Rational design of hyper-glycosylated human luteinizing hormone analogs (a bioinformatics approach).

Glycoengineering is a recently used approach to extend serum half-life of valuable protein therapeutics. One aspect of glycoengineering is to introduce new N-glycosylation site (Asn-X-Thr/Ser, where X ≠ Pro) into desirable positions in the peptide backbone, resulting in the generation of hyper-glycosylated protein. In this study, human luteinizing hormone (LH) was considered for identification of the suitable positions for the addition of new N-linked glycosylation sites. A rational in silico approach was applied for prediction of structural and functional alterations caused by changes in amino acid sequence. As the first step, we explored the amino acid sequence of LH to find out desirable positions for introducing Asn or/and Thr to create new N-glycosylation sites. This exploration led to the identification of 38 potential N-glycan sites, and then the four acceptable ones were selected for further analysis. Three-dimensional (3D) structures of the selected analogs were generated and examined by the model evaluation methods. Finally, two analogs with one additional glycosylation site were suggested as the qualified analogs for hyper-glycosylation of the LH, which can be considered for further experimental investigations. Our computational strategy can reduce laborious and time-consuming experimental analyses of the analogs.

LHRHa aided liposomes targeting to human ovarian tumor cells: preparation and cellular uptake.

In this study, a synthetic nonapeptide similar to luteinizing hormone-releasing hormone (LHRHa), the ligand of an extracellular membrane receptor specific to ovarian tumor cells, was selected as targeting moiety and electrically adsorbed to the negatively charged liposomes composed of phospholipid and monocholesterolsuccinate. Docetaxel, as the first line chemotherapy for ovarian tumor, was chosen to be encapsulated into the liposomes. And a high encapsulate efficiency (93%) and drug loading efficiency (20%) of liposomes were achieved via central composite design. In order to investigate the targeting efficiency of the drug delivery system, in vitro cell uptake was determined and the results showed an increasing uptake of LHRHa aided liposomes compared to normal ones.

Chemical and chemo-enzymatic synthesis of the alpha-Neu p5Ac-(2-->6)- beta-D-GalpNAc-(1-->4)-beta-D-GlcpNAc-(1-->2)-alpha-D-Manp element that is part of N-linked carbohydrate chains of human lutropin.

In the framework of a project aimed at the elucidation of the nature of the functional importance of the N-glycosylation of the alpha-subunit of the glycoprotein hormones human lutropin and human chorionic gonadotropin, the structural element alpha-Neu p5Ac-(2-->6)-beta-D-GalpNac-(1-->4)- beta-D-GlcpNAc-(1-->2)-alpha-D-Manp, which is part of the carbohydrate chains of human lutropin, has been prepared by chemical and chemo-enzymatic synthesis in the form of its propyl glycoside. Condensation of 4-O- acetyl-3,6-di-O-benzyl-2-deoxy-2-phthalimido-alpha/beta-D-glucopyranosyl trichloroacetimidate with allyl 3,4,6-tri-O-benzyl-alpha-D-mannopyranoside gave after deacetylation allyl (3,6-di-O-benzyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl) -(1-->2)-3,4,6-tri-O-benzyl-alpha-D-mannopyranoside. Ethyl 3-O-benzyl-2-deoxy-2-phthalimido-l-thio-beta-D-glucopyranoside was converted into the galacto-derivative ethyl 4,6-di-O-acetyl-3-O-benzyl-2-deoxy-2-phthalimido-1-thio-beta-D -galactopyranoside via an oxidation-reduction route, as well as via SN2-type substitution with acetate. The use of this galacto thioglycoside, after its conversion into the corresponding bromide, as GaIN donor for condensation with the mentioned disaccharide derivative yielded after deacetylation allyl (3-O-benzyl-2-deoxy-2-phthalimido-beta-D-galactopyranosyl)-(1-->4) -(3,6-di-O-benzyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl)-(1-->2) -3,4,6-tri-O-benzyl-alpha-D-mannopyranoside. Methylsulfenyl bromide-silver triflate promoted sialylation of this trisaccharide derivative with O-ethyl S-[methyl (5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D -glycero-alpha-D-galacto-non-2-ulopyranosyl)onate] dithiocarbonate and subsequent deprotection resulted into the aimed tetrasaccharide structural element. Alternatively, this compound was prepared via a block synthesis, which, however, was not superior to the linear strategy. Finally, a stereose lective sialylation of synthetically prepared beta-D-GalpNAc-(1-->4)-beta-D-GlcpNAc-(1-->2)-alpha-D-Manp-(1-->O) CH2CH2CH3 with CMP-Neu5Ac and rat liver alpha-2,6-sialyltransferase was accomplished affording the same tetrasaccharide structural element.

Comparison of the cytotoxic effect of hormonotoxins prepared with the use of heterobifunctional cross-linking agents N-succinimidyl 3-(2-pyridyldithio)propionate and N-succinimidyl 6-[3-(2-pyridyldithio)propionamido]hexanoate.

With the aim of developing cytotoxic hybrid molecules which can be selectively targeted to specific cells in the gonads, a single chain ribosome-inactivating protein, gelonin, was conjugated to ovine luteinizing hormone (oLH) with the use of heterobifunctional cross-linking agents N-succinimidyl3-(2-pyridyldithio)-propionate (SPDP) and long-chain SPDP. Four hormonotoxins were synthesized having a variable spacer arm between oLH and gelonin. The spacer arms in C200A, C210A, C220A, and C230A were 13.6, 22.4, 22.4, and 31.2 A long, respectively. Extensive physiochemical and biochemical analysis revealed a 1:1 molar ratio of the ingredients in its oLH-S-S-gelonin conjugates. The linkage occurred through the epsilon-NH2 group of the alpha-subunit of oLH as judged from RP-HPLC analysis. The hormonotoxins retained substantial receptor binding ability, steriodogenic activity, and immunoreactivity of oLH and gelonin to their respective antibodies. Hormonotoxins bind to Leydig tumor cells via oLH, leaving gelonin free as judged by competitive displacement analysis. The hormonotoxins internalized to a sufficient degree to effectively inhibit protein synthesis. Upon comparison, immunoreactivity, receptor binding steroidogenic activity, and cytotoxicity of oLH-S-S-gelonin conjugates prepared with the use of only LC-SPDP (C230A, 31.2-A spacer arm) and by using both SPDP and LC-SPDP (C210A and C220A, 22.4-A spacer arm) were found to be comparable with that of conjugate prepared with SPDP alone (C200A, 13.6-A spacer arm). Therefore, it may be concluded that the cytotoxicity of oLH-based hormonotoxin remained unaffected with the use of long-chain spacer arms which are believed to be used generally to avoid steric hindrance.

Hormonotoxins. Preparation and characterization of ovine luteinizing hormone-gelonin conjugate.

With the aim of targeting toxins to selected cells in the gonad, we have prepared conjugates of ovine luteinizing hormone (oLH) with a single chain ribosome-inactivating protein called gelonin. The two proteins were thiolated by using N-succinimidyl-3-(2-pyridyldithio)propionate and subsequently reacted under appropriate conditions to form oLH-S-S-gelonin complex. A complete biochemical analysis of thiolated oLH and oLH-gelonin conjugates has been performed. The linkage of the hormone to the toxin probably occurred through a single amino group in the alpha-subunit, with the beta-subunit remaining free. Modification of a single amino group on the alpha-subunit reduced receptor binding and immunological reactivity of the thiolated oLH, but subsequent complexing with the toxin-gelonin did not seriously compromise these activities. oLH and gelonin were calculated to be present in a 1:1 ratio in the hormonotoxin preparation. The conjugate retained significant steroidogenic activity in rat granulosa cells. Upon reaction with mouse tumor Leydig cells (MA-10 cells), the toxin component of the complex became internalized to a sufficient degree to effectively inhibit protein synthesis. The studies provide a rational basis for the design and study of large hormonotoxins.

Hormonotoxins. I. Strategy for synthesis of ovine luteinizing hormone--gelonin conjugate bearing the toxin in the beta-subunit.

The amino groups in the beta-subunit of ovine luteinizing hormone (oLH) were modified by thiolation using N-succinimidyl-3-(2-pyridyldithio) propionate so that it may be coupled in a disulfide linkage to similarly modified ribosome inactivating protein, gelonin. The modified beta-subunit was able to hybridize with free LH alpha-subunit and the complex retained full biological activity. However, when gelonin was coupled to the beta-subunit, the resulting conformational changes masked or eliminated the sites necessary for intersubunit recognition of the free alpha-subunit. This has important implications for the design in the synthesis of gonadotropin-toxin/drug conjugates.

Further characterization of the ovine lutropin alpha and beta subunits prepared by the salt precipitation method.

The subunits of ovine lutropin prepared by acid dissociation and salt precipitation were characterized by end group analysis, tryptic peptide mapping, SDS gel electrophoresis and biological activity. No evidence of internal peptide cleavage was found in the alpha subunit. The subunits possessed low activity. The alpha and beta subunits recombined effectively to generate a complex that had full receptor binding activity and in vitro biological activity. The recombinants of subunits prepared by countercurrent distribution showed only 50% activity in both assays. The salt precipitation method alpha subunit could be completely reduced and reoxidized in the absence of denaturants. The reoxidized alpha subunit combines with the native beta subunit generating full activity. However, this recombined hormone tends to lose activity with time, suggesting that the reoxidation may not fully restore the native structur of the reduced alpha subunit. The native lutropin alpha subunit effectively combined with follitropin beta subunit generating complete follitropin activity.

[Obtaining iodinated luteinizing hormone while preserving its biological properties]. / Poluchenie iodirovannogo liuteiniziruiushchego gormona s sokhraneniem ego biologicheskikh svoistv.

The author describes a method of obtaining biologically-active 125I-labeled luteinzing hormone in iodation with chloramine T. The hormone and chloramine T concentration ratio of 1:2, and the reaction time of 20 sec was used. LH-125I with the specific activity of 27--30 microCi/microgram was bound with the receptor strictly specifically.