Bis(3,5-diiodo-2,4,6-trihydroxyphenyl)squaraine: a novel candidate in photodynamic therapy for skin cancer models in vivo.

Photodynamic therapy (PDT) is based on the light-induced activation of a photosensitizer generating highly reactive oxygen species that induce tissue destruction in malignant tissues. The present study was carried out to assess the photosensitizing potential of bis(3,5-diiodo-2,4,6-trihydroxyphenyl)squaraine in PDT trials in vivo. Male Swiss albino mice were divided into five groups. Skin tumor was induced using 7,12-dimethylbenz(a)anthracene - DMBA in the animals of Groups II, III, IV and V, while animals of Group I served as the control. At the completion of 20 weeks of induction, the tumor bearing mice from Group III, IV and V were given an intraperitoneal injection with the squaraine dye (12.5mg/kg body weight). After 24h, in the Group IV and V animals, the tumor area was exposed to visible light from a 1000W halogen lamp. The mice from groups I to IV were sacrificed two weeks after the PDT treatment and the marker enzymes (myeloperoxidase [MPO], beta-d-glucuronidase, rhodanese, lactate dehydrogenase [LDH], hexokinase, sialic acid and caspase) were assayed in tumor and normal tissues. Animals from Group V were sacrificed after 90 days of PDT treatment and the above parameters were recorded. Reduction in tumor volume and reversal of biochemical markers to near normal levels were observed in the treatment groups. The study assumes importance as it is the first report on PDT-a novel modality, using a squaraine dye for skin cancer therapy in vivo. The uniqueness of the mode of treatment lies in the selective uptake of squaraine dye by the cancer cells and their selective destruction using PDT without affecting the neighbouring normal cells, which is much advantageous over radiation therapy now frequently used. Also in skin cancer models, the progression/cure can be visualized by the naked eye which is another point of advantage, while seeking new modalities for the treatment of cancer.

Biradical intermediates in the photoisomerization of dibenzodihydropentalenofurans to dibenzosemibullvalenes.

The photoisomerization of a few substituted dibenzodihydropentalenofurans to the corresponding dibenzosemibullvalenes is reported. Steady-state photolysis of the dibenzodihydropentalenofurans 3a--d gave the corresponding dibenzosemibullvalenes 2a--d in nearly quantitative yields. The quantum yields of this photoisomerization were found to be in the range 0.17--0.26. Laser flash photolysis studies of the dibenzodihydropentalenofurans 3a-e showed transients, with absorption maxima around 410 nm and decaying by first-order kinetics. The lifetimes were in the range 14--30 micros in degassed benzene at 25 degrees C. These transients were readily quenched (trapped) by molecular oxygen, and the Stern-Völmer quenching constants were found to be in the range (2.45--3.17) x 10(9) M(-1) s(-1). As a representative example, the 1,3-biradical intermediate from 3e was trapped by molecular oxygen to give the corresponding endoperoxide 11e. The transients were weakly quenched by triplet/radical quenchers such as 2,2,6,6-tetramethylpiperinyl-1-oxy (TEMPO) and 4-hydroxy-2,2,6,6-tetramethylpiperinyl-1-oxy (HTEMPO), and the quenching constants are found to be in the range (1.09--3.19) x 10(6) M(-1) s(-1). The decay rates of the transients were found to be temperature dependent and obeyed the Arrhenius equation. For example, the activation energy of the transient from 3a was approximately 4.5 kcal mol(-1) and the Arrhenius preexponential factor log(A/s(-1)) for the decay of the transients was approximately 7.5. On the basis of our studies, these transients were assigned as the ground-state triplet biradicals, generated by the cleavage of the C--O bond of the starting dibenzodihydropentalenofurans.

D-lactic acidosis 23 years after jejuno-ileal bypass.

Accumulation of D-lactate after gastrointestinal surgery, particularly jejuno-ileal bypass, is an uncommon and often misdiagnosed clinical disturbance. The syndrome may be complicated by dizziness, ataxia, confusion, headache, memory loss, and aggressive behavior. Serum chemistries are often deceptive because the anion gap is frequently normal in spite of severe metabolic acidosis. Moreover, the urine anion gap may be positive, incorrectly suggesting a defect in renal net acid excretion. Indeed, the combination of a normal anion gap metabolic acidosis and positive urine anion gap may erroneously suggest a diagnosis of renal tubular acidosis. Importantly, all reported cases of D-lactic acidosis secondary to bypass surgery have been encountered within 5 to 10 years following the surgery. Here we present an unusual case of D-lactic acidosis (complicated by encephalopathy) presenting 23 years after a jejuno-ileal bypass procedure. The patient was initially diagnosed with a drug intoxication secondary to benzodiazepines. Ultimately, the diagnosis of D-lactate encephalopathy was established after challenging the patient with a carbohydrate load. Thus, administration of 40 kcal/kg over 16 hours reproduced the clinical syndrome and was accompanied by a marked increment in serum and urine D-lactate concentration. The patient had sustained resolution of her symptoms after treatment with oral vancomycin.

Enzymatic reaction with unnatural substrates: DNA photolyase (Escherichia coli) recognizes and reverses thymine [2+2] dimers in the DNA strand of a DNA/PNA hybrid duplex.

Peptide nucleic acids (PNA) are mimics with normal bases connected to a pseudopeptide chain that obey Watson-Crick rules to form stable duplexes with itself and natural nucleic acids. This has focused attention on PNA as therapeutic or diagnostic reagents. Duplexes formed with PNA mirror some but not all properties of DNA. One fascinating aspect of PNA biochemistry is their reaction with enzymes. Here we show an enzyme reaction that operates effectively on a PNA/DNA hybrid duplex. A DNA oligonucleotide containing a cis, syn-thymine [2+2] dimer forms a stable duplex with PNA. The hybrid duplex is recognized by photolyase, and irradiation of the complex leads to the repair of the thymine dimer. This finding provides insight into the enzyme mechanism and provides a means for the selective repair of thymine photodimers.

Detection of thymine [2+2] photodimer repair in DNA: selective reaction of KMnO4.

The specific reaction of potassium permanganate with thymine in single-stranded DNA was employed to analyze thymine [2+2] dimer repair in DNA and in DNA/peptide nucleic acid hybrid duplexes. This simple and highly sensitive chemical assay is convenient for monitoring repair of thymine dimers in oligonucleotides.

Phototransformations of C-Benzoylaziridines. Dipolarophilic Trapping of Photogenerated Azomethine Ylides(1).

The phototransformations of a few 2,3-diaroylaziridines and 2-aryl-3-aroylaziridines have been studied by steady-state photolysis and product analysis. The formation of various photoproducts could be substantiated by ring opening via C-C bond cleavage (leading to azomethine ylides), intramolecular hydrogen abstraction, and C-N bond cleavage. Isolation of stereospecific 3-pyrroline derivatives from the photoreaction of benzoylaziridines in the presence of DMAD confirms our previous results concerning the azomethine ylides as major transient intermediates, produced under laser pulse photoexcitation. Dimethyl 1-cyclohexyl-2-benzoylpyrrole-3,4-dicarboxylate (25), one of the photoadducts derived from the reaction of 1a and 1b with DMAD undergoes a novel and unusual photorearrangement to give dimethyl 2-(1-benzoylcyclohexyl)pyrrole-3,4-dicarboxylate (27), the structure of which was confirmed through X-ray crystallographic analysis.

DNA damage induced by furocoumarin hydroperoxides plus UV (360 nm).

When irradiated at 360 nm, furocoumarins with a hydroperoxide group in a side chain efficiently give rise to a type of DNA damage that can best be explained by a photo-induced generation of hydroxyl radicals from the excited photosensitizers. The observed DNA damage profiles, i.e. the ratios of single-strand breaks, sites of base loss (AP sites) and base modifications sensitive to formamidopyrimidine--DNA glycosylase (FPG protein) and endonuclease III, are similar to the DNA damage profile produced by hydroxyl radicals generated by ionizing radiation or by xanthine and xanthine oxidase in the presence of Fe(III)--EDTA. No such damage is observed with the corresponding furocoumarin alcohols or in the absence of near-UV radiation. The damage caused by the photo-excited hydroperoxides is not influenced by superoxide dismutase (SOD) or catalase or by D2O as solvent. The presence of t-butanol, however, reduces both the formation of single-strand breaks and of base modifications sensitive to FPG protein. The cytotoxicity caused by one of the hydroperoxides in L5178Y mouse lymphoma cells is found to be dependent on the near-UV irradiation and to be much higher than that of the corresponding alcohol. Therefore the new type of photo-induced damage occurs inside cells. Intercalating photosensitizers with an attached hydroperoxide group might represent a novel and versatile class of DNA damaging agents, e.g. for phototherapy.