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Biomedical subjects

P Welsh

Publications and source records attributed to P Welsh.

At least 19 recordsLinked to original sources

Radioiodination and astatination of octreotide by conjugation labeling.

Octreotide was coupled to 3-iodobenzoyl and 3-iodonicotinoyl moieties to obtain [N-(3-iodobenzoyl)-D-Phe(1)]octreotide (IBO) and [N-(3-iodonicotinoyl)-D-Phe(1)]octreotide (INO), respectively. The IC(50) values for the binding of IBO and INO to CA20948 rat pancreatic tumor membranes were 0.90 and 0.13 nM, respectively, compared with 0.35 nM for octreotide itself. Starting from N-succinimidyl 3-[(131)I]iodobenzoate and N-succinimidyl 5-[(131)I]iodopyridine-3- carboxylate, [(131)I]IBO and [(131)I]INO were prepared in overall radiochemical yields of 35%-50%. Likewise, ¿N-(3-[(211)At]astatobenzoyl)-D-Phe(1)¿octreotide ([(211)At]ABO) was prepared in similar yield from N-succinimidyl 3-[(211)At]astatobenzoate. In vitro assays with AR42J rat pancreatic tumor cells demonstrated a higher retention of cell-internalized radioiodine activity for [(131)I]INO compared with [(125)I]IBO. Tissue distribution studies with both conjugates revealed low levels of activity in the thyroid suggesting that dehalogenation of these peptides was minimal.

Animals↗

The cytotoxicity and microdosimetry of astatine-211-labeled chimeric monoclonal antibodies in human glioma and melanoma cells in vitro.

The cytotoxicity of alpha-particle-emitting endoradiotherapeutic compounds is of increasing interest because clinical evaluation of these potential therapeutic agents is commencing. Astatine-211 is a radionuclide with a 7.2-h half-life that emits 5.87 and 7.45 MeV alpha particles. In the present work, we have investigated the in vitro cytotoxicity of 211At-labeled chimeric monoclonal antibodies (mAbs) in monolayers of D-247 MG human glioma cells and SK-MEL-28 human melanoma cells. The mAbs studied were 81C6, reactive with the extracellular matrix antigen tenascin, Mel-14, directed against the cell membrane antigen proteoglycan chondroitin sulfate, and a nonspecific control mAb, TPS3.2. Cell uptake increased as a function of activity concentration after a 1-h exposure to the 211At-labeled mAbs. The retention of activity was also measured to calculate cumulative activity associated with the cells and the medium. The clonogenic survival as a function of activity concentration was linear in all cases with no detectable shoulder. Microdosimetric analyses were performed based on measured cell geometry, cumulative activity and Monte Carlo transport of alpha particles. Using 18 kBq/ml activity concentration and 1 h of incubation, a two to five times higher activity bound to the microcolonies was found for the specific mAbs compared to the nonspecific mAb. These calculations indicated that a survival fraction of 0.37 was achieved with 0.24-0.28 Gy for D-247 MG cells and 0.27-0.29 Gy for SK-MEL-28 cells. The microdosimetric cell sensitivity, z0, for D-247 MG cells was significantly lower than for SK-MEL-28 cells (0.08 compared to 0.15 Gy). For both cell lines, reduction in survival to 0.37 required an average of only 1-2 alpha-particle hits to the cell nucleus.

Antibodies, Monoclonal↗

Role of arginine 180 and glutamic acid 177 of ricin toxin A chain in enzymatic inactivation of ribosomes.

The gene for ricin toxin A chain was modified by site-specific mutagenesis to change arginine 180 to alanine, glutamine, methionine, lysine, or histidine. Separately, glutamic acid 177 was changed to alanine and glutamic acid 208 was changed to aspartic acid. Both the wild-type and mutant proteins were expressed in Escherichia coli and, when soluble, purified and tested quantitatively for enzyme activity. A positive charge at position 180 was found necessary for solubility of the protein and for enzyme activity. Similarly, a negative charge with a proper geometry in the vicinity of position 177 was critical for ricin toxin A chain catalysis. When glutamic acid 177 was converted to alanine, nearby glutamic acid 208 could largely substitute for it. This observation provided valuable structural information concerning the nature of second-site mutations.

Animals↗

Role of glutamic acid 177 of the ricin toxin A chain in enzymatic inactivation of ribosomes.

The gene for the A chain of ricin toxin was fused to a beta-galactosidase marker cistron via a DNA sequence encoding a short collagen linker, and the tripartite fusion protein was expressed in Escherichia coli. Site-specific mutagenesis was used to change glutamic acid residue 177 to aspartic acid or alanine. When the mutant proteins were expressed, purified, and tested quantitatively for enzymatic activity, the carboxylate function at position 177 was found not to be absolutely essential for ricin toxin A-chain catalysis.

Blotting, Western↗

Selection and characterization of ricin toxin A-chain mutations in Saccharomyces cerevisiae.

A DNA sequence encoding the A chain of ricin toxin (RTA) from the castor bean plant, Ricinus communis, was placed under GAL1 promoter control and transformed into Saccharomyces cerevisiae. Induction of expression of RTA was lethal. This lethality was the basis for a selection of mutations in RTA which inactivated the toxin. A number of mutant alleles which encoded cross-reactive material were sequenced. Eight of the first nine mutant RTAs studied showed single-amino-acid changes involving residues located in the proposed active-site cleft.

Amino Acid Sequence↗

Susceptibility of various human tissues to transformation in vivo with human papillomavirus type 11.

Human papillomaviruses (HPVs) are associated with proliferative lesions in a variety of human epithelial types. In some cases, the associations are highly specific in that a certain papillomavirus type may infect only one human epithelial cell phenotype. In other cases, one papillomavirus apparently infects several tissue types and not others. Further, HPV replication capacity varies considerably in different epithelia. Due to the lack of a suitable method, it has not been possible, until now, to define the role of the host cell phenotype in determining the outcome of infection with an HPV. We recently developed a system in which human epithelium was exposed to HPV-II and transplanted to athymic mice. Cervix and skin grafts developed into typical condylomata. We now test the hypothesis that the outcome of infection of diverse epithelial types with a single human papillomavirus is largely determined by the phenotype of the original epithelial cell. For example, skin obtained from a number of disparate sites from a single patient varied dramatically in its capacity for morphological transformation with HPV-II. Skin from penis was highly susceptible, but skin from abdomen did not transform. Vocal cord from 3 children and 2 adults responded to HPV-II infection by producing typical laryngeal papillomata. A variety of tissues were obtained from II donor infants and infected with HPV-II. Foreskin and cervical tissues of these children were transformed at a frequency of 100%. Vocal cord was transformed at an incidence of 88% and urethra at 73%. Only 37% of esophagus samples were transformed and both abdominal skin and urinary bladder from the same infants were totally resistant to morphological transformation. In a separate study, ureteral tissues from a child and an adult were completely resistant to HPV-II infection. Papillomavirus replication was readily detected as capsid antigen in foreskin, cervix, and urethra, but was poorly expressed in morphologically-transformed esophagi and vocal cords. In the last two tissues HPV-II DNA and RNA were demonstrated in cells by in situ hybridization techniques. We conclude that the epithelial cell phenotype is a major determinant of HPV-II infection, controlling both morphological transformation and viral replication.

Adolescent↗

Systemic adoptive transfer of immunity and low-dose irradiation eradicate metastases of 13762A rat mammary adenocarcinoma.

Rats cured of poorly immunogenic 13762A tumor by a combination of surgery and cyclophosphamide (CY) treatments produced peritoneal exudate cells (PEC) that prevented tumor growth when transferred to naive recipients, but they were ineffective against established tumor. A highly immunogenic 13762A clone (18A) induced PEC lymphocytes that completely reversed the growth of established primary tumor and of lymph-node metastases. 18A-immune PEC alone strongly inhibited tumors of 7 days' duration, but only moderately suppressed 14-day tumors, and had no effect on 21-day tumors. Irradiation (450 R) of rats prior to tumor transplantation improved the effectiveness of the PEC given at 7 days, but the benefit had gone by 14 days. Long-term T-cell depletion prior to tumor challenge allowed PEC inhibition of 7- and 14-day tumors, but not 21-day tumors. The most potent strategy was the administration of 450 R followed immediately by immune PEC. When rats with 21-day tumors were so treated, the metastases grew temporarily to a maximum diameter of 2-5 cm and then completely regressed. We concluded that a combination of immune T cells and 450 R can cure established, massive metastases, probably through a combination of an increase in the numbers of T-cell effectors and elimination of suppressor cells.

Adenocarcinoma↗

Chemonucleolysis: an evolving concept and clinical review.

Chemonucleolysis has had a controversial 20 years of probation, and despite growing clinical evidence supporting the efficacy of chymopapain, the concept is still disputed. To evaluate chemonucleolysis 84 patients, treated with chymopapain over 12 months, were assessed before injection and reviewed 5-15 months after injection. All patients had lumbar disc disease which had failed to respond to conservative therapy. Chemonucleolysis was most effective in those patients with classical signs and symptoms of prolapsed lumbar disc disease of less than 3 months' duration and where sciatica was the predominant complaint. Poor results were obtained in those patients with pain for more than 6 months' duration and with predominantly low back pain. Workers' compensation patients did not respond favourably. Good short term results with chemonucleolysis can be expected by careful patient selection and adequate and accurate placement of enzyme.

Adult↗

Revascularization of the profunda femoris artery in aortoiliac occlusive disease.

We have presented both early and late results in 236 extremities revascularized by aortofemoral, axillofemoral, or femorofemoral bypass grafts for severe atherosclerotic disease. The superficial femoral artery was occluded in all patients and initial outflow was provided solely through the profunda femoris system. Five different categories have been defined based on the procedure utilized to insure patency of the proximal profunda system. Subsequent patency rates are determined for each category. In reviewing our total experience the profunda femoris system was adequate to maintain both graft patency and limb viability in 90.3 percent of extremities in the early postoperative period. This declined to 78.5 percent at 5 year follow-up. Femoropopliteal bypass was required in 16 patients within the first postoperative month to maintain graft patency or relieve persistent ischemia. It is suggested that the addition of femoropopliteal bypass may improve inmediate and long-term patency rates and offer greater assurance that ischemia will be relieved.

Aorta, Abdominal↗