Long Wavelength Photosensitizers (near 800 nm) for
Imaging and Therapy
Porphyrin-based photosensitizing agents for photodynamic therapy (PDT) possess unique advantages due to their ability to be retained in tumors and to produce cytotoxic singlet oxygen upon exposure to an appropriate wavelength of light. It is well established that photon migration into tumor tissue is highly dependent on the absorption and scattering properties of tissue components. The near-infrared (NIR) region of the spectrum offers certain advantages for photon penetration. The availability of inexpensive light emitting diodes (LEDs) in this region will make PDT more applicable and economical. Moreover, the in vivo imaging is preferably performed in the NIR (700-900 nm) because of efficient optical tissue penetration and minimal auto-fluorescence in this spectral region. At NIR wavelengths, light penetrates several centimeters in tissue (Figure 1) so that the fluorophore can be imaged deep within the body. However, it should be noted that light penetration also depends on tissue type.
Based on these facts, and also realizing the importance of porphyrin-based compounds in tumor-avidity and photosensitizing efficacy, our company has developed variety of porphyrin based PDT agents with long wavelength absorption near 800 nm. Specifically, the bacteriochlorin based photosensitizer (PL-605) showed both PDT efficacy and tumor-imaging capabilities. At a therapeutic/imaging dose the PL-605 did not show any significant skin phototoxicity. It was also found to be a promising imaging agent even at low doses. Results of whole body fluorescence imaging in RIF tumor-bearing C3H mice, with excitation of the fluorescent photosensitizer 24 h post injection are shown in Section B of the Figure above.
The PL-605 exhibited significant PDT efficacy as can be seen in Section C of the above figure, even at a dose of 0.25 umol/kg, on mice models. Our PL-605 is capable of treating large and deeply seated tumors, and has higher tumor-avidity than other existing PDT-drugs on the market. Further, PL-605 can also be used as a non-expensive fluorescence imaging agent.
Photolitec’s technology can be applied to highly effective real time image-guided cancer therapy.