Imaging Self-Assembly Dependent Spatial Distribution of Small Molecules in a Cellular Environment

Abstract

Self-assembly of small molecules, as a more common phenomenon than one previously thought, can be either beneficial or detrimental to cells. Despite its profound biological implications, how the self-assembly of small molecules behave in cellular environment is largely unknown and barely explored. This work studies four fluorescent molecules that consist of the same peptidic backbone (e.g., Phe-Phe-Lys) and enzyme trigger (e.g., a phosphotyrosine residue), but bear different fluorophores on the side chain of the lysine residue of the peptidic motif. These molecules, however, exhibit different ability of self-assembly before and after enzymatic transformation (e.g., dephosphorylation). Fluorescent imaging reveals that self-assembly directly affects the distribution of these small molecules in cellular environment. Moreover, cell viability tests suggest that the states and the location of the molecular assemblies in the cellular environment control the phenotypes of the cells. For example, the molecular nanofibers of one of the small molecules apparently stabilize actin filaments and alleviate the insult of an F-actin toxin (e.g., latrunculin A). Combining fluorescent imaging and enzyme-instructed self-assembly of small peptidic molecules, this work not only demonstrates that self-assembly as a key factor for dictating the spatial distribution of small molecules in cellular environment. In addition, it illustrates a useful approach, based on enzyme-instructed self-assembly of small molecules, to modulate spatiotemporal profiles of small molecules in cellular environment, which allows the use of the emergent properties of small molecules to control the fate of cells.

Self-assembling peptide-based building blocks in medical applications

“…However, the self-assembling tendencies and the distribution of the self-assembled fibers in the cellular environment can be heavily influenced by the nature of the fluorophore, and can also induce cytotoxicity in some cases. Thus, extreme care must be exercised in designing the fluorophore precursors to achieve the desired imaging objectives [84]. …”

Supramolecular biofunctional materials

“…Notably, this small molecule exhibited remarkable cytotoxicity to several cancer cell lines while showed low cytotoxicity to normal cells due to the fact that cancer cells secrete excessive amount of MMP-7. Based on the report of the intracellular EISA of L-peptide derivative (Nap-FFK p Y),[119, 305, 306] Gao et al reported the use of Nap-FFK p Y to co-assemble with indocyanine green (ICG) for in vivo cancer theranostics. The formation of ICG-doped nanofibers not only enhanced the tumor uptake of ICG (by 25-fold compared with free ICG), but also largely extended the retention time of ICG in tumor site, resulting in complete and precise tumor elimination by laser ablation (Figure 16C).…”

Nanoscale assemblies of small molecules control the fate of cells

“…DBD). [52] Upon enzymatic dephosphorylation (Fig. 7a), these precursors transform to their corresponding hydrogelators and exhibit higher contrast than background for imaging.…”

“…Fluorescent confocal images of the HeLa cells incubated with 500 µM of (c) 6a , (d) 7a , (e) 8a , and (f) 9a for 30 min. [52] (Print with the permission from © 2013 American Chemical Society)…”