Timothy C. Thompson

Multistage carcinogenesis induced by ras and myc oncogenes in a reconstituted organ

ras and myc oncogenes were able to induce distinct phenotypic alterations, resembling different types of premalignant lesions, when introduced into approximately 0.1% of the cells used to reconstitute the mouse prostate gland. While ras induced dysplasia in combination with angiogenesis, myc induced a hyperplasia of the otherwise normally developed organ. ras and myc together induced primarily carcinomas. However, tumor progression was also associated with additional genetic alterations involving gene amplification. Our data indicate that specific types of benign premalignant lesions may reflect the activation of different single oncogenes, and that the consecutive activation of multiple oncogenes could be a causal event in the step-like progression of tumorigenesis.

Association of transforming growth factor-β1 with prostate cancer: An immunohistochemical study

Prostate tissue samples from patients with prostatic carcinoma (PC) and/or benign prostatic hyperplasia (BPH) were examined for expression of transforming growth factor-beta 1 (TGF-beta 1) using an immunohistochemical technique. Tissues were stained with CC and LC antisera, which react with extracellular and intracellular TGF-beta 1, respectively. All PC and BPH tissues showed positive extracellular staining; however, CC-immunoreactive material was significantly more extensive in PC compared with BPH, the average positively staining areas being 59% and 26%, respectively. This differential staining pattern was evident in cases in which areas of PC were located adjacent to areas of BPH. LC staining was identified exclusively intracellularly involving both stromal and epithelial cells in cases of PC as well as BPH. However, while stromal cell staining was more pronounced in BPH, epithelial cell staining tended to be more extensive and more intense in PC. The findings suggest that TGF-beta 1 may be biologically important in the development of PC and BPH.

Cancer-Related Axonogenesis and Neurogenesis in Prostate Cancer

Purpose: Perineural invasion is the only interaction between cancer cells and nerves studied to date. It is a symbiotic relationship between cancer and nerves that results in growth advantage for both. In this article, we present data on a novel biological phenomenon, cancer-related axonogenesis and neurogenesis. Experimental Design: We identify spatial and temporal associations between increased nerve density and preneoplastic and neoplastic lesions of the human prostate. Results: Nerve density was increased in cancer areas as well as in preneoplastic lesions compared with controls. Two- and three-dimensional reconstructions of entire prostates confirmed axonogenesis in human tumors. Furthermore, patients with prostate cancer had increased numbers of neurons in their prostatic ganglia compared with controls, corroborating neurogenesis. Finally, two in vitro models confirmed that cancer cells, particularly when interacting with nerves in perineural invasion, induce neurite outgrowth in prostate cancer. Neurogenesis is correlated with features of aggressive prostate cancer and with recurrence in prostate cancer. We also present a putative regulatory mechanism based on semaphorin 4F (S4F). S4F is overexpressed in cancers cells in the perineural in vitro model. Overexpression of S4F in prostate cancer cells induces neurogenesis in the N1E-115 neurogenesis assay and S4F inhibition by small interfering RNA blocks this effect. Conclusions: This is the first description of cancer-related neurogenesis and its putative regulatory mechanism.

Understanding the mechanisms of androgen deprivation resistance in prostate cancer at the molecular level.

CONTEXTnVarious molecular mechanisms play a role in the development of resistance to androgen deprivation therapy in castration-resistant prostate cancer (CRPC).nnnOBJECTIVEnTo understand the mechanisms and biological pathways associated with the progression of prostate cancer (PCa) under systemic androgen depletion or administration of the novel antiandrogens abiraterone, enzalutamide, and ARN-509. This review also examines the introduction of novel combinational approaches for patients with CRPC.nnnEVIDENCE ACQUISITIONnPubMed was the data source. Keywords for the search were castrate resistant prostate cancer, abiraterone, enzalutamide resistance mechanisms, resistance to androgen deprivation, AR mutations, amplifications, splice variants, and AR alterations. Papers published before 1990 were excluded from the review, and only English-language papers were included.nnnEVIDENCE SYNTHESISnThis review summarizes the current literature regarding the mechanisms implicated in the development of CRPC and the acquisition of resistance to novel antiandrogen axis agents. The review focuses on androgen biosynthesis in the tumor microenvironment, androgen receptor (AR) alterations and post-transcriptional modifications, the role of glucocorticoid receptor, and alternative oncogenic signaling that is derepressed on maximum AR inhibition and thus promotes cancer survival and progression.nnnCONCLUSIONSnThe mechanisms implicated in the development of resistance to AR inhibition in PCa are multiple and complex, involving virtually all classes of genomic alteration and leading to a host of selective/adaptive responses. Combinational therapeutic approaches targeting both AR signaling and alternative oncogenic pathways may be reasonable for patients with CRPC.nnnPATIENT SUMMARYnWe looked for mechanisms related to the progression of PCa in patients undergoing hormonal therapy and treatment with novel drugs targeting the AR. Based on recent data, combining maximal AR inhibition with novel agents targeting other tumor-compensatory, non-AR-related pathways may improve the survival and quality of life of patients with castration-resistant PCa.

Loss of caveolin‐1 in prostate cancer stroma correlates with reduced relapse‐free survival and is functionally relevant to tumour progression

Levels of caveolin‐1 (Cav‐1) in tumour epithelial cells increase during prostate cancer progression. Conversely, Cav‐1 expression in the stroma can decline in advanced and metastatic prostate cancer. In a large cohort of 724 prostate cancers, we observed significantly decreased levels of stromal Cav‐1 in concordance with increased Gleason score (p = 0.012). Importantly, reduced expression of Cav‐1 in the stroma correlated with reduced relapse‐free survival (p = 0.009), suggesting a role for stromal Cav‐1 in inhibiting advanced disease. Silencing of Cav‐1 by shRNA in WPMY‐1 prostate fibroblasts resulted in up‐regulation of Akt phosphorylation, and significantly altered expression of genes involved in angiogenesis, invasion, and metastasis, including au2009>u20092.5‐fold increase in TGF‐β1 and γ‐synuclein (SNCG) gene expression. Moreover, silencing of Cav‐1 induced migration of prostate cancer cells when stromal cells were used as attractants. Pharmacological inhibition of Akt caused down‐regulation of TGF‐β1 and SNCG, suggesting that loss of Cav‐1 in the stroma can influence Akt‐mediated signalling in the tumour microenvironment. Cav‐1‐depleted stromal cells exhibited increased levels of intracellular cholesterol, a precursor for androgen biosynthesis, steroidogenic enzymes, and testosterone. These findings suggest that loss of Cav‐1 in the tumour microenvironment contributes to the metastatic behaviour of tumour cells by a mechanism that involves up‐regulation of TGF‐β1 and SNCG through Akt activation. They also suggest that intracrine production of androgens, a process relevant to castration resistance, may occur in the stroma. Copyright

Combined Tumor Suppressor Defects Characterize Clinically Defined Aggressive Variant Prostate Cancers

Purpose: Morphologically heterogeneous prostate cancers that behave clinically like small-cell prostate cancers (SCPC) share their chemotherapy responsiveness. We asked whether these clinically defined, morphologically diverse, “aggressive variant prostate cancer (AVPC)” also share molecular features with SCPC. Experimental Design: Fifty-nine prostate cancer samples from 40 clinical trial participants meeting AVPC criteria, and 8 patient-tumor derived xenografts (PDX) from 6 of them, were stained for markers aberrantly expressed in SCPC. DNA from 36 and 8 PDX was analyzed by Oncoscan for copy number gains (CNG) and losses (CNL). We used the AVPC PDX to expand observations and referenced publicly available datasets to arrive at a candidate molecular signature for the AVPC. Results: Irrespective of morphology, Ki67 and Tp53 stained ≥10% cells in 80% and 41% of samples, respectively. RB1 stained <10% cells in 61% of samples and AR in 36%. MYC (surrogate for 8q) CNG and RB1 CNL showed in 54% of 44 samples each and PTEN CNL in 48%. All but 1 of 8 PDX bore Tp53 missense mutations. RB1 CNL was the strongest discriminator between unselected castration-resistant prostate cancer (CRPC) and the AVPC. Combined alterations in RB1, Tp53, and/or PTEN were more frequent in the AVPC than in unselected CRPC and in The Cancer Genome Atlas samples. Conclusions: Clinically defined AVPC share molecular features with SCPC and are characterized by combined alterations in RB1, Tp53, and/or PTEN. Clin Cancer Res; 22(6); 1520–30. ©2015 AACR.

DNA damage response and prostate cancer: defects, regulation and therapeutic implications

DNA damage response (DDR) includes the activation of numerous cellular activities that prevent duplication of DNA lesions and maintain genomic integrity, which is critical for the survival of normal and cancer cells. Specific genes involved in the DDR such as BRCA1/2 and P53 are mutated during prostate cancer progression, while various oncogenic signaling such as Akt and c-Myc are activated, enhancing the replication stress and increasing the genomic instability of cancer cells. These events may render prostate cancer cells particularly sensitive to inhibition of specific DDR pathways, such as PARP in homologous recombination DNA repair and Chk1 in cell cycle checkpoint and DNA repair, creating opportunities for synthetic lethality or synergistic cytotoxicity. Recent reports highlight the critical role of androgen receptor (AR) as a regulator of DDR genes, providing a rationale for combining DNA-damaging agents or targeted DDR inhibitors with hormonal manipulation or AR inhibition as treatment for aggressive disease. The aims of this review are to discuss specific DDR defects in prostate cancer that occur during disease progression, to summarize recent advances in understanding the regulation of DDR in prostate cancer, and to present potential therapeutic opportunities through combinational targeting of the intact components of DDR signaling pathways.

Targeting Poly(ADP-Ribose) Polymerase and the c-Myb–Regulated DNA Damage Response Pathway in Castration-Resistant Prostate Cancer

The DNA damage response is an appealing target for androgen inhibitor–resistant prostate cancer. Improving Therapy in Prostate Cancer Blocking androgen receptor (AR) signaling is standard therapy for prostate cancer, but tumor growth often recurs. Li et al. examined the gene expression profile in patient samples of primary and metastatic prostate cancer from patients in which AR signaling was blocked. Metastatic disease, which is associated with androgen inhibitor–resistant relapse, correlated with increased expression of genes encoding proteins in the DNA damage response (DDR) and MYB expression. AR and c-Myb shared a subset of target genes that encode DDR proteins; thus, c-Myb may functionally substitute for AR in the regulation of their common DDR targets. Targeting proteins within the Myb-regulated network in combination with a poly[adenosine 5′-diphosphate (ADP)–ribose] polymerase (PARP) inhibitor, which compromises the DDR, generated synergistic lethality in prostate cancer cells in culture and in mouse xenografts, suggesting potential new options for prostate cancer patients. Androgen deprivation is the standard treatment for advanced prostate cancer (PCa), but most patients ultimately develop resistance and tumor recurrence. We found that MYB is transcriptionally activated by androgen deprivation therapy or genetic silencing of the androgen receptor (AR). MYB silencing inhibited PCa growth in culture and xenografts in mice. Microarray data revealed that c-Myb and AR shared a subset of target genes that encode DNA damage response (DDR) proteins, suggesting that c-Myb may supplant AR as the dominant regulator of their common DDR target genes in AR inhibition–resistant or AR-negative PCa. Gene signatures including AR, MYB, and their common DDR-associated target genes positively correlated with metastasis, castration resistance, tumor recurrence, and decreased survival in PCa patients. In culture and in xenograft-bearing mice, a combination strategy involving the knockdown of MYB, BRCA1, or TOPBP1 or the abrogation of cell cycle checkpoint arrest with AZD7762, an inhibitor of the checkpoint kinase Chk1, increased the cytotoxicity of the poly[adenosine 5′-diphosphate (ADP)–ribose] polymerase (PARP) inhibitor olaparib in PCa cells. Our results reveal new mechanism-based therapeutic approaches for PCa by targeting PARP and the DDR pathway involving c-Myb, TopBP1, ataxia telangiectasia mutated– and Rad3-related (ATR), and Chk1.

GLIPR1 tumor suppressor gene expressed by adenoviral vector as neoadjuvant intraprostatic injection for localized intermediate or high-risk prostate cancer preceding radical prostatectomy.

Background: GLIPR1 is upregulated by p53 in prostate cancer cells and has preclinical antitumor activity. A phase I clinical trial was conducted to evaluate the safety and activity of the neoadjuvant intraprostatic injection of GLIPR1 expressing adenovirus for intermediate or high-risk localized prostate cancer before radical prostatectomy (RP). Methods: Eligible men had localized prostate cancer (T1-T2c) with Gleason score greater than or equal to 7 or prostate-specific antigen 10 ng/mL or more and were candidates for RP. Patients received the adenoviral vector expressing the GLIPR1 gene by a single injection into the prostate followed four weeks later by RP. Six viral particle (vp) dose levels were evaluated: 1010, 5 × 1010, 1011, 5 × 1011, 1012, and 5 × 1012 vp. Results: Nineteen patients with a median age of 64 years were recruited. Nine men had T1c, 4 had T2a, and 3 had T2b and T2c clinical stage. Toxicities included urinary tract infection (n = 3), flu-like syndrome (n = 3), fever (n = 1), dysuria (n = 1), and photophobia (n = 1). Laboratory toxicities were grade 1 elevated AST/ALT (n = 1) and elevations of PTT (n = 3, with 1 proven to be lupus anticoagulant). No pathologic complete remission was seen. Morphologic cytotoxic activity, induction of apoptosis, and nuclear p27Kip1 upregulation were observed. Peripheral blood CD8+, CD4+, and CD3+ T-lymphocytes were increased, with upregulation of their HLA-DR expression and elevations of serum IL-12. Conclusions: The intraprostatic administration of GLIPR1 tumor suppressor gene expressed by an adenoviral vector was safe in men, with localized intermediate or high-risk prostate cancer preceding RP. Preliminary evidence of biologic antitumor activity and systemic immune response was documented. Clin Cancer Res; 17(22); 7174–82. ©2011 AACR.

Androgen receptor inhibitor???induced ???BRCAness??? and PARP inhibition are synthetically lethal for castration-resistant prostate cancer

Androgen receptor inhibition induces a “BRCAness” state that may be exploited with PARP inhibitors in patients with advanced prostate cancer. Engineering BRCAness and chemotherapeutic sensitivity BRCA mutations impair a double-strand break DNA repair pathway that forces cells to use a PARP-dependent repair pathway. PARP inhibitors are selectively toxic to breast cancers with BRCA mutations, spurring the search for other tumors or ways in which to apply such exquisitely tumor-targeted therapy. Few other tumors have BRCA mutations as commonly as do breast tumors. However, Li et al. found that a common therapy for prostate cancer patients created a BRCA-deficient state that sensitized tumor cells to PARP inhibitors and leveraged this finding into a potential treatment strategy. Noting that the androgen receptor inhibitor enzalutamide decreased the expression of BRCA1 in prostate cancer cells, the authors treated a mouse model of prostate cancer first with enzalutamide and then with the PARP inhibitor olaparib. Sequential treatment of enzalutamide and olaparib suppressed tumor growth in these mice better than either drug by itself or when both drugs were administered at the same time. The results suggest that “BRCAness” could be therapeutically induced to provide more treatment options not only for prostate cancer patients but also for patients with other types of cancers lacking BRCA mutations. Cancers with loss-of-function mutations in BRCA1 or BRCA2 are deficient in the DNA damage repair pathway called homologous recombination (HR), rendering these cancers exquisitely vulnerable to poly(ADP-ribose) polymerase (PARP) inhibitors. This functional state and therapeutic sensitivity is referred to as “BRCAness” and is most commonly associated with some breast cancer types. Pharmaceutical induction of BRCAness could expand the use of PARP inhibitors to other tumor types. For example, BRCA mutations are present in only ~20% of prostate cancer patients. We found that castration-resistant prostate cancer (CRPC) cells showed increased expression of a set of HR-associated genes, including BRCA1, RAD54L, and RMI2. Although androgen-targeted therapy is typically not effective in CRPC patients, the androgen receptor inhibitor enzalutamide suppressed the expression of those HR genes in CRPC cells, thus creating HR deficiency and BRCAness. A “lead-in” treatment strategy, in which enzalutamide was followed by the PARP inhibitor olaparib, promoted DNA damage–induced cell death and inhibited clonal proliferation of prostate cancer cells in culture and suppressed the growth of prostate cancer xenografts in mice. Thus, antiandrogen and PARP inhibitor combination therapy may be effective for CRPC patients and suggests that pharmaceutically inducing BRCAness may expand the clinical use of PARP inhibitors.