A pyrimidodiazepine, 6-acetyl-2-amino-7, 8-dihydro-9H-pyrimido [4,5-b][1,4]diazepin-4(3H)-one, was chemically synthesized. This compound was shown to mimic the essential role of tetrahydrobiopterin in the human immune response mechanism. It is the only synthetic compound known which is able to carry out this natural function of promoting the binding of interleukin 2 to human T cells. Tetrahydrobiopterin exerts its effect by complexing with class 1 human leucocyte antigen (HLA), the active moiety being a hydroxyl group. Molecular modelling showed the active pyrimidodiazepine to have an oxygen atom in approximately the same spatial position as in tetrahydrobiopterin, suggesting that both molecules may engage in hydrogen bonding at the active site of the HLA molecule.
The following work has been carried out on the regulation of 6(R)5,6,7,8-tetrahydrobiopterin (BH4) and pyrimido(4,5-6)(1,4)diazepine (acetylhomopterin (AHP)) biosynthesis:
molecular characterization of mammalian human guanosine triphosphate cyclohydrolase I (GTP-CH) and regulation of GTP-CH messenger ribonucleic acid (mRNA) expression by cytokines;
molecular characterization of mammalian and human sepiopterin reductase (SR) and regulation of SR and mRNA expression by cytokines;
control of pteridine biosynthesis in the natural killer like cell line YT;
modulation of BH4 synthesis by cysteine;
rearrangement of tetrahydro-6-biopterin into tetrahydro-7-biopterin in murine mast cells;
metabolism of AHP;
detection of AHP in biological samples.
In the area of modulation of interleukin-2 (IL-2) receptor binding by pteridines and AHP work has been conducted on:
structural requirements for the modulatory effect;
mechanisms of IL-2 receptor modulation.
A systematic study will be carried out on the regulatory effect of Ahp on pteridine synthesis and on cytokine mediated cell
proliferation. Ahp is a recently discovered insect metabolite with an unusual pyrimidodiazepine ring system. The proposed work carries important implications, since pteridines such as biopterin are known not only to be cofactors in neurotransmitter synthesis but appear to additionally modify cytokine binding and so to affect the kinetics of DNA synthesis in the cell. An accompanying programme of chemical synthetic work will provide the compounds necessary for the biological investigation.