Single-molecule Immunoassay Research Articles

Ultrasensitive Single-Molecule Biosensor by Periodic Modulation of Magnetic Particle Motion.

Ultrasensitive detection of low-abundance biomarkers by modern single-molecule technologies is critical for better diagnosis of severe diseases, but inevitable nonspecific bindings often cause fluctuations in the single-molecule counting results. Here we present an approach to improve the specificity in a single-molecule immunoassay by translating molecular binding signals into periodic nanomotion of magnetic particles. The sandwiched immunoassay is modified by using a long linker to tether one antibody onto a gold-covered substrate and a magnetic particle with another antibody coated as the reporter. By actively oscillating the particles with alternating magnetic fields, we could reliably identify specific binding through intensity fluctuation in plasmonic images of single particles. As a proof of concept, we demonstrate the detection of IFN-γ at the femtomolar level by the digital counting of specifically bound molecules. This active strategy outperforms existing passive motion-based approaches in sensitivity and speed, paving the way for disease diagnosis with low-abundance biomarkers.

Application of ultrasensitive single molecule immunoassay technology in clinical biomarker detection

Single-molecule immunoassay technology represents an ultrasensitive immunoassay method that enables the resolution and detection of individual biomolecules at the nanoscale. This article highlights various representative techniques and clinical applications of single-molecule immunoassay technology, while also discussing the current challenges and future development directions. Through multiple optimizations at both the technical and commercial levels, single-molecule immunoassay technology exhibits unique advantages in real-time detection, disease diagnosis and treatment, and medical research. This technology is poised to contribute to the advancement of precision medicine by integrating individualized detection methods into clinical practice.

353 Amlitelimab reduces serum IL-13 in a phase 2a clinical trial in atopic dermatitis without impacting T-cell expansion in a T-cell recall assay

Abstract Amlitelimab (SAR445229), a fully human non-depleting, non-cytotoxic, monoclonal antibody, binds to OX40Ligand (OX40L) on antigen-presenting cells (APC) to block OX40-OX40L interactions. In a 16-week, double-blind, Phase 2a trial (NCT03754309), amlitelimab induced clinically meaningful disease activity improvement in patients with moderate-to-severe atopic dermatitis (AD). To assess the effects of amlitelimab on interleukin (IL)-13 and T-cell recall responses. In the trial, 89 patients were randomized to amlitelimab low dose (LD; 200 mg loading/100 mg maintenance every 4 weeks [Q4W]), high dose (HD; 500 mg loading/250 mg maintenance Q4W), or placebo. Serum IL-13 levels were assessed by single molecule immunoassay (259 samples). Using human peripheral blood mononuclear cells from five healthy donors, a T-cell recall assay was performed. At baseline in the trial, IL-13 levels significantly correlated with disease severity (Eczema Area and Severity Index; r = 0.4784, P < 0.0001). Week 16 IL-13 levels were significantly reduced with amlitelimab vs. baseline but not placebo (median fold change [95% confidence interval, CI] from baseline to week 16 with P-values based on two-way Analysis of Variance [ANOVA] of log10-transformed fold change for patients with a complete dataset at week 16: LD 0.345 [0.23–0.44], P < 0.0001; HD 0.390 [0.30–0.63], P = 0.0002; placebo 0.835 [0.34–1.12], P = 0.1544). In a T-cell recall assay, amlitelimab significantly reduced IL-13 protein levels at days 3 and 6 without negatively impacting T-cell expansion, based on the percentage of proliferating CD4+ T-cells vs. isotype control. Amlitelimab decreased IL-13 levels in patients with AD and in a T-cell recall assay without negative effects on T-cell expansion, thus reducing inflammation without blocking T-cell proliferation during recall responses.

345 Treatment with amlitelimab—a novel non-depleting, non-cytotoxic anti-OX40Ligand monoclonal antibody—reduces IL-22 serum levels in a phase 2a randomized, placebo-controlled trial in patients with moderate-to-severe atopic dermatitis

Abstract OX40Ligand (OX40L) upregulation on antigen-presenting cells (APCs) following antigen presentation contributes to the survival and functional activation of T helper (Th) 2 and Th1/17/22 cells, which are central to the inflammation and pathological outcomes in atopic dermatitis (AD). In a Phase 2a trial (NCT03754309), amlitelimab, a fully human, non-depleting, non-cytotoxic anti-OX40L monoclonal antibody, was effective in treating patients with moderate-to-severe AD. To assess the effects of amlitelimab on interleukin (IL)-22, an important Th22-associated disease mediator of AD. 89 patients with moderate-to-severe AD were enrolled in a Phase 2a randomized, double-blind, placebo-controlled, multicentre trial and randomized 1 : 1 : 1 to intravenous amlitelimab low dose (200 mg loading/100 mg maintenance every 4 weeks [Q4W]; n = 29), high dose (500 mg/250 mg Q4W; n = 30) or placebo (Q4W; n = 29) until week 12. The primary efficacy endpoint was the percentage change in Eczema Area and Severity Index (EASI) from baseline to week 16. Other disease severity measurements included SCORing of Atopic Dermatitis (SCORAD) and validated Investigator Global Assessment (vIGA). Serum was collected at baseline, week 4 and week 16, and further collected at week 24 and week 36 in responders, defined as patients who reached vIGA 0/1 at week 16. IL-22 levels were determined by ultrasensitive single-molecule immunoassay (Simoa). Of 88 subjects who received study treatment, 59 were evaluable at week 16. Amlitelimab was well tolerated with an unremarkable safety profile. The mean percentage change in EASI from baseline at week 16 was −80.12% for amlitelimab low dose and −69.97% for amlitelimab high dose vs. −49.37% for placebo (nominal P-values: 0.009 [amlitelimab low dose vs. placebo] and 0.072 [amlitelimab high dose vs. placebo]). Amlitelimab-treated patients who achieved vIGA 0/1 at week 16 had sustained clinical responses up to week 36. No difference in IL-22 serum levels was found between groups at baseline. IL-22 levels correlated with disease severity at baseline, as measured by EASI and SCORAD (r = 0.53, P < 0.0001; and r = 0.36, P = 0.001; respectively). A significant reduction in IL-22 levels was observed at week 16 in amlitelimab-treated patients (low dose P < 0.0001; high dose P = 0.001), but not in the placebo group (P = 0.381). The amlitelimab-induced decrease in IL-22 levels was maintained until week 36 in those defined as vIGA 0/1 responders at week 16. OX40L blockade on APCs represents a promising novel approach in the treatment of AD by effectively targeting underlying T-cell immune dysregulation. Amlitelimab monotherapy not only provided a sustained and clinically meaningful improvement in disease activity compared with placebo in patients with moderate-to-severe AD, but also significantly decreased serum levels of IL-22, a Th22 cell-associated cytokine involved in the underlying immunopathogenesis of AD.

Elevated Levels of the Cytokine LIGHT in Pediatric Crohn's Disease.

LIGHT (homologous to lymphotoxins, exhibits inducible expression, and competes with HSV glycoprotein D for herpes virus entry mediator, a receptor expressed by T lymphocytes), encoded by the TNFSF14 gene, is a cytokine belonging to the TNF superfamily. On binding to its receptors, herpes virus entry mediator and lymphotoxin β receptor, it activates inflammatory responses. We conducted this study to determine whether plasma LIGHT levels are elevated in Crohn's disease (CD) in a pediatric population with the aim of nominating this cytokine as a therapeutic target. We used a single-molecule immunoassay to determine the circulating levels of free LIGHT in plasma from pediatric patients with CD in our biobank (n = 183), a panel of healthy pediatric (n = 9) or adult (n = 22) reference samples, and pediatric biobank controls (n = 19). We performed correlational analyses between LIGHT levels and the clinical characteristics of the CD cohort, including age, Montreal classification, family history, medical/surgical therapy, and routine blood test parameters. LIGHT levels were greatly elevated in CD, with an average of 305 versus 32.4 pg/ml for controls from the biobank (p < 0.0001). The outside reference samples showed levels of 57 pg/ml in pediatric controls and 55 pg/ml in adults (p < 0.0001). We found a statistically significant correlation between white blood cell count and free LIGHT (p < 0.046). We conclude that free, soluble LIGHT is increased 5- to 10-fold in pediatric CD across an array of disease subtypes and characteristics.

Serum phosphorylated tau protein 181 and neurofilament light chain in cognitively impaired heart failure patients

BackgroundChronic heart failure (HF) is known to increase the risk of developing Alzheimer’s dementia significantly. Thus, detecting and preventing mild cognitive impairment, which is common in patients with HF, is of great importance. Serum biomarkers are increasingly used in neurological disorders for diagnostics, monitoring, and prognostication of disease course. It remains unclear if neuronal biomarkers may help detect cognitive impairment in this high-risk population. Also, the influence of chronic HF and concomitant renal dysfunction on these biomarkers is not well understood.MethodsWithin the monocentric Cognition.Matters-HF study, we quantified the serum levels of phosphorylated tau protein 181 (pTau) and neurofilament light chain (NfL) of 146 extensively phenotyped chronic heart failure patients (aged 32 to 85 years; 15.1% women) using ultrasensitive bead-based single-molecule immunoassays. The clinical work-up included advanced cognitive testing and cerebral magnetic resonance imaging (MRI).ResultsSerum concentrations of NfL ranged from 5.4 to 215.0 pg/ml (median 26.4 pg/ml) and of pTau from 0.51 to 9.22 pg/ml (median 1.57 pg/ml). We detected mild cognitive impairment (i.e., T-score < 40 in at least one cognitive domain) in 60% of heart failure patients. pTau (p = 0.014), but not NfL, was elevated in this group. Both NfL (ρ = − 0.21; p = 0.013) and pTau (ρ = − 0.25; p = 0.002) related to the cognitive domain visual/verbal memory, as well as white matter hyperintensity volume and cerebral and hippocampal atrophy. In multivariable analysis, both biomarkers were independently influenced by age (T = 4.6 for pTau; T = 5.9 for NfL) and glomerular filtration rate (T = − 2.4 for pTau; T = − 3.4 for NfL). Markers of chronic heart failure, left atrial volume index (T = 4.6) and NT-proBNP (T = 2.8), were further cardiological determinants of pTau and NfL, respectively. In addition, pTau was also strongly affected by serum creatine kinase levels (T = 6.5) and ferritin (T = − 3.1).ConclusionspTau and NfL serum levels are strongly influenced by age-dependent renal and cardiac dysfunction. These findings point towards the need for longitudinal examinations and consideration of frequent comorbidities when using neuronal serum biomarkers.

34312 Treatment with amlitelimab (KY1005, SAR445229): A novel nondepleting anti-OX40Ligand (OX40L) mAb reduces IL-13 serum levels in a phase 2a randomized placebo-controlled trial in patients with moderate to severe atopic dermatitis

Introduction: OX40Ligand-induced signaling promotes survival and functional activation of OX40+ Th2/Th17/Th22/Th1 cells, which are involved in atopic dermatitis (AD) pathogenesis and disease progression. In a phase 2a trial amlitelimab, a human nondepleting monoclonal anti-OX40Ligand antibody, was effective in treating patients with moderate to severe AD. Here we assessed its effects on interleukin (IL) 13, an important biomarker in AD. Methods and materials: Serum was collected during the Ph2a trial (NCT03754309, Kymab, a Sanofi Company-funded, double-blind, RCT). 89 moderate-to-severe AD patients were randomised 1:1:1 to intravenous amlitelimab low dose (LD, 200 mg loading/100 mg maintenance Q4W), high dose (HD, 500 mg/250 mg Q4W) or placebo (PBO). Disease severity measurement included EASI. Serum IL-13 levels were determined by single molecule immunoassay (Simoa). Results: Of 59 subjects who received amlitelimab, 44 were evaluable at W16. Amlitelimab was well tolerated with unremarkable safety profile. Mean % change in EASI from baseline (BL) at the primary end-point (Week16) was -80.1% for LD and -69.9% for HD vs -49.4% for PBO (P = .009 and .072 respectively). No BL difference in IL13 was found between groups. IL-13 levels correlated with disease severity at BL (r = 0.4784, P < .0001). A significant reduction in IL13 levels was observed at Week16 in Amlitelimab-treated patients (LD P < .0001; HD P = .0003) but not PBO (P = .1558). Conclusions: OX40Ligand blockade on APCs represents a promising novel approach in the treatment of AD. Amlitelimab monotherapy not only induced significant improvement in moderate-to-severe AD patients, but also significantly decreased serum IL13 levels, a Th2 cytokine associated with the underlying immunopathogenesis of AD.

Serum glial fibrillary acidic protein indicates memory impairment in patients with chronic heart failure.

AimsCognitive dysfunction occurs frequently in patients with heart failure (HF), but early detection remains challenging. Serum glial fibrillary acidic protein (GFAP) is an emerging biomarker of cognitive decline in disorders of primary neurodegeneration such as Alzheimer's disease. We evaluated the utility of serum GFAP as a biomarker for cognitive dysfunction and structural brain damage in patients with stable chronic HF.Methods and resultsUsing bead‐based single molecule immunoassays, we quantified serum levels of GFAP in patients with HF participating in the prospective Cognition.Matters‐HF study. Participants were extensively phenotyped, including cognitive testing of five separate domains and magnetic resonance imaging (MRI) of the brain. Univariable and multivariable models, also accounting for multiple testing, were run. One hundred and forty‐six chronic HF patients with a mean age of 63.8 ± 10.8 years were included (15.1% women). Serum GFAP levels (median 246 pg/mL, quartiles 165, 384 pg/mL; range 66 to 1512 pg/mL) did not differ between sexes. In the multivariable adjusted model, independent predictors of GFAP levels were age (T = 5.5; P < 0.001), smoking (T = 3.2; P = 0.002), estimated glomerular filtration rate (T = −4.7; P < 0.001), alanine aminotransferase (T = −2.1; P = 0.036), and the left atrial end‐systolic volume index (T = 3.4; P = 0.004). NT‐proBNP but not serum GFAP explained global cerebral atrophy beyond ageing. However, serum GFAP levels were associated with the cognitive domain visual/verbal memory (T = −3.0; P = 0.003) along with focal hippocampal atrophy (T = 2.3; P = 0.025).ConclusionsSerum GFAP levels are affected by age, smoking, and surrogates of the severity of HF. The association of GFAP with memory dysfunction suggests that astroglial pathologies, which evade detection by conventional MRI, may contribute to memory loss beyond ageing in patients with chronic HF.

Differential levels of plasma biomarkers of neurodegeneration in Lewy body dementia, Alzheimer’s disease, frontotemporal dementia and progressive supranuclear palsy

ObjectivesThis longitudinal study compared emerging plasma biomarkers for neurodegenerative disease between controls, patients with Alzheimer’s disease (AD), Lewy body dementia (LBD), frontotemporal dementia (FTD) and progressive supranuclear palsy (PSP).MethodsPlasma phosphorylated...

Comparison between plasma and cerebrospinal fluid biomarkers for the early diagnosis and association with survival in prion disease

ObjectiveTo compare the diagnostic accuracy and the prognostic value of blood and cerebrospinal fluid (CSF) tests across prion disease subtypes.MethodsWe used a single-molecule immunoassay to measure tau and neurofilament light...

Avidity-Based Affinity Enhancement Using Nanoliposome-Amplified SPR Sensing Enables Low Picomolar Detection of Biologically Active Neuregulin 1.

Biomarkers serve as indicators of disease progression or therapeutic response of an medical intervention, and means for enabling a reliable and sensitive biomarker detection are therefore vital in clinical settings. Most biosensor assays require high-affinity interactions in combination with an enzyme or fluorescent tag to enable detection and frequently employ extensive washing procedures prior to signal readout. Attempts to overcome this limitation by using natural biological partners tend to be demanding, because their very low affinity is frequently not compatible with the need of reaching low limits of detection (LODs), especially for circulating biomarkers that possess short half-lives. To address these challenges, we developed a label-free surface plasmon resonance (SPR) platform for the detection of neuregulin 1 (NRG1) using ErbB4-modified liposomes offering both signal amplification and affinity enhancement via functional multivalent interactions. Through the functional avidity interaction between NRG1 and ErbB4, an LOD of 3.5 picomolar was reached, which is about 60-fold higher than traditional SPR and miniaturized immunoassays. The biosensor displays also an 8-fold higher sensitivity when compared with a single-molecule immunoassay employing the natural binding partner rather than a high-affinity antibody as one of the interaction partners. In fact, the liposome-induced avidity between NRG1 and ErbB4 offered an LOD that was comparable to that obtained using a high-affinity antibody and enabled detection of NRG1 in plasma with a LOD of 36 pM. Employing the liposome-enhanced platform in conjunction with a low-affinity biomarker receptor thus enables the assessment of the functional state of the biomarker at competitive LODs and eliminates the need for high-affinity antibodies.

Characterisation of serum total tau following paediatric traumatic brain injury: a case-control study

Traumatic brain injury (TBI) is a major health problem in children. Blood-based biomarkers interpreted by use of normative values might improve the accuracy of diagnosis. Ultrasensitive assays can quantify serum concentrations of the neuronal microtubule-associated protein tau, which is increased in adult brains following TBI. We aimed to determine if serum total tau correlates with TBI diagnosis, severity, and radiological findings on CT scans in children younger than 18 years. In this case-control study, we included venous blood samples from healthy control children in the Canadian Laboratory Initiative on Pediatric Reference Intervals (CALIPER) biobank. For TBI cases, we recruited children (aged 0-17 years) who presented to the emergency department within 24 h of a TBI in three tertiary-care paediatric hospitals (Toronto, Vancouver, and Melbourne). Children were eligible if they required hospital observation for a minimum of 4 h or admission to the intensive care unit, and were excluded if they had had hospital treatment for a previous TBI, had birth trauma, or their parents could not speak English or French and therefore could not readily give consent. All available control samples were used and a case-control match was therefore not done. Venous and arterial blood samples were collected from patients with TBI within 28 h of injury (day 1). We used an ultrasensitive single-molecule immunoassay to measure serum total tau in blood samples. We first generated reference intervals of serum total tau from the control group, and used these normative data to interpret injury-associated changes in serum total tau in children with TBI. Concentrations of serum tau were measured in all CALIPER participants and patients with TBI, and no participants were excluded before analysis. We included samples from 416 control participants from the CALIPER cohort. Median total tau concentrations did not differ between sexes (p=0·12), but three significant reference intervals based on age groups were identified (1-3 years [0·88-19·2 pg/mL], 4-15 years [0·93-5·31 pg/mL], and 16-19 years [0·79-4·20 pg/mL]). Blood samples were obtained from 158 patients with TBI recruited between April 30, 2011, and June 28, 2013. Serum total tau on day 1 of TBI was negatively associated with Glasgow Coma Scale (GCS) score (rs=-0·42, 95% CI -0·55 to -0·28, p<0·0001). Median total tau was 2·86 pg/mL (IQR 1·52-4·83) in patients with GCS score 13-15 points (n=114), 7·08 pg/mL (3·75-41·1) in those with GCS score 9-12 points (n=13), and 8·48 pg/mL (2·53-70·6) in those with GCS score 3-8 points (n=31). Notably, participants who had GCS scores of 15 points had median total tau concentrations (2·57 pg/mL [1·50-4·61]) indistinguishable from those of control participants (2·46 pg/mL [1·77-3·42]), whereas those with GCS score 13-14 points had elevated total tau (6·41 pg/mL [2·97-42·5]). Serum total tau was not strongly associated with CT findings in patients with mild TBI. Serum total tau might help to differentiate between patients with mild TBI (GCS 13-14 vs GCS 15), but larger studies are needed to validate these results before this biomarker can be used for diagnosis and prognosis. Canadian Institutes of Health Research, Ontario Neurotrauma Foundation, and Victoria Neurotrauma Foundation.

Development of a three-plex single molecule immunoassay enabling measurement of the EGFR ligands amphiregulin, betacellulin and transforming growth factor α simultaneously in human serum samples

BackgroundPrior to large studies in breast cancer patients and healthy individuals we established a sensitive three-plex immunoassay to measure the EGFR ligands amphiregulin (AR), betacellulin (BTC) and transforming growth factor α (TGF-α) simultaneously in human serum samples. MethodThe three-plex immunoassay was developed using single molecule array (Simoa) technology and requires only 20 μL of serum. ResultsAR, BTC and TGF-α were first established as three single-plex assays. Multiplexing the three single-plex assays showed no significant cross reactivity between the reagents. The concentrations of the ligands in serum samples showed correlations r2 ≥ 0.84 between the single-plex and three-plex methods. The three-plex assay demonstrated limit of detection levels at 0.16 ng/L for AR, 0.23 ng/L for BTC and 0.22 ng/L for TGF-α. Total coefficients of variations were 8.5%–31% for AR, 11%–21.8% for BTC and 12.4%–16.2% for TGF-α. Spiking experiments showed a mean recovery of 97% for AR, 86% for BTC and 81% for TGF-α. The concentrations of the EGFR ligands did not change significantly after series of freeze thaw cycles or incubation at 22 °C for up to 24 h. ConclusionThis robust three-plex assay with up to 40-fold increase in sensitivity relative to conventional ELISA is the first published method that has the required sensitivity to measure AR, BTC and TGF-α simultaneously in human blood samples.

Molecular-Counting-Free and Electrochemiluminescent Single-Molecule Immunoassay with Dual-Stabilizers-Capped CdSe Nanocrystals as Labels.

Biorelated single-molecule detection (SMD) has been achieved typically by imaging the redox fluorescent labels and then determining each label one by one. Herein, we demonstrated that the capping agents (i.e., mercaptopropionic acid and sodium hexametaphosphate) can facilitate the electrochemical involved hole (or electron) injecting process and improve the stability of the dual-stabilizers-capped CdSe nanocrystals (NCs), so that the CdSe NCs could be electrochemically and repeatedly inspired to excited states by giving off electrochemiluminescence (ECL) in a cyclic pattern. With the CdSe NCs as ECL label and carcinoembryonic antigen (CEA) as target molecule, a convenient single-molecule immunoassay was proposed by simply detecting the ECL intensity of the dual-stabilizers-capped CdSe NCs in a sandwich-typed immune complex. The limit of detection is 0.10 fg/mL at S/N = 3, which corresponds to about 6-8 CEA molecules in 20 μL of serum sample. Importantly, the ECL spectra of both CdSe NCs and its conjugate with probe antigen in the immune complex were almost identical to the photoluminescence spectrum of bare CdSe NCs, indicating that all emissions were originated from the same excited species. The molecular-counting-free and ECL-based SMD might be a promising alternative to the fluorescent SMD.

A fully-automated, six-plex single molecule immunoassay for measuring cytokines in blood

We report a system and assay for performing fully-automated measurement of 6 proteins simultaneously with single molecule sensitivity. The system combines handling of samples, reagents, and consumables, with a module for imaging single molecule arrays (Simoa) to enable immunoassays that have high sensitivity (~fg/mL), are multiplexed, and are fully-automated. A 6-plex cytokine Simoa assay for IL-6, TNF-α, GM-CSF, IL-10, IL-1β, and IL-1α was developed on the system. The assays had limits of detection in the range 0.01–0.03pg/mL, and the average imprecision (CV) of the Simoa signal was 4.2%. This assay was used to measure the concentrations of these cytokines in the plasma of patients with Crohn's Disease (CD), before and after treatment with anti-TNF-α antibody drugs, and in the serum of Type 1 diabetics. Concentrations of TNF-α and IL-6 in the CD samples determined using the fully-automated, multiplex Simoa assay had good correlation with the manual, single-plex assays previously reported. Drug treatment caused reductions in the mean concentration of all 6 cytokines in the plasma of CD patients. The concentrations of 4 cytokines were significantly higher in diabetics compared to healthy controls. The system could enable the widespread, multiplexed measurement of protein biomarkers with low abundance.

Clinical evaluation of a novel method for the measurement of prostate‐specific antigen, AccuPSATM, as a predictor of 5‐year biochemical recurrence‐free survival after radical prostatectomy: results of a pilot study

Study Type - Diagnostic (validating cohort) Level of Evidence 1b What's known on the subject? and What does the study add? Nadir Ultrasensitive PSA levels has some value for predicting BCR following RD. AccuPSA assays lower limit of PSA quantification of <0.01 pg/ml greatly enhances sensitivity and specificity of nadir PSA to predict BCR following RP. Our pilot study shows an AccuPSA of 3 pg/ml has a sensitory and specificity of 100% and 75% respectively for predicting 5 year BCR following RP. OBJECTIVES • To conduct a proof of concept study to evaluate a novel digital single molecule immunoassay (AccuPSA(TM) ) that detects prostate-specific antigen (PSA) a thousandfold more sensitively than current PSA detection methods. • To determine the ability of the AccuPSA(TM) assay to predict 5-year biochemical recurrence (BCR)-free survival after radical prostatectomy (RP). PATIENTS AND METHODS • A total of 31 frozen serum specimens were obtained from specimen logs maintained at New York University Langone Medical Center and the Johns Hopkins University School of Medicine on men who had undergone RP. Those men without evidence of BCR had a minimum of 5 years' PSA follow-up. • In all cases, preoperative and pathological information were available, as was a serum specimen 3-6 months after RP, with a PSA level of <0.1 ng/mL measured by conventional PSA methods at the time of serum collection. • Specimens were tested using the AccuPSA(TM) method. • A Cox proportional hazard model and Kaplan-Meier analysis were used to determine whether AccuPSA(TM) predicted the risk of BCR. RESULTS • Overall, 11/31 (35.5%) men developed BCR. • Mean AccuPSA(TM) nadir levels were significantly different (P < 0.001) between the non-BCR group (2.27 pg/mL) and the BCR group (46.99 pg/mL). • Using a multivariate Cox proportional hazard model, AccuPSA(TM) nadir level was a significant predictor of BCR-free survival (P < 0.01). • Kaplan-Meier analysis of up to 5 years follow-up showed that 100% of men with AccuPSA(TM) nadir values <3 pg/mL did not develop BCR, whereas 62.5% of men with values >3 pg/mL developed BCR (P= 0.00024). • The sensitivity, specificity, positive predictive value and negative predictive value of the AccuPSA(TM) method was 100%, 75%, 69% and 100%, respectively. CONCLUSIONS • AccuPSA(TM) assay predicts 5-year BCR- free survival after RP. • Identifying a reliable predictor of BCR soon after RP has important implications for frequency of PSA testing, selection of candidates for adjuvant therapy, and reassuring a large subset of men that they are not at risk of recurrence. • Larger studies are needed to validate these findings.

Abstract 5163: Elevations of intracellular kinases AKT1, GSK3β, JNK1, JNK2 and ERK2 in primary breast cancer tissue quantified with a novel multi-panel of single molecule immunoassays

Abstract The MAPK and PI3K signaling cascades are critical pathways in malignant transformation, tumor progression and multi-drug resistance (MDR) of human cancers. Clinical investigations into the role of phosphorylation of specific kinases are hindered by the lack of ultra-sensitive assay technology with requisite isoform- and phophorylation-state specificity. Improved assays are necessary to determine clinical relevance and potential diagnostic utility with a high degree of specificity. We tested adjacent normal and primary breast cancer tissue lysates with a novel panel of ten immunoassays for quantifying the total and phosphorylated forms of AKT1, GSK3β, JNK1, JNK2 and ERK2. The ultra-sensitive assay panel was developed for use with the Erenna® Immunoassay System (Singulex), which uses single molecule detection technology. Analytical sensitivity, inter-assay precision, linearity and specificity were determined and compared to corresponding ELISA assays. The novel assay panel was validated in HeLa and Jurkat cell lysates, region of linearity was determined, and phospho-specificity of each assay was confirmed. All assays were validated for use in human plasma, cell culture lysates, and human tissue specimens. Results in matched breast cancer tissue lysates showed that all total kinase concentrations (tAKT1, tGSK3β, tERK2, tJNK1 and tJNK2) were found to be elevated in primary tumors compared to surrounding adjacent normal tissue, however concentrations of phosphorylated forms (pAKT1, pGSK3β, pERK2, pJNK1 and pJNK2) were not. All ten novel assays displayed exceptional linearity (R2=0.99) and precision (%CV 4.1 – 9.6), and were significantly more sensitive than the corresponding ELISA assay method based upon sample endpoint dilutions. The detection limits of the tAKT1, pAKT1, tGSK3β, pGSK3β, pERK2, tJNK2 and pJNK2 assays were all ≤0.3 pg/mL, while the detection limit of tERK2 was &amp;lt; 2pg/mL, tJNK1 was 4.5 pg/mL, and pJNK1 was 7 pg/mL. The LLoQ of each assay in the panel was sufficient for quantification from a minimum of approximately 100-200 cells, with exception of the total JNK1 assay, which required a minimum of approximately 800 cells in order to be quantifiable. We show that significant elevations in total kinase concentrations of tAKT1, tGSK3β, tERK2, tJNK1 and tJNK2 can be quantified in primary tumors compared to surrounding adjacent tissue using a panel of isoform- and phosphorylation-specific single molecule immunoassays. We have further demonstrated that assays in this panel can quantify analytes from as little as 100 cells, and exhibit superior analytical performance over ELISA based methods. Thus, these novel assays greatly improve upon pre-existing ELISA technology that is limited by assay sensitivity, providing a new tool for clinical investigations of the MAPK and PI3K signaling cascades. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5163. doi:10.1158/1538-7445.AM2011-5163

Abstract A26: Elevations of intracellular kinases AKT1, GSK3β, JNK1, JNK2, and ERK2 in primary breast cancer tissue quantified with a novel multipanel of single-molecule immunoassays

Abstract Purpose: The MAPK and PI3K signaling cascades are critical pathways in malignant transformation, tumor progression and multidrug resistance (MDR) of human cancers. Elucidation of the relative contributions of distinct kinases is made difficult due to many factors, including prevalence of multiple isoforms, posttranslational modifications, synergistic activation and pathway crosstalk. Clinical investigations into the role of phosphorylation of specific kinases are further hindered by the lack of ultrasensitive assay technology with requisite isoform- and phophorylation-state specificity. Improved assays are necessary to determine clinical relevance and potential diagnostic utility with a high degree of specificity. Methods: Adjacent normal and primary breast cancer tissue lysates were analyzed using a novel panel of ten immunoassays for quantifying the total and phosphorylated forms of AKT1, GSK3β, JNK1, JNK2 and ERK2. The ultrasensitive assay panel was developed for use with the Erenna® Immunoassay System (Singulex), which uses single molecule detection technology. Analytical sensitivity, interassay precision, linearity, and specificity were determined and compared to corresponding ELISA assays. The novel assay panel was validated in HeLa and Jurkat cell lysates, region of linearity was determined, and phospho-specificity of each assay was confirmed. All assays were validated for use in human plasma, cell culture lysates, and human tissue specimens. Results: Testing in matched breast cancer tissue lysates showed that all total kinase concentrations (tAKT1, tGSK3β, tERK2, tJNK1 and tJNK2) were found to be elevated in primary tumors compared to surrounding adjacent normal tissue, however concentrations of phosphorylated forms (pAKT1, pGSK3β, pERK2, pJNK1 and pJNK2) were not. All ten novel assays displayed exceptional linearity (R2=0.99) and precision (%CV 4.1 – 9.6), and were significantly more sensitive than the corresponding ELISA assay method based upon sample endpoint dilutions. The detection limits of the tAKT1, pAKT1, tGSK3β, pGSK3β, pERK2, tJNK2 and pJNK2 assays were all ≤0.3 pg/mL, while the detection limit of tERK2 was &amp;lt; 2pg/mL, tJNK1 was 4.5 pg/mL, and pJNK1 was 7 pg/mL. The LLoQ of each assay in the panel was sufficient for quantification from a minimum of approximately 100 to 200 cells, with exception of the total JNK1 assay, which required a minimum of approximately 800 cells in order to be quantifiable. Conclusions: We show that significant elevations in total kinase concentrations of tAKT1, tGSK3β, tERK2, tJNK1 and tJNK2 can be quantified in primary tumors compared to surrounding adjacent tissue using a panel of isoform- and phosphorylation-specific single molecule immunoassays. We have further demonstrated that assays in this panel can quantify analytes from as little as 100 cells, and exhibit superior analytical performance over ELISA based methods. Thus, these novel assays greatly improve upon pre-existing ELISA technology that is limited by assay sensitivity, providing a new tool for clinical investigations of the MAPK and PI3K signaling cascades. Citation Information: Clin Cancer Res 2010;16(14 Suppl):A26.

A single molecule immunoassay by localized surface plasmon resonance

Noble metal nanoparticles exhibit sharp spectral extinction peaks at visible andnear-infrared frequencies due to the resonant excitation of their free electrons, termedlocalized surface plasmon resonance (LSPR). Since the resonant frequency is dependent onthe refractive index of the nanoparticle surroundings, LSPR can be the basis for sensingmolecular interactions near the nanoparticle surface. However, previous studies have notyet determined whether the LSPR mechanism can reach the ultimate sensing limit: thedetection of individual molecules. Here we demonstrate single molecule LSPR detection bymonitoring antibody–antigen unbinding events through the scattering spectra ofindividual gold bipyramids. Both experiments and finite element simulationsindicate that the unbinding of single antigen molecules results in small, discrete < 0.5 nm blue-shifts of the plasmon resonance. The unbinding rate is consistent withantibody–antigen binding kinetics determined from previous ensemble experiments.According to these results, the effective refractive index of a single protein is approximately1.54. LSPR sensing could therefore be a powerful addition to the current toolbox of singlemolecule detection methods since it probes interactions on long timescales and underrelatively natural conditions.

Protein Quantification in Complex Mixtures by Solid Phase Single-Molecule Counting

Here we present a procedure for quantifying single protein molecules affixed to a surface by counting bound antibodies. We systematically investigate many of the parameters that have prevented the robust single-molecule detection of surface-immobilized proteins. We find that a chemically adsorbed bovine serum albumin surface facilitates the efficient detection of single target molecules with fluorescent antibodies, and we show that these antibodies bind for lengths of time sufficient for imaging billions of individual protein molecules. This surface displays a low level of nonspecific protein adsorption so that bound antibodies can be directly counted without employing two-color coincidence detection. We accurately quantify protein abundance by counting bound antibody molecules and perform this robustly in real-world serum samples. The number of antibody molecules we quantify relates linearly to the number of immobilized protein molecules (R(2) = 0.98), and our precision (1-5% CV) facilitates the reliable detection of small changes in abundance (7%). Thus, our procedure allows for single, surface-immobilized protein molecules to be detected with high sensitivity and accurately quantified by counting bound antibody molecules. Promisingly, we can probe flow cells multiple times with antibodies, suggesting that in the future it should be possible to perform multiplexed single-molecule immunoassays.