Multiple large-scale genomic profiling efforts have been undertaken in osteosarcoma to define the genomic drivers of tumorigenesis, therapeutic response, and disease recurrence. The spatial and ...temporal intratumor heterogeneity could also play a role in promoting tumor growth and treatment resistance. We conducted longitudinal whole-genome sequencing of 37 tumor samples from 8 patients with relapsed or refractory osteosarcoma. Each patient had at least one sample from a primary site and a metastatic or relapse site. Subclonal copy-number alterations were identified in all patients except one. In 5 patients, subclones from the primary tumor emerged and dominated at subsequent relapses. MYC gain/amplification was enriched in the treatment-resistant clones in 6 of 7 patients with multiple clones. Amplifications in other potential driver genes, such as CCNE1, RAD21, VEGFA, and IGF1R, were also observed in the resistant copy-number clones. A chromosomal duplication timing analysis revealed that complex genomic rearrangements typically occurred prior to diagnosis, supporting a macroevolutionary model of evolution, where a large number of genomic aberrations are acquired over a short period of time followed by clonal selection, as opposed to ongoing evolution. A mutational signature analysis of recurrent tumors revealed that homologous repair deficiency (HRD)-related SBS3 increases at each time point in patients with recurrent disease, suggesting that HRD continues to be an active mutagenic process after diagnosis. Overall, by examining the clonal relationships between temporally and spatially separated samples from patients with relapsed/refractory osteosarcoma, this study sheds light on the intratumor heterogeneity and potential drivers of treatment resistance in this disease.
The chemoresistant population in recurrent osteosarcoma is subclonal at diagnosis, emerges at the time of primary resection due to selective pressure from neoadjuvant chemotherapy, and is characterized by unique oncogenic amplifications.
Abstract
Background: Dysregulation of DNA repair mechanisms are known to play a major role in tumor progression. Moreover, the tumor microenviroment itself has been shown to enhance this phenomenon. ...For example, studies using reporter genes and endogenous loci have demonstrated increased mutation rates in cells grown in tumors compared to the identical cells grown in culture, or a higher frequency of point mutations in cancer cells cultured under hypoxic conditions, a common feature during tumor growth. An accepted mechanism for these observations is hypoxia-induced down-regulation of MLH1, MSH2 or MSH6 leading to an increased mutation rate, or to hypoxia-induced repression of DNA double strand break repair.
Methods: Expression microarrays were performed using RNA isolated from nine pancreatic cancer cell lines cultured under normoxic (Nx, 20% O2) or hypoxic conditions (Hx, 1% O2) for 24 hours to identify differentially expressed genes. Retroviruses encoding oligos for HIF-1 or HIF-2 knockdown were used to generate stable pancreatic cancer cell lines in which HIF-1 or HIF-2, respectively, expression was blocked. Alternatively, Hx was induced by culture of cells inside an air-tight chamber with inflow and outflow valves that was infused with a mixture of 1% O2, 5% CO2 and 94% N2. Protein levels of HIF-1, HIF-2, MLH1, MSH2, MSH6 and CHK1 were determined by western blotting. Cell proliferation was measured by BrdU incorporation and cell cycle analysis by flow cytometry of propidium iodide stained cells. G2/M check point was studied analyzing Histone H3 phosphorylation by flow cytometry and DNA damage was determined by immunofluorescence of cells stained with anti phospho γ-H2AX antibody (γ-H2AX foci formation)
Results: We first compared the gene expression profiles of 9 different pancreatic cancer cell lines each grown under normoxic versus hypoxic conditions. As previously described, hypoxia led to down-regulation of the mRNA levels of the mismatch repair proteins MLH1, MSH2 and MSH6 as well as down-regulation of several genes involved in the DNA damage response to double strand breaks such as Brca1, Rad51, Ku70 and Ku80. Of interest, a novel downregulated gene identified was CHK1, a master coordinator of DNA repair following genotoxic stress. Growth of pancreatic cancer cells under hypoxic conditions was confirmed to decrease CHK1 mRNA and protein levels and stable knockdown of HIF-1a but not HIF-2 abolished these effects. In contrast to what have been previously reported in other cancer cell types, hypoxia had no effects on cell proliferation in pancreatic cancer cells as assessed by cell cycle analysis or by BrdU incorporation.To determine if hypoxic down-regulation of CHK1 protein levels has functional effects, we determined the ability of pancreatic cancer cells to arrest in the G2/M checkpoint after ionizing radiation. We found that cells cultured under hypoxia were significantly less arrested on G2/M check point after radiation compared to the same irradiated cells grown under normoxic conditions. This hypoxic effect on G2/M checkpoint was abolished on HIF-1 knockdown cells. Finally, pancreatic cancer cells grown under hypoxic conditions accumulated more DNA damage 24 hours after radiation compared to the same irradiated cells grown under normoxic conditions.
Conclusion: Hypoxic conditions decrease CHK1 mRNA and protein levels in pancreatic cancer cells in a HIF1-dependent manner. Impairment on CHK1 function may promote the mutator phenotype of pancreatic cancer cells during tumor progression by allowing unchecked cell divisions despite ongoing DNA damage. This finding also has significance for the use of CHK1 inhibitors for this tumor type.
Citation Format: Salvador Naranjo-Suarez, Elsa Callen, Yi Zhong, Alvin Makohon-Moore, Andre Nussenzweig, Christine Iacobuzio-Donahue. Hypoxia-induced CHK1 repression may enhance the mutator phenotype of pancreatic cancer cells. abstract. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr A68.
Pancreatic cancer is projected to become the second leading cause of cancer-related death in the United States by 2020. A familial aggregation of pancreatic cancer has been established, but the cause ...of this aggregation in most families is unknown. To determine the genetic basis of susceptibility in these families, we sequenced the germline genomes of 638 patients with familial pancreatic cancer and the tumor exomes of 39 familial pancreatic adenocarcinomas. Our analyses support the role of previously identified familial pancreatic cancer susceptibility genes such as BRCA2, CDKN2A, and ATM, and identify novel candidate genes harboring rare, deleterious germline variants for further characterization. We also show how somatic point mutations that occur during hematopoiesis can affect the interpretation of genome-wide studies of hereditary traits. Our observations have important implications for the etiology of pancreatic cancer and for the identification of susceptibility genes in other common cancer types.
The genetic basis of disease susceptibility in the majority of patients with familial pancreatic cancer is unknown. We whole genome sequenced 638 patients with familial pancreatic cancer and demonstrate that the genetic underpinning of inherited pancreatic cancer is highly heterogeneous. This has significant implications for the management of patients with familial pancreatic cancer.
Abstract
Purpose of study: Despite insights gained by bulk DNA sequencing of cancer it remains challenging to resolve “mixed signals”, i.e. the admixture of normal and tumor cells, and/or of distinct ...tumor subclones. Bulk sequencing of pancreatic ductal adenocarcinoma (PDAC) has been particularly problematic due to the high stromal content and resulting low tumor cellularity. Strategies to account for this have included laser capture microdissection yet this is a laborious process not amenable to high-throughput pipelines. We sought to develop and apply a high-throughput, high-depth, targeted single-cell DNA sequencing (scDNA-seq) method to account for these issues, including the ability to extract high quality genomic information from low purity and archival samples.
Experimental procedures: Bulk whole exome sequencing (WES) was performed on 29 biologically distinct samples. For single cell sequencing, we developed a custom panel containing 186 amplicons covering 93 genes that represent the most common germline and somatic targets reported in PDAC. Based on a commercially available system that enables automatic enzymatic and mechanical tissue disruption with integrated fluidic processes, we optimized a nuclei extraction workflow from frozen tissues that is highly compatible with downstream microdroplet-based single-cell encapsulation and library preparation. With it we generated scDNA-seq data from archival tissues of 15 PDAC patients at varying stages of the disease. Results were compared to that found in matched bulk sequencing data.
Summary of new, unpublished data and conclusions: 42 samples were analyzed by single cell sequencing. Our nuclei extraction workflow generated on average 2867 single cell libraries per sample at >80X read depth. The single-cell results aligned well with matched bulk data in terms of the detection of key genetic variants and their variant allele frequency (VAF). We also identified additional driver variants not seen by WES, some with direct clinical evidence. Benefits of this workflow over preexisting methods are its speed of sample preparation, efficiency of sample use (particularly for small samples), flexibility by allowing for storage of excess extracted nuclei, and economy of scale. Together, these features support preparation of large numbers of cancer samples in a relatively short period of time.
Citation Format: Haochen Zhang, Elias-Ramzey Karnoub, Ronan Chaligné, Ignas Masilionis, Alvin Makohon-Moore, Jungeui Hong, Christine Iacobuzio-Donahue. Optimization of high-throughput, high-depth, targeted single-cell DNA sequencing to pancreatic ductal adenocarcinoma abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 59.
Abstract
Introduction: Regardless of the stage at diagnosis most patients with pancreatic ductal adenocarcinoma develop peritoneal disease and some malignant ascites (MA) as well. Prior studies have ...shown that MA negatively affects overall treatment efficacy and survival. Despite the clinical significance of MA it has not been studied to any great extent.
Methods: We collected MA and matched normal tissue samples at autopsy from 20 PDAC patients who were initially diagnosed at stages IIB to IV. Whole exome or targeted sequencing was previously performed on each PDAC. Each MA sample was centrifuged twice at 4000 RPM first and then at 15000 RPM to separate the cell pellet (CP) from the cell-free ascites fluid. We next extracted DNA from the CP, matched normal tissue, and the cell-free DNA (cfDNA) from the ascites fluid, and all were submitted to the Genomics Core for MSK-IMPACT, a targeted cancer gene panel representing 505 genes.
Results: Results of the first five patients are complete and the remaining are in process. Comparison of the CPs and/or cfDNA to the matched tumor samples indicated 100% concordance for detected variants. However, the somatic alterations of the CP specifically versus the matched cfDNA were divergent in all patients analyzed thus far. Virtually all copy number alterations in all patients were deep deletions (range 66 to 187 cancer genes deleted) affecting multiple DNA repair pathways including homologous recombination deficiency and microsatellite repair.
Conclusions: Samples of MA, when both the cell pellet and cfDNA are sequenced, accurately represent the genetic features of the matched PDAC tissue and may serve as an alternative mode of sampling for precision medicine. Differences in the genetics of the CP versus the cfDNA suggest polyclonality in the peritoneal space. Moreover, the finding of deep deletions in targetable DNA repair pathways suggest a therapeutic vulnerability for exploration. Given that paracentesis is often performed in the palliative setting and may be performed multiple times over the course of a patients’ management, it also offers an opportunity to determine how clonal dynamics in the peritoneal space change over time. Patients with MA have poor overall survival compared to patients without MA so these patients may benefit from this type of tracking which could potentially help with their treatment.
Citation Format: Rajya L. Kappagantula, Alvin P. Makohon-Moore, Shigeaki Umeda, Elias-Ramzey R. Karnoub, Jerry P. Melchor, Laura D. Wood, Christine A. Iacobuzio-Donahue. Robust detection of somatic genetic alterations in pancreatic cancer ascites abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2148.
Abstract
The evolution of metastases is responsible for 90% of cancer-related deaths. Genome wide sequencing and phylogenomic methods enable the reconstruction of the evolutionary history of a ...patient's cancer at unprecedented depth. However, due to a lack of samples from multiple spatially-distinct metastases from untreated patients and a lack of phylogenomic tools applicable to noisy and impure sequencing samples, the evolutionary rules governing metastatic spread have remained poorly understood.
We performed whole-genome sequencing (coverage: median 51x) as well as deep targeted sequencing (coverage: median 347x) on 21 samples from multiple regions of the primary tumor and many distinct liver and lung metastases of two treatment-naïve pancreatic ductal adenocarcinoma patients. We developed a tool, called Treeomics, that leverages computational and statistical advances to reconstruct the phylogeny of a cancer with commonly available sequencing technologies. Treeomics employs a uniquely-designed Bayesian inference model to account for error-prone sequencing and varying low neoplastic cell content (estimated purities 16-44%) to calculate the probability that a specific variant is present or absent in each sequenced lesion. Based on Mixed Integer Linear Programming, a mathematically guaranteed optimal evolutionary tree is produced.
We obtained robust phylogenies consistent with the biological processes underlying cancer evolution. The reconstructed phylogenies show that advanced cancer cells of related subclones were equally capable of seeding lung and liver metastases. Treeomics identified sequencing and biological artifacts such as those resulting from insufficient coverage or loss of heterozygosity; almost 7% of the variants were misclassified by conventional methods. Among the identified false-negatives was the common clonal driver mutation in KRAS within a region that has low sequencing read alignability and a significantly reduced coverage. Such artifacts can skew phylogenies by creating illusory tumor heterogeneity among distinct samples. Additionally, we reanalyzed publicly available data from ovarian, prostate and skin cancers. We further illuminated evolutionary relationships among some samples in a conclusive fashion and show that classical distance-based phylogenetic methods can produce evolutionarily implausible results. Treeomics avoids these common pitfalls and infers robust phylogenies confirmed by high bootstrapping values.
The new approach described here efficiently reconstructs the evolutionary history of metastases, detects potential artifacts in noisy high-throughput sequencing data, and finds subclones of distinct origin. These phylogenies shed new light on seeding patterns and metastatic progression, which has significant implications for clinical decision making and may provide predictive value for a patient's prognosis.
Citation Format: Johannes G. Reiter, Alvin P. Makohon-Moore, Jeffrey M. Gerold, Ivana Bozic, Krishnendu Chatterjee, Christine A. Iacobuzio-Donahue, Bert Vogelstein, Martin A. Nowak. Reconstructing the evolutionary history of metastatic cancers. abstract. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2374.
Multiple myeloma (MM) progression is characterized by the seeding of cancer cells in different anatomic sites. To characterize this evolutionary process, we interrogated, by whole genome sequencing, ...25 samples collected at autopsy from 4 patients with relapsed MM and an additional set of 125 whole exomes collected from 51 patients. Mutational signatures analysis showed how cytotoxic agents introduce hundreds of unique mutations in each surviving cancer cell, detectable by bulk sequencing only in cases of clonal expansion of a single cancer cell bearing the mutational signature. Thus, a unique, single-cell genomic barcode can link chemotherapy exposure to a discrete time window in a patient's life. We leveraged this concept to show that MM systemic seeding is accelerated at relapse and appears to be driven by the survival and subsequent expansion of a single myeloma cell following treatment with high-dose melphalan therapy and autologous stem cell transplant.
Abstract
Objective: The osteosarcoma genome is characterized by high levels of genomic instability, however whether there is pervasive ongoing genomic instability, or instability introduced by an ...early catastrophic event, is still unsettled.
Methods: We performed 30-80x whole genome sequencing (WGS) of 37 tumor samples from 8 patients with relapsed or refractory osteosarcoma. Each patient had at least one sample from a primary site and one sample from a metastatic or relapse site. A set of high confidence single nucleotide variants (SNV), copy number alterations (CNA), structural variations (SV) were called for each sample using our pediatric expanded genomics pipeline and an analysis focused on markers of genomic instability was performed using a custom pipeline of computational tools.
Results: Of the 8 patients in our cohort, 4 had localized disease at diagnosis (OSCE4, OSCE5, OSCE6, OSCE9) and 4 had metastatic disease at diagnosis (OSCE1, OSCE2, OSCE3, OSCE10). There were 17 samples from primary sites, 7 pretreatment biopsies, 10 on therapy primary resections, 20 metastatic sites, 15 of which were from lung metastases. We have previously reported on the clonal evolution regarding SNVs and CNAs within this cohort. TP53 structural variants involving intron 1/2 were seen in 6/8 patients (OSCE2, OSCE3, OSCE4, OSCE6, OSCE9, OSCE10). No new structural variants in consensus driver genes emerged in metastatic or relapse samples. Comparing the earliest sample to most recent sample in each patient, only OSCE1, OSCE9, and OSCE10 demonstrated an increase of ≥100 structural variants at the final timepoint. In OSCE2, OSCE5, and OSCE6, there were less structural variants identified at the final timepoint when compared to the earliest timepoint. Homologous recombination deficiency (HRD) scores were calculated for each sample. Only 4/8 patients (OSCE3, OSCE4, OSCE9, OSCE10) had an HRD score in the most recently acquired sample higher than the score from the primary site. Regions of hypermutation consistent with kataegis were identified for each sample, with the number of kataegis events remaining unchanged or decreasing in some instances. Kataegis events co-localized with rearrangement events a majority of the time (range 50-100%, Avg= 72.6%). Complex rearrangements such as chromothripsis and chromoplexy were assesed. In 6 patients there were > 9 chromosomal arms involved in complex rearrangements that were shared between primary sites and metastatic/recurrent sites, while ≤ 4 chromosomal arms were involved with new complex rearrangements unique to the metastatic sites.
Conclusion: The patterns observed in our cohort reveal that osteosarcoma is relatively stable from diagnosis through subsequent relapses, supporting the model that an early catastrophic event accounts for the genomic instability observed in osteosarcoma.
Citation Format: Michael David Kinnaman, Simone Zaccaria, Alvin Makohon-Moore, Gunes Gundem, Juan E. Arango Ossa, Filemon S. Dela Cruz, Paul A. Meyers, Meera Hameed, William D. Tap, Julia Lynne Glade Bender, Elli Papaemmanuil, Andrew Kung, Christine Iacobuzio Donahue. Assessing patterns of genomic instability in recurrent osteosarcoma. abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3556.
Abstract
Objective: Multiple large-scale tumor genomic profiling efforts have been undertaken in osteosarcoma, however little is known about the spatial and temporal intratumor heterogeneity and how ...it may drive treatment resistance. Methods: We performed 30-80x whole genome sequencing (WGS) of 37 tumor samples from 8 patients with relapsed or refractory osteosarcoma. Each patient had at least one sample from a primary site and one sample from a metastatic or relapse site. A set of high confidence single nucleotide variants (SNV), copy number alterations (CNA), structural variations (SV) were called for each sample using our pediatric expanded genomics pipeline and an evolutionary analysis was performed using a custom pipeline of computational tools. Results: Of the 8 patients in our cohort, 4 had localized disease at diagnosis (OSCE4, OSCE5, OSCE6, OSCE9) and 4 had metastatic disease at diagnosis (OSCE1, OSCE2, OSCE3, OSCE10). There were 17 samples from primary sites, 7 were pretreatment biopsies, 10 from on therapy primary resections. 20 samples came from metastatic sites, 15 of which were from lung metastases. Driver gene SNV’s were identified in 5 of 8 patients, including TP53 (OSCE1), ATRX (OSCE3, OSCE10), RB1 (OSCE4), and CDKN2A (OSCE9). There were no new driver SNV’s that emerged post-therapy in any patient. HATCHet, an algorithm that infers clone-specific copy number alterations, identified subclonal CNAs in all but one patient (OSCE2). In the 7 patients with subclonal CNAs, 6 had two copy number clones identified, and 1 patient (OSCE10) had three copy number clones identified. In 5 patients (OSCE1, OSCE4, OSCE5, OSCE6, OSCE10) there is a copy number clone that is subclonal in the primary tumor which emerges and dominates at subsequent relapses. The resistant clone in each of these cases had either MYC gain/amplification. Amplifications in CCNE1 (OSCE1), RAD21 (OSCE4, OSCE5, OSCE10), VEGFA (OSCE1, OSCE9), IGF1R (OSCE6) were also identified as potential drivers in the resistant copy number clones. In two of these patients (OSCE1, OSCE6), this treatment-resistant subclone becomes the dominant copy number clone by the time of primary resection. SNV based phylogenies revealed a heterogenous mix of monoclonal and polyclonal seeding of metastases and monophyletic and polyphyletic modes of dissemination. Over half the new mutations acquired in recurrent disease were attributed to HRD or cisplatin mutational signatures. TP53 structural variants were seen in 6/8 patients (OSCE2, OSCE3, OSCE4, OSCE6, OSCE9, OSCE10). New structural variants involving driver genes were only detected in one relapse sample from patient OSCE10 (DMD deletion). Conclusion: Subclonal copy number clones emerge and dominate in relapsed osteosarcoma, with MYC gain/amplification a defining characteristic in our cohort. Selective pressure from neoadjuvant chemotherapy reveals this clone at the time of primary resection, highlighting that genomic profiling at this time point may be more reflective of its metastatic potential.
Citation Format: Michael D. Kinnaman, Simone Zaccaria, Alvin Makohon-Moore, Gunes Gundem, Juan E. Arango Ossa, Nancy Bouvier, Filemon S. Dela Cruz, Meera Hameed, Julia Lynne Glade Bender, William D. Tap, Paul Meyers, Elli Papaemmanuil, Andrew Kung, Christine A. Iacobuzio-Donahue. Subclonal somatic copy number alterations emerge and dominate in relapsed/refractory osteosarcoma abstract. In: Proceedings of the AACR Special Conference: Sarcomas; 2022 May 9-12; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(18_Suppl):Abstract nr B022.
Cancer is an evolutionary disease, and there is increasing interest in applying tools from evolutionary biology to understand cancer progression. Restriction-site associated DNA sequencing (RADseq) ...was developed for the field of evolutionary genetics to study adaptation and identify evolutionary relationships among populations. Here we apply RADseq to study tumor evolution, which allows for unbiased sampling of any desired frequency of the genome, overcoming the selection bias and cost limitations inherent to exome or whole-genome sequencing. We apply RADseq to both human pancreatic cancer and zebrafish melanoma samples. Using either a low-frequency (SbfI, 0.4% of the genome) or high-frequency (NsiI, 6-9% of the genome) cutter, we successfully identify single nucleotide substitutions and copy number alterations in tumors, which can be augmented by performing RADseq on sublineages within the tumor. We are able to infer phylogenetic relationships between primary tumors and metastases. These same methods can be used to identify somatic mosaicism in seemingly normal, non-cancerous tissues. Evolutionary studies of cancer that focus on rates of tumor evolution and evolutionary relationships among tumor lineages will benefit from the flexibility and efficiency of restriction-site associated DNA sequencing.
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