Homogeneous Mobility Shift Assay Research Articles

Evaluation of the Homogenous Mobility Shift Assay for Infliximab and Adalimumab Anti-drug Antibody Detection in the Clinical Laboratory.

Detecting antidrug antibodies (ADAs) against infliximab or adalimumab is useful for therapeutic drug monitoring. Various ADA detection methods exist, and antibody titer is an output in some algorithms. Homogenous mobility shift assay (HMSA) measures relative ADA concentration and determines drug-ADA complex size in vitro. However, the relevance of complex size determination in drug monitoring remains unclear. Hence, the association between complex size, ADA concentration, and sample detectable neutralizing activity was evaluated. Sera from infliximab-treated and adalimumab-treated patients who tested positive for ADA in the National Screening Service were analyzed using 3 ADA assays. HMSA determined the relative ADA concentrations and complex sizes, competitive ligand-binding assay evaluated the sample neutralizing capacity, and enzyme-linked immunosorbent assay detected immunoglobulin (Ig)G4 ADA. Most ADA-positive samples (>80%) formed drug-ADA dimer complexes, whereas 17% had dimer and multimer complexes, and 3% had multimeric complexes. Multimer presence had 100% positive predictive value for detectable neutralizing activity. ADA concentration and detectable neutralizing activity were moderately correlated (r = 0.65) in adalimumab-treated patients and strongly correlated (r = 0.81) in infliximab-treated patients. In adalimumab-treated patients, multimer presence was a stronger predictor of neutralizing activity than ADA concentration was, but not in infliximab-treated patients. However, in infliximab-treated patient samples, multimer presence revealed a distinct subset with high ADA concentrations, neutralizing activity, and IgG4 ADA. Multimers detected using HMSA had a strong positive predictive value for competitive ligand-binding assay detectable neutralizing activity. Multimeric IgG4-containing ADA-drug complexes revealed a distinct subset of infliximab-treated patient samples, whose clinical relevance merits further investigation.

P966 The intra-patient variability of adalimumab clearance during an intensive sampling study of Crohn’s disease patients receiving maintenance therapy

Abstract Background Lower adalimumab (ADA) clearance (CL) is associated with improved outcomes in Crohn’s disease (CD) and may be a superior pharmacokinetic (PK) measure than ADA concentrations. We compared intra-patient variability in ADA CL and concentrations within a 14-day treatment cycle and across two consecutive cycles under maintenance treatment. Methods In a previous PK study of CD patients receiving maintenance ADA 40mg fortnightly, samples were collected intensively at 3 visits (day 4-6, 7-9, and 13-14 post dose) across 2 consecutive cycles. Available sera from this cohort were subsequently used to measure ADA concentrations (lower limit quantification: <1.6 µg/mL) and antibody to adalimumab (ATA) status using a drug tolerant homogeneous mobility shift assay, and albumin. Apparent ADA CL (L/day) was calculated incorporating these measure parameters in a nonlinear mixed effect model with Bayesian priors (under steady state assumption) with dose and inter-dose interval with ATA and albumin as covariate. Rates of sustained clinical and biochemical remission (Harvey Bradshaw Index (HBI) score consistently <5 and CRP levels consistently <3 mg/L) were estimated for each patient. Longitudinal changes in PK parameters within-and-across cycles were evaluated using intra-patient coefficient of variation and linear mixed effect models. Results Sera was available from 70 study visits in 12 patients (6 males, mean age 36 years). Median ADA concentrations and CL were 8 µg/mL (IQR 6.0-10.4) and 0.374 L/day (IQR 0.29-0.43), respectively, with ATA detected in one patient (#9). Estimated ADA concentrations and CL is presented in the Table. Intra-patient variability in CL was much lower across the two 14-day cycle (9% and 7%, respectively) compared to intra-patient variability in ADA concentration (15% and 13%, respectively). Linear mixed effect models confirmed these findings with no impact of sampling time on CL (intercept=0.46±0.12 L/day; slope estimate=0.002±0.002 L/day; p=0.16) as compared to significant change in ADA concentrations (intercept=10.6±1.2 µg/mL; slope estimate=-0.25±0.03 µg/mL; p<0.01) over inter-dose interval sampling time. Sustained clinical and biochemical remission was achieved in 5/12 patients (42%); none presented with CL >0.8 L/day (a cut-off previously associated with worse outcomes). Of 7 patients without sustained clinical and biochemical remission, two presented with optimal concentrations (> 10 µg/mL), thus suggestive of mechanistic failure, and one developed ATA, lower concentration and higher ADA CL. Conclusion CL is subject to less intra-patient variability than ADA concentrations, supporting its assessment at any time point within a 14-day treatment cycle.

P565 Capillary blood based self-collection device for infliximab therapeutic drug monitoring

Abstract Background Patient friendly new devices may improve therapeutic drug monitoring (TDM) in inflammatory bowel disease (IBD). Our objective was to evaluate an infliximab (IFX) precision guided dosing tool from capillary blood collected using an upper-arm self-collection device amongst IBD patients and compare its performances to gold standard venous blood collected using venipuncture. Methods Patients under maintenance therapy with IFX were recruited from a single IBD center and enrolled in the BEST (Bayesian Estimates Sustaining Trough) study. BEST is a prospective real world evidence clinical utility study to establish the value of an IFX Bayesian forecasting tool in the optimal management of IBD. Blood specimens were collected prospectively, at midcycle or at trough. Capillary blood specimens were collected using an upper arm self-collection device (Tasso Inc., Seattle, WA) connected to a serum separator tube. Paired venous blood was collected using venipuncture. IFX concentrations and antibodies to IFX (ATI) status were measured using drug tolerant homogenous mobility shift assay, albumin levels were measured using nephelometry. IFX Clearance was calculated using nonlinear mixed effect model with Bayesian priors. Statistical analysis consisted of Deming regression. Results Overall, 27 patients (n=9 with UC, mean age=37 years, weight=79 Kg) were enrolled. Median IFX dosing was 10 mg/Kg, and median dosing frequency every 6 weeks. A total of n=58 serum pairs isolated from capillary and venous blood were tested. PK profiles measured from venous blood were optimal during maintenance with no immune response detected (ATI < 3.1 U/mL) and most patients had IFX concentration at trough above 5 µg/mL (98%, median 15.4 µg/mL IQR: 10.9-28.0 µg/mL) and low Clearance (< 0.294 L/day: 89%; median 0.200 L/day IQR: 0.170-0.248 L/day). IFX concentrations and Clearance levels were comparable between venous and capillary blood with high correlation (R2= 0.975; slope =0.928; and R2=0.978; slope =1.035, respectively) (figure). In capillary blood specimens collected at midcycle (median 14 days before the next infusion, n=12 pairs), median IFX concentration was 38.3 µg/mL (IQR: 31.2-64.7 µg/mL) and declined to 21.9 µg/mL (IQR: 14.1-44.5 µg/mL) at trough. There was a high correlation between forecasted and measured trough concentrations in capillary blood (R2=0.925; Deming’s slope=1.093). Similar results were observed with venous blood pairs (R2=0.983; Deming’s slope=1.024). Conclusion IFX therapeutic drug monitoring using patient self-collection of capillary blood performed as well as standard venous blood measurement. This collection method may facilitate the implementation of point of care TDM in clinical practice.

The Combination of Predictive Factors of Pharmacokinetic Origin Associates with Enhanced Disease Control during Treatment of Pediatric Crohn's Disease with Infliximab.

Infliximab (IFX) concentrations are a predictive factor (PF) of pharmacokinetic (PK) origin in the treatment of Crohn's disease (CD). We evaluated Clearance, another PF of PK origin, either alone or in combination with concentrations. They were evaluated from two cohorts, the first designed to receive standard dosing (n = 37), and the second designed to proactively target therapeutic IFX concentrations (n = 108). Concentrations were measured using homogeneous mobility shift assay. Clearance was estimated using the nonlinear mixed effects methods with Bayesian priors. C-reactive protein-based clinical remission (<3 mg/L in the absence of symptoms) was used for the disease control outcome measure. Longitudinal changes in disease control due to factors including time, IFX concentration, and Clearance were analyzed using repeated event analysis. Change in objective function value (∆OFV) was calculated to compare concentration and Clearance. The results indicated that lower baseline Clearance and proactive dosing associated with enhanced disease control during induction (p < 0.01). Higher IFX concentrations and lower Clearance measured at the second, third, and fourth infusion yielded improved disease control during maintenance (p < 0.032). During maintenance, the association with disease control was better with Clearance than with concentrations (∆OFV = -19.2; p < 0.001), and the combination of both further minimized OFV (p < 0.001) with markedly improved clinical yield in the presence of both PF of PK origin. We conclude that the combination of IFX concentration and Clearance are better predictors of therapeutic outcome compared with either one alone.

B-341 Analytical Performances of Homogeneous Mobility Shift Assay for Infliximab and Biosimilars and Resulting Exposure Assessments in Large Cohort of Patients With Inflammatory Bowel Diseases

Abstract Background Biosimilar for infliximab (IFX) are currently available for the treatment of various immune mediated inflammatory diseases including inflammatory bowel disease (IBD). We have validated the homogenous mobility shift assay (HMSA) for IFX biosimilars and describe exposure from a large population of patients with IBD treated with IFX and biosimilars. Methods Validation of the biosimilars, infliximab-dyyb (Inflectra®) and infliximab-abda (Renflexis®), was conducted in a reference clinical laboratory (Prometheus Laboratories, Inc.) for performance equivalence to the 1st international World Health Organization (WHO) IFX standard (16/170) by HMSA. The evaluated performance characteristics consisted of accuracy, precision, sensitivity, specificity, range, and linearity using spiked human serum. Following validation and implementation in the clinical laboratory, the drug median with interquartile range (IQR) and antibody to drug (ATI) prevalence and percentage relative to low-titer antibody cut-point of 10 U/mL (Am J Gastroenterol 2021;00:1-12), using de-identified patients, was evaluated by comparing treatment with IFX or the two validated biosimilars. Results The reportable range for the biosimilars was 0.98 μg/mL (precision: 5.5% CV; accuracy: 110.7% recovery) to 34 µg/mL (precision: 6.3% CV; accuracy: 105.4% recovery). Biosimilar intra-day, inter-day precision (CV) and accuracy (% recovery) across the reportable range were 3.8%, 3.6% and 105.1%, respectively. Furthermore, HMSA calibrated with IFX originator or biosimilar showed congruent results when compared to calibration with the WHO standard for the determination of drug concentrations using 20 clinical samples spanning the reportable range (Fig. 1). Median drug concentrations with IQR were 10.9 µg/mL (4.8–19.7 µg/mL) for infliximab originator, 9.8 µg/mL (3.9–18.1) for infliximab-dyyb, and 9.5 µg/mL (3.6–18.3) for infliximab-abda over a three-year period of testing, which also demonstrated similar ATI positivity rates. Conclusion HMSA is validated to be used as a tool for therapeutic drug monitoring (TDM) of patients treated with IFX originator and biosimilars.

B-340 Performance of a Quality System for Targeted Monoclonal Antibodies in a Reference Clinical Pharmacokinetic Laboratory

Abstract Background The homogenous mobility shift assay (HMSA) laboratory developed test (LDT) quantifies monoclonal antibody drug and anti-drug antibody levels and is useful for the management of inflammatory bowel diseases (IBD). We report the implementation and performance of a quality system for these LDTs, as well as longitudinal trends of exposure and immunization prevalence from a reference clinical pharmacokinetic (PK) laboratory (Prometheus Laboratories, Inc.). Methods Quality control (QC) HMSA data was evaluated to verify conformance to specifications for infliximab (IFX), adalimumab (ADA), vedolizumab (VDZ), ustekinumab (UST) and their respective anti-drug antibodies (antibody to IFX [ATI], ADA [ATA], VDZ [ATV], and UST [ATU]). A QC panel consisting of five serum specimens spanning the reportable range per each drug or anti-drug antibody LDT was established, stored at subzero temperature, and tested monthly over a period of two years. Acceptable performance consisted of 80%–120% accuracy from the target value. All specimens were blinded to operator and processed with the clinical PK load of testing. Exposure and immunization prevalence over three years of testing was evaluated. All patient data were de-identified before analysis. Median drug level (interquartile ranges [IQR]), and anti-drug percent positivity by international classification of disease was also estimated (ICD-10 based). Results The QC results establish that the drug (IFX, ADA, VDZ, UST) and anti-drug (ATI, ATA, ATV, ATU) LDTs report acceptable performance with 80%–120% accuracy over the two-year evaluation period. Median drug concentrations with IQR were assessed for the clinical sample set differentiated by disease classification as depicted in Fig. 1. Anti-drug positivity levels were higher for ATI (mean: 11.5%) and ATA (mean: 13.6%) than those from ATV (mean 2.0%) and ATU (mean: 0.6%). Conclusion The QC data presented supports the performance of HMSA for therapeutic drug monitoring (TDM) of IBD and other immune mediated inflammatory diseases.

B-060 Measurement of Infliximab Clearance using a Bayesian Forecasting Tool and Impact of Albumin and Immunization Status During Maintenance Treatment of Inflammatory Bowel Disease

Abstract Background Accelerated Clearance of monoclonal antibodies such as Infliximab (IFX) is a known predictive factor of pharmacokinetic origin that associates with poor outcome in patients with Inflammatory bowel diseases (IBD). We have implemented a Bayesian forecasting tool for IFX (PredictrPK® IFX) and calculated its Clearance. Our objective was to evaluate the impact of Albumin (ALB) and antibodies to IFX (ATI) on Clearance and exposure from patient specimens with IBD and submitted for testing in the routine clinical pharmacokinetic laboratory. Methods IFX concentration and ATI status were determined from serum using a homogenous mobility shift assay. Serum ALB concentration was determined using nephelometry. Clearance was estimated using inputted IFX concentration, ATI status, ALB, dose and interdose interval, and nonlinear mixed effect modeling with Bayesian priors. Patient specimens were collected anytime 20 days after the infusion and submitted for testing. Median Clearance (expressed as L/day) and estimated IFX trough concentrations by ATI status and lower Albumin levels (&amp;lt;4.0 g/dL) was calculated. Statistical analysis consisted of nonparametric Mann-Whitney tests. Results The prevalence of ATI was 9.1% in this cohort of patient specimens. Median Clearance was 0.246 L/day (IQR: 0.191–0.323 L/day) and median IFX Trough concentration was 11.9 µg/mL (IQR: 6.5–19.9 µg/mL). ATI status associated with lower IFX Trough concentrations and higher Clearance (P &amp;lt; 0.01). Lower ALB concentration regardless of ATI status also associated with lower IFX Trough concentrations (P &amp;lt; 0.01). There was twofold higher Clearance and twelvefold lower IFX Trough concentration in the presence of ATI and lower ALB. Results are presented in Table 1. Conclusion The data are consistent with the notion that IFX immunization and lower ALB impact Clearance and exposure to IFX.

B-304 Performance of Alternative Proficiency Testing Program for Bayesian Forecasting Tool of Infliximab Exposure in Clinical Pharmacokinetic Laboratory

Abstract Background We have developed a Bayesian (PK) forecasting and dosing tool for Infliximab (IFX), a monoclonal antibody targeting Tumor necrosis factor α. This novel dosing tool employs machine learning and proficiency of the algorithm must be established. Our objective was to implement an alternative proficiency testing program (APT) in the routine clinical (PK) laboratory. Methods The test (PredictrPK® IFX) is validated and measures serum IFX and antibodies to IFX (ATI) concentrations using a homogenous mobility shift assay by size exclusion HPLC and albumin (ALB) by nephelometry. Determinations are inputted with weight, dose, and interdose interval provided on test requisition in the Bayesian forecasting PK tool which uses non-linear mixed effect to calculate the individual parameter estimates, Clearance and predicted trough concentrations. APT is conducted using five previously tested patient samples, blinded to testing personnel and retested in the same manner as the routine method of analysis every six months. APT consists of two components, a component evaluating standalone IFX, ATI, and ALB analytes, and a second component evaluating the Bayesian forecasting PK tool in estimating Clearance and trough concentrations. Criteria for acceptable performance is set at target value ± 20% for standalone analytes and forecasted PK estimates. Acceptable ATP score corresponds to 4/5 samples with passing grade. Results The results from two consecutive APT results with six months intervals is presented in Fig. 1. Comparing the results to the original assayed data at the time of collection, the APT results showed IFX concentration, ATI and ALB within 20% of target value. Clearance and estimated trough concentrations calculated using the Bayesian forecasting tool also met acceptability criteria (100% passing grade). Conclusion We have implemented an APT for Bayesian forecasting tool in the clinical PK laboratory.

Adalimumab Clearance, Rather Than Trough Level, May Have Greatest Relevance to Crohn's Disease Therapeutic Outcomes Assessed Clinically and Endoscopically.

We postulated that adalimumab [ADA] drug clearance [CL] may be a more critical determinant of therapeutic outcome than ADA concentration. This was tested in Crohn's disease [CD] patients undergoing ADA maintenance treatment. CD patients from four cohorts received ADA induction and started maintenance therapy. Therapeutic outcomes consisted of endoscopic remission [ER], sustained C-reactive protein [CRP] based clinical remission [defined as CRP levels below 3 mg/L in the absence of symptoms], and faecal calprotectin [FC] level below 100 µg/g. Serum albumin, ADA concentration, and anti-drug antibody status were determined using immunochemistry and homogeneous mobility shift assay, respectively. CL was determined using a nonlinear mixed effect model with Bayesian priors. Statistical analysis consisted of Mann-Whitney test and logistic regression with calculation of odds ratio. Repeated event analysis was conducted using a nonlinear mixed effect model. In 237 enrolled patients [median age 40 years, 45% females], median CL was lower in patients achieving ER as compared with those with persistent active endoscopic disease [median 0.247 L/day vs 0.326 L/day, respectively] [p <0.01]. There was no significant difference in ADA concentration between patients in endoscopic remission compared with those with recurrence [median 9.3 µg/mL vs 11.7 µg/mL, respectively]. Sustained CRP-based clinical remission and FC levels below 100 µg/g were generally associated with lower CL and higher ADA concentration. Repeated event analysis confirmed those findings with better performances of CL than concentration in associating with ER and other outcomes. Lower ADA clearance is associated with an improved clinical outcome for patients with Crohn's disease and may be a superior pharmacokinetic measure than concentration.

S824 Cost-Effectiveness of Precision-Guided Dosing in Adult Crohn’s Disease Patients Initiating Infliximab Maintenance Therapy

Introduction: Crohn’s disease (CD) patients that lose response to biologics experience reduced quality of life (QoL) and costly hospitalizations. Precision-guided dosing provides clinicians with a comprehensive pharmacokinetic (PK) profile that allows for the next biologic dose to be personalized. We analyzed the cost-effectiveness of infliximab (IFX) Precision-guided dosing relative to two IFX dose intensification strategies (DIS). Methods: We developed a hybrid (Markov and decision tree) model of CD patients who had a clinical response to IFX induction and entered IFX maintenance in “remission” or “mild symptoms” health states. The analysis took a US payer perspective, a time horizon of 2 years in the base case, and a cycle length of 4 weeks. There were 3 comparators for IFX dosing: Precision-guided dosing, dose intensification based on symptoms, inflammatory markers, and trough IFX concentration (DIS1), and IFX dose intensification based on symptoms alone (DIS2). Patients that failed IFX initiated ustekinumab (UST), followed by vedolizumab, and conventional therapy. Transition probabilities for IFX were estimated from real-world clinical PK data and interventional clinical trial (PMID: 34978325; 29317275) patient-level data. All other transition probabilities were derived from published randomized clinical trials and cost-effectiveness analyses. Utility values were sourced from previous health technology assessments. Direct costs included biologic acquisition and infusion, surgeries and procedures, conventional therapy, and lab testing. The primary outcomes were total discounted costs, total quality-adjusted life years (QALYs), and incremental cost-effectiveness ratios (ICERs). The robustness of results was assessed via one-way sensitivity and scenario analyses. Results: Total costs and QALYs at 2 years are presented in Table. The ICERs of Precision-guided dosing relative to DIS1 and DIS2 were 171,810 and 127,990, respectively. One-way sensitivity analyses (Figure) demonstrated that the cost-effectiveness of Precision-guided dosing was most sensitive to the time between IFX doses. Precision-guided dosing had the lowest proportion of patients requiring a new biologic through 2 years (0.5% vs 2.4% and 27.7% for DIS1 and DIS2, respectively). Conclusion: Precision-guided dosing provides substantial clinical and QoL benefits for adult CD patients by maintaining clinical remission and avoiding IFX failure; it is cost-effective relative to other DISs at a WTP of $175,000/QALY.Figure 1.: Precision-guided Dosing ICER Relative to DIS2 † Varied by ±10% * Varied by ±5% CD: Crohn's disease, DIS: dose intensification strategy, ICER: incremental cost-effectiveness ratio, IFX: infliximab, M-S: moderate-severe, PMPM: per member per month, Rem: remission Table 1. - Base Case Results (2-year Horizon Discounted) DIS Total QALYs Total Costs ICER Relative to Precision-guided Dosing ICER Relative to DIS1 ICER Relative to DIS2 Incremental NMB vs DIS1 (WTP $150,000/QALY) Incremental NMB vs DIS1 (WTP $50,000/QALY) Incremental NMB vs DIS2 (WTP $150,000/QALY) Incremental NMB vs DIS2 (WTP $50,000/QALY) Precision-guided Dosing* 1.572 $50,753 - 171,810 127,990 -$765 -$4,274 $1,816 -$6,436 DIS1† 1.537 $44,725 171,810 - 95,581 - - $2,581 -$2,162 DIS2 ‡ 1.489 $40,191 127,990 95,581 - -$2,581 $2,162 - - DIS: dose intensification strategy, ICER: incremental cost-effectiveness ratio, NMB: net monetary benefit, QALY: quality-adjusted life year, WTP: willingness to pay.*Model informed precision dosing with homogenous mobility shift assay (Prometheus Laboratories).†Dose intensification based on a combination of symptoms, inflammatory markers and proactive therapeutic drug monitoring. Corresponds to cohorts 1 and 2 of the TAILORIX clinical trial.‡Dose intensification reactive on symptoms only. Corresponds to cohort 3 of the TAILORIX clinical trial.

Infliximab anti-drug antibody (ADA) detection by homogenous mobility shift assay (HMSA): Potential clinical utility of neutralising (NADA) vs non-neutralising binding ADA (BADA)

Detection of ADA to therapeutic large molecule tumour necrosis factor (TNF) inhibitors has established utility in the management of chronic inflammatory diseases.1 ADA are of two types: neutralising (nADA) and binding (bADA).2 HMSA differentiates between dimer and multimer drug-ADA complexes. We describe a 52-year-old male with psoriatic arthritis who was switched to infliximab infusions every 8 weeks with good therapeutic response. However, by the third to fourth maintenance infusion he reported ‘wear-off’ at around 4–6 weeks post-infusion and this pattern persisted.

S728 Clinical Utility of Homogenous Mobility Shift Assay Method for Vedolizumab Bioactivity and Precision Dosing in Inflammatory Bowel Diseases

S728 Clinical Utility of Homogenous Mobility Shift Assay Method for Vedolizumab Bioactivity and Precision Dosing in Inflammatory Bowel Diseases

Therapeutic drug monitoring in Crohn's disease patients treated with anti-TNF: a comparison of two techniques.

Therapeutic drug monitoring is a useful clinical decision aid in managing patients with inflammatory bowel disease treated with anti-tumor necrosis factor (anti-TNF). Various techniques are available to evaluate drug trough levels, and among these a point-of-care (POC) method has been proposed to overcome the limitations inherent to other methodologies. In this study we aimed to evaluate the capability of POC to discriminate between relapse and remission disease phases, and to assess the concordance of the POC and homogeneous mobility shift assay (HMSA) results. Drug trough level of 46 Crohn's disease patients treated with either adalimumab or infliximab were evaluated with both a POC technique and an HMSA at various time points (week-16 and -48) during anti-TNF treatment. Median adalimumab trough level of patients in remission were significantly higher as compared to relapsing patients using both HMSA (week 16, P = 0.0001; week48, P = 0.001) and POC (week 16, P = 0.0003; week 48, P = 0.0012), and similar results were observed with infliximab trough level at week 16 (HMSA, P = 0.019; POC, P = 0.0072). Overall, we observed a good correlation between the techniques for both infliximab (r = 0.76; P < 0.0001) and adalimumab (r = 0.75; P < 0.0001), with no difference in discriminatory accuracy between assays (infliximab: HMSA versus POC c-index, 0.921 versus 0.895, P =0.149; adalimumab: HMSA versus POC c-index, 0.817 versus 0.850, P = 0.197). Both POC and HMSA assays are able to reliably differentiate relapse and remission phases in Crohn's disease patients treated with anti-TNF. These techniques showed good concordance and we feel that their preferential use should be based on local accessibility, physicians' experience and preference, and the need for timeliness availability of results.

P497 The value of endoscopic healing index monitoring for guiding infliximab dosing in patients with Crohn’s disease

Abstract Background The endoscopic healing index (EHI) is a novel multi-protein serum biomarker test developed and validated to assess endoscopic disease activity in patients with Crohn’s disease (CD). Evidence for the use of EHI to guide decision-making during infliximab (IFX) treatment remains scarce. Therefore, we aimed to characterise the relationships between IFX dose, serum IFX concentrations, EHI, and endoscopic remission (ER). Methods Data were obtained from 118 biologic naïve adult patients with CD enrolled in the phase 4 TAILORIX trial (EudraCT 2011 003038 14). All patients had confirmed active CD at baseline based on clinical, biological, and endoscopic criteria. IFX and EHI (scores ranging from 0–100) were measured using a homogenous mobility shift assay (HMSA) and immunoassay, respectively (Prometheus Laboratories). First, the previously published population pharmacokinetic (popPK) model of the TAILORIX study population was revisited to describe the HMSA data. The effect of EHI, faecal calprotectin (FC), C-reactive protein (CRP), and serum albumin (ALB) on IFX clearance was evaluated. Next, a minimal continuous-time Markov model was developed to describe the time course of EHI within patients. EHI was considered as a three-stage ordinal variable (scores 0–19, 20–49, and 50–100) with the lowest score stage (0–19) indicative of ER. The course-modifying effect of IFX on EHI was assessed. Finally, a generalised linear model was used to describe the relationship between EHI and the probability of attaining ER (Simple Endoscopic Score for CD [SES-CD] ≤2). The predictive ability of EHI for ER was compared with that of FC, CRP, ALB, and IFX using a receiver operating characteristic (ROC) curve analysis. Results The revisited two-compartment popPK model described the IFX data with adequate descriptive and predictive accuracies. EHI, FC, CRP, and ALB at week (w)0 were not found to explain interpatient variability in IFX clearance. In contrast, higher IFX at w14 was associated with a higher probability of achieving EHI &amp;lt;20 at w14 (Figure 1). The probability of attaining EHI &amp;lt;20 at w14 was predicted to increase more than four-fold when IFX at w14 was targeted at 10 mg/L instead of 5 mg/L (Table 1). EHI and FC equally well predicted the probability of attaining ER at the same time point (Figure 2, Table 2). Conclusion EHI, FC, ALB, and CRP at w0 should not be considered for a priori IFX dose optimisation. Nevertheless, a posteriori IFX dose optimisation (based on IFX concentrations measurements) towards a predefined IFX concentration at w14 may lead to lower post-induction EHI scores and thus improved ER rates. An IFX target of 10 mg/L at w14 is associated with four-fold higher normalisation of EHI as compared to the commonly used target of 5 mg/L.

S0874 Performance Characteristics of Homogenous Mobility Shift Assay Method Against World Health Organization International Standard for Infliximab Bioactivity and Impact of Dosing Regimens on Exposure

INTRODUCTION: Therapeutic drug monitoring (TDM) of Infliximab remains an important clinical decision tool to improve outcomes in Inflammatory bowel diseases (IBD). However, one limitation of TDM in clinical gastroenterology practice is the lack of standardization across available technology platforms. Recently, the 1st international standard for infliximab (IFX) bioactivity was characterized and produced by World Health Organization (WHO). Our objective was to evaluate the performance characteristics of the Homogenous Mobility Shift assay (HMSA) against WHO calibration. METHODS: All IFX testing was conducted in a clinical laboratory accredited by the American College of Pathologists (Prometheus Biosciences, San Diego) using liquid chromatography size exclusion HMSA calibrated in house using IFX standards purchased independently from WHO. WHO Standard (NIBSC code: 16/170) was purchased as lyophilized powder, re-suspended to a final concentration of 50 µg/ml in normal healthy serum and stored at -80°C. IFX concentrations measured using in-house and WHO calibration methods were compared using de-identified specimens submitted for IFX testing. Data were analyzed using Deming’s regression and linear mixed effect models for repeated measures. IFX levels in relation to dosing intervals from patient specimens presenting with ICD-10 specific IBD codes were also evaluated. RESULTS: Between run (n = 6) precision was 9.5% (median CV; range 3.9–19.4%) and 8.6% (range: 5.2–17.8%) for 28 IFX specimens measured using in-house and WHO calibration, respectively. As presented in Figure 1, IFX levels measured using in-house calibration method (mean 13.8 ± 0.9 µg/ml) were comparable to those recovered from WHO calibration method (mean 13.9 ± 0.9 µg/ml) (Deming’s slope 1.00 CI 95%: 0.97–1.03). Linear mixed effect models also indicated comparable IFX levels between calibrations (slope = 0.986 ± 0.012; intercept = 0.11 ± 0.22; R2 = 0.97). Table 1 highlights IFX exposure levels in a total of 19,013 specimens submitted with dosing information between 2015 and 2020. A 5mg/Kg every 8 weeks dosing interval associated with 57% specimens above 5 µg/ml. Shorter intervals resulted in higher exposure. CONCLUSION: Our data indicate that IFX levels measured by HMSA in the reference laboratory yield comparable estimates to those from WHO. Calibration with WHO standards may facilitate harmonization of TDM in clinical gastroenterology practice.Figure 1Table 1

Accurate Measurement of Adalimumab Using Competitive Homogeneous Mobility Shift Assay

Accurate Measurement of Adalimumab Using Competitive Homogeneous Mobility Shift Assay

Clinical Impact of Corrections to Infliximab and Adalimumab Monitoring Results with the Homogeneous Mobility Shift Assay.

An upward drift for both infliximab and adalimumab concentrations measured by the homogenous mobility shift assay (HMSA) was previously reported. We aimed to investigate the impact of this drift on clinical care of patients with inflammatory bowel disease. This was a retrospective, multicenter study. Providers reviewed the individual patient data and drug concentrations before and after the laboratory corrections and then documented whether a different clinical decision would have been made had the corrected drug concentration been originally reported. A multivariable Cox proportional hazards regression analysis was performed to investigate the association of a documented treatment change with treatment failure, defined as drug discontinuation for primary nonresponse, loss of response, or serious adverse event, adjusting for confounding factors. The study population consisted of 479 patients (infliximab, n = 219; adalimumab, n = 260). Upon review, 14.9% (71/479) patients would have had a different treatment decision made had the corrected drug concentration been initially reported. After a median follow-up of 10.6 months, 25.7% of patients (123/479) had treatment failure. A theoretical different clinical decision based on the corrected drug concentrations was not associated with treatment failure (adjusted hazard ratio (HR): 1.452; 95% confidence interval (CI): 0.805–2.618; p = 0.216), which was consistent for both infliximab (adjusted HR: 1.977; 95% CI: 0.695–5.627; p = 0.201) and adalimumab (adjusted HR: 1.484; 95% CI: 0.721–3.054; p = 0.284). The drift in infliximab and adalimumab concentrations in the HMSA assay affected treatment decisions in 15% of cases. However, this discrepancy was not associated with a higher cumulative probability for treatment failure.

Comparison of Serum Concentrations of Ustekinumab Obtained by Three Commercial Assays in Patients with Crohn's Disease.

BackgroundData on the association of ustekinumab (UST) drug concentrations and clinical outcomes are conflicting. We assessed serum UST drug and anti-UST antibody concentrations using three commercially available assays.MethodsSixty-one blood samples were analyzed for serum UST drug and anti-UST antibody concentrations using three assays: one homogeneous mobility shift assay (HMSA, Prometheus, Assay A), and two enzyme-linked immunosorbent assays (ELISA; Progenika, Dynacare, Assay B and Theradiag, Assay C).ResultsThe median (IQR) serum UST concentrations for the three assays were: Assay A 7.50 (5.35 to 12.88) µg/mL, Assay B 4.02 (2.46 to 6.95) µg/mL and Assay C 4.35 (2.62 to 7.50) µg/mL. A Kruskal–Wallis test confirmed a statistically significant difference between the different assays, X2(2) = 30.606, p < 0.001. Linear regression showed near twofold increased difference in the absolute drug concentrations between the HMSA and either ELISA. Linear quantitative correlation was observed for all three assays (r = 0.836 for A versus B, r = 0.792 for A versus C, r = 0.936 for B versus C; p < 0.01). The intraclass correlation coefficient (ICC) between assay A and B was 0.649 (95% confidence interval [CI] −0.208 to 0.874); assay A and C was 0.671 (95% CI −0.165 to 0.878); and assay B and C was 0.958 (95% CI 0.928 to 0.975); p < 0.001. No anti-UST antibodies were detected.ConclusionA good correlation was observed for serum UST drug concentrations and a good agreement was observed between the ELISA tests. However, agreement was poor between the HMSA and each ELISA tests. Clinical recommendations regarding drug concentrations should be based on assay type used.

Comparison of Assays for Therapeutic Monitoring of Infliximab and Adalimumab in Patients With Inflammatory Bowel Diseases

Comparison data regarding anti-tumor necrosis factor drug concentrations in inflammatory bowel disease (IBD) between the enzyme-linked immunosorbent assay (ELISA) and the homogenous mobility shift assay (HMSA) are scarce.1-3 As decisions in clinical practice depend on the thresholds that define a therapeutic drug concentration, it is important to determine if this varies based on the type of assay used for therapeutic drug monitoring.4 We recently showed a discrepancy between a commercially available ELISA and the HMSA for both infliximab and adalimumab concentrations in patients with IBD.5 Based on the results of the study, Prometheus Laboratories (San Diego, CA) initiated a comprehensive review of their HMSA assays and found that there was an upward drift for both infliximab (from December 2017 to May 2019) and adalimumab (from August 2017 to May 2019), including when our study was performed. Prometheus Laboratories corrected the errant values and reported the revised drug concentrations to physicians (Supplementary Methods). We aimed to compare the corrected infliximab and adalimumab concentrations with the original ELISA values.

P092 COMPARISON OF INFLIXIMAB AND ADALIMUMAB CONCENTRATIONS BETWEEN THE ENZYME-LINKED IMMUNOSORBENT ASSAY AND THE HOMOGENEOUS MOBILITY SHIFT ASSAY (HMSA) IN INFLAMMATORY BOWEL DISEASE: AN UPDATE FOLLOWING IMPLEMENTATION OF CORRECTIVE MEASURES FOR THE HMSA

Abstract Background and aims We previously showed a discrepancy between a commercially available enzyme-linked immunosorbent assay (ELISA) and the homogenous mobility shift assay (HMSA) for both infliximab and adalimumab concentrations in patients with inflammatory bowel disease (IBD).1 Based also on the results of this study, Prometheus Laboratories initiated a comprehensive review of their HMSA assays and found that there was an upward drift for both infliximab and adalimumab over a 2-year period, including when our study was being performed. Prometheus corrected the errant values and reported the revised drug concentrations to physicians. We aimed to compare these two assays following the implementation of these corrective measures. Methods Samples from patients with IBD either on infliximab or adalimumab maintenance therapy were prospectively evaluated using both ELISA (InformTx™, Inform Diagnostics) (for research purposes) and the HMSA (ANSER™, Prometheus Laboratories) (performed clinically). Comparison of drug concentrations between assays was performed as previously described.1 Results In total 74 samples were analysed (infliximab, n=45; adalimumab, n=29). Drug concentrations (median [interquartile range, IQR]) were still significantly higher when measured by the HMSA compared to ELISA for foth infliximab (9 [7.1–12.4] vs. 5.7 [4.8–9] μg/ml; p&amp;lt;0.001, respectively) and adalimumab (12.9 [10.3–16.9] vs. 10.6 [8.6–14] μg/ml; p=0.036, respectively). The correlation of infliximab and adalimumab concentrations between assays is depicted in Figure 1. Agreement between assays was moderate [ICC: 0.658; 95% confidence interval (CI): -0.080 to 0.892; p&amp;lt;0.001] for infliximab and strong (ICC = 0.826, 95%CI: -0.066 to 0.949, p&amp;lt;0.001) for adalimumab. A Bland–Altman plot of infliximab and adalimumab concentrations to compare the two assays is shown in Figure 2. Qualitative agreement in drug concentration status (therapeutic or sub-therapeutic) was only minimal between assays using &amp;gt;5 μg/ml (K = 0.299, p=0.005), &amp;gt;7 μg/ml (K = 0.303, p=0.005) or &amp;gt;10 μg/ml (K = 0.323, p=0.003) as therapeutic drug concentrations for infliximab, while for adalimumab was weak using &amp;gt;10 μg/ml as therapeutic drug concentrations (K = 0.437, p=0.004), although overall agreement using either &amp;gt;5 or &amp;gt;7 μg/ml as therapeutic drug concentrations was 97%. Conclusions These data suggest that although the correlation between the ELISA and the HMSA was very good for both infliximab and adalimumab it is difficult to compare absolute drug concentrations. Until commercial assays are properly cross-validated and standardized, assay-dependent drug concentration thresholds may need to be applied to better interpret therapeutic drug monitoring results and it is advisable that patients are monitored with the same assay. 1Inflamm Bowel Dis. 2019 Sep 27. https://doi.org/10.1093/ibd/izz202. [Epub ahead of print]