Bacterial Delivery of Staphylococcus aureus α-Hemolysin Causes Regression and Necrosis in Murine Tumors

Abstract

Bacterial therapies, designed to manufacture therapeutic proteins directly within tumors, could eliminate cancers that are resistant to other therapies. To be effective, a payload protein must be secreted, diffuse through tissue, and efficiently kill cancer cells. To date, these properties have not been shown for a single protein. The gene for Staphylococcus aureus α-hemolysin (SAH), a pore-forming protein, was cloned into Escherichia coli. These bacteria were injected into tumor-bearing mice and volume was measured over time. The location of SAH relative to necrosis and bacterial colonies was determined by immunohistochemistry. In culture, SAH was released and killed 93% of cancer cells in 24 hours. Injection of SAH-producing bacteria reduced viable tissue to 9% of the original tumor volume. By inducing cell death, SAH moved the boundary of necrosis toward the tumor edge. SAH diffused 6.8 ± 0.3 µm into tissue, which increased the volume of affected tissue from 48.6 to 3,120 µm(3). A mathematical model of molecular transport predicted that SAH efficacy is primarily dependent on colony size and the rate of protein production. As a payload protein, SAH will enable effective bacterial therapy because of its ability to diffuse in tissue, kill cells, and expand tumor necrosis.

Molecular dynamics simulation of water permeation through the alpha-hemolysin channel

“…For example, one could bombard cancer cells with proteins that would damage cells' outer membranes, making them susceptible to chemotherapy [13,14]. It may also be possible to make artificial pores, embed them into membranes, and use them as biosensors [15,16,12,17].…”

Genetically modified bacteria as a tool to detect microscopic solid tumor masses with triggered release of a recombinant biomarker

“…In humans, antibiotics could not be used, and the ZsGreen construct would have to be maintained with a balanced lethal system or be incorporated into the Salmonella genome. 46,47 …”

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.…”