Self-Assembled Porphyrin Nanodiscs with Structure-Dependent Activation for Phototherapy and Photodiagnostic Applications

The abilities to deliver and subsequently activate a therapeutic at the intended site of action are two important challenges in the synthesis of novel nanoparticles. Poor tumor permeability as a result of a dense microenvironment can impede the delivery of nanoparticles to the site of action. The design of a sub-40 nm activatable porphyrin nanodisc, based on protein-induced lipid constriction, is described. The biophotonic nanoparticle, self-assembled from aggregated porphyrin–lipid, is stabilized by an amphipathic alpha helical protein and becomes photoactive when its structure is perturbed. Enzymatic cleavage of the constricting protein leads to conversion of the particle from a disc- to a vesicle-shaped structure and provides further evidence that the apolipoprotein serves a functional role on the nanodisc. Fluorescence measurements of these nanodiscs in a detergent show that fluorescence is over 99% quenched in the intact state with a 12-fold increase in singlet oxygen generation upon disruption. Cellular fluorescence unquenching and dose-dependent phototoxicity demonstrate that these nanodiscs can be internalized and unquenched intracellularly. Finally, nanodiscs were found to display a 5-fold increase in diffusion coefficient when compared with the protein-free control ((3.5 ± 0.1) × 10^–7 <i>vs</i> (0.7 ± 0.03) × 10^–7 cm² s^–1). The ability to incorporate large amounts of photosensitizer drugs into its compact structure allows for phototherapeutic action, fluorescence diagnostic applications, and the potential to effectively deliver photosensitizers deep into poorly permeable tumors

Stimuli-Responsive Photoacoustic Nanoswitch for <i>in Vivo</i> Sensing Applications

Photoacoustic imaging provides high-resolution images at depths beyond the optical diffusion limit. To broaden its utility, there is need for molecular sensors capable of detecting environmental stimuli through alterations in photoacoustic signal. Photosynthetic organisms have evolved ingenious strategies to optimize light absorption through nanoscale ordered dye aggregation. Here, we use this concept to synthesize a stimuli-responsive nanoswitch with a large optical absorbance and sensing capabilities. Ordered dye aggregation between light-harvesting porphyrins was achieved through intercalation within thermoresponsive nanovesicles. This causes an absorbance red-shift of 74 nm and a 2.7-fold increase in absorptivity of the Q_<i>y</i>-band, with concomitant changes in its photoacoustic spectrum. This spectral feature can be reversibly switched by exceeding a temperature threshold. Using this thermochromic property, we noninvasively determined a localized temperature change <i>in vivo</i>, relevant for monitoring thermal therapies of solid tumors. Similar strategies may be applied alongside photoacoustic imaging, to detect other stimuli such as pH and enzymatic activity

Mechanistic Insights into LDL Nanoparticle-Mediated siRNA Delivery

Although small interfering RNA (siRNA) can silence the expression of disease-related genes, delivery of these highly charged molecules is challenging. Delivery approaches for siRNAs are actively being pursued, and improved strategies are required for nontoxic and efficient delivery for gene knockdown. Low density lipoprotein (LDL) is a natural and endogenous nanoparticle that has a rich history as a delivery vehicle. Here, we examine purified LDL nanoparticles as carriers for siRNAs. When siRNA was covalently conjugated to cholesterol, over 25 chol-siRNA could be incorporated onto each LDL without changing nanoparticle morphology. The resulting LDL-chol-siRNA nanoparticles were selectively taken up into cells via LDL receptor mediated endocytosis, resulting in enhanced gene silencing compared to free chol-siRNA (38% gene knock down versus 0% knock down at 100 nM). However, silencing efficiency was limited by the receptor-mediated entrapment of the LDL-chol-siRNA nanoparticles in endolysosomes. Photochemical internalization demonstrated that endolysosome disruption strategies significantly enhance LDL-mediated gene silencing (78% at 100 nM)