Katerina Vareli

Cyanobacterial Cyclopeptides as Lead Compounds to Novel Targeted Cancer Drugs

Cyanobacterial cyclopeptides, including microcystins and nodularins, are considered a health hazard to humans due to the possible toxic effects of high consumption. From a pharmacological standpoint, microcystins are stable hydrophilic cyclic heptapeptides with a potential to cause cellular damage following uptake via organic anion-transporting polypeptides (OATP). Their intracellular biological effects involve inhibition of catalytic subunits of protein phosphatase 1 (PP1) and PP2, glutathione depletion and generation of reactive oxygen species (ROS). Interestingly, certain OATPs are prominently expressed in cancers as compared to normal tissues, qualifying MC as potential candidates for cancer drug development. In the era of targeted cancer therapy, cyanotoxins comprise a rich source of natural cytotoxic compounds with a potential to target cancers expressing specific uptake transporters. Moreover, their structure offers opportunities for combinatorial engineering to enhance the therapeutic index and resolve organ-specific toxicity issues. In this article, we revisit cyanobacterial cyclopeptides as potential novel targets for anticancer drugs by summarizing existing biomedical evidence, presenting structure-activity data and discussing developmental perspectives.

Exploring Biodiversity in the Bacterial Community of the Mediterranean Phyllosphere and its Relationship with Airborne Bacteria

We studied the structure and diversity of the phyllosphere bacterial community of a Mediterranean ecosystem, in summer, the most stressful season in this environment. To this aim, we selected nine dominant perennial species, namely Arbutus unedo, Cistus incanus, Lavandula stoechas, Myrtus communis, Phillyrea latifolia, Pistacia lentiscus, Quercus coccifera (woody), Calamintha nepeta, and Melissa officinalis (herbaceous). We also examined the extent to which airborne bacteria resemble the epiphytic ones. Genotype composition of the leaf and airborne bacteria was analysed by using denaturing gradient gel electrophoresis profiling of a 16S rDNA gene fragment; 75 bands were cloned and sequenced corresponding to 28 taxa. Of these, two were found both in the air and the phyllosphere, eight only in the air, and the remaining 18 only in the phyllosphere. Only four taxa were found on leaves of all nine plant species. Cluster analysis showed highest similarity for the five evergreen sclerophyllous species. Aromatic plants were not grouped all together: the representatives of Lamiaceae, bearing both glandular and non-glandular trichomes, formed a separate group, whereas the aromatic and evergreen sclerophyllous M. communis was grouped with the other species of the same habit. The epiphytic communities that were the richest in bacterial taxa were those of C. nepeta and M. officinalis (Lamiaceae). Our results highlight the remarkable presence of lactic acid bacteria in the phyllosphere under the harsh conditions of the Mediterranean summer, the profound dissimilarity in the structure of bacterial communities in phyllosphere and air, and the remarkable differences of leaf microbial communities on neighbouring plants subjected to similar microbial inocula; they also point to the importance of the leaf glandular trichome in determining colonization patterns.

Hepatotoxic seafood poisoning (HSP) due to microcystins: a threat from the ocean?

Cyanobacterial blooms are a major and growing problem for freshwater ecosystems worldwide that increasingly concerns public health, with an average of 60% of blooms known to be toxic. The most studied cyanobacterial toxins belong to a family of cyclic heptapeptide hepatotoxins, called microcystins. The microcystins are stable hydrophilic cyclic heptapeptides with a potential to cause cell damage following cellular uptake via organic anion-transporting proteins (OATP). Their intracellular biologic effects presumably involve inhibition of catalytic subunits of protein phosphatases (PP1 and PP2A) and glutathione depletion. The microcystins produced by cyanobacteria pose a serious problem to human health, if they contaminate drinking water or food. These toxins are collectively responsible for human fatalities, as well as continued and widespread poisoning of wild and domestic animals. Although intoxications of aquatic organisms by microcystins have been widely documented for freshwater ecosystems, such poisonings in marine environments have only occasionally been reported. Moreover, these poisonings have been attributed to freshwater cyanobacterial species invading seas of lower salinity (e.g., the Baltic) or to the discharge of freshwater microcystins into the ocean. However, recent data suggest that microcystins are also being produced in the oceans by a number of cosmopolitan marine species, so that Hepatotoxic Seafood Poisoning (HSP) is increasingly recognized as a major health risk that follows consumption of contaminated seafood.

Molecular characterization of cyanobacterial diversity and yearly fluctuations of Microcystin loads in a suburban Mediterranean Lake (Lake Pamvotis, Greece)

Cyanobacterial blooms are a frequent phenomenon in eutrophic freshwaters worldwide, and are considered as potential hazards to ecosystems and human health, while it has been shown that on average 60% of these cyanobacterial blooms are toxic. Hepatotoxic blooms are more common than neurotoxic ones and microcystins have been found to be the most prevalent cyanobacterial hepatotoxins. Lake Pamvotis is an ancient (having been in continual existence throughout the Plio-Pleistocene period) suburban Mediterranean Lake used for recreation, fishing and irrigation purposes which has suffered eutrophication for the last three decades. We investigated cyanobacterial species composition and microcystin loads in this lake over a 16-month period. The highest microcystin concentrations were recorded in autumn, one to two months after the midsummer severe bloom. With the exception of the winter months, microcystin concentrations exceed the WHO upper limits for drinking water but not for recreational waters. Seasonal changes of microcystin bioaccumulation in edible species were also investigated. Microcystin concentrations never exceed the WHO upper limits in those species with the exception of bivalves. For a detailed characterization of the cyanobacterial species composition of the lake, we used polymerase chain reaction (PCR) amplification of the internal transcribed spacer (ITS) between 16S and 23S rRNA genes, in combination with denaturing gradient gel electrophoresis (DGGE). ITS sequences from Lake Pamvotis revealed that the cyanobacterial community of this lake is made of two major populations. A population well defined both microscopically and molecularly as Microcystis sp. dominated during autumn, and another population of filamentous cyanobacteria microscopically characterized as Anabaena sp./Aphanizomenon sp. dominated during midsummer blooms. Sequences of filamentous cyanobacteria from Lake Pamvotis revealed that this cyanobacterial population is homogeneous, although divergent from other populations worldwide. Finally, by using a combination of general and genus specific primer sets against the mcyE gene, we identified Microcystis as the only genus responsible for microcystin production in Lake Pamvotis.

Impact of breast cancer surgery on angiogenesis circulating biomarkers: a prospective longitudinal study

BackgroundDebate about the potential effects that surgery might have on cancer cells dormancy and angiogenesis prompted us to investigate the impact of breast surgery on circulating angiogenesis modulating gene transcripts and proteins.MethodsBlood samples from 10 female patients diagnosed with breast cancer and 6 with fibroadenoma were collected before surgery and post-operatively on days 3 and 7 (breast cancer patients only). A set of 84 angiogenesis-associated transcripts were assessed using quantitative PCR arrays, and circulating protein levels (vascular endothelial growth factor A (VEGFA), IL8 and fibroblast growth factor 2 (FGF2) were measured using ELISA in the same samples. The results were investigated against clinicopathological data and patient outcome.ResultsPlasma levels of VEGFA and IL8 after surgery were significantly elevated in the breast cancer group compared to the control group (P = 0.038 and P = 0.021, respectively). In the cohort of breast cancer patients, VEGFA increased on day 3 (P = 0.038) and declined on day 7 (P= 0.017), while IL8 did not change on day 3 but showed a significant decline on day 7 (P = 0.02). FGF2 levels did not change significantly over time. Regarding gene transcripts, we detected upregulation of a significant number of angiogenesis-specific genes in patients with breast cancer versus controls: sphingosine kinase 1(SPHK1), epidermal growth factor (EGF), vascular endothelial growth factor C (VEGFC), neuropilin 1 (NRP1), fibroblast growth factor (FGF1), laminin alpha 5 (LAMA5), collagen type IV alpha 3 (COL4A3), IL8, ephrin B2 (EFNB2), ephrin A3 (EFNA3), tyrosine endothelial kinase (TEK), integrin beta 3 (ITGB3), AKT1, thrombospondin 1 (THBS1), chemokine (C-C motif) ligand 11 (CCL11) and TIMP metallopeptidase inhibitor 3 (TIMP3). Surgery induced an altered expression in several keygenes in breast cancer patients. We identified an upregulation of COL4A3 and downregulation of chemokine (C-X-C motif) ligand 9 (CXCL9), EGF, FGF1, Kinase insert domain receptor (KDR), Placental growth factor (PGF), TIMP3 and VEGFC.ConclusionBreast cancer patients have a different expression profile of circulating angiogenesis biomarkers compared to patients with fibroadenoma. Moreover, mastectomy promotes a transient increase of VEGFA and a shift in the expression patterns of a broad panel of angiogenesis-related circulating gene transcripts.

Alterations of MicroRNAs in Solid Cancers and Their Prognostic Value

MicroRNAs (miRNAs) are evolutionarily conserved, naturally abundant, small, regulatory non-coding RNAs that inhibit gene expression at the post-transcriptional level in a sequence-specific manner. Each miRNA represses the protein expression of several coding genes in a manner proportional to the sequence complementarity with the target transcripts. MicroRNAs play key regulatory roles in organismal development and homeostasis. They control fundamental biological processes, such as stem-cell regulation and cellular metabolism, proliferation, differentiation, stress resistance, and apoptosis. Differential miRNA expression is found in malignant tumors in comparison to normal tissue counterparts. This indicates that miRNA deregulation contributes to the initiation and progression of cancer. Currently, miRNA expression signatures are being rigorously investigated in various tumor types, with the aim of developing novel, efficient biomarkers that can improve clinical management of cancer patients. This review discusses deregulated miRNAs in solid tumors, and focuses on their emerging prognostic potential.

Prothymosin alpha mRNA levels vary with c-myc expression during tissue proliferation, viral infection and heat shock.

Expression of prothymosin α, an acidic nuclear protein implicated in cellular proliferation, has been reported to be regulated by c‐myc in vitro. We have studied the correlation of expression levels between prothymosin α and c‐myc, using three different in vivo systems, viz. normal ontogenic process of placental development, lytic viral infection and heat shock treatment. The two genes have been found to share a similar expression pattern, although prothymosin α mRNA remains always detactable, indicating the existence of yet another mechanism, in addition to c‐myc, which regulates its expression in vivo.

Prothymosin α is localized in mitotic spindle during mitosis

Summry— Prothymosin a is a small, acidic, ubiquitous protein, thought to play a role in cell proliferation, carcinogenesis and apoptosis. We have reported earlier that in the interphase nucleus prothymosin a exhibits a punctuated nuclear distribution associated with transcription sites. Moreover, the protein was found to localize in 1‐6 subnuclear domains where PML and CstF64 proteins were also identified. In the present study we followed the subcellular distribution of prothymosin a during mitosis. Our data identify prothymosin a to colocalize with α‐tubulin in the mitotic spindle throughout mitosis, and to decorate the midbody during cytokinesis. Moreover nocodazole treatment disrupted prothymosin α and α‐tubulin colocalization at the centrosomes of the interphase cell. Prothymosin a was also found to decorate γ‐tubulin identified centrosomes, during mitosis. Taken together our colocalization study suggests involvement of prothymosin a, in the formation, maintenance, or functioning of the mitotic spindle.

PPARgamma: The Portrait of a Target Ally to Cancer Chemopreventive Agents.

Peroxisome proliferator-activated receptor-gamma (PPARgamma), one of three ligand-activated transcription factors named PPAR, has been identified as a molecular target for cancer chemopreventive agents. PPARgamma was initially understood as a regulator of adipocyte differentiation and glucose homeostasis while later on, it became evident that it is also involved in cell differentiation, apoptosis, and angiogenesis, biological processes which are deregulated in cancer. It is now established that PPARgamma ligands can induce cell differentiation and yield early antineoplastic effects in several tumor types. Moreover, several bioactive natural products with cancer protecting potential are shown to operate through activation of PPARgamma. Overall, PPARgamma appears to be a prevalent target ally to cancer chemopreventive agents and therefore pursuing research in this area is of great relevance.