Franco Bordin

PHOTOREACTIONS AT 3655Å BETWEEN PYRIMIDINE BASES AND SKIN‐PHOTOSENSITIZING FUROCOUMARINS

Abstract After irradiation at 3655 Å of an aqueous frozen solution containing thymine and psoralen, a new photocompound was isolated by column chromatography. It contains a furocoumarin and a pyrimidine‐moiety linked together by the formation of a cyclobutane ring (see formulas II and III). By irradiation at 2537 Å in acetic acid solution, the photocompound breaks up again yielding psoralen and thymine. From an aqueous frozen solution containing cytosine and psoralen irradiated at 3655 Å, an analogous photocompound was obtained, which, however, consists of the addition to psoralen of a uracil molecule, instead of a cytosine one (IV, V). It has been stated that the hydrolytic deamination of the cytosine moiety to the uracil one takes place during the working up of the photocompound in aqueous solution after irradiation. Substances with properties similar to those above were obtained from bergapten (5‐methoxy‐psoralen) and thymine, from psoralen and thymidine or thymidylic acid, irradiated at 3655 Å.

Angelicins, angular analogs of psoralens: Chemistry, photochemical, photobiological and phototherapeutic properties

Angelicin and some of its derivatives are naturally occuring compounds which show interesting photobiological properties. In this review various aspects of angelicin and its derivatives have been reported. The natural occurrence and the chemical synthesis both of naturally occurring and synthetic angelicins have been reviewed. Photochemical and photophysical properties of angelicins have been considered with particular reference to the capacity to generate active forms of oxygen, photoreactions with nucleic acids, proteins and unsaturated fatty acids. Photobiological effects have been considered: skin phototoxicity, antiproliferative effects, genotoxicity, ability to induce hemolysis in erythrocytes, inactivation of prokaryotic and eukaryotic microorganism and of viruses. The ability of some angelicins to induce photocarcinogenesis has been reviewed as well as in the activity as photochemotherapeutic agents.

4,5‘‐DIMETHYLANGELICIN: A NEW DNA‐PHOTOBINDING MONOFUNCTIONAL AGENT*

Abstract— 4,5′‐Dimethylangelicin is a new angular furocoumarin showing interesting photochemical and photosensitizing properties. In the dark it forms a complex with native DNA having higher values of the binding parameters than angelicin; by irradiation at 365 nm it is able to photobind with DNA several times faster than angelicin and in about the same degree as psoralen, without forming crosslinkages. It therefore behaves as a pure monofunctional reagent. The same high photobinding capacity with DNA is shown also in vivo in Ehrlich ascites tumor cells and bacterial E. coli cells.

DNA repair and recovery in Escherichia coli after psoralen and angelicin photosensitization

The correlation between DNA repair and recovery of biological functions was studied using three wild type strains of Escherichia coli and two skinphotosensitizing furocoumarins, psoralen and angelicin, which are well known specific reagents of the pyrimidine bases of DNA. In addition to mono-adducts psoralen is able to form a high number of inter-strand cross-links, while angelicin forms only mono-adducts. Both of these damages were repaired, in a short time, in the following way: at first DNA was cut into small pieces that were then rejoined into molecules of normal size, free from cross-links, while the furocoumarin residue was split from DNA almost quantitatively. Recovery of biological functions was studied performing photosensitization experiments in such a manner that the same amounts of psoralen or of angelicin were linked to bacterial DNA. DNA synthesis, tested just after the damage, was inhibited in a similar extent by both drugs. The same bacteria, however, showed a very different colony-forming capacity; angelicin was much less effective than psoralen with a D37 dose about 2.7 times higher. A similar picture was obtained studying DNA synthesis at different times after photosensitization: in the bacteria damaged by angelicin it was restored while no recovery was observed in cells photosensitized by psoralen. These results suggest that both mono-adducts and cross-links can be chemically repaired more or less in a quantitative measure, but that repair of cross-links in much less effective on cell recovery; this behaviour is very probably connected with the different repair mechanisms of mono-adducts and of cross-links.

Novel angular furo and thieno-quinolinones: synthesis and preliminary photobiological studies

A number of new furo and thienoquinolinones carrying an electron-withdrawing function or unsubstituted at the position 3 were synthesized in order to obtain new potential photochemotherapeutic agents with increased antiproliferative activity and decreased toxic side effects. Our interest in studying the SAR of these derivatives also prompted us to investigate the influence of N-methylation on biological activity, by preparing N-methyl derivatives. The antiproliferative activity of all the newly synthesized compounds was evaluated and compared to 8-methoxypsoralen (8-MOP), the drug widely used in PUVA-therapy. The 3-unsubstituted thienoquinolinones were generally the most potent derivatives, followed by the furo-analogues. In particular, the unsubstituted thieno[2,3-h]quinoline-2(1H)one showed the highest activity in T2 bacteriophage, HeLa cells and Ehrlich cells tests. All the compounds, assayed on Escherichia coli WP2 TM9, showed a similar mutagenic activity, very close to that of 8-MOP. Except for 2-oxo-1,2-dihydrothieno[2,3-h]quinoline-3-carboxylic acid, which appeared to be very effective, all compounds generated singlet oxygen to slightly larger amounts when compared to 8-MOP. The N-methyl analogues only induced moderate skin erythemas on albino guinea pigs, while all other derivatives appeared to be entirely inactive. On the basis of these results, the unsubstituted thieno[2,3h]quinoline 2(1H)one seems to be the most interesting potential drug for PUVA photochemotherapy and photopheresis.

FUROCOUMARIN SENSITIZATION INDUCES DNA-PROTEIN CROSS-LINKS

The capacity of some linear and angular furocoumarins to induce DNA‐protein cross‐links by UVA (320–400 nm) irradiation has been evaluated in Chinese hamster ovary cells. Two linear furocoumarins, psoralen and 8‐methoxypsoralen appeared to be capable of inducing DNA‐protein cross‐links to a noticeable extent. 4′‐Methylangelicin and 4,4′‐dimethylangelicin formed only reduced amounts of DNA‐protein cross‐links, while angelicin and 4,6,4′‐trimethylangelicin seemed to be unable to induce significant levels of this lesion. The biological significance of this damage remains to be elucidated, but it might have an important role in furocoumarin sensitization. In the examined compounds, the capacity for inducing DNA‐protein cross‐links appears to be a property of the skin phototoxic furocoumarins. This result suggests the hypothesis of a connection between this damage and the formation of skin erythemas.

PHOTO-C4-CYCLOADDITION OF PSORALEN AND PYRIMIDINE BASES: EFFECT OF OXYGEN AND PARAMAGNETIC IONS

THE PHOTOSENSITIZING properties exerted by some furocoumarins on various biological substrates (Musajo et al., 1962, 1965a, 1967d; Fowlks et al., 1958; Oginsky et al., 1959; Mathews, 1963; Colombo and Levis, 1965; Colombo, 1968) may be explained by a C,-cycloaddition of such substances with the pyrimidine bases of nucleic acids, induced by ultraviolet irradiation at 365 nm (Musajo et al., 1965b, 1965c, 1967~). Studies of the photoreactions (365 nm) between furocoumarins and the simple pyrimidine bases have shown that, while pyrimidines react always with their 5,6-double bond, furocoumarins can react either with their 4’ ,5’-double bond, yielding fluorescent photoadducts (I or 11) (Musajo et al., 1967a) or with their 3,4-double bond, yielding nonfluorescent photoadducts (111 or IV) (Musajo et NI., 1967b; Krauch et al., 1967).

THE EFFECT OF PSORALENS AND ANGELICINS ON PROTEINS IN THE PRESENCE OF UV‐A IRRADIATION

Abstract— The photobinding to proteins of furocoumarins with linear and angular structure (psoralens and angelicins) has been found to occur at relatively high fluences of UV‐A irradiation (66.5 kJm2). The extent of photobinding between serum albumin and the investigated furocoumarins (psoralen, 8‐methylpsoralen, 8‐methoxypsoralen, angelicin and 4,5′‐dimethylangelicin) varies largely with the furocoumarin structure and is correlated with the extent of photodegradation of the same furocoumarins when irradiated alone in aqueous solution. On the other hand, for each furocoumarin, the extent of photobinding varies considerably with different proteins.

Synthesis and antiproliferative activity of some variously substituted acridineand azacridine derivatives

A group of 9-substituted acridine and azacridine derivatives (m-AMSA analogues) were synthesised following classical procedures as potential antitumour agents with inhibitory effects on DNA topoisomerase II. Some were found to have noticeable cytotoxicity against human HL-60 and HeLa cells grown in culture. Their non-covalent interactions with calf thymus DNA have been studied using fluorescence quenching. We evaluated DNA damage produced by the tested compounds by means of DNA filter elution and protein precipitation techniques. Catalytic studies carried out with purified topoisomerase confirmed these agents as antitopoisomerase inhibitors. Chemotherapy of solid-tumour-bearing mice with tested compounds allowed an aza-analogue (compound IIIb), as potent as m-AMSA but less toxic towards the host, to be recognised.

Pyran derivatives: Part XXI. Antiproliferative and cytotoxic properties of novel N-substituted 4-aminocoumarins, their benzo-fused derivatives, and some related 2-aminochromones

The N-substituted tricyclic 2-aminochromone derivatives 1a, 2a, and 2b were obtained by treating the corresponding (methylthio) or (methylsulfinyl) derivatives 10, 11, or 12, respectively, with an excess of the proper amines. Compound 2c was synthesized through the reaction of 2-naphthol with the ethyl N,N-diphenylmalonamate/POCl(3) reagent 14. The N-substituted 4-aminocoumarin bicyclic and tricyclic derivatives 5-8 were prepared by treating the corresponding chloro derivatives with the excess suitable amines. Compounds 1, 2, 5-8 were tested in vitro for their antiproliferative activity (DNA synthesis inhibition in Ehrlich cells) and cytotoxicity (MTT test in HeLa cells). The inhibitory properties of three selected compounds (5c, 5e, 7c) on protein and RNA syntheses in Ehrlich cells were also evaluated. Among the 27 compounds tested, 10 4-aminocoumarin derivatives (5-8) and two 2-aminochromone derivatives (1a and 2a) showed an appreciable antiproliferative activity (IC(50) range: 1.74-13.8 microM), whereas only four compounds 5-8 exhibited a comparable cytotoxic activity (IC(50) range: 4.95-12.9 microM).