Immuno-enhancing activity of the amino-terminal domain of human prealbumin: isolation, characterization and synthesis.

A decapeptide isolated from highly purified preparations of human prealbumin was able to restore azathioprine (Az) sensitivity, a property of a sub-class of T-lymphocytes, to the spleen rosette-forming cells (RFC) of adult thymectomized (ATx) mice in vitro. The peptide was sequenced by the Edman method and shown to correspond to the ten amino-terminal residues of prealbumin, Gly-Pro-Thr-Gly-Thr-Gly-Glu-Ser-Lys-Cys. Synthesis of this peptide by solid phase methodology confirmed its activity both in vitro and in vivo. Synthesis of a number of structural analogues indicated that the amino-terminal deca, undeca and dodecapeptides of prealbumin as well as some of their derivatives were also able to restore Az sensitivity to RFC in vitro and in vivo. The Cys10 residue and the Glu7 residues both contributed significantly to potency in vitro. Removal of up to three amino acids from the N-terminus of the decapeptide led to a progressive loss of activity. The data indicates that the ability of human prealbumin to restore the Az sensitivity to the RFC of adult Tx mice is intrinsic to the protein and resides in the amino-terminal domain of the molecule.

Synthesis of a novel class of heteroaromatic amino acids and their use in the preparation of analogues of luteinizing hormone-releasing hormone.

A novel class of heterocyclic aromatic amino acids based on the 3-(2-benzimidazolyl)alanine system has been generated by chiral synthesis from D- or L-aspartic acid. The use of variously substituted o-phenylenediamines for condensation with the beta-carboxyl function of alpha-benzyl N-(benzyloxycarbonyl)-D-aspartate has led to a series of amino acids of graded hydrophobicity with a steric bulk similar to that of tryptophan. In a similar fashion, we have prepared 3-(2-benzothiazolyl)-D-alanine from o-aminothiophenol and 3-(2-benzoxazolyl)-D-alanine from o-aminophenol. Incorporation of these amino acids into the 6-position of luteinizing hormone-releasing hormone (LH-RH) led to a series of very potent agonist analogues (up to 160 times LH-RH potency), active in doses ranging from 0.1 to 0.5 microgram by twice daily injection in a rat estrus cyclicity suppression assay designed to show the paradoxical antifertility effects of these compounds.

Synthesis and biological activity of some very hydrophobic superagonist analogues of luteinizing hormone-releasing hormone.

The effect of increased hydrophobicity at position 6 of luteinizing hormone-releasing hormone (LH-RH) has been investigated by the incorporation of a series of 15 very hydrophobic, unnatural D-amino acids at this position. The unnatural amino acids studied can be considered analogues of phenylalanine with carbocyclic aromatic side chains consisting of substituted phenyl (e.g., 2,4,6-trimethylphenyl, p-biphenyl) or polycyclic aromatic (e.g., naphthalene, anthracene) units. When enzymatic resolution (subtilisin Carlsberg) of the most hydrophobic amino acids failed, the racemic amino acids were incorporated, and the diastereomeric LH-RH analogues were resolved by preparative high-performance liquid chromatography. The analogues were synthesized by the solid-phase technique. All of the synthetic compounds were very potent LH-RH superagonists, but [6-(3-(2-naphthyl)-D-alanine)]LH-RH, [6-(3-(2-naphthyl)-D-alanine), 7-(N alpha-methylleucine)]LH-RH and [6-(3-(2,4,6-trimethylphenyl)-D-alanine)]LH-RH appear to be among the most potent LH-RH agonist analogues yet reported when tested in a rat estrus cyclicity suppression assay designed to show the paradoxical antifertility effects of these compounds [ED50 approximately 7 x 10(-8) g; twice daily in saline]. These analogues are twice as potent as [D-Trp6,ProNHEt9]LH-RH in this assay system (i.e., approximately 200 times the potency of LH-RH).

Regression of tumors in guinea pigs after treatment with synthetic muramyl dipeptides and trehalose dimycolate.

A high incidence of tumor regression was observed in guinea pigs bearing transplantable, line-10 hepatocellular carcinomas when synthetic muramyl dipeptides combined with trehalose dimycolate in oil-in-water emulsions were injected directly into the tumors. These compounds are promising candidates to replace viable bacillus Calmette-Guérin in cancer immunotherapy in humans and animals.