A model-based meta-analysis of monoclonal antibody pharmacokinetics to guide optimal first-in-human study design

The objectives of this retrospective analysis were (1) to characterize the population pharmacokinetics (popPK) of four different monoclonal antibodies (mAbs) in a combined analysis of individual data collected during first-in-human (FIH) studies and (2) to provide a scientific rationale for prospective design of FIH studies with mAbs. The data set was composed of 171 subjects contributing a total of 2716 mAb serum concentrations, following intravenous (IV) and subcutaneous (SC) doses. mAb PK was described by an open 2-compartment model with first-order elimination from the central compartment and a depot compartment with first-order absorption. Parameter values obtained from the popPK model were further used to generate optimal sampling times for a single dose study. A robust fit to the combined data from four mAbs was obtained using the 2-compartment model. Population parameter estimates for systemic clearance and central volume of distribution were 0.20 L/day and 3.6 L with intersubject variability of 31% and 34%, respectively. The random residual error was 14%. Differences (> 2-fold) in PK parameters were not apparent across mAbs. Rich designs (22 samples/subject), minimal designs for popPK (5 samples/subject), and optimal designs for non-compartmental analysis (NCA) and popPK (10 samples/subject) were examined by stochastic simulation and estimation. Single-dose PK studies for linear mAbs executed using the optimal designs are expected to yield high-quality model estimates, and accurate capture of NCA estimations. This model-based meta-analysis has determined typical popPK values for four mAbs with linear elimination and enabled prospective optimization of FIH study designs, potentially improving the efficiency of FIH studies for this class of therapeutics.     

First human study of a chimeric anti-methamphetamine monoclonal antibody in healthy volunteers

This first-in-human study examined the safety and pharmacokinetics of ch-mAb7F9, an anti-methamphetamine monoclonal antibody, in healthy volunteers. Single, escalating doses of ch-mAb7F9 over the range of 0.2 to 20 mg/kg were administered to 42 subjects who were followed for 147 d. Safety was measured by physical examinations, adverse events, vital signs, electrocardiograms, and clinical laboratory testing. Serum ch-mAb7F9 concentration and immunogenicity analyses were performed. There were no serious adverse reactions or discontinuations from the study due to adverse events. No trends emerged in the frequency, relatedness, or severity of adverse events with increased dose or between active and placebo treated subjects. Ch-mAb7F9 displayed expected IgG pharmacokinetic parameters, including a half-life of 17–19 d in the 3 highest dose groups and volume of distribution of 5–6 L, suggesting the antibody is confined primarily to the vascular compartment. Four (12.5%) of the 32 subjects receiving ch-mAb7F9 were confirmed to have developed a human anti-chimeric antibody response by the end of the study; however, this response did not appear to be dose related. Overall, no apparent safety or tolerability concerns were identified; a maximum tolerated dose was not reached in this Phase 1 study. Ch-mAb7F9 therefore appears safe for human administration.     

First human study of a chimeric anti-methamphetamine monoclonal antibody in healthy volunteers

This first-in-human study examined the safety and pharmacokinetics of ch-mAb7F9, an anti-methamphetamine monoclonal antibody, in healthy volunteers. Single, escalating doses of ch-mAb7F9 over the range of 0.2 to 20 mg/kg were administered to 42 subjects who were followed for 147 d. Safety was measured by physical examinations, adverse events, vital signs, electrocardiograms, and clinical laboratory testing. Serum ch-mAb7F9 concentration and immunogenicity analyses were performed. There were no serious adverse reactions or discontinuations from the study due to adverse events. No trends emerged in the frequency, relatedness, or severity of adverse events with increased dose or between active and placebo treated subjects. Ch-mAb7F9 displayed expected IgG pharmacokinetic parameters, including a half-life of 17–19 d in the 3 highest dose groups and volume of distribution of 5–6 L, suggesting the antibody is confined primarily to the vascular compartment. Four (12.5%) of the 32 subjects receiving ch-mAb7F9 were confirmed to have developed a human anti-chimeric antibody response by the end of the study; however, this response did not appear to be dose related. Overall, no apparent safety or tolerability concerns were identified; a maximum tolerated dose was not reached in this Phase 1 study. Ch-mAb7F9 therefore appears safe for human administration.     

Preclinical characterization of an anti-methamphetamine monoclonal antibody for human use

Ch-mAb7F9, a human-mouse chimeric monoclonal antibody (mAb) designed to bind (+)-methamphetamine (METH) with high affinity and specificity, was produced as a treatment medication for METH abuse. In these studies, we present the preclinical characterization that provided predictive evidence that ch-mAb7F9 may be safe and effective in humans. In vitro ligand binding studies showed that ch-mAb7F9 is specific for and only binds its target ligands (METH, (+)-amphetamine, and 3,4-methylenedioxy-N-methylamphetamine) with high affinity. It did not bind endogenous neurotransmitters or other medications and was not bound by protein C1q, thus it is unlikely to stimulate in vivo complement-dependent cytotoxicity. Isothermal titration calorimetry potency studies showed that METH binding by ch-mAb7F9 is efficient. Pharmacokinetic studies of METH given after ch-mAb7F9 doses in rats demonstrated the in vivo application of these in vitro METH-binding characteristics. While METH had little effect on ch-mAb7F9 disposition, ch-mAb7F9 substantially altered METH disposition, dramatically reducing the volume of distribution and clearance of METH. The elimination half-life of METH was increased by ch-mAb7F9, but it was still very fast compared with the elimination of ch-mAb7F9. Importantly, the rapid elimination of unbound METH combined with previous knowledge of mAb:target ligand binding dynamics suggested that ch-mAb7F9 binding capacity regenerates over time. This finding has substantial therapeutic implications regarding the METH doses against which ch-mAb7F9 will be effective, on the duration of ch-mAb7F9 effects, and on the safety of ch-mAb7F9 in METH users who use METH while taking ch-mAb7F9. These results helped to support initiation of a Phase 1a study of ch-mAb7F9.     

Preclinical characterization of an anti-methamphetamine monoclonal antibody for human use

Ch-mAb7F9, a human-mouse chimeric monoclonal antibody (mAb) designed to bind (+)-methamphetamine (METH) with high affinity and specificity, was produced as a treatment medication for METH abuse. In these studies, we present the preclinical characterization that provided predictive evidence that ch-mAb7F9 may be safe and effective in humans. In vitro ligand binding studies showed that ch-mAb7F9 is specific for and only binds its target ligands (METH, (+)-amphetamine, and 3,4-methylenedioxy-N-methylamphetamine) with high affinity. It did not bind endogenous neurotransmitters or other medications and was not bound by protein C1q, thus it is unlikely to stimulate in vivo complement-dependent cytotoxicity. Isothermal titration calorimetry potency studies showed that METH binding by ch-mAb7F9 is efficient. Pharmacokinetic studies of METH given after ch-mAb7F9 doses in rats demonstrated the in vivo application of these in vitro METH-binding characteristics. While METH had little effect on ch-mAb7F9 disposition, ch-mAb7F9 substantially altered METH disposition, dramatically reducing the volume of distribution and clearance of METH. The elimination half-life of METH was increased by ch-mAb7F9, but it was still very fast compared with the elimination of ch-mAb7F9. Importantly, the rapid elimination of unbound METH combined with previous knowledge of mAb:target ligand binding dynamics suggested that ch-mAb7F9 binding capacity regenerates over time. This finding has substantial therapeutic implications regarding the METH doses against which ch-mAb7F9 will be effective, on the duration of ch-mAb7F9 effects, and on the safety of ch-mAb7F9 in METH users who use METH while taking ch-mAb7F9. These results helped to support initiation of a Phase 1a study of ch-mAb7F9.     

Serum pharmacokinetics and cerebrospinal fluid concentration analysis of the new IgG4 monoclonal antibody GNbAC1 to treat multiple sclerosis: A Phase 1 study

GNbAC1 is a humanized IgG4 monoclonal antibody antagonist of Mulitple Sclerosis Retrovirus Envelope (MSRV-Env), a protein that could play a critical role in multiple sclerosis. This randomized placebo-controlled dose-escalation study evaluated the safety and pharmacokinetics of GNbAC1 in 21 healthy volunteers after single intravenous infusion at doses of 6, 18 and 36 mg/kg. Lumbar punctures were performed at days 2, 15 or 29 to measure GNbAC1 concentrations in cerebrospinal fluid (CSF). GNbAC1 was well tolerated. Serum data show a dose-linear pharmacokinetics. A mean CSF/serum ratio of 0.12% was observed at Day 2, increasing to 0.39% at Day 15 and 0.42% at Day 29. Linear regression analysis shows a relationship between GNbAC1 CSF/serum ratio and albumin CSF/serum ratio and a relationship at the limit of statistical significance with the timing of CSF sampling.     

Defining process design space for monoclonal antibody cell culture

The concept of design space has been taking root as a foundation of in‐process control strategies for biopharmaceutical manufacturing processes. During mapping of the process design space, the multidimensional combination of operational variables is studied to quantify the impact on process performance in terms of productivity and product quality. An efficient methodology to map the design space for a monoclonal antibody cell culture process is described. A failure modes and effects analysis (FMEA) was used as the basis for the process characterization exercise. This was followed by an integrated study of the inoculum stage of the process which includes progressive shake flask and seed bioreactor steps. The operating conditions for the seed bioreactor were studied in an integrated fashion with the production bioreactor using a two stage design of experiments (DOE) methodology to enable optimization of operating conditions. A two level Resolution IV design was followed by a central composite design (CCD). These experiments enabled identification of the edge of failure and classification of the operational parameters as non‐key, key or critical. In addition, the models generated from the data provide further insight into balancing productivity of the cell culture process with product quality considerations. Finally, process and product‐related impurity clearance was evaluated by studies linking the upstream process with downstream purification. Production bioreactor parameters that directly influence antibody charge variants and glycosylation in CHO systems were identified. Biotechnol. Bioeng. 2010;106: 894–905. © 2010 Wiley Periodicals, Inc.     

Preclinical pharmacokinetics of MHAA4549A,a human monoclonal antibody to influenza A virus,and the prediction of its efficacious clinical dose for the treatment of patients hospitalized with influenza A

MHAA4549A is a human immunoglobulin G1 (IgG1) monoclonal antibody that binds to a highly conserved epitope on the stalk of influenza A hemagglutinin and blocks the hemagglutinin-mediated membrane fusion in the endosome, neutralizing all known human influenza A strains. Pharmacokinetics (PK) of MHAA4549A and its related antibodies were determined in DBA/2J and Balb-c mice at 5 mg/kg and in cynomolgus monkeys at 5 and 100 mg/kg as a single intravenous dose. Serum samples were analyzed for antibody concentrations using an ELISA and the PK was evaluated using WinNonlin software. Human PK profiles were projected based on the PK in monkeys using species-invariant time method. The human efficacious dose projection was based on in vivo nonclinical pharmacological active doses, exposure in mouse infection models and expected human PK. The PK profiles of MHAA4549A and its related antibody showed a linear bi-exponential disposition in mice and cynomolgus monkeys. In mice, clearance and half-life ranged from 5.77 to 9.98 mL/day/kg and 10.2 to 5.76 days, respectively. In cynomolgus monkeys, clearance and half-life ranged from 4.33 to 4.34 mL/day/kg and 11.3 to 11.9 days, respectively. The predicted clearance in humans was ～2.60 mL/day/kg. A single intravenous dose ranging from 15 to 45 mg/kg was predicted to achieve efficacious exposure in humans. In conclusion, the PK of MHAA4549A was as expected for a human IgG1 monoclonal antibody that lacks known endogenous host targets. The predicted clearance and projected efficacious doses in humans for MHAA4549A have been verified in a Phase 1 study and Phase 2a study, respectively.     

Toward in vitro-to-in vivo translation of monoclonal antibody pharmacokinetics: Application of a neonatal Fc receptor-mediated transcytosis assay to understand the interplaying clearance mechanisms

Monoclonal antibodies (mAbs) are a rapidly growing drug class for which great efforts have been made to optimize certain molecular features to achieve the desired pharmacokinetic (PK) properties. One approach is to engineer the interactions of the mAb with the neonatal Fc receptor (FcRn) by introducing specific amino acid sequence mutations, and to assess their effect on the PK profile with in vivo studies. Indeed, FcRn protects mAbs from intracellular degradation, thereby prolongs antibody circulation time in plasma and modulates its systemic clearance. To allow more efficient and focused mAb optimization, in vitro input that helps to identify and quantitatively predict the contribution of different processes driving non-target mediated mAb clearance in vivo and supporting translational PK modeling activities is essential. With this aim, we evaluated the applicability and in vivo-relevance of an in vitro cellular FcRn-mediated transcytosis assay to explain the PK behavior of 25 mAbs in rat or monkey. The assay was able to capture species-specific differences in IgG-FcRn interactions and overall correctly ranked Fc mutants according to their in vivo clearance. However, it could not explain the PK behavior of all tested IgGs, indicating that mAb disposition in vivo is a complex interplay of additional processes besides the FcRn interaction. Overall, the transcytosis assay was considered suitable to rank mAb candidates for their FcRn-mediated clearance component before extensive in vivo testing, and represents a first step toward a multi-factorial in vivo clearance prediction approach based on in vitro data.     

A peptide mimetic of an anti-CD4 monoclonal antibody by rational design

The development of rational methods to design 'continuous' sequence mimetics of discontinuous regions of protein sequence has, to now, been only marginally successful. This has been largely due to the difficulty of constraining the recognition elements of a mimetic structure to the relative conformational and spatial orientations present in the parent molecule. Using peptide mapping to determine 'active' antigen recognition residues, molecular modeling, and a molecular dynamics trajectory analysis, we have developed a peptide mimic of an anti-CD4 antibody, containing antigen contact residues from multiple CDRs. The design described is a 27-residue peptide formed by juxtaposition of residues from 5 CDR regions. It displays an affinity for the antigen (CD4) of 0.9nM, compared to 2nM for the parent antibody ST40. Nevertheless, the mimetic shows low biological activity in an anti-retroviral assay.     

Establishment of a monoclonal antibody to human myeloma cell: relation to chemotherapy and extramedullar infiltration

Resistance of myeloma cells to melphalan (L-PAM) is a serious problem. To investigate mechanisms of drug resistance, we generated a monoclonal antibody, clone O3, to melphalan-resistant myeloma cells, KHM-11R. Western blot analysis showed that molecular weight of O3 antigen was approximately 90 kDa. Expression of O3 antigen was approximately two times higher in KHM-11R than in parental melphalan sensitive cell line, KHM-11. O3 was preferentially expressed in plasma cell, B-cell, and monocytic cell lines, but not in T-cell lines. Analysis of bone marrow samples from myeloma patients revealed that 13 of 23 samples expressed O3 antigen at various levels, and that O3 antigen expression in patients correlate with preceding chemotherapy, advanced clinical stage and extramedullar invasion of myeloma cells. Furthermore, patients expressing O3 antigen at the time of diagnosis tended to have poor prognosis. The investigation of O3 antigen in myeloma cells will be useful to reveal the pathophysiology of extramedullar invasion and the mechanism of cell killing by melphalan.     

荧光染料R-藻红蛋白标记小鼠抗人CD4单克隆抗体

以R-藻红蛋白(R-PE)标记小鼠抗人CD4单克隆抗体,形成单色或和用其他荧光染料标记的CD系列单抗组成双色、多色的荧光试剂,应用于流式细胞仪检测分析。用异双功能交联试剂SPDP和SMCC分别活化R-PE和CD4单抗,用DTT使经SPDP活化后的R-PE巯基化,再与用SMCC活化的CD4单抗交联。使用NEM终止交联反应,经Sephacryl S-300柱在AKTA FPLC快速液相色谱系统(简称AKTA)监测下分离纯化。结果用R-PE标记的抗CD4单抗,检测正常人外周血淋巴细胞表面CD4抗原的表达,经流式细胞仪(简称FACS)分析表明,R-PE标记的CD4抗体特异性保持完好,荧光强度较高,还可与用FITC标记的其它CD系列单抗配伍成双标或多标试剂。使用SPDP,SMCC异双功能交联试剂和DTT还原剂,成功地偶联了R-藻红蛋白和CD4单克隆抗体,可应用于流式细胞仪检测分析。     

Pharmacokinetics and tolerability of human mouse chimeric anti-CD22 monoclonal antibody in Chinese patients with CD22-positive non-Hodgkin lymphoma

The safety and pharmacokinetics assessment of antibodies targeting CD22 (e.g., epratuzumab) have been established in western Caucasian populations, but there are no reports of the effects in Chinese populations. This dose-escalation study examines the safety, pharmacokinetics and biologic effects of multiple doses of anti-CD22 human-murine chimeric monoclonal antibody SM03 in 21 Chinese patients with CD22-positive non-Hodgkin lymphoma. Most of drug-related adverse events (AEs) were mild and reversible. Two patients experienced serious AEs (hemorrhage); one patient had grade 4 neutropenia; one patient had asymptomatic grade III prolongation of activated partial thromboplastin time (APTT). Major AEs included fever (71%), prolongation of APTT (42.8%), leukocytopenia (44.4%), alanine transaminase elevation (28.6%), elevated serum creatinine (23.8%) and injection site skin redness (14.3%). Circulating B cells transiently decreased without significant effects on T cells or immunoglobulin levels. Pharmacokinetic data revealed that mean maximum observed SM03 concentration and mean AUC from time zero to infinity increased in a dose-dependent manner up to 360 mg/m² SM03. Mean clearance was similar at doses ≤360 mg/m² and decreased significantly at dose 480 mg/m², supporting saturation of B-cell binding at 360 mg/m². Across all dose levels and histologies, one patient achieved partial response at 480 mg/m² dose; 14 patients had stable disease as best response and four patients progressed. Overall, SM03 was tolerated at doses ranging from 60–480 mg/m² and had potential efficacy in Chinese patients with follicular lymphoma.     

Pharmacokinetics and tolerability of human mouse chimeric anti-CD22 monoclonal antibody in Chinese patients with CD22-positive non-Hodgkin lymphoma

The safety and pharmacokinetics assessment of antibodies targeting CD22 (e.g., epratuzumab) have been established in western Caucasian populations, but there are no reports of the effects in Chinese populations. This dose-escalation study examines the safety, pharmacokinetics and biologic effects of multiple doses of anti-CD22 human-murine chimeric monoclonal antibody SM03 in 21 Chinese patients with CD22-positive non-Hodgkin lymphoma. Most of drug-related adverse events (AEs) were mild and reversible. Two patients experienced serious AEs (hemorrhage); one patient had grade 4 neutropenia; one patient had asymptomatic grade III prolongation of activated partial thromboplastin time (APTT). Major AEs included fever (71%), prolongation of APTT (42.8%), leukocytopenia (44.4%), alanine transaminase elevation (28.6%), elevated serum creatinine (23.8%) and injection site skin redness (14.3%). Circulating B cells transiently decreased without significant effects on T cells or immunoglobulin levels. Pharmacokinetic data revealed that mean maximum observed SM03 concentration and mean AUC from time zero to infinity increased in a dose-dependent manner up to 360 mg/m² SM03. Mean clearance was similar at doses ≤ 360 mg/m² and decreased significantly at dose 480 mg/m², supporting saturation of B-cell binding at 360 mg/m². Across all dose levels and histologies, one patient achieved partial response at 480 mg/m² dose; 14 patients had stable disease as best response and four patients progressed. Overall, SM03 was tolerated at doses ranging from 60–480 mg/m² and had potential efficacy in Chinese patients with follicular lymphoma.     

Effect of antigen-dependent clearance on pharmacokinetics of anti-heparin-binding EGF-like growth factor (HB-EGF) monoclonal antibody

Heparin-binding EGF-like growth factor (HB-EGF) is a member of the EGF family and is an important therapeutic target in some types of human cancers. KM3566 is a mouse anti-HB-EGF monoclonal antibody that neutralizes HB-EGF activity by inhibiting the binding of HB-EGF to its receptors. Based on the results of our pharmacokinetics study, a humanized derivative antibody, KHK2866, is rapidly cleared from serum and shows nonlinear pharmacokinetics in cynomolgus monkeys. In this study, we examined the antigen-dependent clearance of an anti-HB-EGF monoclonal antibody in vivo and in vitro in order to pharmacokinetically explain the rapid elimination of KHK2866. We revealed tumor size-dependent clearance of KM3566 in in vivo studies and obtained good fits between the observed and simulated concentrations of KM3566 based on the two-compartment with a saturable route of clearance model. Furthermore, in vivo imaging analyses demonstrated tumor-specific distribution of KM3566. We then confirmed rapid internalization and distribution to lysosome of KM3566 at a cellular level. Moreover, we revealed that the amounts of HB-EGF on cell surface membrane were maintained even while HB-EGF was internalized with KM3566. Recycled or newly synthesized HB-EGF, therefore, may contribute to a consecutive clearance of KM3566, which could explain a rapid clearance from serum. These data suggested that the rapid elimination in pharmacokinetics of KM3566 is due to antigen-dependent clearance. Given that its antigen is expressed in a wide range of normal tissue, it is estimated that the rapid elimination of KHK2866 from cynomolgus monkey serum is caused by antigen-dependent clearance.     

Enhanced radioimmunotherapeutic efficacy of a monoclonal antibody cocktail against SMMC—7721 human hepatocellular carcinoma

The improved tumoricidal effect of the radioantibody mixture (“cocktail”)has been reported recently for the treatment of colon tumor.In the present study,we demonstrated the enhanced radioimmunotherapeutic efficacy of a monoclonal antibody (MAb) cocktail against human hepatocellular carcinoma.Therapeutic efficacy was determined by measuring the change in tumor size over a period,determining the percentage of growth inhibition of each treatment at various times after radioantibody therapy.Radioimmunotherapy of SMMC-7721 human hepatoma xenografts in athymic unde mice with combination of ^131Ilabeled Hepama-1 and ^131 I-labeled 9403 mouse MAbs was more effective than using either Hepeam-1 or 9403 MAb alone The MAb cocktail could target a greater number of hepatoma cells and increase the magnitude of hepatoma cell uptake of radioantibodies.The in vitro results explain the enhanced effect of the MAb cocktail in in vivo model system.     

hGH单克隆抗体的筛选及双抗体夹心ELISA检测方法的建立

采用杂交瘤法制备单克隆抗体,并用辛酸-硫酸铵法纯化单抗,通过ELISA方法和Western blotting测定抗体的效价与特异性,并进行抗体类型、相对亲和力测定;应用纯化的单抗建立hGH双抗体夹心ELISA检测方法。筛选出两株可以稳定分泌抗hGH单抗的杂交瘤细胞株,分别命名为3E11、2G9,抗体类型均为IgG1,抗体滴度均可达10-10,特异性好,相对亲和力高,以筛选到的两株单抗建立的双抗夹心ELISA法线性范围为0.09～1.5625ng/mL,R2>0.9,灵敏度为0.09ng/mL。筛选出高效抗hGH的单抗,并建立了hGH双抗体夹心ELISA检测方法。     

Effect of antigen-dependent clearance on pharmacokinetics of anti-heparin-binding EGF-like growth factor (HB-EGF) monoclonal antibody

Heparin-binding EGF-like growth factor (HB-EGF) is a member of the EGF family and is an important therapeutic target in some types of human cancers. KM3566 is a mouse anti-HB-EGF monoclonal antibody that neutralizes HB-EGF activity by inhibiting the binding of HB-EGF to its receptors. Based on the results of our pharmacokinetics study, a humanized derivative antibody, KHK2866, is rapidly cleared from serum and shows nonlinear pharmacokinetics in cynomolgus monkeys. In this study, we examined the antigen-dependent clearance of an anti-HB-EGF monoclonal antibody in vivo and in vitro in order to pharmacokinetically explain the rapid elimination of KHK2866. We revealed tumor size-dependent clearance of KM3566 in in vivo studies and obtained good fits between the observed and simulated concentrations of KM3566 based on the two-compartment with a saturable route of clearance model. Furthermore, in vivo imaging analyses demonstrated tumor-specific distribution of KM3566. We then confirmed rapid internalization and distribution to lysosome of KM3566 at a cellular level. Moreover, we revealed that the amounts of HB-EGF on cell surface membrane were maintained even while HB-EGF was internalized with KM3566. Recycled or newly synthesized HB-EGF, therefore, may contribute to a consecutive clearance of KM3566, which could explain a rapid clearance from serum. These data suggested that the rapid elimination in pharmacokinetics of KM3566 is due to antigen-dependent clearance. Given that its antigen is expressed in a wide range of normal tissue, it is estimated that the rapid elimination of KHK2866 from cynomolgus monkey serum is caused by antigen-dependent clearance.     

Production and characterization of a monoclonal antibody for Pefloxacin and mechanism study of antibody recognition

In this report, an artificial antigen (PFLX–BSA: Pefloxacin connected bovine serum albumin) was successfully prepared. The monoclonal antibody against pefloxacin was produced and characterized using a direct competitive ELISA. The linear range of detection was 0.115–6.564 µg/L. The limit of detection defined as IC₁₅ was 0.170 ± 0.05 µg/L and the IC₅₀ was 0.902 ± 0.03 µg/L. The antibody variable region genes were amplified, assembled, and sequenced. A three–dimensional structural model of the variable region was constructed to study the mechanism of antibody recognition using molecular docking analysis. Three predicted essential amino acids, Thr53, Arg97 of heavy chain and Thr52 of light chain, were mutated to verify the theoretical model. Three mutants lost binding activity signi?cantly against pefloxacin as predicted. These may provide useful insights for studying antigen–antibody interaction mechanisms to improve antibody affinity maturation in vitro.