Intronic Cis-Element DR8 in hTERT Is Bound by Splicing Factor SF3B4 and Regulates hTERT Splicing in Non-Small Cell Lung Cancer

Splicing of the hTERT gene to produce the full-length (FL) transcript is necessary for telomerase enzyme activity and telomere-dependent cellular immortality in the majority of human tumors, including non-small cell lung cancer (NSCLC) cells. The molecular machinery to splice hTERT to the FL isoform remains mostly unknown. Previously, we reported that an intron 8 cis-element termed "direct repeat 8" (DR8) promotes FL hTERT splicing, telomerase, and telomere length maintenance when bound by NOVA1 and PTBP1 in NSCLC cells. However, some NSCLC cells and patient tumor samples lack NOVA1 expression. This leaves a gap in knowledge about the splicing factors and cis-elements that promote telomerase in the NOVA1-negative context. We report that DR8 regulates FL hTERT splicing in the NOVA1-negative and -positive lung cancer contexts. We identified splicing factor 3b subunit 4 (SF3B4) as an RNA trans-factor whose expression is increased in lung adenocarcinoma (LUAD) tumors compared with adjacent normal tissue and predicts poor LUAD patient survival. In contrast to normal lung epithelial cells, which continued to grow with partial reductions of SF3B4 protein, SF3B4 knockdown reduced hTERT splicing, telomerase activity, telomere length, and cell growth in lung cancer cells. SF3B4 was also demonstrated to bind the DR8 region of hTERT pre-mRNA in both NOVA1-negative and -positive NSCLC cells. These findings provide evidence that DR8 is a critical binding hub for trans-factors to regulate FL hTERT splicing in NSCLC cells. These studies help define mechanisms of gene regulation important to the generation of telomerase activity during carcinogenesis.

IMPLICATIONS

Manipulation of a core spliceosome protein reduces telomerase/hTERT splicing in lung cancer cells and results in slowed cancer cell growth and cell death, revealing a potential therapeutic strategy.

Computerized Decision Support for Bladder Cancer Treatment Response Assessment in CT Urography: Effect on Diagnostic Accuracy in Multi-Institution Multi-Specialty Study

This observer study investigates the effect of computerized artificial intelligence (AI)-based decision support system (CDSS-T) on physicians’ diagnostic accuracy in assessing bladder cancer treatment response. The performance of 17 observers was evaluated when assessing bladder cancer treatment response without and with CDSS-T using pre- and post-chemotherapy CTU scans in 123 patients having 157 pre- and post-treatment cancer pairs. The impact of cancer case difficulty, observers’ clinical experience, institution affiliation, specialty, and the assessment times on the observers’ diagnostic performance with and without using CDSS-T were analyzed. It was found that the average performance of the 17 observers was significantly improved (p = 0.002) when aided by the CDSS-T. The cancer case difficulty, institution affiliation, specialty, and the assessment times influenced the observers’ performance without CDSS-T. The AI-based decision support system has the potential to improve the diagnostic accuracy in assessing bladder cancer treatment response and result in more consistent performance among all physicians.

Intraobserver Variability in Bladder Cancer Treatment Response Assessment With and Without Computerized Decision Support

We evaluated the intraobserver variability of physicians aided by a computerized decision-support system for treatment response assessment (CDSS-T) to identify patients who show complete response to neoadjuvant chemotherapy for bladder cancer, and the effects of the intraobserver variability on physicians' assessment accuracy. A CDSS-T tool was developed that uses a combination of deep learning neural network and radiomic features from computed tomography (CT) scans to detect bladder cancers that have fully responded to neoadjuvant treatment. Pre- and postchemotherapy CT scans of 157 bladder cancers from 123 patients were collected. In a multireader, multicase observer study, physician-observers estimated the likelihood of pathologic T0 disease by viewing paired pre/posttreatment CT scans placed side by side on an in-house-developed graphical user interface. Five abdominal radiologists, 4 diagnostic radiology residents, 2 oncologists, and 1 urologist participated as observers. They first provided an estimate without CDSS-T and then with CDSS-T. A subset of cases was evaluated twice to study the intraobserver variability and its effects on observer consistency. The mean areas under the curves for assessment of pathologic T0 disease were 0.85 for CDSS-T alone, 0.76 for physicians without CDSS-T and improved to 0.80 for physicians with CDSS-T (P = .001) in the original evaluation, and 0.78 for physicians without CDSS-T and improved to 0.81 for physicians with CDSS-T (P = .010) in the repeated evaluation. The intraobserver variability was significantly reduced with CDSS-T (P < .0001). The CDSS-T can significantly reduce physicians' variability and improve their accuracy for identifying complete response of muscle-invasive bladder cancer to neoadjuvant chemotherapy.

A Randomized Phase II Study of Androgen Deprivation Therapy with or without Palbociclib in RB-positive Metastatic Hormone-Sensitive Prostate Cancer

PURPOSE

Palbociclib, a cyclin-dependent kinase (CDK) 4/6 inhibitor, blocks proliferation in a RB and cyclin D-dependent manner in preclinical prostate cancer models. We hypothesized that cotargeting androgen receptor and cell cycle with palbociclib would improve outcomes in patients with metastatic hormone-sensitive prostate cancer (mHSPC).

PATIENTS AND METHODS

A total of 60 patients with RB-intact mHSPC were randomized (1:2) to Arm 1: androgen deprivation (AD) or Arm 2: AD + palbociclib. Primary endpoint was PSA response rate (RR) after 28 weeks of therapy. Secondary endpoints included safety, PSA, and clinical progression-free survival (PFS), as well as PSA and radiographic RR. Tumors underwent exome sequencing when available. Circulating tumor cells (CTC) were enumerated at various timepoints.

RESULTS

A total of 72 patients with mHSPC underwent metastatic disease biopsy and 64 had adequate tissue for RB assessment. A total of 62 of 64 (97%) retained RB expression. A total of 60 patients initiated therapy (Arm 1: 20; Arm 2: 40). Neutropenia was the most common grade 3/4 adverse event in Arm 2. Eighty percent of patients (Arm 1: 16/20, Arm 2: 32/40; P = 0.87) met primary PSA endpoint ≤4 ng/mL at 28 weeks. PSA undetectable rate at 28 weeks was 50% and 43% in Arms 1 and 2, respectively (P = 0.5). Radiographic RR was 89% in both arms. Twelve-month biochemical PFS was 69% and 74% in Arms 1 and 2, respectively (P = 0.72). TP53 and PIK3 pathway mutations, 8q gains, and pretreatment CTCs were associated with reduced PSA PFS.

CONCLUSIONS

Palbociclib did not impact outcome in RB-intact mHSPC. Pretreatment CTC, TP53 and PIK3 pathway mutations, and 8q gain were associated with poor outcome.

MEK is a promising target in the basal subtype of bladder cancer

While many resources exist for the drug screening of bladder cancer cell lines in 2D culture, it is widely recognized that screening in 3D culture is more representative of in vivo response. Importantly, signaling changes between 2D and 3D culture can result in changes to drug response. To address the need for 3D drug screening of bladder cancer cell lines, we screened 17 bladder cancer cell lines using a library of 652 investigational small-molecules and 3 clinically relevant drug combinations in 3D cell culture. Our goal was to identify compounds and classes of compounds with efficacy in bladder cancer. Utilizing established genomic and transcriptomic data for these bladder cancer cell lines, we correlated the genomic molecular parameters with drug response, to identify potentially novel groups of tumors that are vulnerable to specific drugs or classes of drugs. Importantly, we demonstrate that MEK inhibitors are a promising targeted therapy for the basal subtype of bladder cancer, and our data indicate that drug screening of 3D cultures provides an important resource for hypothesis generation.

Abstract A21: TRIM29 promotes invasion and migration of bladder cancer cells by regulating myosin-intermediate filament network and focal adhesion

Development of invasive progression in human bladder cancer is a key determinant of patient outcomes. Therefore, understanding the drivers of bladder cancer invasive progression is critical to improving patient care. We have previously shown that TRIM29 (also known as ataxia-telangiectasia group D complementing gene, ATDC) is highly expressed in muscle-invasive bladder cancer and plays an important role in driving tumor formation and invasion in vitro and in vivo. TRIM29 is upregulated by TP63 in basal subtype tumors, but the mechanism by which TRIM29 promotes tumor invasion was unknown. To elucidate the mechanism by which TRIM29 drives bladder cancer invasion, we developed a 3-D bladder cancer spheroid invasion assay that allows observation of the invasive process of cancer spheroids in a real-time fashion and observation of protein expression using confocal microscopy. Using this system, we confirmed that TRIM29 is required for bladder cancer stromal invasion. To determine if TRIM29 is specifically required for cell migration, which is an important ability contributing to invasive behavior, scratch assays were performed and we found TRIM29 is required for migration. Cancer cell migration requires modulation of cell adhesion and actin/myosin activation. To examine the role of TRIM29 in cell adhesion and motility, gene knockout or knockdowns of TRIM29 were generated in human bladder cancer cell lines (UM-UC5, UC9, UC13, UC14). Interestingly, TRIM29 KO/KD downregulates the expression of keratin 14 (KRT14), a member of type I keratin family that constitutes intermediate filament (IF) network, as well as myosin IIA (MYH9), a non-muscle motor protein that is essential for cell adhesion and migration. Using immunofluorescent confocal microscopy, we found that TRIM29 also modulates formation of focal adhesion plaques in bladder cancer during cell migration. Taken together, these findings suggest a novel mechanism by which TRIM29 regulates bladder cancer cell motility and invasion.

Citation Format: Yin Wang, Erica R. Gumkowski, Phillip L. Palmbos. TRIM29 promotes invasion and migration of bladder cancer cells by regulating myosin-intermediate filament network and focal adhesion [abstract]. In: Proceedings of the AACR Special Conference on Bladder Cancer: Transforming the Field; 2019 May 18-21; Denver, CO. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(15_Suppl):Abstract nr A21.

Abstract B12: Carcinogen exposure alters keratin 5 expression and K5-Cre recombination in transgenic mouse urothelium

In the urinary bladder, the normal urothelium is divided into three subpopulations of cells: superficial umbrella cells, intermediate cells, and a basal layer, each with distinct expression patterns of uroplakins (UP) and keratin 5 (K5). Many current transgenic mouse models (Tg) for urinary bladder cancer rely on uroplakin or keratin promoters to drive inducible Cre-lox recombination in basal or luminal bladder urothelial cells. Further, many models utilize the chemical carcinogen, N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN), to drive or accelerate tumorigenesis. A major limitation in Tg model systems where genes are knocked out is the requirement for highly penetrant and reproducible Cre activity and subsequent gene deletion in order to see a phenotype. This problem is compounded in long-term experiments such as BBN carcinogenesis that can run for up to six months after Cre induction. We have previously shown that Trim29 (tripartite motif containing 29) is sufficient to drive invasive bladder cancer formation in Tg models and in human bladder tumors. We have now developed a Tg system utilizing K5-Cre-ERT2 to target Trim29 for deletion in K5-expressing basal urothelial cells. In this model, tamoxifen exposure results in Cre expression and Trim29 deletion in K5 basal cells. Whether this would translate into complete loss of Trim29 in the urothelium over time and what effect BBN might have on tamoxifen induction of K5-Cre and loss of Trim29 were unclear. We found that exposure of K5-Cre-ERT2, Trim29 flox/flox mice to tamoxifen for six weeks resulted in loss of Trim29 expression only in the K5+ basal urothelium and that these K5+ Trim29 -/- basal cells did not give rise to intermediate cells or umbrella cells during the six months of follow-up. In contrast, mice treated with 0.05% BBN in drinking water for six months after induction of Cre produced full thickness of Trim29 knockout (KO) in 50% of mice (8/16 mice). Our results indicate that in a nonstressed state, K5 basal cells give rise to other basal cells but do not repopulate intermediate or umbrella cell layers. Furthermore, exposure to BBN resulted in the proliferation of basal cells and the replacement of intermediate cells by basal precursors in the urothelium. These results suggest that K5-Cre promoters may have different effects on transgene recombination in the bladder in the presence or absence of BBN, which induces more universal expression of Cre and its subsequent recombination events. These findings should be considered when interpreting and developing BBN-induced bladder cancer Tg models.

Citation Format: Alan Kelleher, Yin Wang, Luke Broses, Sylvia Zelenka-Wang, Phillip L. Palmbos. Carcinogen exposure alters keratin 5 expression and K5-Cre recombination in transgenic mouse urothelium [abstract]. In: Proceedings of the AACR Special Conference on the Evolving Landscape of Cancer Modeling; 2020 Mar 2-5; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2020;80(11 Suppl):Abstract nr B12.

Abstract B35: Isolation and characterization of circulating tumor cells (CTCs) from bladder cancer patients using a highly sensitive graphene oxide-based microfluidic device (GO chip)

Introduction: A critical research topic in bladder cancer is determining the key regulators in the progression from noninvasive tumor to invasive and ultimately metastatic disease. Although patients with noninvasive bladder cancer can be treated through transurethral resection of bladder tumor and have a high survival rate (~95%), noninvasive bladder tumors recur in 50%-70% of cases. Of these, 10-15% of cases progress to invasive disease. Circulating tumor cells (CTCs) represent the transitional phase of progression between lymphovascular intravasation and distant metastases. Molecular profiling of these CTCs, beyond enumeration, can inform the molecules/pathways important in the invasion process, and potentially help unravel the mechanism of metastasis and provide new targets for therapy. Here we report the application of a highly sensitive graphene oxide-based microfluidic device to isolate and characterize CTCs from bladder cancer patients for the expression of markers implicated in an invasive phenotype.

Methods: An anti-EpCAM and anti-EGFR biotinylated antibody cocktail was immobilized onto the graphene oxide chip (GO chip) to capture CTCs from whole blood. In patient samples, immunofluorescence staining for DAPI (nuclei), cytokeratin (cancer cell marker), EGFR and HER2 (markers of invasive phenotype), and CD45 (white blood cell marker) was used to enumerate CTCs. Cells with a DAPI+CK+CD45- phenotype were counted as CTCs. Blood samples from ten metastatic bladder cancer patients and two healthy controls were processed, stained, and analyzed.

Results: CTCs were found in 10/10 (100%) patients, with an average of 17.70 cells/mL (s = 10.69 cells/mL). 9/10 patients exhibited CTCs that express EGFR, but only one patient had one CTC express HER2.

Conclusion: The antibody-functionalized GO chips were able to successfully capture and enable characterization of CTCs from metastatic bladder cancer patients. EGFR potentially plays an important role in the vascular invasion process.

Citation Format: Zeqi Niu, Molly A. Kozminsky, Kathleen C. Day, Phillip L. Palmbos, Mark L. Day, Sunitha Nagrath. Isolation and characterization of circulating tumor cells (CTCs) from bladder cancer patients using a highly sensitive graphene oxide-based microfluidic device (GO chip) [abstract]. In: Proceedings of the AACR Special Conference on Advances in Liquid Biopsies; Jan 13-16, 2020; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(11_Suppl):Abstract nr B35.

TP63 isoform expression is linked with distinct clinical outcomes in cancer

Background

Half of muscle-invasive bladder cancer patients will relapse with metastatic disease and molecular tests to predict relapse are needed. TP63 has been proposed as a prognostic biomarker in bladder cancer, but reports associating it with clinical outcomes are conflicting. Since TP63 is expressed as multiple isoforms, we hypothesized that these conflicting associations with clinical outcome may be explained by distinct opposing effects of differential TP63 isoform expression.

Methods

Using RNA-Seq data from The Cancer Genome Atlas (TCGA), TP63 isoform-level expression was quantified and associated with clinical covariates (e.g. survival, stage) across 8,519 patients from 29 diseases. A comprehensive catalog of TP63 isoforms was assembled using gene annotation databases and de novo discovery in bladder cancer patients. Quantifications and un-annotated TP63 isoforms were validated using quantitative RT-PCR and a separate bladder cancer cohort.

Findings

DNp63 isoform expression was associated with improved bladder cancer patient survival in patients with a luminal subtype (HR = 0.89, CI 0.80–0.99, Cox p = 0.034). Conversely, TAp63 isoform expression was associated with reduced bladder cancer patient survival in patients with a basal subtype (HR = 2.35, CI 1.64–3.37, Cox p < 0.0001). These associations were observed in multiple TCGA disease cohorts and correlated with epidermal differentiation (DNp63) and immune-related (TAp63) gene signatures.

Interpretation

These results comprehensively define TP63 isoform expression in human cancer and suggest that TP63 isoforms are involved in distinct transcriptional programs with opposing effects on clinical outcome.

ATDC is required for the initiation of KRAS-induced pancreatic tumorigenesis

Pancreatic adenocarcinoma (PDA) is an aggressive disease driven by oncogenic KRAS and characterized by late diagnosis and therapeutic resistance. Here we show that deletion of the ataxia-telangiectasia group D-complementing (Atdc) gene, whose human homolog is up-regulated in the majority of pancreatic adenocarcinoma, completely prevents PDA development in the context of oncogenic KRAS. ATDC is required for KRAS-driven acinar-ductal metaplasia (ADM) and its progression to pancreatic intraepithelial neoplasia (PanIN). As a result, mice lacking ATDC are protected from developing PDA. Mechanistically, we show ATDC promotes ADM progression to PanIN through activation of β-catenin signaling and subsequent SOX9 up-regulation. These results provide new insight into PDA initiation and reveal ATDC as a potential target for preventing early tumor-initiating events.

A surgical orthotopic approach for studying the invasive progression of human bladder cancer

The invasion of bladder cancer into the sub-urothelial muscle and vasculature are key determinants leading to lethal metastatic progression. However, the molecular basis is poorly understood, partly because of the lack of uncomplicated and reliable models that recapitulate the biology of locally invasive disease. We developed a surgical grafting technique, characterized by a simple, rapid, reproducible and high-efficiency approach, to recapitulate the pathobiological events of human bladder cancer invasion in mice. This technique consists of a small laparotomy and direct implantation of human cancer cells into the bladder lumen. Unlike other protocols, it does not require debriding of the urothelial lining, injection into the bladder wall, specialized imaging equipment, bladder catheterization or costly surgical equipment. With minimal practice, the procedure can be executed in <10 min. Tumors develop with a high take rate, and most cell lines exhibit local invasion within 4 weeks of implantation.

3-D Cell Culture System for Studying Invasion and Evaluating Therapeutics in Bladder Cancer

Bladder cancer is a significant health problem. It is estimated that more than 16,000 people will die this year in the United States from bladder cancer. While 75% of bladder cancers are non-invasive and unlikely to metastasize, about 25% progress to an invasive growth pattern. Up to half of the patients with invasive cancers will develop lethal metastatic relapse. Thus, understanding the mechanism of invasive progression in bladder cancer is crucial to predict patient outcomes and prevent lethal metastases. In this article, we present a three-dimensional cancer invasion model which allows incorporation of tumor cells and stromal components to mimic in vivo conditions occurring in the bladder tumor microenvironment. This model provides the opportunity to observe the invasive process in real time using time-lapse imaging, interrogate the molecular pathways involved using confocal immunofluorescent imaging and screen compounds with the potential to block invasion. While this protocol focuses on bladder cancer, it is likely that similar methods could be used to examine invasion and motility in other tumor types as well.

Abstract A62: ATDC is required for KRAS-induced pancreatic tumorigenesis

We have recently demonstrated that ATDC, a novel oncogenic protein, serves as an invasive switch in pancreatic cancer (PDA) by activation of beta–catenin signaling and upregulation of CD44, resulting in EMT and an invasive phenotype during PanIN progression. To further explore the tumorigenic function of ATDC, we generated a floxed ATDC mouse (A F/F) to evaluate the impact of conditional knockout of ATDC on oncogenic Kras-induced PDA initiation and progression. Pancreas-specific ATDC knockout did not cause any histologic abnormalities in pancreas, up to 1 year of age (n=8). Through a series of crosses of LSL-KrasG12D (K), p53F/+ (P), RosaYFP (Y), Pdx1-Cre (C) and AF/F mice, KrasG12D; CY (KCY); KrasG12D; p53+/-; CY (KPCY), KCYA-/- KPCYA-/- mice were generated. Knockout of ATDC in KPCY mice completely prevented the development of ADM and PanIN lesions in 3 month old mice (n= 8), and resulted in the formation of very rare ADM and PanIN1 lesions (2 out of 8) in KPCYA-/- mice at 12 months of age (n=8). In contrast, all KPCY mice developed extensive PanIN (low and high grade) at 3 months of age (n= 8), with the subsequent development of invasive and metastatic cancer at frequencies similar to that reported in the literature. To determine the possible mechanisms by which ATDC inhibited KrasG12D-induced acinar-ductal metaplasia (ADM), we isolated acini from 1.5 month old KCY and KCYA-/- pancreata and performed in vitro 3D cultures and ADM assays. ADM lesions readily formed in 3-D cultures of acini from KCY mice at 5 days, and this was significantly inhibited in acini isolated from KCYA-/- mice (duct-like structures: 95.1±3.5% to 28.0±2.2%*, KCY vs KCYA-/-, n=3, *p&lt;0.05). Expression of ATDC specific shRNA in acini from KCY mice also effectively decreased ADM formation in 3D culture, an effect that was completely reversed by ATDC overexpression using an ATDC-shRNA-resistant expression vector. To further evaluate the role of ATDC in ADM and PanIN formation, we induced caerulein-mediated acute pancreatitis in 1.5 month old WT, CYA-/-, KCY, KCYA-/- mice and analyzed pancreatic tissue 1 and 7 days following cerulein treatment. 1 day post-caerulein treatment, KCY, KCYA-/-, CYA-/- and WT mice exhibited widespread ADM, which was replaced by normal acini by 7 days in WT, CYA-/- and KCYA-/- mice. However, in KCY mice 7 days post-cerulein treatment, extensive ADM and PanIN lesions were present, suggesting that ATDC is required for oncogenic KRAS to promote ADM and PanIN formation. Conclusions: Knockout of ATDC markedly reduces KrasG12D-induced ADM and PanIN formation, highlighting a key biologic function for ATDC in this process and its role in driving progression of KRAS-induced tumorigenesis in the pancreas.

Citation Format: Lidong Wang, Huibin Yang, Ethan V. Abel, Phillip L. Palmbos, Christophe Halbrook, Kenneth Takeuchi, Jiaqi Shi, Yaqing Zhang, Sumithra Urs, Meghna Waghray, Marina Pasca di Magliano, Andrew D. Rhim, Howard C. Crawford, Diane M. Simeone.{Authors}. ATDC is required for KRAS-induced pancreatic tumorigenesis. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr A62.

Abstract IA06: Co-Targeting cell cycle and androgen signaling to personalize therapy for hormone dependent prostate cancer

Prostate cancer (PC) is an androgen driven and dependent disease and androgen deprivation therapy (ADT) is the standard for patients with metastatic hormone sensitive disease. Despite a high response rate, most patients will progress to castration resistance. The expanding molecular knowledge highlights the biologic heterogeneity and adaptive capacity of PC, and provides the rationale for a preemptive multi-targeted therapeutic strategy. Compelling support for the latter strategy is provided by recent data from two randomized trials demonstrating an unprecedented impact on survival with the addition of docetaxel to ADT.

Androgens drive proliferation of PC cells via upregulation of cyclin D which complexes with the cyclin-dependent protein kinases 4/6 (CDK4/6) resulting in phosphorylation of retinoblastoma (Rb) tumor suppressor protein and G1/S progression. Alterations in this pathway contribute to progression to castration-resistance. Palbociclib is a novel specific CDK4/ 6 inhibitor which was recently approved in combination with letrozole for postmenopausal women with ER +, HER2 negative advanced breast cancer. In preclinical prostate cancer models, palbociclib inhibited proliferation and promoted G1 arrest in an Rb and Cyclin D dependent manner. Current data indicate that wild-type Rb expression is present in in 95% vs 75% of patients with newly diagnosed vs metastatic castration resistant PC respectively. We estimate that 80-90% of early metastatic hormone-sensitive PC will harbor intact Rb. Based on the biologic and preclinical data, we developed a multicenter randomized phase II clinical trial (NCT02059213) to test the hypothesis that adding palbociclib to ADT in patients with newly metastatic Rb-positive PC will significantly increase the efficacy of ADT. Patients (n = 60) with new metastatic hormone sensitive PC and Rb intact tumors based on metastatic biopsy are stratified by disease extent and randomized (1:2) to ADT or ADT+ palbociclib. Primary endpoint is confirmed prostate specific antigen (PSA) response (&lt; 4 ng/mL) after 28 weeks of therapy. With 20 patients randomized to ADT and 40 randomized to ADT plus palbociclib there will be a 64.2% power to detect a 20% difference in proportions with a one-sided type I error of 0.10 using the mid p-value method of the Fisher's exact test. Secondary endpoints: safety and tolerability of ADT + palbociclib, rate of undetectable PSA (&lt; 0.2ng/mL), biochemical and clinical progression-free survival, overall PSA and radiographic response rates, assessment of biomarkers which predict therapy response (circulating DNA and tumor cells, tumor protein and transcriptome analysis) and to establish a repository of metastatic hormone sensitive prostate tumor samples.

To date 39 patients have been registered and underwent tumor metastatic disease biopsy (soft tissue 26, bone 13). 2 patients were Rb negative and 5 had inadequate tissue. 32 patients have been randomized to ADT (11 patients) or ADT + palbociclib (21 patients). The study is in progress.

Support: Movember-PCF Challenge Award, Pfizer.

Citation Format: Maha Hussain, Phillip L. Palmbos1, Scott A. Tomlins1, Stephanie Daignault-Newton, Neeraj Agarwal, Przemyslaw Twardowski, Alicia K. Morgans, Emmanuel S. Antonarakis, Karen E. Knudsen, Felix Y. Feng. Co-Targeting cell cycle and androgen signaling to personalize therapy for hormone dependent prostate cancer. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Cancer Cell Cycle - Tumor Progression and Therapeutic Response; Feb 28-Mar 2, 2016; Orlando, FL. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(11_Suppl):Abstract nr IA06.

GM-CSF Mediates Mesenchymal-Epithelial Cross-talk in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDA) is characterized by a dense stroma consisting of a prevalence of activated fibroblasts whose functional contributions to pancreatic tumorigenesis remain incompletely understood. In this study, we provide the first identification and characterization of mesenchymal stem cells (MSC) within the human PDA microenvironment, highlighting the heterogeneity of the fibroblast population. Primary patient PDA samples and low-passage human pancreatic cancer-associated fibroblast cultures were found to contain a unique population of cancer-associated MSCs (CA-MSC). CA-MSCs markedly enhanced the growth, invasion, and metastatic potential of PDA cancer cells. CA-MSCs secreted the cytokine GM-CSF that was required for tumor cell proliferation, invasion, and transendothelial migration. Depletion of GM-CSF in CA-MSCs inhibited the ability of these cells to promote tumor cell growth and metastasis. Together, these data identify a population of MSCs within the tumor microenvironment that possesses a unique ability, through GM-CSF signaling, to promote PDA survival and metastasis.

SIGNIFICANCE

The role of stroma in pancreatic cancer is controversial. Here, we provide the first characterization of MSCs within the human PDA microenvironment and demonstrate that CA-MSCs promote tumorigenesis through the production of GM-CSF. These data identify a novel cytokine pathway that mediates mesenchymal-epithelial cross-talk and is amenable to therapeutic intervention. Cancer Discov; 6(8); 886-99. ©2016 AACR.This article is highlighted in the In This Issue feature, p. 803.

Targeting PARP in Prostate Cancer: Novelty, Pitfalls, and Promise

Metastatic prostate cancer remains a highly lethal disease with no curative therapeutic options. A significant subset of patients with prostate cancer harbor either germline or somatic mutations in DNA repair enzyme genes such as BRCA1, BRCA2, or ATM. Emerging data suggest that drugs that target poly(adenosine diphosphate [ADP]-ribose) polymerase (PARP) enzymes may represent a novel and effective means of treating tumors with these DNA repair defects, including prostate cancers. Here we will review the molecular mechanism of action of PARP inhibitors and discuss how they target tumor cells with faulty DNA repair functions and transcriptional controls. We will review emerging data for the utility of PARP inhibition in the management of metastatic prostate cancer. Finally, we will place PARP inhibitors within the framework of precision medicine-based care of patients with prostate cancer.

ATDC/TRIM29 Drives Invasive Bladder Cancer Formation through miRNA-Mediated and Epigenetic Mechanisms

Bladder cancer is a common and deadly malignancy but its treatment has advanced little due to poor understanding of the factors and pathways that promote disease. ATDC/TRIM29 is a highly expressed gene in several lethal tumor types, including bladder tumors, but its role as a pathogenic driver has not been established. Here we show that overexpression of ATDC in vivo is sufficient to drive both noninvasive and invasive bladder carcinoma development in transgenic mice. ATDC-driven bladder tumors were indistinguishable from human bladder cancers, which displayed similar gene expression signatures. Clinically, ATDC was highly expressed in bladder tumors in a manner associated with invasive growth behaviors. Mechanistically, ATDC exerted its oncogenic effects by suppressing miR-29 and subsequent upregulation of DNMT3A, leading to DNA methylation and silencing of the tumor suppressor PTEN. Taken together, our findings established a role for ATDC as a robust pathogenic driver of bladder cancer development, identified downstream effector pathways, and implicated ATDC as a candidate biomarker and therapeutic target.

ATDC (Ataxia Telangiectasia Group D Complementing) Promotes Radioresistance through an Interaction with the RNF8 Ubiquitin Ligase

Induction of DNA damage by ionizing radiation (IR) and/or cytotoxic chemotherapy is an essential component of cancer therapy. The ataxia telangiectasia group D complementing gene (ATDC, also called TRIM29) is highly expressed in many malignancies. It participates in the DNA damage response downstream of ataxia telangiectasia-mutated (ATM) and p38/MK2 and promotes cell survival after IR. To elucidate the downstream mechanisms of ATDC-induced IR protection, we performed a mass spectrometry screen to identify ATDC binding partners. We identified a direct physical interaction between ATDC and the E3 ubiquitin ligase and DNA damage response protein, RNF8, which is required for ATDC-induced radioresistance. This interaction was refined to the C-terminal portion (amino acids 348-588) of ATDC and the RING domain of RNF8 and was disrupted by mutation of ATDC Ser-550 to alanine. Mutations disrupting this interaction abrogated ATDC-induced radioresistance. The interaction between RNF8 and ATDC, which was increased by IR, also promoted downstream DNA damage responses such as IR-induced γ-H2AX ubiquitination, 53BP1 phosphorylation, and subsequent resolution of the DNA damage foci. These studies define a novel function for ATDC in the RNF8-mediated DNA damage response and implicate RNF8 binding as a key determinant of the radioprotective function of ATDC.

ATDC induces an invasive switch in KRAS-induced pancreatic tumorigenesis

The initiation of pancreatic ductal adenocarcinoma (PDA) is linked to activating mutations in KRAS. However, in PDA mouse models, expression of oncogenic mutant KRAS during development gives rise to tumors only after a prolonged latency or following induction of pancreatitis. Here we describe a novel mouse model expressing ataxia telangiectasia group D complementing gene (ATDC, also known as TRIM29 [tripartite motif 29]) that, in the presence of oncogenic KRAS, accelerates pancreatic intraepithelial neoplasia (PanIN) formation and the development of invasive and metastatic cancers. We found that ATDC up-regulates CD44 in mouse and human PanIN lesions via activation of β-catenin signaling, leading to the induction of an epithelial-to-mesenchymal transition (EMT) phenotype characterized by expression of Zeb1 and Snail1. We show that ATDC is up-regulated by oncogenic Kras in a subset of PanIN cells that are capable of invading the surrounding stroma. These results delineate a novel molecular pathway for EMT in pancreatic tumorigenesis, showing that ATDC is a proximal regulator of EMT.

ATDC/TRIM29 phosphorylation by ATM/MAPKAP kinase 2 mediates radioresistance in pancreatic cancer cells

Pancreatic ductal adenocarcinoma (PDAC) is characterized by therapeutic resistance for which the basis is poorly understood. Here, we report that the DNA and p53-binding protein ATDC/TRIM29, which is highly expressed in PDAC, plays a critical role in DNA damage signaling and radioresistance in pancreatic cancer cells. Ataxia-telangiectasia group D-associated gene (ATDC) mediated resistance to ionizing radiation in vitro and in vivo in mouse xenograft assays. ATDC was phosphorylated directly by MAPKAP kinase 2 (MK2) at Ser550 in an ATM-dependent manner. Phosphorylation at Ser-550 by MK2 was required for the radioprotective function of ATDC. Our results identify a DNA repair pathway leading from MK2 and ATM to ATDC, suggesting its candidacy as a therapeutic target to radiosensitize PDAC and improve the efficacy of DNA-damaging treatment.

Non-castrate metastatic prostate cancer: have the treatment options changed?

Over the past 7 decades androgen-deprivation therapy (ADT) has been the cornerstone of treatment for metastatic non-castrate prostate cancer (NCPC); however, the mechanisms to achieve this goal have evolved over time to include not only bilateral orchiectomy and estrogens, but also gonadotropin-releasing hormone (GnRH) agonists, antagonists, and the inclusion of androgen receptor (AR) blockade. Despite treatment with ADT, most men will progress to castrate-resistant prostate cancer (CRPC). Over the last decade many new treatment options for CRPC have emerged. These new treatments also could have a meaningful role earlier in NCPC. In this review, we outline the biologic drivers of NCPC, review current standard therapy available for NCPC, and discuss the evolving role of new therapeutics in metastatic disease.

Recruitment of Saccharomyces cerevisiae Dnl4-Lif1 complex to a double-strand break requires interactions with Yku80 and the Xrs2 FHA domain

Nonhomologous end joining (NHEJ) in yeast depends on eight different proteins in at least three different functional complexes: Yku70-Yku80 (Ku), Dnl4-Lif1-Nej1 (DNA ligase IV), and Mre11-Rad50-Xrs2 (MRX). Interactions between these complexes at DNA double-strand breaks (DSBs) are poorly understood but critical for the completion of repair. We previously identified two such contacts that are redundantly required for NHEJ, one between Dnl4 and the C terminus of Yku80 and one between the forkhead-associated (FHA) domain of Xrs2 and the C terminus of Lif1. Here, we first show that mutation of the Yku80 C terminus did not impair Ku binding to DSBs, supporting specificity of the mutant defect to the ligase interaction. We next show that the Xrs2-Lif1 interaction depends on Xrs2 FHA residues (R32, S47, R48, and K75) analogous to those known in other proteins to contact phosphorylated threonines. Two potential target threonines in Lif1 (T417 and T387) were inferred by identifying regions similar to a site in the human Lif1 homolog, XRCC4, known to be bound by the FHA domain of polynucleotide kinase. Mutating these threonines, especially T417, abolished the Xrs2-Lif1 interaction and impaired NHEJ epistatically with Xrs2 FHA mutation. Combining mutations that selectively disable the Yku80-Dnl4 and Xrs2-Lif1 interactions abrogated both NHEJ and DNA ligase IV recruitment to a DSB. The collected results indicate that the Xrs-Lif1 and Yku80-Dnl4 interactions are important for formation of a productive ligase-DSB intermediate.

Mycobacteriophage exploit NHEJ to facilitate genome circularization

Ku-dependent nonhomologous end joining (NHEJ) is a double-strand break repair process conserved in all branches of cellular life but has not previously been implicated in the DNA metabolic processes of viruses. We identified Ku homologs in Corndog and Omega, two related mycobacteriophages of Mycobacterium smegmatis. These proteins formed homodimers and bound DNA ends in a manner identical to other Ku's and stimulated joining of ends by the host NHEJ DNA ligase (LigD). Omega and Corndog are unusual in having short 4 base cos ends that would not be expected to self-anneal and would therefore require NHEJ during phage genome circularization. Consistently, M. smegmatis LigD null strains are entirely and selectively unable to support infection by Corndog or Omega, with concomitant failure of genome circularization. These results establish a new paradigm for sequestration of the host cell NHEJ process by bacteriophage and provide a framework for understanding similar transactions in eukaryotic viral infections.

Mutations of the Yku80 C terminus and Xrs2 FHA domain specifically block yeast nonhomologous end joining

The nonhomologous end-joining (NHEJ) pathway of DNA double-strand break repair requires three protein complexes in Saccharomyces cerevisiae: MRX (Mre11-Rad50-Xrs2), Ku (Ku70-Ku80), and DNA ligase IV (Dnl4-Lif1-Nej1). Much is known about the interactions that mediate the formation of each complex, but little is known about how they act together during repair. A comprehensive yeast two-hybrid screen of the NHEJ factors of S. cerevisiae revealed all known interactions within the MRX, Ku, and DNA ligase IV complexes, as well as three additional, weaker interactions between Yku80-Dnl4, Xrs2-Lif1, and Mre11-Yku80. Individual and combined deletions of the Yku80 C terminus and the Xrs2 forkhead-associated (FHA) domain were designed based on the latter two-hybrid results. These deletions synergistically blocked NHEJ but not the telomere and recombination functions of Ku and MRX, confirming that these protein regions are functionally important specifically for NHEJ. Further mutational analysis of Yku80 identified a putative C-terminal amphipathic alpha-helix that is both required for its NHEJ function and strikingly similar to a DNA-dependent protein kinase interaction motif in human Ku80. These results identify a novel role in yeast NHEJ for the poorly characterized Ku80 C-terminal and Xrs2 FHA domains, and they suggest that redundant binding of DNA ligase IV facilitates completion of this DNA repair event.

Nonhomologous End Joining in Yeast

Nonhomologous end joining (NHEJ), the direct rejoining of DNA double-strand breaks, is closely associated with illegitimate recombination and chromosomal rearrangement. This has led to the concept that NHEJ is error prone. Studies with the yeast Saccharomyces cerevisiae have revealed that this model eukaryote has a classical NHEJ pathway dependent on Ku and DNA ligase IV, as well as alternative mechanisms for break rejoining. The evolutionary conservation of the Ku-dependent process includes several genes dedicated to this pathway, indicating that classical NHEJ at least is a strong contributor to fitness in the wild. Here we review how double-strand break structure, the yeast NHEJ proteins, and alternative rejoining mechanisms influence the accuracy of break repair. We also consider how the balance between NHEJ and homologous repair is regulated by cell state to promote genome preservation. The principles discussed are instructive to NHEJ in all organisms.

Mycobacterial Ku and ligase proteins constitute a two-component NHEJ repair machine

In mammalian cells, repair of DNA double-strand breaks (DSBs) by nonhomologous end-joining (NHEJ) is critical for genome stability. Although the end-bridging and ligation steps of NHEJ have been reconstituted in vitro, little is known about the end-processing reactions that occur before ligation. Recently, functionally homologous end-bridging and ligation activities have been identified in prokarya. Consistent with its homology to polymerases and nucleases, we demonstrate that DNA ligase D from Mycobacterium tuberculosis (Mt-Lig) possesses a unique variety of nucleotidyl transferase activities, including gap-filling polymerase, terminal transferase, and primase, and is also a 3' to 5' exonuclease. These enzyme activities allow the Mt-Ku and Mt-Lig proteins to join incompatible DSB ends in vitro, as well as to reconstitute NHEJ in vivo in yeast. These results demonstrate that prokaryotic Ku and ligase form a bona fide NHEJ system that encodes all the recognition, processing, and ligation activities required for DSB repair.

Non-homologous end-joining: bacteria join the chromosome breakdance

The repair of DNA double-strand breaks by non-homologous end-joining (NHEJ) has long been thought to be restricted to eukaryotes. However, recent papers document the existence of operons encoding functional NHEJ complexes in some bacteria. These findings provide new evolutionary insights into the core biochemistry of this repair pathway, and suggest that one function driving the selection of NHEJ in bacteria, and perhaps eukaryotes, relates to prolonged periods of mitotic exit.

Macrophage exposure to particulate titanium induces phosphorylation of the protein tyrosine kinase lyn and the phospholipases Cgamma-1 and Cgamma-2

A frequent long-term complication of total joint arthroplasty is aseptic loosening, the end result of wear debris production, synovial macrophage activation, inflammatory mediator release, and osteolysis about the implant-bone or cement-bone interface. To elucidate the mechanisms of particle-induced macrophage activation and mediator production, we studied early signal transduction events using J774A.1 macrophages and 3 microm titanium particles. Treating macrophages with herbimycin A or genistein, two inhibitors of protein tyrosine kinases (PTKs), inhibited titanium phagocytosis as well as secretion of tumor necrosis factor-alpha (TNF-alpha) and prostaglandin-E2 (PGE2) in a dose-dependent manner. Both processes therefore depend on a PTK signaling cascade. Specifically, macrophage exposure to titanium-induced phosphorylation of multiple proteins including the Src kinase Lyn and phospholipase Cgamma-1 and Cgamma-2. Phosphorylation peaked within 2 min and returned to baseline within 45 min. Similar but not identical phosphorylation patterns were obtained when cells were stimulated with titanium preincubated with serum or albumin, suggesting distinct signal transduction pathways dependent on particle coating.

Genomic characterization of human SEC14L1 splice variants within a 17q25 candidate tumor suppressor gene region and identification of an unrelated embedded expressed sequence tag

Human SEC14L1 shows partial sequence homology to the budding yeast SEC14 protein and the Japanese flying squid retinal-binding protein and was previously generally localized to 17q25. We more precisely mapped SEC14L1 within a discrete region of 17q25 that likely harbors at least one putative breast and ovarian tumor suppressor gene. We determined that this gene consists of 18 exons ranging in size from 70 bp (exon 11) to 3088 bp (exon 17) and spanning at least 58 kb of DNA. Exon 17 contained a highly polymorphic variable number of tandem repeats (VNTR) and was present only in the larger ubiquitously expressed 5.5-kb transcript. The 3.0-kb ubiquitously expressed transcript included sequences at the beginning of exon 17 (designated exon 17a) and the end of exon 17 (designated exon 18), but lacked the internal 2439 bp of exon 17, including the VNTR. This alternative splicing resulted in a predicted protein of 719 residues from the smaller transcript with four more terminal amino acids than the 715 residue protein predicted from the larger transcript. EST H49244 spanned exon 11 of SEC14L1 and was specifically expressed in human peripheral blood leukocytes. One intragenic single nucleotide polymorphism (SNP) was confirmed. SEC14L1 contained the CRAL/TRIO domain also found in alpha-tocopherol transfer protein (TTPA) and cellular retinaldehyde-binding protein (CRALBP). As retinoids have been shown to inhibit the growth of breast cancer cells, loss of the proposed SEC14L1 retinal-binding function may contribute to breast tumorigenesis. As TTPA and CRALBP have been implicated in retinitis pigmentosa (RP), altered SEC14L1 expression may contribute to RP in previously unlinked families. Coding exon-specific PCR primers were designed to aid in future expression and mutational analyses.