advantages: the size minimal perturbation of biomolecular processes in cell imaging,
uniform particle size avoiding wide emission of fluorescence, and cross-linking
structure preventing disintegration of nanoparticles after interaction with cell membranes. It is worth noting that the calix[4]arene quantum dots have excellent luminescence properties. The brightness of nanoparticles was twofold brighter than
commercial quantum dots (QD-585). Finally, the authors applied calix[4]arene
quantum dots to cell imaging and found that the materials can enter HeLa cells
and selectively accumulate in endosomes and lysosomes. The results showed that
calix[4]arene quantum dots maintain structural integrity in physiological media,
organic solvents, and living cells and can be rapidly internalized showing excellent
imaging contrast. This type of calixarene organic quantum dot has broad application
prospects in cytology, histology, and fluorescent tracers in biochemistry [44].
8.7
Calixarenes for Gene Delivery
The ability to tightly bind and compact DNA and the characteristics of calixarenes to
behave as macrocyclic amphiphiles motivated us to test guanidinium-calixarenes
as gene delivery vectors. Current studies show that calix[4]arenes are probably
the most promising among the described calixarenes for gene delivery applications
[17, 58–61]. Their fixed conformation has multiple functional groups at the upper and
lower rims, which allow the preparation of cone-shaped macromolecules that can be
programmed for fractional assembly in the presence of DNA. The intricate calixarenes
designed, especially those with amphiphilic structures, are able to form DNAcalixarene nanoparticles with clear structure, high transfection efficiency and low
toxicity. At present, researches in the field are still insufficient, especially for the
modification of calixarene, which requires more scientists’ attention. In addition,
experiments in vivo are needed to evaluate the effect of calixarene on gene therapy.
Recently, Ungaro’s team synthesized positively charged calixarene derivatives with
upper rim modified by four arginine residues and lower rim of four hexyl groups or only
four arginine residues at the lower rim (Fig. 12a). AFM imaging showed that the
calixarenes with the upper rim-modified arginine reacted with DNA to form nanoparticles with a size of 50–60 nm (Fig. 12b), whereas the derivatives of the lower rimmodified arginine formed more larger aggregate. This apparent difference may be partly
due to the fact that argininocalix[4]arene 1 had a clear amphiphilic nature relative to
ordinary calixarenes. In particular, argininocalix[4]arene 1 showed excellent transfection
efficiency even better than Lipofectamine and PEI in various cell lines (Fig. 12c). In
contrast, tetralysinocalix[4]arene 3 showed little transfection activity. In addition, the
argininocalix[4]arene 2, similar to argininocalix[4]arene 1, which modified the protonated amino groups rather than the guanidine groups, exhibited poor transfection activity,
while DOPE can help to increase their activity. This significant difference between
8 Supramolecular Medicine of Diverse Calixarene Derivatives
217
uniform particle size avoiding wide emission of fluorescence, and cross-linking
structure preventing disintegration of nanoparticles after interaction with cell membranes. It is worth noting that the calix[4]arene quantum dots have excellent luminescence properties. The brightness of nanoparticles was twofold brighter than
commercial quantum dots (QD-585). Finally, the authors applied calix[4]arene
quantum dots to cell imaging and found that the materials can enter HeLa cells
and selectively accumulate in endosomes and lysosomes. The results showed that
calix[4]arene quantum dots maintain structural integrity in physiological media,
organic solvents, and living cells and can be rapidly internalized showing excellent
imaging contrast. This type of calixarene organic quantum dot has broad application
prospects in cytology, histology, and fluorescent tracers in biochemistry [44].
8.7
Calixarenes for Gene Delivery
The ability to tightly bind and compact DNA and the characteristics of calixarenes to
behave as macrocyclic amphiphiles motivated us to test guanidinium-calixarenes
as gene delivery vectors. Current studies show that calix[4]arenes are probably
the most promising among the described calixarenes for gene delivery applications
[17, 58–61]. Their fixed conformation has multiple functional groups at the upper and
lower rims, which allow the preparation of cone-shaped macromolecules that can be
programmed for fractional assembly in the presence of DNA. The intricate calixarenes
designed, especially those with amphiphilic structures, are able to form DNAcalixarene nanoparticles with clear structure, high transfection efficiency and low
toxicity. At present, researches in the field are still insufficient, especially for the
modification of calixarene, which requires more scientists’ attention. In addition,
experiments in vivo are needed to evaluate the effect of calixarene on gene therapy.
Recently, Ungaro’s team synthesized positively charged calixarene derivatives with
upper rim modified by four arginine residues and lower rim of four hexyl groups or only
four arginine residues at the lower rim (Fig. 12a). AFM imaging showed that the
calixarenes with the upper rim-modified arginine reacted with DNA to form nanoparticles with a size of 50–60 nm (Fig. 12b), whereas the derivatives of the lower rimmodified arginine formed more larger aggregate. This apparent difference may be partly
due to the fact that argininocalix[4]arene 1 had a clear amphiphilic nature relative to
ordinary calixarenes. In particular, argininocalix[4]arene 1 showed excellent transfection
efficiency even better than Lipofectamine and PEI in various cell lines (Fig. 12c). In
contrast, tetralysinocalix[4]arene 3 showed little transfection activity. In addition, the
argininocalix[4]arene 2, similar to argininocalix[4]arene 1, which modified the protonated amino groups rather than the guanidine groups, exhibited poor transfection activity,
while DOPE can help to increase their activity. This significant difference between
8 Supramolecular Medicine of Diverse Calixarene Derivatives
217