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The HIV coreceptor CCR5 is a validated target for both the prevention and therapy of HIV infection. PSC-RANTES, an N-terminally modified analogue of one of the natural chemokine ligands of CCR5 (RANTES/CCL5), is a potent inhibitor of HIV entry into target cells. Here, we set out to engineer the anti-HIV activity of PSC-RANTES into another natural CCR5 ligand (MIP-1beta/CCL4), by grafting into it the key N-terminal pharmacophore region from PSC-RANTES. We were able to identify MIP-1beta/CCL4 analogues that retain the receptor binding profile of MIP-1beta/CCL4, but acquire the very high anti-HIV potency and characteristic inhibitory mechanism of PSC-RANTES. Unexpectedly, we discovered that in addition to N-terminal structures from PSC-RANTES, the side chain of Lys33 is also necessary for full anti-HIV potency.

New prevention strategies for use in developing countries are urgently needed to curb the worldwide HIV/AIDS epidemic. The N-terminally modified chemokine PSC-RANTES is a highly potent entry inhibitor against R5-tropic HIV-1 strains, with an inhibitory mechanism involving long-term intracellular sequestration of the HIV coreceptor, CCR5. PSC-RANTES is fully protective when applied topically in a macaque model of vaginal HIV transmission, but it has 2 potential disadvantages related to further development: the requirement for chemical synthesis adds to production costs, and its strong CCR5 agonist activity might induce local inflammation. It would thus be preferable to find a recombinant analogue that retained the high potency of PSC-RANTES but lacked its agonist activity. Using a strategy based on phage display, we set out to discover PSC-RANTES analogs that contain only natural amino acids. We sought molecules that retain the potency and inhibitory mechanism of PSC-RANTES, while trying to reduce CCR5 signaling to as low a level as possible. We identified 3 analogues, all of which exhibit in vitro potency against HIV-1 comparable to that of PSC-RANTES. The first, 6P4-RANTES, resembles PSC-RANTES in that it is a strong agonist that induces prolonged intracellular sequestration of CCR5. The second, 5P12-RANTES, has no detectable G protein-linked signaling activity and does not bring about receptor sequestration. The third, 5P14-RANTES, induces significant levels of CCR5 internalization without detectable G protein-linked signaling activity. These 3 molecules represent promising candidates for further development as topical HIV prevention strategies.

New HIV prevention methods are needed, and among those currently being explored are "microbicides", substances applied topically to prevent HIV acquisition during sexual intercourse. The chemokine analogue PSC-RANTES (N(alpha)(n-nonanoyl)-des-Ser(1)-[ L-thioprolyl(2), L-cyclohexylglycyl(3)]-RANTES(4-68)) is a highly potent HIV entry inhibitor which has shown promising efficacy in its initial evaluation as a candidate microbicide. However, a way must be found to produce the molecule by cheaper means than total chemical synthesis. Since the only noncoded structures are located at the N-terminus, a possible solution would be to produce a protein fragment representing all but the N-terminal region using low-cost recombinant production methods and then to attach, site specifically, a short synthetic fragment containing the noncoded N-terminal structures. Here, we describe the evaluation of a range of different conjugation chemistries in order to identify those with potential for development as economical routes to production of a PSC-RANTES analogue with antiviral activity as close as possible to that of the parent protein. The strategies tested involved linkage through oxime, hydrazone/hydrazide, and Psi[CH2-NH] bonds, as well as through a peptide bond obtained either by a thiazolidine rearrangement or by direct alpha-amino acylation of a protein fragment in which 4 of the 5 lysine residues of the native sequence were replaced by arginine (the fifth lysine is essential for activity). Where conjugation involved replacement of one or more residues with a linker moiety, the point in the main chain at which the linker was introduced was varied. The resulting panel of 22 PSC-RANTES analogues was evaluated for anti-HIV activity in an entry inhibition assay. The [Arg (25,45,56,57)] PSC-RANTES analogue has comparable potency to PSC-RANTES, and one of the oxime linked analogues, 4L-57, has potency only 5-fold lower, with scope for improvement. Both represent promising leads for development as microbicide compounds that could be produced at low cost via semisynthesis.