In this study, we have prepared a DNA–affibody nanoparticle which mimics a antibody in its ability to specifically target the HER2 receptor. This nanoparticle has a smaller size (95 kDa) than the monoclonal antibody, trastuzumab (150 kDa) and at least two-fold greater activity toward BT474 cells than trastuzumab. The DNA in this nanoparticle structure has two functions, namely as a support to anchor two affibody molecules and as a vehicle to non-covalently bind multiple copies of a small molecule drug for drug delivery. Each DNA–affibody nanoparticle can bind ∼53 molecules of doxorubicin (DOX) to form a complex, which exhibits greater selectivity toward and inhibition of breast cancer cells overexpressing HER2 than doxorubicin does. As expected, the nanoparticle exhibits lesser inhibition of cells expressing HER2 at a low level. Thus, the nanoparticle represents a highly efficacious agent for inhibiting cancer cells which overexpress HER2, but with low toxicity toward normal cells.

A fluorescently modified CD4 domain 1 (mD1) protein has been designed and elaborated in an in vitro expression system. This fluorescent probe contains a Förster resonance energy transfer (FRET) pair, which uses a tryptophan residue as the fluorescence donor and an acridon-2-ylalanine (Acd) as the acceptor. When excited at 260 nm, energy was transferred from tryptophan to the Acd residue of mD1, and emitted fluorescence at 420 nm. This fluoresence was quenched after Evans blue (EB) inhibitor or HIV-1 gp120 protein binding, presumably as a consequence of changes in the distance and dipole orientation between the donor and acceptor; the emission intensity at 420 nm decreased in a concentration-dependent fashion. This fluorescent CD4 probe could be developed into a novel tool for HIV-1 gp120 protein detection. It also could be used to screen small molecules that inhibit the gp120–CD4 interaction.

CD4-gp120 interaction is the first step for HIV-1 entry into host cells. A highly conserved pocket in gp120 protein is an attractive target for developing gp120 inhibitors or novel HIV detection tools. Here we incorporate seven phenylalanine derivatives having different sizes and steric conformations into position 43 of domain 1 of CD4 (mD1.2) to explore the architecture of the ‘Phe43 cavity’ of HIV-1 gp120. The results show that the conserved hydrophobic pocket in gp120 tolerates a hydrophobic side chain of residue 43 of CD protein, which is 12.2 Å in length and 8.0 Å in width. This result provides useful information for developing novel gp120 inhibitors or new HIV detection tools.

In this study, we have prepared a DNA–affibody nanoparticle which mimics a antibody in its ability to specifically target the HER2 receptor. This nanoparticle has a smaller size (95 kDa) than the monoclonal antibody, trastuzumab (150 kDa) and at least two-fold greater activity toward BT474 cells than trastuzumab. The DNA in this nanoparticle structure has two functions, namely as a support to anchor two affibody molecules and as a vehicle to non-covalently bind multiple copies of a small molecule drug for drug delivery. Each DNA–affibody nanoparticle can bind ∼53 molecules of doxorubicin (DOX) to form a complex, which exhibits greater selectivity toward and inhibition of breast cancer cells overexpressing HER2 than doxorubicin does. As expected, the nanoparticle exhibits lesser inhibition of cells expressing HER2 at a low level. Thus, the nanoparticle represents a highly efficacious agent for inhibiting cancer cells which overexpress HER2, but with low toxicity toward normal cells.