FinaleMe: Predicting DNA methylation by the fragmentation patterns of plasma cell-free DNA

Analysis of DNA methylation in cell-free DNA reveals clinically relevant biomarkers but requires specialized protocols such as whole-genome bisulfite sequencing. Meanwhile, millions of cell-free DNA samples are being profiled by whole-genome sequencing. Here, we develop FinaleMe, a non-homogeneous Hidden Markov Model, to predict DNA methylation of cell-free DNA and, therefore, tissues-of-origin, directly from plasma whole-genome sequencing. We validate the performance with 80 pairs of deep and shallow-coverage whole-genome sequencing and whole-genome bisulfite sequencing data.

FinaleMe: Predicting DNA methylation by the fragmentation patterns of plasma cell-free DNA

Analysis of DNA methylation in cell-free DNA (cfDNA) reveals clinically relevant biomarkers but requires specialized protocols and sufficient input material that limits its applicability. Millions of cfDNA samples have been profiled by genomic sequencing. To maximize the gene regulation information from the existing dataset, we developed FinaleMe, a non-homogeneous Hidden Markov Model (HMM), to predict DNA methylation of cfDNA and, therefore, tissues-of-origin directly from plasma whole-genome sequencing (WGS). We validated the performance with 80 pairs of deep and shallow-coverage WGS and whole-genome bisulfite sequencing (WGBS) data.

Liquid biopsy detection of genomic alterations in pediatric brain tumors from cell-free DNA in peripheral blood, CSF, and urine

BACKGROUND

The ability to identify genetic alterations in cancers is essential for precision medicine; however, surgical approaches to obtain brain tumor tissue are invasive. Profiling circulating tumor DNA (ctDNA) in liquid biopsies has emerged as a promising approach to avoid invasive procedures. Here, we systematically evaluated the feasibility of profiling pediatric brain tumors using ctDNA obtained from plasma, cerebrospinal fluid (CSF), and urine.

METHODS

We prospectively collected 564 specimens (257 blood, 240 urine, and 67 CSF samples) from 258 patients across all histopathologies. We performed ultra-low-pass whole-genome sequencing (ULP-WGS) to assess copy number variations and estimate tumor fraction and developed a pediatric CNS tumor hybrid capture panel for deep sequencing of specific mutations and fusions.

RESULTS

ULP-WGS detected copy number alterations in 9/46 (20%) CSF, 3/230 (1.3%) plasma, and 0/153 urine samples. Sequencing detected alterations in 3/10 (30%) CSF, 2/74 (2.7%) plasma, and 0/2 urine samples. The only positive results were in high-grade tumors. However, most samples had insufficient somatic mutations (median 1, range 0-39) discoverable by the sequencing panel to provide sufficient power to detect tumor fractions of greater than 0.1%.

CONCLUSIONS

Children with brain tumors harbor very low levels of ctDNA in blood, CSF, and urine, with CSF having the most DNA detectable. Molecular profiling is feasible in a small subset of high-grade tumors. The level of clonal aberrations per genome is low in most of the tumors, posing a challenge for detection using whole-genome or even targeted sequencing methods. Substantial challenges therefore remain to genetically characterize pediatric brain tumors from liquid biopsies.

Genomic and transcriptomic correlates of immunotherapy response within the tumor microenvironment of leptomeningeal metastases

Leptomeningeal disease (LMD) is a devastating complication of solid tumor malignancies, with dire prognosis and no effective systemic treatment options. Over the past decade, the incidence of LMD has steadily increased due to therapeutics that have extended the survival of cancer patients, highlighting the need for new interventions. To examine the efficacy of immune checkpoint inhibitors (ICI) in patients with LMD, we completed two phase II clinical trials. Here, we investigate the cellular and molecular features underpinning observed patient trajectories in these trials by applying single-cell RNA and cell-free DNA profiling to longitudinal cerebrospinal fluid (CSF) draws from enrolled patients. We recover immune and malignant cell types in the CSF, characterize cell behavior changes following ICI, and identify genomic features associated with relevant clinical phenomena. Overall, our study describes the liquid LMD tumor microenvironment prior to and following ICI treatment and demonstrates clinical utility of cell-free and single-cell genomic measurements for LMD research.

Detection of Leptomeningeal Disease Using Cell-Free DNA From Cerebrospinal Fluid

Importance

Leptomeningeal disease (LMD) is a devastating complication of cancer that is frequently underdiagnosed owing to the low sensitivity of cerebrospinal fluid (CSF) cytologic assessment, the current benchmark diagnostic method. Improving diagnostic sensitivity may lead to improved treatment decisions.

Objective

To assess whether cell-free DNA (cfDNA) analysis of CSF may be used to diagnose LMD more accurately than cytologic analysis.

Design, Setting, and Participants

This diagnostic study conducted in a neuro-oncology clinic at 2 large, tertiary medical centers assessed the use of genomic sequencing of CSF samples obtained from 30 patients with suspected or confirmed LMD from 2015 through 2018 to identify tumor-derived cfDNA. From the same CSF samples, cytologic analyses were conducted, and the results of the 2 tests were compared. This study consisted of 2 patient populations: 22 patients with cytologically confirmed LMD without parenchymal tumors abutting their CSF and 8 patients with parenchymal brain metastases with no evidence of LMD. Patients were considered positive for the presence of LMD if previous CSF cytologic analysis was positive for malignant cells. The analysis was conducted from 2015 to 2018.

Main Outcomes and Measures

The primary outcome was the diagnostic accuracy of cfDNA analysis, defined as the number of tests that resulted in correct diagnoses out of the total number of tests assayed. Hypotheses were formed before data collection.

Results

In total, 30 patients (23 women [77%]; median age, 51 years [range, 28-81 years]), primarily presenting with metastatic solid malignant neoplasms, participated in this study. For 48 follow-up samples from patients previously diagnosed via cytologic analysis as having LMD with no parenchymal tumor abutting CSF, cfDNA findings were accurate in the assessment of LMD in 45 samples (94%; 95% CI, 83%-99%), whereas cytologic analysis was accurate in 36 samples (75%; 95% CI, 60%-86%), a significant difference (P = .02). Of 43 LMD-positive samples, CSF cfDNA analysis was sensitive to LMD in 40 samples (93%; 95% CI, 81%-99%), and cytologic analysis was sensitive to LMD in 31 samples (72%; 95% CI, 56%-85%), a significant difference (P = .02). For 3 patients with parenchymal brain metastases abutting the CSF and no suspicion of LMD, cytologic findings were negative for LMD in all 3 patients, whereas cfDNA findings were positive in all 3 patients.

Conclusions and Relevance

This diagnostic study found improved sensitivity and accuracy of cfDNA CSF testing vs cytologic assessment for diagnosing LMD with the exception of parenchymal tumors abutting CSF, suggesting improved ability to diagnosis LMD. Consideration of incorporating CSF cfDNA analysis into clinical care is warranted.

Genome-wide cell-free DNA mutational integration enables ultra-sensitive cancer monitoring

In many areas of oncology, we lack sensitive tools to track low-burden disease. Although cell-free DNA (cfDNA) shows promise in detecting cancer mutations, we found that the combination of low tumor fraction (TF) and limited number of DNA fragments restricts low-disease-burden monitoring through the prevailing deep targeted sequencing paradigm. We reasoned that breadth may supplant depth of sequencing to overcome the barrier of cfDNA abundance. Whole-genome sequencing (WGS) of cfDNA allowed ultra-sensitive detection, capitalizing on the cumulative signal of thousands of somatic mutations observed in solid malignancies, with TF detection sensitivity as low as 10-5. The WGS approach enabled dynamic tumor burden tracking and postoperative residual disease detection, associated with adverse outcome. Thus, we present an orthogonal framework for cfDNA cancer monitoring via genome-wide mutational integration, enabling ultra-sensitive detection, overcoming the limitation of cfDNA abundance and empowering treatment optimization in low-disease-burden oncology care.

Sensitive Detection of Minimal Residual Disease in Patients Treated for Early-Stage Breast Cancer

PURPOSE

Existing cell-free DNA (cfDNA) methods lack the sensitivity needed for detecting minimal residual disease (MRD) following therapy. We developed a test for tracking hundreds of patient-specific mutations to detect MRD with a 1,000-fold lower error rate than conventional sequencing.

EXPERIMENTAL DESIGN

We compared the sensitivity of our approach to digital droplet PCR (ddPCR) in a dilution series, then retrospectively identified two cohorts of patients who had undergone prospective plasma sampling and clinical data collection: 16 patients with ER+/HER2- metastatic breast cancer (MBC) sampled within 6 months following metastatic diagnosis and 142 patients with stage 0 to III breast cancer who received curative-intent treatment with most sampled at surgery and 1 year postoperative. We performed whole-exome sequencing of tumors and designed individualized MRD tests, which we applied to serial cfDNA samples.

RESULTS

Our approach was 100-fold more sensitive than ddPCR when tracking 488 mutations, but most patients had fewer identifiable tumor mutations to track in cfDNA (median = 57; range = 2-346). Clinical sensitivity was 81% (n = 13/16) in newly diagnosed MBC, 23% (n = 7/30) at postoperative and 19% (n = 6/32) at 1 year in early-stage disease, and highest in patients with the most tumor mutations available to track. MRD detection at 1 year was strongly associated with distant recurrence [HR = 20.8; 95% confidence interval, 7.3-58.9]. Median lead time from first positive sample to recurrence was 18.9 months (range = 3.4-39.2 months).

CONCLUSIONS

Tracking large numbers of individualized tumor mutations in cfDNA can improve MRD detection, but its sensitivity is driven by the number of tumor mutations available to track.

Crystallographic orientation errors in mechanical exfoliation

We evaluate the effect of mechanical exfoliation of van der Waals materials on crystallographic orientations of the resulting flakes. Flakes originating from a single crystal of graphite, whose orientation is confirmed using STM, are studied using facet orientations and electron back-scatter diffraction (EBSD). While facets exhibit a wide distribution of angles after a single round of exfoliation ([Formula: see text]), EBSD shows that the true crystallographic orientations are more narrowly distributed ([Formula: see text]), and facets have an approximately [Formula: see text] error from the true orientation. Furthermore, we find that the majority of graphite fractures are along armchair lines, and that the cleavage process results in an increase of the zigzag lines portion. Our results place values on the rotation caused by a single round of the exfoliation process, and suggest that when a 1-2 degree precision is necessary, the orientation of a flake can be gauged by the orientation of the macroscopic single crystal from which it was exfoliated.

Tumor fraction in cell-free DNA as a biomarker in prostate cancer

BACKGROUND

Tumor content in circulating cell-free DNA (cfDNA) is a promising biomarker, but longitudinal dynamics of tumor-derived and non-tumor-derived cfDNA through multiple courses of therapy have not been well described.

METHODS

CfDNA from 663 plasma samples from 140 patients with castration-resistant prostate cancer (CRPC) was subject to sparse whole genome sequencing. Tumor fraction (TFx) estimated using the computational tool ichorCNA was correlated with clinical features and responses to therapy.

RESULTS

TFx associated with the number of bone metastases (median TFx = 0.014 with no bone metastases, 0.047 with 1-3 bone metastases, 0.190 for 4+ bone metastases; P < 0.0001) and with visceral metastases (P < 0.0001). In multivariable analysis, TFx remained associated with metastasis location (P = 0.042); TFx was positively correlated with alkaline phosphatase (P = 0.0227) and negatively correlated with hemoglobin (Hgb) (P < 0.001), but it was not correlated with prostate specific antigen (PSA) (P = 0.75). Tumor-derived and non-tumor-derived cfDNA track together and do not increase with generalized tissue damage from chemotherapy or radiation at the time scales examined. All new treatments that led to ≥30% PSA decline at 6 weeks were associated with TFx decline when baseline TFx was >7%; however, TFx in patients being subsequently maintained on secondary hormonal therapy was quite dynamic.

CONCLUSION

TFx correlates with clinical features associated with overall survival in CRPC, and TFx decline is a promising biomarker for initial therapeutic response.

TRIAL REGISTRATION

Dana-Farber/Harvard Cancer Center (DF/HCC) protocol no. 18-135.

FUNDING

Wong Family Award in Translational Oncology, Dana Farber Cancer Institute Medical Oncology grant, Gerstner Family Foundation, Janssen Pharmaceuticals Inc., and Koch Institute Support (core) grant P30-CA14051 from the National Cancer Institute (NCI).

Structural Alterations Driving Castration-Resistant Prostate Cancer Revealed by Linked-Read Genome Sequencing

Nearly all prostate cancer deaths are from metastatic castration-resistant prostate cancer (mCRPC), but there have been few whole-genome sequencing (WGS) studies of this disease state. We performed linked-read WGS on 23 mCRPC biopsy specimens and analyzed cell-free DNA sequencing data from 86 patients with mCRPC. In addition to frequent rearrangements affecting known prostate cancer genes, we observed complex rearrangements of the AR locus in most cases. Unexpectedly, these rearrangements include highly recurrent tandem duplications involving an upstream enhancer of AR in 70%-87% of cases compared with <2% of primary prostate cancers. A subset of cases displayed AR or MYC enhancer duplication in the context of a genome-wide tandem duplicator phenotype associated with CDK12 inactivation. Our findings highlight the complex genomic structure of mCRPC, nominate alterations that may inform prostate cancer treatment, and suggest that additional recurrent events in the non-coding mCRPC genome remain to be discovered.

Abstract 3001: Broad/IBM Project: Discovery of treatment resistance mechanisms through use of liquid biopsy genomics services

The Broad/IBM Cancer Resistance Project has partnered with Broad Genomics to pilot the use of cutting edge sequencing technology for the analysis of cell free DNA in blood biopsies. Working closely with the Broad's Cancer Program, Broad Genomics has developed a suite of liquid biopsy sequencing products designed to provide optimal flexibility in conducting research studies with a broad range of applications including; biomarker discovery, treatment resistance monitoring, and detection of minimal residual disease (MRD) post-surgery. Cell-free DNA is extracted from the blood, and a dual unique-molecular-indexed library is created. From this library, low coverage whole genome (ultra-low-pass 0.1x coverage) data is generated to survey sample quality and evaluate the tumor fraction in the liquid specimen. Utilizing the same library, additional assays can be selected for processing based on the research aim (Targeted Panel Assays, MRD Detection or Whole Exomes). Since our approach utilizes the same genomic material for whole genome and targeted sequencing assays, it is possible to maximize the information learned from each valuable and limited liquid biopsy specimen. Our study design takes advantage of the discovery potential of combined tissue-based sequencing and serial liquid biopsy analysis to elucidate mechanisms of cancer resistance by tracking the evolution of clonal and subclonal populations in patients samples over time. This collaboration will utilize the ultra-low-pass sequencing and whole exome sequencing together with custom analysis pipelines to correlate the genomic events with patient clinical data. We aim to process 3,000 samples from 1,000 patients over the next 3 years. To date we have processed close to 500 samples through the ultra-low-pass pipeline and 100 samples through the whole exome sequencing pipeline (results to be provided).The ability to successfully investigate treatment resistant cancers from non-invasive liquid biopsies presents new opportunities for identifying markers, understanding dynamics and monitoring tumor dissemination and clonal evolution.

Citation Format: Gad Getz, Carrie Cibulskis, Ignaty Leshchiner, Megan Hanna, Dimitri Livitz, Kara Slowik, Chaya Levovitz, Filippo Utro, Kahn Rhrissorrakrai, Denisse Rotem, Gregory Gydush, Sarah C. Reed, Justin Rhoades, Gavin Ha, Samuel S. Freeman, Christopher Lo, Mark Fleharty, Justin Abreu, Katie Larkin, Michelle Cipicchio, Brendan Blumenstiel, Matt DeFelice, Jonna Grimsby, Susanna Hamilton, Niall Lennon, Viktor A. Adalsteinsson, Laxmi Parida. Broad/IBM Project: Discovery of treatment resistance mechanisms through use of liquid biopsy genomics services [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3001.

Abstract 3247: Genome-wide cell-free DNA mutation integration for sensitive cancer detection

Solid malignancies are often diagnosed at a late stage with dismal prognosis. Even after cancer is diagnosed, we lack sensitive tools to guide difficult therapeutic decisions such as adjuvant therapy. Sensitive cancer detection by blood biopsy can therefore transform care by enabling early detection and residual disease monitoring.

Cell free DNA mutation detection has shown significant promise in its ability to survey the somatic genome and enable detection of cancer mutations in the peripheral blood. However, the combination of low tumor fraction and limiting number of DNA fragments in a typical plasma sample, restrict the probability of detecting early stage cancer in cfDNA through current deep targeted sequencing methods.

Focusing on non-small cell lung cancer (NSCLC), we reasoned that we would need to supplant depth of sequencing with breadth of sequencing to overcome the fundamental limitation of low input of cfDNA. To do so, we apply whole genome sequencing (WGS) that allows us to base sensitive detection on the cumulative signal provided by 10,000-30,000 somatic mutations observed in a substantial proportion of NSCLC. We developed an analytic method that integrates genome-wide mutation signal to obtain a tumor fraction (TF) estimate, and thus allow sensitive detection of residual disease and quantitative dynamic monitoring of disease burden. Benchmarking on artificial plasma showed TF detection sensitivity as low as 1:100,000, two orders of magnitude more sensitive than currently available methods.

To test this method, we performed WGS on resected NSCLC and matched germline samples of 8 NSCLC patients, as well as on matched pre- and post-surgery cfDNA. Patient-specific somatic mutations were identified in the tumor/normal pairs and used for the estimation of TF in the matched plasma samples. We detect pre-surgery circulating tumor DNA (ctDNA) in all of the early-stage pre-operative samples and in ~40% post-operative patients, correlated with post-operative disease progression.

In early cancer detection, tumor DNA is not available, requiring de-novo mutation detection in cfDNA. To do so, we first trained a convolutional neuronal network to distinguish between cancer altered sequencing reads and reads affected by sequencing errors. This was followed by genome-wide pattern matching to a specific genomic signature that mark lung cancer mutations (Tobacco signature) indicating the presence of ctDNA in the patient plasma. Applying this method to the pre-operative early stage lung cancer samples and plasma samples from 5 patients with benign nodules (CT-detected) showed an accurate discrimination between malignant and benign nodules, suggesting a potential role in improving the positive predictive value of lung cancer screening in at-risk populations.

These results show that genome-wide mutation integration is a promising novel approach for ultra-sensitive early detection and residual disease monitoring.

Citation Format: Asaf Zviran, Steven T. Hill, Rafael Schulman, Minita Shah, Sunil Deochand, Gavin Ha, Sarah Reed, Denisse Rotem, Greg Gydush, Justin Rhoades, Kevin Huang, Will Liao, Dillon Maloney, Nathan Omans, Murtaza Malbari, Cathy F. Spinelli, Selena Kazancioglu, Nicolas Robine, Viktor Adalsteinsson, Brian Houck-Loomis, Nasser Altorki, Dan A. Landau. Genome-wide cell-free DNA mutation integration for sensitive cancer detection [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3247.

Abstract LB-225: Liquid biopsies identify trunk mutations and reflect multiple tumors in a patient

Introduction: Precision medicine approaches to guide therapy selection require routine sampling of tumors. However, tumor biopsies are not always accessible and may be confounded by spatial heterogeneity. Liquid biopsies, including analysis of cell-free DNA (cfDNA), present a non-invasive alternative which may reflect multiple tumors in the body. Previous studies have demonstrated exome-wide concordance between single-site tumor biopsies and cfDNA, but little is known about how cfDNA reflects multiple lesions within a patient. Here we sought to determine how cfDNA reflects the body-wide tumor phylogeny, which will inform the use of cfDNA for cancer precision medicine.

Methods: We identified 20 patients with pancreatic cancer who had undergone rapid autopsy. We then screened cfDNA tumor fraction and performed whole-exome sequencing of cfDNA and multiple tumor biopsies for 3 patients with cfDNA tumor fraction &gt;10%. We inferred the tumor phylogeny and then developed a statistical approach to deconvolute the contributions to cfDNA from tumor phylogenetic nodes. Finally, we determined whether shared trunk mutations could be detected in cfDNA and tumor biopsies.

Results: For each patient, we found mutations shared between all sites and cfDNA, including putative driver mutations. We found mutations which were clonal in multiple regions were detectable in cfDNA, whereas mutations private to individual sites were never clonal in cfDNA. Through our deconvolution analysis, we found that cfDNA could not be modeled as a simple linear combination of individual sites, but rather that cfDNA represented multiple nodes in the inferred phylogeny. For two pancreatic adenocarcinoma patients, the inferred ancestor of the metastases had high estimated contribution (&gt;70%) to cfDNA, while the ancestors of the primaries had lower contributions (&lt;10%). Next, we considered trunk mutations, which originate earliest in the tumor phylogenetic tree. When we analyzed precision for detection of trunk mutations, we found on average, 71% of clonal mutations in metastases were truncal, while only 55% of clonal mutations in primary tumors were truncal. Due to copy number deletions, not all trunk mutations were detected in metastases. Finally, on average, cfDNA had equal or better precision than 83% of primaries and 88% of metastases, suggesting cfDNA may provide more accurate trunk SSNV calls than tumor biopsies.

Conclusions: Through analyzing cfDNA and synchronous tumor biopsies from the same patient, we find trunk mutations are enriched in cfDNA as compared to the average single-site biopsy. We also predict that cfDNA represents multiple nodes in the inferred phylogeny. In cases where tumor biopsies are inaccessible, we demonstrate that cfDNA might be a promising alternative to detect trunk SSNVs. These results suggest that cfDNA may be complementary to tumor biopsies for disease monitoring and treatment selection in personalized medicine.

Citation Format: Samuel S. Freeman, Ziao Lin, Gavin Ha, Ignaty Leshchiner, Justin Rhoades, Dimitri Livitz, Daniel Rosebrock, Sarah C. Reed, Gregory Gydush, Christopher Lo, Denisse Rotem, Atish D. Choudhury, Daniel G. Stover, Heather A. Parsons, Jesse S. Boehm, J Christopher Love, Matthew Meyerson, Paul Grandgenett, Michael A. Hollingsworth, Viktor A. Adalsteinsson, Gad Getz. Liquid biopsies identify trunk mutations and reflect multiple tumors in a patient [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-225.

Abstract 1178: Genotype-fitness maps guide targeted therapy combination in lung adenocarcinoma

Targeted EGFR inhibition in lung cancer leads to dramatic responses. Nonetheless, disease evolution to resistance is the rule. As this evolutionary process is fueled by intra-tumoral genetic diversity, a comprehensive mapping of clonal fitness is required to inform strategies to overcome resistance.

To model intra-tumoral diversity in vitro, we performed a genome-wide, over-expression genetic perturbation assay in EGFR-driven non-small cell lung cancer (NSCLC) PC9 cells. Our screen covered 17,255 ORFs (open reading frame constructs) representing 12,728 wildtype and mutated genes, and examined the effects of a first-generation EGFR inhibitor (erlotinib), a third-generation EGFR inhibitor (osimertinib) and a MEK inhibitor (binimetinib) on evolutionary selection, alone or in combination. Specifically, to obtain genotype-to-fitness maps for each drug, we measured clonal abundance up to 4 times during the screen and mathematically resolved their growth behavior. Finally, for each drug, we applied multiple doses to obtain dose-fitness relationships, which may impact tumor evolution in patients due to high inter- and intra-tumoral variability in drug delivery. In total, we have performed 78 genome-wide screens to map the evolutionary landscape of PC9 resistance to targeted therapy.

Erlotinib and osimertinib both result in an overwhelming reduction of fitness, as expected from their clinical benefit. Known clinical resistance mechanisms involving ERBB2, PIK3CA, AXL, and BRAF confer a pronounced fitness advantage in the presence of both drugs, while EGFR (T790M) improves fitness only with erlotinib. Novel resistance mechanisms include alternative tyrosine kinases (NTRK, PDGFRB, CSF1R, KIT), KRAS, G-coupled protein receptors, transcription factors (SOX15, FOXA1), and cellular transporters (ABCG2). Notably, we observe significant divergence in dose-fitness relationships between different resistance mechanisms. For example, PIK3CA confers a modest but persistent advantage across the dose range, in contrast to BRAF which results in a fitness advantage only when sufficiently high drug levels are added.

The fitness landscape for binimetinib resistance appeared to be largely orthogonal to that of the EGFR inhibitors, with decreased fitness noted for many tyrosine kinases as well as KRAS mutations. MEK inhibitor resistance results from RAF family member overexpression (ARAF, BRAF, RAF1) and MAPK activation. The orthogonal resistance landscapes of EGFR inhibition and MEK inhibition translate into highly synergistic effects in drug combination, with effective prediction of combinatorial fitness from the single-agent fitness landscapes using generalized linear models. These results validate this approach as a systematic method to address the combinatorial problem of optimizing drug combinations and doses to directly anticipate and address cancer evolution.

Citation Format: Asaf Zviran, Patrick Bolan, Lisa Brenan, Amy Goodale, Denisse Rotem, Viktor Adalsteinsson, Federica Piccioni, Cory Johannessen, Dan Landau. Genotype-fitness maps guide targeted therapy combination in lung adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1178.

Whole-exome sequencing of cell-free DNA and circulating tumor cells in multiple myeloma

Liquid biopsies including circulating tumor cells (CTCs) and cell-free DNA (cfDNA) have enabled minimally invasive characterization of many cancers, but are rarely analyzed together. Understanding the detectability and genomic concordance of CTCs and cfDNA may inform their use in guiding cancer precision medicine. Here, we report the detectability of cfDNA and CTCs in blood samples from 107 and 56 patients with multiple myeloma (MM), respectively. Using ultra-low pass whole-genome sequencing, we find both tumor fractions correlate with disease progression. Applying whole-exome sequencing (WES) to cfDNA, CTCs, and matched tumor biopsies, we find concordance in clonal somatic mutations (~99%) and copy number alterations (~81%) between liquid and tumor biopsies. Importantly, analyzing CTCs and cfDNA together enables cross-validation of mutations, uncovers mutations exclusive to either CTCs or cfDNA, and allows blood-based tumor profiling in a greater fraction of patients. Our study demonstrates the utility of analyzing both CTCs and cfDNA in MM.

Circulating tumor cells (CTCs) and cell-free DNA (cfDNA) enables characterization of a patient’s cancer. Here, the authors analyse CTCs, cfDNA, and tumor biopsies from multiple myeloma patients to show these approaches are complementary for mutation detection, together enabling a greater fraction of patient tumors to be profiled.

Association of Cell-Free DNA Tumor Fraction and Somatic Copy Number Alterations With Survival in Metastatic Triple-Negative Breast Cancer

Purpose Cell-free DNA (cfDNA) offers the potential for minimally invasive genome-wide profiling of tumor alterations without tumor biopsy and may be associated with patient prognosis. Triple-negative breast cancer (TNBC) is characterized by few mutations but extensive somatic copy number alterations (SCNAs), yet little is known regarding SCNAs in metastatic TNBC. We sought to evaluate SCNAs in metastatic TNBC exclusively via cfDNA and determine if cfDNA tumor fraction is associated with overall survival in metastatic TNBC. Patients and Methods In this retrospective cohort study, we identified 164 patients with biopsy-proven metastatic TNBC at a single tertiary care institution who received prior chemotherapy in the (neo)adjuvant or metastatic setting. We performed low-coverage genome-wide sequencing of cfDNA from plasma. Results Without prior knowledge of tumor mutations, we determined tumor fraction of cfDNA for 96.3% of patients and SCNAs for 63.9% of patients. Copy number profiles and percent genome altered were remarkably similar between metastatic and primary TNBCs. Certain SCNAs were more frequent in metastatic TNBCs relative to paired primary tumors and primary TNBCs in publicly available data sets The Cancer Genome Atlas and METABRIC, including chromosomal gains in drivers NOTCH2, AKT2, and AKT3. Prespecified cfDNA tumor fraction threshold of ≥ 10% was associated with significantly worse metastatic survival (median, 6.4 v 15.9 months) and remained significant independent of clinicopathologic factors (hazard ratio, 2.14; 95% CI, 1.4 to 3.8; P < .001). Conclusion We present the largest genomic characterization of metastatic TNBC to our knowledge, exclusively from cfDNA. Evaluation of cfDNA tumor fraction was feasible for nearly all patients, and tumor fraction ≥ 10% is associated with significantly worse survival in this large metastatic TNBC cohort. Specific SCNAs are enriched and prognostic in metastatic TNBC, with implications for metastasis, resistance, and novel therapeutic approaches.

Tumor fraction in circulating free DNA as a biomarker of disease dynamics in metastatic prostate cancer

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Background: Quantification of circulating free DNA (cfDNA) has been proposed both as a prognostic biomarker and as a biomarker of response and resistance to therapy. However, dynamics of cfDNA derived from both tumor and non-cancerous tissues through dense longitudinal monitoring over the course of treatment with multiple therapeutic modalities have not been well described. Methods: CfDNA isolated from banked and prospectively collected plasma samples from pts with metastatic castration-resistant prostate cancer (mCRPC) was subject to ultra-low pass (~0.1x coverage) whole genome sequencing (ULP-WGS). The fraction of cfDNA derived from tumor rather than non-cancerous tissues (i.e. the tumor fraction, or TFx) in each sample was estimated using a novel computational tool called ichorCNA, and was correlated with clinical features and response to therapy. Results: 663 plasma samples from 140 pts were included (median 3 samples/pt; range 1-20). TFx was correlated with the number of bone metastases (median TFx = 0.014 with no bone mets, 0.047 with 1-3, 0.190 for 4+), and with the presence of distant visceral mets (p < 0.0001). In multi-variate analysis, TFx was positively correlated with Alk Phos (p = 0.0227) and negatively correlated with Hgb (p < 0.001), but was not correlated with PSA (p = 0.75). All new treatment starts leading to > = 30% PSA decline at > = 6 weeks were associated with a decline in TFx from baseline when baseline TFx was > 7% (median TFx change -92.2%, range -70.3% to -100%); however, TFx in patients being subsequently maintained on secondary hormonal therapy without radiographic progression was quite dynamic. The total yield of cfDNA derived from both tumor and non-cancerous tissues tracked closely with TFx, and did not markedly change with initiation of therapies expected to lead to generalized tissue damage, such as chemotherapy and radiation, over the time scales examined. Conclusions: Decline in TFx is a promising biomarker for initial response to therapy, but subsequent temporary rises in TFx do not necessarily indicate the cessation of clinical benefit from secondary hormonal therapies. Analysis of cfDNA may allow a window into short-term tumor dynamics not easily assayed through other methods.

Abstract GS3-07: Genome-wide copy number analysis of chemotherapy-resistant metastatic triple-negative breast cancer from cell-free DNA

Introduction:

Triple-negative breast cancer (TNBC) is a poor prognosis breast cancer subset characterized by relatively few mutations but extensive copy number alterations (CNAs). Cell-free DNA (cfDNA) offers the potential to overcome infrequent tumor biopsies in metastatic TNBC (mTNBC) and interrogate the genomics of chemotherapy resistance.

Methods:

506 archival or fresh plasma samples were identified from 164 patients with mTNBC who had previously received chemotherapy. We performed low coverage whole genome sequencing to determine genome-wide copy number and estimate 'tumor fraction' of cfDNA (TFx) using our recently-developed approach, ichorCNA. In patient samples with TFx &gt;10%, we identified regions that were significantly gained or lost using GISTIC2.0. We compared CNAs of 20 paired primary-metastatic samples and also mTNBCs from cfDNA versus primary TNBCs from TCGA and METABRIC.

Results:

We successfully obtained high quality, low coverage whole genome sequencing data for 478 (94.5%) plasma samples from 158 patients, with 1 to 14 samples per patient. TFx and copy number profiles were highly concordant with paired metastatic biopsy (n=10, range 0-7 days from biopsy to blood draw) with sensitivity of 0.86 and specificity of 0.90 and reproducible in independently-processed blood draws (TFx intraclass correlation coefficient 0.984). Median overall survival from time of first blood draw was 8 months, and TFx was highly correlated independent of primary stage, primary receptor status, age at primary diagnosis, BRCA status, and metastatic line of therapy: adjusted hazard ratio between 4th and 1st quartiles = 2.14 (95% CI 1.40-3.28; p=0.00049). 101/158 patients (63.9%) had at least one sample with TFx &gt;10%, our threshold for high confidence CNA calls. Copy number profiles and percent genome altered were remarkably similar between mTNBCs and primary TNBCs in TCGA and METABRIC (n=433), suggesting that large-scale chromosomal events are infrequent in TNBC metastatic progression. We identified chromosomal gains that demonstrated significant enrichment in mTNBCs relative to paired primary TNBCs (n=20) and also TCGA/METABRIC, including driver genes (NOTCH2, AKT2, AKT3) and putative antibody-drug conjugate targets. Finally, we identify a novel association of gains of 18q11 and/or 19p13 with poor metastatic prognosis, independent of clinicopathologic factors and TFx.

Conclusions:

Here, we present the first large-scale genomic characterization of metastatic TNBC to our knowledge, derived exclusively from cfDNA. 'Tumor fraction' of cfDNA is an independent prognostic marker in mTNBC. Primary and metastatic TNBC have remarkably similar copy number profiles yet we identify alterations enriched and prognostic in mTNBC. Collectively, these data have potential implications in the understanding of metastasis, therapeutic resistance, and novel therapeutic targets.

Citation Format: Stover DG, Parsons HA, Ha G, Freeman S, Barry B, Guo H, Choudhury A, Gydush G, Reed S, Rhoades J, Rotem D, Hughes ME, Dillon DA, Partridge AH, Wagle N, Krop IE, Getz G, Golub TA, Love JC, Winer EP, Tolaney SM, Lin NU, Adalsteinsson VA. Genome-wide copy number analysis of chemotherapy-resistant metastatic triple-negative breast cancer from cell-free DNA [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr GS3-07.

Genomic Heterogeneity as a Barrier to Precision Medicine in Gastroesophageal Adenocarcinoma

Gastroesophageal adenocarcinoma (GEA) is a lethal disease where targeted therapies, even when guided by genomic biomarkers, have had limited efficacy. A potential reason for the failure of such therapies is that genomic profiling results could commonly differ between the primary and metastatic tumors. To evaluate genomic heterogeneity, we sequenced paired primary GEA and synchronous metastatic lesions across multiple cohorts, finding extensive differences in genomic alterations, including discrepancies in potentially clinically relevant alterations. Multiregion sequencing showed significant discrepancy within the primary tumor (PT) and between the PT and disseminated disease, with oncogene amplification profiles commonly discordant. In addition, a pilot analysis of cell-free DNA (cfDNA) sequencing demonstrated the feasibility of detecting genomic amplifications not detected in PT sampling. Lastly, we profiled paired primary tumors, metastatic tumors, and cfDNA from patients enrolled in the personalized antibodies for GEA (PANGEA) trial of targeted therapies in GEA and found that genomic biomarkers were recurrently discrepant between the PT and untreated metastases. Divergent primary and metastatic tissue profiling led to treatment reassignment in 32% (9/28) of patients. In discordant primary and metastatic lesions, we found 87.5% concordance for targetable alterations in metastatic tissue and cfDNA, suggesting the potential for cfDNA profiling to enhance selection of therapy.Significance: We demonstrate frequent baseline heterogeneity in targetable genomic alterations in GEA, indicating that current tissue sampling practices for biomarker testing do not effectively guide precision medicine in this disease and that routine profiling of metastatic lesions and/or cfDNA should be systematically evaluated. Cancer Discov; 8(1); 37-48. ©2017 AACR.See related commentary by Sundar and Tan, p. 14See related article by Janjigian et al., p. 49This article is highlighted in the In This Issue feature, p. 1.

Genome-wide copy number analysis of cell-free DNA from patients with chemotherapy-resistant metastatic triple-negative breast cancer

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Background: Triple-negative breast cancer (TNBC) is a poor prognosis breast cancer subset characterized by relatively few mutations but extensive copy number alterations (CNAs). Cell-free DNA (cfDNA) offers the potential to overcome infrequent tumor biopsies in metastatic TNBC (mTNBC) and interrogate the genomics of chemotherapy resistance. Methods: 506 archival or fresh plasma samples were identified from 164 patients with mTNBC who had previously received chemotherapy. We performed low coverage sequencing to determine genome-wide copy number and estimate ‘tumor fraction’ of cfDNA (TFx). In patient samples with TFx >10%, we identified regions that were significantly gained or lost using GISTIC2.0. We compared CNAs of mTNBCs with primary TNBCs from a publicly-available dataset, METABRIC (TNBC n=277). Results: We successfully obtained high quality, low coverage whole genome sequencing data for 478 (94.5%) plasma samples from 158 patients, with 1 to 14 samples per patient. Archival samples had significantly higher average cfDNA per mL plasma and TFx than fresh samples, potentially due to later average line of therapy. Average TFx of first blood draw was significantly higher in patients with liver metastases (TFx 28.3% vs. 14.4%, p=1.1e-7). 101/158 patients (63.9%) had at least one sample with TFx >10%, our threshold for high confidence CNA calls. Most alterations significantly enriched in chemotherapy-resistant mTNBCs were chromosomal gains, including NOTCH2 and ERCC1. Median overall survival from time of first blood draw was 9 months, and TFx was highly correlated independent of metastatic line of therapy, age at metastatic diagnosis, BRCA status, and primary stage: adjusted hazard ratio between 4th and 1stquartiles = 4.29 (95% CI 1.66-11.1; p=0.0008). Conclusions: It is feasible to perform genome-level copy number analysis from cfDNA in both archival and fresh samples from patients with mTNBC. Copy number alterations enriched in mTNBC may have implications in the understanding of metastasis, therapeutic resistance, and novel therapeutic targets. ‘Tumor fraction’ of cfDNA is correlated with overall survival and may be an independent prognostic marker in mTNBC.

In vitro monomer swapping in EmrE, a multidrug transporter from Escherichia coli, reveals that the oligomer is the functional unit

EmrE is a small multidrug transporter, 110 amino acids long that extrudes various drugs in exchange with protons, thereby rendering Escherichia coli cells resistant to these compounds. Negative dominance studies and radiolabeled substrate-binding studies suggested that EmrE functions as an oligomer. Projection structure of two-dimensional crystals of the protein revealed an asymmetric dimer. To identify the functional unit of EmrE, a novel approach was developed. In this method, quantitative monomer swapping is induced in detergent-solubilized EmrE by exposure to 80 degrees C, a treatment that does not impair transport activity. Oligomer formation is highly specific as judged by several criteria, among them the fact that (35)S-EmrE can be "pulled out" from a mixture prepared from generally labeled cells. Using this technique, we show that inactive mutant subunits are functionally complemented when mixed with wild type subunits. The hetero-oligomers thus formed display a decreased affinity to substrates. In addition, sulfhydryl reagents inhibit the above hetero-oligomer even though Cys residues are present only in the inactive monomer. It is concluded that, in EmrE, the oligomer is the functional unit.

Functional analysis of novel multidrug transporters from human pathogens

Proteins of the Smr family are the smallest multidrug transporters, about 110 amino acids long, that extrude various drugs in exchange with protons, thereby rendering bacteria resistant to these compounds. One of these proteins, EmrE, is an Escherichia coli protein, which has been cloned based on its ability to confer resistance to ethidium and methyl viologen and which has been extensively characterized. More than 60 genes coding for Smr proteins have been identified in several bacteria based on amino acid sequence similarity to the emrE gene. In this work we have analyzed the sequence similarity among these homologues and identified some distinct signature sequence elements and several fully conserved residues. Five of these homologues, from human pathogens Mycobacterium tuberculosis, Bordetella pertussis, and Pseudomonas aeruginosa and from Escherichia coli, were cloned into an E. coli expression system. The proteins were further characterized and show varying degrees of methyl viologen uptake into proteoliposomes and [(3)H]TPP binding in solubilized membranes. The homologues can also form mixed oligomers with EmrE that exhibit intermediate binding characteristics. A comparative study of various homologous proteins provides a tool for deciphering structure-function relationship and monomer-monomer interaction in multidrug transporters and in membrane proteins in general.

Small is mighty: EmrE, a multidrug transporter as an experimental paradigm

EmrE is a multidrug transporter from Escherichia coli that functions as a homooligomer and is unique in its small size. In each monomer there are four tightly packed transmembrane segments and one membrane-embedded charged residue. This residue provides the basis for the coupling mechanism as part of a binding site "time shared" by substrates and protons.

Precious things come in little packages

The 110-amino acid multidrug transporter from E. coli, EmrE, is a member of the family of MiniTexan or Smr drug transporters. EmrE can transport acriflavine, ethidium bromide, tetraphenylphosphonium (TPP+), benzalkonium and several other drugs with relatively high affinities. EmrE is an H+/drug antiporter, utilizing the proton electrochemical gradient generated across the bacterial cytoplasmic membrane by exchanging two protons with one substrate molecule. The EmrE multidrug transporter is unique in its small size and hydrophobic nature. Hydropathic analysis of the EmrE sequence predicts four alpha-helical transmembrane segments. This model is experimentally supported by FTIR studies that confirm the high alpha-helicity of the protein and by high-resolution heteronuclear NMR analysis of the protein structure. The TMS of EmrE are tightly packed in the membrane without any continuous aqueous domain, as was shown by Cysteine scanning experiments. These results suggest the existence of a hydrophobic pathway through which the substrates are translocated. EmrE is functional as a homo-oligomer as suggested by several lines of evidence, including co-reconstitution experiments of wild-type protein with inactive mutants in which negative dominance has been observed. EmrE has only one membrane embedded charged residue, Glu-14, that is conserved in more than fifty homologous proteins and it is a simple model system to study the role of carboxylic residues in ion-coupled transporters. We have used mutagenesis and chemical modification to show that Glu-14 is part of the substrate-binding site. Its role in proton binding and translocation was shown by a study of the effect of pH on ligand binding, uptake, efflux and exchange reactions. We conclude that Glu-14 is an essential part of a binding site, common to substrates and protons. The occupancy of this site is mutually exclusive and provides the basis of the simplest coupling of two fluxes. Because of some of its properties and its size, EmrE provides a unique system to understand mechanisms of substrate recognition and translocation.

Urinary cytokeratin 20 as a marker for transitional cell carcinoma

OBJECTIVES

To determine if detection of cytokeratin 20 (CK20) gene expression, by reverse transcriptase-polymerase chain reaction (RT-PCR) in urine from transitional cell carcinoma (TCC) patients, can provide a new noninvasive tool for the follow-up of patients with urothelial carcinoma of the bladder.

METHODS

Urine was collected from 95 patients previously diagnosed as TCC during their follow-up, and from 27 healthy volunteers. All patients had a transurethal resection of tumor or biopsies obtained from 'suspicious' areas in the bladder. RNA was extracted from cells collected from the urine and RT-PCR was performed with specific primers for the amplification of cytokeratin 8, a general marker for epithelial cells, and of CK 20, a marker for TCC urothelium.

RESULTS

CK20 expression was detected in 86.7% of TCC patients, and only in 3.3% of healthy volunteers (specificity 96.7%). Strong correlation was found between tumor grade and expression of CK20 in urine. All grade III and IV tumors demonstrated positive CK20 expression (100% sensitivity), whereas the sensitivity for lower grades was between 71 and 80%. Among 11 patients with a previous biopsy-proven diagnosis of TCC and a current negative biopsy, in 9 patients CK20 expression was detected. Further follow-up of these patients for a period of 6 months revealed recurrence of TCC in 4 patients.

CONCLUSION

CK20 detection in urine cells is a simple, noninvasive method with a high potential to become the marker of choice for monitoring and follow-up of TCC patients. More information is needed regarding CK20 expression in nonmalignant urological disease, to evaluate its use for routine screening purposes.

EmrE, a small Escherichia coli multidrug transporter, protects Saccharomyces cerevisiae from toxins by sequestration in the vacuole

In this report we describe the functional expression of EmrE, a 110-amino-acid multidrug transporter from Escherichia coli, in the yeast Saccharomyces cerevisiae. To allow for phenotypic complementation, a mutant strain sensitive to a series of cationic lipophilic drugs was first identified. A hemagglutinin epitope-tagged version of EmrE (HA-EmrE) conferring resistance to a wide variety of drugs, including acriflavine, ethidium, methyl viologen, and the neurotoxin 1-methyl-4-phenylpyridinium (MPP+), was functionally expressed in this strain. HA-EmrE is expressed in yeast at relatively high levels (0.5 mg/liter), is soluble in a mixture of organic solvents, and can be functionally reconstituted in proteoliposomes. In bacterial cells, EmrE removes toxic compounds by active transport through the plasma membrane, lowering their cytosolic concentration. However, yeast cells expressing HA-EmrE take up 14C-methyl viologen as well as control cells do. Thus, we investigated the basis of the enhanced resistance to the above compounds. Using Cu2+ ions or methylamine, we could selectively permeabilize the plasma membrane or deplete the proton electrochemical gradients across the vacuolar membrane, respectively. Incubation of yeast cells with copper ions caused an increase in 14C-methyl viologen uptake. In contrast, treatment with methylamine markedly diminished the extent of uptake. Conversely, the effect of Cu2+ and methylamine on a plasma membrane uptake system, proline, was essentially the opposite: while inhibited by the addition of Cu2+, it remained unaffected when cells were treated with methylamine. To examine the intracellular distribution of HA-EmrE, a functional chimera between HA-EmrE and the green fluorescent protein (HA-EmrE-GFP) was prepared. The pattern of HA-EmrE-GFP fluorescence distribution was virtually identical to that of the vacuolar marker FM 4-64, indicating that the transporter is found mainly in this organelle. Therefore, HA-EmrE protects yeast cells by lowering the cytoplasmic concentrations through removal of the toxin to the vacuole. This novel way of detoxification has been previously suggested to function in organisms in which a large vacuolar compartment exists. This report represents the first molecular description of such a mechanism.

Characterization of cDNAs species encoding the Tat protein of caprine arthritis encephalitis virus

Two distinct species of caprine arthritis encephalitis virus (CAEV) tat cDNAs were isolated early after infection of a Himalayan tahr cell line. Sequence analyses predicted that one cDNA (pCEV/e1) represented a polycistronic transcript that encodes Tat and Rev as well as an N-terminally truncated transmembrane protein and a protein, designated X, whose function is unknown; whereas the other cDNA (pCEV/f1) encodes Tat and the env gene products. pCEV/e1 trans-activated a CAEV LTR-chloramphenicol acetyltransferase reporter gene in goat synovial membrane cells. This activity was shown to be encoded by the Tat open reading frame by analysis of a deletion mutant. Because the pCAEV/f1 insert was unstable in plasmid form, its Tat activity could not be convincingly demonstrated. The target sequences for Tat within the CAEV LTR were localized to the U3 region which, when placed in either orientation upstream of heterologous promoters, was able to confer responsiveness to Tat.