In vivo Tumor Targeting Using a Novel Intestinal Pathogen-Based Delivery Approach

Abstract

Efficient methods for tumor targeting are eagerly awaited and must satisfy several challenges: molecular specificity, transport through physiologic barriers, and capacity to withstand extracellular or intracellular degradation and inactivation by the immune system. Through interaction with its hosts, the intestinal pathogen-produced Shiga toxin has evolved molecular properties that are of interest in this context. Its nontoxic B-subunit binds to the cellular toxin receptor, glycosphingolipid Gb 3 , which is highly expressed on human cancers and has recently been reported to be involved in the formation of metastasis in colorectal cancers. Its function as a target for cancer therapy has already been addressed in xenograft experiments. We here show that after oral or i.v. injections in mice, the B-subunit targets spontaneous digestive Gb 3 -expressing adenocarcinomas. The nontumoral mucosa is devoid of labeling, with the exception of rare enteroendocrine and CD11b-positive cells. As opposed to other delivery tools that are often degraded or recycled on cancer cells, the B-subunit stably associates with these cells due to its trafficking via the retrograde transport route. This can be exploited for the in vivo delivery of contrast agents to tumors, as exemplified using fibered confocal fluorescence endoscopy and positron emission tomography (PET) imaging. In conclusion, the data presented in this manuscript lay the groundwork for a novel delivery technology that, in addition to its use for molecular imaging applications such as noninvasive PET, could also be exploited for targeted tumor therapies.

Human colorectal tumors and metastases express Gb3 and can be targeted by an intestinal pathogen-based delivery tool

“…In another study, 6 out of 21 patients with diarrhea induced by S. dysenteriae had antibodies to Shiga holotoxin, but none to STxBderived peptides (29). Our own preclinical data on mouse models for CRC indicate that repeated uptake of STxB by the oral or intravenous route is well tolerated and does not cause adverse side effects (30).…”

“…In the present study, we expanded our previously published preclinical investigations (30) to human tumors. Instead of using established tumor cell lines that have been cultured for long periods of time, potentially leading to the acquisition of multiple genetic aberrations, we decided to study primary cultures of human tumor cells of the colon and rectum.…”

The Intracellular Journey of Shiga Toxins

“…This facilitates the use of StxB as a vector for peptide delivery to the MHC class I pathway for the development of vaccines against specific cancer epitopes (for reviews see [121,123]). It has been shown that exogenous antigens coupled to StxB is targeted to the MHC class I pathway and then presented on the surface of dendritic cells, facilitating activation of cytotoxic T-cells and antitumor immunity [124][125][126]. In this way StxB might function as a non-live, non-toxic vaccine delivery system in cancer therapy.…”

“…For diagnostic purposes and selective imaging of these Gb3-expressing cells, visualizing agents, such as radioactive isotopes, contrast agents or fluorescent dyes, might be coupled to StxB. It has been demonstrated that labeled StxB administered systemically in mouse models accumulates in tumor regions overexpressing Gb3, thus confirming that cancer cells can be targeted in vivo by StxB [124,127].…”

Correlation between Shiga toxin B‐subunit stability and antigen crosspresentation: A mutational analysis

“…Transport to the ER is believed to be required for translocation of the A-subunit to the cytosol where its molecular target -ribosomal RNA -resides [12]. STxB has been used as a tool for the characterization of the retrograde route [13,14], and in biomedical research as a delivery tool for immunotherapy [3,15] and cancer targeting [16,17]. It was shown that STxB delivers exogenous peptides into the MHC class I and II pathways of human and mouse dendritic cells (DCs) and induces humoral and cell-mediated immune responses that protect mice from tumor growth [18][19][20][21][22].…”