Helga Engi

Interaction of tomato lectin with ABC transporter in cancer cells: Glycosylation confers functional conformation of P-gp

Phospho-glycoprotein (P-gp) is a polytopic plasma membrane protein whose overexpression causes multidrug resistance (MDR) responsible for the failure of cancer chemotherapy. P-gp 170 is a member of the ATP-binding cassette (ABC) transporter superfamily and has two potentially interesting regions for drugs interfering with its efflux function, namely the oligosaccharides on the first extracellular loop with unknown function and the two intracellular ATP-binding regions providing the energy for drug efflux function. The polylactoseamine oligosaccharides on the first loop can specifically bind the tomato lectin (TL). The P-gp efflux activities of TL-pre-treated MDR resistant cells were measured in the presence of structurally unrelated resistance modifiers such as phenothiazines, terpenoids and carotenoids. The inhibition of efflux activity was measured via the increased rhodamine uptake by mouse lymphoma cells transfected in human MDR1 gene and in human brain capillary endothelial cells. The tested resistance modifiers inhibit the function of ABC transporter resulting in increased R123 accumulation in MDR1 expressing cells. TL prevented the inhibitory action of phenothiazine and verapamil on brain capillary endothelial and MDR1-lymphoma cells, presumably due to the stabilization of the functional active conformation of P-gp. Our results indicate that the polylactosamine chains of P-gp are part of the functionally active protein conformation.

Interpretation of mtDNA RFLP variability among Aspergillus tubingensis isolates

Aspergillus tubingensis isolates collected from distant geographic areas were earlier classified into six groups on the basis of the mtDNA RFLP variability they exhibited (mtDNA types 2a–2f). In the present work, we investigated the reason for the intraspecific mtDNA variability and we describe here how this fungus, with a relatively small mitochondrial genome, can display intraspecific polymorphism due to intron acquisition and also sporadic point mutations affecting the recognition motifs of the restriction enzymes employed in the RFLP analysis. Three different LAGLI-DADG type group I introns were identified in the cox1 gene amongst the six mtDNA RFLP types. MtDNAs of types 2b and 2d contain all of the three introns, mtDNA of type 2f carries only one, and the other mtDNA types contain two introns each. Comparative analysis showed that the first and second introns of mtDNAs of types 2b and 2d are well distributed among fungi, indicating their active horizontal transfer capacity. The third intron occurs rarely among fungi and is restricted to a limited number of fungal species, namely to A. tubingensis and the yeast Candida stellata. It is interesting that this intron is present in a small mitochondrial genome such as that of A. tubingensis and, considering its rarity, its presence amongst black Aspergillus isolates is recommended to be considered as a tool to establish taxonomical unit(s) or to track down evolutionary divergence of closely related taxonomical units.

Chemoprevention and inhibition of P-glycoprotein in cancer cells by Chinese medicinal herbs.

Many of the herbal extracts used in the Chinese clinical medical routine inhibit the growth of tumor cells. In the present work, extracts of 12 selected herbs were prepared with methanol, chloroform, ethyl acetate and water, and the effects of these on the multidrug resistance (MDR) and P‐glycoprotein of mouse lymphoma cells transfected with the human mdr1 gene and on a human lung alveolar epithelial cell line were investigated. The extracts were tested for antiproliferative effects, and the reversal of MDR in mouse lymphoma cells. The possible chemopreventive effect of the chloroform extracts was studied on the expression of cytomegalovirus (CMV) immediate‐early (IE) antigen in human lung cancer cells (A549). The antimicrobial effects of the extracts were tested on some representative micro‐organisms. Certain of the chloroform extracts of the plant materials were the most effective compounds on the reversal of MDR. Two of the chloroform extracts enhanced the antiproliferative effect of doxorubicin on MDR mouse lymphoma cells. The selected extracts did not show any antibacterial effect with the agar diffusion method. Certain chloroform extracts decreased the intermediate IE antigen expression of CMV in A459 cells. Copyright

Multidrug Resistance Reversal on Cancer Cells by Selected Carotenoids, Flavonoids and Anthocyanins

The multidrug resistance (MDR) proteins which belong to the ATP-binding cassette superfamily are present in a majority of human tumors and are an important final cause of therapeutic failure. Therefore, some compounds which inhibit the function of the MDR-efflux proteins may improve the cytotoxic action in cancer chemotherapy. The mechanism of action was believed to be a competition between their resistance modifiers and the cytotoxic agents for the same binding site of MDR P-glycoprotein (P-gp) due to a complementarity with a hypothetic receptor site with unknown structure. In the absence of the crystal structures of the P-gp, a receptor fitting was not available. Therefore, we tried to indirectly define the receptor structure or mapping of human MDR1-encoded P-gp in the presence of the structurally unrelated carotenoids, flavonoids, isoflavones and terpenoids.

The Role of Stroma in Tumour-Host Co-Existence: Some Perspectives in Stroma-Targeted Therapy of Cancer

Cancer grows at the expense of the host as a parasite or superparasite following the second law of thermodynamics (conservation of energy). When the cancer cell progresses via replication to the special state called “spheroid”, a new phase begins with its intimiate interaction and development of responses from the stroma which together assist in the formation of a full blown cancer. Among the processes involved are the development of blood vessels and lymphatic channels which are essential for maintenance and further growth of the cancer mass. In this way the condition of “parasitism” is completed with simultaneous suppression of the immune response of the host to the histoincompatability of the tumor mass. Stroma/parenchyma promotes cancer invasion by feeding cancer cells and inducing immune tolerance. The dynamic changes in composition of stroma and biological consequences as feeder of cancer cells and immune tolerance can give a perspective for rational drug design in anti-stromal therapy. There are differences between normal and cancer cells at subcellular level such as compartmentalzation and structure of cytoskeleton and energy distribution (that is low generally, but locally high in normal cells). In cancer cannibalism of normal cells, the growing cancer mass is a factor for progression and invasion. Cancer cells have been shown to kill normal cells and the products of cell death used for progression of growth of the cancer cell. Serum and growth factors produced by tumor stroma also provide the needed nutrients and conditions for further tumor growth. Cancer cannot feed off other cancer cells and therefore grow poorly. Probably, although not yet proven, the inability of cancer to “parasitise” other cancer cell types is probably due to some kind of competition or interference. The tumor is in charge of its own development due to its induction proteinases, lipid mobilization factors and angiogenetic factors as well as its ability to negate immune responses of the host response to what is in essence a foreign body. In our review co-existence of normal and cancer cells in tumor with the growth promoting factors, and the immune tolerance mediating factors produced in the stromal and cancer cells/tissues will be discussed with perspective of stroma targeted therapy.