Organisational interventions for preventing and minimising aggression directed towards healthcare workers by patients and patient advocates

BACKGROUND

Workplace aggression is becoming increasingly prevalent in health care, with serious consequences for both individuals and organisations. Research and development of organisational interventions to prevent and minimise workplace aggression has also increased. However, it is not known if interventions prevent or reduce occupational violence directed towards healthcare workers.

OBJECTIVES

To assess the effectiveness of organisational interventions that aim to prevent and minimise workplace aggression directed towards healthcare workers by patients and patient advocates.

SEARCH METHODS

We searched the following electronic databases from inception to 25 May 2019: Cochrane Central Register of Controlled Trials (CENTRAL) (Wiley Online Library); MEDLINE (PubMed); CINAHL (EBSCO); Embase (embase.com); PsycINFO (ProQuest); NIOSHTIC (OSH-UPDATE); NIOSHTIC-2 (OSH-UPDATE); HSELINE (OSH-UPDATE); and CISDOC (OSH-UPDATE). We also searched the ClinicalTrials.gov (www.ClinicalTrials.gov) and the World Health Organization (WHO) trials portals (www.who.int/ictrp/en).

SELECTION CRITERIA

We included randomised controlled trials (RCTs) or controlled before-and-after studies (CBAs) of any organisational intervention to prevent and minimise verbal or physical aggression directed towards healthcare workers and their peers in their workplace by patients or their advocates. The primary outcome measure was episodes of aggression resulting in no harm, psychological, or physical harm.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methods for data collection and analysis. This included independent data extraction and 'Risk of bias' assessment by at least two review authors per included study. We used the Haddon Matrix to categorise interventions aimed at the victim, the vector or the environment of the aggression and whether the intervention was applied before, during or after the event of aggression. We used the random-effects model for the meta-analysis and GRADE to assess the quality of the evidence.

MAIN RESULTS

We included seven studies. Four studies were conducted in nursing home settings, two studies were conducted in psychiatric wards and one study was conducted in an emergency department. Interventions in two studies focused on prevention of aggression by the vector in the pre-event phase, being 398 nursing home residents and 597 psychiatric patients. The humour therapy in one study in a nursing home setting did not have clear evidence of a reduction of overall aggression (mean difference (MD) 0.17, 95% confidence interval (CI) 0.00 to 0.34; very low-quality evidence). A short-term risk assessment in the other study showed a decreased incidence of aggression (risk ratio (RR) 0.36, 95% CI 0.16 to 0.78; very low-quality evidence) compared to practice as usual. Two studies compared interventions to minimise aggression by the vector in the event phase to practice as usual. In both studies the event was aggression during bathing of nursing home patients. In one study, involving 18 residents, music was played during the bathing period and in the other study, involving 69 residents, either a personalised shower or a towel bath was used. The studies provided low-quality evidence that the interventions may result in a medium-sized reduction of overall aggression (standardised mean difference (SMD -0.49, 95% CI -0.93 to -0.05; 2 studies), and physical aggression (SMD -0.85, 95% CI -1.46 to -0.24; 1 study; very low-quality evidence), but not in verbal aggression (SMD -0.31, 95% CI; -0.89 to 0.27; 1 study; very low-quality evidence). One intervention focused on the vector, the pre-event phase and the event phase. The study compared a two-year culture change programme in a nursing home to practice as usual and involved 101 residents. This study provided very low-quality evidence that the intervention may result in a medium-sized reduction of physical aggression (MD 0.51, 95% CI 0.11 to 0.91), but there was no clear evidence that it reduced verbal aggression (MD 0.76, 95% CI -0.02 to 1.54). Two studies evaluated a multicomponent intervention that focused on the vector (psychiatry patients and emergency department patients), the victim (nursing staff), and the environment during the pre-event and the event phase. The studies included 564 psychiatric staff and 209 emergency department staff. Both studies involved a comprehensive package of actions aimed at preventing violence, managing violence and environmental changes. There was no clear evidence that the psychiatry intervention may result in a reduction of overall aggression (odds ratio (OR) 0.85, 95% CI 0.63 to 1.15; low-quality evidence), compared to the control condition. The emergency department study did not result in a reduction of aggression (MD = 0) but provided insufficient data to test this.

AUTHORS' CONCLUSIONS

We found very low to low-quality evidence that interventions focused on the vector during the pre-event phase, the event phase or both, may result in a reduction of overall aggression, compared to practice as usual, and we found inconsistent low-quality evidence for multi-component interventions. None of the interventions included the post-event stage. To improve the evidence base, we need more RCT studies, that include the workers as participants and that collect information on the impact of violence on the worker in a range of healthcare settings, but especially in emergency care settings. Consensus on standardised outcomes is urgently needed.

A Review of the Literature of Mirtazapine in Co-Occurring Depression and an Alcohol Use Disorder

BACKGROUND

Prior medication studies involving individuals with major depression in combination with an alcohol use disorder (MDD/AUD) have mainly focused on SSRI and tricyclic antidepressants, with generally ineffective results. Consequently, effective treatments for that common comorbid condition remain elusive. Mirtazapine is an antidepressant medicine with a unique pharmacological profile, whose effectiveness for treating non-comorbid depression reportedly may exceed that of SSRIs.

OBJECTIVE/METHODS

We now review the published literature regarding the tolerability and efficacy of mirtazapine for the treatment of the depression and the pathological alcohol ingestion of individuals with co-occurring MDD/AUD, including a review of four of our own small studies and two studies conducted outside the United States.

RESULTS/CONCLUSIONS

The findings of these studies suggest that mirtazapine is well tolerated among persons with comorbid MDD/AUD. Results also provide some evidence of efficacy for mirtazapine for decreasing the level of depression of persons with co-occurring MDD/AUD, and suggest that decreases in depression may occur relatively quickly after starting treatment, but provide no evidence of effectiveness for decreasing the level of alcohol ingestion. Large-scale double-blind, placebo-controlled studies are warranted to further clarify the tolerability and efficacy of mirtazapine among individuals with MDD/AUD.

Interventions for preventing the spread of infestation in close contacts of people with scabies

BACKGROUND

Scabies, caused by Sarcoptes scabiei variety hominis or the human itch mite, is a common parasitic infection. While anyone can become infected, it causes significant morbidity in immunocompromised hosts and it spreads easily between human hosts where there is overcrowding or poor sanitation. The most common symptom reported is itch which is worse at night. As the symptoms are attributed to an allergic reaction to the mite, symptoms usually develop between four to six weeks after primary infection. Therefore, people may be infected for some time prior to developing symptoms. During this time, while asymptomatic, they may spread infection to others they are in close contact with. Consequently, it is usually recommended that when an index case is being treated, others who have been in close contact with the index case should also be provided with treatment.

OBJECTIVES

To assess the effects of prophylactic interventions for contacts of people with scabies to prevent infestation in the contacts.

SEARCH METHODS

We searched electronic databases (Cochrane Occupational Safety and Health Review Group Specialised Register, CENTRAL (The Cochrane Library), MEDLINE (Ovid), Pubmed, EMBASE, LILACS, CINAHL, OpenGrey and WHO ICTRP) up to November 2013.

SELECTION CRITERIA

Randomised controlled trials (RCTs) or cluster RCTs which compared prophylactic interventions which were given to contacts of index cases with scabies infestation. Interventions could be compared to each other, or to placebo or to no treatment. Both drug treatments and non-drug treatments were acceptable.

DATA COLLECTION AND ANALYSIS

Two authors intended to extract dichotomous data (developed infection or did not develop infection) for the effects of interventions and report this as risk ratios with 95% confidence intervals. We intended to report any adverse outcomes similarly.

MAIN RESULTS

We did not include any trials in this review. Out of 29 potentially-relevant studies, we excluded 16 RCTs as the data for the contacts were either not reported or were reported only in combination with the outcomes for the index cases. We excluded a further 11 studies as they were not RCTs. We also excluded one study as not all subjects were examined at baseline and follow-up, and another as it was a case study.

AUTHORS' CONCLUSIONS

The effects of providing prophylactic treatments for contacts of people with scabies to prevent infestation are unknown. We need well-designed RCTs of the use of prophylactic measures to prevent the transmission of scabies conducted with people who had the opportunity for prolonged skin contact with an index case, such as family members, healthcare workers or residential care personnel, within the previous six weeks.

Ageing, cognitive disorders and professional practice

BACKGROUND

the workforce is ageing. The contribution of older workers is considerable. Their occupational health profiles differ from those of younger workers.

OBJECTIVE

we wished to establish whether consideration has been given by regulatory and professional bodies of the impact of ageing-related conditions such as dementia on professional practice.

METHODS

We e-mailed a questionnaire to 22 regulatory and professional bodies in the UK and the Republic of Ireland. We asked whether there are supports for their practitioners should they develop age-related diseases, (particularly cognitive disorders),whether the body considered that the practitioner was responsible for their own health, and whether the body has resources to arrange for medical review for their professionals if concerns arose regarding competence. Where bodies did not respond, information relating to the questions was extracted from their on-line resources.

RESULTS

thirteen bodies responded. None of these had specific supports to assist older workers. Some knew of other supports (occupational health, employee assistance supports, benevolent funds or counselling services). All of the bodies who responded either have or are developing structures to deal with concerns regarding their practitioners.

CONCLUSION

The absence of specific policies for age-related diseases, (particularly dementia), among professional and regulatory bodies is a challenge for an ageing workforce in the liberal professions. Closer working between geriatric medicine, old age psychiatry, occupational health and professional bodies is recommended to develop age-attuned policies and systems which protect the public while supporting the professionals in both work and timely transition from work.

Frequency and consequences of violence in community pharmacies in Ireland

BACKGROUND

Violence in community pharmacies in Ireland is thought to be common but underreported. The frequency and consequences of violence has not been studied previously.

AIMS

To establish the frequency and nature of violence in community pharmacies over 12 months, and to investigate the impact of violence on employees and possible consequence for the industry.

METHODS

A two-part survey was distributed to community pharmacies in Ireland in 2011 (n = 200). The first part related to pharmacy demographics, the frequency of various violent events (verbal abuse, threats etc.), the respondents' worry regarding violence and its impact on their co-workers. The second part concerned individual employees' subjective response to a violent event, using the Impact of Event Scale-Revised (IES-R).

RESULTS

Fifty-seven per cent of the pharmacies responded, with 77% reporting some violent event (verbal or physical), over the past year. Eighteen per cent reported physical assault, and 63% were worried about workplace violence. There was no association between late night opening hours or pharmacy size and violence frequency. Positive statistically significant correlations were present between all types of violence and absenteeism and employee fear levels. An IES-R score could be calculated for 75 respondents; the median IES-R score was 8 with 19% reporting clinically significant scores.

CONCLUSIONS

Violence is common in Irish community pharmacies and impacts on employees and the industry.

In vitro comparison of two different methods of cell washing

The storage of red blood cells (RBC) results in increased concentrations of plasma free hemoglobin, potassium, glucose, and lactate, among other undesirable substances. These concentrations continue to increase as RBC products age and can cause deleterious effects to the patient. In the setting of cardiac surgery, the autotransfusion devices are routinely used to wash blood that is shed from the surgical site. These devices could also be used to wash stored RBC units obtained from the blood bank. The objective of this study was to compare the product created by washing a unit of RBCs with the AutoLog autotransfusion device in the operating room to the washed products from a standard cell washer in the blood bank.

Eleven outdated RBC units (stored for >42 days at 4°C) were split in half. One half was washed using the Medtronic AutoLog device; the other half was washed using the blood bank’s Cobe 2991 Cell Processor. Analytes were measured on samples from the unwashed parent unit and from the washed daughter units. The parameters measured included hematocrit, free hemoglobin, lactate, lactate dehydrogenase (LDH), potassium, glucose, and pH.

When compared to the original untreated RBCs, the glucose, lactate, and potassium levels were decreased when washed in an autotranfusion device. Additionally, the free hemoglobin and LDH levels were significantly lower with the Medtronic Autolog cell saver than in the COBE 2991 Cell Processor.

Washing the RBC donor units in an autotransfusion device prior to transfusion can effectively attenuate the increases seen in glucose, potassium, free hemoglobin, and LDH associated with RBC storage lesion.

Zero balance ultrafiltration for the correction of acute acidosis after a period of prolonged deep hypothermic circulatory arrest

A 36-year-old woman with normal renal function underwent a total arch replacement requiring 110 minutes of deep hypothermic circulatory arrest. Prior to rewarming, a pH of 7.063 with a base deficit of 10.8 was obtained. Zero-balance ultrafiltration (Z-BUF) was initiated during rewarming 7 minutes after resumption of cardiopulmonary bypass. After one hour (10L) of Z-BUF, all electrolyte and acid-base disturbances were fully corrected. Our case illustrates that Z-BUF offers a valuable option for the correction of severe electrolyte and acid-base disturbances in adults undergoing cardiac surgery. Its use should be considered in addition to the more standard pharmacologic approaches to such derangements as it offers rapid and predictable electrolyte and acid-base correction and potential anti-inflammatory benefits.

SNPs in dopamine D2 receptor gene (DRD2) and norepinephrine transporter gene (NET) are associated with continuous performance task (CPT) phenotypes in ADHD children and their families

Haplotype-tagging SNP analyses were conducted to identify molecular genetic substrates of quantitative phenotypes derived from performance on a Continuous Performance Task (CPT). Three hundred sixty-four individuals were sampled from 152 families ascertained on the basis of at least one child having ADHD. Probands, their affected and unaffected siblings, and parents were administered a CPT. Four different components of performance were analyzed and tested for association with SNPs from 10 candidate genes involved in monoaminergic function. After correcting for multiple comparisons and controlling for multiple individuals from the same family, significant associations were identified between commission errors and SNPs in the DRD2 gene (rs2075654, rs1079596), and between reaction time variability and a SNP in the NET gene (rs3785155). These findings suggest that commission errors and reaction time variability are excellent candidates as ADHD endophenotypes based on previously published criteria. Results also shed light on the molecular genetic basis of specific processes that may underlie the disorder.

Refined crystallographic structure of Pseudomonas aeruginosa exotoxin A and its implications for the molecular mechanism of toxicity

Exotoxin A of Pseudomonas aeruginosa asserts its cellular toxicity through ADP-ribosylation of translation elongation factor 2, predicated on binding to specific cell surface receptors and intracellular trafficking via a complex pathway that ultimately results in translocation of an enzymatic activity into the cytoplasm. In early work, the crystallographic structure of exotoxin A was determined to 3.0 A resolution, revealing a tertiary fold having three distinct structural domains; subsequent work has shown that the domains are individually responsible for the receptor binding (domain I), transmembrane targeting (domain II), and ADP-ribosyl transferase (domain III) activities, respectively. Here, we report the structures of wild-type and W281A mutant toxin proteins at pH 8.0, refined with data to 1.62 A and 1.45 A resolution, respectively. The refined models clarify several ionic interactions within structural domains I and II that may modulate an obligatory conformational change that is induced by low pH. Proteolytic cleavage by furin is also obligatory for toxicity; the W281A mutant protein is substantially more susceptible to cleavage than the wild-type toxin. The tertiary structures of the furin cleavage sites of the wild-type and W281 mutant toxins are similar; however, the mutant toxin has significantly higher B-factors around the cleavage site, suggesting that the greater susceptibility to furin cleavage is due to increased local disorder/flexibility at the site, rather than to differences in static tertiary structure. Comparison of the refined structures of full-length toxin, which lacks ADP-ribosyl transferase activity, to that of the enzymatic domain alone reveals a salt bridge between Arg467 of the catalytic domain and Glu348 of domain II that restrains the substrate binding cleft in a conformation that precludes NAD+ binding. The refined structures of exotoxin A provide precise models for the design and interpretation of further studies of the mechanism of intoxication.

New approaches to antigen delivery

An improved understanding of immunologic events associated with immunization, the identification of promising new antigens, and an increased capacity to generate these antigens through chemical and biotechnology methods have led to many new vaccine opportunities. Inappropriate antigen exposure, however, can result in unwanted outcomes, such as incomplete protection, allergic reactions, autoimmunity, infection, or even tolerization. Thus, proper antigen delivery is critical for achieving the desired outcome. A number of vaccination approaches have now been described with varied degrees of success. The relative success of these approaches can be correlated with antigen delivery to specific presentation cells and stimulation of the immune system at sites where protective immunity is most appropriate. In addition, a greater understanding of mechanisms involving cells and effector molecules in the events of immunity may allow for improved possibilities for initiating, augmenting, and maintaining the response to a delivered antigen. This review provides insights into the various strategies currently being explored to optimize antigen delivery and the immune response to that antigen.

The quality of care for Medicare patients with peptic ulcer disease

OBJECTIVE

The aim of this study was to examine quality of care for hospitalized Medicare beneficiaries with peptic ulcer disease.

METHODS

Collaborating with five Peer Review Organizations, we used 1995 Medicare claim files to select samples of inpatients with a principal diagnosis of peptic ulcer disease. Quality of care indicators developed by content experts included percentages for ulcer patients tested for Helicobacter pylori (H. pylori); biopsied patients who received tissue tests; H. pylori-positive patients who received appropriate therapy; and ulcer patients screened for preadmission nonsteroidal anti-inflammatory drug (NSAID) use and counseled about risks.

RESULTS

Of 2,644 patients eligible for medical record review, 56% were tested for H. pylori, and 73% of those testing positive were treated appropriately; 84% of patients with endoscopic biopsies received a tissue test for H. pylori; 74% of patients were screened for preadmission NSAID use, 24% had documented counseling of NSAID use, and only 2% had documented counseling on the ulcer risk of NSAID use. Statistically significant regional variation occurred in four of six quality indicators. Outpatient records were reviewed for 529 patients to document prior outpatient H. pylori in this population; only 2% (n = 12) were tested for H. pylori in the year before admission.

CONCLUSIONS

Opportunities exist to improve quality of care by testing for and treating H. pylori in hospitalized Medicare beneficiaries with peptic ulcer disease and to improve screening for NSAIDs and counseling on ulcer risks.

Effect of nitric oxide upon gas transfer and structural integrity of a polypropylene membrane oxygenator

Gaseous nitric oxide (NO) may act as a membrane passivator during cardiopulmonary bypass by inhibition of platelet and leukocyte adhesion, activation, and aggregation. However, NO and its by-product nitrogen dioxide (NO2) are potently reactive and may be capable of degradation of membrane oxygenator constituents in an oxygen-rich environment. To test these concepts, nine polypropylene hollow fiber membrane oxygenators received 224 +/- 10 ppm NO and 6.7 +/- 1.7 ppm NO2 in 73% oxygen (O2), and six oxygenators received 73% O2, while being perfused with heparinized thrombocytopenic bovine blood for 6 hours. Oxygenators were used for measurement of O2 and carbon dioxide (CO2) transfer rates, structural integrity by pulsing with 22 psi water at 0.5 Hz for 6 hours, and scanning electron microscopic (SEM) examination of structural integrity. Transfer rates between groups at 0, 1, 3, and 6 hours revealed no differences in O2 or CO2. No oxygenator failed hydraulic tests of structural integrity or exhibited "wet-out" during bypass. No evidence of material degradation was shown in the SEM appearance of oxygenators. There were no differences in hematologic values. These data support the safety of gaseous NO in polypropylene membrane oxygenators for limited-term cardiopulmonary bypass.

Efficacy of treatment modalities in refractive amblyopia

BACKGROUND

The pediatric clinic of the State College of Optometry/University Optometric Center develops a yearly quality management plan to monitor patient care. One of the areas retrospectively reviewed for all outcomes is refractive amblyopia.

METHODS

A retrospective review of records was performed on patients diagnosed with refractive amblyopia. With the use of a prescribed protocol, each patient's progress was tracked for a period of 6 months. Major emphasis was placed on outcome as related to treatment modality. Treatment alternatives were optical correction alone, optical correction in conjunction with patching, and optical correction and patching with vision therapy.

RESULTS

Improvement criteria included a 2-line increase in visual acuity on the Snellen chart and an increase of 20 seconds of arc of stereopsis, as measured by the Wirt circles. The groups that patched with correction and those that received vision therapy had similar visual acuity improvement's; however, the latter group had a significantly greater improvement in stereopsis. Both groups performed significantly better in both categories when compared to the group receiving optical correction alone.

CONCLUSIONS

Though patching alone may be sufficient for improvement of visual acuity, binocular performance is significantly better when vision therapy is included in the treatment regimen.

Functional expression of the chicken low density lipoprotein receptor-related protein in a mutant chinese hamster ovary cell line restores toxicity of Pseudomonas exotoxin A and degradation of alpha2-macroglobulin

The low density lipoprotein receptor-related protein (LRP) is responsible for the clearance of several physiological ligands including a complex of proteinase and alpha2-macroglobulin (alpha2M) and for the entrance of Pseudomonas exotoxin A (PEA) into cells. We have prepared expression plasmids for the full-length chicken LRP (designated LRP100) and two intermediates encoding 25 and 67% of the receptor (designated LRP25 and LRP67, respectively) using overlapping cDNA fragments. LRP25 and LRP67 encode the N-terminal 22 and 64%, respectively, of LRP100 plus the transmembrane and intracellular domains. Transient transfection of these plasmids into COS-7 cells yielded recombinant proteins of expected molecular mass and immunoreactivity. However, LRP100 was incompletely processed into alpha- (515-kDa) and beta- (85-kDa) chains and was poorly transported from the endoplasmic reticulum to the Golgi compartment. Stable transformants of LRP100, LRP67, and LRP25 were generated in a mutant Chinese hamster ovary cell line that lacked expression of endogenous LRP and was resistant to PEA. All forms of recombinant LRP proteins were transported from the endoplasmic reticulum to the Golgi apparatus in Chinese hamster ovary cells as shown by their sensitivity to endoglycosidase H and resistance to neuraminidase. Cell surface iodination and subcellular fractionation studies indicated that all three LRP variants were expressed on the plasma membrane. Furthermore, expression of the three LRP variants restored, to various degrees, sensitivity to PEA and the ability to degrade methylamine-activated alpha2M (alpha2M*). These data suggest that deletion of large internal portions of LRP, including the processing site, does not prevent transport of LRP to the plasma membrane, nor does it abolish the interaction of LRP with alpha2M* or PEA. This LRP expression system may allow for the characterization of domains within LRP responsible for its multifunctionality.

Furin-mediated cleavage of Pseudomonas exotoxin-derived chimeric toxins

Pseudomonas exotoxin (PE) requires proteolytic cleavage to generate a 37-kDa C-terminal fragment that translocates to the cytosol and ADP-ribosylates elongation factor 2. Cleavage within cells is mediated by furin, occurs between arginine 279 and glycine 280, and requires an arginine at both P1 and P4 residues. To study the proteolytic processing of PE-derived chimeric toxins, TGFalpha-PE38 (transforming growth factor fused to the domains II and III of PE) and a mutant form, TGFalpha-PE38gly279, were each produced in Escherichia coli. When assessed on various epidermal growth factor (EGF) receptor-positive cell lines, TGFalpha-PE38 was 100-500-fold more toxic than TGFalpha-PE38gly279. In contrast to PE, where cleavage by furin is only evident at pH 5.5, furin cleaved TGFalpha-PE38 over a broad pH range, while TGFalpha-PE38gly279 was resistant to cleavage. TGFalpha-PE38 was poorly toxic for furin-deficient LoVo cells, unless it was first pretreated in vitro with furin. Furin treatment produced a nicked protein that was 30-fold more toxic than its unnicked counterpart. Using the single chain immunotoxin HB21scFv-PE40 as a substrate, furin-mediated processing of an antibody-based immunotoxin was also evaluated. HB21scFv-PE40, which targets cells expressing the transferrin receptor, was cleaved in a similar fashion to that of TGFalpha-PE38 and nicked HB21scFv-PE40 exhibited increased toxicity for LoVo cells. In short-term experiments, the rate of reduction in protein synthesis by furin-nicked immunotoxins was increased compared with unnicked protein, indicating that cleavage by furin can be a rate-limiting step. We conclude that furin-mediated cleavage of PE-derived immunotoxins is important for their cytotoxic activity.

Informed consent in emergency medicine: ethics under fire

Many ethical issues in emergency medicine involve the question of informed consent. In this article, the ethical basis for informed consent, the essential elements of a morally valid informed consent, and the inadequacy of the law as a moral guide for informed consent are discussed. The ways in which the nature of emergency medicine affects the application of moral principles are examined, and specific guidelines for assessing a patient's decision-making capacity regarding informed consent are provided.

Recombinant immunotoxins

Pseudomonas exotoxin has been genetically modified so that it targets cancer cells. This was accomplished by deleting its cell binding domain and replacing it with Fv fragments of antibodies that react with breast, colon, and other cancers. Several recombinant immunotoxins are now in clinical trials.

Pseudomonas exotoxin A mutants. Replacement of surface-exposed residues in domain III with cysteine residues that can be modified with polyethylene glycol in a site-specific manner

Pseudomonas exotoxin A (PE) is composed of three structural and functional domains. Domain Ia is responsible for cell recognition, domain II for translocation of PE across the cell membrane, and domain III for ADP-ribosylation of elongation factor 2. To investigate the role of the amino acids exposed on the surface of domain III, we replaced 15 of these, generating 29 different mutants at positions 412, 416, 418, 490, 513, 516, 522, 551, 576, 590, 599, 604, 606, 607 and 608. All but one mutant retained substantial ADP-ribosylation and cytotoxic activities. Modification of proteins with monomethoxy-polyethylene glycol (mPEG) prolongs their circulation in the blood stream and reduces their immunogenicity. Unlike PEGylated enzymes acting on small molecule substrates, PEGylated toxins may lose those functions that are based on macromolecular interactions. Therefore, we selectively PEGylated mutant PEs at positions 490, 513, 516, 522, 604, and 606. Most PEs modified by a 5-kDa mPEG via a disulfide or a thioether bond retained high cytotoxic activity. However, when a 20-kDa mPEG was used there was a decrease in cytotoxic activity with the disulfide-bonded molecules being more active. Positions 522 and 604 are good sites for PEGylation, but 490 is not. We also found that PEGylation of PE 522C prolonged its in vivo circulation time in mice.

TGF alpha-PE40 inhibits non-small cell lung cancer growth

The ability of a chimeric toxin containing transforming growth factor alpha (TGF alpha) and truncated Pseudomonas exotoxin A to inhibit NSCLC growth was investigated. TGF alpha-PE40 inhibited binding of 125I-EGF to NSCLC cell lines with an IC50 value of 0.5-3 micrograms/ml. Similarly, other forms of the fusion protein, TGF alpha-PE38 and TGF alpha-PE40Asp553, which have active TGF alpha binding domains, inhibited specific 125I-EGF binding to NSCLC cells with IC50 values of 0.1-2 and 0.05-05 microgram/ml respectively. TGF alpha-PE40 inhibited 35S-methionine uptake by NSCLC cells with an ED50 value of 1-30 ng/ml. TGF alpha-PE38, which has one of the two disulfide pairs of PE40, inhibited amino acid uptake with ED50 values of 3-50 ng/ml whereas TGF alpha-PE40Asp553, which lacks ADP ribosylation activity, had an ED50 > 100 ng/ml. TGF alpha-PE40 inhibited colony formation of NSCLC cells with an LD50 value of 0.008-0.1 ng/ml. Similarly, TGF alpha-PE38 inhibited NSCLC colony formation with LD50 values of 0.002-0.1 ng/ml whereas TGF alpha-PE40Asp553 had an LD50 > 10 ng/ml. Also, TGF alpha-PE40 and TGF alpha-PE38 inhibited NSCLC xenograft formation in nude mice whereas TGF alpha-PE40Asp553 was inactive. These data suggest that TGF alpha-PE40 and TGF alpha-PE38 may be useful agents to inactivate NSCLC cells.

Ethical considerations

The doctor's oath to serve the good of the patient requires the recognition that the patient's good consists of more than simply his or her biomedical health status. This article proposes a scheme for identifying the primary decision maker in clinical settings, particularly when the patient's own decision-making capacity is in question. A few of the many ethical controversies encountered in the practice of trauma medicine are examined and discussed.

[Gene cloning, expression of fusion protein TGF alpha-PE 40 and its inhibition activity on cancer cell growth]

Recombinant plasmid pYX382 and pYX3825 were constructed by fusing the cDNA encoding transforming growth factor type alpha (TGF alpha) to Pseudomonas exotoxin gene (PE) in which the cell recognition domain was deleted. The chimeric proteins produced by host E. Coli cells BL21 transformed by plasmid pYX382 and pYX3825 are termed TGF alpha-PE 40 which reacts with antibody against TGF alpha or antibody against PE in immunoblotting to show a 46 kd protein band reflecting the fusion of 56 kD TGF alpha peptide and 40 kD truncated Pseudomonas exotoxin molecule. An additional signal sequence OmpA was inserted into upstream region of TGF alpha cDNA in plasmid pYX3825 resulting in the partly secreting of expression product into medium and periplasm of the cells. TGF alpha-PE 40 was purified from medium by MONO Q ion exchange column and TSK 250 gel filtration column attached to Pharmacia EPLC system. The TGF alpha-PE 40 molecules showed a very strong activities inhibiting the protein synthesis and killing the cancer cells overexpressing EGF receptor on the cell surface.

The N-terminal region of the 37-kDa translocated fragment of Pseudomonas exotoxin A aborts translocation by promoting its own export after microsomal membrane insertion

The 37-kDa C-terminal fragment of Pseudomonas exotoxin A (PE; termed PE37 and composed of aa 280-613 of PE) translocates to the cell cytosol to cause cell death. PE37 requires a C-terminal endoplasmic reticulum retention sequence to be cytotoxic, indicating that the toxin may translocate to the cytosol from the endoplasmic reticulum. We show here that the N-terminal region of nascent PE37 can be inserted into the membrane of canine pancreatic microsomes by the preprocecropin signal sequence but then is exported or released from microsomes. The 34 N-terminal amino acids of the toxin fragment are sufficient to arrest translocation and prevent the microsomal accumulation of nascent chains that otherwise are sequestered into microsomes. These data support a role for the N-terminal region of PE37 in the translocation of the toxin from the endoplasmic reticulum to the cytosol in mammalian cells.

Alanine scanning mutagenesis identifies surface amino acids on domain II of Pseudomonas exotoxin required for cytotoxicity, proper folding, and secretion into periplasm

Pseudomonas exotoxin A (PE) is a single polypeptide chain that contains 613 amino acids and is arranged into three major structural domains. Domain Ia is responsible for cell recognition, domain II for translocation of PE across the membrane, and domain III for ADP-ribosylation of elongation factor 2. Recombinant PE can be produced in Escherichia coli and is efficiently secreted into the periplasm when an OmpA signal sequence is present. To investigate the role of the amino acids located on the surface of domain II in the action of the toxin against mammalian cells, we substituted alanine for each of the 27 surface amino acids present in domain II. Surprisingly, all 27 mutant proteins had some alteration in cytotoxicity when tested on human A431 or MCF7 cells or mouse L929 cells. Native PE has a compact structure and therefore is relatively protease resistant and very little ADP-ribosylation activity is detected in the absence of the denaturing agents like urea and dithiothreitol. Several of the mutations resulted in altered protease sensitivity of the toxin. Seven of the mutant molecules exhibited ADP-ribosylation activity without urea and dithiothreitol, indicating they are partially unfolded. Out of these seven mutants, six had increased cytotoxic activity on at least one of the target cell lines and the other retained its native cytotoxic potency.

In vitro and in vivo suppression of interleukin-2-activated killer cell activity by chimeric proteins between interleukin-2 and Pseudomonas exotoxin

The biological effects of IL-2 are mediated through high (complex of alpha and beta chain) or intermediate (beta chain) affinity IL-2 receptors. Previously, chimeric proteins composed of IL-2 and Pseudomonas exotoxin (IL-2-PE) were shown to be specifically cytotoxic to cells bearing IL-2 receptors. It has also been shown that IL-2-PE chimeric proteins can abrogate T cell-mediated immune response in vitro. In the current study, we have investigated the effects of IL-2-PE on LAK activity both in vivo and in vitro. We administered either IL-2-PE40 (comprised of IL-2 and 40-kDa portion of PE) or IL-2-PE66 (comprised of IL-2 and 66-kDa molecule of PE) to normal C57BL/6 mice for 3 or 8 days and LAK activity was assessed in various organs of mice. We found that IL-2-PE40 generated LAK activity in various compartments of mice and the level of activity was slightly lower than that observed with an equivalent amount of recombinant (r) IL-2 alone. However, IL-2-PE66 failed to generate LAK activity which would have been induced due to an equivalent concentration of rIL-2. IL-2-PE66 also did not induce LAK activity from the splenocytes during in vitro culture while IL-2-PE40 generated good LAK activity. An equivalent amount of IL-2 also generated potent LAK activity. The suppression of LAK activity by IL-2-PE66 was also evident in cells preactivated with IL-2; however, this inhibition was partial. The suppressive activity of IL-2-PE66 was shown to be mediated through IL-2 receptor interactions as excess amounts of rIL-2 were able to abrogate its effect. Both IL-2 toxins were equivalently cytotoxic to IL-2 receptor-bearing HUT 102 cells and both were able to compete from high and intermediate affinity IL-2 receptors. Taken together, our data indicate that IL-2-PE66 is highly cytotoxic to LAK cells while IL-2-PE40 is less cytotoxic. Thus, data from our study and from other published reports indicate that IL-2-PE66 is more potent immunosuppressive agent than IL-2-PE40.

A recombinant form of Pseudomonas exotoxin directed at the epidermal growth factor receptor that is cytotoxic without requiring proteolytic processing

Pseudomonas exotoxin A is composed of three structural domains that mediate cell recognition (I), membrane translocation (II), and ADP-ribosylation (III). Within the cell, the toxin is cleaved within domain II to produce a 37-kDa carboxyl-terminal fragment, containing amino acids 280-613, which is translocated to the cytosol and causes cell death. In this study, we constructed a mutant protein (PE37), composed of amino acids 280-613 of Pseudomonas exotoxin A, which does not require proteolysis to translocate. PE37 was targeted specifically to cells with epidermal growth factor receptors by inserting transforming growth factor-alpha (TGF-alpha) after amino acid 607 near the carboxyl terminus of Pseudomonas exotoxin A. PE37/TGF-alpha was very cytotoxic to cells with epidermal growth factor receptors. It was severalfold more cytotoxic than a derivative of full-length Pseudomonas exotoxin A containing TGF-alpha in the same position, probably because the latter requires intracellular proteolytic processing to exhibit its cytotoxicity, and proteolytic processing is not 100% efficient. Deletion of 2, 4, or 7 amino acids from the amino terminus of PE37/TGF-alpha greatly diminished cytotoxic activity, indicating the need for a proper amino-terminal sequence. In addition, a mutant containing an internal deletion of amino acids 314-380 was minimally active, indicating that other regions of domain II are also required for the cytotoxic activity of Pseudomonas exotoxin A.

Monoclonal antibody C242-Pseudomonas exotoxin A. A specific and potent immunotoxin with antitumor activity on a human colon cancer xenograft in nude mice

Two immunotoxins were constructed by chemically coupling the monoclonal antibody C242 to Pseudomonas exotoxin A (PE) or a modified form, NlysPE40, that lacks the cell binding domain of PE. Monoclonal antibody C242 recognizes a specific sialylated carbohydrate epitope on a high molecular weight membrane glycoprotein present on cells of human colon, pancreatic, and cervical cancers. C242-PE and C242-NlysPE40 were very cytotoxic for cells expressing this antigen with 50% inhibition of protein synthesis occurring on Colo205 cells at 0.2 ng/ml (0.9 pM) for C242-PE and 6.0 ng/ml (31 pM) for C242-NlysPE40. The two immunotoxins also exhibited a strong antitumor effect on a human colon cancer xenograft grown in nude mice. The specificity and potency of these two C242 immunotoxins warrant their further development for the treatment of cancer.

Targeting growth factor receptors with fusion toxins

Recombinant toxins which bind to growth factor receptors have been prepared and used to kill cells responsible for malignant or autoimmune disease. Our strategy has been to genetically fuse ligands to different forms of Pseudomonas exotoxin which due to mutations or deletions do not bind to normal cells. The resulting recombinant chimeric toxins, in concentrations often less than 1 ng/ml, selectively kill cells expressing the appropriate growth factor receptor. The ligand may be a growth factor, such as transforming growth factor alpha (TGF alpha), interleukin 6 (IL6) or interleukin 2 (IL2), or single chain antigen binding proteins, such as the variable heavy and light regions of the monoclonal antibody anti-Tac. These chimeric toxins kill not only established cell lines but also fresh tumor cells from patients and display anti-tumor activity toward human malignant tumors in nude mice. While clinical trials are beginning with some of these agents, work continues to improve the effectiveness of recombinant chimeric toxins, and to widen the scope of disorders which might be treated by this approach.

Characterization of a cellular protease that cleaves Pseudomonas exotoxin

Pseudomonas exotoxin (PE) is a 66-kDa bacterial toxin that is proteolytically cleaved by cells to produce an N-terminal fragment of 28 kDa and a C-terminal 37-kDa fragment which translocates to the cytosol and inhibits protein synthesis (M. Ogata, V.K. Chaudhary, I. Pastan, and D.J. FitzGerald, J. Biol. Chem. 265:20678-20685, 1990). When cells were broken by homogenization, the appropriate proteolytic activity was found associated with cellular membranes and not in a soluble fraction. Proteolysis of PE by crude membranes was stimulated by divalent cations, was ATP independent, and had a pH optimum of 5.5. When cells were disrupted by nitrogen cavitation and fractionated on Percoll gradients, proteolytic activity was present in fractions corresponding to the density of plasma membranes or endosomes but not in fractions containing lysosomes. Proteolytic activity was recovered in detergent extracts after crude membranes were treated with Nonidet P-40 or octylglucoside. Proteolysis of PE by either crude membranes or detergent extracts generated fragments of 28 and 37 kDa. The sizes of these fragments resembled those produced by intact cells. However, when the nontoxic mutant, PEgly276, which cannot be cleaved appropriately by intact cells, was incubated with membranes or extracts there was no production of the 28- and 37-kDa fragments.

Recombinant toxins for cancer treatment

Recombinant toxins target cell surface receptors and antigens on tumor cells. They kill by mechanisms different from conventional chemotherapy, so that cross resistance to conventional chemotherapeutic agents should not be a problem. Furthermore, they are not mutagens and should not induce secondary malignancies or accelerate progression of benign malignancies. They can be mass-produced cheaply in bacteria as homogeneous proteins. Either growth factor-toxin fusions or antibody-toxin fusions can be chosen, depending on the cellular target.

Increased cytotoxic activity of Pseudomonas exotoxin and two chimeric toxins ending in KDEL

Pseudomonas exotoxin (PE) is a 66,000 molecular weight protein secreted by Pseudomonas aeruginosa. PE is made up of three domains, and PE40 is a form of PE which lacks domain Ia (amino acids 1-252) and has very low cytotoxicity because it cannot bind to target cells. The sequence Arg-Glu-Asp-Leu-Lys (REDLK) at the carboxyl terminus of Pseudomonas exotoxin has been shown to be important for its cytotoxic activity (Chaudhary, V. K., Jinno, Y., FitzGerald, D. J., and Pastan, I. (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 308-312). In this study, we tested the effect of altering the carboxyl sequence of PE from REDLK to the characteristic endoplasmic reticulum retention sequence, KDEL, or to KDEL repeated three times (KDEL)3. We also made similar changes at the carboxyl terminus of two chimeric toxins in which domain I of PE (amino acids 1-252) was either replaced with transforming growth factor alpha (TGF alpha) to make TGF alpha-PE40 or with a single chain antibody (anti-Tac) reacting with the human interleukin 2 receptor to make anti-Tac(Fv)-PE40. Statistical analyses of our results demonstrate that PE and its derivatives ending in KDEL or (KDEL)3 are significantly more active than PE or derivatives ending in REDLK. We have also found that brefeldin A, which is known to perturb the endoplasmic reticulum, inhibits the cytotoxic action of PE. Our results suggest that the altered carboxyl terminus may enable the toxin to interact more efficiently with a cellular component involved in translocation of the toxin to the cytosol.

Continuous arterial and venous blood gas monitoring during cardiopulmonary bypass

A new monitoring technique, based on optical fluorescence chemistry, allows continuous monitoring of all blood gas variables during cardiopulmonary bypass. To evaluate the clinical performance of this monitor, we drew 220 arterial and 216 venous blood samples from 15 patients, and simultaneous blood gas values displayed by the monitor were compared with standard laboratory measurements. The continuous monitor predicted laboratory values with varying degrees of accuracy. (R2 values by linear regression: arterial oxygen tension 0.86, venous oxygen tension 0.36, arterial carbon dioxide tension 0.58, venous carbon dioxide tension 0.72, arterial pH 0.53, venous pH 0.58; pH 0.53, venous pH 0.58; p less than 0.0001). Monitor values of arterial oxygen tension overestimated laboratory values (bias = + 43.5 mm Hg), but the laboratory reference method likely underestimated true arterial oxygen tension in the high range achieved on bypass. Monitoring of venous oxygen tension was imprecise (precision = +/- 6.51 mmHg), regardless of whether stable conditions existed during the sampling period. Monitoring of carbon dioxide tension and pH showed small bias (carbon dioxide tension within 2 mm Hg, pH within 0.03) and good precision (carbon dioxide tension within 3 mm Hg, pH within 0.03). With the development of unstable conditions on bypass, monitor arterial oxygen tension values showed a changing relationship to corresponding laboratory values. In conclusion, arterial and venous carbon dioxide tension and pH monitoring provide acceptably accurate alternatives to laboratory measurement of these variables during cardiopulmonary bypass. Arterial oxygen tension monitoring accurately indicates changes in oxygen tension in the arterial oxygen tension range typically produced during extracorporeal circulation. Oxygen tension monitoring in the venous oxygen tension range is too imprecise for clinical decision-making purposes.

Treatment of corneal allograft rejection with the cytotoxin IL-2-PE40

IL-2-PE40 is a recombinant chimeric protein composed of IL-2, fused to a modified pseudomonas exotoxin. This molecule is extremely toxic to activated T cells expressing high-affinity IL-2R. We used this new molecule for selective immunosuppression to treat corneal allograft rejection in the rat, using Fisher and Lewis rats, a strain combination differing only in medial and minor histocompatibility antigens. The effect of IL-2-PE40 on the immunologic response was studied using both a heterotopic corneal graft model and orthotopic grafts. At the dose of 0.31 micrograms/g given intraperitoneally every 12 hr, IL-2-PE40 produced a significant reduction of both total lymph node cells and cytotoxic-T-cell (CTL) activity in draining lymph nodes (DLN) of heterotopically grafted animals. IL-2-PE40 treatment also significantly reduced the clinical rejection score and cumulative rejection rate (CRR) in orthotopic grafts and appears to be a very effective immunosuppressive agent.

Cytotoxic effects of a recombinant chimeric toxin on rapidly proliferating vascular smooth muscle cells

BACKGROUND

Restenosis after percutaneous transluminal coronary angioplasty is associated with activation of medial smooth muscle cells (SMCs); they proliferate, migrate to the subintima, and narrow the vessel lumen. Cancer cells often express more cell surface receptors than do normal cells. This has allowed tumor cells to be specifically targeted using cytotoxic agents. We have examined whether a similar concept can be applied to rapidly proliferating but nontransformed SMCs. Pseudomonas exotoxin (PE; MW, 66 kDa) is a potent toxin that kills cells by inhibiting protein synthesis; its toxicity is diminished when its cell recognition domain is deleted to produce a 40-kDa protein (PE40).

METHODS AND RESULTS

A complementary DNA encoding transforming growth factor alpha (TGF alpha) was ligated to that encoding PE40 and the chimeric toxin TGF alpha-PE40, which is cytotoxic to cancer cells displaying epidermal growth factor (EGF) receptors, was expressed in Escherichia coli. The ability of this toxin to kill proliferating SMCs was tested. When cells were seeded at low density (2,500 cells/cm2) and grown in medium supplemented with 10% fetal bovine serum, they were found to be rapidly proliferating; these cells were very sensitive to the cytotoxic effects of TGF alpha-PE40 (ID50, 4.0 +/- 0.17 ng/ml). In contrast, cytotoxicity was 30-fold less (ID50, 125 +/- 23 ng/ml; p less than 0.0004) when cells were in a quiescent state (grown in medium supplemented with 0.5% fetal bovine serum).

CONCLUSIONS

Competition studies using excess EGF indicated that the cytotoxic effects of TGF alpha-PE40 are specifically mediated by the EGF receptor. EGF receptor binding analysis demonstrated that rapidly proliferating SMCs display 10-fold more EGF receptors than do quiescent SMCs in vitro. Thus, a chimeric toxin targeted toward the EGF receptor can selectively kill rapidly proliferating SMCs. Whether this toxin or other chimeric toxins directed against other cell surface receptors will effectively inhibit SMCs proliferating in vivo or be useful in preventing restenosis remains to be determined.

Expression of high-affinity interleukin 4 receptors on murine sarcoma cells and receptor-mediated cytotoxicity of tumor cells to chimeric protein between interleukin 4 and Pseudomonas exotoxin

The presence of interleukin 4 receptor (IL-4R) on methylcholanthrene (MCA-106, MCA-102, and MC-38)- and viral DNA (G-2TS and 14-2TS)-induced murine sarcoma cells was demonstrated. MCA-106 tumor cells express about 500 to 1348 (median, 800) interleukin 4 (IL-4) binding sites/cell with a dissociation constant (Kd) of 115 +/- 26 pM (mean +/- SD, n = 4). By Northern blot analysis, tumor cells exhibited a single mRNA species of 3.9 kilobases. Other murine sarcoma (MCA-102), colon adenocarcinoma (MC-38), G-2TS, and 14-2TS tumor cells express low numbers of IL-4R. By immunoperoxidase staining, 81 to 92% of the cells from fresh MCA-106 tumors were positive for IL-4 receptors, while only 7 to 10% of tumor-infiltrating cells were Thy 1.2 and less than 1% Mac-1 positive. Using a chimeric protein composed of IL-4 and Pseudomonas exotoxin (IL-4-PE40), we observed that IL-4-PE40 was cytotoxic (determined by inhibition of protein synthesis by [3H]leucine uptake) to MCA-106 tumor cells in a dose-dependent manner. A nonchimeric protein (PE40) that cannot bind to the IL-4R did not inhibit protein synthesis in tumor cells. A chimeric mutant protein (IL4-PE40 asp553) that can bind to IL-4 receptors but does not have the capability to inhibit protein synthesis was not cytotoxic to tumor cells. These studies strongly suggest that IL-4R on murine MCA-106 sarcoma cells is internalized when occupied by IL-4 PE40. Furthermore, a neutralizing antibody (11B11) to IL-4 completely abolished the protein synthesis-inhibitory activity of IL-4-PE40. G-2TS tumor cells which expressed low numbers of IL-4 receptors were not vulnerable to cytotoxicity by IL-4-PE40. Taken together, these data suggest that IL-4 receptor may be a target for IL-4-toxin therapy.

Immunospecific suppression of encephalitogenic-activated T lymphocytes by chimeric cytotoxin IL-2-PE40

We examined the action of a chimeric protein, IL-2-PE40, on the development of a T cell-mediated disease of the central nervous system with numerous similarities to multiple sclerosis, experimental autoimmune encephalomyelitis (EAE). EAE is caused by IL-2 receptor-bearing T cells specific for myelin basic protein (BP). We report here that the treatment of Lewis rats with IL-2-PE40 delayed and shortened the course of EAE induced by BP in adjuvant and dramatically prevented EAE mediated by anti-myelin basic protein T line cells. The absence of paralytic signs, the absence of cell infiltration in the central nervous system, and the abatement of cellular immunity to myelin basic protein in the treated rats are direct consequences of the specific mechanism of action of IL-2-PE40. Our data support the notion that IL-2-PE40 may be efficient as an immunosuppressive agent for those disorders in which activated T cells play a crucial role.

Redirecting Pseudomonas exotoxin

Pseudomonas exotoxin (PE) is a three-domain bacterial toxin that kills mammalian cells by gaining entry to the cytosol and inactivating protein synthesis. The pathway of toxin entry includes binding to a surface receptor, internalization via coated pits and endosomes, proteolytic processing, reduction of disulfide bonds and finally the translocation of an enzymatically active C-terminal fragment to the cytosol. Once in the cytosol this fragment inhibits protein synthesis by ADP ribosylating elongation factor 2. Because of its potency PE and its derivatives have been directed to kill various target cells. It is hoped this strategy will lead to the development of a novel kind of therapeutic agent for the treatment of various human diseases including cancer, AIDS and various immunological disorders.

Administration of IL-2-PE40 via osmotic pumps prevents adjuvant induced arthritis in rats. Improved therapeutic index of IL-2-PE40 administered by continuous infusion

IL-2-PE40 is a chimeric cytotoxin composed of interleukin 2 (IL-2) fused to a truncated form of Pseudomonas exotoxin (PE) that lacks its binding domain. IL-2-PE40 has been shown to exhibit therapeutic potency in several models in vivo when administered i.p. twice a day. Here we show that the continuous administration of IL-2-PE40 by an osmotic pump specifically prevents the development of adjuvant induced arthritis in rats with an improved therapeutic efficacy as compared to daily repeated i.p. injections. Stabilization of IL-2-PE40 at 37 degrees C for the continuous administration by pumps was achieved by adding NAD, the substrate for the enzyme portion of the chimeric toxin.

Analysis of Pseudomonas exotoxin activation and conformational changes by using monoclonal antibodies as probes

Pseudomonas exotoxin (PE) is a protein toxin composed of three structural domains. In its native form, the toxin is a 66,000-Mr proenzyme that must be activated to express full ADP-ribosylating activity. To study the process of activation and accompanying conformational changes, we have isolated 10 monoclonal antibodies to a 40,000-Mr fragment of the toxin (PE40) that exhibits full enzyme activity but lacks the toxin's cell-binding domain and contains amino acids 253 to 613 (comprising domains II, Ib, and III). By using mutant PE molecules in which all of domain I and portions of domains II, Ib, and III were deleted, the locations of the epitopes for each of the antibodies were determined. Eight of these monoclonal antibodies were further characterized. Of these eight, all reacted with soluble PE40 and an interleukin-2-PE40 conjugate, but only two reacted strongly with native soluble PE. However, all eight reacted with PE after it had been immobilized on nitrocellulose or after it had been activated to express full ADP-ribosylating activity. Antibodies were also assessed for their ability to neutralize the cytotoxic activity of either PE or interleukin-2-PE40. These antibodies should be useful as probes for monitoring the activation and processing of PE that occur during endocytosis and in determining the location of epitopes that are important for toxin activity.

Mutagenesis of Pseudomonas exotoxin in identification of sequences responsible for the animal toxicity

Pseudomonas exotoxin (PE) is composed of three structural domains that are responsible for cell recognition, membrane translocation, and ADP-ribosylation. The deletion of the cell recognition domain (domain Ia) of PE results in a molecule that does not bind to target cells and has low toxicity in mice (Hwang, J., FitzGerald, D.J.P., Adhya, S., and Pastan, I. (1987) Cell 48, 129-136). To determine the specific sequences required for cell binding as well as cell and animal toxicity, a series of domain I mutants was constructed. Using a T7 promoter-based expression system and an OmpA signal sequence, large amounts of the various mutant toxins were secreted into the periplasm from which they were easily purified in milligram quantities. The data indicate that amino acids at positions 246, 247, and 249 have an important role in the toxicity of PE. Conversion of these amino acids to glutamic acid or glycine but not to lysine or deletion of amino acids 241-250 diminishes the toxicity of PE. When combined with a mutation at position 57 a molecule is created that has very low toxicity against cultured cells or in mice.

Anti-Tac(Fv)-PE40, a single chain antibody Pseudomonas fusion protein directed at interleukin 2 receptor bearing cells

Anti-Tac(Fv)-PE40 is a chimeric single chain immunotoxin in which anti-Tac variable heavy and light chains held together by a peptide linker are attached to PE40, a truncated form of Pseudomonas exotoxin. This molecule was shown to be extremely cytotoxic for interleukin 2 (IL2) receptor bearing cells in tissue culture (Chaudhary, V. K., Queen, C., Junghans, R. P., Waldmann, T. A., FitzGerald, D. J., and Pastan, I. (1989) Nature 339, 394-397). Here we describe various forms of anti-Tac(Fv)-PE40 protein in which the order of the variable domains of anti-Tac has been switched and also three different types of peptide linkers have been used. All these proteins were purified to near homogeneity and were found to have similar cytotoxic activities against various human cells expressing the p55 subunit of the IL2 receptor. Anti-Tac(Fv)-PE40 was also found to have a very potent suppressive activity against phytohemagglutinin-activated human lymphoblasts and in a human mixed lymphocyte reaction. Anti-Tac(Fv)-PE40 appeared in the blood rapidly in mice after intraperitoneal administration and could be detected in the blood for up to 8 h. Anti-Tac(Fv)-PE40 warrants evaluation as an anti-tumor and immunosuppressive agent in humans.

TGF alpha-anti-Tac(Fv)-PE40: a bifunctional toxin cytotoxic for cells with EGF or IL2 receptors

Conventional immunotoxins and chimeric toxins made in bacteria are directed to only one receptor or antigen on target cells. In this report we describe the construction of a chimeric molecule TGF alpha-anti Tac(Fv)-PE40 which is composed of human transforming growth factor type alpha attached to anti-Tac(Fv) which is in turn attached to PE40, a form of pseudomonas exotoxin, devoid of its cell recognition domain. TGF alpha-anti-Tac(Fv)-PE40 is a bifunctional toxin that is produced in E. coli and is active on cells bearing either IL2 or EGF receptors.