Transcriptomic Profiling of Plasma Extracellular Vesicles Enables Reliable Annotation of the Cancer-Specific Transcriptome and Molecular Subtype

Longitudinal monitoring of patients with advanced cancers is crucial to evaluate both disease burden and treatment response. Current liquid biopsy approaches mostly rely on the detection of DNA-based biomarkers. However, plasma RNA analysis can unleash tremendous opportunities for tumor state interrogation and molecular subtyping. Through the application of deep learning algorithms to the deconvolved transcriptomes of RNA within plasma extracellular vesicles (evRNA), we successfully predicted consensus molecular subtypes in patients with metastatic colorectal cancer. Analysis of plasma evRNA also enabled monitoring of changes in transcriptomic subtype under treatment selection pressure and identification of molecular pathways associated with recurrence. This approach also revealed expressed gene fusions and neoepitopes from evRNA. These results demonstrate the feasibility of using transcriptomic-based liquid biopsy platforms for precision oncology approaches, spanning from the longitudinal monitoring of tumor subtype changes to the identification of expressed fusions and neoantigens as cancer-specific therapeutic targets, sans the need for tissue-based sampling.

SIGNIFICANCE

The development of an approach to interrogate molecular subtypes, cancer-associated pathways, and differentially expressed genes through RNA sequencing of plasma extracellular vesicles lays the foundation for liquid biopsy-based longitudinal monitoring of patient tumor transcriptomes.

Significance of Distinct Liquid Biopsy Compartments in Evaluating Somatic Mutations for Targeted Therapy Selection in Cancer of Unknown Primary

PURPOSE

Cancer of unknown primary (CUP) accounts for 2-5% of all cancer diagnoses, wherein standard investigations fail to reveal the original tumor site. Basket trials allocate targeted therapeutics based on actionable somatic mutations, independent of tumor entity. These trials, however, mostly rely on variants identified in tissue biopsies. Since liquid biopsies (LB) represent the overall tumor genomic landscape, they may provide an ideal diagnostic source in CUP patients. To identify the most informative liquid biopsy compartment, we compared the utility of genomic variant analysis for therapy stratification in two LB compartments (circulating cell-free (cf) and extracellular vesicle (ev) DNA).

METHODS

CfDNA and evDNA from 23 CUP patients were analyzed using a targeted gene panel covering 151 genes. Identified genetic variants were interpreted regarding diagnostic and therapeutic relevance using the MetaKB knowledgebase.

RESULTS

LB revealed a total of 22 somatic mutations in evDNA and/or cfDNA in 11/23 patients. Out of the 22 identified somatic variants, 14 are classified as Tier I druggable somatic variants. Comparison of variants identified in evDNA and cfDNA revealed an overlap of 58% of somatic variants in both LB compartments, whereas over 40% of variants were only found in one or the other compartment.

CONCLUSION

We observed substantial overlap between somatic variants identified in evDNA and cfDNA of CUP patients. Nonetheless, interrogation of both LB compartments can potentially increase the rate of druggable alterations, stressing the significance of liquid biopsies for possible primary-independent basket and umbrella trial inclusion.

Abstract PR013: Transcriptomic profiling of liquid biopsy in colorectal cancer

Objective: Consensus molecular subtype (CMS) is a predictive factor for treatment outcomes of chemotherapies for metastatic colorectal cancer (CRC). CMS classification is based on transcriptomic profiles of CRC specimens obtained by tumor biopsy. Tumor biopsy often provides limited information due to the heterogeneity within tumor and spatial heterogeneity between the primary tumor and distant metastases. In addition, repeated tissue biopsy to monitor the treatment response is not practical. Liquid biopsy is a minimally invasive method for the real-time monitoring of cancer-derived biomarkers. Among liquid biopsy biomarkers, extracellular vesicles (EVs) have a unique potential because they possess nucleic acids. We explored the use of CRC plasma EVs in predicting the molecular subtype of CRCs using RNA-seq. Methods: EVs were isolated from 10 different CMS-stratified colorectal cancer cell lines and a normal control. Whole transcriptome RNA-seq on cellular RNA (cRNA) and cell-derived evRNA was done to determine if EVs could be used to predict the CMS subtype of their cells of origin. We then sought to perform molecular subtyping of plasma EVs from patients with CRC. RNA-seq was performed on tumor tissues and matched plasma EVs from 46 patients with CRC and 59 healthy controls (age/gender matched). The bulk transcriptome from CRC plasma EVs was deconvoluted to predict the cancer percentage (CIBERSORTx) and to utilize cancer-specific transcriptome for CMS subtyping (DeMixT). Artificial neural network (ANN)-based CMS subtype classifier was used to classify molecular subtypes. Results: There was 100% concordance between CMS subtype of evRNA with that of the cRNA. We showed that, RNA mixtures containing as low as 1% cancer cell RNA could be accurately classified into the correct CMS class. Imputed proportions of cancer in plasma of CRC patients ranged from 0.89% to 2.08%. Receiver operating characteristic (ROC) curve showed area under the curve of 0.961 with specificity and sensitivity of 0.96 and 0.9, respectively. Plasma evRNA was classified into CMS classes and there was 67% (31/46) concordance between the predicted subtype of liquid biopsies and the tumor samples. In patients with tumor purity greater than 10%, the concordance was higher at 75% (27/36). Conclusions: EVs could be used to accurately predict CMS subtypes of their cells of origin. We created a pipeline using low-input RNA library preparation from plasma EV to estimate the cancer RNA portion present in the bulk transcriptome and predict the molecular subtypes of colorectal cancers. Molecular subtyping of evRNA may help to track CMS changes of the tumor in patients undergoing treatment.

Citation Format: Vahid Bahrambeigi, Jaewon J. Lee, Kimal I. Rajapakshe, Bret M. Stephens, Jason T. Henry, Sarah Dhebat, Mark W. Hurd, Ryan Sun, Scott Kopetz, Anirban Maitra, Paola A. Guerrero. Transcriptomic profiling of liquid biopsy in colorectal cancer [abstract]. In: Proceedings of the AACR Special Conference on Colorectal Cancer; 2022 Oct 1-4; Portland, OR. Philadelphia (PA): AACR; Cancer Res 2022;82(23 Suppl_1):Abstract nr PR013.

Occult polyclonality of preclinical pancreatic cancer models drives in vitro evolution

Heterogeneity is a hallmark of cancer. The advent of single-cell technologies has helped uncover heterogeneity in a high-throughput manner in different cancers across varied contexts. Here we apply single-cell sequencing technologies to reveal inherent heterogeneity in assumptively monoclonal pancreatic cancer (PDAC) cell lines and patient-derived organoids (PDOs). Our findings reveal a high degree of both genomic and transcriptomic polyclonality in monolayer PDAC cell lines, custodial variation induced by growing apparently identical cell lines in different laboratories, and transcriptomic shifts in transitioning from 2D to 3D spheroid growth models. Our findings also call into question the validity of widely available immortalized, non-transformed pancreatic lines as contemporaneous "control" lines in experiments. We confirm these findings using a variety of independent assays, including but not limited to whole exome sequencing, single-cell copy number variation sequencing (scCNVseq), single-nuclei assay for transposase-accessible chromatin with sequencing, fluorescence in-situ hybridization, and single-cell RNA sequencing (scRNAseq). We map scRNA expression data to unique genomic clones identified by orthogonally-gathered scCNVseq data of these same PDAC cell lines. Further, while PDOs are known to reflect the cognate in vivo biology of the parental tumor, we identify transcriptomic shifts during ex vivo passage that might hamper their predictive abilities over time. The impact of these findings on rigor and reproducibility of experimental data generated using established preclinical PDAC models between and across laboratories is uncertain, but a matter of concern.

Elucidation of Tumor-Stromal Heterogeneity and the Ligand-Receptor Interactome by Single-Cell Transcriptomics in Real-world Pancreatic Cancer Biopsies

PURPOSE

Precision medicine approaches in pancreatic ductal adenocarcinoma (PDAC) are imperative for improving disease outcomes. With molecular subtypes of PDAC gaining relevance in the context of therapeutic stratification, the ability to characterize heterogeneity of cancer-specific gene expression patterns is of great interest. In addition, understanding patterns of immune evasion within PDAC is of importance as novel immunotherapeutic strategies are developed.

EXPERIMENTAL DESIGN

Single-cell RNA sequencing (scRNA-seq) is readily applicable to limited biopsies from human primary and metastatic PDAC and identifies most cancers as being an admixture of previously described epithelial transcriptomic subtypes.

RESULTS

Integrative analyses of our data provide an in-depth characterization of the heterogeneity within the tumor microenvironment, including cancer-associated fibroblast subclasses, and predicts for a multitude of ligand-receptor interactions, revealing potential targets for immunotherapy approaches.

CONCLUSIONS

Our analysis demonstrates that the use of de novo biopsies from patients with PDAC paired with scRNA-seq may facilitate therapeutic prediction from limited biopsy samples.

Defining the Comprehensive Genomic Landscapes of Pancreatic Ductal Adenocarcinoma Using Real-World Endoscopic Aspiration Samples

PURPOSE

Most patients with pancreatic ductal adenocarcinoma (PDAC) present with surgically unresectable cancer. As a result, endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA) is the most common biospecimen source available for diagnosis in treatment-naïve patients. Unfortunately, these limited samples are often not considered adequate for genomic analysis, precluding the opportunity for enrollment on precision medicine trials.

EXPERIMENTAL DESIGN

Applying an epithelial cell adhesion molecule (EpCAM)-enrichment strategy, we show the feasibility of using real-world EUS-FNA for in-depth, molecular-barcoded, whole-exome sequencing (WES) and somatic copy-number alteration (SCNA) analysis in 23 patients with PDAC.

RESULTS

Potentially actionable mutations were identified in >20% of patients. Further, an increased mutational burden and higher aneuploidy in WES data were associated with an adverse prognosis. To identify predictive biomarkers for first-line chemotherapy, we developed an SCNA-based complexity score that was associated with response to platinum-based regimens in this cohort.

CONCLUSIONS

Collectively, these results emphasize the feasibility of real-world cytology samples for in-depth genomic characterization of PDAC and show the prognostic potential of SCNA for PDAC diagnosis.

Surfaceome profiling enables isolation of cancer-specific exosomal cargo in liquid biopsies from pancreatic cancer patients

Background

Detection of circulating tumor DNA can be limited due to their relative scarcity in circulation, particularly while patients are actively undergoing therapy. Exosomes provide a vehicle through which cancer-specific material can be enriched from the compendium of circulating non-neoplastic tissue-derived nucleic acids. We carried out a comprehensive profiling of the pancreatic ductal adenocarcinoma (PDAC) exosomal 'surfaceome' in order to identify surface proteins that will render liquid biopsies amenable to cancer-derived exosome enrichment for downstream molecular profiling.

Patients and methods

Surface exosomal proteins were profiled in 13 human PDAC and 2 non-neoplastic cell lines by liquid chromatography-mass spectrometry. A total of 173 prospectively collected blood samples from 103 PDAC patients underwent exosome isolation. Droplet digital PCR was used on 74 patients (136 total exosome samples) to determine baseline KRAS mutation call rates while patients were on therapy. PDAC-specific exosome capture was then carried out on additional 29 patients (37 samples) using an antibody cocktail directed against selected proteins, followed by droplet digital PCR analysis. Exosomal DNA in a PDAC patient resistant to therapy were profiled using a molecular barcoded, targeted sequencing panel to determine the utility of enriched nucleic acid material for comprehensive molecular analysis.

Results

Proteomic analysis of the exosome 'surfaceome' revealed multiple PDAC-specific biomarker candidates: CLDN4, EPCAM, CD151, LGALS3BP, HIST2H2BE, and HIST2H2BF. KRAS mutations in total exosomes were detected in 44.1% of patients undergoing active therapy compared with 73.0% following exosome capture using the selected biomarkers. Enrichment of exosomal cargo was amenable to molecular profiling, elucidating a putative mechanism of resistance to PARP inhibitor therapy in a patient harboring a BRCA2 mutation.

Conclusion

Exosomes provide unique opportunities in the context of liquid biopsies for enrichment of tumor-specific material in circulation. We present a comprehensive surfaceome characterization of PDAC exosomes which allows for capture and molecular profiling of tumor-derived DNA.

Circulating Nucleic Acids Are Associated With Outcomes of Patients With Pancreatic Cancer

BACKGROUND & AIMS

We aimed to investigate the clinical utility of circulating tumor cell DNA (ctDNA) and exosome DNA (exoDNA) in pancreatic cancer.

METHODS

We collected liquid biopsy samples from 194 patients undergoing treatment for localized or metastatic pancreatic adenocarcinoma from April 7, 2015, through October 13, 2017 (425 blood samples collected before [baseline] and during therapy). Additional liquid biopsy samples were collected from 37 disease control individuals. Droplet digital polymerase chain reaction was used to determine KRAS mutant allele fraction (MAF) from ctDNA and exoDNA purified from plasma. For the longitudinal analysis, we analyzed exoDNA and ctDNA in 123 serial blood samples from 34 patients. We performed analysis including Cox regression, Fisher exact test, and Bayesian inference to associate KRAS MAFs in exoDNA and ctDNA with prognostic and predictive outcomes.

RESULTS

In the 34 patients with potentially resectable tumors, an increase in exoDNA level after neoadjuvant therapy was significantly associated with disease progression (P = .003), whereas ctDNA did not show correlations with outcomes. Concordance rates of KRAS mutations present in surgically resected tissue and detected in liquid biopsy samples were greater than 95%. On univariate analysis, patients with metastases and detectable ctDNA at baseline status had significantly shorter times of progression-free survival (PFS) (hazard ratio [HR] for death, 1.8; 95% CI, 1.1-3.0; P = .019), and overall survival (OS) (HR, 2.8; 95% CI, 1.4-5.7; P = .0045) compared with patients without detectable ctDNA. On multivariate analysis, MAFs ≥5% in exoDNA were a significant predictor of PFS (HR, 2.28; 95% CI, 1.18-4.40; P = .014) and OS (HR, 3.46; 95% CI, 1.40-8.50; P = .007). A multianalyte approach showed detection of both ctDNA and exoDNA MAFs ≥5% at baseline status to be a significant predictor of OS (HR, 7.73, 95% CI, 2.61-22.91, P = .00002) on multivariate analysis. In the longitudinal analysis, an MAF peak above 1% in exoDNA was significantly associated with radiologic progression (P = .0003).

CONCLUSIONS

In a prospective cohort of pancreatic cancer patients, we show how longitudinal monitoring using liquid biopsy samples through exoDNA and ctDNA provides both predictive and prognostic information relevant to therapeutic stratification.

Single-Cell Transcriptomics of Pancreatic Cancer Precursors Demonstrates Epithelial and Microenvironmental Heterogeneity as an Early Event in Neoplastic Progression

PURPOSE

Early detection of pancreatic ductal adenocarcinoma (PDAC) remains elusive. Precursor lesions of PDAC, specifically intraductal papillary mucinous neoplasms (IPMNs), represent a bona fide pathway to invasive neoplasia, although the molecular correlates of progression remain to be fully elucidated. Single-cell transcriptomics provides a unique avenue for dissecting both the epithelial and microenvironmental heterogeneities that accompany multistep progression from noninvasive IPMNs to PDAC.

EXPERIMENTAL DESIGN

Single-cell RNA sequencing was performed through droplet-based sequencing on 5,403 cells from 2 low-grade IPMNs (LGD-IPMNs), 2 high-grade IPMNs (HGD-IPMN), and 2 PDACs (all surgically resected).

RESULTS

Analysis of single-cell transcriptomes revealed heterogeneous alterations within the epithelium and the tumor microenvironment during the progression of noninvasive dysplasia to invasive cancer. Although HGD-IPMNs expressed many core signaling pathways described in PDAC, LGD-IPMNs harbored subsets of single cells with a transcriptomic profile that overlapped with invasive cancer. Notably, a proinflammatory immune component was readily seen in low-grade IPMNs, composed of cytotoxic T cells, activated T-helper cells, and dendritic cells, which was progressively depleted during neoplastic progression, accompanied by infiltration of myeloid-derived suppressor cells. Finally, stromal myofibroblast populations were heterogeneous and acquired a previously described tumor-promoting and immune-evading phenotype during invasive carcinogenesis.

CONCLUSIONS

This study demonstrates the ability to perform high-resolution profiling of the transcriptomic changes that occur during multistep progression of cystic PDAC precursors to cancer. Notably, single-cell analysis provides an unparalleled insight into both the epithelial and microenvironmental heterogeneities that accompany early cancer pathogenesis and might be a useful substrate to identify targets for cancer interception.See related commentary by Hernandez-Barco et al., p. 2027.

Abstract 2599: Circulating nucleic acids as biomarkers of prognosis and chemorefractory status in metastatic pancreatic cancer

Background: Prognostic and therapeutic stratification of pancreatic ductal adenocarcinoma (PDAC) patients remains elusive due to a lack of effective biomarkers, and a predilection towards metastatic disease. Peripheral blood-based liquid biopsies for tumor markers has emerged as a potential minimally invasive strategy for tumor monitoring. We have implemented a liquid biopsy assay utilizing DNA derived from vesicles known as exosomes (exoDNA) and circulating tumor DNA (ctDNA) in the metastatic setting to determine the potential utility of these liquid biopsy compartments in tumor management.

Methods: A total of 318 plasma samples from 123 metastatic pancreatic patients were prospectively collected. ExoDNA and ctDNA were then extracted from matched plasma samples. Digital PCR, was used to identify codon 12/13 KRAS gene mutations. We assessed clinical endpoints in relation to progression free survival (PFS) and overall survival (OS) using univariate and multivariate analyses. In a metastatic PDAC patient, six serial liquid biopsies and seven tissue biopsies taken throughout disease progression underwent whole genome sequencing for detection of copy number events.

Results: Detection rates of KRAS mutations in exoDNA and ctDNA at baseline treatment naïve staus were 61.0% and 52.9%, respectively. On multivariate COX regression analysis, exoDNA KRAS mutant allelic fraction (MAF) ≥ 5% was a significant predictor of poorer PFS (HR 2.28, 95% CI 1.18-4.40, P=0.014) and OS (HR 3.46, 95% CI 1.40-8.50, P=0.007) in metastatic patients. Among 34 patients, liquid biopsy tumor monitoring was performed across 127 serial blood draws during a median followup time of 11.1 months. The presence of an exoDNA MAF peak ≥ 1% during tumor monitoring was significantly correlated to radiological progression (p=0.0003). Specifically, detection of an exoDNA MAF peak ≥ 1% preceded radiological progression by a median of 50 days compared to a median of 0 days for CA19-9 (p=0.03). CtDNA did not emerge as a significant predictor of survival outcomes in our cohort. In a patient with multiple longitudinal liquid biopsies, comprehensive genomic profiling of exoDNA further demonstrated our ability to capture additional mutational events as they emerged during therapy and correlated to progression including amplifications in ERBB2 and MYC and deletions in CDKN2A and SMAD4.

Conclusions: Liquid biopsies in PDAC provide direct evidence of those patients likely to experience poorer outcomes allowing for more effective therapeutic stratification. Liquid biopsies also demonstrate utility in characterization of putative emerging driver events during disease progression.

Citation Format: Vincent Bernard, Dong U. Kim, F. Anthony San Lucas, Jonathan Castillo, Kelvin Allenson, Feven C. Mulu, Bret M. Stephens, Jonathan Huang, Eugene Koay, Cullen M. Taniguchi, Milind Javle, Robert A. Wolff, Matthew H. Katz, Gauri R. Varadhachary, Hector A. Alvarez, Anirban Maitra. Circulating nucleic acids as biomarkers of prognosis and chemorefractory status in metastatic pancreatic cancer [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 2599.

Adenoid size is related to severity but not the number of episodes of obstructive apnea in children

OBJECTIVE

The objective of this study was to determine the extent to which adenotonsillar hypertrophy contributes to the severity of obstructive sleep apnea (OSA) in children.

STUDY DESIGN

Thirty-three consecutive children who were referred to a sleep disorders center for evaluation of suspected OSA had standard lateral neck roentgenography performed. Adenoid size was determined by measuring the adenoidal-nasopharyngeal (AN) ratio. Tonsil size was quantitated on physical examination. The severity of OSA was determined by full-night polysomnography in the sleep laboratory.

RESULTS

All of the patients reported snoring with trouble breathing, apneas, or both problems witnessed by a parent. The patients' respiratory disturbance index ranged from 0 to 95.3 (mean +/- SD 12.5 +/- 9.1). The patients' AN ratio ranged from 0.48 to 0.98 (0.76 +/- 0.14); 30 (91%) of the 33 patients had AN ratios greater than published normal means, and 16 (48%) had AN ratios more than 2 standard deviations above published means. Although the AN ratio and tonsil size did not predict the number of apneas, a significant relationship was seen between the AN ratio and the duration of obstructive apneas (r = 0.48, p < 0.01). Obesity (percent ideal body weight) was the only independent predictor for the number of respiratory events per hour of sleep (r = 0.49, p < 0.01). Percent ideal body weight was also the major predictor of the lowest oxyhemoglobin saturation (r = -0.58, p < 0.0001), but the AN ratio also contributed to the variance in saturation, with a correlation coefficient (r) of 0.69 for the two factors (p < 0.0001).

CONCLUSION

Lymphoid hyperplasia affects the severity of apnea more than the number of obstructive apneas. The pathophysiologic characteristics of OSA in children probably involve complex interactions between pharyngeal size and mechanics.

Report on Treatment of a Case of Shrapnel Wound of the Mandible, in which Bony Union was re-established after great loss of Substance

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