Single walled carbon nanohorns as photothermal cancer agents.
BACKGROUND
Nanoparticles have significant potential as selective photo-absorbing agents for laser based cancer treatment. This study investigates the use of single walled carbon nanohorns (SWNHs) as thermal enhancers when excited by near infrared (NIR) light for tumor cell destruction.


METHODS
Absorption spectra of SWNHs in deionized water at concentrations of 0, 0.01, 0.025, 0.05, 0.085, and 0.1 mg/ml were measured using a spectrophotometer for the wavelength range of 200-1,400 nm. Mass attenuation coefficients were calculated using spectrophotometer transmittance data. Cell culture media containing 0, 0.01, 0.085, and 0.333 mg/ml SWNHs was laser irradiated at 1,064 nm wavelength with an irradiance of 40 W/cm² for 0-5 minutes. Temperature elevations of these solutions during laser irradiation were measured with a thermocouple 8 mm away from the incident laser beam. Cell viability of murine kidney cancer cells (RENCA) was measured 24 hours following laser treatment with the previously mentioned laser parameters alone or with SWNHs. Cell viability as a function of radial position was determined qualitatively using trypan blue staining and bright field microscopy for samples exposed to heating durations of 2 and 6 minutes alone or with 0.085 mg/ml SWNHs. A Beckman Coulter Vi-Cell instrument quantified cell viability of samples treated with varying SWNH concentration (0, 0.01, 0.085, and 0.333 mg/ml) and heating durations of 0-6 minutes.


RESULTS
Spectrophotometer measurements indicated inclusion of SWNHs increased light absorption and attenuation across all wavelengths. Utilizing SWNHs with laser irradiation increased temperature elevation compared to laser heating alone. Greater absorption and higher temperature elevations were observed with increasing SWNH concentration. No inherent toxicity was observed with SWNH inclusion. A more rapid and substantial viability decline was observed over time in samples exposed to SWNHs with laser treatment compared with samples experiencing laser heating or SWNH treatment alone. Samples heated for 6 minutes with 0.085 mg/ml SWNHs demonstrated increasing viability as the radial distance from the incident laser beam increased.


CONCLUSIONS
The significant increases in absorption, temperature elevation, and cell death with inclusion of SWNHs in laser therapy demonstrate the potential of their use as agents for enhancing photothermal tumor destruction.
Department of Mechanical Engineering and School of Biomedical Engineering and Sciences, Virginia Tech, Virginia 24061, USA. jonwhit@vt.edu
Jon R
JR
Whitney
Saugata
S
Sarkar
Jianfei
J
Zhang
Thao
T
Do
Taylor
T
Young
Mary Kyle
MK
Manson
Thomas A
TA
Campbell
Alex A
AA
Puretzky
Christopher M
CM
Rouleau
Karen L
KL
More
David B
DB
Geohegan
Christopher G
CG
Rylander
Harry C
HC
Dorn
Marissa Nichole
MN
Rylander
D000818:Animals; D003131:Combined Modality Therapy; D053685:Laser Therapy / Q000379:methods*; D037742:Nanotubes, Carbon; D009369:Neoplasms / Q000628:therapy*; D014407:Tumor Cells, Cultured
D037742:Nanotubes, Carbon