Targeted delivery of an ADP-ribosylating bacterial toxin into cancer cells.

The actin cytoskeleton is an attractive target for bacterial toxins. The ADP-ribosyltransferase TccC3 from the insect bacterial pathogen Photorhabdus luminescence modifies actin to force its aggregation. We intended to transport the catalytic part of this toxin preferentially into cancer cells using a toxin transporter (Protective antigen, PA) which was redirected to Epidermal Growth Factor Receptors (EGFR) or to human EGF receptors 2 (HER2), which are overexpressed in several cancer cells. Protective antigen of anthrax toxin forms a pore through which the two catalytic parts (lethal factor and edema factor) or other proteins can be transported into mammalian cells. Here, we used PA as a double mutant (N682A, D683A; mPA) which cannot bind to the two natural anthrax receptors. Each mutated monomer is fused either to EGF or to an affibody directed against the human EGF receptor 2 (HER2). We established a cellular model system composed of two cell lines representing HER2 overexpressing esophageal adenocarcinomas (EACs) and EGFR overexpressing esophageal squamous cell carcinomas (ESCCs). We studied the specificity and efficiency of the re-directed anthrax pore for transport of TccC3 toxin and established Photorhabdus luminescence TccC3 as a toxin suitable for the development of a targeted toxin selectively killing cancer cells.

STAT3 expression, activity and functional consequences of STAT3 inhibition in esophageal squamous cell carcinomas and Barrett's adenocarcinomas.

Signal transducer and activator of transcription 3 (STAT3) is altered in several epithelial cancers and represents a potential therapeutic target. Here, STAT3 expression, activity and cellular functions were examined in two main histotypes of esophageal carcinomas. In situ, immunohistochemistry for STAT3 and STAT3-Tyr705 phosphorylation (P-STAT3) in esophageal squamous cell carcinomas (ESCC, n=49) and Barrett's adenocarcinomas (BAC, n=61) revealed similar STAT3 expression in ESCCs and BACs (P=0.109), but preferentially activated P-STAT3 in ESCCs (P=0.013). In vitro, strong STAT3 activation was seen by epidermal growth factor (EGF) stimulation in OE21 (ESCC) cells, whereas OE33 (BAC) cells showed constitutive weak STAT3 activation. STAT3 knockdown significantly reduced cell proliferation of OE21 (P=0.0148) and OE33 (P=0.0243) cells. Importantly, STAT3 knockdown reduced cell migration of OE33 cells by 2.5-fold in two types of migration assays (P=0.073, P=0.015), but not in OE21 cells (P=0.1079, P=0.386). Investigation of transcriptome analysis of STAT3 knockdown revealed a reduced STAT3 level associated with significant downregulation of cell cycle genes in both OE21 (P<0.0001) and OE33 (P=0.01) cells. In contrast, genes promoting cell migration (CTHRC1) were markedly upregulated in OE21 cells, whereas a gene linked to tight-junction stabilization and restricted cell motility (SHROOM2) was downregulated in OE21 but upregulated in OE33 cells. This study shows frequent, but distinct, patterns of STAT3 expression and activation in ESCCs and BACs. STAT3 knockdown reduces cell proliferation in ESCC and BAC cells, inhibits migration of BAC cells and may support cell migration of ESCC cells. Thereby, novel STAT3-regulated genes involved in ESCC and BAC cell proliferation and cell migration were identified. Thus, STAT3 may be further exploited as a potential novel therapeutic target, however, by careful distinction between the two histotypes of esophageal cancers.