Thermotropic and hydration studies of membranes formed from gemini pseudoglyceryl lipids possessing polymethylene spacers

Physical-Chemical Characterization of Bilayer Membranes Derived from (±) α-Tocopherol-Based Gemini Lipids and Their Interaction with Phosphatidylcholine Bilayers and Lipoplex Formation with Plasmid DNA

Membrane formation and aggregation properties of two series of (±) α-tocopherol-based cationic gemini lipids without and with hydroxyl functionalities at the headgroup region (TnS n = 3, 4, 5, 6, 8, and 12; THnS n = 4, 5, 6, 8, and 12) with varying polymethylene spacer lengths were investigated extensively while comparing with the corresponding properties of the monomeric counterparts (TM and THM). Liposomal suspensions of each cationic lipid were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), zeta potential measurements, and small-angle X-ray diffraction studies. The length of the spacer and the presence of hydroxyl functionalities at the headgroup region strongly contribute to the aggregation behavior of these gemini lipids in water. The interaction of each tocopherol lipid with a model phospholipid, 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC)-derived vesicles, was thoroughly examined by differential scanning calorimetry (DSC) and 1,6-diphenyl-1,3,5-hexatriene (DPH)-doped fluorescence anisotropy measurements. The binding efficiency of the cationic tocopherol liposomes with plasmid DNA (pDNA) was followed by an ethidium bromide (EB) exclusion assay and zeta potential measurements, whereas negatively charged micellar sodium dodecyl sulfate (SDS)-mediated release of the pDNA from various preformed pDNA-liposomal complexes (lipoplex) was studied by an ethidium bromide (EB) reintercalation assay. The structural transformation of pDNA upon complexation with liposome was characterized using circular dichroism (CD) spectroscopic measurements. Gemini lipid-pDNA interactions depend on both the presence of hydroxyl functionalities at the headgroups and the length of the spacer chain between the headgroups. Succinctly, we performed a detailed physical-chemical characterization of the membranes formed from cationic monomeric and gemini lipids bearing tocopherol as their hydrophobic backbone and describe the role of inserting the -OH group at the headgroup of such lipids.

Nature of the charged head group dictates the anticancer potential of lithocholic acid-tamoxifen conjugates for breast cancer therapy

Anticancer drug Tamoxifen is modified to charged lithocholic acid derived amphiphile for enhanced cytotoxicity against breast cancer cells.

Bile acid amphiphiles with tunable head groups as highly selective antitubercular agents

Hard-charged amphiphiles are highly selective against mycobacteria, whereas soft-charged amphiphiles are active against Gram-positive and Gram-negative bacteria.

Design, synthesis, and mechanistic investigations of bile acid-tamoxifen conjugates for breast cancer therapy

We have synthesized two series of bile acid tamoxifen conjugates using three bile acids lithocholic acid (LCA), deoxycholic acid (DCA), and cholic acid (CA). These bile acid-tamoxifen conjugates possess 1, 2, and 3 tamoxifen molecules attached to hydroxyl groups of bile acids having free acid and amine functionalities at the tail region of bile acids. The in vitro anticancer activities of these bile acid-tamoxifen conjugates show that the free amine headgroup based cholic acid-tamoxifen conjugate (CA-Tam3-Am) is the most potent anticancer conjugate as compared to the parent drug tamoxifen and other acid and amine headgroup based bile acid-tamoxifen conjugates. The cholic acid-tamoxifen conjugate (CA-Tam3-Am) bearing three tamoxifen molecules shows enhanced anticancer activities in both estrogen receptor +ve and estrogen receptor -ve breast cancer cell lines. The enhanced anticancer activity of CA-Tam3-Am is due to more favorable irreversible electrostatic interactions followed by intercalation of these conjugates in hydrophobic core of membrane lipids causing increase in membrane fluidity. Annexin-FITC based FACS analysis showed that cells undergo apoptosis, and cell cycle analysis showed the arrest of cells in sub G0 phase. ROS assays showed a high amount of generation of ROS independent of ER status of the cell line indicating changes in mitochondrial membrane fluidity upon the uptake of the conjugate that further leads to the release of cytochrome c, a direct and indirect regulator of ROS. The mechanistic studies for apoptosis using PCR and western analysis showed apoptotsis by intrinsic and extrinsic pathways in ER +ve MCF-7 cells and by only an intrinsic pathway in ER -ve cells. In vivo studies in the 4T1 tumor model showed that CA-Tam3-Am is more potent than tamoxifen. These studies showed that bile acids provide a new scaffold for high drug loading and that their anticancer activities strongly depend on charge and hydrophobicity of lipid-drug conjugates.

Vesicle and stable monolayer formation from simple "click" chemistry adducts in water

Click chemistry has been successfully extended into the field of molecular design of novel amphiphatic adducts. After their syntheses and characterizations, we have studied their aggregation properties in aqueous medium. Each of these adducts forms stable suspensions in water. These suspensions have been characterized by dynamic light scattering (DLS) studies and transmission electron microscopy (TEM). The presence of inner aqueous compartments in such aggregates has been demonstrated using dye (methylene blue) entrapment studies. These aggregates have been further characterized using X-ray diffraction (XRD), which indicates the existence of bilayer structures in them. Therefore, the resulting aggregates could be described as vesicles. The temperature-induced order-to-disorder transitions of the vesicular aggregates and the accompanying changes in their packing and hydration have been examined using high-sensitivity differential scanning calorimetry, fluorescence anisotropy, and generalized polarization measurements using appropriate membrane-soluble probe, 1,6-diphenylhexatriene, and Paldan, respectively. The findings of these studies are consistent with each other in terms of the apparent phase transition temperatures. Langmuir monolayer studies confirmed that these click adducts also form stable monolayers on buffered aqueous subphase at the air-water interface.

Understanding membranes through the molecular design of lipids

Lipids are amphiphilic molecules that are composed of hydrophilic and hydrophobic regions. A typical membranous aggregate (vesicles, water-filled lipid nanospheres) is formed upon the self-organization of lipids in water from a diverse collection of amphiphiles producing a dynamic supramolecular structure that shows phase behavior and ordering as required for specific biological functions. The determination of various physical properties of lipid aggregates is the key to determining structure-function relationships. Over the years, we have designed and synthesized a wide variety of lipid molecular systems for the investigation of their membrane-forming properties and have used them for purposes such as gene delivery and enzyme activation. In this feature article, we focus on our work on various types of lipids including ion-paired amphiphiles, cholesterol-based lipids, aromatic lipids, macrocyclic lipids containing disulfide tethers, cationic dimeric lipids, and so forth. The emphasis is on experimental design and bottom-line conclusions.

Spacer-modulated aggregation of the cyanine dye on the vesicles of gemini amphiphiles

A series of gemini amphiphiles (bis(2'-heptadecyl-3'-ethylimidazolium)-1,n-alkane dibromide, abbreviated as Gn, n = 2, 4, 6, 8, 10) was found to form vesicles under ultrasonication in aqueous solution at very low concentration (5 microM), which was confirmed by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The adsorption and interaction of a cyanine dye (3,3'-disulfopropyl-4,5,4',5'-dibenzo-9-methyl-thiacarbocyanine triethylammonium salt, abbreviated as MTC) on the vesicles was investigated. It was found that the cyanine dye could exhibit different colors when interacting with the vesicles. The UV-vis spectral measurements revealed the formation of the H or J aggregates of the cyanine dye on the vesicles, which is spacer length dependent: the short spacer length prefers the formation of the H-aggregate, whereas the longer spacer favors the J-aggregate formation. In addition, these aggregates showed different absorption positions from those on the planar films. Furthermore, by mixing the G2 and G10 vesicles in different ways, the selective aggregation of the cyanine dye on the vesicles was realized.

Effect of the hydrocarbon chain and polymethylene spacer lengths on gene transfection efficacies of gemini lipids based on aromatic backbone

Design, syntheses, and gene delivery efficacies of fifteen novel gemini (dimeric) and three monomeric cationic lipids anchored on an aromatic backbone have been described. Each new lipid has been used for liposome formation, and optimal formulations were used to determine the structure-activity correlation of the gene transfection efficacies of these lipids in HeLa and HT1080 cells. The results of the present investigation bring out the effect of hydrocarbon chain lengths and the length of the spacer between the headgroups on gene transfection efficiencies of the cationic gemini lipids based on aromatic backbone. The lipids bearing n-C 14H 29 hydrocarbon chain lengths have been found to be the best transfecting agents compared to their counterparts with n-C 16H 33 and n-C 12H 25 chains in HeLa cells. On the other hand, in HT1080 cells, the lipids based on n-C 12H 25 and n-C 14H 29 chains were found to be more potent transfecting agents than lipids possessing n-C 16H 33 chains. Transmission electron microscopy examination revealed the existence of spherical lipid-DNA complexes.