Cytotoxicity of purified listeriolysin O on mouse and human leukocytes and leukaemia cells

Cytotoxic Activity of LLO Y406A Is Targeted to the Plasma Membrane of Cancer Urothelial Cells

Identification of novel agents for bladder cancer treatment is highly desirable due to the high incidence of tumor recurrence and the risk of progression to muscle-invasive disease. The key feature of the cholesterol-dependent toxin listeriolysin O mutant (LLO Y406A) is its preferential activity at pH 5.7, which could be exploited either directly for selective targeting of cancer cells or the release of accumulated therapeutics from acidic endosomes. Therefore, our goal was to compare the cytotoxic effect of LLO Y406A on cancer cells (RT4) and normal urothelial cells (NPU), and to identify which cell membranes are the primary target of LLO Y406A by viability assays, life-cell imaging, fluorescence, and electron microscopy. LLO Y406A decreased viability, altered cell morphology, provoked membrane blebbing, and induced apoptosis in RT4 cells, while it did not affect NPU cells. LLO Y406A did not cause endosomal escape in RT4 cells, while the plasma membrane of RT4 cells was revealed as the primary target of LLO Y406A. It has been concluded that LLO Y406A has the ability to selectively eliminate cancer urothelial cells through pore-forming activity at the plasma membrane, without cytotoxic effects on normal urothelial cells. This promising selective activity merits further testing as an anti-cancer agent.

Stabilized nanosystem of nanocarriers with an immobilized biological factor for anti-tumor therapy

OBJECTIVE

The inadequate efficiency of existing therapeutic anti-cancer regiments and the increase in the multidrug resistance of cancer cells underscore the need to investigate novel anticancer strategies. The induction of apoptosis in tumors by cytotoxic agents produced by pathogenic microorganisms is an example of such an approach. Nevertheless, even the most effective drug should be delivered directly to targeted sites to reduce any negative impact on other cells. Accordingly, the stabilized nanosystem (SNS) for active agent delivery to cancer cells was designed for further application in local anti-tumor therapy. A product of genetically modified Escherichia coli, listeriolysin O (LLO), was immobilized within the polyelectrolyte membrane (poly(ethylenimine)|hyaluronic acid) shells of 'LLO nanocarriers' coupled with the stabilizing element of natural origin.

METHODS AND RESULTS

The impact of LLO was evaluated in human leukemia cell lines in vitro. Correspondingly, the influence of the SNS and its elements was assessed in vitro. The viability of targeted cells was evaluated by flow cytometry. Visualization of the system structure was performed using confocal microscopy. The membrane shell applied to the nanocarriers was analyzed using atomic force microscopy and Fourier transform infrared spectroscopy techniques. Furthermore, the presence of a polyelectrolyte layer on the nanocarrier surface and/or in the cell was confirmed by flow cytometry. Finally, the structural integrity of the SNS and the corresponding release of the fluorescent solute listeriolysin were investigated.

CONCLUSION

The construction of a stabilized system offers LLO release with a lethal impact on model eukaryotic cells. The applied platform design may be recommended for local anti-tumor treatment purposes.

Role of nitric oxide in the regulation of immune responses during rabies virus infection in mice

Rabies virus (RABV) stimulates nitric oxide (NO) production, which either triggers T cell differentiation or suppresses T cell function depending on its concentration. Herein, we assessed the potential role of NO in regulation of immune responses during RABV infection in mice model. The experimental animals were divided into four groups and 100LD50 of challenge virus standard (CVS) strain of RABV was inoculated intracerebrally on day 0 and subsequently aminoguanidine (AG; inducible nitric oxide synthase inhibitor) was injected intraperitoneally twice a day, up to 6 days. The samples were collected at 2, 4, 6, 8, 9, 10 and 12 days post infection (DPI). The immune cells including CD4+, CD8+ T lymphocytes and natural killer (NK) cells were estimated from peripheral blood mononuclear cells (PBMCs) and splenocytes. Serum total NO concentration, histopathology, immunohistochemistry, direct fluorescent antibody technique and TUNEL assay was performed. Infection with CVS resulted in significant early increase in CD4+, CD8+ and NK cells in blood and spleen until 2 DPI. From 4 DPI onwards significant reduction was noticed in these parameters which coincided with increased NO on 4 DPI, rising to maximum on 8 DPI, until their death on 10 DPI. Conversely, the CVS-AG treated group showed lower levels of NO and increased number of CD4+, CD8+ and NK cells. Increased number of cells in blood and spleen coincided with increased survival time, delayed development of clinical signs, reduced viral load and less apoptotic cells. NO played important role in regulation of immune responses during RABV infection. The findings of present study confirmed the role of NO and/or iNOS using iNOS inhibitor (aminoguanidine) in immune response during RABV infection, which would further help in understanding the virus immunopathogenesis with adoption of newer antiviral strategies to counter the progression of disease.