Cellular Entry and Nuclear Targeting By a Highly Anionic Molecular Umbrella

Abstract

A fluorescently-labeled, persulfated molecular umbrella (1) has been synthesized from cholic acid, lysine, spermine and Coumarin 343 and found capable of entering live HeLa cells. The distribution of 1 throughout the cytoplasm and the nucleus was diffuse and punctate, respectively. This finding, together with its ability to cross liposomal membranes by passive diffusion, suggests that passive diffusion plays a significant role in the ability of 1 to enter cells. The fact that 1 is concentrated at the nucleus raises the possibility that molecular umbrellas of this type could be used for the nuclear targeting of drugs.Molecular umbrellas are a unique class of conjugates that are composed of two or more facial amphiphiles that are covalently bound to a central scaffold. Such molecules have been found to possess the ability of crossing liposomal membranes by passive diffusion. 1-4 Our working hypothesis has been that the amphiphilic "wings" of a molecular umbrella first bind to the surface of the liposomal membrane, that translocation proceeds through a shielded conformation in which the hydrophilic faces of the molecule point toward one another as it passes through the hydrocarbon interior, and that the umbrella is then released from the adjacent monolayer into the adjoining aqueous phase. In Scheme 1 we illustrate our current model for umbrella transport of a hydrophilic agent across a lipid bilayer. Here, the shaded and unshaded rectangles represent hydrophobic and hydrophilic faces of the facially amphiphilic units, respectively, and the lightly shaded oval represents a covalently attached, hydrophilic agent. Thus, the umbrella first approaches the membrane in a fully exposed conformation (structure A). Hydrophobic interactions with the membrane interior then leads to an adsorbed state in which the hydrophilic faces are in contact with the polar head group region and the hydrophobic faces are in intimate contact with the hydrocarbon region of the lipid bilayer (structure B). Subsquent absorption into the interior of the membrane, being driven by hydrophobic forces, then affords structure C. Translocation to the adjoining leaflet, 180° rotation and reversal of steps B and A (not shown) then releases the conjugate from the other side of the membrane. In essence, we have postulated that the molecular umbrella masks its own hydrophilicity as well as that of an attached polar agent as it crosses the hydrocarbon interior of the bilayer.In the work that is reported herein, we sought to answer a long-standing question that bears directly on the potential of molecular umbrellas as drug carriers. Specifically, can a molecular

Cell Nucleus-Targeting Zwitterionic Carbon Dots

“…S11 ). It should be noted that, although the CDs were not modified with any nucleus-targeted signals or chemicals, the CDs were successfully internalized into the cells as well as the nucleus which is attributed to the zwitterionic surface state and small size of CDs 22 23 24 25 26 27 28 29 30 31 32 33 34 35 . The positively charged surface group on the CDs can effectively interact with the negatively charged cell membranes to enter the cytoplasm 23 via clathrin- and caveolae-mediated pathway along with the involvement of passive diffusion 24 25 .…”

“…Cytoplasmic and nuclear uptake of nanoparticle cargo in live cells can be determined by the size 22 and surface charge 23 24 25 26 27 28 29 . In addition, positively charged nanoparticles are preferentially internalized by cells and negatively charged ones interact with nuclei whose pH is consistently 0.3 to 0.5 units above that of the cytosol 23 24 25 26 27 28 29 . Based on this observation, it is expected that the preparation of zwitterionic CDs with both positively and negatively charged functional groups, can facilitate cytoplasmic uptake and subsequent nuclear translocation of theranostic drug-vehicle conjugates.…”

Bioconjugate-Based Molecular Umbrellas

“…To address this question, we synthesized a fluorescently-labeled molecular umbrella analog of 18 (i.e., 19 ) and investigated its interaction with live HeLa cells (Figure 23) (35). …”

A Fine Line Between Molecular Umbrella Transport and Ionophoric Activity

“…Specifically, we showed that a bioconjugate derived from one spermine, four lysine and eight cholic acid groups, having all of its hydroxyl groups sulfated (i.e., 1 ), exhibits significant anti-HIV and anti-HSV activity (Figure 1) (5,6). In a related investigation, we showed that a fluorescently-labelled analog of 1 readily enters live HeLa cells, and provided evidence that passive transport may be playing a significant role in this internalization process (7). …”