Hypericin and pulsed laser therapy of squamous cell cancer in vitro

This in vitro study compares continuous wave and pulsed laser light at longer wavelengths for activation of the phototoxic drug hypericin in human cancer cells.

Two-photon pulsed laser light now allows high-resolution fluorescent imaging of cancer cells and should provide deeper tissue penetration with near infrared light for improved detection as well as phototoxicity in human tumors.

Cultured Seoul National University (SNU)-1 tumor cells from a squamous cell carcinoma (SCC) were incubated with hypericin before photoirradiation at four laser wavelengths. Phototoxicity of hypericin sensitized SCC cells was measured by dimethyl thiazoldiphenyl (MTT) tetrazolium bromide cell viability assays and by confocal fluorescence microscopy via 532-nm and infrared two-photon pulsed laser light.

Phototoxic response increased linearly with hypericin dose of 0.1-2 microM, light exposure time of 5-120 sec, and pulsed dye laser wavelengths of 514-593 nm. Light energy delivery for 50% cell phototoxicity (LD50) response was 9 joules at 514 nm, 3 joules at 550 nm, and less than 1 joule at the 593 nm hypericin light absorption maxima. Fluorescence confocal microscopy revealed membrane and perinuclear localization of hypericin in the SNU cells with membrane damage seen after excitation with visible 532 nm continuous wave light or two-photon 700-950 nm picosecond pulsed laser irradiation.

Hypericin may be a powerful tumor targetting drug when combined with pulsed laser light in patients with recurrent head and neck SCC.