Dissecting the Molecular Mechanism of Apoptosis during Photothermal Therapy Using Gold Nanoprisms

Abstract

The photothermal response of plasmonic nanomaterials can be exploited for a number of biomedical applications in diagnostics (biosensing and optoacoustic imaging) and therapy (drug delivery and photothermal therapy). The most common cellular response to photothermal cancer treatment (ablation of solid tumors) using plasmonic nanomaterials is necrosis, a process that releases intracellular constituents into the extracellular milieu producing detrimental inflammatory responses. Here we report the use of laser-induced photothermal therapy employing gold nanoprisms (NPRs) to specifically induce apoptosis in mouse embryonic fibroblast cells transformed with the SV40 virus. Laser-irradiated "hot" NPRs activate the intrinsic/mitochondrial pathway of apoptosis (programmed cell death), which is mediated by the nuclear-encoded proteins Bak and Bax through the activation of the BH3-only protein Bid. We confirm that an apoptosis mechanism is responsible by showing how the NPR-mediated cell death is dependent on the presence of caspase-9 and caspase-3 proteins. The ability to selectively induce apoptotic cell death and to understand the subsequent mechanisms provides the foundations to predict and optimize NP-based photothermal therapy to treat cancer patients suffering from chemo- and radioresistance.

The True Complexity of Photothermal Therapy: A Brief Perspective

“…One important factor of the abovementioned unpredictability lies on the arduous control of the retention of nanoparticles inside a specific organelle, or the difficulty to generate a controlled diffusion of the nanostructures across the entire cell. At first glance it may seem that the heat generated can be retained in a single cell compartment at lower intensities or, if the irradiation is increased, it can literally "melt" the biological membranes [2], starting the diffusion of the nanoparticles throughout the cell [15] (Fig. 1).…”

“…What is more, the high specificity of some of these nanoplatforms also grants us with a new tool to further understand the function of certain subcellular components and signaling routes, and how they influence the fate of exposed cells during PTT. In a recent publication, Perez-Hernández et al [15] were able to specifically induce the apoptotic cell death pathway following PTT using gold nanoprisms localized inside the lysosomes by studying several of the steps involved in this complex signaling pathway. They concluded that the death of the cells was mainly mediated by the mitochondrial signaling pathway of apoptosis, hypothesizing that its activation might come from the cleavage of Bid, a pro-apoptotic protein, by the enzymes released from the lysosome where the nanoparticles are localized.…”

“…This would allow utilizing a differential diffusion of the target molecules depending on their size. This process may open a wide range of possibilities to be applied in both drug delivery or to see if the release of the content of certain organelles is altering the normal cell functions, which has already being suggested in the past [15].…”

“…Different pathways happen in different subcellular locations, and several steps of one single pathway can occur in a different location from one another. A clear example is the different steps of apoptosis, which can occur in a number of subcellular locations from the plasmatic membrane, cytoplasm and mitochondria, and that can be influenced by alterations in other organelles, like lysosomes [15]. This issue just grows more complex when the nanoparticles are able to locate in different organelles at the same time, before, during or after laser irradiation.…”

Treatment of natural mammary gland tumors in canines and felines using gold nanorods-assisted plasmonic photothermal therapy to induce tumor apoptosis

“…It has been reported that different intracellular locations or shapes of NPs regulate the switch between necrosis and apoptosis. 21,22 In this study, we were able to cause cancer cell apoptosis in vitro and in vivo by adjusting the laser exposure time.…”