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Biomedical subjects

M Levitt

Publications and source records attributed to M Levitt.

At least 109 records · Page 6Linked to original sources
PubMed1990

NMR-derived model for a peptide-antibody complex.

The TE34 monoclonal antibody against cholera toxin peptide 3 (CTP3; VEVPGSQHIDSQKKA) was sequenced and investigated by two-dimensional transferred NOE difference spectroscopy and molecular modeling. The VH sequence of TE34, which does not bind cholera toxin, shares remarkable homology to that of TE32 and TE33, which are both anti-CTP3 antibodies that bind the toxin. However, due to a shortened heavy chain CDR3, TE34 assumes a radically different combining site structure. The assignment of the combining site interactions to specific peptide residues was completed by use of AcIDSQRKA, a truncated peptide analogue in which lysine-13 was substituted by arginine, specific deuteration of individual polypeptide chains of the antibody, and a computer model for the Fv fragment of TE34. NMR-derived distance restraints were then applied to the calculated model of the Fv to generate a three-dimensional structure of the TE34/CTP3 complex. The combining site was found to be a very hydrophobic cavity composed of seven aromatic residues. Charged residues are found in the periphery of the combining site. The peptide residues HIDSQKKA form a beta-turn inside the combining site. The contact area between the peptide and the TE34 antibody is 388 A2, about half of the contact area observed in protein-antibody complexes.

Amino Acid Sequence↗
PubMed1990

Potential misinterpretation of cervical spondylosis with cord compression caused by metallic artifacts in magnetic resonance imaging of the postoperative spine.

Tiny metallic particles produced by the contact of untempered surgical instruments with a diamond drill produce magnetic susceptibility artifacts that can both limit the diagnostic quality of postoperative magnetic resonance imaging of the cervical spine and cause diagnostic error. A case of cervical pseudospondylosis with apparent cord compression due to such an artifact is presented. The source of these metallic particles is considered, and the nature of the susceptibility artifact is discussed.

Female↗
PubMed1989

p53: a frequent target for genetic abnormalities in lung cancer.

Allele loss is a hallmark of chromosome regions harboring recessive oncogenes. Lung cancer frequently demonstrates loss of heterozygosity on 17p. Recent evidence suggests that the p53 gene located on 17p13 has many features of such an antioncogene. The p53 gene was frequently mutated or inactivated in all types of human lung cancer. The genetic abnormalities of p53 include gross changes such as homozygous deletions and abnormally sized messenger RNAs along with a variety of point or small mutations, which map to the p53 open reading frame and change amino acid sequence in a region highly conserved between mouse and man. In addition, very low or absent expression of p53 messenger RNA in lung cancer cell lines compared to normal lung was seen. These findings, coupled with the previous demonstration of 17p allele loss in lung cancer, strongly implicate p53 as an anti-oncogene whose disruption is involved in the pathogenesis of human lung cancer.

Base Sequence↗
PubMed1989

Probing antibody diversity by 2D NMR: comparison of amino acid sequences, predicted structures, and observed antibody-antigen interactions in complexes of two antipeptide antibodies.

The interactions between the aromatic amino acids of two monoclonal antibodies (TE32 and TE33) with specific amino acid residues of a peptide of cholera toxin (CTP3) have been determined by two-dimensional (2D) transferred NOE difference spectroscopy. Aromatic amino acids are found to play an important role in peptide binding. In both antibodies two tryptophan and two tyrosine residues and one histidine residue interact with the peptide. In TE33 there is an additional phenylalanine residue that also interacts with the peptide. The residues of the CTP3 peptide that have been found to interact with the antibody are val 3, pro 4, gly 5, gln 7, his 8, and asp 10. We have determined the amino acid sequences of the two antibodies by direct mRNA sequencing. Computerized molecular modeling has been used to build detailed all-atom models of both antibodies from the known conformations of other antibodies. These models allow unambiguous assignment of most of the antibody residues that interact with the peptide. A comparison of the amino acid sequences of the two anti-CTP3 antibodies with other antibodies from the same gene family reveals that the majority of the aromatic residues involved in the binding of CTP3 are conserved although these antibodies have different specificities. This similarity suggests that these aromatic residues create a general hydrophobic pocket and that other residues in the complementarity-determining regions (CDRs) modulate the shape and the polarity of the combining site to fit the specific antigens.

Amino Acid Sequence↗
PubMed1989

Postcordotomy spontaneous dysesthesias in macaques: recurrence after spinal cord transection.

Monkeys chronically attack the hypoalgesic hindlimb after thoracic contralateral anterolateral cordotomy or hemisection. This compulsive behavior could be induced by innocuous stimulation in the hypoalgesic region, and it also appeared to occur spontaneously. The postcordotomy spontaneous compulsive self-directed behavior was studied in 4 macaques after subsequent upper lumbar crush spinal transection. Despite the paraplegia and bilateral analgesia/anesthesia, this spontaneous abnormal behavior continued to be directed to the same hindlimb as before transection, but not to the opposite hindlimb. Hence, it is concluded that the recurring syndrome originated from the initial contralateral cordotomy. The rationale for the presumption of postcordotomy spontaneous dysesthesias is presented, and the experimental results are offered in refutation of alternative interpretive hypotheses. In conjunction with previous findings, these results lead to the argument that postcordotomy dysesthesias are caused by a neuropathological compensatory response to partial deafferentation of brain somatosensory neurons.

Afferent Pathways↗
PubMed1989

Inhibition of adrenocortical, mitochondrial and microsomal monooxygenases by SU-10'603, a steroid 17 alpha-hydroxylase inhibitor.

SU-10'603 is a pyridine derivative that is widely used as a steroid 17 alpha-hydroxylase inhibitor. Studies were done to evaluate its effects in vitro on several other monooxygenases in guinea pig adrenal mitochondrial and microsomal preparations. In adrenal mitochondria, SU-10'603 produced a concentration-dependent inhibition of 11 beta-hydroxylation; 50% inhibition was obtained at a concentration of approximately 0.5 mM. Its potency was similar to that of the 11 beta-hydroxylase inhibitor, metyrapone. SU-10'603 was a more potent inhibitor of cholesterol sidechain cleavage (CSC) than of 11 beta-hydroxylation; a 50% decline in CSC activity was produced by an inhibitor concentration of approximately 0.1 mM. In adrenal microsomal preparations, SU-10'603 had no effect on the rate of 21-hydroxylation of 17 alpha-hydroxyprogesterone. However, SU-10'603 was a potent inhibitor of adrenal microsomal xenobiotic metabolizing monooxygenases (benzo[a]pyrene hydroxylase, benzphetamine demethylase), effecting approximately 50% inhibition of both reactions at a concentration of 0.05 mM. The results indicate that SU-10'603 inhibits several monooxygenases in the guinea pig adrenal cortex and is thus not specific for 17 alpha-hydroxylation.

Adrenal Cortex↗
PubMed1989

Stabilization of phage T4 lysozyme by engineered disulfide bonds.

Four different disulfide bridges (linking positions 9-164, 21-142, 90-122, and 127-154) were introduced into a cysteine-free phage T4 lysozyme at sites suggested by theoretical calculations and computer modeling. The new cysteines spontaneously formed disulfide bonds on exposure to air in vitro. In all cases the oxidized (crosslinked) lysozyme was more stable than the corresponding reduced (noncrosslinked) enzyme toward thermal denaturation. Relative to wild-type lysozyme, the melting temperatures of the 9-164 and 21-142 disulfide mutants were increased by 6.4 degrees C and 11.0 degrees C, whereas the other two mutants were either less stable or equally stable. Measurement of the equilibrium constants for the reduction of the engineered disulfide bonds by dithiothreitol indicates that the less thermostable mutants tend to have a less favorable crosslink in the native structure. The two disulfide bridges that are most effective in increasing the stability of T4 lysozyme have, in common, a large loop size and a location that includes a flexible part of the molecule. The results suggest that stabilization due to the effect of the crosslink on the entropy of the unfolded polypeptide is offset by the strain energy associated with formation of the disulfide bond in the folded protein. The design of disulfide bridges is discussed in terms of protein flexibility.

Disulfides↗
PubMed1989

A humanized antibody that binds to the interleukin 2 receptor.

The anti-Tac monoclonal antibody is known to bind to the p55 chain of the human interleukin 2 receptor and to inhibit proliferation of T cells by blocking interleukin 2 binding. However, use of anti-Tac as an immunosuppressant drug would be impaired by the human immune response against this murine antibody. We have therefore constructed a "humanized" antibody by combining the complementarity-determining regions (CDRs) of the anti-Tac antibody with human framework and constant regions. The human framework regions were chosen to maximize homology with the anti-Tac antibody sequence. In addition, a computer model of murine anti-Tac was used to identify several amino acids which, while outside the CDRs, are likely to interact with the CDRs or antigen. These mouse amino acids were also retained in the humanized antibody. The humanized anti-Tac antibody has an affinity for p55 of 3 x 10(9) M-1, about 1/3 that of murine anti-Tac.

Amino Acid Sequence↗
PubMed1988

Aromatic rings act as hydrogen bond acceptors.

Simple energy calculations show that there is a significant interaction between a hydrogen bond donor (like the greater than NH group) and the centre of a benzene ring, which acts as a hydrogen bond acceptor. This interaction, which is about half as strong as a normal hydrogen bond, contributes approximately 3 kcal/mol (1 cal = 4.184 J) of stabilizing enthalpy and is expected to play a significant role in molecular associations. It is of interest that the aromatic hydrogen bond arises from small partial charges centred on the ring carbon and hydrogen atoms: there is no need to consider delocalized electrons. Although some energy calculations have included such partial charges, their role in forming such a strong interaction was not appreciated until after aromatic hydrogen bonds had been observed in protein-drug complexes.

Benzene↗
PubMed1988

Adriamycin and cisplatin in the treatment of stage III and IV epithelial ovarian carcinoma.

A total of 342 eligible, previously untreated patients with Stage III or IV epithelial ovarian carcinoma were treated with Adriamycin and cisplatin, both at 50 mg/m2, for nine courses. Of the 210 patients who had clinically detectable disease after initial surgery, 85 (41%) had a complete clinical response and 45 (21%) had a partial clinical response. A total of 197 were clinically free of disease at the completion of chemotherapy and 175 of these had a second-look laparotomy; 55 had no macroscopic or microscopic evidence of residual disease after multiple random biopsies were examined histologically (complete surgical/histologic response). The major determinants of complete surgical/histologic response were diameter of largest residual tumor prior to treatment, ECOG performance status, and grade, patients with grade 3 tumors having a higher complete response rate than those with grade 1 or 2 tumors. The major determinants of survival were ECOG performance status and diameter of largest residual tumor prior to treatment. Median survival of the total group was 1.8 years.

Adult↗
PubMed1988

Accurate simulation of protein dynamics in solution.

Simulation of the molecular dynamics of a small protein, bovine pancreatic trypsin inhibitor, was found to be more realistic when water molecules were included than when in vacuo: the time-averaged structure was much more like that observed in high-resolution x-ray studies, the amplitudes of atomic vibration in solution were smaller, and fewer incorrect hydrogen bonds were formed. Our approach, which provides a sound basis for reliable simulation of diverse properties of biological macromolecules in solution, uses atom-centered forces and classical mechanics.

Animals↗
PubMed1988

Increased nausea and vomiting induced by naloxone in patients receiving cancer chemotherapy.

To evaluate the role of endogenous opiates in chemo-therapy-induced nausea and vomiting, the narcotic-antagonist naloxone was administered to six pediatric patients receiving cancer chemotherapy. Naloxone was administered by continuous intravenous (i.v.) infusion after randomized, double-blind controlled assignment at a dose of 0, 10 or 40 micrograms/kg/h for 12 h. Each patient was studied for four consecutive and identical courses of chemotherapy (eight courses for each naloxone dose or 24 courses in all). A dose-related increase in nausea (nausea score 2.5 +/- 2.24, 3.83 +/- 2.73, and 5.75 +/- 2.86/12 h, p = 0.003), vomiting (emetic events 6.0 +/- 7.50, 8.08 +/- 6.71, and 10.3 +/- 8.91/12 h, p = 0.035), and patient aversion (course preference rank 1.5 +/- 0.45, 2.83 +/- 1.17, and 3.25 +/- 0.42/4 courses, p = 0.014) was observed. The infusion of naloxone in the absence of chemotherapy was without effect. These results support a role for endogenous opiates in regulating chemotherapy-induced nausea and vomiting, and further suggest that narcotic agents may be effective antiemetics in this setting.

Adolescent↗
PubMed1988

Experimental deafferentation syndromes.

Animal models of dysesthesias have been established, and reveal the following major points. Dysesthesias of peripheral nerve or dorsal root origin have a central neural cause. Chronic dysesthesias of spinal origin have a cause which resides in the brain. The origins of these effects are lesions in the spinothalamic system. The causes of these effects are abnormal functionings among opiate, catecholamine, and purine pathways. Denervation supersensitivity is suggested.

Afferent Pathways↗
PubMed1988

Early stage ovarian cancer: a randomized clinical trial comparing whole abdominal radiotherapy, melphalan, and intraperitoneal chromic phosphate: a National Cancer Institute of Canada Clinical Trials Group report.

Two hundred fifty-seven eligible patients with stage I, IIA "high risk" ovarian carcinoma and IIB, IIIO (disease confined to pelvis), were randomized to either total abdominal radiotherapy (arm A) 2,250 rad in 20 fractions (107 patients), melphalan (arm B) 8 mg/m2/d X 4 every 4 weeks X 18 courses (106 patients), or intraperitoneal chromic phosphate (arm C) 10 to 20 mCi (44 patients). All patients were initially treated with pelvic radiotherapy; arm A, 2,250 rad in ten fractions; and arms B and C, 4,500 rad in 20 fractions. Entry to arm C was discontinued early because of toxicity. In a multifactor analysis using proportional hazards models, no significant difference in survival was observed although there was a marginally significant difference in disease-free survival (P = .015) with arm B being superior to arm A. Stage (P less than .0001), grade (P less than .0001), and histology (P less than .008) were predictors of survival in the multifactor analysis. Performance status, age, and residual disease were significant predictors in the single factor analysis but were not predictive when correction was made for the effects of stage, grade, and histology. Five-year survival rates are 62% for arm A, 61% for arm B, and 66% for arm C. Median duration of follow-up is 8 years. Long-term complications of radiotherapy were seen in 19 patients on arm A, 11 on arm B, and 11 on arm C. Four patients who had received melphalan developed either a myelodysplastic syndrome or acute leukemia. Violations in covering the whole abdominal target volume were correlated with survival.

Chromium↗
PubMed1987

Contribution of tryptophan residues to the combining site of a monoclonal anti dinitrophenyl spin-label antibody.

Two Fab fragments of the monoclonal anti dinitrophenyl (DNP) spin-label antibody AN02 were prepared by recombination of specifically deuterated heavy and light chains. In the recombinant H(I)L(II) all the tyrosines and phenylalanines were perdeuterated as were the tryptophan residues of the heavy chain. In the recombinant H(II)L(I) all the tyrosines and phenylalanines were perdeuterated as were the tryptophan residues of the light chain. Saturation of three resonances of H(I)L(II), assigned to tryptophan protons of the light chain, resulted in magnetization transfer to the aromatic proton at position 6 of the DNP ring and to the CH2 protons of the glycines linked to the DNP in a diamagnetic hapten (DNP-DG). Saturation of three resonances of H(II)L(I) assigned to tryptophan protons of the heavy chain resulted in magnetization transfer to the CH2 protons of the glycines in DNP-DG. From the dependence of the magnetization transfer on the irradiation time, the cross relaxation rates between the involved protons were estimated. The inferred distances between these protons of the hapten and certain tryptophan protons are 3-4 A. It is concluded that in the combining site of AN02 there is one tryptophan from the light chain and one tryptophan from the heavy chain that are very near the hapten. When all tyrosines and phenylalanines were perdeuterated and all tryptophan aromatic protons were deuterated except for the protons at positions 2 and 5, titration of the Fab fragments with variable amounts of paramagnetic hapten showed that one proton from the light chain tryptophan is near (less than 7 A) the unpaired electron and that three other protons are significantly closer than 15 A.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1987

A predictive index of cure versus no cure in advanced ovarian carcinoma patients--replacement of second-look laparotomy as a diagnostic test.

Three hundred forty-two Stage III and IV epithelial ovarian carcinoma patients received cytoreductive surgery followed by Adriamycin and cisplatin, 50 mg/m2 each, q 4 weeks for 9 courses. One hundred ninety-seven were clinically NED at completion of treatment and 173 of these 197 had a second-look laparotomy. One hundred twenty had persistent disease. Fifty-three were second-look negative and had no further treatment. Thirty of these latter patients relapsed--all (with one exception) within 2 years. Those not relapsing after negative second-look are considered "cured" (median follow-up 42 months, range 24-68 months) and all others "failures." Stage was a significant predictor of treatment failure--there were no Stage IV "cures." In Stage III patients, age and largest residual tumor diameter post initial surgery were significant predictors of failure. Performance status was marginally significant. In our series, any patient with Stage IV disease or Stage III disease with at least two of the following three poor prognostic factors had a chance of cure of 2.2% (2 "cures" out of 90 patients): age greater than 60 years, macroscopic residual initially, or initial performance status of 2 or 3. Under normal circumstances a second-look procedure to identify persistent disease in this group of patients does not appear justified.

Adult↗