Spectroscopic Monitoring of the Enrichment of Chlorin e6 in Tumors of the Skin

Dr. Dirk Hüttenberger, Apocare Pharma GmbH and Avantes

For the optimization of photodynamic therapy the spectroscopic detection of photosensitizer molecules, which are selectively enriched in tumour cells, can be useful. In patients with cancer lesions, Chlorin e6 was administered and the typical fluorescence peak was measured using blue light excitation.

The green porphyrin Chlorin e6 is known as a photosensitizer for systemic photodynamic therapy (PDT) for cancer treatment. The molecules accumulate after an intravenous administration selectively in tumor cells. With blue LED or laser light sources the molecules can be excited to a red fluorescence. In order to this, tumor cells and the dimension of tumors can be monitored. Under red light excitation photochemical processes are leading to the generation of singlet oxygen, which is a highly reactive and cell toxic substance. Tumour cells can be killed very selectively and with low side effects to the patients.

Figure 1: Maximum of the fluorescence signal in the course of time. Tumor tissue in comparison to normal skin.

Experimental Conditions

In single case studies Chlorin e6 was given to patients with morbus bowen´s disease (precancerous lesion) and basal cell carcinoma. The patients were treated with different doses from 0,5 mg/kg body weight to 1 mg/kg body weight. The fluorescence signal at 670 nm which is proportional to the amount of Chlorin e6 was measured with a fiber optic spectrometer system (AvaSpec-2048-USB2, Avantes BV, The Netherlands) and illumination with an LED light source at 400 nm (AvaLight-LED Light source, Avantes BV, The Netherlands). The light was delivered over a bifurcated reflection probe (FCR-19UV200-2ME-S2 15, Avantes) with 15 illumination fibers and 4 read fibers.

Figure 2: Basalioma behind the ear before and half a year after treatment.

Results

With a dose of 0,8 mg/kg bodyweight the optimal accumulation in tumor tissue was reached 3 h after application. In basal cell carcinomas of the skin, we reached tumor to tissue ratios of 12:1.

In morbus bowen´s lesions ratios of 7 to 1 were reached. Lower doses of 0,5 mg/kg bw led to lower enrichment and a further bolus was given to reach the 0,8 mg level (see Figure 1). At the point of maximum enrichment the therapy was performed with a 2 W red diode laser (Vision, Germany) successfully.

Conclusion

The fiber-spectroscopic measurement of the amount of photosensitizer helps to optimize the PDT-treatment, in order to find the right light dose and the optimal point of time for the treatment. Chlorin e6 as a tumor selective agent showed a high tumor to tissue ratio and with the excellent acceptance with low side effects it is a highly potent photosensitizer. In future fiber optic probes, positioned over endoscopes, will be tested for measurements in inner organs like lung and bladder.

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