Inhibition of Tumor Growth and Metastasis by a Combination of Escherichia coli–mediated Cytolytic Therapy and Radiotherapy

Abstract

We have reported that Escherichia coli K-12 colonizes hypoxic and necrotic tumor regions after intravenous injection into tumor-bearing mice. In this study, we established a novel strategy for cancer therapy using engineered bacteria to enhance the therapeutic effects of radiation. E. coli strain K-12 was engineered to produce cytolysin A (ClyA), and its effects on tumor growth in primary and metastatic tumor models were evaluated. A single treatment with E. coli-expressing ClyA significantly decreased tumor growth rates initially (9 days after treatment); however, the tumors tended to grow thereafter. With only radiotherapy (RT; 21 Gy), the tumor growth rates were retarded, but not the tumor sizes. A combination of therapy with E. coli-expressing ClyA and radiation [a total of 5 x 10(7) colony-forming units (CFU) and 21 Gy] resulted in significant tumor shrinkage and even complete disappearance of tumors in mice with tumors derived from murine CT26 colon cancer. Furthermore, treatment with E. coli-expressing ClyA markedly suppressed metastatic tumor growth and prolonged the survival time in mice. The results described here indicate that therapy with engineered E. coli could significantly improve the results of RT, and could exert a striking inhibitory effect on the development of lung metastasis.

Radiotherapy combined with an engineered <i>Salmonella typhimurium</i> inhibits tumor growth in a mouse model of colon cancer

“…S.t ΔppGpp/pBAD-ClyA greatly improved the efficiency of the RT and significantly inhibited tumor growth, and the total cumulative radiation dose was reduced to 21 Gy, which is lower than the traditional dosage. However, S.t ΔppGpp/pBAD-ClyA combined with RT could not completely eliminate tumor cells, and this was different from a previous report that used an E.coli K-12/pA-ClyA strain [16]. This main reason for this is probably related to the different bacteria strains, because S.t ΔppGpp/pBAD-ClyA is more sensitive to RT than the E.coli K-12/pA-ClyA strain.…”

“…Therefore, the presence of S. typhimurium in the tumor is extended by RT. Our previously study already proved that E. coli could colonize tumors and survive after RT treatment in a mouse tumor model [16]. …”

Salmonella-Mediated Cancer Therapy: Roles and Potential

“…In work from our group, radiation therapy significantly enhanced tumor shrinkage and even induced the complete disappearance of tumors in CT26 tumor models with E. coli-expressing ClyA [31].…”

“…Our group reported the expression of cytolysin A, a pore-forming toxin, in Salmonella [7] and E. coli [31]. For safety reasons, the expression of the toxin was tightly controlled by a pBAD expression system in which the promoter is induced by L-arabinose.…”

Engineered bacteria as therapeutic agents

“…One of them is the direct destruction of tumor cells through the secretion of bacterial toxins in situ (e.g. Staphylococcus aureus alpha hemolysin) [29,30] or the expression of pro-drug converting enzymes that locally convert non-toxic prodrugs into drugs, like E. coli cytosine deaminase (CD) that transforms non-toxic prodrug 5-Fluorocytosine into toxic 5-Fluorouracil, resulting in a bacterial-directed enzyme prodrug therapy (BDEPT) localized in tumor areas [31]. BDEPT provides an excellent tumor selectivity since the drug is produced in situ, however, and similarly to conventional chemotherapy, its efficiency is highly dependent on physico-chemical properties of the prodrug that will define its ability to reach deep areas of the tumor in which bacteria (and therefore the converting enzyme) are located.…”