Faculty Courses Undergraduate Studies Undergraduate Research Graduate Seminars Links

Usha Ramachandran

T-20 (commercially known as Fuzeon) belongs to the latest class of drugs called fusion inhibitors. It is used as an important part of combination treatment for people who have HIV-1 viruses that have become resistant to other available anti-HIV drugs. Human immunodeficiency virus generally infects cells expressing the CD4 receptor and a chemokine receptor (like CCR5 and CXCR4).

The first step in the fusion cascade is the interaction between gp120 (a HIV-1 surface glycoprotein) and CD4 receptor. Following this, gp120 interacts with the chemokine receptor of the target cell. This interaction induces conformational changes in gp41 and releases gp120 from the gp120-gp41 complex. This gp41 subunit then mediates the fusion of the viral cell with the target cell.

The last step in the fusion involves the folding rearrangement of the viral surface glycoprotein gp41 into a very stable six-helix bundle (Labranche et. al, 2001). This structure comprises three copies of a helical gp41 segment called C-peptide folded onto a three-helix core consisting of three copies of another gp41 segment called N-peptide. This structural change of gp41 plays an important role in the fusion of the viral cell with the target cell.

T-20, which is a FDA-approved 36 residue long peptide, overlaps with the C-peptide sequence. This peptide is speculated to interfere with the essential folding step and thus prevent the formation of the stable six- helix bundle. It is suggested that T-20 interferes with the N- peptide domain of gp-41 (Jiang et al., 2000).

Currently, only large-scale synthesis methods (involving HPLC and Reverse Phase chromatography) can be applied in the production of this peptide. This method is very expensive, thus making T-20’s market value a major concern. Need for inexpensive methods of synthesizing this peptide drug is an immediate requirement.

The goal of this project is to develop new methods for the synthesis of T-20. New Cobalt complex (that is being developed in the lab) is to be used as N-terminal protection groups in separate segment synthesis of T-20. The peptide fragments thus synthesized will be purified and condensed to construct the full length T-20 peptide. This method when developed will provide an inexpensive way of synthesizing T-20. Unlike the other protected groups used in peptide chemistry, this Co complex is acid and base stable and can be easily cleaved by simple reduction (Ex: by DTT). Its advantage is the presence of the +2 charge, which greatly enhances the solubilities of the protected peptide segments in organic and aqueous- organic solvents. In addition, the +2 charge enables the use of cation exchange chromatography in the purification of these peptide fragments.

We have so far synthesized two fragments of T-20 and are currently developing the Cobalt complex. Synthesis of the Cobalt complex involves 5 different intermediates. The first intermediate has been successfully synthesized with a good yield. The second has been synthesized. However, the production is yet to be optimized to give a good yield. On completing the construction of these peptide fragments, the effectiveness of the protecting group (cobalt complex) in enhancing the peptides’ solubilities and bettering the purification process will be tested.

Bibliography

1.  Celia C. Labranche, George Galasso, John P. Moore, Dani p. Bolognesi, Martin S. Hirsch, Scott M. Hammer, Review “HIV fusion and its inhibition”, Antiviral research, 95-115, 2001.

• Shibo Jiang and Asim K. Debnath, “Development of HIV entry inhibitors targeted to the coiled coil regions of gp41”, Biochemical and Biophysical Research Communications, 269, 2000.

© 2005 All rights reserved.