Psoralen as a Photosensitizers for Photodynamic Therapy by Means of In Vitro Cherenkov Light

Abstract

Possible enhancements of DNA damage with light of different wavelengths and ionizing radiation (Rhenium-188—a high energy beta emitter (Re-188)) on plasmid DNA and FaDu cells via psoralen were investigated. The biophysical experimental setup could also be used to investigate additional DNA damage due to photodynamic effects, resulting from Cherenkov light. Conformational changes of plasmid DNA due to DNA damage were detected and quantified by gel electrophoresis and fluorescent staining. The clonogene survival of the FaDu cells was analyzed with colony formation assays. Dimethyl sulfoxide was chosen as a chemical modulator, and Re-188 was used to evaluate the radiotoxicity and light (UVC: λ = 254 nm and UVA: λ = 366 nm) to determine the phototoxicity. Psoralen did not show chemotoxic effects on the plasmid DNA or FaDu cells. After additional treatment with light (only 366 nm—not seen with 254 nm), a concentration-dependent increase in single strand breaks (SSBs) was visible, resulting in a decrease in the survival fraction due to the photochemical activation of psoralen. Whilst UVC light was phototoxic, UVA light did not conclude in DNA strand breaks. Re-188 showed typical radiotoxic effects with SSBs, double strand breaks, and an overall reduced cell survival for both the plasmid DNA and FaDu cells. While psoralen and UVA light showed an increased toxicity on plasmid DNA and human cancer cells, Re-188, in combination with psoralen, did not provoke additional DNA damage via Cherenkov light.

Investigation of Photodynamic Therapy Promoted by Cherenkov Light Activated Photosensitizers—New Aspects and Revelations

“…As previous studies have shown, “psoralen is not toxic and does not damage the DNA”, when not activated [ 39 ]. The Cherenkov radiation spectrum for an energy similar to the maximum beta energy of Re-188, the emission maximum of CL, is close to the absorption maximum of psoralen [ 46 ].…”

“…Psoralen, as partially used in these investigations, is already used in the form of PUVA therapy (psoralen activated by UVA radiation therapy) and much research has been conducted [ 6 , 36 , 37 , 38 , 39 , 40 , 41 ]. Using a megavolt beam, UVA is induced by photon irradiation, which activates the phototoxic properties of psoralen [ 1 , 39 , 42 , 43 , 44 , 45 ]. Yoon et al also used trioxsalen as a derivative of psoralen for their research in the field of PDT.…”

“…When this approach was transferred to radionuclides in the field of nuclear medicine, no visible effect was found when different activation methods and the setups were investigated with radiation, light and radioactivity [ 39 ]. Although a similar setup was used, there are differences from the current investigations.…”

“…Here, a volume of approximately 350 mL (Re-188 in distilled water) and an additional water flask (another 350 mL) were used. Thus, a higher CL intensity is expected along with a higher applied dose (8 MBq [ 39 ] vs. 1.5 GBq) and longer irradiation times.…”

Photodynamic Therapy: From the Basics to the Current Progress of N-Heterocyclic-Bearing Dyes as Effective Photosensitizers

“…Indian medical literature dated 1400 BC, the Atharva Veda, reports treating vitiliginous skin with babchi (Psoralea corylifolia) extracts, a plant from which it is now known that 8-methoxypsoralen is the furan-containing coumarin-based molecule that induced the photodynamic effect [16,18]. Even today, this core of photosensitizing molecules is widely studied for its potential phototherapeutic use [19,20]. Also, in Greek, Chinese, and Roman civilizations, there is evidence of the use of energy from the sun as a remedy for the treatment of various diseases.…”