Cytoplasmic redistribution and cleavage of AUF1 during coxsackievirus infection enhance the stability of its viral genome.

Coxsackievirus B3 (CVB3) is a causative agent of viral myocarditis, hepatitis, pancreatitis, and meningitis in humans. The adenosine-uridine (AU)-rich element RNA binding factor 1 (AUF1) is an integral component in the regulation of gene expression. AUF1 destabilizes mRNAs and targets them for degradation by binding to AU-rich elements in the 3' untranslated region (UTR) of mRNAs. The 3'-UTR of the CVB3 genome contains canonical AU-rich sequences, raising the possibility that CVB3 RNA may also be subjected to AUF1-mediated degradation. Here, we reported that CVB3 infection led to cytoplasmic redistribution and cleavage of AUF1. These events are independent of CVB3-induced caspase activation but require viral protein production. Overexpression of viral protease 2A reproduced CVB3-induced cytoplasmic redistribution of AUF1, while in vitro cleavage assay revealed that viral protease 3C contributed to AUF1 cleavage. Furthermore, we showed that knockdown of AUF1 facilitated viral RNA, protein, and progeny production, suggesting an antiviral property for AUF1 against CVB3 infection. Finally, an immunoprecipitation study demonstrated the physical interaction between AUF1 and the 3'-UTR of CVB3, potentially targeting CVB3 genome toward degradation. Together, our results suggest that cleavage of AUF1 may be a strategy employed by CVB3 to enhance the stability of its viral genome.

Immuno-Oncology Advances in Genitourinary Cancers.

Immuno-oncology (IO) has made monumental gains in the past decade in the genitourinary space. In this review, we highlight advances with IO in renal cell carcinoma where it now has become standard-of-care frontline therapy in the metastatic setting but also discuss challenges with the initial approach. In urothelial carcinoma, we discuss the growing use of IO including exciting recent updates with IO-based regimens that may soon become the new standard of care. We further discuss difficulties with IO in prostate cancer, germ cell tumors, and penile squamous cell carcinoma. Finally, we highlight advances in IO approaches beyond checkpoint inhibition including the role of the gut microbiome and T-cell redirecting therapies.

BRCA2, ATM, and CDK12 Defects Differentially Shape Prostate Tumor Driver Genomics and Clinical Aggression.

PURPOSE: DNA damage repair (DDR) defects are common across cancer types and can indicate therapeutic vulnerability. Optimal exploitation of DDR defects in prostate cancer requires new diagnostic strategies and a better understanding of associated clinical genomic features. EXPERIMENTAL DESIGN: We performed targeted sequencing of 1,615 plasma cell-free DNA samples from 879 patients with metastatic prostate cancer. Depth-based copy-number calls and heterozygous SNP imbalance were leveraged to expose DDR-mutant allelic configuration and categorize mechanisms of biallelic loss. We used split-read structural variation analysis to characterize tumor suppressor rearrangements. Patient-matched archival primary tissue was analyzed identically. RESULTS: BRCA2, ATM, and CDK12 were the most frequently disrupted DDR genes in circulating tumor DNA (ctDNA), collectively mutated in 15% of evaluable cases. Biallelic gene disruption via second somatic alteration or mutant allele-specific imbalance was identified in 79% of patients. A further 2% exhibited homozygous BRCA2 deletions. Tumor suppressors TP53, RB1, and PTEN were controlled via disruptive chromosomal rearrangements in BRCA2-defective samples, but via oncogene amplification in context of CDK12 defects. TP53 mutations were rare in cases with ATM defects. DDR mutations were re-detected across 94% of serial ctDNA samples and in all available archival primary tissues, indicating they arose prior to metastatic progression. Loss of BRCA2 and CDK12, but not ATM, was associated with poor clinical outcomes. CONCLUSIONS: BRCA2, ATM, and CDK12 defects are each linked to distinct prostate cancer driver genomics and aggression. The consistency of DDR status in longitudinal samples and resolution of allelic status underscores the potential for ctDNA as a diagnostic tool.

Activating AKT1 and PIK3CA Mutations in Metastatic Castration-Resistant Prostate Cancer.

BACKGROUND: Activating mutations in AKT1 and PIK3CA are undercharacterised in metastatic castration-resistant prostate cancer (mCRPC), but are linked to activation of phosphatidylinositol 3-kinase (PI3K) signalling and sensitivity to pathway inhibitors in other cancers. OBJECTIVE: To determine the prevalence, genomic context, and clinical associations of AKT1/PIK3CA activating mutations in mCRPC. DESIGN, SETTING, AND PARTICIPANTS: We analysed targeted cell-free DNA (cfDNA) sequencing data from 599 metastatic prostate cancer patients with circulating tumour DNA (ctDNA) content above 2%. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: In patients with AKT1/PIK3CA mutations, cfDNA was subjected to PTEN intron sequencing and matched diagnostic tumour tissue was analysed when possible. RESULTS AND LIMITATIONS: Of the patients, 6.0% (36/599) harboured somatic clonal activating mutation(s) in AKT1 or PIK3CA. Mutant allele-specific imbalance was common. Clonal mutations in mCRPC ctDNA were typically detected in pretreatment primary tissue and were consistent across serial ctDNA collections. AKT1/PIK3CA-mutant mCRPC had fewer androgen receptor (AR) gene copies than AKT1/PIK3CA wild-type mCRPC (median 4.7 vs 10.3, p = 0.003). AKT1 mutations were mutually exclusive with PTEN alterations. Patients with and without AKT1/PIK3CA mutations showed similar clinical outcomes with standard of care treatments. A heavily pretreated mCRPC patient with an AKT1 mutation experienced a 50% decline in prostate-specific antigen with Akt inhibitor (ipatasertib) monotherapy. Ipatasertib also had a marked antitumour effect in a patient-derived xenograft harbouring an AKT1 mutation. Limitations include the inability to assess AKT1/PIK3CA correlatives in ctDNA-negative patients. CONCLUSIONS: AKT1/PIK3CA activating mutations are relatively common and delineate a distinct mCRPC molecular subtype with low-level AR copy gain. Clonal prevalence and evidence of mutant allele selection propose PI3K pathway dependency in selected patients. The use of cfDNA screening enables prospective clinical trials to test PI3K pathway inhibitors in this population. PATIENT SUMMARY: Of advanced prostate cancer cases, 6% have activating mutations in the genes AKT1 or PIK3CA. These mutations can be identified using a blood test and may help select patients suitable for clinical trials of phosphatidylinositol 3-kinase inhibitors.

Eligibility of real-world patients with chemo-refractory, K-RAS wild-type, metastatic colorectal cancer for palliative intent regorafenib monotherapy.

The CORRECT trial demonstrated survival benefits with regorafenib monotherapy in patients with treatment-refractory, metastatic colorectal cancer (mCRC). However, the trial's stringent eligibility criteria for regorafenib may limit its external validity. We aimed to examine treatment attrition rates and eligibility for regorafenib in routine practice. We identified patients at the British Columbia Cancer Agency diagnosed with mCRC who demonstrated disease progression or intolerable toxicity on 2 or more lines of systemic therapy. During the study timeframe, panitumumab and cetuximab were only used in the chemo-refractory setting. Data on clinicopathologic variables and patient outcomes were ascertained and analyzed. Eligibility was determined using the CORRECT trial criteria. A total of 391 patients were identified, among whom only 39% were eligible for regorafenib: 35% in the panitumumab group and 51% in the cetuximab group. The main reasons for ineligibility in all patients were Eastern Cooperative Oncology Group Performance Status (ECOG PS) > 1 (69%), an elevated total bilirubin (21%), and thromboembolic events in the past 6 months (10%). No difference in eligibility for regorafenib was observed between patients previously receiving panitumumab or cetuximab (P = 0.914; 95% CI 0.550-1.951). Kaplan-Meier analyses showed that regorafenib-eligible compared to regorafenib-ineligible patients had an increased median overall survival of 5.3 versus 2.1 months, respectively (P < 0.001). However, Cox proportional hazard analyses showed that only ECOG PS rather than trial eligibility was correlated with outcomes. The strict eligibility criteria disqualify most patients with treatment-refractory mCRC for regorafenib therapy. Future trials should broaden the eligibility criteria to improve external validity.

The Master Neural Transcription Factor BRN2 Is an Androgen Receptor-Suppressed Driver of Neuroendocrine Differentiation in Prostate Cancer.

Mechanisms controlling the emergence of lethal neuroendocrine prostate cancer (NEPC), especially those that are consequences of treatment-induced suppression of the androgen receptor (AR), remain elusive. Using a unique model of AR pathway inhibitor-resistant prostate cancer, we identified AR-dependent control of the neural transcription factor BRN2 (encoded by POU3F2) as a major driver of NEPC and aggressive tumor growth, both in vitro and in vivo Mechanistic studies showed that AR directly suppresses BRN2 transcription, which is required for NEPC, and BRN2-dependent regulation of the NEPC marker SOX2. Underscoring its inverse correlation with classic AR activity in clinical samples, BRN2 expression was highest in NEPC tumors and was significantly increased in castration-resistant prostate cancer compared with adenocarcinoma, especially in patients with low serum PSA. These data reveal a novel mechanism of AR-dependent control of NEPC and suggest that targeting BRN2 is a strategy to treat or prevent neuroendocrine differentiation in prostate tumors. SIGNIFICANCE: Understanding the contribution of the AR to the emergence of highly lethal, drug-resistant NEPC is critical for better implementation of current standard-of-care therapies and novel drug design. Our first-in-field data underscore the consequences of potent AR inhibition in prostate tumors, revealing a novel mechanism of AR-dependent control of neuroendocrine differentiation, and uncover BRN2 as a potential therapeutic target to prevent emergence of NEPC. Cancer Discov; 7(1); 54-71. ©2016 AACR.This article is highlighted in the In This Issue feature, p. 1.

PD-L1 is highly expressed in Enzalutamide resistant prostate cancer.

Efficacy of Enzalutamide (ENZ) in castration resistant prostate cancer (CRPC) patients is short-lived. Immunotherapy like T cell checkpoint blockade may improve patient survival. However, when and where checkpoint molecules are expressed in CRPC and whether immune evasion is a mechanism of ENZ resistance remains unclear. Thus, we investigated whether clinically relevant immunotherapy targets, specifically PD-L1/2 , PD-1 and CTLA-4, are upregulated in ENZ resistant (ENZR) patients and in a pre-clinical model of ENZ resistance. We show for the first time that patients progressing on ENZ had significantly increased PD-L1/2+ dendritic cells (DC) in blood compared to those naïve or responding to treatment, and a high frequency of PD-1+T cells. These data supported our pre-clinical results, in which we found significantly increased circulating PD-L1/2+ DCs in mice bearing ENZR tumors compared to CRPC, and ENZR tumors expressed significantly increased levels of tumor-intrinsic PD-L1. Importantly, the expression of PD-L1 on ENZR cells, or the ability to modulate PD-L1/2+ DC frequency, was unique to ENZR cell lines and xenografts that did not show classical activation of the androgen receptor. Overall, our results suggest that ENZ resistance is associated with the strong expression of anti-PD-1 therapy targets in circulating immune cells both in patients and in a pre-clinical model that is non-AR driven. Further evaluation of the contribution of tumor vs. immune cell PD-L1 expression in progression of CRPC to anti-androgen resistance and the utility of monitoring circulating cell PD-L1 pathway activity in CRPC patients to predict responsiveness to checkpoint immunotherapy, is warranted.

Immune and non-immune functions of the immunoproteasome.

The biological importance of the ubiquitin-proteasome system in the control of myriad cellular processes has been well-recognized; however, the pathophysiological significance of the immunoproteasome, the inducible form of the proteasome, has not been well-comprehended until lately. The primary function of the immunoproteasome was originally believed to improve MHC-I antigen presentation. It now becomes evident that the immunoproteasome possesses broader biological functions. It regulates proinflammatory cytokine production, and T cell differentiation and proliferation. Alongside immune functions, the immunoproteasome has been demonstrated to relieve oxidative stress by the efficient turnover of oxidatively-damaged proteins and by allaying the formation of harmful protein aggregates. Furthermore, it has been implicated to regulate tumor cell growth and control muscle mass. Finally, the immunoproteasome has recently drawn considerable attention as a potential novel therapeutic target for cancer and autoimmune disease. This review will give an overview of the structure and function of the immunoproteasome, highlight its functional diversity in both immune and non-immune responses, and discuss the relationship between the dysregulation of the immunoproteasome and the development of several human diseases.