Retrospective Multicenter Cohort Study on Safety and Electroencephalographic Response to Lacosamide for Neonatal Seizures.

BACKGROUND: There is growing evidence supporting the safety and effectiveness of lacosamide in older children. However, minimal data are available for neonates. We aimed to determine the incidence of adverse events associated with lacosamide use and explore the electroencephalographic seizure response to lacosamide in neonates. METHODS: A retrospective cohort study was conducted using data from seven pediatric hospitals from January 2009 to February 2020. For safety outcomes, neonates were followed for ≤30 days from index date. Electroencephalographic response of lacosamide was evaluated based on electroencephalographic reports for ≤3 days. RESULTS: Among 47 neonates, 98% received the first lacosamide dose in the intensive care units. During the median follow-up of 12 days, 19% of neonates died, and the crude incidence rate per 1000 patient-days (95% confidence interval) of the adverse events by diagnostic categories ranged from 2.8 (0.3, 10.2) for blood or lymphatic system disorders and nervous system disorders to 10.5 (4.2, 21.6) for cardiac disorders. Electroencephalographic seizures were observed in 31 of 34 patients with available electroencephalographic data on the index date. There was seizure improvement in 29% of neonates on day 1 and also in 29% of neonates on day 2. On day 3, there was no change in 50% of neonates and unknown change in 50% of neonates. CONCLUSIONS: The results are reassuring regarding the safety of lacosamide in neonates. Although some neonates had fewer seizures after lacosamide administration, the lack of a comparator arm and reliance on qualitative statements in electroencephalographic reports limit the preliminary efficacy results.

Pharmacokinetics of Staccato® alprazolam in healthy adult participants in two phase 1 studies: An open-label smoker study and a randomized, placebo-controlled ethnobridging study.

OBJECTIVE: Staccato® alprazolam is a single-use, drug-device combination delivering alprazolam to the deep lung that is being evaluated as treatment for rapid and early seizure termination. This article reports pharmacokinetic (PK) data from two phase 1 studies of Staccato alprazolam in healthy adult participants. METHODS: The smoker study (EPK-002/NCT03516305) was an open-label, nonrandomized, single-dose, PK study in smokers and nonsmokers aged 21-50 years, administered a single inhaled dose of 1 mg Staccato alprazolam. The ethnobridging study (UP0101/NCT04782388) was a double-blind, placebo-controlled study in Japanese, Chinese, and Caucasian participants aged 18-55 years randomized 4:1 to a single inhaled dose of Staccato alprazolam 2 mg or Staccato placebo. RESULTS: In the smoker study, 36 participants (18 smokers, 18 nonsmokers) were enrolled and received Staccato alprazolam. Following Staccato administration, alprazolam was rapidly absorbed, with a median time to peak drug plasma concentration (Tmax) of 2 min in both smokers (range = 2-30 min) and nonsmokers (range = 2-60 min). Staccato alprazolam was rapidly absorbed to a similar extent in both smokers and nonsmokers. The most commonly reported treatment-emergent adverse events (TEAEs) were somnolence and dizziness. In the ethnobridging study, 10 participants each of Japanese, Chinese, and Caucasian ethnicities were randomized 4:1 to Staccato alprazolam or Staccato placebo. Following Staccato administration, alprazolam was rapidly absorbed and distributed, with a median Tmax of 1.5-2 min in Japanese (range = 1-2 min), Chinese (range = 1-34 min), and Caucasian (range = 1-120 min) participants. Somnolence and sedation were the most commonly reported TEAEs. In both studies, there were no deaths, and no participants reported serious or severe TEAEs, or discontinued due to TEAEs. SIGNIFICANCE: Alprazolam was rapidly absorbed, and therapeutic drug levels were achieved within 2 min postdose when administered to the lung with the Staccato device. Staccato alprazolam was generally well tolerated and displayed a safety profile consistent with that known from other alprazolam applications. No new safety signals were identified.

Epidemiology of focal onset seizures in children aged >1 month to 4 years in Europe, United States, and Canada: A literature review.

The present study aims to report the currently available epidemiology of focal onset seizures in children aged >1 month to 4 years with the help of a literature review. The terms 'seizure*' OR 'epilepsy' combined with pediatric and epidemiology terms were used to search Embase, PubMed, and Web of Science up to November 16, 2021. Due to the scarcity of epidemiology data on focal onset seizures, the incidence and prevalence were estimated using the proportion of focal onset seizures in epilepsy patients from the most recently published articles. The estimated annual incidence per 100,000 children of focal onset seizures in children of 0-4 years of age ranged from 25.1 (95 % confidence interval [CI] 18.9-32.7) in the United Kingdom to 111.8 in the United States. The estimated period prevalence of focal onset seizures in children 0-4 years of age ranged from 0.15 % (99 % CI 0.13-0.18) in Canada to 0.61 % in the United States. Neurodevelopmental outcomes and psychiatric disorders were the most commonly reported comorbidities in children with epilepsy of age 0-4 years. Presence of focal onset seizures in children with different epilepsy syndromes needs to be thoroughly considered in the treatment planning of this population of interest.

Safety of intravenous lacosamide in hospitalized children and neonates.

OBJECTIVE: Seizures are common in critically ill children and neonates, and these patients would benefit from intravenous (IV) antiseizure medications with few adverse effects. We aimed to assess the safety profile of IV lacosamide (LCM) among children and neonates. METHODS: This retrospective multicenter cohort study examined the safety of IV LCM use in 686 children and 28 neonates who received care between January 2009 and February 2020. RESULTS: Adverse events (AEs) were attributed to LCM in only 1.5% (10 of 686) of children, including rash (n = 3, .4%), somnolence (n = 2, .3%), and bradycardia, prolonged QT interval, pancreatitis, vomiting, and nystagmus (n = 1, .1% each). There were no AEs attributed to LCM in the neonates. Across all 714 pediatric patients, treatment-emergent AEs occurring in >1% of patients included rash, bradycardia, somnolence, tachycardia, vomiting, feeling agitated, cardiac arrest, tachyarrhythmia, low blood pressure, hypertension, decreased appetite, diarrhea, delirium, and gait disturbance. There were no reports of PR interval prolongation or severe cutaneous adverse reactions. When comparing children who received a recommended versus a higher than recommended initial dose of IV LCM, there was a twofold increase in the risk of rash in the higher dose cohort (adjusted incidence rate ratio = 2.11, 95% confidence interval = 1.02-4.38). SIGNIFICANCE: This large observational study provides novel evidence demonstrating the tolerability of IV LCM in children and neonates.

Safety and tolerability of short-term infusions of intravenous lacosamide in pediatric patients with epilepsy: An open-label, phase 2/3 trial.

OBJECTIVE: The objective of this study is to evaluate the safety and tolerability of intravenous (IV) lacosamide infusion in patients aged ≥1 month to <17 years with epilepsy. METHODS: This Phase 2/3 open-label trial (EP0060; NCT02710890) enrolled patients in two age cohorts (cohort 1: ≥8 to <17 years; cohort 2: ≥1 month to <8 years). Eligible patients were receiving oral lacosamide as adjunctive treatment or monotherapy (in an open-label long-term trial or by prescription) or were not receiving lacosamide before enrolment. Patients initiated IV lacosamide (2-12 mg/kg/day or 100-600 mg/day; 15-60 minutes infusion) as a replacement for oral lacosamide or as adjunctive treatment. The primary outcomes were treatment-emergent adverse events (TEAEs) and discontinuations due to TEAEs. RESULTS: In total, 103 patients were enrolled and completed the trial; 55 patients were included in cohort 1 (≥8 to <17 years), 48 in cohort 2 (≥1 month to <8 years). During the 4 weeks before screening, 74 (71.8%) patients had focal seizures, 12 (11.7%) had generalized seizures, and two (1.9%) had unclassified seizures. Most patients (74 [71.8%]) initiated lacosamide as adjunctive IV treatment. The mean overall duration of exposure to IV lacosamide was 1.18 days. Seventy-nine (76.7%) patients had one IV lacosamide infusion, 20 (19.4%) had two, one (1.0%) had three, and three (2.9%) had 10 infusions. Overall, five (4.9%) patients had a total of seven TEAEs. The only TEAEs reported in two or more patients were increased blood triglycerides (two [1.9%]). No serious or severe TEAEs were reported, and no patients discontinued due to TEAEs. No TEAEs were considered drug-related by the investigator. No consistent or clinically relevant treatment-related changes from baseline were observed for hematology, clinical chemistry parameters, vital signs, or 12-lead electrocardiograms. SIGNIFICANCE: IV lacosamide was generally well tolerated in pediatric patients (≥1 month to <17 years) with epilepsy, and no new safety concerns were identified.

Long-term safety and tolerability of lacosamide monotherapy in patients with epilepsy: Results from a multicenter, open-label trial.

The primary objective of this trial (SP1042; NCT02582866) was to assess long-term safety and tolerability of lacosamide monotherapy (200-600 mg/day) in adults with focal (partial-onset) seizures or generalized tonic-clonic seizures (without clear focal origin). This Phase III, long-term, open-label, multicenter, follow-up trial enrolled patients with epilepsy who were taking lacosamide in, and completed, the previous double-blind trial (SP0994; NCT01465997). Primary safety outcomes were treatment-emergent adverse events (TEAEs), discontinuations due to TEAEs, and serious TEAEs. One hundred and six patients were enrolled and received lacosamide: 84 (79.2%) completed the trial and 22 (20.8%) discontinued. The median duration of exposure was 854.0 days, with a median modal dose of 200 mg/day. Ninety-six (90.6%), 64 (60.4%), and 44 (41.5%) patients had ≥12, ≥24, and ≥36 months of lacosamide exposure, respectively. At least one TEAE was reported by 61 (57.5%) patients. The most common (≥4%) TEAEs were headache (10 [9.4%]), nasopharyngitis (eight [7.5%]), and back pain (five [4.7%]). One (0.9%) patient discontinued due to a TEAE (sudden unexpected death in epilepsy; not considered drug-related), 14 (13.2%) patients reported serious TEAEs, and seven (6.6%) patients reported TEAEs that were considered drug-related. Overall, long-term lacosamide monotherapy was generally well tolerated up to 600 mg/day, with no new safety signals identified.

Effects of lacosamide and carbamazepine on lipids in a randomized trial.

OBJECTIVE: The effects of anticonvulsants on lipids are the subject of considerable concern and investigation, but there are almost no data on this issue from randomized trials. We evaluated serum lipid profiles in adults with newly diagnosed epilepsy, following randomization to lacosamide (LCM) or carbamazepine (CBZ) monotherapy. METHODS: We analyzed data from a Phase 3, international, randomized, double-blind trial of LCM vs CBZ for the initial treatment of focal epilepsy. Serum lipid profiles in patients not taking lipid-lowering agents and providing blood samples under fasting conditions before treatment, and following 3 or 12 months of treatment with LCM or CBZ at various doses were analyzed. RESULTS: At 12 months, 271 patients satisfied the inclusion criteria for the analysis. No change was observed in LCM-treated patients for total cholesterol, cholesterol fractions, or triglycerides. CBZ-treated patients showed an increase of 21.1 mg/dL in total cholesterol, 12.6 mg/dL in low-density lipoprotein (LDL) cholesterol, 12.5 mg/dL in non-high density lipoprotein (non-HDL) cholesterol, and 8.5 mg/dL in HDL cholesterol; triglycerides remained unchanged. The proportion of patients with elevated total cholesterol levels (above the upper limit of the reference range) did not change in the LCM treatment group (37.0% at Baseline; 34.8% at 12 months), but increased from 30.8% (at Baseline) to 49.6% (at 12 months) in the CBZ treatment group. SIGNIFICANCE: This study provides Class II evidence that CBZ elevates serum lipids, whereas LCM has no effect on lipids. It supports LCM as an appropriate choice for new-onset focal epilepsy.

Efficacy and safety of adjunctive lacosamide in the treatment of primary generalised tonic-clonic seizures: a double-blind, randomised, placebo-controlled trial.

OBJECTIVE: To evaluate efficacy and safety of lacosamide (up to 12 mg/kg/day or 400 mg/day) as adjunctive treatment for uncontrolled primary generalised tonic-clonic seizures (PGTCS) in patients (≥4 years) with idiopathic generalised epilepsy (IGE). METHODS: Phase 3, double-blind, randomised, placebo-controlled trial (SP0982; NCT02408523) in patients with IGE and PGTCS taking 1-3 concomitant antiepileptic drugs. Primary outcome was time to second PGTCS during 24-week treatment. RESULTS: 242 patients were randomised and received ≥1 dose of trial medication (lacosamide/placebo: n=121/n=121). Patients (mean age: 27.7 years; 58.7% female) had a history of generalised-onset seizures (tonic-clonic 99.6%; myoclonic 38.8%; absence 37.2%). Median treatment duration with lacosamide/placebo was 143/65 days. Risk of developing a second PGTCS during 24-week treatment was significantly lower with lacosamide than placebo (Kaplan-Meier survival estimates 55.27%/33.37%; HR 0.540, 95% CI 0.377 to 0.774; p<0.001; n=118/n=121). Median time to second PGTCS could not be estimated for lacosamide (>50% of patients did not experience a second PGTCS) and was 77.0 days for placebo. Kaplan-Meier estimated freedom from PGTCS at end of the 24-week treatment period (day 166) for lacosamide/placebo was 31.3%/17.2% (difference 14.1%; p=0.011). More patients on lacosamide than placebo had ≥50% (68.1%/46.3%) or ≥75% (57.1%/36.4%) reduction from baseline in PGTCS frequency/28 days, or observed freedom from PGTCS during treatment (27.5%/13.2%) (n=119/n=121). 96/121 (79.3%) patients on lacosamide had treatment-emergent adverse events (placebo 79/121 (65.3%)), most commonly dizziness (23.1%), somnolence (16.5%), headache (14.0%). No patients died during the trial. CONCLUSIONS: Lacosamide was efficacious and generally safe as adjunctive treatment for uncontrolled PGTCS in patients with IGE.

Reducing Patient Burden in Clinical Trials Through the Use of Historical Controls: Appropriate Selection of Historical Data to Minimize Risk of Bias.

Historical data have been used to augment or replace control arms in some rare disease and pediatric clinical trials. With greater availability of historical data and new methodology such as dynamic borrowing, the inclusion of historical data in clinical trials is an increasingly appealing approach for larger disease areas as well, as this can result in increased power and precision and can minimize the burden on patients in clinical trials. However, sponsors must assess whether the potential biases incurred with this approach outweigh the benefits and discuss this trade-off with the regulatory agencies. This paper discusses important points for the appropriate selection of historical controls for inclusion in the analysis of primary and/or key secondary endpoint(s) in clinical trials. The general steps are as follows: (1) Assess whether a trial is a suitable candidate for this approach. (2) If it is, then carefully identify appropriate historical trials to minimize selection bias. (3) Refine the historical control set if appropriate, for example, by selecting subsets of studies or patients. Identification of trial settings that are amenable to historical borrowing and selection of appropriate historical data using the principles discussed in this paper has the potential to lead to more efficient estimation and decision making. Ultimately, this efficiency gain results in lower patient burden and gets effective drugs to patients more quickly.

Investigation of the predictive validity of laser-EPs in normal, UVB-inflamed and capsaicin-irritated skin with four analgesic compounds in healthy volunteers.

AIMS: The aim of the present study was to assess the predictivity of laser-(radiant-heat)-evoked potentials (LEPs) from the vertex electroencephalogram, using an algesimetric procedure, testing the anti-nociceptive/anti-hyperalgesic effects of single oral doses of four marketed analgesics (of different compound classes) vs. placebo, in healthy volunteers with three skin types. METHODS: This was a randomized, placebo-controlled, single-blind, five-way-crossover trial. Twenty-five healthy male/female Caucasians were included (receiving celecoxib 200 mg, pregabalin 150 mg, duloxetine 60 mg, lacosamide 100 mg or placebo) in a Williams design, with CO2 laser-induced painful stimuli to normal, ultraviolet (UV) B-inflamed and capsaicin-irritated skin. LEPs and visual analogue scale ratings were taken at baseline and hourly for 6 h postdose from all three skin types. RESULTS: In normal skin, the averaged postdose LEP peak-to-peak-(PtP)-amplitudes were reduced by pregabalin (-2.68 µV; 95% confidence interval (CI) -4.16, 1.19) and duloxetine (-1.73 µV; 95% CI -3.21, -0.26) but not by lacosamide and celecoxib vs. placebo. On UVB-irradiated skin, reflecting inflammatory pain, celecoxib induced a pronounced reduction in LEP PtP amplitudes vs. placebo (-6.2 µV; 95% CI -7.88, -4.51), with a smaller reduction by duloxetine (-4.54 µV; 95% CI -6.21, -2.87) and pregabalin (-3.72 µV; 95% CI -5.40, -2.04), whereas lacosamide was inactive. LEP PtP amplitudes on capsaicin-irritated skin, reflecting peripheral/spinal sensitization, as in neuropathic pain, were reduced by pregabalin (-3.78 µV; 95% CI -5.31, -2.25) and duloxetine (-2.32 µV; 95% CI -3.82, -0.82) but not by celecoxib or lacosamide vs. placebo, which was in agreement with known clinical profiles. Overall, PtP amplitude reductions were in agreement with subjective ratings. CONCLUSIONS: LEP algesimetry is sensitive to analgesics with different modes of action and may enable the effects of novel analgesics to be assessed during early clinical development.

Antibody-mediated status epilepticus: a retrospective multicenter survey.

BACKGROUND: In recent years, an increasing number of auto-antibodies (AB) have been detected in the CSF and serum of patients with new onset epilepsy. Some of these patients develop convulsive or nonconvulsive status epilepticus (AB-SE), necessitating intensive medical care and administration of multiple antiepileptic and immunomodulatory treatments of uncertain effectiveness. OBJECTIVES: In this retrospective multicenter survey we aimed to determine the spectrum of gravity, the duration and the prognosis of the disorder. In addition, we sought to identify the antibodies associated with this condition, as well as determine whether there is a most effective treatment regime. METHODS: 12 European Neurology University Clinics, with extensive experience in the treatment of SE patients, were sent a detailed questionnaire regarding symptoms and treatment of AB-SE patients. Seven centers responded positively, providing a total of 13 patients above the age of 16. RESULTS: AB-SE affects mainly women (12/13, 92%) with a variable age at onset (17-69 years, median: 25 years). The duration of the disease is also variable (10 days to 12 years, median: 2 months). Only the 3 oldest patients died (55-69 years). Most patients were diagnosed with anti NMDAR encephalitis (8/13) and had oligoclonal bands in the CSF (9/13). No specific treatment regimen (antiepileptic, immunomodulatory) was found to be clearly superior. Most of the surviving 10 patients (77%) recovered completely or nearly so within 2 years of index poststatus. CONCLUSION: AB-SE is a severe but potentially reversible condition. Long duration does not seem to imply fatal outcome; however, age older than 50 years at time of onset appears to be a risk factor for death. There was no evidence for an optimal antiepileptic or immunomodulatory treatment. A prospective multicenter study is warranted in order to stratify the optimal treatment algorithm, determine clear risk factors of unfavorable outcome and long-term prognosis.

Increased resting-state perfusion after repeated encoding is related to later retrieval of declarative associative memories.

Electrophysiological studies in animals have shown coordinated reactivation of neuronal ensembles during a restricted time period of behavioral inactivity that immediately followed active encoding. In the present study we directly investigated off-line processing of associative memory formation in the human brain. Subjects' regional cerebral blood flow (rCBF) as a surrogate marker of neural activity during rest was measured by MR-based perfusion imaging in a sample of 14 healthy male subjects prior to (Pre2) and after (Post) extensive learning of 24 face-name associations within a selective reminding task (SR). Results demonstrated significant Post-Pre2 rCBF increases in hippocampal and temporal lobe regions, while in a control comparison of two perfusion scans with no learning task in-between (Pre2-Pre1) no differences in rCBF emerged. Post perfusion scanning was followed by a surprise cued associative recall task from which two types of correctly retrieved names were obtained: older names already correctly retrieved at least once during one of the SR blocks, and recent names acquired during the last SR block immediately prior to the Post scan. In the anterior hippocampus individual perfusion increases were correlated with both correct retrievals of older and recent names. By contrast, older but not recently learned names showed a significant correlation with perfusion increases in the left lateral temporal cortex known to be associated with long-term memory. Recent, but not older names were correlated with dopaminergic midbrain structures reported to contribute to the persistence of memory traces for novel information. Although the direct investigation of off-line memory processing did not permit concomitant experimental control, neither intentional rehearsal, nor substantial variations in subjects' states of alertness appear to contribute to present results. We suggest that the observed rCBF increases might reflect processes that possibly contribute to the long-term persistence of memory traces.

Evaluation of cognition, structural, and functional MRI in juvenile myoclonic epilepsy.

PURPOSE: Previous studies using advanced imaging techniques have suggested subtle structural and functional changes in patients with juvenile myoclonic epilepsy (JME), mainly associated with the frontal lobes. In addition, it has been reported that these patients show neuropsychological deficits, often summarized as frontal lobe dysfunction. The aim of this study was a comprehensive analysis of neuropsychological parameters, and functional and structural magnetic resonance imaging (MRI) in an independent cohort of patients with JME. METHODS: We studied 19 JME patients and 20 age-, sex-, and education-matched controls using a battery of standardized neuropsychological tests, optimized voxel-based morphometry (VBM), and two domain-specific working-memory paradigms combined with functional MRI (fMRI). RESULTS: Our investigations did not reveal statistically significant differences between the groups of JME patients and normal controls in either the VBM or the fMRI study of working memory. The neuropsychological examination showed a slightly worse performance for the JME patients across most tests used, reaching statistical significance for semantic and verbal fluency. CONCLUSIONS: In our cohort of JME patients, we could not reproduce the findings of frontal gray matter changes from previous studies, and we could not detect an fMRI correlate of previously reported differences in working memory in JME. The neuropsychological deficits may be attributed partially to antiepileptic medication. We conclude that structural and functional frontal lobe deficits in JME patients have to be interpreted with care. One reason for a variation between different cohorts may be the genetic heterogeneity of the disease.

Cervical spinal MRI in a patient with a vagus nerve stimulator (VNS).

Cranial MRI has been shown to be a safe procedure in patients with a vagus nerve stimulator (VNS), but body MRI may cause overheating of the stimulator lead. Here we report a case of a patient with an implanted vagus nerve stimulator who required a cervical spinal MRI due to a rapidly progressive paraparesis. The spinal MRI was performed in a 1.5T scanner without complications showing a nearly complete compression of the spinal cord.

GLUT1 mutations are a cause of paroxysmal exertion-induced dyskinesias and induce hemolytic anemia by a cation leak.

Paroxysmal dyskinesias are episodic movement disorders that can be inherited or are sporadic in nature. The pathophysiology underlying these disorders remains largely unknown but may involve disrupted ion homeostasis due to defects in cell-surface channels or nutrient transporters. In this study, we describe a family with paroxysmal exertion-induced dyskinesia (PED) over 3 generations. Their PED was accompanied by epilepsy, mild developmental delay, reduced CSF glucose levels, hemolytic anemia with echinocytosis, and altered erythrocyte ion concentrations. Using a candidate gene approach, we identified a causative deletion of 4 highly conserved amino acids (Q282_S285del) in the pore region of the glucose transporter 1 (GLUT1). Functional studies in Xenopus oocytes and human erythrocytes revealed that this mutation decreased glucose transport and caused a cation leak that alters intracellular concentrations of sodium, potassium, and calcium. We screened 4 additional families, in which PED is combined with epilepsy, developmental delay, or migraine, but not with hemolysis or echinocytosis, and identified 2 additional GLUT1 mutations (A275T, G314S) that decreased glucose transport but did not affect cation permeability. Combining these data with brain imaging studies, we propose that the dyskinesias result from an exertion-induced energy deficit that may cause episodic dysfunction of the basal ganglia, and that the hemolysis with echinocytosis may result from alterations in intracellular electrolytes caused by a cation leak through mutant GLUT1.

The binary Clostridium botulinum C2 toxin as a protein delivery system: identification of the minimal protein region necessary for interaction of toxin components.

The binary Clostridium botulinum C2 toxin is composed of the enzyme component C2I and the binding component C2II, which are individual and non-linked proteins. Activated C2IIa mediates cell binding and translocation of C2I into the cytoplasm. C2I ADP-ribosylates G-actin at Arg-177 to depolymerize actin filaments. A fusion toxin containing the N-terminal domain of C2I (residues 1-225) transports C3 ADP-ribosyltransferase from Clostridium limosum into cells (Barth, H., Hofmann, F., Olenik, C., Just, I., and Aktories, K. (1998) Infect. Immun. 66, 1364-1369). We characterized the adaptor function of C2I and its interaction with C2IIa. The fusion toxin GST-C2I(1-225)-C3 was efficiently transported by C2IIa, indicating that C2IIa translocates proteins into the cytosol even when the C2I(1-225) adaptor was positioned in the middle of a fusion protein. Amino acid residues 1-87 of C2I were sufficient for interaction with C2IIa and for translocation of C2I fusion toxins into HeLa cells. Residues 1-87 were the minimal part of C2I to bind to C2IIa on the cell surface, as detected by fluorescence-activated cytometry. An excess of C2I(1-87) (but not of further truncated C2I fragments) competed with Alexa488-labeled C2I for binding to C2IIa. Also, the fragment C2I(30-431) and the fusion toxin C2I(30-225)-C3 competed with C2I-Alexa488 for binding to C2IIa. C2I(30-225)-C3 did not induce cytotoxic effects on cells when applied together with C2IIa, indicating that amino acid residues 1-29 are involved in translocation of C2I but are not absolutely essential for binding to C2IIa.