Extracellular vesicles as a potential source of tumor-derived DNA in advanced pancreatic cancer

Tumor-derived extracellular vesicles (EVs) are reported to contain nucleic acids, including DNA. Several studies have highlighted the potential of EV-derived DNA (evDNA) as a circulating biomarker, even demonstrating that evDNA can outperform cell-free DNA (cfDNA) in terms of sensitivity. Here, we evaluated EVs as a potential source of tumor-derived DNA in patients with advanced pancreatic cancer. evDNA from both DNase-treated and untreated EV samples was analyzed to determine whether the DNA was primarily located internally or outside (surface-bound) the EVs. To assess whether methodology affected the results, we isolated EVs using four different methods for small EV isolation and differential centrifugation for isolating large EVs. Our results indicated that the DNA content of EVs was significantly less than the cfDNA content isolated from the same plasma volume (p < 0.001). Most of the detected evDNA was also located on the outside of the vesicles. Furthermore, the fraction of tumor-derived DNA in EVs was similar to that found in cfDNA. In conclusion, our results suggest that quantification of evDNA, as a source of tumor-derived DNA, does not add information to that obtained with cfDNA, at least not in patients with advanced pancreatic cancer.

Monitoring of circulating tumour DNA in advanced pancreatic ductal adenocarcinoma predicts clinical outcome and reveals disease progression earlier than radiological imaging

Pancreatic ductal adenocarcinoma (PDAC) is a lethal disease with a need for better tools to guide treatment selection and follow-up. The aim of this prospective study was to investigate the prognostic value and treatment monitoring potential of longitudinal circulating tumour DNA (ctDNA) measurements in patients with advanced PDAC undergoing palliative chemotherapy. Using KRAS peptide nucleic acid clamp-PCR, we measured ctDNA levels in plasma samples obtained at baseline and every 4 weeks during chemotherapy from 81 patients with locally advanced and metastatic PDAC. Cox proportional hazard regression showed that ctDNA detection at baseline was an independent predictor of progression-free and overall survival. Joint modelling demonstrated that the dynamic ctDNA level was a strong predictor of time to first disease progression. Longitudinal ctDNA measurements during chemotherapy successfully revealed disease progression in 20 (67%) of 30 patients with ctDNA detected at baseline, with a median lead time of 23 days (P = 0.01) over radiological imaging. Here, we confirmed the clinical relevance of ctDNA in advanced PDAC with regard to both the prediction of clinical outcome and disease monitoring during treatment.

Comprehensive ctDNA measurements improve prediction of clinical outcomes and enable dynamic tracking of disease progression in advanced pancreatic cancer

PURPOSE

Circulating tumor DNA (ctDNA) has emerged as a promising tumor-specific biomarker in pancreatic cancer, but current evidence of the clinical potential of ctDNA is limited. In this study, we used comprehensive detection methodology to explore the utility of longitudinal ctDNA measurements in patients with advanced pancreatic cancer.

EXPERIMENTAL DESIGN

A targeted eight-gene next-generation sequencing panel was used to detect point mutations and copy number aberrations (CNAs) in ctDNA from 324 pre-treatment and longitudinal plasma samples obtained from 56 patients with advanced pancreatic cancer. The benefit of ctDNA measurements to predict clinical outcome and track disease progression was assessed.

RESULTS

We detected ctDNA in 35/56 (63%) patients at baseline and found that it was an independent predictor of shorter progression-free survival (PFS) and overall survival (OS). After initiation of treatment, ctDNA levels decreased significantly before significantly increasing by the time of progression. In some patients, ctDNA persistence was observed after the first chemotherapy cycles, and it was associated with rapid disease progression and shorter OS. Longitudinal monitoring of ctDNA levels in 27 patients for whom multiple samples were available detected progression in 19 (70%) patients. The median lead time of ctDNA measurements on radiologically determined progression/time of death was 19 days (p = 0.002), compared to 6 days (p = 0.007) using carbohydrate antigen 19-9.

CONCLUSIONS

ctDNA is an independent prognostic marker that can be used to detect treatment failure and disease progression in patients with advanced pancreatic cancer.

Mutation-Agnostic Detection of Colorectal Cancer Using Liquid Biopsy-Based Methylation-Specific Signatures

Detection of methylation patterns in circulating tumor DNA (ctDNA) can offer a novel approach for cancer diagnostics given the unique signature for each tumor type. We developed a next-generation sequencing (NGS)-based assay targeting 32 CpG sites to detect colorectal cancer-specific ctDNA. NGS was performed on bisulfite-converted libraries and status dichotomization was done using median methylation ratios at all targets. We included plasma samples from patients with metastatic colorectal (n = 20) and non-colorectal cancers (n = 8); and healthy volunteers (n = 4). Median methylation ratio was higher in colorectal cancer compared with non-colorectal cancers (P = .001) and normal donors (P = .005). The assay detected ctDNA in 85% of patients with colorectal cancer at a specificity of 92%. Notably, we were able to detect methylated ctDNA in 75% of patients in whom ctDNA was not detected by other methods. Detection of methylated ctDNA was associated with shorter median progression-free survival compared to non-detection (8 weeks versus 54 weeks; P = .027).

Abstract 5152: Mutation-agnostic detection of colorectal cancer-specific cell-free DNA using targeted methylation sequencing

BACKGROUND: Tumor-specific methylation changes in DNA CpG sites commonly occur in cancer and are believed to drive oncogenesis through gene silencing. Detection of methylation changes in circulating cell-free DNA (cfDNA) can offer a novel approach for cancer diagnostics.

METHODS: Plasma samples from healthy controls and from patients with advanced colorectal and non-colorectal cancers were included in the study. Bisulfite conversion of cfDNA extracted from plasma was performed using EZ DNA Methylation Lightning Kit (Zymo Research) and was followed by library preparation using Accel-NGS Methyl-Seq DNA Library Kit (Swift Biosciences) and target enrichment using xGen Hybridization Capture for NGS Kit (IDT). Targeted methylation sequencing was done using NextSeq500 mid-output flow cell (300 cycles) (Illumina). Detection rates of methylation ratios in colorectal cancer samples were compared to non-colorectal cancers and healthy controls.

RESULTS: First, we reviewed methylation changes in nearly 9,000 CpG sites in colorectal cancer (through TCGA database) and healthy controls. Subsequently, 32 CpG sites with greater than 50% methylation ratio in colorectal cancer and less than 1% methylation ratio in healthy controls were selected to develop targeted methylation sequencing based cfDNA assay. The assay was performed in 32 plasma samples from 20 individuals with advanced colorectal cancer who had tumor KRAS mutation, 8 individuals with advanced non-colorectal cancer who had tumor KRAS mutation (ovarian, n=2; endometrial, n=2; pancreatic, n=2; and lung cancer, n=2), and 4 healthy controls. Colorectal cancer specific methylation changes in cfDNA were detected in 85% (17/20) of colorectal cancer patients with a specificity of 92%. In colorectal cancer patients with confirmed KRAS mutation in cfDNA, methylation changes were detected in 92% (11/12) in comparison to 75% (6/8) in colorectal cancer patients without KRAS mutation in cfDNA. Median methylation ratio for target CpG sites was higher in colorectal cancer patients compared to patients with non-colorectal cancers and healthy controls (p&lt;0.001). In 17 colorectal cancer patients with plasma samples collected before initiation of systemic cancer therapy, detection of methylation changes in cfDNA was associated with a shorter median progression-free survival compared to no detection (PFS; 8 weeks versus 54 weeks; p=0.027).

CONCLUSIONS: Targeted methylation sequencing of cfDNA demonstrated high sensitivity and specificity for detection of colorectal cancer-specific cfDNA. Colorectal cancer patients with methylated cfDNA had shorter PFS while on cancer therapy.

Citation Format: Mohamed A. Gouda, Dzifa Y. Duose, Morten Lapin, Stephanie Zalles, Helen J. Huang, Yuanxin Xi, Xiaofeng Zheng, Amira I. Aldesoky, Alshimaa M. Alhanafy, Mohamed A. Shehata, Jing Wang, Scott Kopetz, Funda Meric-Bernstam, Ignacio I. Wistuba, Rajyalakshmi Luthra, Filip Janku. Mutation-agnostic detection of colorectal cancer-specific cell-free DNA using targeted methylation sequencing [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 5152.

Prognostic value of disseminated tumor cells in unresectable pancreatic ductal adenocarcinoma: a prospective observational study

BACKGROUND

Although pancreatic ductal adenocarcinoma (PDAC) rarely metastasizes to the skeleton, disseminated tumor cells have been detected in bone marrow samples from patients with this disease. The prognostic value of such findings is currently unclear. Thus, the current study aimed to clarify the prognostic information associated with disseminated tumor cell detection in samples from patients with PDAC.

METHODS

Bone marrow aspirates were obtained from 48 patients with locally advanced (n = 11) or metastatic (n = 37) PDAC, before and after 2 months of chemotherapy. Disseminated tumor cells were detected with an mRNA panel and quantitative reverse transcription PCR. We used the highest levels measured in healthy bone marrow (n = 30) as a threshold to define the positive detection of disseminated tumor cells. Progression-free and overall survival were analyzed with Kaplan-Meier and Cox proportional hazards regression analyses.

RESULTS

Disseminated tumor cells were detected in 15/48 (31%) bone marrow samples obtained before starting chemotherapy and in 8/25 (32%) samples obtained during chemotherapy. Patients with disseminated tumor cells detected before therapy had significantly shorter progression-free (p = 0.03; HR = 2.0) and overall survival (p = 0.03; HR = 2.0), compared to those without disseminated tumor cells in the bone marrow. When restricting disseminated tumor cell detection to keratins KRT7 and KRT8, the prognostic information was substantially stronger (p = 1 × 10-6; HR = 22, and p = 2 × 10-5; HR = 7.7, respectively). The multivariable Cox regression analysis demonstrated that disseminated tumor cell detection prior to treatment had independent prognostic value. In contrast, disseminated tumor cells detected during treatment did not have prognostic value.

CONCLUSIONS

Disseminated tumor cells detected before commencing chemotherapy had prognostic value in patients with inoperable PDAC.

Novel hybridization- and tag-based error-corrected method for sensitive ctDNA mutation detection using ion semiconductor sequencing

Circulating tumor DNA (ctDNA) analysis has emerged as a clinically useful tool for cancer diagnostics and treatment monitoring. However, ctDNA detection is complicated by low DNA concentrations and technical challenges. Here we describe our newly developed sensitive method for ctDNA detection on the Ion Torrent sequencing platform, which we call HYbridization- and Tag-based Error-Corrected sequencing (HYTEC-seq). This method combines hybridization-based capture with molecular tags, and the novel variant caller PlasmaMutationDetector2 to eliminate background errors. We describe the validation of HYTEC-seq using control samples with known mutations, demonstrating an analytical sensitivity down to 0.1% at > 99.99% specificity. Furthermore, to demonstrate the utility of this method in a clinical setting, we analyzed plasma samples from 44 patients with advanced pancreatic cancer, revealing mutations in 57% of the patients at allele frequencies as low as 0.23%.

Monitoring of Dynamic Changes and Clonal Evolution in Circulating Tumor DNA From Patients With IDH-Mutated Cholangiocarcinoma Treated With Isocitrate Dehydrogenase Inhibitors

PURPOSE

IDH mutations occur in about 30% of patients with cholangiocarcinoma. Analysis of mutations in circulating tumor DNA (ctDNA) can be performed by droplet digital polymerase chain reaction (ddPCR). The analysis of ctDNA is a feasible approach to detect IDH mutations.

METHODS

We isolated ctDNA from the blood of patients with IDH-mutated advanced cholangiocarcinoma collected at baseline, on therapy, and at progression to isocitrate dehydrogenase (IDH) inhibitors.

RESULTS

Of 31 patients with IDH1R132 (n = 26) or IDH2R172 mutations (n = 5) in the tumor, IDH mutations were detected in 84% of ctDNA samples analyzed by ddPCR and in 83% of ctDNA samples analyzed by next-generation sequencing (NGS). Patients with a low variant allele frequency of ctDNA detected by NGS at baseline had a longer median time to treatment failure compared to patients with high variant allele frequency of ctDNA (3.6 v 1.5 months; P = .008). Patients with a decrease in IDH-mutated ctDNA on therapy by ddPCR compared with no change/increase had a trend to a longer median survival (P = .07). Most frequent emergent alterations in ctDNA by NGS at progression were ARID1A (n = 3) and TP53 mutations (n = 3).

CONCLUSION

Detection of IDH mutations in ctDNA in patients with advanced cholangiocarcinoma is feasible, and dynamic changes in ctDNA can correspond with the clinical course and clonal evolution.

High-Grade Cervical Intraepithelial Neoplasia (CIN) Associates with Increased Proliferation and Attenuated Immune Signaling

Implementation of high-risk human papilloma virus (HPV) screening and the increasing proportion of HPV vaccinated women in the screening program will reduce the percentage of HPV positive women with oncogenic potential. In search of more specific markers to identify women with high risk of cancer development, we used RNA sequencing to compare the transcriptomic immune-profile of 13 lesions with cervical intraepithelial neoplasia grade 3 (CIN3) or adenocarcinoma in situ (AIS) and 14 normal biopsies from women with detected HPV infections. In CIN3/AIS lesions as compared to normal tissue, 27 differential expressed genes were identified. Transcriptomic analysis revealed significantly higher expression of a number of genes related to proliferation, (CDKN2A, MELK, CDK1, MKI67, CCNB2, BUB1, FOXM1, CDKN3), but significantly lower expression of genes related to a favorable immune response (NCAM1, ARG1, CD160, IL18, CX3CL1). Compared to the RNA sequencing results, good correlation was achieved with relative quantitative PCR analysis for NCAM1 and CDKN2A. Quantification of NCAM1 positive cells with immunohistochemistry showed epithelial reduction of NCAM1 in CIN3/AIS lesions. In conclusion, NCAM1 and CDKN2A are two promising candidates to distinguish whether women are at high risk of developing cervical cancer and in need of frequent follow-up.

Liquid Biopsies in Solid Cancers: Implementation in a Nordic Healthcare System

Simple Summary

We here review liquid biopsy methods and their use in the diagnostics and treatment of patients with solid cancers. More specifically, circulating tumor DNA, circulating tumor cells, and their current and future clinical applications are considered. Important factors for further integration of liquid biopsy methods in clinical practice are discussed, with a special focus on a Nordic Healthcare system.

Abstract

Liquid biopsies have emerged as a potential new diagnostic tool, providing detailed information relevant for characterization and treatment of solid cancers. We here present an overview of current evidence supporting the clinical relevance of liquid biopsy assessments. We also discuss the implementation of liquid biopsies in clinical studies and their current and future clinical role, with a special reference to the Nordic healthcare systems. Our considerations are restricted to the most established liquid biopsy specimens: circulating tumor DNA (ctDNA) and circulating tumor cells (CTC). Both ctDNA and CTCs have been used for prognostic stratification, treatment choices, and treatment monitoring in solid cancers. Several recent publications also support the role of ctDNA in early cancer detection. ctDNA seems to provide more robust clinically relevant information in general, whereas CTCs have the potential to answer more basic questions related to cancer biology and metastasis. Epidermal growth factor receptor-directed treatment of non-small-cell lung cancer represents a clinical setting where ctDNA already has entered the clinic. The role of liquid biopsies in treatment decisions, standardization of methods, diagnostic performance and the need for further research, as well as cost and regulatory issues were identified as factors that influence further integration in the clinic. In conclusion, substantial evidence supports the clinical utility of liquid biopsies in cancer diagnostics, but further research is still required for a more general application in clinical practice.

Abstract LB-252: Single-cell mRNA profiling reveal transcriptional heterogeneity among pancreatic circulating tumor cells

Background: Single-cell analysis of the transcriptional heterogeneity of circulating tumor cells have the prospect of better understanding the biology of these cells and their involvement in the metastatic process. In addition, such analyses may reveal new knowledge about the mechanisms leading to chemotherapy resistance and tumor progression in pancreatic cancer patients.

Methods: Single circulating tumor cells were enriched from blood samples (n = 50) from patients with advanced pancreatic cancer using our previously established negative depletion strategy MINDEC, and detected by immuno-fluorescence microscopy. The single cells were isolated by micromanipulation, reverse transcribed, pre-amplified, and analyzed using single cell multiplex mRNA profiling to reveal transcriptional heterogeneity.

Results: Circulating tumor cells were detected in 29 (58%) of the examined blood samples. A total of 48 potential circulating tumor cells were isolated, in which 17 cells had detectable mRNA levels and were identified as circulating tumor cells by expression of

epithelial (KRT8, KRT19, EPCAM, E-Cadherin) or mesenchymal (Vimentin, N-Cadherin, ZEB1) markers. These pancreatic circulating tumor cells were revealed to heterogeneously express the examined transcripts, and also showed aberrant expression of cancer stem cell (CD24, CD44, ALDH1A1) markers and the extracellular matrix marker SPARC. Hierarchical clustering and principal component analyses revealed epithelial-like and mesenchymal-like circulating tumor cell subpopulations, which were distinct from white blood cells and cancer cell line cells. Further analyses of the transcript SPARC suggested a relation to epithelial-mesenchymal transition in pancreatic circulating tumor cells.

Conclusion: The analysis of single pancreatic circulating tumor cells defines distinct subpopulations and reveals aberrant expression of transcripts relevant for the dissemination of circulating tumor cells to distant sites.

Citation Format: Morten Lapin, Kjersti Tjensvoll, Satu Oltedal, Milind Javle, Rune Smaaland, Bjørnar Gilje, Oddmund Nordgård. Single-cell mRNA profiling reveal transcriptional heterogeneity among pancreatic circulating tumor cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-252. doi:10.1158/1538-7445.AM2017-LB-252

Single-cell mRNA profiling reveals transcriptional heterogeneity among pancreatic circulating tumour cells

Background

Single-cell mRNA profiling of circulating tumour cells may contribute to a better understanding of the biology of these cells and their role in the metastatic process. In addition, such analyses may reveal new knowledge about the mechanisms underlying chemotherapy resistance and tumour progression in patients with cancer.

Methods

Single circulating tumour cells were isolated from patients with locally advanced or metastatic pancreatic cancer with immuno-magnetic depletion and immuno-fluorescence microscopy. mRNA expression was analysed with single-cell multiplex RT-qPCR. Hierarchical clustering and principal component analysis were performed to identify expression patterns.

Results

Circulating tumour cells were detected in 33 of 56 (59%) examined blood samples. Single-cell mRNA profiling of intact isolated circulating tumour cells revealed both epithelial-like and mesenchymal-like subpopulations, which were distinct from leucocytes. The profiled circulating tumour cells also expressed elevated levels of stem cell markers, and the extracellular matrix protein, SPARC. The expression of SPARC might correspond to an epithelial-mesenchymal transition in pancreatic circulating tumour cells.

Conclusion

The analysis of single pancreatic circulating tumour cells identified distinct subpopulations and revealed elevated expression of transcripts relevant to the dissemination of circulating tumour cells to distant organ sites.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-017-3385-3) contains supplementary material, which is available to authorized users.

MINDEC-An Enhanced Negative Depletion Strategy for Circulating Tumour Cell Enrichment

Most current methods of circulating tumour cell (CTC) enrichment target the epithelial protein EpCAM, which is commonly expressed in adenocarcinoma cells. However, such methods will not recover the fraction of CTCs that have a non-epithelial phenotype due to epithelial–mesenchymal transition. For phenotype-independent CTC enrichment, we developed a new enhanced negative depletion strategy—termed MINDEC—that is based on multi-marker (CD45, CD16, CD19, CD163, and CD235a/GYPA) depletion of blood cells rather than targeted enrichment of CTCs. Here we validated the performance of MINDEC using epithelial and mesenchymal cancer cell lines, demonstrating a mean recovery of 82 ± 10%, high depletion (437 ± 350 residual white blood cells (WBCs)/mL peripheral blood), linearity between spiked and recovered cells (correlation coefficient: r = 0.995), and a low detection limit (≥1 cell recovered in all four replicates spiked with 3 cells). For clinical validation of this method, we enumerated CTCs in peripheral blood samples from patients with metastatic pancreatic cancer, detecting CTCs in 15 of 21 blood samples (71%) from 9 patients. The promising performance of the MINDEC enrichment strategy in our study encourages validation in larger clinical trials.

The Splicing Efficiency of Activating HRAS Mutations Can Determine Costello Syndrome Phenotype and Frequency in Cancer

Costello syndrome (CS) may be caused by activating mutations in codon 12/13 of the HRAS proto-oncogene. HRAS p.Gly12Val mutations have the highest transforming activity, are very frequent in cancers, but very rare in CS, where they are reported to cause a severe, early lethal, phenotype. We identified an unusual, new germline p.Gly12Val mutation, c.35_36GC>TG, in a 12-year-old boy with attenuated CS. Analysis of his HRAS cDNA showed high levels of exon 2 skipping. Using wild type and mutant HRAS minigenes, we confirmed that c.35_36GC>TG results in exon 2 skipping by simultaneously disrupting the function of a critical Exonic Splicing Enhancer (ESE) and creation of an Exonic Splicing Silencer (ESS). We show that this vulnerability of HRAS exon 2 is caused by a weak 3' splice site, which makes exon 2 inclusion dependent on binding of splicing stimulatory proteins, like SRSF2, to the critical ESE. Because the majority of cancer- and CS- causing mutations are located here, they affect splicing differently. Therefore, our results also demonstrate that the phenotype in CS and somatic cancers is not only determined by the different transforming potentials of mutant HRAS proteins, but also by the efficiency of exon 2 inclusion resulting from the different HRAS mutations. Finally, we show that a splice switching oligonucleotide (SSO) that blocks access to the critical ESE causes exon 2 skipping and halts proliferation of cancer cells. This unravels a potential for development of new anti-cancer therapies based on SSO-mediated HRAS exon 2 skipping.

Clinical relevance of circulating KRAS mutated DNA in plasma from patients with advanced pancreatic cancer

We used KRAS mutations to investigate the clinical relevance of circulating tumor DNA (ctDNA) measurements in patients with advanced pancreatic cancer. Fifty-three blood samples were collected from 14 prospectively recruited patients prior to chemotherapy (gemcitabine or FOLFIRINOX) and subsequently every month during treatment. Samples were processed by density centrifugation and plasma DNA isolation. A Peptide-nucleic acid-clamp PCR was then used to detect KRAS mutations (present in >90% of pancreatic cancers) as a surrogate marker for ctDNA. Plasma samples from 29 healthy individuals were analyzed as a reference group. Results were compared to conventional monitoring measures and survival data. Median follow-up time was 3.7 months (range 0.6-12.9 months). Ten (71%) patients had a positive KRAS status in the plasma samples obtained prior to chemotherapy, indicating the presence of ctDNA. Among the patients who were ctDNA-positive before chemotherapy, nine (90%) experienced disease progression during follow-up, compared to one (25%) of four ctDNA-negative patients (P = 0.01). The pre-therapy ctDNA level was a statistically significant predictor of both progression-free and overall survival (P = 0.014 and 0.010, respectively). Of the 14 patients, ten had ≥2 follow-up samples; in several of these patients, the ctDNA level changed substantially during the course of chemotherapy. Changes in ctDNA levels corresponded both with radiological follow-up data and CA19-9 levels for several patients. This pilot study supports the hypothesis that ctDNA may be used as a marker for monitoring treatment efficacy and disease progression in pancreatic cancer patients. Recruitment of more patients is ongoing to corroborate these findings.

Abstract 5241: Clinical relevance of circulating tumor DNA in plasma from pancreatic cancer patients

Background: Circulating tumor DNA (ctDNA) may originate from necrotic or apoptotic tumor cells in the primary tumor, metastatic lesions or in the circulation. There is evidence that the ctDNA level may reflect the total tumor burden in a patient. We wanted to investigate whether changes in the ctDNA level might be used to monitor disease progression in pancreatic cancer patients with locally or advanced disease. Methods: Blood samples (9 mL in EDTA tubes) were collected from 15 prospectively recruited patients with locally advanced and/or metastatic pancreatic cancer before initiation of treatment, and subsequently every month during chemotherapy. The samples were processed by LymphoprepTM (Axis Shield) density centrifugation before plasma DNA isolation using the QIAamp Circulating Nucleic Acid kit (Qiagen). A high-fidelity polymerase-based PNA clamp PCR method (Gilje et al., 2008, Oltedal et al., 2010) was then used for the detection of KRAS mutations in exon 12 and 13, as a surrogate marker for ctDNA. KRAS mutations have previously been reported to be present in &gt;90% of the pancreatic cancers. Plasma samples from 29 healthy individuals were also analysed as a reference group for the PNA clamp PCR method. The results were compared with conventional biochemical and radiological monitoring measures. Results: The majority of the patients (80%) had metastatic disease and they were treated either by gemcitabine or FOLFORINOX. Nine (60%) patients had a positive KRAS status in the plasma samples obtained before initiation of chemotherapy, indicating presence of ctDNA. Moreover, 11 of the 15 included patients had ≥2 follow-up samples, and in several of these patients the ctDNA level changed substantially during the course of chemotherapy. In total, 17/38 (44.7%) patient samples were positive for plasma DNA KRAS mutations during chemotherapy. Changes in the ctDNA level seemed to correspond both to radiological follow-up data and changes in CA19-9 for several patients. Analyses of the total plasma DNA fraction with regard to disease monitoring, gave more inconclusive results in this small pilot study. Conclusion: Our pilot study gives support to the hypothesis that ctDNA may be used as a marker for monitoring treatment efficacy and disease progression in pancreatic cancer patients. This will be further investigated.

Citation Format: Kjersti Tjensvoll, Morten Lapin, Tove Buhl, Satu Oltedal, Katrine Steen-Ottosen Berry, Bjørnar Gilje, Jon Arne Søreide, Millind Javle, Oddmund Nordgård, Rune Smaaland. Clinical relevance of circulating tumor DNA in plasma from pancreatic cancer patients. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5241. doi:10.1158/1538-7445.AM2015-5241

Evidence for protein dielectric relaxations in reaction centers associated with the primary charge separation detected from Rhodospirillum rubrum chromatophores by combined photovoltage and absorption measurements in the 1-15 ns time range

Fast photovoltage measurements in Rhodospirillum rubrum chromatophores in the nanosecond time range, escorted by time-resolved absorption measurements, are described. Under reducing conditions, the photovoltage decayed significantly faster than the spectroscopically detected charge recombination of the radical pair P(+)H(A)(-). This indicates the occurrence of considerable dielectric relaxations. Our data and data from the literature were analyzed by means of a reaction scheme consisting of three states, namely, A, P, and P(+)H(A)(-). A time-dependent DeltaG(t) was introduced by assuming a time-dependent rate constant of the back-reaction, k(-1)(t). With the exception of the latter rate constant, all other parameters of the model are reliably known within narrow limits. This allowed us to distinguish between the three cases assumed for DeltaG degrees (t): (1)DeltaG degrees (t) = constant; (2)DeltaG degrees (t) as published by Peloquin et al. [Peloquin, J. M., Williams, J. C., Lin, X. M., Alden, R. G., Taguchi, A. K. W., Allen, J. P., and Woodbury, N. W. (1994) Biochemistry 33, 8089-8100]; and a (3)DeltaG degrees (t) that fits the present data. The assumption that (1)DeltaG degrees (t) = constant is incompatible with our photovoltage data, and (2)DeltaG degrees (t) is incompatible with the constraint that the ratio of fluorescence yields in the closed and open state is F(m)/F(o) approximately 2. We specify a (3)DeltaG degrees (t) that should be valid for photosynthetic reaction centers in vivo. Furthermore, the overall kinetics of the electric relaxation, e(t), in response to the primary charge separation were determined.