Purification of Treponema pallidum from Infected Rabbit Tissue: Resolution into Two Treponemal Populations

Virulent Treponema pallidum organisms, extracted from infected rabbit testes, were subjected to velocity sedimentation in discontinuous gradients of Hypaque, a high density, low viscosity material. After centrifugation of extracts at 20 C for 45 min at 100,000 x g, treponemes separated into two distinct bands based upon their relative velocities, although some variation was observed in the densities of the two bands and the number of treponemes per band. Rabbit tissue components sedimented more rapidly. Dark field and electron microscopy of preparations after velocity sedimentation indicated that treponemes retained general structural characteristics and no tissue contamination occurred in the treponemal fractions. Purification of treponemes in Hypaque resulted in their loss of motility and infectivity based upon animal inoculation. Antigenicity with respect to reactivity with antibody was preserved as shown by the high fluorescence intensity of treponemes in the fluorescent treponemal antibody adsorption test.

Characteristics of Lisch nodules in patients with neurofibromatosis type 1

PURPOSE

To assess the prevalence and location of Lisch nodules among patients with neurofibromatosis type 1.

PATIENTS AND METHODS

This was a prospective observational case series in which 369 consecutive patients from a neurofibromatosis clinic participated. Predetermined inclusion and exclusion criteria were applied to these participants. The presence of Lisch nodules was determined by one of the authors (SMC). The percentage of patients with neurofibromatosis type 1 with Lisch nodules was calculated. Lisch nodules were characterized as being distributed superiorly, inferiorly, or equally in each eye. The percentage of eyes in each group was ascertained.

RESULTS

Among patients of all ages with neurofibromatosis type 1, 63.2% had Lisch nodules, whereas 92% of postpubertal patients had Lisch nodules. Among eyes with Lisch nodules, 80% had an inferior distribution.

CONCLUSIONS

This study corroborated previously reported data regarding the prevalence of Lisch nodules in patients with neurofibromatosis type 1 and found that Lisch nodules were predominantly located inferiorly on the iris. The authors propose that exposure to sunlight may be the mechanism for this distribution of hamartomatous nodules.

Severe pupil distortion following transchamber repair of a cyclodialysis cleft

This report describes a potential complication following the repair of a traumatic cyclodialysis cleft in a pediatric patient using a novel technique. A healthy 11-year-old boy suffered a blunt traumatic tennis ball injury to his left eye. He underwent repair of a retinal dialysis with detachment shortly after the injury. Postoperatively, he developed persistent hypotony, shallow anterior chamber, and hypotony maculopathy. An occult cyclodialysis cleft was suspected. Examination under anesthesia revealed a small cyclodialysis deft. The cleft was closed by transchamber placement of prolene sutures across the cleft under direct visualization through a Tano lens. Postoperative course was complicated by severe pupillary distortion despite subsequent suture removal.

Endophthalmitis in patients with disseminated fungal disease

BACKGROUND/PURPOSE

Fungal endophthalmitis caused by dissemination from extraocular fungal infections has been reported to vary between 9% and 45%. However, recent clinical experience disagrees with that. This study is an investigation of patients in an inner city teaching hospital, the risks associated with endogenous fungal endophthalmitis, and this incidence.

METHODS

All ophthalmology consultations between February 1995 and August 2000 that might be associated with disseminated fungal infection were examined in a prospective manner. Patients were excluded if there was no evidence of a positive fungal culture from any site at any time. Visual symptoms were recorded along with ophthalmologic and systemic examination features. Information was gathered, including the identity of cultured organisms, the sites from which the organisms were obtained, and the patients' disposition.

RESULTS

During this interval, 170 consultation requests contained the words "endophthalmitis" or "retinitis" and/or indicated concern about disseminated fungal infections. Extraocular fungal infections were found in 114 patients, but only 82 of them had evidence of systemic dissemination. Some patients had more than one organism. The following are listed in decreasing frequency of occurrence: Candida albicans, Torulopsis glabrata, Candida tropicalis, Candida parapsilosis, Candida krusei, Aspergillus niger, and others. Only two patients had evidence of chorioretinitis and progressed to fungal endophthalmitis.

CONCLUSIONS

Endophthalmitis was rare among these patients with known fungal infections. Less than 2% had any related ophthalmic manifestations. Nevertheless, since treatment can save vision, evidence of intraocular infection should be sought as eagerly as before.

Flavin specificity and subunit interaction of Vibrio fischeri general NAD(P)H-flavin oxidoreductase FRG/FRase I

Apoenzyme of the major NAD(P)H-utilizing flavin reductase FRG/FRase I from Vibrio fischeri was prepared. The apoenzyme bound one FMN cofactor per enzyme monomer to yield fully active holoenzyme. The FMN cofactor binding resulted in substantial quenching of both the flavin and the protein fluorescence intensities without any significant shifts in the emission peaks. In addition to FMN binding (K(d) 0.5 microM at 23 degrees C), the apoenzyme also bound 2-thioFMN, FAD and riboflavin as a cofactor with K(d) values of 1, 12, and 37 microM, respectively, at 23 degrees C. The 2-thioFMN containing holoenzyme was about 40% active in specific activity as compared to the FMN-containing holoenzyme. The FAD- and riboflavin-reconstituted holoenzymes were also catalytically active but their specific activities were not determined. FRG/FRase I followed a ping-pong kinetic mechanism. It is proposed that the enzyme-bound FMN cofactor shuttles between the oxidized and the reduced form during catalysis. For both the FMN- and 2-thioFMN-containing holoenzymes, 2-thioFMN was about 30% active as compared to FMN as a substrate. FAD and riboflavin were also active substrates. FRG/FRase I was shown by ultracentrifugation at 4 degrees C to undergo a monomer-dimer equilibrium, with K(d) values of 18.0 and 13.4 microM for the apo- and holoenzymes, respectively. All the spectral, ligand equilibrium binding, and kinetic properties described above are most likely associated with the monomeric species of FRG/FRase I. Many aspects of these properties are compared with a structurally and functionally related Vibrio harveyi NADPH-specific flavin reductase FRP.

Interferon-alpha 2a treatment of neuro-Behcet disease

Behcet disease is a multisystemic, chronic, recurrent inflammatory disorder characterized as a triad of hypopyon uveitis, oral aphthae, and genital ulcers. Neurologic involvement in Behcet disease (neuro-Behcet) is common. Neuro-Behcet disease typically manifests late after disease onset, rarely coincides with ocular involvement, and often heralds a poor prognosis for final vision and survival. We present a case of neuro-Behcet disease with neurologic onset concomitant with systemic and ocular involvement that was responsive to treatment with interferon-alpha 2a.

Conformationally variable Rab protein surface regions mapped by limited proteolysis and homology modelling

Tryptic proteolysis of the small GTPases Rab4 and Rab5 is a multi-step, nucleotide-dependent process. Using N-terminal peptide sequencing, matrix-assisted laser desorption ionization-time-of-flight MS and molecular modelling, we identified the three initial sites of proteolysis in Rab5 as Arg-4, Arg-81 and Arg-197. Arg-4 and Arg-81 lie within regions previously implicated in Rab5 endocytic function, and Arg-197 lies in a region involved in membrane targeting. Topologically, Arg-81 lies within the conformationally variable Switch II region shown to be important for protein-protein interactions of other GTPases. Homology modelling studies on Rab5 indicate that the Arg-81 side chain is buried in the Rab5 GTP conformation, but is solvent-accessible in the GDP conformation, explaining the dependence of proteolysis on nucleotides. Peptide mapping of Rab4 was performed to take advantage of additional scissile bonds within Switch II to determine more precisely the limits of the nucleotide-dependent protease-accessible region. The Rab4 cleavage sites corresponded to Arg-81 and Pro-87 of Rab5, and taken together with the finding that Rab5 was not cleaved at Arg-91 this analysis defines an eight-residue surface-exposed conformationally variable region lying in the centre of Switch II. A sequence comparison of Rab proteins shows these eight residues to have a loosely conserved motif that we term Switch II(v) for its relative variability. C-terminal to Switch II(v) is a highly conserved Rab-specific YYRGA motif that we term Switch II(c) for its constant sequence. N-terminal to Switch II(v) is a sequence-invariant G-domain involved in nucleotide binding and hydrolysis. We propose that the Rab Switch II(v) region imparts specificity to nucleotide-dependent protein-protein interactions.

Antitumor activity of DAB389IL-2 fusion toxin in mycosis fungoides

BACKGROUND

DAB389IL-2 is a novel fusion toxin that retargets the cytotoxic A-chain of diphtheria toxin to interleukin-2 (IL-2) receptor-expressing tumors.

OBJECTIVE

The purpose of this phase I trial was to study the toxicity, maximum tolerated dose, and clinical efficacy of DAB389IL-2 in IL-2 receptor expressing lymphoproliferative malignancies, including cutaneous T-cell lymphoma.

METHODS

DAB389IL-2 was administered intravenously daily for 5 days every 3 weeks. Dose escalation occurred between patient groups. Patients were monitored for laboratory and clinical toxicity, kinetics, immune response, and clinical efficacy.

RESULTS

Thirty-five patients with cutaneous T-cell lymphoma (including 30 patients with mycosis fungoides) were treated. Previously, conventional therapy had not worked for 34 of the patients. Thirteen patients (37%) achieved an objective response, including a complete response in five patients (14%). Complete response was achieved in patients with extensive erythroderma and tumor stage mycosis fungoides. Adverse events consisted of reversible fever/chills, hypotension, nausea/vomiting, and elevation of hepatic transaminase. Doses of less than 31 microg/kg per day were well tolerated. Clinical responses were observed at all dose levels.

CONCLUSION

DAB389IL-2 is well tolerated at doses of less than 31 microg/kg per day, and it induced clinical responses in previously treated mycosis fungoides, providing evidence for the antitumor activity of this molecule.

Phase I trial of a ligand fusion-protein (DAB389IL-2) in lymphomas expressing the receptor for interleukin-2

The purpose of this study was to evaluate the safety, tolerability, pharmacokinetics, and possible antitumor activity of a ligand fusion-protein, DAB389IL-2, in a phase I trial. This was a multicenter, open-label, dose-escalation trial. Patients with preserved organ function and histologically confirmed relapsed cutaneous T-cell lymphoma (CTCL), other non-Hodgkin's lymphomas (NHL), or Hodgkin's disease (HD) were eligible if their cancer was shown to express the interleukin (IL)-2 receptor by an immunohistochemical assay for the p55 or the p75 subunit. Patients received up to eight courses of DAB389IL-2 given as a short intravenous infusion daily for 5 days with subsequent courses every 21 days. The maximum tolerated dose (MTD) and tumor response was determined according to standard criteria. Seventy-three patients (44 men/29 women), aged 16 to 81 years (mean, 50.7) with CTCL (n = 35), NHL (n = 17), and HD (n = 21) were enrolled. The patients were extensively treated, failing 0 to 15 previous therapies (median, 4). Patients received one to six courses (mean, 3.3) of DAB389IL-2 over a range of 3 to 31 micrograms/kg/day. The dose-limiting toxicity was asthenia, establishing the maximum tolerated dose of 27 micrograms/kg/day. Approximately half of all patients had significant titers of antibody to diphtheria toxin or to DAB389IL-2 at the time of enrollment compared with 92% with titers at the end of treatment. The presence of antibody did not preclude clinical response. There were five complete (CR) and eight partial (PR) remissions in patients with CTCL with one CR and two PR occurring in NHL. The median time to response was 2 months and the duration of response was 2 to 39+ months. No responses were documented in patients with HD. DAB389IL-2 is well tolerated with an MTD of 27 micrograms/kg/day. This ligand fusion-protein showed antitumor effects in patients with IL-2 receptor expressing CTCL and NHL. Additional trials in these diseases are warranted.

Lactose repressor protein: functional properties and structure

The lactose repressor protein (LacI), the prototype for genetic regulatory proteins, controls expression of lactose metabolic genes by binding to its cognate operator sequences in E. coli DNA. Inducer binding elicits a conformational change that diminishes affinity for operator sequences with no effect on nonspecific binding. The release of operator is followed by synthesis of mRNA encoding the enzymes for lactose utilization. Genetic, chemical and physical studies provided detailed insight into the function of this protein prior to the recent completion of X-ray crystallographic structures. The structural information can now be correlated with the phenotypic data for numerous mutants. These structures also provide the opportunity for physical and chemical studies on mutants designed to examine various aspects of lac repressor structure and function. In addition to providing insight into protein structure-function correlations, LacI has been utilized in a wide variety of applications both in prokaryotic gene expression and in eukaryotic gene regulation and studies of mutagenesis.

Combinatorial mutations of lac repressor. Stability of monomer-monomer interface is increased by apolar substitution at position 84

To examine the monomer-monomer subunit interface in the lac repressor, a mutation that generates dimeric protein (deletion of C-terminal amino acids to disrupt the dimer-dimer interface) has been combined with amino acid substitutions that alter the monomer-monomer interface (substitution at Lys84 or Tyr282). Dimeric proteins with significantly increased stability to urea denaturation were formed by the introduction of the apolar amino acids Ala or Leu in lieu of Lys84 in concert with the deletion of 11 C-terminal amino acids. K84A/-11 deletion protein retained wild-type affinity for operator DNA, while K84L/-11 deletion protein displayed operator affinity similar to its parent tetramer. To assess further the influence of monomer-monomer interface stability on assembly and DNA binding, triple mutants were generated with Y282D, an alteration that disrupts assembly completely in the wild-type background. The triple mutants were dimeric, but they exhibited diminished dimer stability to urea denaturation and decreased operator affinity compared with the double mutations. These results demonstrate directly the stabilizing influence of apolar substitution at position 84 on the monomer-monomer interface.

Interleukin-2 receptor-specific fusion toxin inhibits barotrauma-induced arterial atherosclerosis

Immunocytochemical analyses of human plaques and experimental arterial lesions have implicated activated lymphocytes and monocytes in the pathogenesis of atherosclerosis, as demonstrated by the expression of interleukin-2 (IL-2) membrane receptors and major histocompatibility complex class II epitopes. The objective is to determine if targeting these cells with an IL-2 receptor-specific chimeric toxin, DAB486-IL-2, can inhibit experimental post-angioplasty vascular neointimal thickening. Twenty-two atherogenically modeled rabbits were treated in vivo with DAB486-IL-2 (0.1 mg/kg per day i.v.; n = 11) or placebo (n = 11) for 10 days following aortic balloon angioplasty (4 atm x 30 s each x 2 dilatations). In vitro 3H-leucine incorporation studies of mononuclear leukocyte and vascular smooth muscle cell protein synthesis inhibition by DAB486-IL-2 were also performed. Angioplasty sites were examined for evidence of hyperproliferative atherosclerotic narrowing by quantitative angiography and histomorphometry of neointimal cross-sectional area at baseline and 6 weeks after injury. In vitro Concanavalin-A stimulated rabbit mononuclear leukocyte protein synthesis was 50% inhibited by DAB486-IL-2 at a concentration (IC50) of 6 x 10(-11) M. Rabbit vascular smooth muscle cells were approximately 150-fold less sensitive to DAB486-IL-2 (IC50 = 10(-8) M). In vivo studies showed no change in angioplasty site angiographic minimum luminal diameter at 6 weeks in DAB486-IL-2 treated animals (from 2.96 +/- 0.52 to 2.96 +/- 0.48 mm; percent cross-sectional area reduction = 1 +/- 10%; P = N.S.). In control animals, luminal diameter decreased from 2.79 +/- 0.4 to 2.32 +/- 0.52 mm at 6 weeks, and percent cross-sectional area was reduced by 34 +/- 14% (P < 0.01 vs. placebo). Quantitative histomorphometric angioplasty segmental intimal cross-sectional area reduction of treated and placebo vessels also differed significantly (19 +/- 16% vs. 31 +/- 21%; P < 0.05). DAB486-IL-2 caused no adverse effects on animal survival, weight or hepatic transaminase levels. We conclude that post-angioplasty administration of the chimeric toxin DAB486-IL-2 inhibits angiographic narrowing and neointimal thickening in the atherogenic rabbit model. Although this IL-2 receptor-specific molecule was cytotoxic in vitro for activated mononuclear leukocytes and vascular smooth muscle cells, systemic toxicity did not occur in vivo at a dose comparable to that evaluated in clinical trials of this agent. Potential anti-proliferative effects of this chimeric toxin may be mediated by direct local inhibition of leukocyte-mediated inflammation, or through the indirect modification of vascular cell mitogenesis and cytokine release.

Diphtheria toxin-related cytokine fusion proteins: elongation factor 2 as a target for the treatment of neoplastic disease

We have used protein engineering and recombinant DNA methodologies in order to construct a fusion protein in which human interleukin-2 (IL-2) is genetically linked to the catalytic and transmembrane domains of diphtheria toxin. The fusion toxin, DAB486IL-2, is highly cytotoxic for only those cells which display the high affinity interleukin-2 receptor (IL-2R) on their surface. In phase I/II clinical studies the intravenous administration of DAB486IL-2 has been found to be safe, well tolerated and may lead to the induction of durable remissions in patients presenting with a variety of IL-2R positive lymphomas.

Inhibition of nonlysosomal calcium-dependent proteolysis by glycine during anoxic injury of rat hepatocytes

BACKGROUND/AIMS

The mechanism by which glycine protects against hepatocyte death during anoxia remains unclear. Nonlysosomal proteolysis, including calpain proteolysis, has been implicated as a mechanism of lethal cell injury. However, the effect of glycine on nonlysosomal proteolysis is unknown. The aim of this study was to ascertain if glycine cytoprotection is associated with inhibition of nonlysosomal proteolysis.

METHODS

Rat hepatocyte suspensions were rendered anoxic using an anaerobic chamber. Cell viability was measured by propidium iodide fluorometry. Nonlysosomal protease activity was quantitated by the release of trichloroacetic acid-soluble free amines or tyrosine. Calpain protease activity was measured using a fluorogenic substrate.

RESULTS

Glycine and alanine (but not valine) markedly improved cell viability during anoxia in a concentration-dependent manner. During anoxia, the majority of nonlysosomal proteolysis (60%) was dependent on extracellular Ca2+. Glycine only inhibited that portion of nonlysosomal proteolysis that was dependent on extracellular Ca2+. Amino acids inhibited the anoxia-stimulated increase in calpain protease activity with the same specificity and concentration-dependence observed for cytoprotection. Glycine was more potent in directly inhibiting purified m-calpain as compared with mu-calpain protease activity.

CONCLUSIONS

Glycine may exert its cytoprotective activity during lethal anoxic hepatocyte injury, in part by inhibiting Ca(2+)-dependent degradative, nonlysosomal proteases, including calpains.

Diagnostic role of serum CA 19-9 for cholangiocarcinoma in patients with primary sclerosing cholangitis

Primary sclerosing cholangitis (PSC) predisposes to the development of cholangiocarcinoma, a usually fatal complication that is difficult to diagnose. Serum concentrations of CA 19-9, a tumor-associated antigen, are frequently increased in patients with only cholangiocarcinoma. The aim of this study was to assess the value of an increased serum CA 19-9 level for the diagnosis of cholangiocarcinoma in patients with preexisting PSC. We analyzed serum samples from 9 patients with PSC and superimposed cholangiocarcinoma and from 28 patients with only PSC. Serum concentrations of CA 19-9 were measured in a blinded manner with use of an immunoradiometric assay. The serum CA 19-9 concentrations were increased in 8 of 9 patients (89%) with PSC and cholangiocarcinoma (mean +/- SE, 391 +/- 86 U/ml; range, 4 to 677), whereas they were increased in only 4 of 28 patients (14%) with only PSC (mean +/- SE, 61 +/- 16 U/ml; range, 2 to 370). The sensitivity of a CA 19-9 value greater than 100 U/ml for cholangiocarcinoma in PSC was 89%, and the specificity was 86%. The measurement of serum concentrations of CA 19-9 is a promising test for detecting cholangiocarcinoma in patients with PSC.

Model of lactose repressor core based on alignment with sugar-binding proteins is concordant with genetic and chemical data

Using primary sequence similarity to arabinose-binding protein, D-glucose/D-galactose-binding protein, and ribose-binding protein (Vyas, N. K., Vyas, M. N., and Quiocho, F. A. (1991) J. Biol. Chem. 266, 5226-5237; Mowbray, S. L., and Cole, L. B. (1992) J. Mol. Biol. 225, 155-175), the core domain (residues 62-323) of the bacterial regulatory protein lac repressor has been aligned to these sugar-binding proteins of known structure. Although the sequence identity is not striking, there is strong overall homology based on two separate matrix scoring systems (minimum base change per codon (MBC/C) and amino acid homology per residue (AAH/R)) (mean score: MBC/C < 1.25, AAH/R > 5.50; random sequences: MBC/C = 1.45, AAH/R = 4.46). Similarly, the predicted secondary structure of the repressor exhibits excellent agreement with the known secondary structures of the sugar-binding proteins. Using this primary sequence alignment, the tertiary structure of the core domain of the lac repressor has been modeled based on the known structures of the sugar-binding proteins as templates. While the structure deduced for the repressor is hypothetical, the model generated allows a comparison between the predicted tertiary arrangement and the wealth of genetic and chemical data elucidated for the repressor. Important residues involved in operator and sugar binding and in protein assembly have been identified using genetic methods, and placement of these residues in the model is consistent with their known function. This approach, therefore, provides a means to visualize the core domain of the lac repressor that allows interpretation of genetic and chemical data for specific residues and rational design of future experiments.

Prevention of smooth muscle cell outgrowth from human atherosclerotic plaque by a recombinant cytotoxin specific for the epidermal growth factor receptor

Smooth muscle cell proliferation in the intima of arteries is a principal event associated with vascular narrowing after balloon angioplasty and bypass surgery. Techniques for limiting smooth muscle cell proliferation, however, have not as yet yielded any therapeutic benefit for these conditions. This may reflect the present lack of sufficiently potent and specific inhibitors of smooth muscle cell proliferation. DAB389 EGF is a genetically engineered fusion protein in which the receptor-binding domain of diphtheria toxin has been replaced by human epidermal growth factor. We evaluated the effect of this fusion toxin on human vascular smooth muscle cells in culture. Incubation of proliferating cells with DAB389 EGF yielded a dose-dependent inhibition of protein synthesis, as assessed by uptake of [3H]leucine, with an IC50 of 40 pM. The cytotoxic effect was inhibited in the presence of excess EGF or with monoclonal antibody to the EGF receptor. We further studied the effect of the fusion toxin on smooth muscle cell outgrowth from human atherosclerotic plaque. Outgrowth was markedly inhibited after as little as 1 h of exposure to the fusion protein. Furthermore, complete inhibition of proliferation of cells within the plaque could be attained. These results demonstrate that DAB389 EGF is highly cytotoxic to human smooth muscle cells proliferating in culture and can prevent smooth muscle cell outgrowth from "growth-stimulated" human atherosclerotic plaque. DAB389 EGF may therefore be of therapeutic value in vascular diseases characterized by smooth muscle cell accumulation.

Recombinant fusion toxins--a new class of targeted biologic therapeutics

The design and construction of a new class of recombinant therapeutic agents, receptor-specific cytotoxins, has occurred within the last 5 years. Development of a number of receptor-targeted fusion toxins has been based on a detailed understanding of the structure-function relationships of both diphtheria toxin and Pseudomonas exotoxin A, and availability of the nucleic acid sequences of each structural gene. A variety of fusion toxins in which the native receptor-binding domain of either diphtheria toxin or Pseudomonas exotoxin A has been genetically replaced with either a polypeptide hormone or growth factor have been constructed. These fusion toxins selectively intoxicate receptor-bearing cells in vitro and are active in a variety of animal model systems. DAB486IL-2, and IL-2 receptor targeted cytotoxin, is the first fusion toxin to be evaluated in patients. Phase I/II clinical trials have been performed in refractory leukemia/lymphoma, severe rheumatoid arthritis, and Type 1 diabetes. DAB486IL-2 has been administered to more than 200 patients, has been well tolerated, and has shown encouraging signs of potential efficacy in all three clinical indications. Thus, DAB486IL-2 represents a new class of targeted biological therapeutic response modifiers whose mode of action is based on selective elimination of target cells.

Anti-arthritic effects demonstrated by an interleukin-2 receptor-targeted cytotoxin (DAB486IL-2) in rat adjuvant arthritis

DAB486IL-2 is an interleukin-2 receptor-specific cytotoxin which selectively targets and kills cells which bear the high-affinity form of the IL-2 receptor. Since elimination of activated T lymphocytes may be useful in the treatment of rheumatoid arthritis, the effect of DAB486IL-2 treatment in an animal model of arthritis was investigated. We demonstrated that rats treated with DAB486IL-2 during the induction phase of disease have delayed onset of symptoms and significantly reduced severity of inflammation as well as a depressed proliferative response to mycobacterial stimulation in vitro. In addition, the presence of preexisting antibodies to the molecule had no impact on the anti-arthritic effects observed in this model. These data suggest that DAB486IL-2 may have therapeutic potential in the treatment of rheumatoid arthritis.

Prolongation of murine thyroid allografts by interleukin 2 (DAB486)-toxin and RS-61443

We evaluated the efficacy of interleukin 2 (DAB486)-toxin (IL-2-diphtheria toxin fusion protein; IL-2-toxin) in combination with RS-61443 to prolong murine thyroid allograft survival. B10.BR thyroid allografts were transplanted beneath the renal subcapsule in recipient (C57BL/10 mice and graft survival determined 21 days later. Treatment with IL-2-toxin (25 microg/day for 14 days) was unable to prolong graft survival significantly. RS-61443 treatment (21 days) achieved significant graft prolongation only at doses of 300 mg/kg daily or greater. When both drugs were used in combination (IL-2-toxin, 25 microg/day for 14 days RS-61443 200 mg/kg daily for 21 days), statistically significant (P < 0.0001) graft prolongation was obtained. Our results suggest that IL-2-toxin in combination with subtherapeutic RS-61443 levels significantly prolongs murine thyroid allograft survival. IL-2-toxin and RS-61443, because of their unique and complementary mechanisms, hold promise for more selective immunosuppression.

Cytotoxic properties of DAB486EGF and DAB389EGF, epidermal growth factor (EGF) receptor-targeted fusion toxins

Elevated expression of the receptor for epidermal growth factor (EGF) is a characteristic of several malignancies including those of the breast, bladder, prostate, lung, and neuroglia. To therapeutically target the cytotoxic action of diphtheria toxin to EGF receptor-expressing tumor cells, we have constructed a hybrid gene in which the sequences for the binding domain of diphtheria toxin have been replaced by those for human EGF. The resulting fusion toxins, DAB486EGF and DAB389EGF, bind specifically to the EGF receptor and inhibit protein synthesis in a variety of EGF receptor expressing human tumor cell lines with an IC50 as low as 0.1 pM. Comparisons of DAB486EGF and DAB389EGF showed that DAB389EGF was consistently 10- to 100-fold more cytotoxic than DAB486EGF. Like diphtheria toxin, the cytotoxic action of DAB389EGF results from ADP-ribosylation of elongation factor-2 and is sensitive to the action of chloroquine. Studies of the kinetics of cellular intoxication showed that a 15-min exposure of EGF receptor-expressing A431 cells to DAB389EGF results in complete protein synthesis inhibition within 4 h. Furthermore, inhibition of protein synthesis results in elimination of human tumor cell colonies. These findings show that DAB389EGF is a potential therapeutic agent for a wide variety of EGF receptor-expressing solid tumors.

Impact of interleukin-2-receptor-targeted cytotoxins on a unique model of murine interleukin-2-receptor-expressing malignancy

DAB486IL-2 is a genetically engineered fusion protein consisting of a portion of diphtheria toxin fused to human IL-2. It is specifically cytotoxic for tumor cells which bear high-affinity IL-2 receptors (IL-2R). DAB389IL-2 is a similarly constructed hybrid protein which is smaller than DAB486IL-2 and is slightly more potent in vitro. We have developed a murine model of IL-2R-expressing malignancy to study the in vivo efficacy of these genetically engineered cytotoxins. Following intravenous administration of CP3 cells, C57BL/6 mice develop tumors which are lymphatic in distribution. When mice are injected i.v. with 10(6) CP3 cells, 90% of the animals show signs of observable tumor by day 10 to 20; death occurs in 50% of untreated animals by day 30. Intravenous treatment of mice with DAB486IL-2 (10 micrograms daily for 10 days), beginning 24 hr after administration of CP3 cells, increases mean survival time by approximately 50%. In comparative studies, DAB389IL-2 is more potent in vivo than DAB486IL-2, with approximately 90% of treated animals with no evidence of tumor at 60 days. The mechanism of action of tumor inhibition by DAB486IL-2 is specific, since treatment of animals which have IL-2R-negative EL4 tumors has not resulted in increased survival time. In addition, treatment of such tumors with DAglu53B486IL-2, a fusion protein which can bind to the IL-2R but is incapable of inhibiting protein synthesis, is ineffective.

Selective elimination of HIV-1-infected cells with an interleukin-2 receptor-specific cytotoxin

Infection by human immunodeficiency virus type 1 (HIV-1) is associated with cellular activation and expression of the interleukin-2 (IL-2) receptor. A genetically engineered fusion toxin, DAB486 IL-2, that contains the enzymatic site and translocation domain of diphtheria toxin and the receptor binding domain of IL-2 specifically kills cells that express high-affinity IL-2 receptors. This toxin selectively eliminated the HIV-1-infected cells from mixed cultures of infected and uninfected cells and inhibited production of viral proteins and infectious virus. Thus, cellular activation antigens present a target for early antiviral intervention.

Suppression of immune responses to acetylcholine receptor by interleukin 2-fusion toxin: in vivo and in vitro studies

The pathogenesis of the autoimmune disease, myasthenia gravis (MG), involves an antibody-mediated attack against acetylcholine receptors (AChRs). Since the relevant antibody response is T cell dependent, a therapeutic strategy aimed at T lymphocytes actively participating in the immune reaction to AChR should result in relatively selective suppression of AChR antibody. During an active immune response, T cells express receptors for interleukin 2 (IL2). In this study, we have used a genetically engineered fusion protein comprised of the binding region of IL2 and the toxic portion of diphtheria toxin (DAB486-IL2), to attempt to treat an experimental animal model of MG in rodents. We examined the effects of treatment with DAB486-IL2 in vivo on primary, ongoing, and secondary antibody responses to purified Torpedo AChR. Treatment of mice with intraperitoneal injections of DAB486-IL2 beginning at the time of immunization inhibited the primary AChR antibody response by 50% during the treatment period. Ongoing and secondary antibody responses to AChR were not suppressed in vivo by treatment with DAB486-IL2. In comparison, DAB486-IL2 was far more potent in suppressing antibody responses and lymphoproliferation in cell culture. At a dose comparable to that given in vivo, cellular proliferation and antibody production were virtually eliminated in a secondary response in vitro. The suppressive effect of DAB486-IL2 was much more pronounced when it was given at the time of initial antigen stimulation, as compared with its effect when given during an already established antibody response. These findings suggest that the effect of the fusion toxin on AChR antibody production was due predominantly to inhibition of T cells rather than B cells.

Inhibition of human antigen-specific memory B cell response in vitro by a diphtheria toxin-related interleukin 2 fusion protein

Recombinant diphtheria toxin-related interleukin-2 fusion protein (DAB486IL-2) is specifically cytotoxic for cells bearing the high-affinity IL-2 receptor (p55/75). We evaluated the effects of DAB486IL-2 on the generation of tetanus toxoid (TT)-specific IgG antibody-forming cells in 6-day cocultures of human splenocytes and TT-coupled Sepharose beads. The results indicate that a significant portion (30-75%) of the anti-tetanus toxoid IgG response in vitro was susceptible to inhibition by 10(-10) M DAB486IL-2. The inhibition required both the IL-2 portion of the fusion protein and an active toxin moiety and was greater when the IL-2 toxin was added on Day 3 as compared with Day 0 of culture. The induction of the p55 (Tac) subunit of the IL-2R was demonstrable by two-color flow cytometry on a small percentage (5%) of B cells and on a higher percentage (10%) of non-B cells 3 days after exposure to TT-coupled Sepharose. Short-term (2 hr) treatment of T and B cell subpopulations separated on Day 3 of culture followed by remixing indicated that while activated T helper cells were most strongly inhibited by DAB486IL-2, up to 50% of the TT-specific IgG response was inhibited by treatment of B cells alone with DAB486IL-2. Our results suggest that a strategy of eliminating human memory B cells by a combination of antigen activation and properly timed administration of a recombinant lymphokine-toxin fusion protein is feasible.

Interleukin 2 receptor-targeted cytotoxicity. Receptor binding requirements for entry of a diphtheria toxin-related interleukin 2 fusion protein into cells

The receptor binding requirements for entry of the NAD+ ADP-ribosyltransferase component of DAB486-IL 2 into target cells were examined. Experiments utilizing cell lines bearing either high-affinity or individual subunits of the interleukin 2 receptor (IL 2R) as well as human peripheral blood mononuclear cells with natural killer activity demonstrate that the high-affinity receptor facilitates delivery of fragment A from DAB486-IL 2 to the cytosol approximately 1000 times more efficiently than either the intermediate-(p75) or low-affinity (p55) forms of the IL 2R. We show that elongation factor 2 (EF-2) in these cells is not quantitatively or qualitatively altered indicating that the relative resistance to intoxication displayed by IL 2R variant cell lines cannot be attributed to an altered intracellular target of the hybrid toxin. We also demonstrate that an alteration in the binding of DAB486-IL 2 to the p75 subunit of the IL 2R may account for the selective cytotoxicity of DAB486-IL 2 for cells bearing the heterodimeric high-affinity IL 2R.

The impact of PROs on orthopaedic practice

The practicing orthopaedic surgeon is beginning to feel the impact of the Medicare review process as conducted by the PRO system. Retrospective review, payment denials, preauthorization, substandard care review and similar activities by the PRO will have a direct effect on how orthopaedic surgeons care for patients and document their practices. The following is a brief description of some of these activities and suggestions as to how the practicing orthopaedist can respond to these changes.

Cytotoxicity of interleukin 2-toxin toward lymphocytes from patients with adult T-cell leukemia

The inhibitory effect of a diphtheria toxin-related interleukin 2 fusion protein, IL-2-toxin, on protein synthesis in adult T-cell leukemia/lymphoma (ATL) cells was examined in vitro. Peripheral blood ATL cells from 12 patients (six acute type, four chronic type, and two smoldering type ATL) and the lymph node cells from three ATL patients (two acute type and one lymphoma type ATL) were examined. At a concentration of 10(-8) M, IL-2-toxin inhibited protein synthesis by 60 to 98% in lymph node ATL cells, whereas protein synthesis in peripheral blood ATL cells was inhibited from 20 to 57% in acute type, and from 3 to 13% in chronic type. In contrast, IL-2-toxin had no measurable effect on T-cells from either patients with smoldering type ATL or normal controls. The cytopathic effects of IL-2-toxin were blocked by the addition of anti-CD25 monoclonal antibody, suggesting that the inhibition of protein synthesis in target cells was mediated by the IL-2 receptor (IL-2R). The degree of inhibition of protein synthesis, however, was not closely correlated with expression of CD25 antigen (low-affinity Mr 55,000 glycoprotein, IL-2R, Tac antigen) on ATL cells. There was an apparent correlation between the degree of inhibition and the rate of protein synthesis in ATL cells. We demonstrate that ATL cells from patients with acute or lymphoma type disease were more sensitive to IL-2-toxin than cells from chronic or smoldering disease. These findings suggest that the high affinity IL-2R present on acute and lymphoma type ATL cells may serve as a target for therapy with this recombinant chimeric toxin.

Interleukin 2-diphtheria toxin fusion protein can abolish cell-mediated immunity in vivo

De novo expression of the interleukin 2 receptor (IL-2R) is a critical and pivotal event in initiation of an immune response. Targeting the low-affinity IL-2-binding p55 subunit of the high-affinity IL-2R with the rat anti-mouse IgM monoclonal antibody M7/20 suppresses a variety of T-cell-mediated reactions, including transplant rejection, autoimmunity, and delayed-type hypersensitivity (DTH). A hybrid IL-2-toxin gene was constructed from the diphtheria toxin gene by replacing the DNA encoding the diphtheria toxin receptor-binding domain with the DNA encoding the receptor-binding domain of IL-2, and the fusion protein encoded by the hybrid gene was expressed in Escherichia coli [Williams, D.P., Parker, K., Bacha, P., Bishai, W., Borowski, M., Genbauffe, F., Strom, T.B. & Murphy, J.R. (1987) Protein Eng. 1, 493-498]. We examined the action of the chimeric IL-2-toxin fusion protein on an in vivo T-cell mediated response, DTH. The IL-2-toxin fusion protein was found to be a potent immunosuppressive agent. Treatment of mice with the IL-2-toxin blocks DTH and prevents expansion of IL-2R+ T cells. Indeed, IL-2-toxin treatment targets IL-2R+ T cells in vivo and is shown to selectively eliminate their appearance in draining lymph nodes. DTH suppression was observed even in mice possessing high titers of antibodies to diphtheria toxoid.

Propranolol and depression: a reevaluation based on a pilot clinical trial

A wide range of neuropsychiatric side effects are attributed to propranolol including visual hallucinations, somnulence, memory impairment, decrease in response time, dizziness, confusional states, insomnia, nightmares, fatigue, sedation and depression. Benson et al., in a summary review of several clinical studies of 5,846 patients being treated with a variety of beta adrenergic blocking agents, listed depression as a rare side effect of propranolol that was usually reported only after long term treatment at high doses. Despite the widely circulated attribution that depression is a side effect of propranolol, there is a paucity of evidence to directly link this drug with clinically significant mood disturbance. For example, the most widely quoted reference attributing propranolol as a depressogenic agent was a "letter to the editor" which was a retrospective, uncontrolled, unblinded study that did not use a standardized depression rating scale. Most of the evidence linking propranolol to depressive symptoms have derived from scattered case reports in which the onset of depressive symptoms were attributed to this agent. Given the well known cyclic onset and remissions of affective disorders, and the prevalence of depression in the general medical population as a whole, the role of propranolol in these cases is debatable.

Isolation of hybridoma cell lines and characterization of monoclonal antibodies against cholera enterotoxin and its subunits

Hybridoma cell lines which produced monoclonal antibodies against cholera toxin were isolated. These cell lines were detected with an enzyme-linked immunosorbent assay screening procedure with purified cholera toxin or subunit A of cholera toxin. Seven cell lines were characterized with respect to their reactivity with cholera toxin subunits by Western blot analysis. Five clones produced antibodies which were directed against subunit A, and two clones produced antibodies which reacted with subunit B. These antibodies were also characterized by Western blot analysis for reactivity with the heat-labile enterotoxin produced by porcine and human enterotoxinogenic strains of Escherichia coli. Monoclonal antibodies which reacted with subunit A of cholera toxin also reacted with subunit A of both porcine and human heat-labile enterotoxins. In contrast, monoclonal antibodies to subunit B of cholera toxin did not react with subunit B of the heat-labile enterotoxin. Antibodies directed against subunit B neutralized the biological activity of cholera toxin in vitro in the S49 mouse lymphosarcoma assay. In contrast to polyclonal anti-subunit A antisera, monoclonal anti-subunit A from four of five clones had small but measurable neutralizing capacities in vitro.

Cholera toxin is synthesized in precursor form on free polysomes in Vibrio cholerae 569B

Membrane-bound and free polysomes have been isolated from Vibrio cholerae 569B. Nacent polypeptide chains were completed in a cell-free translation mixture containing Escherichia coli S-300 extracts and [3H]leucine or [35S]methionine. Cholera toxin-related polypeptides synthesized in vitro were immunologically detected after treatment with either anti-subunit A or anti-subunit B serum. Immunoreactive translation products were removed from reaction mixtures with formalinized Cowan's strain of Staphylococcus aureus, electrophoresed on sodium dodecyl sulfate-polyacrylamide gels, and visualized by fluorography. Anti-subunit A serum precipitated two major polypeptide species (molecular weights 52,000 and 45,000) from translation mixtures programed with free polysomes, whereas anti-subunit B serum precipitated only the 45,000-molecular-weight polypeptide. No cholera toxin-related polypeptides were detectable in translation mixtures programed with membrane-bound polysomes. Purified subunit A and cholera toxin competed for anti-subunit A binding sites and blocked the immunoprecipitation of the 35S-labeled 52,000- and 45,000-dalton polypeptides from in vitro translation mixtures. The data presented suggest that cholera toxin is synthesized in the cytoplasm in a precursor form on free polysomes and is secreted post-translationally.

Capacity of virulent Treponema pallidum (Nichols) for deoxyribonucleic acid synthesis

Treponema pallidum (Nichols) was extracted from infected rabbit tissue, and cell lysates were prepared for monitoring thymidine kinase and deoxyribonucleic acid polymerase activities. No thymidine kinase could be demonstrated in preparations of T. pallidum or the cultivable T. phagedenis biotype Reiter. Significant levels of deoxyribonucleic acid polymerase were detected in both treponemal samples. Interestingly, comparisons of polymerase activity among a spectrum of bacterial genera revealed a direct correlation between enzyme concentrations and estimated generation time. Incorporation of [3H]uridine and [3H]thymidine into macromolecules by intact T. pallidum and the Reiter treponeme was examined. Selective ribonuclease-deoxyribonuclease digestion and cesium chloride gradient banding demonstrated that T. pallidum, independent of the host, and T. phagedenis were capable of synthesizing deoxyribonucleic acid only from the [3H]-uridine precursor.

Ribosomal ribonucleic acid synthesis by virulent Treponema pallidum

Ribosomal ribonucleic acid (rRNA) synthesis by virulent Treponema pallidum was monitored by incorporation of [(3)H]uridine into trichloroacetic acid-precipitable counts and examination of radiolabeled rRNA on polyacrylamide gels. Verification that rRNA synthesis originated with T. pallidum was based upon co-electrophoresis with Escherichia coli rRNA, proportionate reductions in the amount of rRNA synthesized when numbers of treponemes were decreased, and inclusion of appropriate animal cell controls. The rate of treponemal rRNA synthesis was greater at temperatures of 37 and 39 degrees C than at 33 degrees C; rRNA synthesis was inhibited at 4 and 42 degrees C and was effectively inhibited by actinomycin D. Kinetic experiments indicated that the majority of rRNA synthesis occurred early after extraction of treponemes from infected rabbit testicular tissue. Polyacrylamide gel profiles demonstrated the capacity of virulent T. pallidum to synthesize and process RNA to 23s, 16s, and 4 to 5s classes. Although motility of T. pallidum appeared unaffected during longer periods of incubation, pulselabeling experiments confirmed significant reductions in the rate of rRNA synthesis. When the effect of various environmental conditions upon rRNA synthesis was investigated, optimal synthesis was found to occur in an atmosphere of 20% oxygen whereas virtually no synthesis was observed under anaerobic or low-oxygen conditions.

Virulent Treponema pallidum: aerobe or anaerobe

Substrate degradation and protein synthesis served as indicators of metabolism in virulent Treponema pallidum. Opitmal metabolic activity in these spirochetes was observed at 10 to 20% O2 concentrations, with markedly reduced activity at higher or lower O2 levels or under anaerobiosis; alternate functioning electron acceptors that might substitute for O2 were not found. Carbon monoxide and cyanide at concentrations that inactivate cytochrome oxidase were not effective metabolic poisons for T. pallidum, although Micrococcus lutea, a strict aerobe with cytochrome-dependent respiration, was inhibited under similar experimental conditions. Motility of virulent T. pallidum was vigorous in the presence of O2 and sluggish or inhibited in its absence, reinforcing the role of O2 in T. pallidum metabolism.

Carbon sources utilized by virulent Treponema pallidum

Carbon sources utilized by virulent Treponema pallidum organisms extracted from infected rabbit tissue have been investigated. Utilization of 14C-labeled compounds by T. pallidum was monitored by degradation of these compounds to 14CO2. Experiments have consistently shown that of 22 carbon sources examined, [14C]glucose and [14C]pyruvate are selectively degraded to 14CO2 under the experimental conditions employed. When [1-14C]pyruvate, [2-14C]pyruvate, and [3-14C]pyruvate are tested, virulent T. pallidum preferentially degrade and release the carboxyl group as 14CO2. End product analyses indicate that CO2 and acetate are the major products of pyruvate degradation by T. pallidum.