KCTD1 is a new modulator of the KCASH family of Hedgehog suppressors.

The Sonic Hedgehog (Hh) signal transduction pathway plays a critical role in many developmental processes and, when deregulated, may contribute to several cancers, including basal cell carcinoma, medulloblastoma, colorectal, prostate, and pancreatic cancer. In recent years, several Hh inhibitors have been developed, mainly acting on the Smo receptor. However, drug resistance due to Smo mutations or non-canonical Hh pathway activation highlights the need to identify further mechanisms of Hh pathway modulation. Among these, deacetylation of the Hh transcription factor Gli1 by the histone deacetylase HDAC1 increases Hh activity. On the other end, the KCASH family of oncosuppressors binds HDAC1, leading to its ubiquitination and subsequent proteasomal degradation, leaving Gli1 acetylated and not active. It was recently demonstrated that the potassium channel containing protein KCTD15 is able to interact with KCASH2 protein and stabilize it, enhancing its effect on HDAC1 and Hh pathway. KCTD15 and KCTD1 proteins share a high homology and are clustered in a specific KCTD subfamily. We characterize here KCTD1 role on the Hh pathway. Therefore, we demonstrated KCTD1 interaction with KCASH1 and KCASH2 proteins, and its role in their stabilization by reducing their ubiquitination and proteasome-mediated degradation. Consequently, KCTD1 expression reduces HDAC1 protein levels and Hh/Gli1 activity, inhibiting Hh dependent cell proliferation in Hh tumour cells. Furthermore, analysis of expression data on publicly available databases indicates that KCTD1 expression is reduced in Hh dependent MB samples, compared to normal cerebella, suggesting that KCTD1 may represent a new putative target for therapeutic approaches against Hh-dependent tumour.

Superhydrophilic and tribological improvements of polymeric surfaces via plasma enhanced chemical vapor deposition ceramic coatings.

The main object of this study is the treatment of polymeric (PVC, PC) surfaces with the aim of inducing enhanced superhydrophilic characteristics together with nanohardness features; this would allow polymeric surfaces to have longer durability and prevent the accumulation of dirt on the surface which could disable the proper use of these polymeric surfaces. Indeed plastic surfaces are difficult substrates to be covered effectively and functionalized, mainly due to their high sensitivity to heat treatments and irradiation in the UV-Vis range together with their inert behavior. Their functionalization is achieved through the deposition of ceramic coatings such as titania (TiO2), on the polymeric surfaces via PECVD (Plasma Enhanced Chemical Vapor Deposition) at low temperatures. Characterizations are carried out by contact angle analysis for the superhydrophilic characteristics, and by nanoindentation analysis for the tribological features. A cold PECVD discontinuous method allowed us to improve nanohardness, reaching a value of 1.39 GPa which is nearly ten times higher than that of the uncoated polymeric substrate, and seems a promising solution for improving uniformity of the coatings. Superhydrophilic behavior of the activated TiO2 surfaces showed contact angle values lower than 10 degrees.

Calcineurin and GSK-3 inhibition sensitizes T-cell acute lymphoblastic leukemia cells to apoptosis through X-linked inhibitor of apoptosis protein degradation.

The calcineurin (Cn)-nuclear factor of activated T cells signaling pathway is critically involved in many aspects of normal T-cell physiology; however, its direct implication in leukemogenesis is still ill-defined. Glycogen synthase kinase-3ß (GSK-3ß) has recently been reported to interact with Cn in neuronal cells and is implicated in MLL leukemia. Our biochemical studies clearly demonstrated that Cn was able to interact with GSK-3ß in T-cell acute lymphoblastic leukemia (T-ALL) cells, and that this interaction was direct, leading to an increased catalytic activity of GSK-3ß, possibly through autophosphorylation of Y216. Sensitivity to GSK-3 inhibitor treatment correlated with altered GSK-3ß phosphorylation and was more prominent in T-ALL with Pre/Pro immunophenotype. In addition, dual Cn and GSK-3 inhibitor treatment in T-ALL cells promoted sensitization to apoptosis through proteasomal degradation of X-linked inhibitor of apoptosis protein (XIAP). Consistently, resistance to drug treatments in primary samples was strongly associated with higher XIAP protein levels. Finally, we showed that dual Cn and GSK-3 inhibitor treatment in vitro and in vivo is effective against available models of T-ALL, indicating an insofar untapped therapeutic opportunity.

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.

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.

New studies on the interaction between 8-methoxypsoralen and DNA in vitro.

Some aspects of the interactions between DNA and 8-methoxypsoralen (8-MOP) in its ground state (complex formation) or in its excited state (photobinding) have been investigated. 8-MOP shows a low affinity towards DNA in the complex formation; this fact minimizes the possible biological consequences deriving from this interaction, when it occurs in vivo. In covalent photobinding to DNA, 8-MOP forms mainly monofunctional adducts, and to a lesser extent bifunctional adducts, showing a behavior similar to that of other linearly condensed furocoumarins (psoralens); the ratio between mono- and bifunctional adducts was found to be 9:1. The covalent photobinding to DNA does not occur at random along the macromolecule, but preferentially at the level of specific receptor sites. The regions having an alternate sequence of A-T seem to be the best receptor sites for the formation of monoadducts while the regions containing an alternate sequence of A-T and C-G appeared to be the preferential sites for the cross-linkage formation.

Synthesis and biological activity of (hydroxymethyl)- and (diethylaminomethyl)benzopsoralens.

Some benzopsoralens, carrying a hydroxymethyl or a diethylaminomethyl group at the 3, 5, 8, and 11 positions, were prepared, and their biological activity was compared with that of 4-(hydroxymethyl)benzopsoralen (BP). 5-(Hydroxymethyl)benzopsoralen (7b), 11-(hydroxymethyl)benzopsoralen (7c), and 11-(diethylaminomethyl)benzopsoralen (8c) induced marked antiproliferative effects in mammalian cells by simple incubation in the dark; this activity appeared to be related to their ability to inhibit topoisomerase II. Benzopsoralens appeared to be more active, especially BP and 7c, upon UVA activation. Compounds carrying a methyl group at the 4 position together with a hydroxymethyl or diethylaminomethyl at the 8 position (7d and 8d, respectively) were also effective, although to a lower extent; instead, a substituent at the 3 position canceled all activity. Benzopsoralens did not induce interstrand cross-links in DNA in vitro, as seen in the induction of cytoplasmic <> mutations and double-strand breaks in yeast. This behavior is also compatible with their low mutagenic activity in E. coli WP2 and with the absence of any phototoxicity on the skin. For these features, benzopsoralens seem to be interesting potential drugs for PUVA photochemotherapy and photopheresis. The activity shown in the dark is not sufficient for their possible use as antitumor drugs, but it does offer a new model for the study of topoisomerase inhibitors.

Methylangelicins: new potential agents for the photochemotherapy of psoriasis. Structure-activity study on the dark and photochemical interactions with DNA.

The interactions both in the ground and in the excited state between various methylangelicins, previously prepared with the aim to increase the low photobiological activity of the parent angelicin 1, and DNA have been studied. In general, the new methylangelicins show an increased capacity to photobind monofunctionally to DNA and a parallel increment of photobiological activity in comparison with the parent 1. This increase appears to be connected with various factors, such as the augmented affinity toward DNA for the dark complex formation and the electronic effect connected with the introduction into 1 of one or two methyl groups. The new compounds, on the basis of their photobiological activity and their lack of skin phototoxicity, appear as possible agents for the photochemistry of skin diseases characterized by cell hyperproliferation.

6-Methylangelicins: a new series of potential photochemotherapeutic agents for the treatment of psoriasis.

The possible presence of methylpsoralens as undesired inquinants in synthetic methylangelicins has been avoided through a synthetic pathway starting from umbelliferones carrying a methyl group in the 6-position. The new 6-methylangelicins show a high affinity toward DNA, forming in the dark a molecular complex; the complexed angelicins under UV-A irradiation photobind effectively to the macromolecule, forming only monoadducts. The new compounds show an evident antiproliferative activity by inhibiting DNA synthesis on Ehrlich cells; great differences, however, can be seen between the various compounds. All the compounds are lacking of skin erythemogenic activity. Some of the new 6-methylangelicins, evaluated in terms of mutagenic activity, demonstrate to be less effective than 8-methoxypsoralen (8-MOP), used for a comparison. On the basis of antiproliferative activity, lack of skin phototoxicity, and low mutagenicity, two compounds have been chosen for clinical evaluation. The compounds tested on seven psoriatic patients by topical application and UV-A irradiation proved to be more effective than 8-MOP, used in the same conditions.

New monofunctional reagents for DNA as possible agents for the photochemotherapy of psoriasis: derivatives of 4,5'-dimethylangelicin.

With the aim of obtaining new agents for the photochemotherapy of psoriasis, we have prepared monofunctional reagents for DNA by starting from 4,5'-dimethylangelicin (2), an angular furocoumarin, and introducing in a 4'-(hydroxymethyl) (3), 4'-(methoxymethyl) (4), or 4'-(aminomethyl) group (5), in way analogous to what other authors have done previously on trioxsalen, a DNA bifunctional reagent. These new compounds form complexes with DNA in the ground state and by successive irradiation (UV-A) undergo monofunctional photoaddition to the macromolecule. Photobinding to DNA was highest for 3 and gradually lower for 4 and 5, respectively. These compounds do not form interstrand photocross-linkages in DNA and do not show any skin phototoxicity. Fluorimetric studies show that their 4',5' double bond is involved in the photoaddition to DNA. Their photobiological activity evaluated on Ehrlich ascites tumor cells and on T2 phages was strictly connected with their photobinding to DNA. The effect of the introduction of hydroxymethyl and methoxymethyl groups in angular 2 is somewhat similar to that previously described for trioxsalen: the introduction of an aminomethyl group in 2 markedly increases the affinity in the dark for DNA but under UV-A irradiation strongly inhibits photobinding to the macromolecule. By contrast, in the analogous derivative of trioxsalen both the affinity for DNA in the dark and the photobinding to DNA increased.

Angular furoquinolinones, psoralen analogs: novel antiproliferative agents for skin diseases. Synthesis, biological activity, mechanism of action, and computer-aided studies.

With the aim of obtaining new potential photochemotherapeutic agents, having increased antiproliferative activity and decreased undesired effects, we have prepared some new furoquinolinones. Two of them have been studied in detail: 1,4,6,8-tetramethyl-2H-furo[2,3-h]-quinolin-2-one (8), and 4,6,8,9-tetramethyl-2H-furo[2,3-h]quinolin-2-one (10). These compounds form a molecular complex with DNA, undergoing intercalation inside the duplex macromolecule, as shown by linear flow dichroism. The complexed ligands, by subsequent irradiation with UV-A light, photobind with the macromolecule forming only monocycloadducts with thymine with cis-syn configuration. In order to evaluate the electronic effects induced by the nitrogen atom in position 1 of 8, semiempirical calculations have been performed on both 4,6,4'-trimethylangelicin (TMA) and 8. The results obtained do not clearly differentiate between the two molecules which, at this level of approximation, show the possibility of photoreaction with both the 3,4- and 8,9-olefinic bonds for 8 and the 3,4- and 4',5'-bonds for TMA. In the lower energy conformation of intercalated 8, the furan ring is turned toward the minor groove of the polynucleotide, in such a way that photoreaction of this ring with thymine is favored. These compounds unexpectedly inhibit DNA and RNA synthesis in Ehrlich cells, in the dark. They also show a strong photoantiproliferative activity, 2 orders of magnitude higher than 8-methoxypsoralen (8-MOP), the most used drug for photochemotherapy. Their mutagenic activity on Escherichia coli is similar to that of TMA and 8-MOP. On the basis of these results, the compounds should deserve evaluation of their activity in the treatment of hyperproliferative skin diseases.

4'-Methylangelicins: new potential agents for the photochemotherapy of psoriasis.

Three derivatives of angelicin (1) [4'-methyl-, 4,4'-dimethyl-, and 4',5-dimethylangelicin (2a-c)] have been prepared with the aim of obtaining new agents for the photochemotherapy of psoriasis. These compounds form a complex in the dark with DNA that shows an affinity for the macromolecule higher than that of the parent angelicin (1). A correlation between their octanol/water partition coefficients and the association constants of the complexes has been observed. Compounds 2a-c photobind to DNA to a much higher extent than 1 and also more effectively than 8-methoxypsoralen (8-MOP), taken as reference compound. When activated with UV-A, the three compounds strongly inactivate T2 phage and inhibit epidermal DNA synthesis in mice. Moreover, they show a mutagenic activity markedly lower than that of 8-methoxypsoralen on Escherichia coli wild-type strain. Due to its lack of skin phototoxicity, its low mutagenic activity, and its antiproliferative activity, 2c was chosen for clinical evaluation. It proved to be effective in clearing psoriasis in two patients.

DNA damage and cytotoxicity induced in mammalian cells by a tetramethylfuroquinolinone derivative.

1,4,6,8-Tetramethyl-2H-furo[2,3-h]quinolin-2-one [FQ] is an angelicin isoster characterized by a strong photosensitizing activity FQ shows a significant antiproliferative activity also in the dark, i.e., without UVA activation. The cytotoxic activity of FQ in the dark was detected in HeLa cells and in normal human lymphocytes; FQ showed notable antiproliferative effects, barely lower in comparison with ellipticine, used as a reference Similar results were obtained studying the FQ's capacity for forming chromosome aberrations. For both FQ and ellipticine, the chromosomal damage correlated closely with cell killing, when compared with ellipticine at the same levels of survival, FQ appeared to be much less genotoxic. Using alkaline elution we have investigated the ability of FQ to damage DNA. The formation of equivalent amounts of single-strand breaks (SSB) and DNA-protein cross-links (DPC) was observed; in addition, these lesions appeared to be located at the same sites in DNA. Experiments carried out with neutral elution demonstrated the formation of double-strand breaks (DSB). All these data are consistent with an inhibition of topoisomerase II; this hypothesis was confirmed performing an enzymatic test in vitro using topoisomerase II from Drosophila melanogaster embryos.

Different superstructural features of the complexes between spermine and the light responsive elements of the two pea genes rbcS-3A and rbcS-3.6. Gel electrophoresis and circular dichroism studies.

Two light responsive elements (LREs), DNA sequences, 62 base pairs long, relevant to the light control during transcription of the pea genes rbcS-3A and rbcS-3.6, were synthesized and ligated to obtain multimers with defined superstructural features. Their gel electrophoretic mobilities were studied in the presence of the tetracation, spermine, since it was previously suggested, on the basis of theoretical analysis, that spermine can increase DNA bending and thus could be useful in revealing DNA superstructural features. In fact, the difference between the curvatures of the two LREs, derived from gel electrophoresis retardation ratios, increases in the presence of spermine. Circular dichroism spectra of the complexes between spermine and the two LREs, at different neutralization ratios, show that the polyamine is able to induce the formation of asymmetric arrangements of complexes of molecules. The chirality of these complexes appears dramatically different for the two LREs, suggesting that their different superstructural features give rise to different interactions with the polyamine.

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.

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

Some photochemical and photobiological properties of 4,6,8,9-tetramethyl-2H-furo[2,3-h]quinolin-2-one (HFQ) were studied in comparison with its isomer 1,4,6,8-tetramethyl-2H-furo[2,3-h]quinolin-2-one (FQ) and 8-methoxypsoralen (8-MOP). The HFQ photobinds to DNA forming furan-side monoadducts (MAHFQ) that have molecular structure very similar to those of FQ (MAFQ). Unlike MA8-MOP and MAFQ, MAHFQ no longer photoreact. The HFQ, like FQ, produces moderate amounts of singlet oxygen but no superoxide anions. The HFQ and FQ induce numbers of DNA-protein cross-links (DPC), much more plentiful than those of 8-MOP (about two and seven times, respectively) but no interstrand cross-links. The mechanism of DPC formation was studied in vivo in mammalian cells by alkaline elution and in vitro using a new test mixing histones and DNA from calf thymus. The latter is a very useful technique for the double irradiation protocol. The DNA (or histones) are separately exposed to a first UVA dose in the presence of the sensitizer; then, after its unbound molecules have been removed, histones (or DNA) are added to assemble the chromatin-like complex that is irradiated again. According to in vitro and in vivo methods, DPC appear to be formed by FQ and 8-MOP by a biphotonic process that starts with monoadduct induction in DNA, followed by their conversion into DPC. In the resulting lesions, the sensitizer molecule forms a covalent bridge between the two macromolecules (DPC at length greater than zero). Instead, HFQ induces DPC by a monophotonic process; thus, HFQ is probably not a physical part of the bridge between DNA and proteins, which may be linked together directly, like DPC at zero length induced by UVC.

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.

Biological properties of some benzopsoralen derivatives.

The biological activity of some benzopsoralen derivatives, prepared with the aim of obtaining new drugs for photochemotherapy, has been studied. The more interesting compounds are 4-hydroxymethyl-4',5'-benzopsoralen and 4-hydroxymethyl-4',5'-tetrahydro-benzopsoralen, which were found to be active in the dark also: DNA and RNA synthesis were both inhibited in Ehrlich cells, even if in a partially reversible fashion, while protein synthesis remained unaffected. In Chinese hamster ovary cells cultured in vitro, the clonal growth was strongly inhibited by incubation in the dark with both drugs, while a number of chromosomal aberrations was observed in the fraction of growing cells. Using alkaline elution, DNA strand breaks were detected. In addition, in the presence of aphidicolin, a specific inhibitor of DNA polymerase, the clonal growing capacity was completely restored; in contrast, the number of DNA strand breaks remained unchanged. All these results suggest that DNA topoisomerases are probably the target of these two benzopsoralens. These compounds are also good sensitizers; by UV-A irradiation they have a good capacity to produce singlet oxygen, but they appeared to be unable to induce erythemas on guinea-pig skin. Under UV-A light, they induced a strong inhibition of DNA synthesis in Ehrlich cells. Thus, benzopsoralens appear to be capable of inducing strong antiproliferative effects by two different mechanisms, by UV-A irradiation and in the dark.

Photobiological properties of 1'-thieno-4,6,4'-trimethylangelicin.

Some photobiological properties of 1'-thieno-4,6,4'-trimethylangelicin (TTMA), a new isoster of 4,6,4'-trimethylangelicin (TMA) were studied in comparison with the parent compound. The TTMA absorbs UVA light and photobinds in vitro to DNA more efficiently than TMA; however, in Ehrlich cells in vivo TTMA linked to DNA to a lesser extent than the parent compound. In general, the formation of damage into DNA is in line with this last result: In fact, TTMA and TMA form equivalent amounts of interstrand cross-links (ISC) both in vitro in linearized PM2 DNA and in vivo in HeLa cells. In this system TTMA induces DNA-protein cross-links (DPC) more efficiently than TMA; on the contrary, no significant amounts of single-strand breaks were detected with both compounds. The antiproliferative activity of TTMA is consistent with these results, being only slightly more pronounced than that of TMA. Experiments carried out using double irradiation demonstrated that these drugs are capable of inducing antiproliferative effects by biphotonic reactions, including the formation of both ISC and DPC. Thus, replacement of the oxygen atom by a sulfur increases the UV absorption of the drug and its capacity to photobind to DNA in vitro but does not yield a comparable enhancement of its photosensitizing properties in vivo; this might be due to various reasons, for instance to an increase in the lipophilic character that could modify the behavior in vivo.

4,4',5'-trimethyl-8-azapsoralen, a new-photoreactive and non-skin-phototoxic bifunctional bioisoster of psoralen.

Photochemical and photobiological properties of a new isoster of psoralen, 4,4',5'-trimethyl-8-azapsoralen (4,4',5'-TMAP), have been studied. This compound shows a high DNA-photobinding rate, higher than that of 8-methoxypsoralen (8-MOP), forming both monoadducts and inter-strand cross-links. The yield of cross-links, however, is markedly lower than that of 8-MOP. Antiproliferative activity of 4,4',5'-TMAP, in terms of DNA synthesis inhibition in Ehrlich ascites tumor cells, is higher than that of 8-MOP. Mutagenic activity on E. coli WP2 R46+ cells appeared similar to or even lower than that of 8-MOP. This new compound applied on depilated guinea pig skin and irradiated with UVA did not show any skin-phototoxicity. On the basis of these properties 4,4',5'-TMAP appears to be a potential photochemotherapeutic agent.