associated preneoplastic histologic lesions. This study assesses the frequency of PTEN deletion by interphase FISH analysis in CaP and prostatic intra-epithelial neoplasia (PIN). Dual-color FISH was performed using DNA probes for bands 10q23.3 (PTEN locus) and chromosome 10 centromere using 35 radical prostatectomy specimens. PTEN deletions were not found in 3/3 of stroma, 6/6 samples of benign glandular epithelium, and 12/12 samples of low-grade PIN. However, PTEN deletions were found in 3/13 (23%) of high-grade PIN and 24/35 (68%) of CaP. Concordance was observed between PTEN deletion status and the overall cellular PTEN protein expression levels, as assessed by immunohistochemistry. The high frequency of PTEN deletion observed in CaP versus precursor lesions implicates a pivotal role for PTEN haploinsufficiency in the transition from preneoplastic PIN to CaP. Moreover, this observation is an important consideration for novel therapeutic trials in CaP in which biologic efficacy is influenced by the activity level of PTEN. These findings draw attention to the usefulness of this relatively simple FISH assay for future applications in clinical laboratories.

Telomeres and telomerase in prostatic intraepithelial neoplasia and prostate cancer biology

Telomeres are terminal, repeated deoxyribonucleic acid (DNA) sequences that stabilize and protect the ends of the chromosomes. Mounting evidence indicates that by initiating chromosomal instability, short dysfunctional telomeres may be involved in prostate carcinogenesis. Although the exact cause of the telomere shortening observed in prostate cancer remains a mystery, telomere loss is known to occur during cell division and oxidative DNA damage, 2 byproducts of chronic inflammation, which is a common histologic finding in the prostate. In addition to prostate cancer causation, telomeres may also play a role in disease progression, and there are indications that tumor telomere content may prove useful as a prognostic marker. Once established, prostate cancer cells almost invariably activate the telomeric DNA polymerase enzyme telomerase, the detection of which may prove useful for diagnostic purposes. Interestingly, telomerase activity is suppressed in prostate cancer cells after androgen withdrawal, raising the possibility that androgen ablative therapies may re-instigate telomere loss, and consequent genetic instability, in surviving cancer cells, thus contributing to the emergence of an androgen-independent, lethal phenotype. A more thorough understanding of telomere biology as it relates to prostate cancer should provide new opportunities for disease prevention, diagnosis, prognostication, and treatment.

Molecular biology of prostate cancer

Development of any cancer reflects a progressive accumulation of alterations in various genes. Oncogenes, tumour suppressor genes, DNA repair genes and metastasis suppressor genes have been investigated in prostate cancer. Here, we review current understanding of the molecular biology of prostate cancer. Detailed understanding of the molecular basis of prostate cancer will provide insights into the aetiology and prognosis of the disease, and suggest avenues for therapeutic intervention in the future.

Bortezomib as a potential treatment for prostate cancer

Androgen ablation and chemotherapy provide effective palliation for most patients with advanced prostate cancer, but eventually progressing androgen-independent prostate cancer threatens the lives of patients usually within a few years, mandating improvement in therapy. Proteasome inhibition has been proposed as a therapy target for the treatment of solid and hematological malignancies. The proteasome is a ubiquitous enzyme complex that is a hub for the regulation of many intracellular regulatory pathways; because of its essential function, this enzyme has become a new target for cancer treatment. Studies with bortezomib (VELCADE, formerly known as PS-341) and other proteasome inhibitors indicate that cancer cells are especially dependent on the proteasome for survival, and several mechanisms used by prostate cancer cells require proteasome function. Bortezomib has been studied extensively in vitro and in vivo, and anticancer activity has been seen in cell and animal models for several solid tumor types, including prostate cancer. A Phase I trial to determine the maximum tolerated dose of once-weekly bortezomib has been completed. This trial included a large fraction of patients with androgen-independent prostate cancer. The maximum tolerated dose was reached at 1.6 mg/m(2). A correlation was seen among bortezomib dose, proteasome inhibition, and positive modulation of serum prostate-specific antigen. There was also evidence of down-regulation of serum interleukin 6, a downstream nuclear factor kappaB effector. This Phase I trial and preclinical studies support additional testing of bortezomib in combination with radiation or chemotherapy for androgen-independent prostate cancer.

[Laser microdissection in the molecular oncology of prostate cancer]

Nearly all diseases, including prostate cancer (PCA), occur in mixed tissues with different cell types interconnected by multiple interactions. Laser microdissection permits a separate analysis of specific cell types necessary to understand tumorigenesis. Microdissection can be combined with different molecular methods for analyses at the levels of the genome, the transcriptome or the proteome. With respect to the molecular pathogenesis of PCA, normal glands can be compared to preneoplasias, and these in turn to the carcinoma. Different malignancy grades, as well as intra- and extraprostatic tumor parts, can be specifically analysed and molecular markers of aggressiveness can be identified. The molecular signatures obtained provide the basis for functional studies. New prognostic markers and therapeutic targets can be expected from such approaches in the near future. A far reaching goal is the computer representation of multiple molecular components and their interactions, "E-cell in cyberspace", in which prognostic behaviour and therapeutic responsiveness can be approximately predicted.

Spectral karyotype (SKY) analysis of human prostate carcinoma cell lines

BACKGROUND

Well-characterized in vitro model systems provide an invaluable tool for studying prostate cancer in the laboratory. Detailed karyotypes have been reported using modern techniques such as multiplex fluorescence in situ hybridization (M-FISH) and spectral karyotyping (SKY) for LNCaP, DU 145, NCI-H660, and PC-3 cell lines. However, karyotypic data for more recently established prostate carcinoma cell lines are still limited.

METHODS

Classical (G-banding) and SKY analyses were performed on ten prostate carcinoma cell lines: 22Rv1, CWR-R1, DuCaP, LAPC-4, MDA PCa 1, MDA PCa 2a, MDA PCa 2b, PC-346C, PSK-1, and VCaP.

RESULTS

Chromosomal abnormalities were identified in all cell lines, although the number and complexity varied greatly among them. PC-346C, established from a primary tumor, exhibited the lowest number (3) of clonal structural abnormalities, while DuCaP, established from a metastasis from a hormone-refractory patient, exhibited both the highest number (31) and largest complexity of structural abnormalities. In various subsets of these models, breakpoints were identified in chromosomal regions previously described as being involved in prostate cancer (e.g., 8p, 10q, 13q, and 16q).

CONCLUSIONS

The present study provides a comprehensive karyotypic analysis of a large number of prostate carcinoma cell lines, and offers a valuable resource for future investigations.

Clinical implications of radiation-induced genomic instability

Radiation-induced genomic instability encompasses a range of measurable end points such as chromosome destabilization, sister chromatid exchanges, gene mutation and amplification, late cell death and aneuploidy, all of which may be causative factors in the development of clinical disease, including carcinoma. Clinical implications of genomic instability can be broadly grouped into two main areas: as a marker for increased cancer risk/early detection, and as a consequence of radiation therapy (IR) that may be causative of, or a strong marker for, the induction of a therapy-induced second malignancy. Research in human populations has been limited, but broadly encompasses three populations: those exposed to alpha-particle irradiation, those with a cancer diagnosis who were examined for lymphocyte sensitivity to IR as a biomarker for risk of cancer induction, and those who successfully completed radiation therapy for an index cancer and who were examined for the induction of a second malignancy. This review examines each of those populations in turn and offers some potential future research directions to better elucidate the role of radiation-induced genomic instability in clinical disease.

Evidence of multifocality of telomere erosion in high-grade prostatic intraepithelial neoplasia (HPIN) and concurrent carcinoma

Mechanisms underlying prostate cancer (CaP) initiation and progression are poorly understood. A chromosomal instability mechanism leading to the generation of numerical and structural chromosomal changes has been implicated in the preneoplastic and neoplastic stages of CaP. Telomere dysfunction is one potential mechanism associated with the onset of such instability. To determine whether there was alteration in telomere length and chromosome number, 15 paraffin-embedded prostatectomy specimens were investigated using quantitative peptide nucleic acid (PNA) FISH analysis of representative foci of carcinoma, putative precancerous lesions (high-grade prostatic intraepithelial neoplasia, HPIN) and nondysplastic prostate epithelium. A significant decrease in telomere length was shown in both HPIN and CaP in comparison with normal epithelium. In addition, elevated rates of aneusomy suggested that increased levels of chromosomal aberrations were associated with decreased telomere length. Moreover, multiple foci of HPIN were shown to have a heterogeneous overall reduction of telomere length. This reduction was more evident in the histologic regions of the prostate containing CaP. Such observations lend support to the hypothesis that telomere erosion may be a consistent feature of CaP oncogenesis and may also be associated with the generation of chromosomal instability that characterizes this malignancy.

Resolution of genotypic heterogeneity in prostate tumors using polymerase chain reaction and comparative genomic hybridization on microdissected carcinoma and prostatic intraepithelial neoplasia foci

Prostate cancer (CaP) is a multifocal heterogenous disease. A major challenge in CaP research is to identify genetic biomarkers that herald aggressive transformation. To investigate the effect of tumor heterogeneity on the analysis of genomic aberration, we compared the results of comparative genomic hybridization (CGH) analysis of DNA extracted from tumor bulk against that of DNA amplified by degenerate oligonucleotide primed polymerase chain reaction (DOP-PCR) from homogeneous cell population obtained by laser capture microdissection of discrete tumor foci. Sampling by microdissection, aberrations were observed in three of three foci of carcinoma involved with prostatic capsule, and in two of three prostatic intraepithelial neoplasia (PIN) foci examined. Carcinoma foci consistently exhibited more extensive aberrations than the PIN samples obtained from the same tumor. Within these samples, the different tumor foci exhibited gain of 8q, whereas PIN showed no consistent aberration. Using bulk extracted DNA, CGH detected aberrations in only 3 of 21 samples investigated, despite the known trisomy 8 status, as revealed by fluorescence in situ hybridization. The results of this study demonstrate that CGH analysis using bulk dissected fresh tissue is insufficiently sensitive to fully detect the chromosomal numerical aberrations in CaP. Given the considerable intratumor genomic heterogeneity, CGH with microdissection and DOP-PCR amplification provides a more complete repertoire of aberrations as well as a better phenotype-genotype correlation in prostate tumors.