A Novel Proposal: Glycosylated Dendritic Nanoparticles for Targeted Delivery of Genetic Payload to Cancer Cells

The highly ordered nature of dendrimers has given them the ability to form supramolecular structures including dendritic nanoparticles (DNPs) from Janus dendrimers discovered as a nanomaterial decades ago. Recently, applications to translate DNPs as synthetic vectors for targeted mRNA delivery within the body have been developed in Ionizable Amphiphilic Janus Dendrimers (IAJDs). Separately, it has been demonstrated that glycosylation can target cancer cells due to their irregular metabolic activities. Due to the highly modifiable nature of IAJDs, and knowledge of the physical conformation of monomers within DNPs, it is realistic to create surface-modified nanoparticles with sugar moieties that can target cancer cells with unique metabolic activity.

In no way does this proposal guarantee the success of a glycosylated IAJD. In fact, there are basic principles that differ between the aforementioned molecules, so joining the molecules may not join their respective functions. IAJDs are governed by the idea of “self-assembly.” Some scientists argue IAJDs are not true dendrimers, instead likening them to dendrons, the subcomponents that are typically covalently linked into the larger branching dendrimer structure. In an IAJD however, the molecules are not carefully linked through induced primary bond formation; instead, their “self-assembly” into a 3-dimensional spherical macrostructure is a result of automatic secondary bonds when the molecules are injected into aqueous solution. Contrarily, the PAMAM dendrimers used in [2] are true dendrimers. From a 3-d mechanistic perspective, they may interact very differently with a cell membrane.

In this light, let us think about what mechanisms we are trying to combine by combining these two different technologies. The IAJD technology is used because we want to deliver an mRNA payload. This only works because self-assembly mechanisms leave a hollow nanoparticle which can encapsulate mRNA molecules. The glycosylation method previously used on PAMAM dendrimers is used because we want to target cancer cells. This mechanism works by exploiting the different metabolism of cancerous cells versus healthy cells. Theoretically, the mechanisms should work independently. The only wrinkle I can foresee is glycosylation affecting endosomal escape, the mechanism through which IAJD nanoparticles fuse with the cell membrane, releasing their mRNA payload into the cell cytoplasm. As IAJDs are inactive in-vitro the only confirmation of this is in-vivo.

Despite this, it may be effective use glucose and galactose as the sugar moieties to glycosylate the IAJDs.

For our IAJD base we will use the only commercially available IAJD, IAJD-97. Its synthesis is described in [3]. The chemical structure is given in starting material of Figure 3. Reactions for click conjugation of sugar azides should be adapted from [2]. Reactions include the click addition of fluorescently labelled Cy5 to verify through in-vivo testing, the appropriate targeting and transfection of this novel nanoparticle.

The final compound should be a fluorescently active and glycosylated IAJD monomer. This can self-assemble into IAJD nanoparticles where the sugar and fluorescently active domain are sometimes available on the external surface. However, to achieve this, because we have changed the chemistry so drastically from the original IAJD structure, we must comment on the self-assembly mechanism further.

I propose a simple mechanism to mitigate the disruption of self-assembly due to the bulky monomers. In fact, the bulky nature of the dendrimer extensions conveniently arranges of the monomers such that the bulky sugars are on the surface more thermodynamically favorable. Therefore, if we simply integrate a larger ratio of unmodified IAJD-97 molecules with the glycosylated molecules, we should allow for adequate spacing between the glycosylated molecules such that they can still form a nanoparticle and arrange the sugars on the outside.

It would be remiss if I didn’t note that the focus on a specific locus with a fluorescently tagged molecule didn’t raise an opportunity for further studies. Primarily, I think this holds prevalent similarities to exploit an opportunity in increased retention of the payload. Recent publications by Paula Hammond ([4]) explain that covalently bonding the payload to their lipid nanoparticles increased retention of the payload in cancer cells. They confirmed the mechanism of this effect through fluorescent tagging and found that lipids that were covalently bonded to the payload in the nanoparticle transferred to the lipid membrane of the cancer cell. This meant that the payload remained covalently bonded to the cancer cell and allowed for continued immunostimulation.

There are some fundamental differences between Hammond’s work and this proposal. Firstly, is the payload. It is harder to covalently conjugate an mRNA payload (which is more susceptible to degradation in the biologic environment) versus the cytokine protein Hammond uses. Secondly, is the type of nanoparticle. A dendritic nanoparticle has dendrimers, not lipids, as monomers. It is questionable whether a dendrimer would integrate itself into the lipid membrane. A gut reaction would suggest that a dendrimer would therefore not integrate easily, but some characterization of dendrimersomes suggests it may be more like the mechanics of the cell membrane than a liposome is. Therefore, it is possible, and if this works it opens the doors to more opportunities for therapeutic application of dendritic nanoparticles with enhanced cellular retention.

This communication is not experimental. Still, I hope, it is useful as a novel model to describe a reasonable advancement for cancer-cell targeting.