Abstract 5374: Effect of carbon nanotube amount and subcellular location on the near infrared (NIR) photothermal ablation of cells
Authors: Murali Vasanth Siruvallur , Mikoryak Carole , Wang Ruhung , Draper Rockford K. 
Published: May 2015

Abstract
Background and Objective: Single-walled carbon nanotubes (SWNTs) are readily taken up by cells, strongly absorb in the NIR (700-1100 nm) region, and efficiently convert absorbed NIR into heat. These properties have made SWNTs an interesting facilitator for the NIR mediated thermal ablation of cancer cells. In the application of SWNTs to thermal ablation, it is not known what amount of cell-associated SWNTs is required to achieve a defined level of cell killing upon NIR irradiation. In addition, it has not been quantitatively demonstrated whether SWNTs bound to the plasma membrane or internalized into vesicles are more efficient in killing cells. The overall objective of this project is to assess NIR mediated killing as a function of cell-associated SWNT amount and SWNT subcellular location.
Methods: The study was performed in three phases. The first phase involved non-covalent functionalization of SWNTs by bovine serum albumin. Non-targeted uptake and NIR irradiation of cells was performed to find the optimal laser power density, NIR exposure time and SWNT concentration to kill cells. SWNTs associated with cells were then extracted and quantified by a sodium dodecyl sulfate-polyacrylamide gel electrophoresis technique (Wang et al., 2009, Anal. Chem. 81:2944-2952) and the SWNT amount was correlated with cell killing.
The second phase included the non-covalent functionalization of SWNTs with phospholipid-PEG conjugated folic acid (PL-PEG-FA) as a targeting ligand. The SWNTs were internalized by receptor-mediated endocytosis at 37°C, the optimum laser conditions were determined as in the first phase, and the amount of internalized SWNTs were quantified and correlated with NIR-mediated cell killing.
In the third phase, cells were incubated with the PL-PEG-FA SWNTs at 4°C to allow binding to the cell surface without internalization, followed by measuring the amount of
surface-bound SWNTs. The amount of surface-bound SWNTs was then correlated with NIR-mediated cell death.
Results: An increase in killing of cells incubated with SWNTs was observed in both the non-targeted and targeted systems as a function of NIR laser power density, NIR exposure time and incubated SWNT concentration. With the folate targeted system, there was more cell death when SWNTs were internalized into vesicles compared to when an equivalent amount of SWNTs were confined to the cell surface.
Conclusion: SWNTs internalized by cells, either by fluid phase endocytosis, or by receptor-mediated endocytosis via the folate receptor, were effective in killing cells upon NIR irradiation. However, SWNTs confined to the cell surface after binding to folate receptors at low temperature were not as efficient in killing cells upon NIR irradiation. This suggests that NIR-mediated thermal ablation therapy will be more effective when SWNTs are targeted to a receptor and are internalized by receptor-mediated endocytosis.
Citation Format: Vasanth Siruvallur Murali, Carole Mikoryak, Ruhung Wang, Rockford K. Draper. Effect of carbon nanotube amount and subcellular location on the near infrared (NIR) photothermal ablation of cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5374. doi:10.1158/1538-7445.AM2014-5374