Cytotoxicity of a recombinant diphtheria toxin-granulocyte colony-stimulating factor fusion protein on human leukemic blast cells

Granulocyte colony-stimulating factor (G-CSF) is a potent stimulator of the growth of normal and malignant hematopoietic cells and synergizes with other factors such as interleukin-3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GM-CSF). The action of G-CSF is mediated through a specific membrane receptor, however it is not clear if all of the effects of G-CSF are direct or indirect. As a step towards addressing this problem, a recombinant diphtheria toxin (DT)-related human G-CSF fusion protein has been constructed and purified from E. coli. The 70,000 dalton chimeric protein has immunologic determinants characteristic of both DT and G-CSF. At high concentrations, DAB486-G-CSF is cytotoxic towards G-CSF-dependent OCI/AML1 cells, but not factor independent OCI/AML3 cells; colony formation by G-CSF-responsive leukemic blasts from a patient with acute myeloblastic leukemia (AML) was also inhibited. The G-CSF fusion toxin displayed ADP-ribosyltransferase activity in a cell-free system. Genetic conjugation of G-CSF to an enzymatically inactive DT mutant, CRM197, resulted in a 200-fold reduction in the ability of G-CSF to stimulate normal bone marrow colony formation. These results suggest that fusion of G-CSF to DT sequences interferes with some of the activity but not the specificity of the ligand binding domain of the molecule. Nevertheless, DAB486-G-CSF may be included with the increasing number of other toxin-hormone fusion proteins whose toxicity is directed towards specific receptor-bearing cells, and may represent a novel approach towards the study and treatment of leukemia.

Hydration of the fat-free body mass in children and adults: implications for body composition assessment

Previous studies have shown that children have a higher aqueous fraction of the fat-free body mass (FFM) than young adults. In older adults, methodological differences among studies limit evaluation of potential age-related differences in the water content of the FFM (W/FFM). Therefore, we determined W/FFM in 28 healthy white prepubescent children (age = 5-10 yr), 31 young adults (age = 22-39 yr), and 62 older adults (age = 65-84 yr), using 2H2O dilution to estimate total body water and a multicomponent approach based on body density, total body water, and regional bone mineral density to estimate FFM. To quantify the extent to which variation in W/FFM affects percent fat estimation error, differences in percent fat between our multicomponent approach and the Siri two-component model were related to W/FFM. Prepubescent children (72.7 +/- 1.6%) and older adults (72.5 +/- 1.4%) were found to have significantly higher (P < 0.01) mean W/FFM than young adults (70.8 +/- 1.2%). Differences in percent fat between the multicomponent and two-component models ranged from -10 to 6% fat and were significantly associated with W/FFM (r = -0.62, P < 0.0001). We conclude that prepubescent children and older adults, on average, have a higher W/FFM than young adults, and that, in adults, individual differences in W/FFM account for a substantial portion of the percent fat estimation errors associated with the use of two-component body composition models.

Relationship of body fat percentage and fat distribution with dehydroepiandrosterone sulfate in premenopausal females

Dehydroepiandrosterone (DHEA) has an antiobesity effect in rodents, and elevated endogenous levels of its sulfate ester (DHEAS) are associated with reductions in risk for cardiovascular disease (CVD) in men. To examine the association of body fat and fat distribution, established correlates of CVD and CVD risk factors, with circulating DHEAS levels in women, we measured trunk and limb skinfold thicknesses and circumferences, total and regional body fat from dual energy x-ray absorptiometry (DXA), and serum levels of DHEAS in 96 healthy Caucasian females aged 28-39 yr. Body mass index, percentage fat from DXA and the waist-to-hip ratio were not significantly correlated (r < or = 0.15, P > or = 0.156) with serum DHEAS levels, regardless of statistical control for age, smoking behavior, and fasting status. However, the ratio of trunk/total skinfold thicknesses (r = 0.23, P = 0.030) and the percentage of total fat located on the trunk from DXA (r = 0.32, P = 0.002) were positively correlated with DHEAS, whereas the ratio of leg/total skinfold thicknesses (r = -0.25, P = 0.015) and the percentage of total fat located on the legs from DXA (r = -0.25, P = 0.015) were inversely correlated with DHEAS after adjusting for age, smoking, and fasting status. With the exception of the trunk/total skinfold thickness ratio, the correlations of DXA- and skinfold-derived estimates of fat distribution remained significant (P < or = 0.033) even after further adjustment for percentage fat or body mass index. It is concluded that increased amounts of total fat located on the trunk and decreased amounts of total fat located on the legs are associated with increased serum DHEAS concentrations in normally menstruating females.

Detection of small changes in body composition by dual-energy x-ray absorptiometry

The ability of dual-energy x-ray absorptiometry (DEXA) to detect small changes in body composition was studied in 17 men and women during a dehydration-rehydration protocol. Scale weight (BW) and total mass (TM) from DEXA were highly related (r > 0.99) as were estimates of fat-free mass (r = 0.99) and percent fat (r = 0.97) from DEXA and densitometry. Changes in BW of approximately 1.5 kg due to fluid loss and gain were highly correlated (r = 0.90) with both changes in TM and soft-tissue mass (STM) by DEXA but less so (r = 0.67) with changes in lean-tissue mass (LTM). Mean changes in TM, STM, and LTM were not different (P > 0.05) from changes in BW. Estimates of bone mass and fat were unaffected by changes in hydration. We conclude that DEXA is able to detect small individual changes in TM and STM and is also useful for detecting group changes in LTM.

Recombinant interleukin-2 analogs. Dynamic probes for receptor structure

Interleukin-2 (IL-2) and its receptor complex have become one of the most studied members of a growing family of protein hormones characterized by structural similarities in both ligands and their receptors. Structure-function studies of IL-2 have been complicated by the multimeric nature of its receptor. Two receptor subunits (55- and 75-kDa type I cell surface proteins) can participate to form the high affinity binding site. Although the IL-2 is apparently unique in some respects, similar subunit cooperativity has now been shown to be a common feature for other members of this receptor family. The availability of cell lines expressing the individual IL-2 receptor subunits has allowed detailed analysis of subunit binding characteristics. Results regarding the relationship of molecular recognition at each subunit to the mechanism of ligand binding at the high affinity site, however, have led to different interpretations. In this study we have employed previously prepared C-terminal IL-2 mutant proteins to examine receptor binding at all three classes using a variety of equilibrium and kinetic techniques. These results indicate that the high affinity IL-2 receptor complex includes the p55/p75 heterodimer prior to IL-2 binding and that both receptor subunits participate simultaneously in ligand capture.

Body fatness and risk for elevated blood pressure, total cholesterol, and serum lipoprotein ratios in children and adolescents

BACKGROUND

Recent studies have shown considerable variation in body fatness among children and adolescents defined as obese by a percentile rank for skinfold thickness.

METHODS

We examined the relationship between percent body fat and risk for elevated blood pressure, serum total cholesterol, and serum lipoprotein ratios in a biracial sample of 3320 children and adolescents aged 5 to 18 years. Equations developed specifically for children using the sum of subscapular (S) and triceps (T) skinfolds were used to estimate percent fat. The S/T ratio provided an index of trunkal fat patterning.

RESULTS

Significant overrepresentation (greater than 20%) of the uppermost quintile (UQ) for cardiovascular disease (CVD) risk factors was evident at or above 25% fat in males (32.2% to 37.3% in UQ) and at or above 30% fat in females (26.6% to 45.4% in UQ), even after adjusting for age, race, fasting status, and trunkal fat patterning.

CONCLUSIONS

These data support the concept of body fatness standards in White and Black children and adolescents as significant predictors of CVD risk factors. Potential applications of these obesity standards include epidemiologic surveys, pediatric health screenings, and youth fitness tests.

Immunotoxins and cytokine toxin fusion proteins

Paul Ehrlich first suggested the simple and elegant concept of creating specific cell toxins or "magic bullets" through the fusion of cell-specific antibodies and toxins. In practice it has proven difficult to create safe and effective "magic bullets." In the past several years, several immunotoxins have been applied to clinical testing. These immunotoxins have been created by the biochemical coupling of cell- or lineage-specific monoclonal antibodies to plant toxins or fragments thereof. These immunotoxins have been used to treat bone marrow transplant recipients and patients with autoimmune disorders. In recent years, another strategy has also been pursued to create hybrid toxins. Rather than use antibodies as the targeting moiety, cytokines have been used to target a select population of cells bearing a high copy number of receptors for the specific cytokine. Rather than biochemically couple a cytokine to the toxin, the cytokine and toxin are fused by a peptide bond established via genetic engineering. A prototype IL-2 diphtheria toxin-related fusion protein is now being tested in the clinic for treatment of hematopoietic malignancies and autoimmune disorders.

Protein engineering of diphtheria-toxin-related interleukin-2 fusion toxins to increase cytotoxic potency for high-affinity IL-2-receptor-bearing target cells

We have used site-directed insertion and point mutagenesis in an attempt to increase the cytotoxic potency and receptor-binding affinity of the diphtheria-toxin-related interleukin-2 (IL-2) fusion toxins. Previous studies have demonstrated that both the DAB486-IL-2 and DAB389-IL-2 forms of the fusion toxin consist of three functional domains: the N-terminal fragment-A-associated ADP-ribosyltransferase, the hydrophobic-membrane-associating domains, and the C-terminal receptor-binding domain of human IL-2. By insertion mutagenesis we have increased the apparent flexibility of the polypeptide chain between the membrane-associating domains and the receptor-binding domain of this fusion toxin. In comparison to DAB486-IL-2, the cytotoxic potency of the insertion mutants was increased by approximately 17-fold for high-affinity IL-2-receptor-bearing cell lines in vitro. Moreover, competitive displacement experiments using [125I]rIL-2 demonstrate that the increase in cytotoxic potency correlates with an increase in receptor-binding affinity for both the high and intermediate forms of the IL-2 receptor.

Conformational perturbation of interleukin-2: a strategy for the design of cytokine analogs

Interleukin-2 (IL-2) is a representative of a growing family of small proteins termed lymphokines which are responsible for mediating cell differentiation, growth and function in the immune system. Many of these proteins are being evaluated for their clinical potential. From the perspective of drug development, structure-function analysis of these molecules and their receptors require the use methodologies different than those traditionally employed for small peptides and other natural products. However, similar pharmacologic principles apply and an understanding of ligand-receptor interactions and the associated responses is required in order to efficiently pursue agonist and antagonist design. Although IL-2 is a protein of only 133 amino acid residues for which a low resolution X-ray structure does exist, the complexity of its receptor system has provided an added challenge to structure-function studies. Consequently, little is known concerning the receptor contact residues for this protein. We have attempted to utilize established principles of protein and peptide structure to manipulate the conformation of IL-2 in a manner which has provided analogs helpful for receptor interaction studies. These proteins have not only providing useful information on the nature of the IL-2 receptor but have also revealed potential strategies for the design of IL-2 agonists and antagonists.

Cellular processing of the interleukin-2 fusion toxin DAB486-IL-2 and efficient delivery of diphtheria fragment A to the cytosol of target cells requires Arg194

We have used site-directed mutagenesis to examine the role played by Arg191, Arg193, and Arg194 of the fusion toxin DAB486-IL-2 in the intoxication of high affinity interleukin-2 receptor-bearing T-lymphocytes. These arginine residues are positioned in the proteolytically sensitive 14-amino acid loop subtended by the disulfide bond between Cys187 and Cys202 in this fusion toxin. DAB486-IL-2 was formed by the genetic substitution of the native diphtheria toxin receptor binding domain with human interleukin-2 (Williams, D.P., Parker, K., Bacha, P., Bishai, W., Borowski, M., Genbauffe, F., Strom, T.B., and Murphy, J.R. (1987) Protein Eng. 1, 493-498). We demonstrate that substitution of Arg194 with Gly results in a 1000-fold loss of DAB486-IL-2 potency. Since trypsin "nicking" of the Gly194 mutant restores biologic activity, we conclude that Arg194 is required for the cellular processing of the fusion toxin which results in the release of fragment A into the cytosol.

Immunotoxins and cytokine toxin fusion proteins

Paul Ehrlich first suggested the simple and elegant concept of creating specific cell toxins or 'magic bullets' through the fusion of cell specific antibodies and toxins. In practice it has proven difficult to create safe and effective 'magic bullets'. In the past several years, several immunotoxins have been applied to clinical testing. These immunotoxins have been created by the biochemical coupling of cell or lineage specific monoclonal antibodies to plant toxins or fragments thereof. These immunotoxins have been used to treat bone marrow transplant recipients and patients with autoimmune disorders. In recent years, another strategy has also been pursued to create hybrid toxins. Rather than use antibodies as the targeting moiety, cytokines have been used to target a select population of cells bearing a high copy number of receptors for the specific cytokine. Rather than biochemically couple a cytokine to the toxin, the cytokine and toxin are fused by a peptide bond established via genetic engineering. A prototype IL-2 diphtheria toxin-related fusion protein is now being tested in the clinic for treatment of hematopoietic malignancies and autoimmune disorders.

Structure/function analysis of interleukin-2-toxin (DAB486-IL-2). Fragment B sequences required for the delivery of fragment A to the cytosol of target cells

We have used cassette and deletion mutagenesis to analyze the structural features of fragment B-related sequences in the fusion toxin DAB486-IL-2 (where IL-2 represents interleukin-2) that are necessary for the efficient delivery of fragment A to the cytosol of target cells. We demonstrate that whereas an intact disulfide bond between Cys461 and Cys471 may be required for the cytotoxic action of native diphtheria toxin, this bond is not required for the cytotoxic action of DAB486-IL-2. The in-frame deletion of the 97 amino acids from Thr387 to His485 of DAB486-IL-2 increases both the potency and the apparent dissociation constant (Kd) of the resulting fusion toxin for high affinity interleukin-2 receptor-bearing target cells. In contrast, the inframe deletion of either the 191 amino acids between Asp291 and Gly483 or the 85 amino acids between Asn204 and Ile290 results in a 1000-fold loss in potency. These regions contain the putative membrane-spanning regions and the amphipathic membrane surface-associating regions of fragment B, respectively. These results indicate that the efficient delivery of the ADP-ribosyltransferase from DAB486-IL-2 to the cytosol requires the membrane-associating domains of fragment B. This function has been postulated to play a role in the diphtherial intoxication of eukaryotic cells. However, unlike native diphtheria toxin, fragment B sequences distal to Thr387 do not enhance the potency of DAB486-IL-2.

Sympathetic ophthalmia and subretinal neovascularization

We report a case of sympathetic ophthalmia with subretinal neovascularization of the macula. The subretinal neovascularization developed after penetrating trauma to the fellow eye. The occurrence of subretinal neovascularization in sympathetic ophthalmia is not surprising since disintegrative changes and breaks in Bruch's membrane have been reported in sympathetic ophthalmia. Subretinal neovascularization has also been reported in Vogt-Koyanagi-Harada syndrome, which is histopathologically similar to sympathetic ophthalmia.

Physician supply and distribution in Georgia

Physician supply in Georgia must be considered an urgent issue. Several important points must be recognized and addressed. The lowest physicians rates are in the more rural county population groupings. The only county population grouping with a surplus of physicians is in the over 150,000 population. The majority of physicians are concentrated in the metropolitan counties. Sixteen percent of all physicians practice in the 134 counties having less than 50,000 population. The majority of physicians are in primary care specialties. Family practice is the most dominant specialty in rural areas. By the year 2000, Georgia can expect to add 5,600 physicians due to growth. By the year 2000, Georgia can expect to lose 2,600 physicians due to retirement. Family practitioners are the most uniformly distributed of the specialties examined. They are also the specialty most needed. The average age of Georgia physicians is 46. General surgeons are in the oldest average age group (50), whereas internists are in the youngest (44). Older physicians are concentrated in the more rural areas. A significant number of all physicians are over age 55. The majority of these will be retired by the year 2000. Physicians over age 65 represent 9.2% of all physicians from the survey. In Georgia, 13.6% of all physicians were Foreign Medical School Graduates. They tend to locate their practices in medically underserved areas. The specialty choices most frequently favored by FMGs are: pediatrics, internal medicine, family practice, and obstetrics/gynecology. A total of 71.2% of all physicians accept Medicare patients; 83.8% accept Medicare patients. Ninety-two percent of all obstetricians accept obstetric patients, but this participation is threatened by problems with malpractice insurance.

Design, synthesis and expression of a human interleukin-2 gene incorporating the codon usage bias found in highly expressed Escherichia coli genes

A synthetic gene encoding human interleukin-2 (IL-2) was designed such that the codon usage bias resembled that found in highly expressed Escherichia coli genes. The percentage of preferred codons was increased from 43% in the native cDNA sequence to 85% in the synthetic sequence. The cDNA and synthetic IL-2 genes were placed under the control of the trc promoter and expressed in E. coli JM101. While Northern blot analysis of IL-2 mRNA from each genetic construct demonstrated equivalent message half-lives, immunoblot and bioactivity analyses showed the synthetic gene to direct the synthesis of up to 16 times more IL-2 than the native cDNA sequence.

Lithium-induced downbeat nystagmus

Two patients who were treated with lithium for psychiatric illness developed primary position downbeat nystagmus. Previous reports have suggested that lithium causes this type of nystagmus, but other known causes were present in most cases. Several months after stopping the lithium, one patient had marked resolution, while the second patient had only minimal improvement. Valproate sodium proved to be useful in suppressing the nystagmus in the second patient. Lithium carbonate is a cause of primary position downbeat nystagmus. The nystagmus may be permanent or require several months of abstinence for improvement.

Interleukin 2 receptor-targeted cytotoxicity. Interleukin 2 receptor-mediated action of a diphtheria toxin-related interleukin 2 fusion protein

The IL-2 toxin-mediated inhibition of protein synthesis in high affinity IL-2-R-positive murine and human T cell lines has been examined. Both excess free IL-2 and mAb to the Tac epitope of the p55 subunit of IL-2-R are shown to block the action of IL-2 toxin; whereas, agents that interact with other receptors or antigens on the T cell surface have no effect. We show that IL-2 toxin, like diphtheria toxin, must pass through an acidic vesicle in order to intoxicate target T cells. Finally, we demonstrate that the IL-2 toxin-mediated inhibition of protein synthesis in both human and murine T cells that bear the high affinity IL-2-R is due to the classic diphtheria toxin fragment A-catalyzed ADP ribosylation of elongation factor 2.

Cell receptor specific targeted toxins: genetic construction and characterization of an interleukin 2 diphtheria toxin-related fusion protein

We have genetically replaced the diphtheria toxin receptor binding domain with a DNA insert encoding the T-cell growth factor interleukin-2 (IL-2). The toxin-related IL-2 fusion gene encodes a 70,586 dalton protein, pro-IL-2-toxin. The mature form of IL-2-toxin is exported to the periplasmic space of recombinant Escherichia coli and has a molecular weight of 68,086. IL-2-toxin has been partially purified from periplasmic extracts of recombinant E. coli, and it is shown to contain immunologic determinants intrinsic to both its diphtheria toxin and IL-2 components. The chimeric toxin is targeted toward IL-2 receptor bearing T-cells in vitro.

Diphtheria toxin receptor binding domain substitution with interleukin-2: genetic construction and properties of a diphtheria toxin-related interleukin-2 fusion protein

We have genetically replaced the diphtheria toxin receptor binding domain with a synthetic gene encoding interleukin-2 (IL-2) and a translational stop signal. The diphtheria toxin-related T-cell growth factor fusion gene encodes a 70 586-d polypeptide, pro-IL-2-toxin. The mature form of IL-2-toxin has a deduced mol. wt of 68,086 and is shown to be exported to the periplasmic compartment of Escherichia coli (pABI508), and contain immunologic determinants intrinsic to both its diphtheria toxin and IL-2 components. IL-2-toxin has been purified from periplasmic extracts of recombinant strains of E. coli (pABI508) by immunoaffinity chromatography using immobilized anti-IL-2. The purified chimeric toxin is shown to selectively inhibit protein synthesis in IL-2 receptor bearing targeted cells, whereas cell lines which do not express the IL-2 receptor are resistant to IL-2-toxin action.