5-Lipoxygenase inhibitors induce potent anti-proliferative and cytotoxic effects in human tumour cells independently of suppression of 5-lipoxygenase activity.

BACKGROUND AND PURPOSE: Certain 5-lipoxygenase (5-LO) inhibitors exhibit anti-carcinogenic activities against 5-LO overexpressing tumour types and cultured tumour cells. It has been proposed therefore that 5-LO products significantly contribute to tumour cell proliferation. To date, the relationship between the inhibitory mechanisms of 5-LO inhibitors, which vary widely, and tumour cell viability has not been evaluated. This study addresses the anti-proliferative and cytotoxic potency of a number of 5-LO inhibitors with different inhibitory mechanisms in 5-LO-positive and 5-LO-negative tumour cells. EXPERIMENTAL APPROACH: Cell viability was measured by the WST-1 assay; cell proliferation was assessed using the bromodeoxyuridine (BrdU) incorporation assay. Cell death was analysed by annexin V staining, Western blot analysis of PARP (poly ADP-ribose polymerase) cleavage and a cytotoxicity assay. 5-LO product formation was quantified by a 5-LO activity assay. KEY RESULTS: The common 5-LO inhibitors AA-861, Rev-5901 and MK-886 induced cytotoxic and anti-proliferative effects in 5-LO-positive Capan-2 pancreatic cancer cells; BWA4C and CJ-13,610 only caused anti-proliferative effects, while zileuton failed to impair cell viability. Moreover, the concentrations of the 5-LO inhibitors required to induce anti-proliferation and cytotoxicity highly exceeded those for suppression of 5-LO. Supplementation with mitogenic 5-LO products failed to protect Capan-2 cells from the effects of 5-LO inhibitors. Finally, the cytotoxic and anti-proliferative 5-LO inhibitors also potently reduced the viability of 5-LO-deficient tumour cell lines (HeLa, Panc-1 and U937). CONCLUSIONS AND IMPLICATIONS: Certain 5-LO inhibitors cause cytotoxic and anti-proliferative effects independently of suppression of 5-LO activity. Thus, the role of 5-LO overexpression in tumour cell viability remains unclear and requires further elucidation.

Sunscreens - which and what for?

It is well established that sun exposure is the main cause for the development of skin cancer. Chronic continuous UV radiation is believed to induce malignant melanoma, whereas intermittent high-dose UV exposure contributes to the occurrence of actinic keratosis as precursor lesions of squamous cell carcinoma as well as basal cell carcinoma. Not only photocarcinogenesis but also the mechanisms of photoaging have recently become apparent. In this respect the use of sunscreens seemed to prove to be more and more important and popular within the last decades. However, there is still inconsistency about the usefulness of sunscreens. Several studies show that inadequate use and incomplete UV spectrum efficacy may compromise protection more than previously expected. The sunscreen market is crowded by numerous products. Inorganic sunscreens such as zinc oxide and titanium oxide have a wide spectral range of activity compared to most of the organic sunscreen products. It is not uncommon for organic sunscreens to cause photocontact allergy, but their cosmetic acceptability is still superior to the one given by inorganic sunscreens. Recently, modern galenic approaches such as micronization and encapsulation allow the development of high-quality inorganic sunscreens. The potential systemic toxicity of organic sunscreens has lately primarily been discussed controversially in public, and several studies show contradictory results. Although a matter of debate, at present the sun protection factor (SPF) is the most reliable information for the consumer as a measure of sunscreen filter efficacy. In this context additional tests have been introduced for the evaluation of not only the protective effect against erythema but also protection against UV-induced immunological and mutational effects. Recently, combinations of UV filters with agents active in DNA repair have been introduced in order to improve photoprotection. This article reviews the efficacy of sunscreens in the prevention of epithelial and nonepithelial skin cancer, the effect on immunosuppression and the value of the SPF as well as new developments on the sunscreen market.

Identification of a major facilitator protein from Escherichia coli involved in efflux of metabolites of the cysteine pathway.

A chromosomal fragment has been identified in a gene bank from Escherichia coli, which augmented the yield of cysteine in an industrial production strain. Subcloning and genetic analysis showed that an open reading frame coding for a product of 299 amino acids (Orf299) was responsible. Orf299 was synthesized in the T7 polymerase/promoter system and exhibited the properties of an integral membrane protein. Mutational interruption of orf299 did not cause a distinct phenotype; however, transformants overexpressing orf299 had lost the ability to grow in minimal medium unless it was supplemented with a source of reduced sulphur compounds, and they excreted considerable amounts of cysteine and O-acetyl-L-serine, especially in the presence of thiosulphate. Most of the cysteine was found to be masked in 2-methyl-2,4-thiazolidinedicarboxylic acid. N-acetyl-L-serine was also present in the medium, but it is open to question whether it represents a primary excretion product. Measurement of the induction status of the cysteine regulon by means of a cysK'-'lacZ gene fusion demonstrated that the regulon is not induced upon growth in the presence of a poor sulphur source and that the introduction of a constitutive cysB allele alleviates this deficiency. The results indicate that orf299 codes for an export pump for different metabolites of the cysteine pathway. Its relation to other efflux systems and the physiological role are discussed.

Crystal structure of mistletoe lectin I from Viscum album.

The crystal structure of the ribosome-inactivating protein (RIP) mistletoe lectin I (ML-I) from Viscum album has been solved by molecular replacement techniques. The structure has been refined to a crystallographic R-factor of 24.5% using X-ray diffraction data to 2.8 A resolution. The heterodimeric 63-kDa protein consists of a toxic A subunit which exhibits RNA-glycosidase activity and a galactose-specific lectin B subunit. The overall protein fold is similar to that of ricin from Ricinus communis; however, unlike ricin, ML-I is already medically applied as a component of a commercially available misteltoe extract with immunostimulating potency and for the treatment of human cancer. The three-dimensional structure reported here revealed structural details of this pharmaceutically important protein. The comparison to the structure of ricin gives more insights into the functional mechanism of this protein, provides structural details for further protein engineering studies, and may lead to the development of more effective therapeutic RIPs.

[Culture of Plasmodium berghei with the short life span in mouse erythrocytes: evaluation of chloroquine resistance in three strains of the malaria parasite]. / Korotkozhivushchaia kul'tura Plasmodium berghei v éritrotsitakh myshei: opredelenie ustoichivosti k khlorokhinu u trekh shtammov maliariinogo parazita.

This comparative study was made to examine chroloquine inhibition of C14-hypoxanthine incorporation (preferably nucleic acid precursor for plasmodium) in the short-living red blood cell cultures in mice infected with P. berghei strains differently sensitive to the agent 24 hours after incubation. These included 1) chloroquine-sensitive H strain; 2) LNK-65 strain having a spontaneously 2-3-fold decreased sensitivity to the agent; 3) strain LNK-65 ChR selected for high resistance to chloroquine. IC50 (chloroquine concentrations that ensure 50% inhibition of the incorporation of nucleic acid precursor into the cells of the parasite) was estimated for 3 P. berghei strains that were differently sensitive to chloroquine. These in vitro values adequately reflect the sensitivity of these strains to the agent in vivo.

Oxytocin pathways mediate the cardiovascular and behavioral responses to substance P in the rat brain.

Stimulation of brain periventricular and hypothalamic substance P receptors induces a pressor response and tachycardia associated with mesenteric and renal vasoconstriction and hindlimb vasodilation resembling thus the classical defense reaction. This cardiovascular response is brought about by the activation of the sympathoadrenal system and is accompanied by grooming behavior. To address the role of oxytocinergic pathways in the brain in the mediation of these responses, we investigated the effects of central pretreatment of rats with oxytocin antisense, mixed base, and sense oligodeoxynucleotides on mean arterial pressure, heart rate, and grooming behavior induced by intracerebroventricular injections of substance P (50 pmol). Central pretreatment of conscious rats with the oxytocin antisense oligodeoxynucleotide (intracerebroventricular injections, 8 and 4 hours before administration of substance P) attenuated the mean arterial pressure (by 55%) and heart rate responses (by 58%) as well as grooming behavior induced by the peptide. A complete recovery of all substance P-induced responses was observed 28 hours after antisense oligodeoxynucleotide pretreatment. Intracerebroventricular pretreatment of rats with mixed base and sense oligodeoxynucleotides did not affect the cardiovascular and behavioral responses to substance P. The signal for oxytocin mRNA in the paraventricular nucleus was reduced only in rats pretreated with the antisense oligodeoxynucleotide. These results demonstrate that oxytocin neurons in the paraventricular nucleus, which innervate the cardiovascular centers in the hindbrain and the spinal cord, mediate the increases in blood pressure and heart rate induced by stimulation of substance P receptors in the forebrain. These neurons may also transmit signals, which are generated by substance P in the hypothalamus and are responsible for the sympathoadrenal activation in response to stress.