Introduction
An excellent approach for spatiotemporal targeting of tumors, regardless
of their origin or location, is
application of genetically modified
non-pathogenic anaerobic bacteria (e.g. Salmonella , E.
coli , Clostridium, Bifidobacterium ) which can be preferentially
localized and proliferative in tumor site (1). Contrary to the
conventional cancer therapies, bacteria can also penetrate easily in
tumor site and be engineered in a way to respond in conditions specific
to the tumors (2). Despite this, rendering these genera of bacteria in
to non-toxic forms for human results in attenuation of their toxicity
against cancer cells (3). Therefore, numerous strategies have been
applied for further improving their anti-tumoral activities. One such a
strategy is to engineer bacteria to secret specific group of cytolytic
proteins such as toxins (e.g. Staphylococcus aureus alpha
hemolysin) or enzymes with capability of converting non-toxic prodrugs
in to cytotoxic ones (e.g. E. coli cytosine deaminase, converting
5-Fluorocytosine in to 5-Fluorouracil) (4).
An even more specific cancer targeted therapy could be achieved through
the application of specific promoters capable of controlling gene
expression in response to specific inducers such as hypoxia. As a common
feature of most aggressive tumors, hypoxia is clinically associated with
poor clinical outcomes and development of resistance to most
chemotherapeutics and radiotherapy (5). Recently, Nasr and Eidgahi have
successfully developed an engineered nirB promoter without any
responding region for nitrite and nitrate, making it preferable and
selective for expression only under hypoxic tumor condition but not in
the presence of chemical inducers (6).
Long acting natriuretic peptide (LANP) together with kaliuretic peptide
(KP) and vessel dilator (VDL) comprise three of the four cardiac
peptides which have shown to suppress the growth of up to 97% of cancer
cells in vitro. 80% of human pancreatic adenocarcinomas together with
86% of human small-cell lung carcinomas (SCLC) have shown to be
successfully eradicated in athymic mice through the application of these
peptides. Furthermore, administration of cardiac peptides significantly
reduced the number of human breast adenocarcinoma cells within 24h of
application in vitro. Among these peptides, Vessel dilator appears to
hold the strongest anticancer property, reducing up to 97% of human
prostate cancer cell throughout the first 24 hours (7-9).
In presented study, we developed a
novel spatiotemporal cancer targeted therapy applying engineeredE.coli bacteria with capability of expressing cardiac peptides
under hypoxic condition of tumor. Creating a hypoxia-inducible system,
the cardiac peptide genes were coupled to the synthetic nirB promoter
sequence reported by Nasr and Eghbali. The stimulation of synthetic nirB
promoter was demonstrated using fluorometry and the expression and
function of cardiac peptides were demonstrated by immunoblotting and
cell culturing. A murine breast cancer model was used to investigate the
potency of hypoxia-inducible cardiac peptide secretion using E.
coli in suppressing tumor growth.