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LED Photodynamic Therapy For Cancer

Photodynamic therapy (PDT) is a cancer treatment modality that recently has been applied as adjuvant therapy for brain tumours.

PDT consists of intravenously injecting a photosensitizer, which preferentially accumulates in tumour cells, into a patient and then activating the photosensitizer with a light source. This results in free radical generation followed by cell death.

The development of more effective light sources for PDT for brain tumours has been facilitated by applications of space light-emitting diode array technology; thus permitting deeper tumour penetration of light and use of better photosensitizers.

Lutetium Texaphyrin (Lutex) and Benzoporphyrin Derivative (BPD) are new, second generation photosensitizers that can potentially improve PDT for brain tumours.

Lutex and BPD have major absorption peaks at 730 nm and 680 nm respectively, which gives them two distinct advantages. First, longer wavelengths of light penetrate brain tissue easily so that larger tumours could be treated; and second, the major absorption peaks mean that more of the drug is activated upon exposure to light.

Tumorcidal effects of Lutex and BPD have been studied in vitro using canine glioma and human glioblastoma cell cultures.

Using light-emitting diedes (LED) with peak emissions of 728 nm and 680 nm as a light source, a greater than 50 percent cell kill was measured in both cell lines by tumour DNA synthesis reduction.

The effectiveness of Lutex and BPD against tumour cells in vitro thus established, we have taken the first step toward determining their in vivo efficacy by performing experiments to determine the largest doses of both Lutex, or BPD, and light that can be administered to dogs before toxicity is seen, i.e. the maximum tolerated dose (MTD).

Using this dose allows us to effect maximum tumour cell destruction during in vivo studies. For longer wavelengths of light, the improved NASA LED-technology is required.

LEDs are an effective alternative to lasers for PDT. Laser conversion to near-infrared wavelengths is inherently costly and inefficient, using an argon ion or KTP/YAG laser beam that is converted by a dye module, usually to 630nm.

LEDs have been frequently used to emit longer wavelength broad spectrum near-infrared light of 25-30 nm bandwidths. LED lamps traditionally consist of an array of semiconducting LED chips. In recent years, improvements in semiconductor technology have substantially increased the light output of LED chips.
A novel type of LED chip is based on the semiconductor Aluminium Gallium Arsenide (AlGaAs).

These LED chips have been manufactured to emit light with peak wavelengths of 680 and 730 nm, which are optimal wavelengths for the absorption spectrum of the new photosensitizers used for cancer PDT.

Human trials have begun at the Medical College of Wisconsin, Naval Special Warfare Command and NASA-Marshall Space Flight Centre.