Synthesis and bioevaluation of substituted chalcones, coumaranones and other flavonoids as anti-HIV agents.

A series of chalcone, flavone, coumaranone and other flavonoid compounds were screened for their anti HIV-1 activity in two cell culture models using TZM-bl and PM1 cells. Within the systems evaluated, the most promising compounds contained either an α- or ß-hydroxy-carbonyl motif within their structure (e.g., 8 and 9). Efficacious substituents were identified and used to design new HIV inhibitors with increased potency and lower cytotoxicity. Of the scaffolds evaluated, specific chalcones were found to provide the best balance between anti-HIV potency and low host cell toxicity. Chalcone 8l was shown to inhibit different clinical isolates of HIV in a dose-dependent manner (e.g., IC50 typically⩽5µM). Inhibition of HIV infection experiments using TZM-bl cells demonstrated that chalcone 8l and flavonol 9c had IC50 values of 4.7µM and 10.4µM, respectively. These insights were used to design new chalcones 8o and 8p. Rewardingly, chalcones 8o and 8p (at 10µM) each gave >92% inhibition of viral propagation without impacting PM1 host cell viability. Inhibition of viral propagation significantly increased (60-90%) when PM1 cells were pre-incubated with chalcone 8o, but not with the related flavonol 9c. These results suggested that chalcone 8o may be of value as both a HIV prophylactic and therapy. In summary, O-benzyl-substituted chalcones were identified as promising anti-HIV agents for future investigation.

θ-Defensins: cyclic peptides with endless potential.

θ-Defensins, the only cyclic peptides of animal origin, have been isolated from the leukocytes of rhesus macaques and baboons. Their biogenesis is unusual because each peptide is an 18-residue chimera formed by the head-to-tail splicing of nonapeptides derived from two separate precursors. θ-Defensins have multiple arginines and a ladder-like tridisulfide array spanning their two antiparallel ß-strands. Human θ-defensin genes contain a premature stop codon that prevents effective translation of the needed precursors; consequently, these peptides are not present in human leukocytes. Synthetic θ-defensins with sequences that correspond to those encoded within the human pseudogenes are called retrocyclins. Retrocyclin-1 inhibits the cellular entry of HIV-1, HSV, and influenza A virus. The rhesus θ-defensin RTD-1 protects mice from an experimental severe acute respiratory syndrome coronavirus infection, and retrocyclin-1 protects mice from infection by Bacillus anthracis spores. The small size, unique structure, and multiple host defense activities of θ-defensins make them intriguing potential therapeutic agents.

Evolution of primate theta-defensins: a serpentine path to a sweet tooth.

Retrocyclins (ancestral human theta-defensins) are cyclic antimicrobial octadecapeptides that interfere with viral uptake and protect human cells from infection by T- and M-tropic strains of HIV-1 in vitro. As are other theta-defensins, retrocyclins are lectins that bind gp120, CD4, and galactosylceramide-all of which are implicated in HIV-1 uptake. Although theta-defensin mRNA transcripts are present in human bone marrow, spleen, thymus, testis, and skeletal muscle, a premature stop codon aborts their translation. We found six theta-defensin (DEFT) genes in the human genome; five on chromosome 8p23 and one on chromosome 1. All six of these pseudogenes, as well as their homologues in chimpanzees and gorillas, contained the same premature stop codon mutation. Whereas we found intact DEFT genes in DNA from several Old World Monkeys, Hylobates syndactylus (a lesser ape) and orangutans, no homologues were present in DNA from six New World Monkeys and five prosimians. We conclude that DEFT genes and theta-defensins arose in Old World Monkeys by mutation of a pre-existing alpha-defensin gene. Although intact DEFT genes survive in some nonhuman primates, our hominid ancestors lost their ability to produce theta-defensins after the orangutan and hominid lineages diverged. It is possible (but may be difficult to prove) that this mutation rendered our species more susceptible to infection by HIV-1.