Adina N. Lazar

Biopharmaceutical applications of calixarenes

During the last 15 years, water soluble calixarenes and especially para-sulphonato-calix[n]arene and amphiphilic calixarenes have been the subject of growing interest in the biological domain. This article provides an overview of the studies, by our group and other research groups, that led to the elucidation of biological and biopharmaceutical activity of these calixarenes. The different studies concerning the specific interac- tions of calixarenes with molecules such as organic and inorganic ions, peptides, polar or neutral organic molecules and biomolecules including proteins and lipids are discussed. The interactions have been studied in solution and in the solid and gaseous using a wide range of methods such as NMR spectroscopy, RP-HPLC, micro-calorimetry, X-ray crystallography, atomic force microscopy, Langmuir balance, etc. Increasingly detailed knowledge is being obtained on the mechanism of the interactions of the calixarenes with biomolecules. At this time, the calixarenes have demonstrated neither toxicity or immune responses, further increasing their interest in the field of biopharmaceutical applications. Undoubtedly, the use of calixarenes as biopharmaceutical molecules will show a large increase in the future.

Multidrug-resistant cancer cells contain two populations of P-glycoprotein with differently stimulated P-gp ATPase activities: evidence from atomic force microscopy and biochemical analysis

Considerable interest exists about the localization of P-gp (P-glycoprotein) in DRMs (detergent-resistant membranes) of multidrug resistant cancer cells, in particular concerning the potential modulating role of the closely related lipids and proteins on P-gp activity. Our observation of the opposite effect of verapamil on P-gp ATPase activity from DRM and solubilized-membrane fractions of CEM-resistant leukaemia cells, and results from Langmuir experiments on membrane monolayers from resistant CEM cells, strongly suggest that two functional populations of P-gp exist. The first is located in DRM regions: it displays its optimal P-gp ATPase activity, which is almost completely inhibited by orthovanadate and activated by verapamil. The second is located elsewhere in the membrane; it displays a lower P-gp ATPase activity that is less sensitive to orthovanadate and is inhibited by verapamil. A 40% cholesterol depletion of DRM caused the loss of 52% of the P-gp ATPase activity. Cholesterol repletion allowed recovery of the initial P-gp ATPase activity. In contrast, in the solubilized-membrane-containing fractions, cholesterol depletion and repletion had no effect on the P-gp ATPase activity whereas up to 100% saturation with cholesterol induced a 58% increased P-gp ATPase activity, while no significant modification was observed for the DRM-enriched fraction. DRMs were analysed by atomic force microscopy: 40-60% cholesterol depletion was necessary to remove P-gp from DRMs. In conclusion, P-gp in DRMs appears to contain closely surrounding cholesterol that can stimulate P-gp ATPase activity to its optimal value, whereas cholesterol in the second population seems deprived of this function.

Solid-state caging of 1,10-phenanthroline π–π stacked dimers by calix[4]arene dihydroxyphosphonic acid

The calix[4]arene dihydroxyphosphonic acid-1,10-phenanthroline complex shows caging of the guest molecules as a pi-pi stacked dimer in a cavity formed by intermolecular hydrogen bonds and aromatic walls formed by the calixarene.

Guest-induced chain folding in amphiphilic calixarene structures

Amphiphilic calixarenes represent a promising class of derivatives, potentially useful for transporting molecules because of their ability to self-organize as Solid Lipid Nanoparticles in water. The current study shows that after derivatization of the para-H-calix[4]arene with hexanoyl chains, the resultant amphiphilic calixarenes retain their properties to complex small organic molecules. The solid structures of the complexes of para-hexanoyl-calix[4]arene with methanol, dimethylformamide–methanol, dimethyl sulfoxide–methanol and nitrobenzene are reported. As for the p-tert-butyl calix[4]arene, aliphatic guests are stabilized by a variety of short-range interactions including C–H⋯π or π−π interactions. Moreover, the presence of the grafted hydrophobic chains generates an extension of the hydrophobic calixarene cavity and thus provides another site where complexation can take place. The structures show that the geometry of the hexanoyl chains is modified by the presence of the guest molecules and that the chains fold over to aid encapsulation of the guest.

Assembly modes in the solid state structure of the complexes of melamine mono- cations with para -calix[4]arene sulfonic acid and calix[4]arene dihydroxyphosphonic acid

The crystal structures of the complexes between melamine mono-cations and para-calix[4]arene sulfonic acid and calix[4]arene dihydroxyphosphonic acid have been determined. In both cases the structure is based on a bilayer motif of calixarene molecules intercalated by motifs of melamine mono-cations. While in the complex with calix[4]arene dihydroxyphosphonic acid the motifs of melamine cations are parallel to the in-layer arrangement of the calixarene, for para-sulfonatocalix[4]arene there is 17.6° displacement between the axes of the two motifs generating a laminate structure.

A new packing motif for para-sulfonatocalix[4]arene: the solid state structure of the para-sulfonatocalix[4]arene D-arginine complex

The solid-state structure of the complex of para-sulfonatocalix[4]arene with d-arginine, contains a water channel diagonal to a zigzag bilayer of the host, within the bilayer six crystallographically independent molecules of arginine are present, four being included in the calix cavities.

Protein–calixarene interactions: complexation of Bovine Serum Albumin by sulfonatocalix[n]arenes

The complexation of Bovine Serum Albumin with sulfonatocalix[n]arenes has been demonstrated by means of electrospray mass spectrometry, dynamic light scattering and atomic force microscopy; with sulfonatocalix[4]arene one strong and two weaker binding sites are detected; the effects on the structure of thin films formed by surface deposition of BSA show that the sulfonatocalix[n]arenes act to reticulate the films and produce essentially planar systems.

Helical aquatubes of calix[4]arene di-methoxycarboxylic acid

Two trimeric units of calix[4]arene di-methoxycarboxylic acid form a six-pointed star architecture that, in turn, generates triple helical aquatubes which intermesh between themselves by aromatic-aromatic interdigitation of the macrocycle.

Anion recognition effects in the structuring of bovine serum albumin films

Abstract Films formed by the deposition of solutions of Bovine Serum Albumin (BSA) in the presence of various sodium salts have been investigated by both Optical and Atomic Force Microscopy, with the aim of assessing the effects of anion recognition on the micro-structuring of such films. Depending on the anion present the structures formed vary from dendritic spherulite structures, through block structures to pseudo-dendritic ‘devils comb’ structures. The angular orientation of these structures depends strongly on the nature of the anion. The effects of the film processing temperature have been investigated and in the case of the nitrate anion shows notable changes both in spacing and orientation of the dendritic structures.

Stepped layers in the complexes of para-sulfonatocalix[6]arene with dimethylammonium and bis-6-aminohexylammonium cations

Solid-state structures of para-sulfonatocalix[6]arene with dimethylammonium and bis-6-aminohexylammonium cations are mainly based on hydrogen bond interactions. In the two complexes the calixarene molecule adopts a chair conformation with small varieties in geometry influenced by the number and types of intra- and intermolecular interactions developed by polar substituents. A stepped layer topology is induced by this chair conformation in the two complexes. Structural motifs present in the two systems generate channels, which in the first complex include dimethylformamide solvent molecules, while in the second case they include water molecules.