Biomedical subjects
E Goncalves
Publications and source records attributed to E Goncalves.
[Taxotere (docetaxel) and CPT 11 (irinotecan): phase I trials].
Two new drugs from two new chemotherapy compound families were developed concomitantly: Taxoter (docetaxel), a taxane derivate and CPT 11 (irinotecan) a topoisomerase inhibitor. Six phase I trials of Taxoter were performed. The limiting toxicity is neutropenia. The recommended dosage for phase II trial is 100 mg/m2 administered in 1 hour perfusion, every 21 days. Neutropenic fever is unfrequent. Other toxicities are mucositis, skin toxicity, hypersensibility reaction, weight gain and oedema. None of these toxicities were limiting. Six phase I studies were conducted to determine the maximum tolerated dose of CPT 11 (irinotecan). Two different schedules were studied: the weekly 30-90 minutes infusion and an infusion administered every three weeks in one day or daily over three or five consecutive days. The limiting toxicity of the weekly schedule is diarrhea. Therefore the recommended dosage is 100-150 mg/m2/week. While dose limiting toxicities in the three week schedule are diarrhea as well as neutropenia. The recommended dose is 350 mg/m2. Since diarrhea appeared to be the major problem in achieving high dose intensity with CPT 11, a dose escalation trial with drug support against diarrhea was performed. A recommended dosage of 500 mg/m2 is therefore described. These two drugs are under evaluation in a large spectrum of tumors. Their original mechanism of action suggests interesting therapeutic properties. Clinical studies in combination with other drugs are in progress to define the role of topoisomerase I inhibitors and taxane in cancer therapy.
Role of the transmembrane domain and flanking amino acids in internalization and down-regulation of the insulin receptor.
We have characterized the internalization and down-regulation of the insulin receptor and nine receptors with mutations in the transmembrane (TM) domain and/or flanking charged amino acids to define the role of this domain in receptor cycling. When expressed in Chinese hamster ovary cells, all had normal tetrameric structure and normal insulin-stimulated autophosphorylation/kinase activity. Replacement of the TM domain with that of the platelet-derived growth factor receptor, insertion of 3 amino acids, and substitution of Asp for Val938 or of Ala for either Gly933 or Pro934 had no effect on internalization. Replacement of the TM domain with that of c-neu or conversion of the charged amino acids on the cytoplasmic flank to uncharged amino acids, on the other hand, resulted in a 40-60% decrease in insulin-dependent internalization rate constants. By contrast, substitution of Ala for both Gly933 and Pro934 increases lateral diffusion mobility and accelerates internalization rate. These changes in internalization were due to decreased or increased rates of redistribution of receptors from microvilli to the nonvillous cell surface. In all cases, receptor down-regulation and receptor-mediated insulin degradation paralleled the changes in internalization. Thus, the structure of the transmembrane domain of the insulin receptor and flanking amino acids are major determinants of receptor internalization, insulin degradation, and receptor down-regulation.
Transmembrane domain inversion blocks ER release and insulin receptor signaling.
Activation of the insulin receptor, like other tyrosine kinase receptors, appears to require dimerization. We have shown previously that, even in the absence of insulin, full receptor activation can be induced by changes in the receptor transmembrane domain (TMD), suggesting that TMD dimerization is sufficient for receptor activation. To further understand the importance of the TMD in insulin receptor activation, we have inverted the entire TMD sequence including flanking basic amino acids, residue-for-residue. This mutation was predicted to alter the ability of a TMD alpha-helix to form homodimers and higher level aggregates. Despite apparently normal protein folding on either side of the membrane, this mutation caused ER retention and, for those receptors that reached the cell surface, blockade of insulin-stimulated kinase signal transmission. However, the signaling blockade could be overcome by proteolytic activation with trypsin. In contrast, shifting only the basic cytoplasmic residues to the opposite side of the TMD or mutation to neutral residues had no detectable effect on assembly, biosynthesis, topology, or signaling. These findings extend our previous observations to suggest that TMD interactions within the membrane are not only sufficient for receptor activation, but may be required. TMD interactions also appear to be necessary for oligomeric assembly and biosynthetic maturation of the insulin receptor.
Substitution of the erbB-2 oncoprotein transmembrane domain activates the insulin receptor and modulates the action of insulin and insulin-receptor substrate 1.
The mechanism through which insulin binding to the extracellular domain of the insulin receptor activates the intrinsic tyrosine kinase in the intracellular domain of the protein is unknown. For the c-neu/erbB-2 (c-erbB-2) protooncogene, a single point mutation within the transmembrane (TM) domain converting Val-664 to Glu (erbB-2V-->E) results in elevated levels of tyrosine kinase activity and cellular transformation. We report the construction of a chimeric insulin receptor in which the TM domain of the receptor has been substituted with that encoded by erbB-2V-->E. When expressed in Chinese hamster ovary cells this chimeric receptor displays maximal levels of autophosphorylation and kinase activity in the absence of insulin. This activity results in an increase in the level of insulin-receptor substrate 1 phosphorylation but a down-regulation in insulin-receptor substrate 1 protein and desensitization to insulin stimulation of glycogen synthesis. By contrast, basal levels of DNA synthesis are elevated to levels approximately 60% of those observed in serum-stimulated cells. Over-expression of chimeric insulin receptors containing the c-erbB-2 TM domain or a single point mutation in the insulin receptor TM domain of Val-938-->Asp, on the other hand, shows none of these alterations. Thus, the TM domain encoded by erbB-2V-->E contains structural features that can confer ligand-independent activation in a heterologous protein. Constitutive activation of the insulin receptor results in a relative increase in basal levels of DNA synthesis, but an apparent resistance to the metabolic effects of insulin.
Optimizing transmembrane domain helicity accelerates insulin receptor internalization and lateral mobility.
Transmembrane (TM) domains of integral membrane proteins are generally thought to be helical. However, a Gly-Pro sequence within the TM domain of the insulin receptor is predicted to act as a helix breaker. CD analyses of model TM peptides in a lipid-like environment show that substitution of Gly and Pro by Ala enhances helicity. On this basis, Gly933 and Pro934 within the TM domain of the intact human insulin receptor were mutated to Ala (G-->A, P-->A, GP-->AA) to assess effects of altered helicity on receptor functions. Mutated and wild-type receptors, expressed stably in cultured CHO cells at equivalent levels, were properly assembled, biosynthetically processed, and exhibited similar affinities for insulin. Receptor autophosphorylation and substrate kinase activity in intact cells and soluble receptor preparations were indistinguishable. In contrast, insulin-stimulated receptor internalization was accelerated 2-fold for the GP-->AA mutant, compared to a wild-type control or the G-->A and P-->A mutants. Insulin degradation, which occurs during receptor endocytosis and recycling, was similarly elevated in cells transfected with GP-->AA mutant receptors. Fluorescence photobleaching recovery measurements showed that the lateral mobility of GP-->AA mutant receptors was also increased 2- to 3-fold. These results suggest that lateral mobility directly influences rates of insulin-mediated receptor endocytosis and that rates of endocytosis and lateral mobility are retarded by a kinked TM domain in the wild-type receptor. Invariance of Gly-Pro within insulin receptor TM domain sequences suggests a physiologic advantage for submaximal rates of receptor internalization.
Substitution of the insulin receptor transmembrane domain with the c-neu/erbB2 transmembrane domain constitutively activates the insulin receptor kinase in vitro.
To examine the role of the transmembrane domain (TM) of the insulin receptor in insulin-induced receptor kinase activation, we prepared four mutated insulin receptors: 1) a Val938----Asp substitution (IR/TMv----D), 2) insertion of a 3-amino acid repeat (Val938-Phe939-Leu940) (IR/TM+3), or the entire TM was replaced by the corresponding domain of either the 3) platelet-derived growth factor (PDGF) receptor (IR/TMPDGFR) or 4) c-neu/erbB2 proto-oncogene product (IR/TMc-neu). Each mutant receptor was stably expressed in Chinese hamster ovary cells, assessed by fluorescence-activated cell sorting, insulin binding, and biosynthetic labeling. All mutant receptors exhibited normal affinity for insulin. Pulse-chase experiments showed that each proreceptor was processed into alpha- and beta-subunits, although the rate of IR/TMV----D conversion was reduced approximately 3-fold. With IR/TMPDGFR, IR/TMV----D, and IR/TM+3 basal and insulin-stimulated levels of autophosphorylation and tyrosine kinase activation were normal, both in wheat germ agglutinin (WGA)-purified receptor preparations and intact cells. By contrast, following WGA purification or isolation of crude membranes, IR/TMc-neu was a constitutively active autokinase and substrate kinase in vitro. However, in intact cells insulin-stimulated autophosphorylation and kinase activity appeared normal. We conclude that although there is considerable latitude in acceptable structure, residues within the insulin receptor transmembrane domain can play a functional role in regulation of insulin receptor tyrosine kinase activity.
Differential effect of a new thyromimetic on triiodothyronine transport into myoblasts and hepatoma and neuroblastoma cells.
3,5-Dibromo-3'-pyridazinone-L-thyronine (L-94901), a member of a novel class of thyromimetics, reduces cholesterol plasma levels with little effect on cardiac function in rats. Because receptor binding of L-94901 in isolated heart and liver nuclei is similar but binding in liver nuclei in vivo was 50-fold higher than in cardiac nuclei, we studied its effect on triiodothyronine (T3) transport across the plasma membrane of myoblasts, hepatoma cells and neuroblasts. Previously, we had demonstrated saturable, stereospecific and energy dependent transport of T3 into the three cell lines. After equilibrium of intact cells with hormone, nuclear binding of T3 was decreased by L-94901 in all three cell lines. While whole cell uptake and whole cell binding of T3 was only slightly affected by L-94901, kinetic analysis of the initial rate of uptake showed uncompetitive or noncompetitive inhibition and a differential decrease in Vmax. Furthermore, the Ki for the liver and brain derived cells was 10-fold lower than for the muscle derived cells. This effect on the plasma membrane transport of T3 may explain the differential effect reported in the intact animal.
[Seraspenide (acetylSDKP): phase I-II trial study of inhibitor of hematopoiesis protects against toxicity of aracytine and ifosfamide monochemotherapies].
Seraspenide, a synthetic tetrapeptide, inhibits cell cycle entry of normal hematopoietic stem cells. In mice it protects hemopoiesis against the damage caused by cytarabine, cyclophosphamide and carboplatin. Seraspenide has been given to 53 cancer patients undergoing monochemotherapy with cytarabine and ifosfamide in a double-blind cross-over randomized study. A significant protection of peripheral blood cells has been observed. Seraspenide has been devoided of toxicity.
Thyroid hormone transport in a human glioma cell line.
The uptake of 3,5,3'-triiodothyronine (T3) and thyroxine (T4) was studied in human glioma cells (Hs 683) and compared with that in several other neural cell lines. At 25 degrees C or 37 degrees C, total cell uptake rose rapidly and reached equilibrium within 60 min. The glioma cells had the highest uptake: 47.6 fmol of L-T3 and 43.4 fmol of L-T4 per 10(6) cells at 37 degrees C. These were inhibited 77% and 72%, respectively, by excess unlabeled hormone. Uptake in the nuclei reached equilibrium between 90 and 120 min and was also highest in glioma cells: 1.46 fmol of L-T3 and 0.49 fmol of L-T4 per 10(6) cells. When expressed as percent of total cell uptake, however, glioma cells had the lowest values (3.1% for L-T3 and 1.1% for L-T4). Also in contrast to other cell lines, glioma cells transported L-T4 almost as effectively as L-T3. D-T3 and D-T4 total cell uptake was 86% and 96% lower than that of the respective L-isomers, and the nuclear uptake as a fraction of the cell uptake was similar. Kinetic analysis of the initial rate of cell uptake gave Vmax values for D-T3 and D-T4 that were 97% and 98% lower than for the L-isomers. Antimycin and monodansylcadaverine decreased the Vmax as well as the equilibrium cell and nuclear uptake of the L-isomers. The apparent nuclear affinity constant for L-T4 in intact cells was inhibited 90% in the presence of antimycin, whereas no effect was observed in isolated nuclei.(ABSTRACT TRUNCATED AT 250 WORDS)
Familial phaeochromocytoma: successful treatment with 131I-MIBG.
We report the case of a family in which the mother died of hypertensive encephalopathy following the relapse of a phaeochromocytoma. Two of her children are still alive. Both children had malignant phaeochromocytomas that have been treated by surgery and 131I-MIBG. The first child presented with phaeochromocytoma of the right suprarenal gland at the age of 7 years. Surgery was performed. At the age of 14 years, he developed a tumour of the left suprarenal gland and two pulmonary metastases demonstrated by 131I-MIBG. The three tumours were removed, but new lesions occurred. The boy then was treated with 200 mCi (7,400 MBq) of 131I-MIBG given twice, and is now free of disease more than 2 years after treatment. His sister presented at the age of 12 years with phaeochromocytoma of the left suprarenal gland, the only lesion recognized by 131I-MIBG. The tumour was removed, but 5 months later, she developed phaeochromocytoma in the right suprarenal gland. She was treated with 200 mCi (7,400 MBq) of 131I-MIBG and surgery was performed 6 months later. Histology of the suprarenal gland could not demonstrate the persistence of phaeochromocytoma cells. The child is now free of disease more than 2 years after treatment.
The transport of thyroxine into mouse neuroblastoma cells, NB41A3: the effect of L-system amino acids.
Thyroid hormones must cross the plasma membrane to interact with nuclear or other intracellular receptors. In brain cells, most of the T3 in the nucleus is derived intracellularly from T4. While a saturable transport system has been demonstrated for T3 in a number of cell types, the evidence for such a system for T4 is less well established. In a mouse neuroblastoma cell line (NB41A3) the transport of T4 was found to be stereospecific, saturable, and energy dependent. When cells were incubated with radiolabeled hormone, the nuclear accumulation of L-T4 was 3.8-fold higher than that of D-T4, whereas isolated nuclei had a similar Ka for both enantiomers. Exposure of cells to antimycin and monodansylcadaverine decreased nuclear uptake of L-T4 (Ki of 197 and 55 microM, respectively), but had little effect on D-T4 uptake. Furthermore, L-system neutral amino acids, in particular L-phenylalanine at physiological concentrations, were shown to be competitive inhibitors of both T3 and T4 transport. In the presence of 0.1 mM L-phenylalanine the Km of the saturable plasma membrane transport of L-T3 increased 2.3-fold, and that of L-T4 increased 2.1-fold. In contrast, 1.0 mM L-serine or D-phenylalanine had little effect on L-T4 transport. This interaction of L-system amino acid and thyroid hormone transport may be of physiological importance.