  In this research, combined effect of chlorin e6 and noninvasive 20 kHz,
low-powered ultrasound on melanoma cells is proposed for the first time. The
proposed combination incorporates the application of safe low-frequency
ultrasound that is used for transdermal drug delivery. We demonstrate that
impact of the 20 kHz ultrasound on chlorin e6 leads to strong sonodynamic
effect in melanoma cells. We also show that chlorin e6 keeps its monomeric form
in the cells and does not aggregate after exposure to ultrasound. We propose a
two-step model where sonoluminescence serves as an internal light source for
the chlorin e6 photoactivation.
