Near-IR Picosecond Pulsed Laser Induced Suppression of Metabolic Activity in Malignant Human Brain Cancer: An In-Vitro Study

Abstract

The role of low light intensity in suppressing metabolic activity of malignant human brain cancer (glioblastoma) cell line was investigated through the application of a 1,552 nm wavelength pulsed picosecond laser. Human glioblastomas were grown in T-75 flasks and were utilized when the cells were 50–70% confluent and thereafter transferred into 96 well plates and exposed in their growth culture medium with serum under various energy doses (i.e., fluence) ranging from 0.115–50 J/cm². All exposure doses were reached with an average intensity of 0.115 W/cm²; 25 kHz repetition rate with 1.6 μJ per pulse; pulse duration = 2.93 ps. The glioblastomas exhibited a maximal decline in the metabolic activity (down 50–60%) relative to their respective sham exposed control counterparts between the fluence dose values of 5.0–10 J/cm². The cellular metabolic activities for various treatment doses were measured through the colorimetric MTS metabolic assay 3 days after the laser exposure. Interestingly, the metabolic activity was found to return back to the sham exposed control levels as the fluence of exposure was increased up to 50 J/cm². Addition of (the enzyme) Catalase in the growth medium prior to the laser exposure was found to diminish the laser induced metabolic suppression for all fluence treatment conditions, thus suggesting a functional role of H₂O₂ in the metabolic suppression. In view of this evidence, a hypothesis is formulated which attributes the classical biphasic response, in part, to the light induced production of H₂O₂. Furthermore, it was observed that if the glioblastoma cells were allowed to reach 100% confluency within the T-75 flasks the characteristic laser induced metabolic suppression was found to be severely abrogated. Exploratory steps were also undertaken to maximize the suppression in the metabolic activity through repetitive laser dose of exposure every 24 hours for 3 consecutive days. In addition, the efficacy in the metabolic suppression of the 1,552 nm pulsed laser was also compared to a continuous wave broad band continuous wave heating lamp source channeled through a fiber-optic bundle with identical intensity of exposure. Taken together, our findings reveal that near-IR low level light exposures could potentially be a viable tool in reducing the metabolic activity of cancers; however, due to the cellular “biphasic” response to the non-ionizing irradiation, further research needs to be undertaken to determine exposure parameters which would optimize metabolic and cellular growth suppression in-vivo.