Epidermal growth factor labeled beta-amanitin-poly-L-ornithine: preparation and evidence for specific cytotoxicity

Synthesis and preliminary evaluation of octreotate conjugates of bioactive synthetic amatoxins for targeting somatostatin receptor (sstr2) expressing cells

Targeted cancer therapy represents a paradigm-shifting approach that aims to deliver a toxic payload selectively to target-expressing cells thereby sparing normal tissues the off-target effects associated with traditional chemotherapeutics. Since most targeted constructs rely on standard microtubule inhibitors or DNA-reactive molecules as payloads, new toxins that inhibit other intracellular targets are needed to realize the full potential of targeted therapy. Among these new payloads, α-amanitin has gained attraction as a payload in targeted therapy. Here, we conjugate two synthetic amanitins at different sites to demonstrate their utility as payloads in peptide drug conjugates (PDCs). As an exemplary targeting agent, we chose octreotate, a well-studied somatostatin receptor (sstr2) peptide agonist for the conjugation to synthetic amatoxins via three tailor-built linkers. The linker chemistry permitted the evaluation of one non-cleavable and two cleavable self-immolative conjugates. The immolating linkers were chosen to take advantage of either the reducing potential of the intracellular environment or the high levels of lysosomal proteases in tumor cells to trigger toxin release. Cell-based assays on target-positive Ar42J cells revealed target-specific reduction in viability with up to 1000-fold enhancement in bioactivity compared to the untargeted amatoxins. Altogether, this preliminary study enabled the development of a highly modular synthetic platform for the construction of amanitin-based conjugates that can be readily extended to various targeting moieties.

Clinical importance of toxin concentration in Amanita verna mushroom

Poisoning from Amanita group of mushrooms comprises approximately 3% of all poisonings in our country and their being responsible for nearly the entire fatal mushroom poisonings makes them important. These mushrooms contain primarily two types of toxins, amatoxins and phallotoxins. Phallotoxins have a more limited toxicity potential and they primarily consist of phalloidin (PHN) and phallacidin (PCN). Amatoxins, on the other hand, are very toxic and they primarily consist of alpha-amanitin (AA), beta-amanitin (BA) and gamma-amanitin (GA). Toxin levels can vary among various species, even among varieties of the same species, of Amanita mushroom family. Revealing the differences between the toxin compositions of the Amanita species that grow in our region may contribute to the clinics of poisonings. Our study aims at showing in detail the toxin levels in various parts of Amanita verna mushroom. A. verna mushrooms needed for toxin analysis were collected from Kozak Plateau near Ayvalik county of Balıkesir, Turkey in April 2013. The mushrooms were divided into their parts as pileus, gills, stripe and volva. Following the procedures required before the analysis, the AA, BA, GA, PHN and PCN levels were measured using the RP-HPLC method. While the lowest level of amatoxin was in the volva of the mushroom, the highest was measured in the gills. This was followed by pileus and stripe where the levels were close to each other. Similarly, the highest level of phallotoxin was measured in the gills. Gamma toxin and phalloidin were at lower amounts than the other toxins. A. verna is frequently confused with edible mushrooms with white caps due to its macroscopic similarity. If just one of them is eaten by mistake by an adult person with no mushroom experience, it can easily poison them. The amount of amatoxin is more as compared to Amanita phalloides and A. phalloides var. alba. Particularly, the AA and BA levels are approximately three times higher, whereas GA levels are lower. Similarly, the level of PCN is approximately four times higher as compared to A. phalloides and A. phalloides var. alba; by contrast, the level of PNH is about a half of theirs. In summary, it can be said that A. verna is a more toxic mushroom than A. phalloides and has a higher rate of mortality. With our study, the amatoxin and phallotoxin concentrations and distribution in A. verna mushrooms were shown in detail for the first time and it would be useful to carry out more similar studies with other members of Amanita family growing in various parts of the world.

Targeting the EGF receptor for ovarian cancer therapy

Ovarian carcinoma is the leading cause of death from gynecologic malignancy in the US. Factors such as the molecular heterogeneity of ovarian tumors and frequent diagnosis at advanced stages hamper effective disease treatment. There is growing emphasis on the identification and development of targeted therapies to disrupt molecular pathways in cancer. The epidermal growth factor (EGF) receptor is one such protein target with potential utility in the management of ovarian cancer. This paper will discuss contributions of EGF receptor activation to ovarian cancer pathogenesis and the status of EGF receptor inhibitors and EGF receptor targeted therapies in ovarian cancer treatment.

PankoMab: a potent new generation anti-tumour MUC1 antibody

Recently, we described a new carbohydrate-induced conformational tumour-epitope on mucin-1 (MUC1) with the potential for improvement of immunotherapies [29, 30]. PankoMab is a novel antibody, which binds specifically to this epitope and was designed to show the highest glycosylation dependency and the strongest additive binding effect when compared to other MUC1 antibodies. This enables PankoMab to differentiate between tumour MUC1 and non-tumour MUC1 epitopes. It has a high-affinity towards tumour cells (e.g. KD [M] of 0.9 and 3x10(-9 )towards NM-D4 and ZR75-1, respectively) and detects a very large number of binding sites (e.g. 1.0 and 2.4x10(6 )for NM-D4 and ZR75-1, respectively). PankoMab is rapidly internalised, and after toxin coupling is able to induce very effectively toxin-mediated antigen-specific tumour cell killing. PankoMab reveals a potent tumour-specific antibody-dependent cell cytotoxicity (ADCC). PankoMab is, therefore, distinguished by a combination of advantages compared to other MUC1 antibodies in clinical development, including higher tumour specificity, higher affinity, a higher number of binding sites, largely reduced binding to shed MUC1 from colon and pancreatic carcinoma patients, no binding to mononucleated cells from peripheral blood (except approximately 7% of activated T cells), stronger ADCC activity and rapid internalisation as required for toxin-mediated cell killing. This renders it a superior antibody for in vivo diagnostics and various immunotherapeutic approaches.

Photo-immobilization of epidermal growth factor enhances its mitogenic effect by artificial juxtacrine signaling

Photo-reactive epidermal growth factor (EGF) was synthesized by coupling EGF with azidobenzoic acid and was immobilized onto the wells of a polystyrene culture plate by photo-irradiation. The photo-immobilized EGF enhanced the growth of anchorage-dependent cells more than native or azidobenzoyl derivatized EGF. A small amount of photo-immobilized EGF was sufficient to enhance the growth of cells and the maximal mitogenic effect was greater than that of native or derivatized EGF. On the other hand, the photo-immobilized EGF did not enhance growth of anchorage-independent cells. In addition, signal transduction in the cells adhered only on the EGF-immobilized surface was observed by staining of phosphotyrosine residues by anti-phosphotyrosine antibodies. These results showed that the enhanced cell growth was due to direct interaction between the cells and the immobilized EGF. Photo-immobilization could be a universal means of fixing growth factors onto an artificial matrix that is devoid of chemically functional groups scaffolding growth factors and could provide a new tool to elucidate signal transduction mechanism and could lead to the development of a new protein-free cell culture system or tissue engineering materials.

Fifty years of amanitin

Pharmacokinetic studies have provided new insights into human Amanita poisoning, but it appears to be impossible to treat this intoxication by immunotherapy. New synthetic analogs have revealed structure-activity relationships that were unknown so far. The main toxin, alpha-amanitin, is in constant use as a tool in molecular biology and in biological research. First experiments have been reported in which amanitin bound to polymers could be internalized into tumor cells via a receptor-mediated endocytosis.