ABSTRACT
Rapidly growing cells show an increased demand for nutrients and vitamins. The objective of our work is to exploit the supply route of vitamin B12 to deliver new derivatives of this vital vitamin to hyperproliferative cells. To date, radiolabeled ((57)Co and (111)In) vitamin B12 derivatives showed labeling of tumor tissue but also undesired high accumulation of radioactivity in normal tissue. By abolishing the interaction of a tailored vitamin B12 derivative to its transport protein transcobalamin II and therefore interrupting transcobalamin II receptor and megalin mediated uptake in normal tissue, preferential accumulation of a radiolabeled vitamin in cancer tissue could be accomplished. We identified transcobalamin I on tumors as a possible new receptor for this preferential accumulation of vitamin-mediated targeting. The low systemic distribution of radioactivity and the high tumor to blood ratio opens the possibility of a more successful clinical application of vitamin B12 for imaging or therapy.
Subject(s)
Antineoplastic Agents/therapeutic use , Vitamin B 12/analogs & derivatives , Vitamin B 12/therapeutic use , Biological Transport/drug effects , Carcinoma , Cell Line, Tumor , Humans , Kidney Neoplasms , Melanoma , Transcobalamins/drug effects , Transcobalamins/metabolism , Urinary Bladder NeoplasmsABSTRACT
Serum vitamin B(12) radioimmunoassays may give falsely low results in patients with folate deficiency, multiple myeloma, megadose of vitamin C and following radioisotope organ scan. We evaluated 10 consecutive healthy women on oral contraceptives (OC) who had falsely low vitamin B(12) levels, as reflected by normal urine methylmalonic acid and plasma homocysteine. After 1-month cessation of OCs, vitamin B(12) returned to the normal range in all women. Transcobalamin I (TCI) blood level was decreased in 60% of patients. OCs may cause temporary low vitamin B(12) blood levels of no clinical significance that can be associated with low TCI levels
Subject(s)
Contraceptives, Oral/adverse effects , Vitamin B 12 Deficiency/diagnosis , Adult , Contraceptives, Oral/administration & dosage , Contraceptives, Oral/blood , Diagnostic Errors , False Positive Reactions , Female , Homocysteine/blood , Humans , Methylmalonic Acid/urine , Transcobalamins/drug effects , Transcobalamins/metabolism , Vitamin B 12 Deficiency/etiologyABSTRACT
The influence of mitogens on the expression of surface membrane TC-II receptors of human blood lymphocytes and internalization of (TS-II+57Co-CNCbl) complex into cytoplasm were investigated. Mature lymphocytes have a very small number of surface receptors to plasma TC-II but their expression is increased significantly by PHA or Con-A stimulation. CBl transport to cytoplasma is activated in definite sequence by two different mechanisms. Stimulated cells take free CBl without participation of TC-II in early hours of mitogen action (12-42 hrs) before maximal 3H-thymidine incorporation into DNA. On day 3 of cultivation, specific mechanism of CBl transport triggers and the number of lymphoblast receptors is increased manifold. Radioactive CBl enters cytoplasma due to interaction of TC-II-CN [57Co] CBl of the medium with surface membrane receptor of the cells. Thus, the definition of TC-II receptors as an important functional parameter may serve a marker of proliferating cells.
Subject(s)
Lymphocyte Activation/drug effects , Lymphocytes/drug effects , Mitogens/pharmacology , Receptors, Cell Surface/drug effects , Transcobalamins/drug effects , Cell Membrane/drug effects , Cell Membrane/metabolism , Cells, Cultured/drug effects , Cells, Cultured/metabolism , Cobalt Radioisotopes , Concanavalin A/pharmacology , Humans , Lymphocytes/metabolism , Phytohemagglutinins/pharmacology , Receptors, Cell Surface/metabolism , Transcobalamins/metabolism , Tritium , Vitamin B 12/bloodABSTRACT
A cobalamin-binding protein has been purified from chicken egg-white by using a combination of conventional and high performance ion-exchange chromatography. Following initial purification by DEAE-cellulose, ammonium sulphate precipitation, Sephacryl S-200 CM-cellulose and affinity chromatography, appropriate fractions were further purified using the Pharmacia fast protein liquid chromatography (FPLC) system. Using this method of purification, egg-white CBP has been purified more rapidly and with greater recovery than with conventional column chromatography. The homogeneity of this protein was verified by SDS-PAGE. The Mr was 37,000 by SDS-PAGE and 39,000 by gel filtration, which indicated that it was a glycoprotein. The stokes radius was 4.1 nm and pI was 4.3. The protein bound 57COB12 with a molar ratio of 1/1 and kd of 0.40 microM. The egg-white CBP was composed of 294 amino acid residues. Thiol groups and metal ions were not connected with the Cbl-binding activities.
