The cytotoxic activity of the bacteriophage lambda-holin protein reduces tumour growth rates in mammary cancer cell xenograft models.
BACKGROUND
The potential use of gene therapy for cancer treatment is being intensively studied. One approach utilises the expression of genes encoding cytotoxic proteins. Such proteins can affect cellular viability, for example by inhibiting the translation machinery or disturbing membrane integrity. The bacteriophage Lambda (lambda)-holin protein is known to form a lesion in the cytoplasmic membrane of E. coli, triggering bacterial cell lysis and thereby enabling the release of new bacteriophage particles. The aim of this study was to evaluate whether the lambda-holin protein has a cytotoxic impact on eukaryotic cells and whether it holds potential as a new therapeutic protein for cancer gene therapy.


METHODS
To explore this possibility, stably transfected human cell lines were established that harbour a tetracycline (Tet)-inducible system for controlled expression of the lambda-holin gene. The effect of the lambda-holin protein on eukaryotic cells was studied in vitro by applying several viability assays. We also investigated the effect of lambda-holin gene expression in vivo using a human breast cancer cell tumour xenograft as well as a syngeneic mammary adenocarcinoma mouse model.


RESULTS
The lambda-holin-encoding gene was inducibly expressed in eukaryotic cells in vitro. Expression led to a substantial reduction of cell viability of more than 98%. In mouse models, lambda-holin-expressing tumour cell xenografts revealed significantly reduced growth rates in comparison to xenografts not expressing the lambda-holin gene.


CONCLUSIONS
The lambda-holin protein is cytotoxic for eukaryotic cells in vitro and inhibits tumour growth in vivo suggesting potential therapeutic use in cancer gene therapy.
Agu
Chukwuma A
CA
Research Institute of Virology and Biomedicine, University of Veterinary Medicine Vienna, Veterinärplatz 1, A-1210 Vienna, Austria.
Klein
Reinhard
R
Schwab
Sonja
S
König-Schuster
Marielle
M
Kodajova
Petra
P
Ausserlechner
Michael
M
Binishofer
Bernhard
B
Bläsi
Udo
U
Salmons
Brian
B
Günzburg
Walter H
WH
Hohenadl
Christine
C
D000818:Animals; D010582:Bacteriophage lambda / Q000235:genetics* / Q000378:metabolism; D001943:Breast Neoplasms / Q000628:therapy*; D002470:Cell Survival; D015316:Genetic Therapy; D006367:HeLa Cells; D006801:Humans; D007150:Immunohistochemistry; D051379:Mice; D008807:Mice, Inbred BALB C; D016513:Mice, SCID; D014183:Transplantation, Heterologous; D014764:Viral Proteins / Q000235:genetics* / Q000378:metabolism
D014764:Viral Proteins