12ème Symposium International sur le VIH
et les maladies infectieuses émergentes
Toulon juin 2002

4.c. AIDS immunologic thrombocytopenia (AIT):
Platelet integrin gpIIb-IIIa is homologous to the cleavage site of HIV-1 protease.

TRAN M.K.G.

4.c. AIDS immunologic thrombocytopenia (AIT):
Platelet integrin gpIIb-IIIa is homologous to the cleavage site of HIV-1 protease.

EXTENDED VERSION /VERSION LONGUE

* Association Positifs,
¹Univ. Paris-Sud, Fac. Pharmacy, Therapeutic Chemistry, 92290 Chatenay.
²Centre Medical Europe, 75009 Paris.

INTRODUCTION.

Over 45 million people¹, including children, are infected with human immunodeficiency virus (HIV), the causative agent of acquired immune deficiency syndrome (AIDS) and this number is still increasing.
One potential therapeutic target is the HIV protease enzyme, which plays a key role in viral maturation². Murphy and al.³ suggested that the thrombocytopenia in patients with AIDS were due to auto-immune destruction of platelets. GPIIb-IIIa complexes represent a novel target for antithrombocytopenia therapy. Nardi⁴ described a major 18-mer antigenic determinant on platelet GPIIIa (49-66) CAPESIEFPVSEARVLED as the target of the anti-platelet antibodies.

Furthermore, AIDS Immunologic Thrombocytopenia (AIT) are indistinguishable from classical immunologic thrombocytopenia. The incidence of severe thrombocytopenia (<10,000 platelets/ml) is about 30-50%.
The pathogeny is complicated, involving a central thrombocytopenia by medullary insufficiency and auto-antibodies. The pathogenic anti-platelet auto-antibodies are directed against platelet integrin GPIIb-IIIa at the platelet's surface, and their affinity is very high (Kd=10^-9 M). Their injection in mice cause an acute thrombocytopenia, proving their pathogenic nature.

OBJECTIVE.

We try to understand the mechanism of formation of such antibodies, as we were intrigued by the sequence 7-FP-8 located in the middle of the determinant, which reminds the FP cleavage site of HIV-1 protease, and the presence of a proline P58, a classical immunodominant residue.

METHODS.

We screened linearly the amino acid sequences of HIV-proteins in the Los Alamos databank with the FP dipeptide as a probe.

RESULTS

A molecular homology between platelet integrin GPIIb-IIIa and the cleavage site of HIV-1 protease is observed.
The tetrapeptide FPVS is common to platelet GPIIIa (57-60) and HIV-1 (strain F1. BE.VI850) cleavage site between protease and reverse transcriptase p66.

Other strains contain a related isoleucine I instead of valine V (FPIS).

A second result seemed to confirm this direction of research: another virus, Parvovirus B19⁷, contained also an homologous sequence with platelet GPIIb-IIIa. An auto-immune thrombocytopenia can occur after Parvovirus infection⁸ and this virus has also been found in HIV-1 infection as the cause of aplasia.

CONCLUSION AND PERSPECTIVE.

Immune thrombocytopenia may be pathophysiologically correlated with high affinity deleterious anti-platelet antibodies, able to induce acute thrombocytopenia in mice. The common immunodominant epitope centered on FP between platelet. GPIIIa-IIb and the cleavage site of HIV-1 protease suggests a cross-reactivity mechanism of formation of these antibodies. Parvovirus B19 may also play a role in some cases of AIT.

Our study suggests, on one hand, the preparation of peptide-derived inhibitors like Phenylalanine-Proline and the other hand synthetic molecules with a low molecular weight as peptidomimetics like derivated 4-hydroxy-

1. We can design a cyclized peptide with a cystine bridge and protected from proteolysis by a dextrogyre D-amino acid at the NH2-terminal and the amino alcohol at the C-terminal, like Sandostatinā®.
2. Another possibility to make a retro-inverso peptide (Van Regenmortel M., 1996)
3. A third possibility is to include a dextrogyre D-residue in the active site, like interleukin-1 beta inhibitor.

Phenylalanine-Proline sequence (F-P). Steric Energy minimized with CS Chem3D Ultra coumarin (Kirkiacharian S., 2002, under print) or homoisoflavanone for example.

4-Hydroxycoumarin

Homoisoflavanone

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1. W.H.O. 2002's estimation
2. Romines K.R. et al., J. Med. Chem., (1995), 38, 1884-1891
3. Murphy M.F, Metcalfe P., Waters A.H., Carne C.A., Weller I.V., Linch D.C. and Smith A., Br. J. Haematol., (1987), 66(3), 337-340
4. Nardi M.A., Liu L.-X. and Karpatkin S., Proc. Natl. Acad. Sci. USA, (1997), 94, 7589-7594
5. Panorama du Médecin, n°2204 du 22 novembre 1985
6. Kirkiacharian S. et al., Il Farmaco (under print)
7. Gallinella G. unpublished, submitted to NCBI: NC_00883
8. Scheurlen W. et al., J. Clin. Virol., (2001), 20, 173-178

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