Cell-penetrating peptides (CPP), which are short peptides that are capable of crossing the plasma membrane of a living cell, are under development as delivery vehicles for therapeutic agents that cannot themselves enter the cell. One well-studied CPP is the 10-amino acid peptide derived from the human immunodeficiency virus type 1 (HIV-1) Tat protein. In experiments to test the hypothesis that multiple cationic amino acids within Tat peptide confer antiviral activity against HIV-1, introduction of Tat peptide resulted in concentration-dependent inhibition of HIV-1 IIIB infection. Using Tat peptide variants containing arginine substitutions for two nonionic residues and two lysine residues, HIV-1 inhibition experiments demonstrated a direct relationship between cationic charge and antiviral potency. These studies of Tat peptide as an antiviral agent raise new questions about the role of Tat in HIV-1 replication and provide a starting point for the development of CPPs as novel HIV-1 inhibitors. 1. Introduction Cell penetrating peptides (CPP) are short peptides that can efficiently cross the plasma membrane, which is otherwise a formidable barrier to many extracellular molecules [1–3]. CPPs are capable of not only traversing the cell membrane, but also serving as a vehicle for transporting a variety of cargos, including nucleic acids, polymers, nanoparticles, and drugs that cannot otherwise gain entry to the cell [3]. Although the functions of various CPPs have been repeatedly verified in a variety of cells and conditions, the mechanism of CPP uptake is not yet fully understood and may involve energy-dependent and -independent mechanisms [4]. Of the numerous peptides shown to have cell penetrating properties, a 10-amino acid (aa) peptide derived from the human immunodeficiency virus type 1 (HIV-1) Tat protein has been well studied as an effective CPP and an attractive drug delivery agent [5]. The Tat peptide has received particular emphasis as a CPP due to its simplicity and capacity for modification to suit the delivery context or cargo [5, 6]. The core peptide is a 10-aa sequence comprised of six arginine and two lysine residues, as well as two non-ionic amino acids (Table 1). However, numerous Tat peptides of varied lengths and terminal sequences have been investigated with the goals of modifying activity or attaching different cargo [6]. A multitude of studies have determined that the activity of the Tat peptide as a CPP involves interactions with the cellular membrane and cytoskeleton [7], and is influenced by numerous variables related to the
References
[1]
C. Foerg, K. M. Weller, H. Rechsteiner et al., “Metabolic cleavage and translocation efficiency of selected cell penetrating peptides: a comparative study with epithelial cell cultures,” American Association of Pharmaceutical Scientists Journal, vol. 10, no. 2, pp. 349–359, 2008.
[2]
I. Nakase, T. Takeuchi, G. Tanaka, and S. Futaki, “Methodological and cellular aspects that govern the internalization mechanisms of arginine-rich cell-penetrating peptides,” Advanced Drug Delivery Reviews, vol. 60, no. 4-5, pp. 598–607, 2008.
[3]
V. P. Torchilin, “Tat peptide-mediated intracellular delivery of pharmaceutical nanocarriers,” Advanced Drug Delivery Reviews, vol. 60, no. 4-5, pp. 548–558, 2008.
[4]
A. T. Jones, “Gateways and tools for drug delivery: endocytic pathways and the cellular dynamics of cell penetrating peptides,” International Journal of Pharmaceutics, vol. 354, no. 1-2, pp. 34–38, 2008.
[5]
J. M. Gump and S. F. Dowdy, “TAT transduction: the molecular mechanism and therapeutic prospects,” Trends in Molecular Medicine, vol. 13, no. 10, pp. 443–448, 2007.
[6]
H. Brooks, B. Lebleu, and E. Vivès, “Tat peptide-mediated cellular delivery: back to basics,” Advanced Drug Delivery Reviews, vol. 57, no. 4, pp. 559–577, 2005.
[7]
A. Mishra, G. H. Lai, N. W. Schmidt et al., “Translocation of HIV TAT peptide and analogues induced by multiplexed membrane and cytoskeletal interactions,” Proceedings of the National Academy of Sciences of the United States of America, vol. 108, no. 41, pp. 16883–16888, 2011.
[8]
B. J. Doranz, K. Grovit-Ferbas, M. P. Sharron et al., “A small-molecule inhibitor directed against the chemokine receptor CXCR4 prevents its use as an HIV-1 coreceptor,” Journal of Experimental Medicine, vol. 186, no. 8, pp. 1395–1400, 1997.
[9]
A. Lapidot, A. Peled, A. Berchanski et al., “NeoR6 inhibits HIV-1-CXCR4 interaction without affecting CXCL12 chemotaxis activity,” Biochimica et Biophysica Acta, vol. 1780, no. 6, pp. 914–920, 2008.
[10]
S. Lee-Huang, V. Maiorov, P. L. Huang et al., “Structural and functional modeling of human lysozyme reveals a unique nonapeptide, HL9, with anti-HIV activity,” Biochemistry, vol. 44, no. 12, pp. 4648–4655, 2005.
[11]
P. Bergman, L. Walter-Jallow, K. Broliden, B. Agerberth, and J. S？derlund, “The antimicrobial peptide LL-37 inhibits HIV-1 replication,” Current HIV Research, vol. 5, no. 4, pp. 410–415, 2007.
[12]
F. C. Krebs, S. R. Miller, M. L. Ferguson, M. Labib, R. F. Rando, and B. Wigdahl, “Polybiguanides, particularly polyethylene hexamethylene biguanide, have activity against human immunodeficiency virus type 1,” Biomedicine and Pharmacotherapy, vol. 59, no. 8, pp. 438–445, 2005.
[13]
S. R. Passic, M. L. Ferguson, B. J. Catalone et al., “Structure-activity relationships of polybiguanides with activity against human immunodeficiency virus type 1,” Biomedicine and Pharmacotherapy, vol. 64, no. 10, pp. 723–732, 2010.
[14]
N. Thakkar, V. Pirrone, S. Passic et al., “Persistent interactions between biguanide-based compound NB325 and CXCR4 result in prolonged inhibition of human immunodeficiency virus type 1 infection,” Antimicrobial Agents and Chemotherapy, vol. 54, no. 5, pp. 1965–1972, 2010.
[15]
N. Thakkar, V. Pirrone, S. Passic et al., “Specific interactions between the viral coreceptor CXCR4 and the biguanide-based compound NB325 mediate inhibition of human immunodeficiency virus type 1 infection,” Antimicrobial Agents and Chemotherapy, vol. 53, no. 2, pp. 631–638, 2009.
[16]
K. Lozenski, T. Kish-Catalone, V. Pirrone, et al., “Cervicovaginal safety of the formulated biguanide-based human immunodeficiency virus type 1 (HIV-1) inhibitor NB325 in a murine model of microbicide application,” Journal of Biomedicine and Biotechnology, vol. 2011, Article ID 941061, 10 pages, 2011.
[17]
R. A. Wilkinson, S. H. Pincus, J. B. Shepard et al., “Novel compounds containing multiple guanide groups that bind the HIV coreceptor CXCR4,” Antimicrobial Agents and Chemotherapy, vol. 55, no. 1, pp. 255–263, 2011.
[18]
J. A. Martellini, A. L. Cole, N. Venkataraman et al., “Cationic polypeptides contribute to the anti-HIV-1 activity of human seminal plasma,” FASEB Journal, vol. 23, no. 10, pp. 3609–3618, 2009.
[19]
N. Venkataraman, A. L. Cole, P. Svoboda, J. Pohl, and A. M. Cole, “Cationic polypeptides are required for anti-HIV-1 activity of human vaginal fluid,” Journal of Immunology, vol. 175, no. 11, pp. 7560–7567, 2005.
[20]
H. Xiao, C. Neuveut, H. L. Tiffany et al., “Selective CXCR4 antagonism by Tat: implications for in vivo expansion of coreceptor use by HIV-1,” Proceedings of the National Academy of Sciences of the United States of America, vol. 97, no. 21, pp. 11466–11471, 2000.
[21]
M. Kuppuswamy, T. Subramanian, A. Srinivasan, and G. Chinnadurai, “Multiple functional domains of Tat, the trans-activator of HIV-1, defined by mutational analysis,” Nucleic Acids Research, vol. 17, no. 9, pp. 3551–3561, 1989.
[22]
A. K. Cardozo, V. Buchillier, M. Mathieu et al., “Cell-permeable peptides induce dose- and length-dependent cytotoxic effects,” Biochimica et Biophysica Acta, vol. 1768, no. 9, pp. 2222–2234, 2007.
[23]
B. Ensoli, G. Barillari, S. Z. Salahuddin, R. C. Gallo, and F. Wong-Staal, “Tat protein of HIV-1 stimulates growth of cells derived from Kaposi's sarcoma lesions of AIDS patients,” Nature, vol. 345, no. 6270, pp. 84–86, 1990.
[24]
A. Nath, K. Psooy, C. Martin et al., “Identification of a human immunodeficiency virus type 1 Tat epitope that is neuroexcitatory and neurotoxic,” Journal of Virology, vol. 70, no. 3, pp. 1475–1480, 1996.
[25]
G. R. Campbell, E. Pasquier, J. Watkins et al., “The glutamine-rich region of the HIV-1 Tat protein is involved in T-cell apoptosis,” Journal of Biological Chemistry, vol. 279, no. 46, pp. 48197–48204, 2004.
[26]
A. Chauhan, A. Tikoo, A. K. Kapur, and M. Singh, “The taming of the cell penetrating domain of the HIV Tat: myths and realities,” Journal of Controlled Release, vol. 117, no. 2, pp. 148–162, 2007.
[27]
B. Romani, S. Engelbrecht, and R. H. Glashoff, “Functions of Tat: the versatile protein of human immunodeficiency virus type 1,” Journal of General Virology, vol. 91, part 1, pp. 1–12, 2010.
[28]
J. B. Rothbard, T. C. Jessop, R. S. Lewis, B. A. Murray, and P. A. Wender, “Role of membrane potential and hydrogen bonding in the mechanism of translocation of guanidinium-rich peptides into cells,” Journal of the American Chemical Society, vol. 126, no. 31, pp. 9506–9507, 2004.
