Photoinduction of micronuclei by 4,4',6-trimethylangelicin and 8-methoxypsoralen in different experimental models

Application of the concept of relative photomutagenic potencies to selected furocoumarins in V79 cells

Furocoumarins are phototoxic and photomutagenic natural plant constituents found in many medicinal plants and food items. Since plants contain mixtures of several furocoumarins, there is a need for a comparative risk assessment of a large number of furocoumarins. Previously, we have introduced the concept of relative Photomutagenicity Equivalency Factors (PMEFs) derived from the slope of the concentration-response curve of photomutagenicity of individual furocoumarins in V79 cells using the HPRT mutation assay in the presence of UVA irradiation at 125mJ/cm(2). Here we have applied this method to the furocoumarins bergamottin, isopimpinellin and psoralen using 5-methoxypsoralen (5-MOP) as a reference compound with a PMEF of 1.0. We found that neither bergamottin nor isopimpinellin, two furocoumarins abundant in plants, food etc., exerted any significant photomutagenicity while psoralen was clearly photomutagenic with a PMEF of 0.36. Similarly, isopimpinellin was not phototoxic in V79 cells, while bergamottin showed some cytotoxicity which, however, was completely independent of UVA irradiation. Only psoralen was photocytotoxic showing a similar concentration-response relationship for photomutagenicity, and for photocytotoxicity (at 72h after irradiation). Data from the micronucleus assay for DNA damage at 20h after irradiation were in complete agreement with the HPRT mutation data. Our findings indicate that individual furocoumarins differ enormously in their photomutagenic potency, and that a specific toxicological risk assessment is required for each furocoumarin instead of an assessment based on the sum of furocoumarins in a given sample.

Phototoxicity, distribution and kinetics of association of UVA-activated chlorpromazine, 8-methoxypsoralen, and 4,6,4′-trimethylangelicin in Jurkat cells

Extracorporeal phototherapy (ECP) is a therapeutic approach based on photobiological effects of 8-methoxypsoralen (8-MOP) on white blood cells isolated from the blood, exposed to UVA and then reinfused into the patient. 8-MOP is presently the only drug approved for clinical application of ECP; therefore, identification of other photosensitizers with better photochemical and pharmacokinetic properties might enhance the efficacy of this treatment modality. Among such alternative drugs are 4,6,4'-trimethylangelicin (TMA) and chlorpromazine (CPZ), which have previously been studied in an animal model for ECP. In this current study, cellular bioavailability of 8-MOP, TMA and CPZ was investigated in vitro, using low doses of UVA relevant for the clinical setting of ECP. Our fluorescence microscopy study revealed that 8-MOP and CPZ penetrated readily into the cells, where they accumulated with similar kinetics. No distinct fluorescence was observed in cells incubated with TMA. We found that the phototoxic efficiency of 8-MOP was an order of magnitude greater than that of CPZ, i.e., to obtain a similar reduction in survival of cells subjected to photosensitization by the drugs, the concentration of CPZ needed to be 10 times higher than that of 8-MOP. The photoactivated TMA exhibited the highest pro-apoptotic efficiency. A clear indication of photoinduced formation of reactive oxygen species and peroxidation of lipids was observed only in CPZ-sensitized cells, suggesting different mechanisms for phototoxicity mediated by CPZ and by the two furocoumarins.

Electrospray mass spectrometry in the differentiation of some isomeric trimethylfurocoumarins

Electrospray mass spectrometry (ES-MS) was successfully employed for the structural differentiation of six isomeric trimethylfurocoumarins of possible pharmaceutical interest. Two different approaches were employed. The first was based on MS(n) experiments of MH(+) ions. Although the product ion spectra of MH(+) of the isomers are very similar, the MS(3) spectra of the collisionally generated [MH[bond]CO](+) ions show some characteristic differences. The second approach was based on complexation of the molecules with Li(+), Na(+) and K(+) using ESI-MS of sample solutions containing alkali ions in a 100:1 molar ratio with respect to the analyte. Significant differences were observed in complex production yields, and these were related to the dimension of the alkali ion and to the steric availability of chelating groups in the different isomers.

In silico rationalization of the structural and physicochemical requirements for photobiological activity in angelicine derivatives and their heteroanalogues

In PUVA (Psoralen plus UVA) chemotherapy 8-methoxypsoralen is the most widely used compound, although its efficacy is endowed with undesired side effects. In order to have an evident anti-proliferative activity with a reduced phototoxicity, many linear and angular derivatives have been synthesised. In this paper we describe a QSAR study in which, by means of the neural networks methodology, a useful model for predicting biological activity, expressed as ID50 (the UVA dose that reduces to 50% the DNA synthesis in Ehrlich cells), has been derived. A decision tree that is able to discriminate between active and inactive compounds has been built based on recursive partitioning. The study shows the key structural features responsible for the activity and could be a helpful tool in the rational design of new, less toxic, photochemotherapeuthic agents.

DNA damage and biological effects induced by photosensitization with new N(1)-unsubstituted furo[2,3-h]quinolin-2(1H)-ones

New furoquinolinones unsubstituted at the N(1) position were prepared and their photobiological activities were studied in comparison with 4,6,8,9-tetramethylfuro[2,3-h]quinolin-2(1H)-one (HFQ) and 8-MOP. The anti-proliferative activity of furoquinolinones 3a-f was tested upon UVA irradiation in mammalian cells, studying DNA synthesis and clonal growth capacity, and in micro-organisms, evaluating T2 infectivity. Almost all compounds appeared to be more active than 8-MOP, and free of any mutagenic activity and skin phototoxicity. Among them, compound 3b was the most effective one. Similarly to HFQ, compound 3b appeared to be very active also in DNA damaging, forming monoadducts and DPC(L=0), but no ISC and DPC(L>0), both responsible for furocoumarin genotoxicity and phototoxicity. Moreover, Ehrlich ascites cells, photoinactivated by the new furoquinolinone 3b and injected into recipient mice, proved to be capable of inducing protection against a successive challenge performed with the same tumor cells. For all these features, 3b seemed to be a new promising potential drug for PUVA therapy and photopheresis.

Synthesis, photobiological activity and photoreactivity of methyl-thieno-8-azacoumarins, novel bioisosters of psoralen

4,4'-dimethyl-thieno-8-azacoumarin (6) and 4,4',5'-trimethyl-thieno-8-azacoumarin (8) were synthesised. Their photobiological activity was tested on human tumour cell lines. Interestingly, for 6, a photocytotoxic ability higher in HL-60, comparable in HeLa cells, with respect to that of the well-known drug 8-methoxypsoralen (8-MOP), was demonstrated. The covalent photoaddition to DNA occurs by means of the molecular mechanism already demonstrated for furocoumarins. However, it is noteworthy that no skin phototoxicity appears.

Photobiological properties of 1-(3'-hydroxypropyl)-4,6,8-trimethylfur

A new furoquinolinone derivative, 1-(3'-hydroxypropyl)-4,6,8-trimethylfuro[2,3-h]quinolin-2(1H)-one (HPFQ, 4), was prepared, in which the nitrogen atom in position 1 carries a hydroxypropyl chain. The antiproliferative activity of HPFQ was studied in comparison with its analogue 1,4,6,8-tetramethylfuro[2,3-h]quinolin-2(1H)-one (FQ) and 8-methoxypsoralen (8-MOP). By incubation in the dark, HPFQ, although retaining antitopoisomerase II activity, appeared less effective than FQ. Upon UVA irradiation, HPFQ produced little amounts of singlet oxygen, but detectable levels of superoxide anion; like FQ, HPFQ induced numbers of DNA-protein cross-links, but no interstrand cross-links in mammalian cells. The HPFQ phototoxicity was comparable to that of FQ and 8-MOP, while mutagenic activity, scored in two Escherichia coli strains, seemed much less remarkable.

DNA damage induced by 4,6,8,9-tetramethyl-2H-furo[2,3-h]quinolin-2-one, a new furocoumarin analog: biological consequences

4,6,8,9-Tetramethyl-2H-furo[2,3-h]quinolin-2-one (HFQ) and its isomer FQ (1,4,6,8-tetramethyl-2H-furo[2,3-h]quinolin-2-one) showed very strong antiproliferative activity in mammalian cells, about two times greater than 8-methoxypsoralen (8-MOP). Both compounds induced DNA-protein cross-links (DPC) but not interstrand cross-links. The FQ generated DPC in a biphotonic process, yielding a new kind of diadduct, whereas HFQ induced DPC by a monophotonic one, probably without its physical participation in the covalent bridge. These lesions gave different toxic responses. Sensitization of FQ led to extensive DNA fragmentation and to a number of chromosomal aberrations. Conversely, HFQ seemed to be completely inactive and 8-MOP gave intermediate results. A strict relationship between DPC formation and induction of chromosomal aberrations was observed. The HFQ did not induce light skin erythemas, whereas FQ was more phototoxic than 8-MOP, thus suggesting that FQ lesions, DPC in particular, may be implicated in skin phototoxicity. Ehrlich ascites cells, a transplantable mouse tumor, inactivated by furoquinolinone sensitization and injected into healthy mice, protected them from a successive challenge by viable tumor cells. This response appeared to be based on an immune mechanism. Comparable amounts of base substitution revertants were scored when testing furoquinolinones and 8-MOP in bacteria but no DPC were detected. This suggests that classic mutagenesis tests on bacteria are insufficient to give adequate information on furocoumarin genotoxicity. Given its features, HFQ can be regarded as an interesting new agent for psoralen plus UVA photochemotherapy and photopheresis.

The application of the micronucleus test in Chinese hamster V79 cells to detect drug-induced photogenotoxicity

Recent reports on the photochemical carcinogenicity and photochemical genotoxicity of fluoroquinolone antibacterials led to an increasing awareness for the need of a standard approach to test for photochemical genotoxicity. In this study the micronucleus test using V79 cells was adapted to photogenotoxicity testing. Results of using different UVA/UVB relationships enabled us to identify a suitable irradiation regimen for the activation of different kinds of photosensitizers. Using this regimen, 8-methoxypsoralen and the fluoroquinolones lomefloxacin, grepafloxacin and Bay Y 3118 were identified to cause micronuclei and toxicity upon photochemical activation. Among the phenothiazines tested, chlorpromazine and 2-chlorophenothiazine, were positive for both endpoints, whereas triflupromazine was only slightly photoclastogenic in the presence of strong phototoxicity. Among the other potential human photosensitizers tested (oxytetracycline, doxycycline, metronidazole, emodin, hypericin, griseofulvin), only hypericin was slightly photogenotoxic. Photochemical toxicity in the absence of photochemical genotoxicity was noted for doxycycline and emodin. With the assay system described, it is possible to determine photochemical toxicity and photochemical genotoxicity concomitantly with sufficient reliability.