Joseph J Sacco

Emerging roles of deubiquitinases in cancer‐associated pathways

Deubiquitinases (DUBs) are emerging as important regulators of many pathways germane to cancer. They may regulate the stability of key oncogenes, exemplified by USP28 stabilisation of c‐Myc. Alternatively they can negatively regulate ubiquitin‐dependent signalling cascades such as the NF‐κB activation pathway. We review the current literature that associates DUBs with cancer and discuss their suitability as drug targets of the future.

The deubiquitylase Ataxin-3 restricts PTEN transcription in lung cancer cells

The phosphatidylinositol-3-kinase (PI3K) pathway is commonly hyperactivated in cancer. One mechanism by which this occurs is by silencing of the phosphatase and tensin homolog (PTEN), a tumor suppressor and major antagonist of the pathway, through genetic, epigenetic or posttranscriptional mechanisms. Here, we used an unbiased siRNA screen in non-small-cell lung cancer cells to identify deubiquitylases (DUBs) that have an impact on PI3K signaling by regulating the abundance of PTEN. We found that PTEN expression was induced by depleting any of three members of the Josephin family DUBs: ataxin 3 (ATXN3), ataxin 3-like (ATXN3L) and Josephin domain containing 1 (JOSD1). However, this effect is not mediated through altered PTEN protein stability. Instead, depletion of each DUB increases expression of both the PTEN transcript and its competing endogenous RNA, PTENP1. In ATXN3-depleted cells, under conditions of transcriptional inhibition, PTEN and PTENP1 mRNAs rapidly decay, suggesting that ATXN3 acts primarily by repressing their transcription. Importantly, the PTEN induction observed in response to ATXN3 siRNA is sufficient to downregulate Akt phosphorylation and hence PI3K signaling. Histone deacetylase inhibitors (HDACi) have been suggested as potential mediators of PTEN transcriptional reactivation in non-small-cell lung cancer. Although PTEN exhibits a very limited response to the broad-spectrum HDACi Vorinostat (SAHA) in A549 cells, we find that combination with ATXN3 depletion enhances PTEN induction in an additive manner. Similarly, these interventions additively decrease cell viability. Thus, ATXN3 provides an autonomous, complementary therapeutic target in cancers with epigenetic downregulation of PTEN.

Systemic listeriosis following vaccination with the attenuated Listeria monocytogenes therapeutic vaccine, ADXS11-001

Joseph J. Sacco, Mererid Evans, Kevin J. Harrington, Stephen Man, Ned Powell, Richard J. Shaw, and Terry M. Jones Department of Molecular and Clinical Cancer Medicine, Institute of Translational Medicine, University of Liverpool, Liverpool, UK; Clatterbridge Cancer Centre, Bromborough, Wirral, UK; Velindre Hospital, Cardiff, Cardiff, UK; Institute of Cancer and Genetics, School of Medicine, Cardiff University, Cardiff, UK; The Institute of Cancer Research, London, UK; Aintree University Hospital HNS Foundation Trust, Liverpool, UK

Challenges and strategies in precision medicine for non-small cell lung cancer

Lung cancer is the most common cause of cancer- related death worldwide, causing over 1.2 million deaths each year. Non-small-cell lung cancer (NSCLC) consists of a group of malignancies that are pathologically and molecularly diverse but that are all characterised by a poor prognosis. Survival rates for lung cancer patients have improved very slowly and only to a modest degree owing partly to poor funding for research into this malignancy and stigma associated with smoking, as well as relative chemo-resistance. However, in recent years, NSCLC has become an exemplar for precision medicine, mainly following development of drugs targeting the receptors of epidermal growth factor and anaplastic lymphoma kinase. While epidermal growth factor receptor and anaplastic lymphoma kinase inhibitors are only applicable to a minority of patients and benefits are almost invariably short-lived, current studies indicate that at least 50% of patients with NSCLC have a targetable mutation. With a growing armamentarium of inhibitors against these targets in development, there is a hope that a greater proportion of patients will benefit from precision medicine and that such benefits will be sustained. However, there remain significant challenges in the development of precision medicine in NSCLC. These include: identification and validation of new targets; ensuring biopsies are fit for purpose; tumour heterogeneity; requirements for serial tumour assessments; and not least cost. In this review, we will discuss the current status of precision medicine in NSCLC as well as how basic and translational research are paving the way towards overcoming the above challenges. In addition, we will pay attention to clinical strategies in respect to liquid biopsies and the potential use of extracellular vesicles such as exosomes in cancer therapeutics.

Modulating the DNA Damage Response to Improve Treatment Response in Cervical Cancer

Cervical cancer is the fourth most common cause of cancer-related death in women worldwide and new therapeutic approaches are needed to improve clinical outcomes for this group of patients. Current treatment protocols for locally advanced and metastatic disease consist of ionising radiation and chemotherapy. Chemoradiation induces cytotoxic levels of DNA double-strand breaks, which activates programmed cell death via the DNA damage response (DDR). Cervical cancers are unique given an almost exclusive association with human papillomavirus (HPV) infection; a potent manipulator of the DDR, with the potential to alter tumour sensitivity to DNA-damaging agents and influence treatment response. This review highlights the wide range of therapeutic strategies in development that have the potential to modulate DDR and sensitise cervical tumours to DNA-damaging agents in the context of HPV oncogenesis.

Kinome-wide transcriptional profiling of uveal melanoma reveals new vulnerabilities to targeted therapeutics

Metastatic uveal melanoma (UM) is invariably fatal, usually within a year of diagnosis. There are currently no effective therapies, and clinical studies employing kinase inhibitors have so far demonstrated limited success. This is despite common activating mutations in GNAQ/11 genes, which trigger signalling pathways that might predispose tumours to a variety of targeted drugs. In this study, we have profiled kinome expression network dynamics in various human ocular melanomas. We uncovered a shared transcriptional profile in human primary UM samples and across a variety of experimental cell‐based models. The poor overall response of UM cells to FDA‐approved kinase inhibitors contrasted with much higher sensitivity to the bromodomain inhibitor JQ1, a broad transcriptional repressor. Mechanistically, we identified a repressed FOXM1‐dependent kinase subnetwork in JQ1‐exposed cells that contained multiple cell cycle‐regulated protein kinases. Consistently, we demonstrated vulnerability of UM cells to inhibitors of mitotic protein kinases within this network, including the investigational PLK1 inhibitor BI6727. We conclude that analysis of kinome‐wide signalling network dynamics has the potential to reveal actionable drug targets and inhibitors of potential therapeutic benefit for UM patients.

Gene expression profiling in bladder cancer identifies potential therapeutic targets

Despite advances in management, bladder cancer remains a major cause of cancer related complications. Characterisation of gene expression patterns in bladder cancer allows the identification of pathways involved in its pathogenesis, and may stimulate the development of novel therapies targeting these pathways. Between 2004 and 2005, cystoscopic bladder biopsies were obtained from 19 patients and 11 controls. These were subjected to whole transcript-based microarray analysis. Unsupervised hierarchical clustering was used to identify samples with similar expression profiles. Hypergeometric analysis was used to identify canonical pathways and curated networks having statistically significant enrichment of differentially expressed genes. Osteopontin (OPN) expression was validated by immunohistochemistry. Hierarchical clustering defined signatures, which differentiated between cancer and healthy tissue, muscle-invasive or non-muscle invasive cancer and healthy tissue, grade 1 and grade 3. Pathways associated with cell cycle and proliferation were markedly upregulated in muscle-invasive and grade 3 cancers. Genes associated with the classical complement pathway were downregulated in non-muscle invasive cancer. Osteopontin was markedly overexpressed in invasive cancer compared to healthy tissue. The present study contributes to a growing body of work on gene expression signatures in bladder cancer. The data support an important role for osteopontin in bladder cancer, and identify several pathways worthy of further investigation.

Patterns of BAP1 protein expression provide insights into prognostic significance and the biology of uveal melanoma: The prognostic and biological significance of BAP1 in uveal melanoma

Uveal melanoma (UM) is a rare aggressive intraocular tumour with a propensity for liver metastases, occurring in ∼50% of patients. The tumour suppressor BAP1 is considered to be key in UM progression. Herein, we present the largest study to date investigating cellular expression patterns of BAP1 protein in 165 UMs, correlating these patterns to prognosis. Full clinical, histological, genetic, and follow‐up data were available for all patients. BAP1 gene sequencing was performed on a subset of 26 cases. An independent cohort of 14 UMs was examined for comparison. Loss of nuclear BAP1 (nBAP1) protein expression was observed in 54% (88/165) UMs. nBAP1 expression proved to be a significant independent prognostic parameter: it identified two subgroups within monosomy 3 (M3) UM, which are known to have a high risk of metastasis. Strikingly, nBAP1‐positiveM3 UMs were associated with prolonged survival compared to nBAP1‐negative M3 UMs (Log rank, p = 0.014). nBAP1 protein loss did not correlate with a BAP1 mutation in 23% (6/26) of the UMs analysed. Cytoplasmic BAP1 protein (cBAP1) expression was also observed in UM: although appearing ‘predominantly diffuse’ in most nBAP1‐negative UM, a distinct ‘focal perinuclear’ expression pattern – localized immediately adjacent to the cis Golgi – was seen in 31% (18/59). These tumours tended to carry loss‐of‐function BAP1 mutations. Our study demonstrates loss of nBAP1 expression to be the strongest prognostic marker in UM, confirming its importance in UM progression. Our data suggest that non‐genetic mechanisms account for nBAP1 loss in a small number of UMs. In addition, we describe a subset of nBAP1‐negative UM, in which BAP1 is sequestered in perinuclear bodies, most likely within Golgi, warranting further mechanistic investigation.

The deubiquitylase USP15 regulates topoisomerase II alpha to maintain genome integrity

Ubiquitin-specific protease 15 (USP15) is a widely expressed deubiquitylase that has been implicated in diverse cellular processes in cancer. Here we identify topoisomerase II (TOP2A) as a novel protein that is regulated by USP15. TOP2A accumulates during G2 and functions to decatenate intertwined sister chromatids at prophase, ensuring the replicated genome can be accurately divided into daughter cells at anaphase. We show that USP15 is required for TOP2A accumulation, and that USP15 depletion leads to the formation of anaphase chromosome bridges. These bridges fail to decatenate, and at mitotic exit form micronuclei that are indicative of genome instability. We also describe the cell cycle-dependent behaviour for two major isoforms of USP15, which differ by a short serine-rich insertion that is retained in isoform-1 but not in isoform-2. Although USP15 is predominantly cytoplasmic in interphase, we show that both isoforms move into the nucleus at prophase, but that isoform-1 is phosphorylated on its unique S229 residue at mitotic entry. The micronuclei phenotype we observe on USP15 depletion can be rescued by either USP15 isoform and requires USP15 catalytic activity. Importantly, however, an S229D phospho-mimetic mutant of USP15 isoform-1 cannot rescue either the micronuclei phenotype, or accumulation of TOP2A. Thus, S229 phosphorylation selectively abrogates this role of USP15 in maintaining genome integrity in an isoform-specific manner. Finally, we show that USP15 isoform-1 is preferentially upregulated in a panel of non-small cell lung cancer cell lines, and propose that isoform imbalance may contribute to genome instability in cancer. Our data provide the first example of isoform-specific deubiquitylase phospho-regulation and reveal a novel role for USP15 in guarding genome integrity.

PO-027 Potential use of BH3 mimetics in the treatment of head and neck cancer

Introduction Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer worldwide. The limited success and significant toxicities associated with current therapies highlight the need for more efficacious treatment strategies. BH3 mimetics are an emerging class of drugs that target the anti-apoptotic BCL-2 family members, which are overexpressed proteins in many cancers, contributing to evasion of apoptosis and resistance to many therapeutic regimens. The BCL-2 specific inhibitor, venetoclax, is currently used to treat haematological malignancies, whereas specific inhibitors for BCL-XL and MCL-1 are entering clinical trials. We aim to determine the potential of BH3 mimetics in the treatment of HNSCC. Material and methods HNSCC tissue microarrays (TMAs) were immunohistochemically stained for BCL-2, BCL-XL and MCL-1, protein levels assessed semi-quantitatively as low, moderate or high and correlated with patient survival. Cell lines and primary cells were treated with ABT-199 (BCL-2 specific), A1331852 (BCL-XL specific) and/or S63845 (MCL-1 specific), and apoptosis induction and replicative potential were assessed. Results and discussions TMAs revealed that HNSCC tumours express moderate to high levels of BCL-XL and MCL-1, but low levels of BCL-2. Indeed treatment with a BCL-2 inhibitor had little effect on cell death in HNSCC cell lines; nor did treatment with A1331852 or S63845 as single agents. However, a combination of MCL-1 and BCL-XL inhibition induced extensive apoptotic cell death and a marked reduction in clonogenic cell growth, suggesting a dependence on these two anti-apoptotic proteins for tumour cell survival. A comparison of MCL-1 and BCL-XL expression levels against overall survival of HNSCC patients over a five year period post-surgery revealed that high MCL-1 levels were associated with low median survival. In contrast, the correlation between high BCL-XL expression and median survival was statistically not significant, although it may be clinically relevant. Conclusion BCL-2 is poorly expressed in HNSCC tumours, diminishing the potential of using venetoclax in HNSCC. In contrast, both BCL-XL and MCL-1 are highly expressed in HNSCC, and may be important prognostic indicators. Therefore targeting BCL-XL and MCL-1 together may be therapeutically beneficial, although the toxicity of this combination must be assessed before human trials can be considered.