Matti Annala

Evaluation of methods for modeling transcription factor sequence specificity

Genomic analyses often involve scanning for potential transcription factor (TF) binding sites using models of the sequence specificity of DNA binding proteins. Many approaches have been developed to model and learn a proteins DNA-binding specificity, but these methods have not been systematically compared. Here we applied 26 such approaches to in vitro protein binding microarray data for 66 mouse TFs belonging to various families. For nine TFs, we also scored the resulting motif models on in vivo data, and found that the best in vitro–derived motifs performed similarly to motifs derived from the in vivo data. Our results indicate that simple models based on mononucleotide position weight matrices trained by the best methods perform similarly to more complex models for most TFs examined, but fall short in specific cases (<10% of the TFs examined here). In addition, the best-performing motifs typically have relatively low information content, consistent with widespread degeneracy in eukaryotic TF sequence preferences.

A prostate cancer susceptibility allele at 6q22 increases RFX6 expression by modulating HOXB13 chromatin binding

Genome-wide association studies have identified thousands of SNPs associated with predisposition to various diseases, including prostate cancer. However, the mechanistic roles of these SNPs remain poorly defined, particularly for noncoding polymorphisms. Here we find that the prostate cancer risk-associated SNP rs339331 at 6q22 lies within a functional HOXB13-binding site. The risk-associated T allele at rs339331 increases binding of HOXB13 to a transcriptional enhancer, conferring allele-specific upregulation of the rs339331-associated gene RFX6. Suppression of RFX6 diminishes prostate cancer cell proliferation, migration and invasion. Clinical data indicate that RFX6 upregulation in human prostate cancers correlates with tumor progression, metastasis and risk of biochemical relapse. Finally, we observe a significant association between the risk-associated T allele at rs339331 and increased RFX6 mRNA levels in human prostate tumors. Together, our results suggest that rs339331 affects prostate cancer risk by altering RFX6 expression through a functional interaction with the prostate cancer susceptibility gene HOXB13.

Genomic Alterations in Cell-Free DNA and Enzalutamide Resistance in Castration-Resistant Prostate Cancer

Importance The molecular landscape underpinning response to the androgen receptor (AR) antagonist enzalutamide in patients with metastatic castration-resistant prostate cancer (mCRPC) is undefined. Consequently, there is an urgent need for practical biomarkers to guide therapy selection and elucidate resistance. Although tissue biopsies are impractical to perform routinely in the majority of patients with mCRPC, the analysis of plasma cell-free DNA (cfDNA) has recently emerged as a minimally invasive method to explore tumor characteristics. Objective To reveal genomic characteristics from cfDNA associated with clinical outcomes during enzalutamide treatment. Design, Setting, and Participants Plasma samples were obtained from August 4, 2013, to July 31, 2015, at a single academic institution (British Columbia Cancer Agency) from 65 patients with mCRPC. We collected temporal plasma samples (at baseline, 12 weeks, end of treatment) for circulating cfDNA and performed array comparative genomic hybridization copy number profiling and deep AR gene sequencing. Samples collected at end of treatment were also subjected to targeted sequencing of 19 prostate cancer-associated genes. Exposure Enzalutamide, 160 mg, daily orally. Main Outcomes and Measures Prostate-specific antigen response rate (decline ≥50% from baseline confirmed ≥3 weeks later). Radiographic (as per Prostate Cancer Working Group 2 Criteria) and/or clinical progression (defined as worsening disease-related symptoms necessitating a change in anticancer therapy and/or deterioration in Eastern Cooperative Group performance status ≥2 levels). Results The 65 patients had a median (interquartile range) age of 74 (68-79) years. Prostate-specific antigen response rate to enzalutamide treatment was 38% (25 of 65), while median clinical/radiographic progression-free survival was 3.5 (95% CI, 2.1-5.0) months. Cell-free DNA was isolated from 122 of 125 plasma samples, and targeted sequencing was successful in 119 of 122. AR mutations and/or copy number alterations were robustly detected in 48% (31 of 65) and 60% (18 of 30) of baseline and progression samples, respectively. Detection of AR amplification, heavily mutated AR (≥2 mutations), and RB1 loss were associated with worse progression-free survival, with hazard ratios of 2.92 (95% CI, 1.59-5.37), 3.94 (95% CI, 1.46-10.64), and 4.46 (95% CI, 2.28-8.74), respectively. AR mutations exhibited clonal selection during treatment, including an increase in glucocorticoid-sensitive AR L702H and promiscuous AR T878A in patients with prior abiraterone treatment. At the time of progression, cfDNA sequencing revealed mutations or copy number changes in all patients tested, including clinically actionable alterations in DNA damage repair genes and PI3K pathway genes, and a high frequency (4 of 14) of activating CTNNB1 mutations. Conclusions and Relevance Clinically informative genomic profiling of cfDNA was feasible in nearly all patients with mCRPC and can provide important insights into enzalutamide response and resistance.

Insulin-like growth factor-binding protein 2-driven glioma progression is prevented by blocking a clinically significant integrin, integrin-linked kinase, and NF-κB network

Insulin-like growth factor-binding protein 2 (IGFBP2) is increasingly recognized as a glioma oncogene, emerging as a target for therapeutic intervention. In this study, we used an integrative approach to characterizing the IGFBP2 network, combining transcriptional profiling of human glioma with validation in glial cells and the replication-competent ASLV long terminal repeat with a splice acceptor/tv-a glioma mouse system. We demonstrated that IGFBP2 expression is closely linked to genes in the integrin and integrin-linked kinase (ILK) pathways and that these genes are associated with prognosis. We further showed that IGFBP2 activates integrin β1 and downstream invasion pathways, requires ILK to induce cell motility, and activates NF-κB. Most significantly, the IGFBP2/integrin/ILK/NF-κB network functions as a physiologically active signaling pathway in vivo by driving glioma progression; interfering with any point in the pathway markedly inhibits progression. The results of this study reveal a signaling pathway that is both targetable and highly relevant to improving the survival of glioma patients.

Emergence of FGFR family gene fusions as therapeutic targets in a wide spectrum of solid tumours

The emergence of fibroblast growth factor receptor (FGFR) family fusions across diverse cancers has brought attention to FGFR‐derived cancer therapies. The discovery of the first recurrent FGFR fusion in glioblastoma was followed by discoveries of FGFR fusions in bladder, lung, breast, thyroid, oral, and prostate cancers. Drug targeting of FGFR fusions has shown promising results and should soon be translating into clinical trials. FGFR fusions form as a result of various mechanisms – predominantly deletion for FGFR1, translocation for FGFR2, and tandem duplication for FGFR3. The ability to exploit the unique targetability of FGFR fusions proves that FGFR‐derived therapies could have a promising future in cancer therapeutics. Drug targeting of fusion genes has proven to be an extremely effective therapeutic approach for cancers such as the recurrent BCR–ABL1 fusion in chronic myeloid leukaemia. The recent discovery of recurrent FGFR family fusions in several cancer types has brought to attention the unique therapeutic potential for FGFR‐positive patients. Understanding the diverse mechanisms of FGFR fusion formation and their oncogenic potential will shed light on the impact of FGFR‐derived therapy in the future. Copyright

Treatment Outcomes and Tumor Loss of Heterozygosity in Germline DNA Repair–deficient Prostate Cancer

BACKGROUND Germline mutations in DNA repair genes were recently reported in 8-12% of patients with metastatic castration-resistant prostate cancer (mCRPC). It is unknown whether these mutations associate with differential response to androgen receptor (AR)-directed therapy. OBJECTIVE To determine the clinical response of mCRPC patients with germline DNA repair defects to AR-directed therapies and to establish whether biallelic DNA repair gene loss is detectable in matched circulating tumor DNA (ctDNA). DESIGN, SETTING, AND PARTICIPANTS We recruited 319 mCRPC patients and performed targeted germline sequencing of 22 DNA repair genes. In patients with deleterious germline mutations, plasma cell-free DNA was also sequenced. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS Prostate-specific antigen response and progression were assessed in relation to initial androgen deprivation therapy (ADT) and subsequent therapy for mCRPC using Kaplan-Meier analysis. RESULTS AND LIMITATIONS Of the 319 patients, 24 (7.5%) had deleterious germline mutations, with BRCA2 (n=16) being the most frequent. Patients (n=22) with mutations in genes linked to homologous recombination were heterogeneous at initial presentation but, after starting ADT, progressed to mCRPC with a median time of 11.8 mo (95% confidence interval [CI] 5.1-18.4). The median time to prostate-specific antigen progression on first-line AR-targeted therapy in the mCRPC setting was 3.3 mo (95% CI 2.7-3.9). Ten out of 11 evaluable patients with germline BRCA2 mutations had somatic deletion of the intact allele in ctDNA. A limitation of this study is absence of a formal control cohort for comparison of clinical outcomes. CONCLUSIONS Patients with mCRPC who have germline DNA repair defects exhibit attenuated responses to AR-targeted therapy. Biallelic gene loss was robustly detected in ctDNA, suggesting that this patient subset could be prioritized for therapies exploiting defective DNA repair using a liquid biopsy. PATIENT SUMMARY Patients with metastatic prostate cancer and germline DNA repair defects exhibit a poor response to standard hormonal therapies, but may be prioritized for potentially more effective therapies using a blood test.

A linear model for transcription factor binding affinity prediction in protein binding microarrays

Protein binding microarrays (PBM) are a high throughput technology used to characterize protein-DNA binding. The arrays measure a proteins affinity toward thousands of double-stranded DNA sequences at once, producing a comprehensive binding specificity catalog. We present a linear model for predicting the binding affinity of a protein toward DNA sequences based on PBM data. Our model represents the measured intensity of an individual probe as a sum of the binding affinity contributions of the probes subsequences. These subsequences characterize a DNA binding motif and can be used to predict the intensity of protein binding against arbitrary DNA sequences. Our method was the best performer in the Dialogue for Reverse Engineering Assessments and Methods 5 (DREAM5) transcription factor/DNA motif recognition challenge. For the DREAM5 bonus challenge, we also developed an approach for the identification of transcription factors based on their PBM binding profiles. Our approach for TF identification achieved the best performance in the bonus challenge.

Analysis of circulating cell-free DnA identifies multiclonal heterogeneity of BRCA2 reversion mutations associated with resistance to PARP inhibitors

Approximately 20% of metastatic prostate cancers harbor mutations in genes required for DNA repair by homologous recombination repair (HRR) such as BRCA2 HRR defects confer synthetic lethality to PARP inhibitors (PARPi) such as olaparib and talazoparib. In ovarian or breast cancers, olaparib resistance has been associated with HRR restoration, including by BRCA2 mutation reversion. Whether similar mechanisms operate in prostate cancer, and could be detected in liquid biopsies, is unclear. Here, we identify BRCA2 reversion mutations associated with olaparib and talazoparib resistance in patients with prostate cancer. Analysis of circulating cell-free DNA (cfDNA) reveals reversion mutation heterogeneity not discernable from a single solid-tumor biopsy and potentially allows monitoring for the emergence of PARPi resistance.Significance: The mechanisms of clinical resistance to PARPi in DNA repair-deficient prostate cancer have not been described. Here, we show BRCA2 reversion mutations in patients with prostate cancer with metastatic disease who developed resistance to talazoparib and olaparib. Furthermore, we show that PARPi resistance is highly multiclonal and that cfDNA allows monitoring for PARPi resistance. Cancer Discov; 7(9); 999-1005. ©2017 AACR.See related commentary by Domchek, p. 937See related article by Kondrashova et al., p. 984See related article by Goodall et al., p. 1006This article is highlighted in the In This Issue feature, p. 920.

Fusion genes and their discovery using high throughput sequencing

Fusion genes are hybrid genes that combine parts of two or more original genes. They can form as a result of chromosomal rearrangements or abnormal transcription, and have been shown to act as drivers of malignant transformation and progression in many human cancers. The biological significance of fusion genes together with their specificity to cancer cells has made them into excellent targets for molecular therapy. Fusion genes are also used as diagnostic and prognostic markers to confirm cancer diagnosis and monitor response to molecular therapies. High-throughput sequencing has enabled the systematic discovery of fusion genes in a wide variety of cancer types. In this review, we describe the history of fusion genes in cancer and the ways in which fusion genes form and affect cellular function. We also describe computational methodologies for detecting fusion genes from high-throughput sequencing experiments, and the most common sources of error that lead to false discovery of fusion genes.

Transcriptome Sequencing Reveals PCAT5 as a Novel ERG-Regulated Long Noncoding RNA in Prostate Cancer.

Castration-resistant prostate cancers (CRPC) that arise after the failure of androgen-blocking therapies cause most of the deaths from prostate cancer, intensifying the need to fully understand CRPC pathophysiology. In this study, we characterized the transcriptomic differences between untreated prostate cancer and locally recurrent CRPC. Here, we report the identification of 145 previously unannotated intergenic long noncoding RNA transcripts (lncRNA) or isoforms that are associated with prostate cancer or CRPC. Of the one third of these transcripts that were specific for CRPC, we defined a novel lncRNA termed PCAT5 as a regulatory target for the transcription factor ERG, which is activated in approximately 50% of human prostate cancer. Genome-wide expression analysis of a PCAT5-positive prostate cancer after PCAT5 silencing highlighted alterations in cell proliferation pathways. Strikingly, an in vitro validation of these alterations revealed a complex integrated phenotype affecting cell growth, migration, invasion, colony-forming potential, and apoptosis. Our findings reveal a key molecular determinant of differences between prostate cancer and CRPC at the level of the transcriptome. Furthermore, they establish PCAT5 as a novel oncogenic lncRNA in ERG-positive prostate cancers, with implications for defining CRPC biomarkers and new therapeutic interventions.