Purification and characterization of a Shiga toxin A subunit-CD4 fusion protein cytotoxic to human immunodeficiency virus-infected cells

Hetero-Pathogenic O181:H4 EAHEC Strain of Sequence Type ST678 Associated with Hemolytic-Uremic Syndrome in Schoolchildren in Russia

BACKGROUND

In the last decade, the importance of hetero-pathogenic enteroaggregative Shiga-toxin-producing E. coli for public health has increased. Recently, we described the genetic background of the EAHEC O181:H4 strain of ST678 carrying the stx2 gene in prophage and five plasmids, including the plasmid-carrying aggR and aaiC genes. Here, we present the morphological and enzymatic characteristics of this strain, as well as susceptibility to antimicrobials, biofilm formation, etc. Methods: Bacterial morphology was studied using an electron microscope. Susceptibility to antimicrobials was determined using the microdilution method. Cytotoxicity was estimated in Vero cells. Virulence was studied on mice.

RESULTS

The morphological and enzymatic properties of the hetero-pathogenic EAHEC strain were typical for E. coli; electron microscopy revealed the specific flagella. The strain was susceptible to most antibiotics and disinfectants but resistant to ampicillin and ciprofloxacin and showed a high degree of biofilm formation. Cytotoxicity towards Vero cells was estimated as 80%.

CONCLUSIONS

The emergence of a new O181:H4 EAHEC strain poses a potential threat to humans because of the virulence potential that must be taken into account in the epidemiological analysis of outbreaks and sporadic cases of foodborne infections associated with hemolytic-uremic syndrome.

Inhibition of vascular endothelial growth factor receptor signaling in angiogenic tumor vasculature

Neovascularization takes place in a large number of pathologies, including cancer. Significant effort has been invested in the development of agents that can inhibit this process, and an increasing number of such agents, known as antiangiogenic drugs, are entering clinical trials or being approved for clinical use. The key players involved in the development and maintenance of tumor neovasculature are vascular endothelial growth factor (VEGF) and its receptors (VEGFRs), and therefore VEGF/VEGFR signaling pathways have been a focus of anticancer therapies for several decades. This review focuses on two main approaches designed to selectively target VEGFRs, inhibiting VEGFR with small molecule inhibitors of receptor tyrosine kinase activity and inhibiting the binding of VEGF to VEGFRs with specific antibodies or soluble decoy VEGF receptors. The major problem with these strategies is that they appeared to be effective only in relatively small and unpredictable subsets of patients. An alternative approach would be to subvert VEGFR for intracellular delivery of cytotoxic molecules. We describe here one such molecule, SLT-VEGF, a fusion protein containing VEGF121 and the highly cytotoxic catalytic subunit of Shiga-like toxin.

P-glycoprotein function at the blood-brain barrier imaged using 11C-N-desmethyl-loperamide in monkeys

11C-Loperamide is an avid substrate for P-glycoprotein (P-gp), but it is rapidly metabolized to 11C-N-desmethyl-loperamide (11C-dLop), which is also a substrate for P-gp and thereby contaminates the radioactive signal in the brain. Should further demethylation of 11C-dLop occur, radiometabolites with low entry into the brain are generated. Therefore, we evaluated the ability of 11C-dLop to quantify the function of P-gp at the blood-brain barrier in monkeys.

METHODS

Six monkeys underwent 12 PET scans of the brain, 5 at baseline and 7 after pharmacologic blockade of P-gp. A subset of monkeys also underwent PET scans with 15O-water to measure cerebral blood flow. To determine whether P-gp blockade affected peripheral distribution of 11C-dLop, we measured whole-body biodistribution in 4 monkeys at baseline and after P-gp blockade.

RESULTS

The concentration of 11C-dLop in the brain was low under baseline conditions and increased 5-fold after P-gp blockade. This increase was primarily caused by an increased rate of entry into the brain rather than a decreased rate of removal from the brain. With P-gp blockade, uptake of radioactivity among brain regions correlated linearly with blood flow, suggesting a high single-pass extraction. After correction for cerebral blood flow, the uptake of 11C-dLop was fairly uniform among brain regions, suggesting that the function of P-gp is fairly uniformly distributed in the brain. On whole-body imaging, P-gp blockade significantly affected distribution of radioactivity only to the brain and not to other visually identified source organs. The effective dose estimated for humans was approximately 9 microSv/MBq.

CONCLUSION

PET with 11C-dLop can quantify P-gp function at the blood-brain barrier in monkeys. The single-pass extraction of 11C-dLop is high and requires correction for blood flow to accurately measure the function of this efflux transporter. The low uptake at baseline and markedly increased uptake after P-gp blockade suggest that 11C-dLop will be useful to measure a wide range of P-gp functions at the blood-brain barrier in humans.

Shiga-like toxin-VEGF fusion proteins are selectively cytotoxic to endothelial cells overexpressing VEGFR-2

Growing endothelial cells at sites of angiogenesis may be more sensitive than quiescent endothelial cells to toxin-VEGF fusion proteins, because they express higher numbers of VEGF receptors. We have constructed, expressed and purified a protein containing the catalytic A-subunit of Shiga-like toxin I fused to VEGF(121) (SLT-VEGF/L). SLT-VEGF/L inhibits protein synthesis in a cell-free translation system and induces VEGFR-2 tyrosine autophosphorylation in cells overexpressing VEGFR-2 indicating that both SLT and VEGF moieties are properly folded in the fusion protein. SLT-VEGF/L selectively inhibits growth of porcine endothelial cells expressing 2-3x10(5) VEGFR-2/cell with an IC(50) of 0.1 nM, and rapidly induces apoptosis at concentrations >1 nM. Similar results are observed with human transformed embryonic kidney cells, 293, engineered to express 2.5x10(6) VEGFR-2/cell. In contrast, SLT-VEGF/L does not affect three different types of endothelial cells (PAE/KDR(low), HUVE, MS1) expressing between 5x10(3) and 5x10(4) VEGFR-2/cell, and quiescent endothelial cells overexpressing VEGFR-2. Growth inhibition and induction of apoptosis by SLT-VEGF/L require intrinsic N-glycosidase activity of the SLT moiety, but occur without significant inhibition of protein synthesis. The selective cytotoxicity of SLT-VEGF proteins against growing endothelial cells overexpressing VEGFR-2 suggests that they may be useful in targeting similar cells at sites of angiogenesis.